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Annual meeting of the Florida State Horticultural Society

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Title:
Annual meeting of the Florida State Horticultural Society
Cover title:
Proceedings of the Florida State Horticultural Society for ..
Abbreviated Title:
Annu. meet. Fla. State Hort. Soc.
Creator:
Florida State Horticultural Society -- Meeting
Place of Publication:
[Florida?]
Publisher:
The Society
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Frequency:
Annual
regular
Language:
English
Physical Description:
v. : ill., ports. ; 24 cm.

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Subjects / Keywords:
Horticulture -- Congresses ( lcsh )
Gardening -- Congresses -- Florida ( lcsh )
Gardening -- Congresses ( lcsh )
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serial ( sobekcm )
conference publication ( marcgt )

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Bibliography of agriculture
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Biological abstracts
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Chemical abstracts
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PESTDOC
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RINGDOC
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VETDOC
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Nuclear science abstracts
Citation/Reference:
Selected water resources abstracts
Dates or Sequential Designation:
64th (Oct. 30, 31, and Nov. 1, 1951)-89th (1976).
Funding:
Florida Historical Agriculture and Rural Life

Record Information

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Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location:
Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
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AAA7465 ( NOTIS )
88647898 ( LCCN )
0097-1219 ( ISSN )

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of the

FLORIDA STATE

HORTICULTURAL SOCIETY




VOLUME 69

1956.


Published by the Society




FLORIDA STATE HORTICULTURAL SOCIETY, 1956


SIXTY-NINTH ANNUAL ME-ETING

of the

FLORIDA STATE


HORTICULTURAL SOCIETY
















held at
ORLANDO, FLORIDA November 7, 8 and 9
1956








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


FLORIDA STATE

HORTICULTURAL SOCIETY



Executive Committee


195 6


PRESIDENT R. A. CARLTON West Palm Beach


SECRETARY
DR. ERNEST L. SPENCER
Bradenton

PUBLICATION SECRETARY

RALPH P. THOMPSON
Winter Haven


TREASURER R. R. REED
Tampa

EDITING SECRETARY
W. L. TAIT
Winter Haven


SECTIONAL VICE-PRESIDENTS


CITRUS
C. A. ROOT
Winter Garden

KROME MEMORIAL
Roy' 0. NELSON
South Miami


VEGETABLES
Louis F. RAUTH
Delray Beach ORNAMENTAL DiR. T. J. SHEEHAN
Gainesville


PROCESSING DR. R. D. GELIWE
Lakeland


MEMBER.S-AT-LARGE
HOWARD A. TH-ULLBERY, Lake Wales Dii. F. S. JAM.ISON, Gainesville

FRANK L. HOLLAND, Winter Haven J, ARTHuR LEWIS, Miami
E. S, REASONER, Bradenton






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


FLORIDA STATE

HORTICULTURAL SOCIETY



Executive Committee


1957


PRESIDENT
ROBERT E. NORRIS
Tavares


SECRETARY
DR. ERNEST L. SPENCER
Bradenton

PUBLICATION SECRETARY
RALPH P. THOMPSON
Winter Haven


TREASURER
R. R. REED
Tampa

EDITING SECRETARY
W. L. TAIT
Winter Haven


SECTIONAL VICE-PRESIDENTS


CITRUS
CHARLES D. KIME, JR.
Waverly

KROME MEMORIAL DR. PAUL L. HARDING
Orlando


VEGETABLES
NORMAN C. HAYSLIP
Ft. Pierce

ORNAMENTAL S. A. ROSE Gainesville


PROCESSING DR. JAMES M. BONNELL Plant City

MEMBERS-AT-LARGE R. A. CARLTON, West Palm Beach FRED J. WESEMEYER, Ft. Myers
FRANK L. HOLLAND, Winter Haven DR. GEORGE D. RUEHLE, Homestead
DR. R. D. GERWE, Lakeland







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Coasitation


Article I-NAME-This organization shall be known as the Florida State Horticultural Society.
Article IL-OBJECTIVE-The objective of this Society shall be the advancement and development of horticulture in Florida.

Article Ill-YEAR-The year shall begin January 1 and close December 31.

Article IV-CLASSIFICATION OF MEMBERSHIP-There shall be three classifications of membership, all of which carry voting privileges:
A-Annual
B-Sustaining
C-Patron
Nothing in this article shall be construed as operating against or cancelling the privileges of Life Members accepted as Life Members prior to the adoption of this constitution.
Article V-ELIGIBILITY FOR MEMBERSHIP-Any individual, firm or partnership interested in the development and advancement of horticulture in Florida shall be eligible for membership.
Article VI-DUES-Dues shall be paid annually according to classification at rate as prescribed in By-laws.
Article ViI-ANNUAL MEETING - The Society shall hold an annual meeting each year in accordance with the By-laws unless prevented from doing so by causes beyond its control.
Article VIII -SECTIONS - The Society shall be divided into sections representing various horticultural interests as provided in the By-laws.
Article IX-OFFICERS-The officers shall consist of a President, a Vice President from each section, a Secretary, a Publication Secretary. an Editing Secretary, and a Treasurer, which officers shall be elected by a majority vote of the membership present at the annual meeting and shall assume their respective offices at the beginning of the new year.


Article N-SUCCESSION-In the absence of the President or his inability to serve temporarily the Vice President of the Citrus Seeton shall serve instead. If the position of President is vacated, the Executive Committee shall designate his successor.

Article XI-EXECUTIVE COMMITTEE The Executive Committee shall consist of not more than 15 persons including the immediate Past President and all Officers above named, the others to be elected at same time and in same manner as prescribed in Article IX. The President shall be chairman of the Executive Committee. The Executive Committee shall have authority to act for the Society hetxveen annual meetings.

Article XIl-MEETINGS OF THE EXECUTIVE COMMITTEE-The Executive Committee shall meet upon call of the Chairman at such time and place as may be approved by a majority of the Committee. A majority of the Committee shall constitute a quorum. The Committee may be canvassed by mail and vote by ballot in like manner.

Article XIII - COMMITTEES - The President shall xvith the approval of the Executive Committee appoint all standing or special committees as provided in the By-laws.

Article XIV-DUTIES OF OFFICERS The President shall be the official head of the Society to preside at all Executive Committee meetings and at the general session of the annual meeting. He shall be directly responsible to the Executive Committee and may be removed from office for cause by an affirmative vote of a majority of the full Executive Committee.

The Vice Presidents shall be members of the Executive Committee. The Vice President of the Citrus Section shall assume the duties of the President in the temporary absence of the President. The Vice Presidents of the various sections shall preside over the particular sections of which they are representatives at the annual meeting.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Secretary shall record all records of all meetings of the Executive Committee and shall be responsible except as mav otherwise be designated in the By-laws fo , recording and keeping proceedings of the annual meeting. He shall likewise issue and mail out statements of dues to the membership, notices of meetings and perform such other dutes as ordinarily accrue to that position.
The Publication Secretary and Editing Secretary shall perform such duties as may be prescribed and authorized by the E executive Committee.
The Treasurer shall be responsible for all funds paid into the Society and shall issue and


countersign all vouchers paying bills or accounts against the Society. The Treasurer shall be placed under bond in an amount determined by the Executive Committee, premium on which shall be paid by the Society.
Article XV-AMENDMENTS-This Constitution may be amended at any annual meeting upon the recommendation of a majority of the Executive Committee when approved by a majority vote of the membership present.
Article XVI-EFFECTIVE DATE - This Constitution shall become effective immediately upon approval by a majority vote of the Iembersbip at the annual meeting in October 1951.


5. SECTIONS-The Society shall consist of the following sections:
Citrus Section
Vegetable Section
Krome Memorial Institute
(Tropical and Sub-Tropical Fruits)
Ornamental and Floriculture Section
Processing Section
Other sections may be added on recommendation of a majority of the Executive Committee when approved by a majority vote of the membership present at an annual meeting.

COMMITTEES
Nominating Conimittee-The President not less than thirty days before annual meeting shall appoint a nominating committee consisting of not less than two persons from each section, which committee shall make nominations at the annual meeting of the Officers and other members of the Executive Committee for the ensuing year; Provided that the members representing various sections shall seek advice of each section in open meeting concerning


1. The Society's year shall begin January
1 and end December 31.

2. Dues-dues shall be paid annually for the current vear and shall be payable to the Treasurer of the Society. Dues shall be as follows:


Annual Membership Sustaining Membership Patron Membership


$ 4.00 $ 10.00 $100.00


3. Annual Meeting-the Society shall hold an annual meeting in the fall of each year at a place and time selected by a majority vote of the Executive Committee. The order of business at the annual meeting shall be determined in advance each year by the Executive Committee.
4. The meetings of the Society shall be devoted only to horticultural topics, from scientific and practical standpoints, and the presiding officer shall rule out of order all motions, resolutions, and discussions tending to commit the Society to partisan politics or mercantile ventures.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


the nomination of Vice President for that section. Such nominations by the committee however shall not preclude nominations from the floor.
Program Committee-The Vice Presidents of the various sections shall constitute a Program Committee of which the President shall be the Chairman and the Secretary and Treasurer shall be ex officio members.
Atiditing Committee - The President with the approval of the Executive Committee shall appoint an auditing committee which committee shall confer with the Treasurer in preparing an audit to be presented by the Treasurer at the annual meeting. The President shall appoint such other committees as may be deemed advisable and approved by the Executive Committee.

DEPOSITORY
The Executive Committee shall have authority to select a depository or establish a trusteeship for funds of the Society as it may deem in the best interest of the society. All Patron Membership dues and all donations, unless otherwise specified by donor, shall be invested by the Treasurer in United 'States Government bonds. The earnings from these bonds shall be left as accrued values or reinvested in the United States Government


bonds unless it is ordered by the Executive Committee of the Society that such earnings can be made available for operating expense.
APPROVAL OF BILLS
All bills before being paid shall be approved by the President, Secretary or Treasurer, and vouchers drawn to pay such bills shall be signed by the President or in his absence the Vice President of the Citrus Section and countersigned by the Treasurer.
HONORARY MEMBERS
Any individual who has rendered especially meritorious service to the Society and to the advancement of horticulture in Florida may be designated by a two-thirds vote of the full Executive Committee and approved by a majority vote of the -Society as an Honorary Member of the Society. Such honorary members shall not be required to pay dues.
AMENDMENTS
These By-laws may be amended at any annual meetk by an affirmative majority vote of the membership present when such amendrnents have been approved and recommended by a majority of the Executive Committee. . These By-laws shall take effect immediately upon adoption by the membership at the annual meeting in October, 1951.





FLORIDA STATE HORTICULTURAL SOCIETY, 1,956


OCE C
(Plz -di

of the

FLORIDA STATF




1956



VOLUME LXIX PRINTED 1957


CONTENTS

Officers for 1956 -------------------------------------------------------------------------------------------- I ------------------------------ 11
Officers for 1957 ------------------------------------- ------------------------------------------------------- ------------------------------- III
Constitution and By-Laws -------------------------------------- --------------------------------------------------------------------- IV
President's Annual Address, R. A. Carlton, West Palm Beach ---------------- --------------------------------- 1
Plant Research in the Atomic Age, George L. McNew, Boyce Thompson Institute for
Plant Research, Inc., Yonkers, N. Y ------------------------------------------------------------------------------- 4
The Mediterranean Fruit Fly Eradication Program in Florida, Ed L. Ayers, Plant
Commissioner, State Plant Board of Florida, Gainesville, and G. G. Rohwer,
Area Supervisor, U. S. Department of Agriculture, Lake Alfred --------------------------------- 12
Award of Honorary Memberships --------------------------------------------- ------- ------------------------------------------- 15


CITRUS SECTION

Injury and Loss of Citrus Trees Due to Tristeza Disease in an Orange County Grove,
Mortimer Cohen, State Plant Board of Florida, Gainesville ---------------------------------------- 19
Effect of Phosphate Fertilization on Root Growth, Soil pH, and Chemical Constituents at Different Depths in an Acid Sandy Florida Citrus Soil, Paul F. Smith,
U. S. D. A. Horticultural Station, Orlando ----------------------------------------- ----------------------- 25
Starting -and Maintaining Burrowing Nematode-Infected Citrus Under Greenhouse
Conditions, William A. Feder and Julius Feldmesser, U. S. D. A. Hort cultural
Station" Orlando -------------------------------------------------------------------------------------------- ----------------- 29












FLORIDA STATE HORTICULTURAL SOCIETY, 1956


viii


Preliminary Investigations on Dieback of Young Transplanted Citrus Trees, Gordon R.
Grimm, U. S. D. A. Horticultural Station, Orlando ---------------------------------------------------- 31
The Possibility of Mechanical Transmission of Nematodes in Citrus Groves, A. C.
Tarjan, Florida Citrus Experiment Station, Lake Alfred -------------------------------------------- 34

Transmission of Tristeza Virus by Aphids in Florida, Paul A. Norman and Theodore
J. Grant, U. S. D. A. Horticultural Station, Orlando ------------------------------------------------ 38

Physiologic Races of the Burrowing Nematode in Relation to Citrus Spreading Decline,
E. P. DuCharme, Florida Citrus Experiment Station, Lake Alfred, and W.
Birchfield, State Plant Board of Florida, Gainesville ------------------------------------------------- 42

Citrus Rootstock Selections Tolerant to the Burrowing Nematode, Harry W. Ford,
Florida Citrus Experiment Station, Lake Alfred ------------ --------------------------------------------- 44

The New 4-H Club Program for Citrus Production Training, Jack T. McCown, Florida
Agricultural Extension Service, Gainesville___ ------------------------------------------------------------ 52

Field Observations of Several Methods of Managing Closely-Set Citrus Trees, Fred
P. Lawrence, Florida Agricultural Extension Service, Gainesville, and Robert
E. Norris, Florida Agricultural Extension Service, Tavares ------------------------------------ 54

Timing Fertilization of Citrus in the Indian River Area, Herman J. Reitz, Florida
Citrus Experiment Station, Lake Alfred -- ------------------------------------------------------------------ 58
Is Stem Pitting of Grapefruit a Threat to the Florida Grower? L. C. Knorr and W. C.
Price, Florida Citrus Experiment Station, Lake Alfred -------------------------------------------- 65

Seasonal Changes in the juice Content of Pink and Red Grapefruit During 1955-56,
E. J. Deszyck and S. V. Ting, Florida Citrus Experiment Station, Lake Alfred -------- 68

Effectiveness of Different Zinc Fertilizers on Citrus, C. D. Leonard, Ivan Stewart and
George Edwards, Florida Citrus Experiment Station, Lake Alfred ------------------------ 72

Increased Utilization of Grapefruit Through Improvement in Quality of Processed
Products, F. W. Wenzel and E. L. Moore, Florida Citrus Experiment Station,
Lake Alfred ------------- ---------------------------- -------------- --------------------------------------------------------- 79

Long Range Relationships Between Weather Factors and Scale Insect Populations,
Robert M. Pratt, Florida Citrus Experiment Station, Lake Alfred ---------------------------- 87

Notes on the Use of Systox for Purple Mite Control on Citrus, Roger B. Johnson,
Florida Citrus Experiment Station, Lake Alfred ------------------ ------------------------------------- 93

Progress Report on Greasy Spot and Its Control, W. L. Thompson, John R. King and
E. J. Deszyck, Florida Citrus Experiment Station, Lake Alfred -------------------------------- 98

Use of 1, 2-Dibromo-3-Chloropropayie on Living Citrus Trees Infecte d with the Burrowing Nematode, Julius Feldmesser and William A. Feder, U. S. D. A.
Horticultural Station, Orlando - ---------- ------------------------------------------------------------------ ------- 105





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


PROCESSING SECTION

Rapid Determination of Peel Oil in Orange juice for Infants, R. W. Kilburn and L. W.
Petros, Florida Citrus Canners Cooperative, Lake NNVales --------------------107
Effects of Finisher Pressure on Characteristics of Valencia Orange Concentrate, 0. W.
Bissett and M. K. Veldhuis, U. S. Citrus Products Station, Wlinter Haven ---------109
A Study of the Degrees Brix and Brix-Acid Ratios of Grapefruit Utilized hv Florida
Citrus Processors for, the Seasons 1952-53 Through 1955-56, E. C. Stenstrom and G. F. Westbrook, Citrus and Vegetable Inspection Division, State Departm ent of Agriculture, W inter Haven ---------------------------------------113
Diacetyl Production in Orange juice by Organisms Grown in a Continuous Culture
System, Lloyd D. Witter, Metal Division, Research and Development Department, Continental Can Co., Inc., Chicago, Ill.----------------------------- 120
Standardization of Florida Citrus Products, Arthur R. Pobjecky, Southern Fruit Distributors, Inc., O rlando --------------------------------------------------- 125
Citrus Vitamin P. Boris Sokoloff, Isidor Chiamelin, Morton Biskind, William C. Martin, Clarence Saelhof, Shiro Kato, Hugo Espinal, Taekyung Kim, Maxwell Simpson, Norman Andree and George Renninger, Southern Bio-Research Laboratory, Florida Southern College,' Lakeland ------------------------------- 128
Vacuum Cooling of Florida Vegretables, R. K. Showalter and B. D. Thompson,, Florida
Agricultural Experiment Station, Gainesville --------------------------------132
The Quality, Control of Chilled Orange juice from the Tree to the Consumer, Leo J.
Lister, Halco Products, Inc., Fairvilla, and Arthur C. Fay, H. P. Hood, and
Sons, B oston, M ass. - -------------- ----------------------- ---------- ----- 136
Hydrocooling Cantaloupes, K. E, Ford, Georgia Experiment Station, Experiment,
G e o rg ia -- - - - --- --- - - - - - - - - --- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --- 1 3 8
The Sloughing Disease of Grapefruit, W. Grierson and Roger Patrick, Florida Citrus
Experim ent Station, Lake Alfred ------------------------- --------------- 140
Effect of Variety and Fresh Storage Upon the Quality of Frozen Sweet Potatoes,
Maurice W. Hoover and Victor F. Nettles, Florida Agricultural Experiment
Station, Gainesville ---------------------------------------------------------- 142
Storage Studies on 420 Brix Concentrated Orange juices Processed from juices Heated
at Varying Folds. 11. Chemical Changes with Particular Reference 'to Pectin; A. H. Rouse, C. D. Atkins and E. L. Moore, Florida Citrus Experiment Station, L ak e A lfred -- -- - - -- - -- - - - -- - -- - --- - - - - --- - -- -- -- - -- - -- - - -- - - -- -- 145
Purification of Naringin, R. Hendrickson and J. WV. Kesterson, Florida Citrus Experim ent Station, Lake A lfred --------------- ------------------------------- 149

Sectionizing Marsh Seedless Grapefruit, Gray Singleton, Shirriff,Horsey Corporation,
L td ., P lan t C ity ---- - - ----- -- - - - -- - -- - - - - - - - - --- - -- - - - - - - - - - - -- - - - - - - - - --- 15 2

An Effective Highl Pressure Cleaning System for Citrus Concentrating Plants, D. I.
Murdock and C. H. Brokaw, Minute Maid Corporation, Orlando ---------------154






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Some Studies on the Use of Sodium Nitrite as a Corrosion Inhibitor in the Canning
Industry, J. R. Marshall, Tampa Laboratory of Research and Technical Department, American Can Co., Tampa -------------------------------------159
Reducing Losses in Harvesting and Handling Tangerines, W. Grierson, Florida Citrus
Experim ent Station, Lake Alfred ---------------------------------------- 165

Quality of Canned Grapefruit Sections from Plots Fertilized with Varying Amounts
of Potash, F. W. Wenzel, R. L. Huggart, E. L. Moore, J. W. Sites, E. J.
Deszyck, R. W. Barron, R. W. Olsen, A. H. Rouse and C. D. Atkins, Florida
Citrus Experiment Station, Lake Alfred ---------------------------------- 170
Storage Studies on 420 Brix Concentrated Orange juices Processed from juices Heated
at Varying Folds. 1. Physical Changes and Retention of Cloud, E. L. Moore,
A. H. Rouse and C. D. Atkins, Florida Citrus Experiment Station, Lake Alfred ----176 Effect of Thermal Treatment and Concentration on Pectinesterase, Cloud and Pectin
in Citrus juices Using a Plate Type Heat Exchanger, C. D. Atkins, A. H. Rouse
and E. IL. Moore, Florida Citrus Experiment Station, Lake Alfred --------------- 181
Distribution and Handling of Frozen Fruits, Vegetables and juices, George J. Lorant,
Birds Eye Laboratories, Albion, New York --------------------------------- 185
Dried-Citrus-Pulp Insect Problem and Its Possible Solution with Insecticide-Coated
Paper Bags, Hamilton Laudani, Dean F. Davis, George R. Swank and A. H.
Yeomans, Stored-Products Insects Laboratory, Savannah, Georgia - ----------I---191


VEGETABLE SECTION

Progress Report on Cantaloupe Varieties, B. F. Whitner. Jr. Central Florida Experim ent Station, Sanford -------------------------------------- ---------- 195
Phytotoxicity of Fungicides to Cantaloupes. 'Robert A. Conover, Sub-Tropical Experim ent Station, H om estead ------------ ------------------------------------- 198
Irrigation of Sebago Potatoes at Hastings, Florida, Donald L. Myhre, Florida Agricultural Experiment Station, Potato Investigations Laboratory, Hastings -----------200

Use of Certain Herbicides in Fields of Growing Tomatoes - Progress Report, John C.
Noonan, Sub-Tropical Experiment Station, Homestead ---------------------- 204

Crop Production in Soil Fumigated with Crag Mylone as Affected by Rates, Application Methods and Planting Dates, D. S. Burgis and A. J. Overman, Gulf Coast
Experim ent Station, Bradenton ----------------------------------------- I- 207

Breeding Objectives and the Establishment of New Breeding Lines of Southernpeas,
A. P. Lorz, Florida Agricultural Experiment Station, Gainesville -------------- 210

Factors Influencing Consumer Preference of Southern Peas (Cowpeas), Maurice W.
Hoover, Florida Agricultural Experiment Station, Gainesville ---------------- 213

Outlook for the Production of Southern Field Peas for Freezing, James Montelaro,
M inute M aid Corporation, Plymouth -------------------------------------- 216






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Insect Problems in the Production of Southern Peas (Cowpeas), John W. Wilson,
Central Florida Experiment Station, Sanford, and WV. G. Genung, Everglades
Experim ent Station, Belle Glade -----------------------------------------217
Influence of Nitrogen, Phosphorus, Potash and Lime on the Growth and Yield of
Strawberries, R. A. Dennison and C. B. Hall, Florida Agricultural Experiment
Station, G ainesville ---- ---- ------- --- - ------------------------------- - 224
Lime-Iduced Manganese Deficiency of Strawberries, C. B. Hall and R. A. Dennison,
Florida Agricultural Experiment Station, Gainesville ------------------------- 228
Cucumber Fungicides for the West Coast of Florida, Grover Sowell, Jr., Gulf Coast
Experim ent Station, Bradenton ----------------- ---- ------------------------- 230
Notes on Current Developments of Gray Mold, Botrytis Cinerea Fr. of Tomato and Its
Control, R. S. Cox, Everglades Experiment Station, Belle Glade, and N. C.
Hayslip, Indian River Field Laboratory, Ft. Pierce_ ------------------------- 235
Evaluation of Control Methods for Blackheart of Celery and Blossom-End Rot of
Tomatoes, C. M. Geraldson, Gulf Coast Experiment Station, Bradenton --------- 236
Control of Diseases in the Celery Seedbed, R. S. Cox, Everglades Experiment Station , B elle G lad e -- - - - - - -- - - -- -- - - -- -- - - - -- - - -- - -- -- -- - - - - --- - - - --- - - - 24 2
The Assay of Streptomvcin as it Relates to the Control of Bacterial Spot, Grover
Sowell, Jr., Gulf Coast Experiment Station, Bradenton -----------------------244
Control of Pole Bean Rust with Maneb-Sulfur Dust, Robert A. Conover, Sub-Tropical
Experim ent Station, H om estead --------------------- -------- ---------------- 247
Fungicidal, Herbicidal and Nematocidal Effects of Fiimigants Applied to Vegetable
Seedbeds on Sandy Soil, A. J. Overman and D. S. Burgis, Gulf Coast Experiment Station, Bradenton --------------- ------------------------------------- 250
Variety Tests of Commercial Types and New Breeding Lines of Southernpea, L. H.
Halsey, Florida Agricultural Experiment Station, Gainesville ---------------- 255
Results of Different Seeding and Fertilizer Rates for Potatoes at Hastings, E. N.
MeCubbin, Florida Agricultural Experiment Station, Potato Investigations
L aboratory, H astings --------------------------------------- - --- --- ----------- 259
Production of Spinach for Processing on Muck Soils of Central Florida, M. M. Hooper,
Vegetable Grower, Apopka ------- ------------------------------------- 261


KROME MEMORIAL SECTION

The Concept, Duties, and Operations of the Florida Avocado and Lime Commission,
C. F. Ivins, Florida Avocado and Lime Commission, Homestead --------------- 262

Notes on Tropical Fruits in Central America, Wilson Popenoc, Escuela Agricola
Panamericana, Tegucigalpa, Honduras -- -------------------------------- 267

Marketing of Limes and Avocados in Florida, Harold E. Kendall, South Florida
Growvers Association, Inc., Goulds -------------------------- -------------- 270








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Sub-Tropical Fruit Program of Dade County, John D. Campbell, County Agricultural Agent, Homestead ---------------------------------------------------------------------------------------- 272
Some Observations on Lime and Avocado Grove Cultural and Maintenance Practices
in Dade COUDtv, Norman E. Sutton, Grove Management, Inc., Goulds -------------------- 274
Future of Florida Minor Tropical Fruit Industry in Doubt, Nixon Smiley, Miami
Herald Farm and Garden Editor and Director, Fairchild Tropical Garden,
M iam i ------------------------------------------------------------------------------------ ----------------------------------------- 275
,Krome Memorial Avocado Variety Committee Report, F. B. Lincoln, Chairman,
H om estead ------------------------------------------- -------------------------------------------------------------------------- 276
Pollination and Floral Studies of the Minneola Tangelo, Margaret J. Mustard, S. John
Lynch and Roy 0. Nelson, Division of Research and Industry, University of
M iami, Coral Gables --- - ------------ -------- --- ---------------------------------------------------------------------- 277
Changes In Physical Characters and Chemical Constituents of Haden Mangos During
Ripening at 80' F., Mortimer J. Soule, Jr., and Paul L. Harding, U. S. D. A.
Horticultural Station, Orlando ------------------------------------------------------------------------------------- 282
Further Rooting Trials of Barbados Cherry, Roy 0. Nelson and Seymour Goldweber,
Division of Research and Industry, University of Miami* Coral Gables ---------------- 285
Research on Sub-Tropical Fruits as a Result of Mediterranean Fruit Fly Eradication
Program, Geo. D. Ruehle, Sub-Tropical Experiment Station, Homestead -------------- 287
Some Effects of Nitrogen, Phosphorus and Potassium Fertilization on the Yield and
Tree Growth of Avocados, S. John Lynch and Seymour Goldweber, Division
of Research and Industry, University of Miami, Coral Gables --------------------------------- 289
A Comparison of Three Clones of Barbados Cherry and the Importance of improved
Selections for Commercial Plantings, R, Bruce Ledin, Sub-Tropical Experiment Station, Homestead ---- ------------------------------------------ -------------------------------------------- 293
Rare Fruit Council Activities, 1956, William F. Whitman, Salvatore Mauro, Seymour
W . Youngbans, Miami Beach ----------------- -------------------- ---------------------------------------------------- 297
Some Notes on a Weevil Attacking Mahogany Trees, F. Gray Butcher and Seymour
Goldweber, Division of Research and Industry, 'University of Miami, Coral
G ables ___, ----------------------- ------------------- ------------------------------------------------------ ---------------------------- 303
Response of Lychees to Girdling, T. W. Young, Sub-Tropical Experiment Station,
H om estead --------------------------- ------- --------------------------------- - ------------------ ------------------------- 305
Some Aspects of the Lychee as a Commercial Crop, Gordon Palmer, Florida Lychee
Growers Association, Osprey ------------------- ------- I ----------------------------------------------------------- 309
The Effects of Longtime Avocado Culture on the Composition of Sandy Soil in Dade
County, John L. Malcolm, Sub-Tropical Experiment Station, Homestead ----- ------- 313
Rooting of Peach Cuttings Under Mist as Affected by Media and Potassium Nutrition,
Mario Jalil, Escuela Agricola Panamericana, Honduras, and Ralph H. Sharpe,
0
Agricultural Experiment Station, Gainesville ------------- ---------------------------------------------- 324






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Some Effects of Nitrogen, Phosphorus and Potassium Fertilization onl the Growth,
Yield, and Fruit Quality of Persian Limes, Seymour Goidweber, Manley Boss
and S. John Lynch, Division of Research and industry, University of Miami,
C o ra l G a b le s - - - - - - - - -- - -- - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- 3 2 8



ORNAMENTAL SECTION

Mist Propagation of Roses, S. E. McFadden, Jr., Department of Ornamental Horticulture, University of Florida, Gainesville ---------------- ----------------- 333
Gladiolus Botrvtis Control, R. 0. Magie, Gulf Coast Experiment Station, Bradent o n - - - - - -- - - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - --- 3 3 7
Some Notes on Philodendron Hybrids, Erdman West and H. N. Miller, Florida Agricultural Experiment Station, Gainesville _--------------------------------- 343
Fertilization of Gladiolus, S. S. Woltz, Gulf Coast Experiment Station, Bradenton ---------347
Studies on the Nutritional Requirements of Chrysanthemums, S. S. Woltz, Gulf Coast
Experim ent Station, Bradenton ------- --- ------------------------------- 352
Virus Ring Spot of Peperomia Obtusifolia and Peperomia Obtusifolia var. Variegata,
M. K. Corbett, Florida Agricultural Experiment Station, Gainesville.------------ 357
How to Landscape Our Outdoor Space for Living, Thomas B. Mack, Florida Southern
C ollege, L akeland ---------------- ----- --- ----- ---- -------- ----------- 360
Regional Performance of Hemerocallis in Florida, Eunice T. Knight, Apopka ------------363
The Palm Society, Dent Smith, The Palm Society, Daytona Beach -------------------- 366
Comparison of Happiness Rose Production on Four Rootstocks, S. E. McFadden, Jr.,
Department of Ornamental Horticulture, University of Florida, Gainesville. ------ 368 Florida Nursery Law,' Paul E. Frierson, State Plant Board of Florida, Gainesville ---------370 Research in the Ornamental Field in Control of Mediterranean Fruit Fly, E. W. MeElwee, Florida Agricultural Experiment Station, Gainesville -------------------379
The Florida Flower and Nursery Industry, Cecil N. Smith, Florida Agricultural Experim ent Station, G ainesville .--------------- - --------- ----------------- 380
The Downward Movement of Phosphorus in Potting Soils as Measured by P", Daniel
0. Spiuks and William L. Pritchett, University of Florida, Gainesville ---------385
Twelve Bauhinias For Florida, R. Bruce Ledin, Sub-Tropical Experiment Station,
H o m estead - --- - - - - - - ----- - -- - -- - - - - - -- --- - - -- - - ---- - - - - - - - - -- ---- - - - -- - - - --- 3 8 8
Pesticides and Plant Injury, S. H. Kerr, Florida Agricultural Experiment Station,
G a in e sv ille -- - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - 3 9 8

The Effect of Parathion as a Corm and Soil Treatment for Gladiolus, E. G. Kelsheimer, Gulf Coast Experiment Station, Bradenton ------------------I --------- 403

The Genus Solandra in Florida, R. D. Dickey, Florida Agricultural Experiment Station , G ain esville -- -- - -- -- -- - - -- - -- --- --- --- - -- --- - - - -- ---- --- -- - --- - ----- 4 65








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


XIV


Studies on Chemical Weed Control in Plumosus Fern, C. C. Helms, Jr., J. M. Crall and
E. 0. Burt, Watermelon and Grape Investigations Laboratory, Leesburg ---------------- 407
Fungicides and Plant Injury, Albert P. Martinez, State Plant Board of Florida,
Gainesville ----- -------------------------------------------------------- ---- -------- ----------------------------------------- 413
The Hunting Billbug a Serious Pest of Zoysia, E. G. Kelsheimer, Gulf Coast Experim ent Station, Bradenton --------------------------------------------------------------------------------------------- 415


ANNUAL REPORTS

Necrology ---------------------------------------------------------------- ------------ - --------------------------------------------------------- 419
Report of Executive Com mittee -------------------------------------------- -------------------------------------------------------- 421
General Business M eeting -------------------------------------- ------- --------- ---------------- ---------------------------------------- 421
Resolutions ---------------------------------------------------------------- ---- -------- - ------------------------------------------------------- 421
Report of Treasurer --------------------------------- ----- ----------------- ------------------- ---------- -------- ------------------------ 422
List of M embers ------------ --------------------------- ----- -------- -------------- __ --------------- - --------------------------------------- 423
Index --------------- - -------------------------------------------------- ----- - ------------------------------------------------------------------------- 433


















R. A. CARLTON
West Palm Beach
One of the duties imposed upon the President of this Society is an annual address on the activities of your Society and the general state of Horticulture in Florida. I am glad to report that your Society is now the third largest Horticultural Society in the United States and the seventh oldest society. It is exceeded membership by the Wisconsin and Michigan Horticultural Societies in that order. The oldest society is in Ohio and was organized in 1847. The Wisconsin Society which has the largest membership has received State aid since 1879 which may account in some measure for the size of its membership.
In the preparation of this address it was natural to reflect upon the changes that have occurred in the activities of the Society in the more than 30 years in which I have been a member, and more or less active in the Society's functions. When I became a member, the horticultural crops of the State were struggling along on an unbalanced program of nutrition, and your Society was struggling in about the same manner.
Colonel Bayard F. Floyd had been Secretary since 1917 and most of the Presidents and Executive Committeemen of those days insisted on the Colonel running it as a one man show, and imposed upon him the complete responsibility for the program, arrangements for the meetings, and everything else requiring much work and time. I recall that some of the young upstarts in the Society about 25 years ago, myself included, became somewhat critical of some of the Colonel's best efforts at program and meeting arrangements. As usual, everybody thought something should be done but nobody wanted to do any work. This state of mild criticism prevailed until about 1939 when the speaker and some others approached the Colonel about forming a Vegetable Section of the Society. The Colonel was quite agreeable and cooperative but flatly declined to accept any responsibility for a program for such a section. Being brash and bold, I accepted this responsibility and during the next five years I learned how easy


it is to talk too much. Anyway, during those years working with Colonel Floyd I gained a deep appreciation of the problems he had faced through the years and sincerely regretted any criticism I ever bad of his efforts. His untimely death in 1945 prevented the Society from ever awarding him any honorarium, if it had been possible for the Society to accord him anything commensurate with the services he had rendered.
It affords me great pleasure to report that during the past year your Society operated under a new deal compared to the years outlined above. This year it was a pleasant experience to see ho v all your General Officers worked together as a team to develop the program and arrangements for this meeting. The Chairman of each Section readily accepted the responsibility of developing the program for his Section, and the Executive Committeemen from the Society at large were most helpful to the General Officers in arranging the many details of this meeting. I wish to express my sincere appreciation for the help and cooperation I have received from one and all, Some of my foregoing remarks have emphasized the fact your Society has been most fortunate in the selection of a Secretary. This good fortune still prevails in Dr. Ernest L. Spencer. He has all the attributes of other good secretaries with an additional one of getting more work out of other people without making anybody mad.
During the past two years your Society created a Fellowship in Virology at the University of Florida. This Fellowship was awarded to Mr. Robert Bozarth, a graduate of Everglades High School in 1948 and the College of Agriculture, University of Florida, in 1952. He is presently directing' his study on the viruses of gladiolus. When these viruses have been isolated they will be identified by symptoms, host reaction, cross protection, and by the use of the Spinco Ultra Centrifuge attempts will be made to purify and crystallize the viruses. These studies will aid in the developing of practical and economical control measures that can be applied by the growers. Realizing full well the complex field involved in research on crop viruses, the recipient of


THE PRESIDENT'S ADDRESS






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


$150.00 to remove roots and do a thorough job of treating the soil. The State. Plant Board expects to complete the removal of all infested acreage by July 1, 1957, and treat the acreage from which trees and roots have been removed. This clearly indicates fine progress in the control and eradication of this production problem,
Despite the dual threats of fruit fly and spreading decline and other problems, the citrus industry continues to set new records of production with an estimated 138,000,000 boxes of fruit to be harvested in the coming season. Except for the war years, the citrus section never had it so good, due in a large measure to its hand maiden the Processing Section which utilized 71 percent of last season's crop. The Processing Section is diligently making every effort to improve quality and increase consumer demand for its products. Much progress is being accomplished as reflected in increased consumption of all processed citrus products.
In the field of the Krome Memorial Section of your Society, much progress may be noted. Nutritional sprays of zinc, manganese and iron cbelates have revolutionized the production picture on the limestone soils of Dade County where much of the commercial acreage of subtropical fruits are planted. Mechanical improvements in land preparation and development on this unusual soil has also contributed to increased acreage. Two lime concentrate plants in Dade County are contributing much to stabilizing the market for Persian limes. Some 6500 acres are now planted to this fruit crop in Dade County,
New mango varieties are encouraging increased plantings of this fruit. This is one fruit immigrant that the longer it stays with us the better it gets. New variety developments are a far throw from the the first Mulgoba tree that fruited successfully in West Palm Beach around the turn of the century. Some of you have heard the beloved Dr. David Fairchild tell the Society of his hopes and fears of the early plantings of mangos in Florida. The annual Mango Forum and exhibit is a state-wide organization and I believe is a fitting example of Dr. Fairchild's fondest hopes for this fruit in the western world.
Lychees have reached commercial production and a growers association was formed in


this Fellowship expressed his problems well I thought and I quote, "To use a bit of double talk, we are experimenting with experiments to carry on the experiment." This certainly indicates heknows what he is up against.
During April a major outbreak of the Mediterranean fruit fly occurred in Dade County, Florida and since that time this insect has been found in some 26 -counties. The reoccurrence of this insect in the State had been expected by many due to the, increase in air travel to the State from all parts of the world, and the reduced inspection service at ports of entry. Many of us who remembered the hectic days of the eradication campaign in 1929 were appalled by prospects of a similar experience. However, time had wrought many changes in 'techniques of control, insecticides and bait attractants used in eradication of this insect. No one could fail to be impressed by the fact that with the discovery of an outbreak of this insect today, this spot, and many miles of area surrounding would be thoroughly sprayed within a matter of hours. Respraying of such areas would occur almost in the twinkling of an eye, in opinion of some of us, who were constantly faced with wash jobs on our cars. A full report will be made to the Society at this meeting on the status of the control program of this insect. I feel the control agencies have done a remarkably good job on this problem and should be congratulated on avoiding much confusion and hysteria that usually accompanies a control and eradication program of this magnitude.
Your Societv has been much concerned in recent years N ith the control and erad I cation of spreading decline in citrus. I do not have figures later than June Ist, 1956, but at that time inspection had been made on 4,421 grove properties comprising approximately 18,000 acres. Infested groves were 960, comprising about 7,500 acres. Inspection had been made of 2,243 nurseries of which 306 were found to be infested. Beginning July Ist, 1955, the State Plant Board started its program of pulling trees from infested grove properties and treating the soil to eradicate spreading decline. As of June 1, 1956, 200 grove properties comprising 1440 acres had been pulled and treated at a cost per acre of approximately $305.00. This total cost may be broken down with $89.00 cost to push and bum trees, and






CARLTON: PRESIDENT'S ADDRESS


1951. This association is actively working on production and marketing problems.
In the realm of the Vegetable Section, U.S.D.A. Truck Crop statistics reveal the Florida growers brought 385,000 acres of vegetable crops to the point of harvest last season, with shipments of 155,000 carrot equivalents. Acreage of vegetable crops has increased 21 percent and volume of shipments 42 percent in the past five years. In the same five year period returns on vegetables at the F.O.B. level have increased 31 percent. Tomatoes continue to be the most important vegetable crop grown in the State with the value of last year's crop exceeding the value of all animal products sold in the State. Last season 4.6 percent of the State's tomato production was shipped as vine-ripened and this supply resulted in much attention being directed toward this new development from a marketing standpoint, A study is now being made by Agricultural Economics Department of the College of Agriculture on the market outlook for vine-ripened tomatoes. The Chairman of this year's Vegetable Section of your Society is a successful vine-ripened tomato grower. I predict that the marketing of vineripened tomatoes is here to stay and that Florida will soon develop this activity into a major enterprise.
Last season Florida harvested 37,700 acres of sweet corn, which was a crop not grown commercially in the State 15 years ago. The State now furnishes a continuous supply of this crop to the markets from October until July.
Notable advances have been made by all phases of the vegetable industry in mechanization of production and harvesting processes. One of the newest harvesting machines to come to my attention is for tomatoes. This machine has an overall width of 365 feet. Such developments are resulting in larger growing operations.
The Ornamental Section of your Society is a phase of horticulture that has increased phenomenally in recent years, The gladiolus industry has expanded since 1940 from 4,500 acres producing 5,000,000 dozen blooms to 11,600 acres producing 20,000,000 dozen blooms. The growing of chrysanthemums has jumped from 5 acres in 1950 to 230 acres


with a large part of this enterprise located in Martin County. Last season 46 growers harvested 3,500,000 bunches of pompons and 72,000 dozen standard blooms valued at $3,500,000.00. This is a good example of a hot house enterprise being adapted to production in the open under Florida's climate.
A sizeable industry has developed on the woody peat soils of Highlands County in the production of caladium bulbs. This enterprise has meant much to the economy of that area. The importance of large ornamental nursery business in the State is well known,
The eternal light of your Society is its published proceedings. Volume 68, relating to the 1955 meeting contains 400 pages. In the 69 years of the Society's existence its proceedings have reported th best history of Florida's horticulture both practical and technical.
Several years ago an index was published of volumes 5 through 37 of the proceedings. Three years ago your Executive Committee decided to compile an index of volumes 38 through 68 and this was completed this summer and now published and available to members. This work of indexing the proceedings was done with the intent of encouraging members to better use their proceedings as reference material for any phase of horticulture in which they might be interested.
I realize that 1, and possibly many other members, have not used their proceedings in the past as we should have, and possibly this was due in part to a lack of an index which would permit us to refer quickly and efficiently to any person or subject covered in the proeedings.
The Society has grown too large and complex for any member to attend the sessions and near all the papers which might be of interest and value to them. Study of the proceedings is the only way then in which the Society may be of the most value to you. I would be remiss in duty if I didn't urge every member here to use and appreciate the work and knowledge recorded in your Society's proceedings, I am not one to s rmonize, but if I were, an appropriate text might be found in Matthew 5.15: "Neither do men light a candle and place it under a bushel, but upon a candlestick; and it giveth light unto all who are in the house."







FLORIDA STATE'HORTICULTURAL SOCIETY, 1956

PLANT RESEARCH IN THE ATOMIC AGE


GEoRIGE L. McNEiv
Boyce Thompson Instittice
for Plant Research, Inc.
Yonkers, N. Y.

When your fine secretary invited me to appear on this program last June, I demurred long enough to prove my modesty and then hastened to accept before he changed his mind. As usual, I always enjoy a trip to your unique state. It is a particular honor and pleasure to appear before such a venerable and respected society as yours to discuss certain new aspects of agricultural research.
At the very ouitset we should come to an understanding that nothing I am going to say in the next hour will revolutionize Florida's agriculture. You will probably not find a single item to help you increase soil fertility, suppress insects or alleviate plant diseases. After all, you have one of the better, if not the best, agricultural research services in the United States to provide such information. Since it would be foolhardy for me to attempt to compete with such talent in your own fine institutions, I w ill spend this hour discussing selected items of research behind their research. Perhaps we can take a stroll behind the scenes to see what sort of principles of life and living processes are being investigated in order to provide a jumping off place for future research in agriculture.

THE CHALLENGE OF THE MOnuaN ERSA
Our newspapers like to refer to this as the atomic age. Perhaps this is fitting because it is an era of change, growth and violent adjustments. To many of our citizens it has become an era of frustration, uncertainty and worry as we face a violently explosive international situation and see our economy shaken and unstable on the rapidly shifting'sands of technological change and social unrest.
Although we know that atomic violence hangs over our heads by day and night, I would not have us live in fear and trepidation. There is another side to this whole picture that we should never forget. The same forces that threaten us can be diverted to our peacetime use and civilized progress, It is this


story of progress through research in the common great cause of humanity that we will inspect here today.

THE NEW ERA IN RrsEARcH
The opportunities in research were never more promising of glorious success than today. Scientists have behind them a mass of knowledge to be used as a foundation and new research tools that were -undreamed of three decades ago. For the first time in the history of science man can trace the metabolism of a living thing by use of radioactive, ,unstable atoms. You can label a part of a tissue as it grows,- a molecule in process of digestion, or even the parasite or pest that attacks the crop. The tissue, the molecule, the parasite, or the insect then becomes so conspicuously unique that it can be traced wherever it goes and yet it behaves exactly the same as all of its less conspicuous brethren.
The physical chemist has given the biologist a host of other relatively simple tools to help in manipulating and separating the labelled molecules. By use of paper partition chromatography one can separate out all the amino acids, ketones, aldehydes, acids, growth hormones, ete., then identify them and measure their concentration. 'Assays tbat would have taken many months to perform can now be done in 48 hours. Best of all,' however, the new techniques reveal related but previously unknown compounds to whet the curiosity and initiative of the investigator. No less significant is the use of elution column chromatography, ultracentrifuges, electrophoresis equipment and a host of other devices to separate and purify components with biological activity.
If there is any question about the identity and concentration of any material there are spectrophotometric devices to substantiate one's opinions and guide his research. For example, just think of this fact, One of our scientists tells me that we can now make a complete amino acid analysis of a single female housefly in two days. If we find an undescribed amino compound we can elute it and get a complete fingerprint of its characteristic bonds within two hours by use of infrared absorption. You can do all this if the miserable old





MeNEW: PLANT RESEARCH


fly bad as much as a few micrograms of the Aernical in her body.
This example could be multiplied a hundred-fold by choice of other devices and techniques-the physical chemist who pulls two closely related viruses apart in an electrophoresis apparatus by minute differences in their surface charges or by differences in their mass or density in an ultracentrifuge, or the X-ray crystallographer who plots the arrangement o( invisible and active atoms one to another in a crystal lattice that one barely sees under the most powerful microscope. This is a great era in which to live. Every scientist worthy of the name should thrill to the opportunities before him to understand the universe.
For many decades the botanist and horticulturist have been interested in the outside of plants. They did a. necessary job of describing the orgar s and determining the relation of one plant to another. We learned bow to change these external appearances by breeding, altering their nutrition, or exposing them to chemicals. However, no one knew exactly what bad been done or why plants reacted the way they do. Today a new viewpoint is coming into plant research. We are more interested in what a plant does than what it looks like.
The activities going on inside of millions of - tiny cells in each tissue arouses one's imagination. There is a beehive of activity in one of these cells-with a volume of less than one-billionth of a cubic ineb-that would put the best man-made factory to shame. For example, if one provides the leaves of a plant with labelled C"O., within five minutes there may be detected 57 new organic compounds in the tissue. Within a couple of hours some of the very complex new molecules are being secreted from the roots. One must admit that the dynamics of cell operations are tremendOtis.
The activities of these cells are of interest to men because anyone who can control the cell can change the'tissue and thereby regulate the entire plant to our selfish purposes. One can make cells grow faster, change their shape, inactivate them completely, change their heredity; render them more nutritious or make them immune to disease by use of the appropriate chemicals. Therefore the scientist who will take the time and effort to Understand cell functions should be able to uncover basic


principles of life which he can exploit in making plants more serviceable to man. By the same token, the man who would control insects, diseases and weeds has an obligation to study them carefully to determine their strengths and weaknesses.
By so doing, the biologist can orient the efforts of the chemist in developing new types of chemicals to solve many problems in plant culture. The examples we will consider here today lie in this general area on the frontiers of science. They are chosen from work of various scientists at Boyce Thompson Institute, not because they are the only work in the area or even superior to that of others but because of my familiarity with them.
FUNGICIDAL BULLETS
Men have been at war with the fungi since time eternal. You people here in Florida need not be reminded that tremendous quantities of chemicals must be applied to plants to prevent fungous diseases. You contribute a substantial share of the 125 million dollars spent each year in the United States on control of plant diseases.
In spite of this terrific investment we are only partially successful in reducing the ravages by fungi. According to our best estimates they still destroy 7% of our potential agricultural productivity, This amounts to about 2.8 billion dollars a year. To get down to brass tacks it means that every man, woman and child in the United States pays $24.20 a year in tribute to the fungi. Each family would be horrified if it entered $96 a year in its housebold budget as the cost of plant diseases but such are the facts.
Obviously we need better methods of controlling diseases. Some people may make their contribution by breeding resistant plants, improving crop rotations etc., but we have elected to see what can be done in improving fungicides. There are several good fungicides but we need more and the only way we are going to get them is invent them. We have decided to learn all we can about the ones now available so we can develop better ones. Here are a few examples of recent developments,
Sulfur operates in a unique fashion. The particle of sulfur deposited on a leaf or fruit volatilizes and reaches the spore in the vapor phase. By use of radioactive sulfur (S') Drs.








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Miller and McCallan have shown that the sulfur atom is taken up by the spore and is almost immediately reduced to hydrogen sulfide. It is released within a couple of minutes from the spore and, contrary to previous conceptions, the H,S does not act as a fungicide in destroying the spore. Please note that facts such as these could be determined only by using isotope tracer techniques.
Once these facts were out in the open our scientists began to wonder how sulfur could destroy a spore without entering into cell reactions. Biochemical studies have shown that the spore suffers irremedial damage when it gives up two hydrogens to reduce each sulfur. For each molecule of sulfur reduced, the spore releases a molecule of carbon dioxide. By the time the spore has reduced 15,000 to 25,000 parts of sulfur per million units of body weight it succumbs.
The search in this area goes on to determine what organic acid in the spore is undergoing decarboxylation. Insofar as we know, sulfur is unique among the fungicides in its ability to destroy a spore solely by robbing it of materials. All other fungicides enter the spore and react with vital cell constituents. Sulfur is a hit and run bullet that bleeds the spore to death.
The organic fungicides are far more fascinating. They can be designed in a wide variety of forms with only minor differences in configuration. By trial and error, chemists have learned that there is a rigid requirement of chemical structure to attain effective fungitoxicity. Why does a minor change in chemical structure affect the fungicidal activity so drastically? It is becoming increasingly clear that the changes either influence the ability to penetrate the fungous body, to enter into certain vital cell reactions and disrupt them, to change resistance to the cell's detoxification mechanisms or to modify the stability and persistence of the molecule.
Most of you know that there are two quinone fungicides on the market under the tradenames of Spergon (chloranil) and Phygon (dichlone). Many of you may have heard me say in years past that dichlone was about 20 times as fungicidal as chloranil. This appears to be true when one measures their effect on spore germination but it is contrary to what one would expect from their chemical at-


tributes. Dr. Owens has cast much light in this area by recent studies on the effect of several dozen quinones and hydroquinones on enzyme systems. Ie found that there was a very close correlation between fungitoxicity and ability to inhibit sulfhydryl- and aminobearing enzymes. An exception was observed in comparing benzoquinone and naphthoquinone analogues. He was finally able to show that benzoquinone appeared to be less active than naphthoquinone because it was detoxified more readily by entering into extraneous reactions. Dark-colored spores secrete substances that inactivate much of the benzoquinone before it can penetrate and destroy the spore.
Most of us have wondered what roles are played by the halogens on the organic molecules so commonly used as insecticides, fungicides and herbicides. Dr. Burchfield has carefully studied the effect of placement of two types of chlorine in the symmetrical triazines, a new class of fungicides developed by Dr. Schuldt in cooperation with chemists of the Ethyl Corporation. These compounds have the following structure:


6 (chloroanilino)-2,4-dichloro-_s-triazine

The two chlorines on the triazine nucleus were found to be essential for reaction with sulfhydryl-bearing enzymes and related compounds. If they are replaced with other groups the molecule becomes impotent because it cannot react in the cell environment. The chlorine on the anilino group serves a multiple function. When placed ortho to the nitrogen it activates the chlorine on the triazine nucleus. One might describe it as a booster charge because of its effect on electron density at the vital part of the molecule. Therefore, if the chlorine is substituted at this point activity may be increased several-fold, depending upon the species of fungus affected.
This booster effect declines as the chlorine is pushed farther away into the meta or para






MeNEW: PLANT RESEARCH


positions on the phenyl ring. In spite of this diminishing effect the parachloroanilino compound is much more active than its meta analogue. This has been shown to be due to its greater ability to penetrate the spore wall of certain fungi.
The concepts on spore penetration have changed drastically in the last three years. We are learning, that certain groups such as the parachlorophenyl, or the long alkyl chain of 14 to 17 carbon atoms alter the lipoid solubility of a molecule enough to regulate completely the ability to penetrate the waxy and oily layers in the fungous wall. Merely by changing the length of the carbon chain in the 2-position of the imidazoline nucleus it is possible to render the molecule safer for use on plants and more destructive for spores at the same time. Clyodin was developed by Drs. Wellman and McCallan merely by lengthning the carbon chain from eleven atoms where it rendered the molecule violently injurious to the plant and relatively weak for the fungus to 17 carbon atoms where the reverse situation held.
In studies employing radioactive molecules, Dr. Miller has been able to show that fungicides not only penetrate the spore wall at unbelievably fast rates but may also change the permeability of spore membranes. If spores are placed in a suspension containing 2 p.p.m. of glyodin they will accumulate up to 6000 p.p.m. of their own body weight within 2 to 5 minutes. Interestingly enough, such a spore destroyed by this organic chemical will take up just as much mercury or silver fungicide as a normal living one. Likewise, hie found that mercury and silver did not interfere with each other although it had been assumed that heavy metals might be expected to occupy similar reaction sites. The spores actually took up more mercury after they had been exposed to silver than comparable untreated spores. This was traced to a change in the semipermeable membranes of the spore. Silver affects the spore so its cell constituents are lost more readily and external chemicals penetrate more actively.
By patient studies such as these we are cataloguing the effects of changes in chemical structure on the activities of various, types of molecules. The ultimate goal of course is to define all the characteristics of a fungicide so


we can design one that will penetrate the fungous hody, enter into a vital reaction with an enzyme or metabolite, hut not be detoxified by extraneous reactions. This is a big order hut it is not an impossible one,

VIRUS MULTIPLICATIONS AND PATHOGENESIS
One of the great areas of knowledge to be developed is the nature of virus infections in plants. In spite of the monumental strides forward in the past thirty years, the riddle of how viruses multiply and cause disease remains unsolved. The presence of virus protein does not necessarily cause disease symptoms. Investigators have isolated and identified heavy weight proteins from apparently normal plants so removal of proteins from normal pathways of metabolism does not explain the disease conditions. As a matter of fact nucleic acid may be combined with proteins without inciting symptoms as witnessed hy the research on recovery of tobacco from ring spot done by Dr. Price, a former member of our staff, now with the Citrus Experiment Station.
On the assumption that there is some physiological disturbance other than the abnormal use of protein, Dr. Porter has been investigating the biochemical changes in plants during the incipient stages of infection before disease symptoms appear. The first reaction of a plant to the tobacco mosaic virus appears to be an abnormal synthesis 'of amino acids. By use of paper chromatography he has been able to demonstrate a net increase in alanine, threonine, aspartic acid, lysine, gamma aminobutyric acid, asparagine and serine within 72 to 96 hours. After attaining this peak concentration they began to decrease so they were present in subnormal concentrations after 192 hours. Clutamine followed the same pattern except that it attained a much higher peak and within a shorter period after inoculation of the virus. Apparently there is some mechanism of nitrogen assimilation triggered by the virus before it begins to multiply much less create symptoms. As soon as the virus begins to multiply, the concentration of amino acids declines. The mechanism by which these changes are implemented is imperfectly understood and obviously justifies much more investigation if we are to understand the physiological basis of pathogenesis by viruses.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Within the past five years the scientific world has come to understand much more about the virus particle itself. Dr. Magdoff has been studying the physical properties of southern bean mosaic virus by X-ray diffraction. Interest is being directed primarily toward the spatial relationship of nucleic acid to the protein and to the packing of subunits of the virus in crystals. We now know that viruses may be degraded by removing nucleic acids and can be restored to activity by recombination of these two components, so studies of this sort become extremely important.
There is no more exciting area of research than these on virus proteins. The very basis of life is involved in, the studies on ribonucleic acid and protein synthesis. In due season, as techniques are perfected on viruses, one may expect such studies to be extended to the mechanisms of heredity. Far in the future the redesigning of chromosomes by chemical methods far more advanced than the primitive use of colchicine today to induce polyploidy.

THE MECHANISM oF ACQUIRED RESISTANCE OF INSECTS TO INSECTICIDES

One of the serious problems facing the agriculturist is the tendency of insects to acquire resistance to insecticides. For example, greenhouse operators have found that red spider mites develop resistant populations within a few months to two years after a newv chemical is introduced. In the past decade they have run through five new chemicals that were found only by a tremendous investment in funds and research time. The mites are so tiny that we have not had the courage to begin a study of them. There are equally interesting cases of resistance in houseflies , mosquitoes, flea beetles, lice, etc., that can be used. Currently our people are working on the resistance of houseflies to chlorinated hydrocarbons since they present an excellent subject for study on the comparative biochemistry of resistant and susceptible populations. By use of pure culture techniques to avoid microbiological contaminants, paper chromatography to separate and measure cellular components such as amino acids, and use of Geiger counters to follow the pathway of metabolism of unstable atoms such as S"' we


are obtaining considerable information on) what happens when an insect becomes resistant.
Dr. Moorefield has continued studies which he began while he was a student at the Universitv of Illinois. The flies resistant to DDT have a new type of enzyme known as dehydrociorinase. This material makes it possible for the insect to detoxify the chemical by removing HCl from the molecule. The enzyme does not require a metallic constituent to activate it and appears to be a specific sulfhydryl type of material. Within the past year, Dr. Moorefield has shown that the ability to produce this enzyme is latent in the larvae of an ordinary population of DDT-sus6eptible insects but probably does not occur uniformly in all individuals. When larvae are exposed to DDT only those with exceptional ability to generate this enzyme mature. Because of this, the resistant adults have demonstrable quantities of dehydrochlorinase while comparable susceptible insects do not.
It is perfectly obvious that we need to know more about the metabolic processes of insects which permit them to detoxify chemicals or develop alternate metabolic pathways to escape the lethal effects of insecticides. Since sulfhydryl compounds allegedly play such an important role, Dr. Cotty and Dr. Hilchey have been studying sulfur metabolism. Contrary to ordinary beliefs that animals must obtamn their sulfur from organic materials in plants, these investigators have demonstrated that insects can convert sulfates 'into sulfur amino acids. By use of paper chromatography to separate the various acids and measure their concentrations and by feeding sulfates and other materials labelled with S'~ they have been able to trace the process in aseptically reared cockroaches and houseflies. The sulfates are converted into methionine and the methionine is changed into cystine through an intermediate cystathionine. The cystathionine seems to serve as a unidirectional regulant since cystine cannot be converted back into methionine. The cystine may be converted into taurine and excreted as such.
Preliminary evidence indicates that some resistant houseflies have exceptional ability to synthesize glutathione but further research along these lines will be required to establish the point.





MeNEW: PLANT RESEARCH


THE PROCESSES OF ABSCISSION FoRMATION'
One of the very vital processes in plants is the ability to sh d leaves and blossoms. The process depends upon the formation of an abscission layer of cells at the base of the leaves or blossoms but beyond this knowledge very little is known, We know that many plant disease agents produce a biochemical change that causes diseased leaves to fall so one may assume that chemical messengers are involved in abscission cell formation, Since we know so little about the chemical stimuli we have very imperfect control over defoliation of cotton to facilitate picking or removal of leaves from nursery stock to improve its storage qualities. Neither do we know bow to prevent shattering of foliage from forage legumes, or loss of leaves from diseased plants and blossoms from cut flowers such as the rose.
Sometime ago we set out to design a new type of heterocyclic sulfur fungicide. We failed completely insofar as making a fungicide was concerned but we did notice that some of the compounds bad ability to cause the leaves to drop from beans. Over a period of two years we have synthesized a variety of related compounds and succeeded in d developing a new class of defoliants that can be applied either through the roots or directly to the foliage.
The remarkable thing about these new materials is that they cause a simple physiological defoliation without burning or distorting the leaves, As a matter of fact they duplicate the natural processes of leaf shedding almost precisely, A couple of days after the material is added to soil the innermost leaves begin to change color, Some members of the series cause the leaves to take on a red tinge ' then become yellow and finally drop from the plant. Defoliation proceeds steadily outward and upward until the entire plant is defoliated. If the plant is held for several weeks it completes its dormant period. New buds break forth and the plants resume normal growth. These materials offer such a wonderful opportunity, to study the biochemistry of defoliation that we were prompted to organize a study of defoliation by natural processes, freezing and chemicals.
Dr. Plaisted has found that within a matter of a couple of days after a defoliant is applied


to cotton, the number of free amino acids in the petiole increases from three to about twelve. A similar phenomenon has been observed in the leaves of deciduous trees in the fall and Dr. Weinstein found that rose petals undergo an increase in soluble nitrogen after cutting. This promising lead suggested that the first stage in abscission formation is the stimulation of amino acid production and that these amino acids would facilitate formation of new cells in the abscission layer.
Unfortunately the story on abscission will not prove so simple. A careful study of the total nitrogen balance indicates that the amino acids are the result of senescence in which proteolysis occurs rather than the incitants of a.new process. However, we do have one fascinating lead in Dr. Plaisted's work, He has found an active principle in shattered blossoms t at causes abscission of foliage in normal healthy plants. Studies are underway to isolate this factor and learn more about its bebavior. The significance of this research to date is that we are building tip a set of experimental procedures for regulating and studying this vital, but very seriously neglected field.
THE REGULATION OF PLANT GROWTH
If studies such as those described on the fungicides, viruses, insecticides and foliage abscission seem far-fetched, unrealistic and not likely to ever produce significant practical results, I would like for you to bear with me a moment while we outline the consequences of another basic research program. About 25 years ago the Institute assigned Dr. Zimmerman and Dr. Hitchcock to a study of how plants grow. They were free to study any aspect of plant growth and differentiation that appealed to them. Their attention was gradually focused on methods of altering the normal balance of growth hormones or chemical stimuli in plants by adding chemicals to the plant.
From this research there came knowledge on the use of ethylene gas to anaesthetize cells or regulate maturation 'Processes in cells, and root-inducing substances that have been useful in plant propagation. Interest in indole and








FLORIDA STATE HORTICULTURAL SOCIETY, '1956


naphthalene compounds lcd to a study of other types of acids, especially chlorinated derivatives of benzoic acid and eventually to aryloxy acids such as 2,4-D. By 1941 they had described the selective growth regulant ability of 2,4-D and opened the doors to a new era in wecd control and the development of specific growth regulants.
There is no need to dwell upon how the American public grasped the opportunity to remove broadleafed weeds from lawns, roadsidcs, wheatfields, pastures and cornfields. Within ten years, consumption of 2,4-D exceeded 25 million pounds a ycar. Even more important was the contagious enthusiasm of dozens of chemical companies to hunt for other classes of regulants and selective herbicides and of scores of experiment stations to employ weed specialists to study the chemical control of weeds. An entire new profession sprang up within a decade. A national society and four regional weed control conferences were organized so thousands of scientists meet annually to discuss progress and plan for the future. This probably has been the most progressive and dynamic branch of agricultural science in the past two decades.
Peculiarly enough, 2,4-D came into existencc because someone was interested in growth processes. These men were not as-, signed to work on weed control. There is good reason to believe that they might never have discovered such a material had they been told that they were to study weed control because they would have had no background, either from experience or literature knowledge to suggest that selective growth regulants should have been used. If ever there was an example to show how science makes its big steps forward, this is one.
Science needs depth and breadth of understanding. The men of science must dig beneath the surface to find more than meets their eyes. If research projects are defined so specifically that scientists must follow narrow, rigidly prescribed objectives, their effectiveness will be minimized because it is these big steps forward that clear the way for the workmen of science to build a new house of knowledge. Let us look at four rooms in the 2,4-D house to see what has happened since 1941.


The 2,4-D molecule has three significant features. These are the two chlorines on the benzene ring:






1


the oxygen linkage between the ring and acid groups, and the free carboxyl group, Exploratory research has indicated that the oxygen link may be replaced with nitrogen to give a weaker class of regulant but so far nothing of practical significance has developed in this area.
Study soon showed that the halogens played very dominant roles. The chlorine para to the oxygen was found to be indispensable but the ortho chlorine could be eliminated or replaced by a methyl group to give a compound only slightly less effective. However, when a third chlorine was added to one of the free positions a gamut of effects was obtained. A chlorine in the 8-position to give the 2,3,4,-trichloro compound has very little effect on regulant ability. When added in the 6-position so both positions ortho to the oxygen are blocked, the compound is essentially inactive. When the chlorine is added in the 5-position to give 2,4,5-triclilorophenoxyacetic acid there is a slight diminution of regulant activity for some plants and an increase in the caustic or lethal effect on others. This new compound will destroy raspberries and woody plants that are very resistant to 2,4-D. This was the first major step forward and has been tremendously important in brush control on ranges and farm pastures.
The next step came from a study of the carboxyl grouping. McNew and Hoffman found in 1946 that the acid group could be converted ,to a salt, amid or ester without destroying activity. In other words the 0-C-0OH
group could be changed without destroying regulant ability provided a free carbonyl (C 0) grouping remained. This fact was exploited fully in the next few years by three lines of development. The volatility of the material was reduced so it would be less hazard-





McNEW: PLANT RESEARCH


ous for use around valuable susceptible plants by converting it to metallic or other salts. The acid was rendered readily dispersible in water by converting it to the very soluble triethanolamine salts, Finally, it was converted to one of the esters which were more effective in the arid western areas than the salts because of their volatility and lipid solubility properties.
The third change came from further studies in the Institute laboratories on 2,4-dichlorophenoxyethanol and its sulfate ester. Dr. King found that these materials were essentially inactive on plants normally susceptible to 2,4-D. Thus the replacement of the free carbonyl group by a hydroxyl group was fatal to the herbicidal activity. The project might have died at this point had he not noticed that the ethyl sulfate ester, since named, Crag Herbicide 1, would prevent germination of weed seeds whben it was sprayed on the soil. He showed that the compound was activated into a herbicide by ordinary soil but not by steam sterilized soil. It remained for Dr. Vlitos to show that Bacillus cereus var. mycoides, a common soil bacterium, produces a sulfatase enzyme that removes the sulfate radicle. Other bacteria in the soil oxidize the resultant ethanol derivative to 2,4-D acid. Thus soil microorganisms can generate 2,4-D in the soil in sufficient quantities to kill wveeds. This is a safer, more selective type of compound than 2,4-D. By extending this principle to other analogues of the phenoxy-ethanol series a whole complement of new compounds is being evolved that can be used to destroy weeds in fields of such sensitive crops as tomato.
The fourth development came from studying the effect of increasing the length of the carbon chain in the acid. Dr. Wain of England has confirmed earlier observations by Synerholm and Zimmerman that 2,4,-dichioroaryloxy compounds with an even number of carbon atoms in the side acid are more toxic than the compounds with an odd number. This has been shown to be due to the ability of plants to metabolize this part of the molecule by removing two carbons at a time to convert the material back to 2,4-D. Because of this 2,4dichlorophenoxybutanol may be converted into 2,4-D by some plants. Peculiarly enough, the legumes such as peas and alfalfa do not have this ability so the butanol derivative does


not hurt them even as it destroys wild mustard and other weeds growing in pea or alfalfa. fields.
These four developments within the first decade of the 2,4-D era show what can be done by the ingenuity, curiosity and alertness of scientists once they are given a new tool to work with. Of course these four achievements stand out like brilliant gems of intellectual attainment but one must remember the tens of thousands of hours of patient research and hundreds of ideas that failed. They are the overhead that must inevitably be paid for every advance in research.

SUMMARY
We have foraged far afield in our discussion here today. Some of you may be confused by the complexity of the details as to chemical structures or the nature of cell activities. You have my humble apologies for overburdening you. However, the details are not too important. They are nothing more than illustrations of the basic principles we have been elucidating. If you can leave here with a positive impression as to the general principles involved we will feel that all the hours spent in preparation and travelling down here were well spent. Let us look at these principles.
Principle 1. The scientific agriculturist is turning his attention from exterior considerations to a study of cell metabolism. This new trend is absolutely necessary if we are to make systematic progress in the future. Remember, the person who can control the operation of cells can determine the fate of the individual plant, the disease agent, the insect, etc.
Principle 2. It is possible to design molecules to do almost fantastic things to a cell. Although our knowledge is in a most primitive state there is a great gleam of light shining down upon uis. It is possible to design molecules that fit like the key in the lock of cell morphology and physiology. Molecules can be made to penetrate one type of tissue and not another, to change cell permeability, to enter into different metabolic pathways, and even to differ in their stability and reactiveness. Remember that the future will see new kinds of molecules in the garden. They will take the place of insects, diseases and weedy plants and make plants rebel at their own genetics.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Principle 3. The type of basic research that must be pursued in this great development does not come easily. It takes time, patience and many, many dollars. It is necessary that every one of us understands this and encourages it, Men must be encouraged to seek basic principles of life processes so investigators such as themselves can use intelligence in creating new processes of farming and new products. The scientist who operates from a sound set of basic principles is efficient, effective and adaptable. Without these principles he must experiment by blind probing. Eventually blind research becomes too expensive to support because of the low, rate of progress.
Principle 4. There never was a time when biologists had better research tools at their disposal than today. The things that can be done in a -most routine fashion simply were not dreamed of twenty years ago. There is a certain measure of hazard to the tremendous


technological strides of our lifetime but the long range view is that more good will come from it than harm. People will be fed better, clothed warmer, and housed more satisfactorily because of scientific progress. We are confident that the future is brighter for having knowledge of the atorn even though it may do great damage in the bands of a moron or a moronic society.
Before every scientist there is an opportunity to serve as never before, There are available new tools, more money, and more challenge than ever before. If this nation and its democratic processes are to continue strong, healthy and progressive its security will come through skillful use of every mental and physical resource at our command. Therefore it is not only a privilege to be a scientist in such a great era, it is a moral obligation to serve skillfully and progressively with the long range viewpoint uppermost in our minds.


ED L. AYERS, COMMISSIONER
State Plant Board of Florida
Gainesville

G, G. RorvvvER, AREA SUPERVISOR
U. S. Department of Agriculture
Lake Alfred
Modern warfare against a major agricultural insect-enemy in Florida has come into its own in the present Mediterranean Fruit Fly Eradication Program. The combination of aircraft and improved chemical control procedures, supported by an intensive inspection prograrn, has beaten the fly back and should effect complete eradication within a matter of months.
More than 25years ago this same insect invaded Florida and was eradicated after a long and expensive fight that exhausted 18 months in time and $7,500,000 in state and federal appropriations. that was a campaign that created a great deal of criticism with its policy of destroying all host fruits and vegetables.


In addition, the arsenic used in spraying host plants did much damage to those plants and trees.
That was modern warfare in those daysutilization of the best known methods of eradicating a fly that had seriously affected fruit and vegetable production in other parts of the world. Regardless of procedures followed the outcome was the successful eradication of the Medfly, the only time in agricultural history that this insect had been eradicated from any country.
The present campaign. against the Medfly began only a few days after a Miami resident reported io the Dade County Agent's office that larvae had been found in a backyard planting of grapefruit, Tentative identification of the larvae as that of the Medfly was made by state and federal laboratories, and the positive identification followed the receipt by these same laboratories of fly specimens trapped in the Miami -area.
The early weeks of the campaign could not have been much different from those of the


THE MEDITERRANEAN FRUIT FLY

ERADICATION PROGRAM IN FLORIDA






AYERS: MEDITERRANEAN FRUIT FLY


first fight, for the methods were very similar. Until research men could formulate an effective program, the eradication plan moved along the old lines of destruction of host fruits and vegetables and the ground spraying of host plants and trees.
Today, however, the modern idea is the use of chemical control procedures tested and approved in other campaigns against the same fly. In this instance, the testing ground was H~awaii, where the Medfly is only one of three major fruit fly threats. The Florida fight has offered the first complete test for these chemicals and procedures.
Within two weeks after the initial find a network of traps had been cast over the state in an effort to delimit the infestations; and the malathion spray formula, involving a protein hydrolysate bait, had been given its first test in the heavily infested areas of Miami.
When fly catches disclosed that the infestations were more widespread in Florida than at first thought, spraying took to the air with the employment of aircraft equipped for this purpose. These aerial applications marked the real break with the past and the time-consuming procedure of destroying host fruits and vegetables was discarded.
The spray mixture of malathion, an organic phosphate, and a protein hydrolysate bait proved successful under Florida conditions. Malathion, used in the form of 25 percent wettable powder, was selected for the program because it possesses the lowest mamnmalian toxicity of any effective toxicant available for Medfly control.
The theory of aerial application of insecticides has been applied to the program and proved an unqualified success as evidenced by the fact that the Medfly apparently has been eradicated from almost half the state's 27 infested counties within the space of six months and insecticidal treatments discontinued. To accomplish this malathion bait sprays, through October, have been applied to 750,000 acres one or more times. The repeat treatments to this acreage have accounted for the treatment of more than 5,000,000 acres. Dieldrin surface treatments have been applied under host plants to 28,000 acres.
During the early months malathion was utilized at the rate of one-half pound of toxi-


cant per acre, but this dosage has beens cut to approximately three-tenths of a pound in recent months.
The attractant first used in the mixture was an enzymatic protein hydrolysate from brewer's yeast or casein, employed at the rate of one pound per acre. Later a less expensive attractant, an acid hydrolysate of corn protein in liquid form was used at th rate of one quart per acre. Only one pint of this liquid attractant now is used, mixed with three-tenths of a pound of actual malathion and enough water to compose one liquid gallon of mixture. This spray is applied at the rate of one gallon to an acre.
In the early stages of the campaign the spray was applied at 10-day intervals in order to kill each new generation of the fly. This schedule was set up on the basis of a normal life cycle of approximately 30 days. In a breakdown of this cycle, roughly 10 days each are allotted to the larval and pupal stages, and the period required before the female fly becomes sexually mature enough to lay eggs. The eggs hatch in one to two days.
The purpose of the 10-day spray schedule was to kill the immature fly in the pre-oviposition period. The use of dicldrin for the treatment of soil surfaces is designed 'to kill the larvae leaving the fruit to enter the ground to pupate, and also kill adult flies emerging from the soil. Dieldrin granular 30-40 mesh is applied at the rate of 50 pounds of 10 percent material per acre, or approximately five pounds actual dicldrin per acre. The material is applied to the soil under host fruits.
When the infestations persisted in some limited areas after several months of spraying field inspections disclosed that some adult flies were appearing in traps after the 30-day life cycle period. Some of this occurrence was attributed to heavy showers, but research proved that the fly larvae were still alive and active in over-ripe guava drops 19 days after the first spray. Larval development was delayed to approximately 21 days in over-ripe mango drops and as long as 25 days in some mummified grapefruit, sour orange, and tangerine shiners. This prolongation of one stage in the reproduction process meant a greatly extended life cycle which had to be. compensated for through extending the bait spray treatments.








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Spray applications have been cut to sevenday intervals in recent months and the possibifity of flies escaping the poison spray reduced to an infinitesimal point. Effectiveness of the spray has been attested to by recent findings which disclose an exceptional drop in the fly populations in the state. Twelve counties have been released from the aerial spray program, and two others are scheduled for release in the next two weeks. In addition, four of these counties no longer are subject to fumigation regulations for fruits and vegetables originating in those counties.
The decrease in fly finds is more than encouraging in the light of trapping reports. During the summer months when the fly apparently was making most headway, the field total never exceeded the August figure of 18,000 traps, Finds at that time were numbered at more than 2,000 flies. That was listed.as encouraging in the light of 5,000 finds from 4,000 traps in June. But even more progress is noted in the latest figures which disclose less than 600 finds from 48,000 traps.
Effectiveness of the trapping operation was increased by the improvisation of a new type of trap designed by a research entomologist with the program. This trap is a horizontal plastic model open at opposite ends.
The principal attractant used in the trapping operation is oil of angelica seed, which is mixed with a poison, three percent DDVP (Dimethyl Dichloro Vinyl Phosphate). Chlordane or DDT powder is dusted in the dry traps to kill ants that might remove the flies.
One of the important parts of the program, the roadblock, has been discontinued as a result of the sharp drop in fly infestations.
The system of roadblocks was established in the first weeks of the program and continued until last month when vehicular inspections were considered no longer necessary. Check points were set up around heavily infested areas to protect other parts of the state from equally as heavy infestations.
In five months of operation the roadblock inspectors checked more than 4,000,000 vehicles and confiscated many tons of host fruits, vegetables and plants. This was of inestimable value to the eradication program, since it was established beyond a doubt that the fly moved to other points in the state along well-traveled highways. This movement paralleled that of


vehicular traffic. It is impossible to estimate how far and how fast the insect would have traveled without roadblocks to halt that progress.
Complete eradication of the Medfly is the aim of the program and must be accomplished in order to protect the agricultural interests of Florida and of the United States.
The use of dieldrin for soil applications and of malatbion for foliar treatment has permitted Florida to move practically all fruit and vegetable crops to date. That is in sharp contrast to the first eradication program in which host fruits and vegetables were destroyed.
In short, the present program is eradicating the fly and permitting the marketing of commoditles under almost normal circumstances. In this, fumigation has played an extremely important role and will continue to play that role until the Medfly has been completely eradicated. EDB (ethylene dibromide) is used to fumigate citrus and other host fruits and MB (methyl bromide) many host vegetables. Both gases are used in specially constructed or modified gas-tight fumigation houses equipped with special air circulation and gas volitization equipment. At the end of October more than 175 fumigation chambers bad been approved for use in the Medfly program in connection with fumigating material regulated on account of the Mediterranean Fruit Fly Quarantine. In addition, 37 fruit processing plants had so modified their processing procedures to permit them to handle the regulated fruit without endangering further spread of the Medfly,
Presence of the Medfly in other countries is marked by increased cost and reduced production. This is especially true in lands around the Mediterranean Sea where the European and Mediterranean Plant Protection Organization has set up a committee to study the fly and its control, Last meeting of this body was held in September of this year at Bonn, Germany. Since no eradication program has been devised in that part of the world, the emphasis was on fumigation and physical controls.
Germany, incidentally, is vitally interested in the fly, since the p st has been prevalent there since 1954. The Medfly was first discovered there in 1936, but did not appear in damaging proportions until last year. Imported fruit is believed to be the cause for the in-






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stations, since the winters in Germany are considered severe enough to eliminate local incidences of the fly. Nevertheless, the peach crop in Germany has been infested in particular cases to 100 percent, enough to affect the national economy. Apricots, apples, pears, and tomatoes also have been infested in that countrv.
Peaches grown in Egypt also have been 100 percent infested when no control is applied; certain parts of Brazil no longer export citrus, and Spain ships only early varieties of citrus which must be marketed before ripening properly.
Reports of this kind emphasize the fact that the Medfly must be eradicated from Florida.


Although the program is many months away from that successful conclusion, there is every reason to believe that eradication will be accomplished within the space of one year. The program is being financed by state and federal governments, with each appropriating an equal half of the over-all eradication fund of $10,000,000. That is a small figure on the basis of the present day dollar value when compared with the cost of the first fight,
The cooperation of personnel of the Florida Department of Agriculture, State Experiment Stations, other civilian and military governmental agencies and the general public has been of inestimable value to the eradication program.


LLOYD STANLEY TENNY
Lloyd Stanley Termy was bom near Hilton, N.Y. eighty years ago this month and was reared on a farm. He received his A.B. Degree from the University of Rochester in 1902, served as Assistant Pathologist with the U. S. Department of Agriculture from 1902 to 1904 , as Assistant Pornologist 1904 to 1907 and as Pomologist for the U.S.D.A. until 1908 when he returned to Cornell for further study. From 1911 to 1913 Mr. Termy was with Cornell's Agricultural Extension Department, being advanced to Professor of Extension. He was the first state leader of county Agricultural Agents in New York and helped organize the first Farm Bureaus.
Mr. Tenny was Secretary-Manager of the Florida Growers & Shippers League from 1913 to 1916, Secretary of Florida East Coast Associates 1916-17, and Secretary-Treasurer of the Coral Reef Nurseries from 1917 to 1918.
Mr. Termy was Vice President of the Eastern Fruit and Produce Exchange of Rochester, N. Y., and of the North American Fruit Exchange of New York City and president of the Southern States Produce Distributors from 1918 to 1921. The Bureau of Agricultural Economics called him as Assistant Chief 1921 to 1926 and as Chief in 1928. He was Vice President of the California Vineyardists Association in 1928-29; President of the Federal Fruit Stabilization Corporation of California


1929-30; and General Manager of the Chicago Mercantile Exchange from 1929 to 1943 when he retired. He is now living in Hendersonville, North Carolina.
Few men have so profoundly influenced Florida Agriculture in five short years as did Mr. Tenny. He was one of the BIG FIVE (consisting of P. H. Rolfs, H. Harold Hume, W., J. Krome, Wilmon Newell and Lloyd S. Tenny) who played a tremendous part in Florida Horticulture. Mr. L. B. Skinner (for years President of this Society) brought Mr. Termy to Florida to organize the Grower's and Shipper's League in 1913. Soon thereafter Dr. E. W. Berger took to his office samples of Citrus Canker because Mr. Tenny had been a Pathologist. Mr. Termy recognized it as a very serious threat and "sold" the Florida authorities on the idea that eradication would be cheaper in the long run than control. How right be turned out to be!!!
Soon, the eradication of Citrus Canker was made the number one objective of the Grower's and Shipper's League because Florida had no department in its government which could undertake it, no funds and no law. just imagine!!! Mr. Tenny threw himself into the fight with all of his tremendous energy, skill, knowledge and resourcefulness. He whipped together an organization, raised the finances and together with others of the BIG FIVE drew up and secured the passage of the "FLORIDA PLANT ACT OF 1915." Having


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FLORIDA STATE HORTICULTURAL SOCIETY, 1956


secured the law that was necessary, he helped the others select the "PLANT COMMISSIONER" Dr. Wilmon Newell; the "State Nursery Inspector" and the "Port Inspection Department," which in cooperation with the U.S.D.A. was responsible for the inspection of all plants entering the State from foreign countries,
Having helped make the Plant Board a going concern, Mr. Tenny turned his attention to the task for which he had been brought to Florida, that of getting better rail rate schedules for Florida growers and shippers.
It is not too much to say that but for the timely arrival of Mr. Tenny the Florida citrus industry might very easily have been wiped out by Citrus Canker. Like all other members of the BIG FIVE, Mr. Tenny was a giant. The Florida State Horticultural Society takes pleasure in making Mr. Lloyd Stanley Tenny an Honorary Member and regrets that the state of his health requires that it be in absentia.

ARTHUR FORREST CAMP
Dr, Arthur Forrest Camp came to Florida from California in 1923, and during the ensuing thirty-three years has compiled a record of service to horhculture equalled by fewsurpassed by none.
He graduated from the University of California with honors in 1920; and was awarded his Doctor's Degree in 1923 by Washington University, St. Louis, Missouri, and immediately started on a career that was to be devoted not only to horticultural advancement in Florida but to advancement on an international scale,
From 1923 to 1929 Dr. Camp served in several important research positions with the Florida Experiment Station at Gainesville, and in 1929 was made Horticulturist In Charge, Department of Horticulture. This same year he was made an agent of the U.S.D.A., and played an outstanding part in the eradication of the, Mediterranean fruit fly. In 1930 he returned to the Experiment Station and served as head of the Horticulture Department until 1936 when be became Horticulturist In Charge, Citrus Experiment Station. Since 1944 Dr. Camp has served as Vice-Director, Agriculture Experiment Stations, in charge of the Citrus Experiment Station. He personally carried on research until 1944, and under his guidance


the Citrus Experiment Station has grown in both size and stature until it now occupies and enjoys an outstanding position in the field of horticultural research.
Dr. Camp has over one-hundred publications on citrus and other tropical and sub-tropical crops. Some of these publications, especially those dealing with the fertilization and nutrition of citrus have been and are being used as guideposts in production management. His development of a coordinated system of spraying and fertilizing citrus is in a large measure responsible for the tremendous per-acre production citrus growers now enjoy as compared to the 1930s. The development of such a program has been worth untold millions to the citrus industry, as it has enabled growers to maintain a rather uniform per-box cost over the last twenty-five years while per-acre costs have gone steadily upward.
As an agent of the Florida Citrus Commission, Florida Citrus Mutual and the Florida State Plant Board, Dr. Camp has been called upon for fact-finding trips to South and Central American countries, Spain, Japan, California, and Texas. His reports following these trips enabled the various agencies to formulate plans to protect and promote citrus in Florida. Ile is considered the citrus industry's outstanding spokesman on technical subjects, and has been called on many times to state the industry's case before legislative committees of both the State and Federal governments.
Dr. Camp has done consulting work on Citrus production, marketing and processing in many foreign countries for governments, companies, cooperatives, and individuals including Cuba, Jamaica, Haiti, Honduras, Nicaragua, Costa Rica, Guatemala, Argentina, Brazil, Paraguay, Peru, Surinam, Bermuda, Mexico, Sweden, Spain, and Japan. He was made an Honorary Citizen of Argentina in recognition of assistance given the citrus industry in that country.
Dr. Camp was instrumental in setting up and carrying out research into the tristeza problem, a new disease that posed a threat to Florida citrus and one that decimated many groves in South America. Thanks to this work tristeza no longer poses the threat that it once did,
Dr. Camp is an honorary member of the Kiwanis Club and Gamma Sigma Epsilon,





AWARD OF HONORARY MEMBERSHIPS


and a member of the Florida State Horticultural Society, American Society for Horticultural Science, American Association for the Advancement of Science. He is in American Men of Science, Who Knows-and What and Who's Who in American Education. He is a grove owner, and the president of the Haines City Citrus Growers Association.
It is with tremendous pleasure that the Florida State Horticultural Society recognizes the great service that Dr. Camp *has rendered to the horticulture of the State of Florida and other countries and his leadership in the field of citrus research that has been largely responsible for the enviable position the Florida Citrus Industry holds today.

HAROLD G. CLAYTON
It is a great privilege to present to the membership of this Society a distinguished native Floridian who has, by unanimous vote of the Executive Committee, been designated to receive an Honorary Membership in the Society. I
Harold G. Clayton was born February 27, 1892, at Ocala, Fla. He grew up and attended public schools in Tampa; received B.S. Degree in agriculture from University of Florida in 1914; received M.S.A. Degree from same institution in 191 ' 6. After a brief period of farm work he was made County Agent in Manatee County, in March 1917. He entered military service in World War I on May 15, 1918 and served until December 6, 1918. Early in 1919 be returned to county agent work and in October 1919 he was made District Agent with the Agricultural Extension Service at Gainesville. He continued as District Agent until November 1934, at which time he was asked by the Director of the Extension Service to assume administrative direction of the Agricultural Adjustment Administration, later the Production and Marketing Administration, and now Agricultural Stabilization and Conservation Committee. He served in this- position until July 1, 1947. During this period he continued to hold a cooperative appointment with Extension Service. On July 1, 1947 he was made Director of the Florida Agricultural Extension Service, the position he held until May 31, 1956 when he retired,
H. G. Clayton married the former Miss Harriet Ray, of Tampa. The Claytons have


one child, Peggy, who is now Mrs. Peggy Clayton May, and two' grandchildren.
As Secretary to the State Agricultural Adjustment Administration Committee, a member of the State Defense Council, Chairman of the State USDA War Board during World War H, he rendered outstanding service to Florida agriculture by arranging for the procurement and proper distribution of vital agricultural supplies and by stimulating farm people to extraordinary effort in war crop production, in buying U.S. War Bonds, in salvage drives, and in other activities connected with the war effort.
Through his knowledge of Florida agriculture, his careful study and understanding of the functions of all agencies concerned with agriculture, and his persistent efforts to work in close harmony with all agencies and groups, he has been instrumental in bringing about effective working relationships between these agencies and groups for the maximum service to Florida agriculture and the solution of major agricultural problems.
While serving as district agent, he was active in promoting 4-11 Club work and in cooperation with the state 4-H Club agents he helped to start the state's 4-H camping system, which today is outstanding in the Nation.
From 1947 he served as Administrator to the State Soil Conservation Board, He was appointed to this position by two different boards since the State Soil Conservation Board was completely reorganized by the 1953 Legislature.
He served as Chairman of the State Seed Certification Advisory Committee.
He was a member of the Farmers Home Administration State Advisory Committee.
He was a member of the State Agricultural Stabilization and Conservation Committee.
He collaborated with Florida Forest Service and Soil Conservation Service in a weather modification evaluation study.
During his service as Director of the Florida Agricultural Extension Service the number of county agents increased from 61 to 66. (Florida has one county which is not classified as an agricultural county.) The number of assistant county agents has increased from 18 to 54; the number of home demonstration











FLORIDA STATE HORTICULTURAL SOCIETY, 1956


agents from 41 to 52, and the number of assistant home demonstration agents from 9 to 22. The total staff of specialists has been increased from 14 to 33. Mr. Clayton's wide knowledge of and service to horticulture in Florida is reflected again by the fact that this increase in. specialists' services covers every phase of horticulture in our state.
Mr. Clayton has for many years been a faithful member of this Society and a regular attendant and keen observer at its meetings; learning the needs, problems, views, of people actually engaged in various horticultural enterprises; using his knowledge and his ability to strengthen and direct the Agricultural Extension Service for the common good.


Always modest-never once grasping for spotlight or for front page-devoted to Florida, her horticulture, her agriculture, her farm youth-never asking for anything for himself other than an opportunity to serve others always trying to see the other fellow's point of view. A person whose soundness of judgment has been recognized by those at the highest levels in our state government and institutions. A man who has by both precept and example rendered outstanding service to this Society and to Florida horticulture. Always a gentleman-a person of highest character-who, has in every way measured fully to the highest standards of honorary membership in this distinguished Society.





COHEN: TRISTEZA DISEASE


CftZli

INJURY AND LOSS OF CITRUS TREES DUE

TO TRISTEZA DISEASE IN AN

ORANGE COUNTY GROVE'


MORTIMER COHEN
State Plant Board
Gainesville

Soon after the discovery of tristeza in Florida, it became apparent that careful study over an extended period of time would be necessary to assess accurately the amount of damage done by this disease. and to make predictions regarding future losses. In July 1952, therefore, a large grove near Winter Garden in which many trees with tristeza had been found, was mapped tree-by-tree, by a group of Plant Board inspectors.
In the mapping, trees were rated on the following scale:
0 -Healthy
1 -Slight decline
2 -Moderate decline
3 -Severe decline
X-Dead or missing
R-Replant tree
Infected trees in this grove are of mature size and are not stunted. The large size of the trees and the observable spread of disease in the planting are taken to indicate that the disease was brought in by natural means, probably by aphids, rather than through infected budwood. This is in contrast to the situation in other parts of the state where the majority of infected trees apparently had tristeza virus introduced with the original bud.

'/The information reported in this paper is not due to the efforts of a single individual but is the result of the cooperative work of many individuals now or formerly on the Plant Board staff. Among the people whose efforts have materially aided in the collection and assembly of the data presented in the Paper are: J. N. Busby, K. E. Bragdon, A. C. Crews, L. W. Holley, Dr. L. C. K~norr, Mrs. Enid Matherly. John Perry, C. R. Roberts, Mrs. Jean Smith. Howard Van Pelt.


This grove has been mapped twice a year since July 1952, the last mapping having been completed in July 1956. The entire area included in the study is shown in Figure 1, which also provides a graphic comparison between the condition of the grove in July 1952 and in July 1956. The entire grove area consists of about 80 acres. Approximately 20 acres, planted entirely to Temple oranges on sour orange stock, are not included in our statistical summary because many trees in that portion of the grove showed signs of decline from water damage in 1954 and it was desired to restrict the study, as much as possible, to the effect of tristeza only. The remaining 60 acres consists of 4169 trees, of which 88 per cent are Temples on sour orange rootstock, mainly 26 to 30 years old. Also in the grove are 297 Valencia trees on sour orange stock, about 200 trees on grapefruit stock, and a small number for which the rootstock is undetermined. Properties owned by 4 different individuals are included in this 60 acre block. It should be stressed that this is not a neglected planting but that normal practices of cultivation and fertilization are being followed.
Figure 1 shows only trees rated 2, 3, X or RI that is, trees in definite decline, missing or replanted. Trees rated 1, those in slight decline, are not included, because slight symptoms are sometimes due to transient causes and not to tristeza. This map contrasts trees affected in July 1952 (shown as 0's) with the large number of additional trees affected by July 1956 (shown as X's). The many trees which went into serious decline in the 4-year interval between the 2 mappings can be clearly seen. All portions of the grove were not affected equally. Some of the older areas planted with Temple orange on sour orange stock were the most severely affected












Fig. 1. Spread of disease in an orange grove near Winter Garden from July 1952 to July 1956. Map shows trees in moderate or severe decline, dead, missing or replanted. Trees with slight symptoms of decline are not shown. All trees are of the Temple orange variety except for the indicated block of Valencias.


X
X 0 0 Li0

0 0 000
XO 0

XX XX 0 X
X X 0 0000
0 XO
0 x X X XX XXXX X X
X 0 0
X X
00X X X
X X X XX XX 0
X XXOX X X
XXX X XXX
XXX XX 0XXX
0 X XXOX X
XXX XXX X
X XXX X
X 0 X
X X


X 0
X 0 0
XX 0
X
XXXO
XX X
X X 0 X
X
X 0 X X XX X
XX
0 OOX 0 X X XXXO0
X X X
00000 0XX 00 0 X XX XXXX
XX 0X XXX
0XX X 0


X X XXY


X 0 0 X


I X X X OX
XX X X
0
X 0 X
0 X 0 K
XX X 0 X
X X XX
XO XX X
X X
X X


XX X K
X 0 OXX
OXX XXXXOXXX XX 0 0 X XXOXX XXX 00 OX XXX
X 0
0 X XXOOOXXO XXX 0 0
0 X XOXXOXO0 0
X I IXXXXIX X XOX XO
XXX X XOXXXXXXX OX XO0
X OXXX X X X 00000 o x XX XXXO XXX
X X X X XX X 0
X0 X X O


X 0


0 X 00
0 0 X liX
0 X
1 0


X X
0 X 0
O0 XX XX
XX .XX
K X
XX

X XX XX 0
X OXXX K X
0 O0 0
0 000 XX
X X 0 X
XX 0 XOO 0
X X XX XX X
X XX X 0
XXX X XX
X X 0
X X
X X X X XO
XX X X XX
X X XX XXX XX XXX X XOX


0
0


K
K


XXX
X0 X

0
XX

X
XX

K 0


XX
XXX X X X X

XX X XX
X XXX
000 X 0
0 X X


X X OX

X XO 0 00


X X

X X X o X X


OX 0 0
X XX XX X
XX XXX X X X 0XX
XXX X OXOX X'0
XX X X 0
XX X X X
XX X X XXOXX XX 0 X X XXX XXX X x
OOXOOX X X X XOXX
OOXtO X XXXO X XX XXXXX XX XX XO X XX X XO00 O X X X XX X XX XXX K X 0 XX XOXXXXX XX XXX X 0 XOXXXX 000 XX OX XX OX XXX X XXX
OXXO O X OXXXX 0 XO00 XOX X X XXOX XXO X
XO00 OXXXXX XXX OOXXX XOO XXO0 0 X
XOXX XXOOX XXO 0 X K XXXX X X0X 1XX XXO XX XOXX X XO00 0 X XX
OXX XXXOX XX XXOXO X XXXXX
XOXX XX X XXL
XOX X XX OX XXX XXX
00 0OX 0 IXOX


0 X
X X X 0
0
3K X
X
XO






XX0 X
XXX

0
X

X K
OX


X X XX

YU
X
3 0


10X


XXX XX
X X


Xi 0 X 'XX 0000 XX
0 0
XX
X
0
0 X
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X
O 0
OX X


XXXXX
KXOX
XXX
X 0


X 0 X
X
00


0 X X
0 X X
X 0 OX
0 X X X
X X 0 X X
X 0 XX XX
XX X
XX X X
X
X X XO XX
X XX

X 0 OX 0


0 0 0
X X X X
X 0 X X 0


MAP: 0 - Trees in decline, dead, missing or replanted in July, 1952
X - Additional trees affected by July, 1956


XX XX 0
0

0 X


X X
X
X


SXXX


C








COHEN: TRISTEZA DISEASE


but the eastern portion of the area studied was not as badly affected as the middle portion. Trees in the Valencia .orange block, which is thoroughly infected with psorosis as well as tristeza, were not as severely injured, on the average, as trees in the Temple blocks. The western-most planting consists of Temple trees which are approximately 8 years old. A relatively low proportion of these trees showed symptoms of decline.
Most striking is the relative absence of disease in all trees on grapefruit rootstock. These are located in some of the rows directly south of the Valencia block. This situation is discussed below.
The increase in the number of trees in decline from 1952 to 1956 did not come about abruptly, but was the result of a steady trend, as is shown diagrammatically in Figure 2 where the number of trees in classes 2, 8, X and R at each mapping is indicated by a line graph. Trees in class 1, those in slight decline, are not included in this graph. The


I FIG. 2


0 (
JULYr D .


Tma UnD A, 3, X OD RIN M, oRG CMrY W vI
R"M JULY X"52 70 JULY P5,


JULY FEB. AUG. VAR. AUC. JA. JULY
1953 11% 155 i56


TABLE 1


DISEASED, MISSING, AND REPLANT TREES IN AN ORANGE GROVE NEAR WINTER GARDEN

NUMBER OF TREES


CLASS OF DECLINE PERCNTAGI
DEAD OR TOTAL OF ALL
DATE SLIGHT MODERATE SEVERE MISSING REPLANTS AFFECTED TREES


July 1952 285 186

Dec. 1952 360 173

July 1953 241 201

Feb. 1954 452 264

Aug. 1954 4 298

Mar. 1955 1540 307

Aug. 1955 393 209

Jan. 1956 433 196

July 1956 385 158


22 19 107


27 100

30 135

37 137


220 137


66 7 346


220 269 479


619 820 874

1125 1312 2266 1321 1382


14.8%

19.6 20.9 26.9

31.4 54.3 31.6

33.1


.1511 36.3








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


total number of trees in classes 2, 3, X and R increased from 334 in July 1952 to 1126 -in July 1956. Thus 27 per cent of all trees in the grove were in definite decline or missing, dead, or replanted by July 1956. If this rate of increase of diseased trees continues for the next 4 years, July 1960 will see 46 per cent of all trees in the grove in this category of seriously affected trees.
It is interesting also to compare the number of trees in all classes during the successive mappings from 1952 to 1956 as shown in table 1. The major increase in "total trees affected" during this period is in replant trees and trees dead or missing, but the number of trees in intermediate stages of decline has also remained at a higher level than was observed during the first two mappings. In March 1955, a three-and-one-half-fold increase over the previous reading in the number of trees in slight decline was recorded. The count occurred after a relatively dry winter. The transient nature of this apparent decline is indicated by the fact that most of these trees were again rated as healthy in the subsequent 3 mappings. If one projects the data in Table 1 to July 1960, and includes also trees showing slight symptoms of decline, it will be found that 57.8 per cent of all trees in this grove will have been affected by the end of 4 more years, provided the present rate of increase in the number of trees in decline continues.
What is the evidence that these trees are suffering from tristeza disease? Numerous trees have been examined for the presence of honeycombing-that pattern of tiny holes in the bark below the bud union which has proven to be quite reliable in Florida as a field test for the presence of advanced tristeza in trees on sour orange rootstock. A high proportion of the trees examined have shown this symptom.
A more specific method for determining if plants are suffering from tristeza disease is the histological examination of the bark from the bud union of suspect trees as described by Schneider (1). Bark samples collected at random from 38 trees in decline in the grove were examined using this method. Of the 33 trees examined, 30 were found to be positive for tristeza, Six of the histologically tristezapositive trees were indexed on key lime seedlings, and all 6 were found, by the trans-


mission test also, to be carrying the tristeza virus.
It is interesting to contrast the results of these histological tests with similar tests made on trees in the 20-acre area previously mentioned as having been excluded from the study because its trees had suffered from water damage. Bark samples from 11 trees in decline in the water-damage area were examined and 10 of these were found to be negative for tristeza.
It is quite clear, therefore, that, in the 60 acres under study, tristeza was the major cause of decline. On the basis of this evidence it can be estimated that upwards of 90 percent of the diseased trees studied were injured by tristeza disease.
When trees in this grove once begin to deteriorate, they do not recover, but continue to decline and eventually die. This can be seen by observing the fate of trees found in decline when the grove was first mapped in July 1952. Figure 3 summarizes the information on all the trees rated as being in slight, moderate, or severe decline in July 1952. Of a total of 483 trees in all categories in 1952, 294 were dead, missing or replanted by July 1956, and 396 trees or 82 percent were more seriously in decline than in 1952.
As might have been expected, more of the trees at first judged to be in slight decline
Fla. S
Rtling in Juy 1956 of Tres W,,d In Slight, 0 w.r.te. ,od S eor
'D 11in M uy 11,5 2 in t Cit-u G,-r o ,, wia Nlt- C~m



1956 __________ 1


'195
1956 1956


195? 0 trees ii ,eo.,t do *io.n in 1952




er or - ,lfn,

Helthy Slight Mod.r.te Se.ere Dad or






COHEN: TRISTEZA DISEASE


proved to have been affected by a temporary condition, and a higher proportion of these trees showed recovery. If the 203 trees which were found to be in moderate or severe decline are considered alone, it is seen that 189 trees or 93 percent were more seriously in decline in 1956 than-in 1952.
The fact that trees in decline generally do not improve but continue to decline further is an additional indication that tristeza is responsible for the condition of the grove. It is enlightening, in this connection, to compare the fate of trees in that area of, the grove which was affected by water damage with trees from an area in which tristeza was the prime disease factor. In a portion of the water damage area in August 1954, 274 trees were rated as showing some degree of decline. Two years later only 22 percent of these trees showed any deterioration; some of these, no doubt, were suffering from tristeza. On the other hand, in a comparable area in another part of the grove where no water damage had been noted and where 180 trees were in decline in August 1954, 52 percent of the trees had deteriorated by July 1956.
When tristeza was first found in Florida, most pathologists expected to see a repetition of the damage done in South America. One of the warnings issued by pathologists was to avoid planting citrus on grapefruit rootstock because it, like sour orange rootstock, had been found in South America to make a combination non-tolerant to tristeza. After extensive examination of Florida citrus groves,
however, State Plant Board inspectors have not been able to find any trees on grapefruit rootstock which were in decline because of tristeza infection. When the grove in this study was examined, it was found that the bud union on about 200 trees had a configuration which indicated that the rootstock was grapefruit rather than sour orange. These trees have been watched since 1952 and it is of interest to examine Figure 4 which is a map of the portion of the grove containing the trees on grapefruit rootstock. Figure 4 shows both the rootstock and tree condition in August 1955. Trees on grapefruit rootstock are mixed in with trees on sour orange rootstock thus providing an excellent comparison of the behavior of trees on these two rootstocks under identical environmental conditions. Even a casual examination of


FL0. .
COL;DITIO OF I"0.,S IN A PLANTING 0N NIMD SOUI ORAN
AND CNAPO/NUIT ROOTSTOCKS
AUcUST 1955


S147 3 12 11I 10 Y' 7 e .A- 3 I


00 OG'z\ O. 00 OO@@ Q0GGQQ0i,
088000 0000@w@ , 8
rJ0EJE1*1GIAZ
Z'3
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L310000AE] D3OO 2 EJ 8LiU -)


p a, N s to o SAR Os- .
o 'Pfl
'6 - .


Tr. Coaditi-n R J.IAN


Figure 4 will reveal that very few of the trees on grapefruit rootstock are in decline while a very high proportion of the adjoining trees on sour orange rootstock are diseased. Bark samples were taken from 9 of the grapefruit trees which did show some sign of decline, and were examined microscopically. None of the specimens was found to have histological indications of tristeza.
These observations do not prove that citrus trees on grapefruit rootstock cannot be inlured by tristeza in Florida, since these trees may eventually show tristeza injury, but it is very apparent that grapefruit cannot be considered to be in the same class as sour orange insofar as susceptibility to tristeza in Florida is concerned.
One of the purposes for undertaking the study of the grove near Winter Garden was to explore the possibilities for predicting future outbreaks of tristeza in Florida. To carry out this aim, two small plots containing 58 trees in all were set up for special study of trees on sour orange rootstock. Trees in one plot had Valencia orange tops, and Temple orange tops were used in the second plot. Bark samples have been taken periodically from trees in these plots and prepared for microscopic examination. In the course of this study, 6 previously healthy trees in these plots have developed histological symptoms of tristeza. These histological symptoms were evident from six months to 2 years before there was any visual indication in the field








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


that these trees were diseased. This confirms the observations made by Schneider (1) on trees with quick decline disease in California. Thus, a tool actually is available for shorttime prediction of future deterioration of citrus trees from tristeza disease.
Since it is obvious that histological symptoms of tristeza must be preceded by entrance of the virus into a tree, a number of healthy-appearing trees were indexed on key lime seedlings to determine if any of them were carrying the virus of tristeza. In this way it was hoped the interval between the introduction of the virus and the first appearance of histological symptoms could also be approximated. This phase of the work has produced most surprising results. So far, 21 trees in this grove which are histologically, normal have been checked by transmission test for the presence of tristeza. Of these, 15 trees or 71 percent have been found to be positive for tristeza. Furthermore, 4 out of 5 trees on grapefruit rootstock which were similarly indexed proved to be carrying tristeza virus although, as previously mentioned, there is no indication, in Florida, that trees on grapefruit rootstock are injured by this disease. If the foregoing sampling of the trees in this grove can be considered representative it must be concluded that about three quarters of the healthy-appearing trees in this grove are carrying the virus of tristeza.
The most surprising aspect of this project is that only one of the trees tested has so far shown histological signs of tristeza disease, although a few of these trees are known by indexing to have been carrying the virus for almost 3 years, and most of the trees are known to have been infected for almost 2 years. It should be mentioned that similar virus-carrying susceptible trees, which appear healthy and do not show histological signs of


tristeza,' have been found elsewhere in Orange county, and a few have been found in other counties in the state (2). The significance of this finding is not fully understood. It may be that the virus has an extremely long incubation period before it begins to affect the phloemn of the host tree. (Phloemn breakdown is one of the earliest features of the histological picture of a tree in decline with tristeza disease). Another citrus virus disease with an incubation period of many years is already known-psorosis disease
-but it has not been suggested previously that 'this might also be the case with tristeza. A second possibility is that an additional factor as yet unknown, in addition to the virus indexed, must be present before the disease can begin to run its course. In any case, this matter is being studied actively, and continued observation of these trees certainly should throw more light upon the problem.
The above considerations should not obscure the central fact that tristeza disease in Florida has caused serious losses to citrus. Although this paper describes conditions in a single grove only, many other groves in Orange county and elsewhere have been damaged by tristexa. At present, many of the factors involved in producing an outbreak of this disease are not understood and cannot be predicted. Growers who plant groves on sour orange rootstock, the only rootstock used in Florida on which trees are definitely not tolerant to tristeza, are risking the life of their planting. is it wise, therefore, to continue the use of this dangerous rootstock where other rootstocks can do the job safely?
LITERATURE CITED
1. Schneider. Henry. 1954. Anatomy of bark of bud union, trunk, and roots of quick-decline-affected sweet orange trees on sour orange rootstock. lgardia 22: 567-581.
2. Cohen. Mortimer. 1956. Incidence of tristeza virus in Florida in trees not yet showing field symptom s. Phytopath . 46: 9 (abs tract).





SMITH: PHOSPHATE FERTILIZATION


EFFECT OF PHOSPHATE FERTILIZATION ON

ROOT GROWTH, SOIL pH, AND CHEMICAL

CONSTITUENTS AT DIFFERENT DEPTHS IN AN ACID SANDY FLORIDA CITRUS SOIL"


PAUL F. SMITH
Horticultural Crops Research Branch
Agricultural Research Service
United States Department of Agriculture
Orlando

In recent years, certain studies (4, 10) have been made to explore the relation betwveen fertilization practices and root development of citrus in the sandy soils of Florida. Those reports were concerned primarily with the effect of nitrogen sources and rates and methods of timing on the density of roots in the top 5 feet of soil, where the changes in chemical composition were relatively small. With adequate liming, nitrogen appears to have little or no permanent effect on soil composition (10).
The present studies involved deep sampling in a long-term phosphate experiment in which there has been a large permanent change in the phosphorus status of the soil because of the accumulation of applied phosphate. Previous reports (7, 8) describing the results from this experiment for the first 6 years, failed to show any beneficial response in tree growth, yield, or fruit quality to applied phosphate. No additional data on these factors are presented here, but the results through the 13th year are still essentially the same. The present report is concerned with the density of small roots, soil pH, and certain chemical constituents in the soil in relation to the rate of phosphate fertilization.
ExPERIMENTAL METHODS
Pineapple orange trees on Rough lemon stock were planted on a virgin plot of ground in a random block experiment in 1942 and certain plots have never received any phos'/This study was made possible by the generous cooperation of Loren H. Ward of Orlando, Florida, in whose grove the experiment lies. The technical assistance of G. K. Scudder, Jr., and G. flrnciar is
gratefully acknowledged.


pate. The soil is a transitional type between Lakeland and Eustis fine sands, previously identified as Lakeland (7, 8). The plan followed is to apply 0, 1, 3, and 8 units of P.A., respectively, to different plots for each 4 units of nitrogen used, There are six 12tree plots for each phosphate level. The P.O, comes from 20 percent superphosphate, and compensatory amounts of gypsum are given so that all plots receive the amount of CaSO, carried by the highest level of superphosphate. The highest rate of P20. was the usual comnmercial rate at the time the experiment was started, hut current recommendations (6) call for a drastic reduction. The experimental rates of P.O. described above will be referred to as none, low, medium, and high in discussing treatments.
All trees have regularly received 3 applications a year of a mixed fertilizer containing little or no organic material and no superphosphate. The current mixture is 10-0-10-3 (MgO) - 0.5 (MnO)-0.5 (ZnO)-0.1 (B-.o.,) applied at the rate of 24 lb. per tree per year. Copper also was included for the first 10 years but omitted since. Zinc was applied in spray form only once and that was in the spring of 1954. For the first 9 years the appropriate quantities of superphosphate and gypsum were also applied 3 times a year and to the same area as covered by the mixed fertilizer. From the 10th year on, these materials have been applied all in one spring application. No attempt has been made to compensate for the calcium carried as the phosphate salts, but a relatively high rate of diolomitic limestone has been regularly applied to all plots.
In July 1955 eight 2-inch cores of soil were taken from each plot. The most uniform trees were selected, and in most cases only one core was taken per tree. The cores were. taken at the tree-drip line and to a depth of 5 feet. The samples were taken by depths of 0-6 in., 6-12 in., 12-24 in., 24-42 in., and 42-60 in. The 8 cores of soil for the respective depths







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


I LSD@ 0.05


500.

400 PPM0.

P 200.

100.


III


OLMH OLMH OLMH OLMH OLMH


5.0.

I4.0.

2- W.0.
V)
02.03. I
I
02

Ui 1.0.

0Al


I LSD 0 0.05









iilii lii 11lli


OLMH OLMH OLMH OLMH OLMH


I LSD 0 0.05


PPJ

K


II 11111111 ll iii


oE~I ~L~iI ~LMH 0LMtt OLMH


I LSD 0 0.05









IIIII


80.


60 PPM


20


ilib ,,, l,,,,,.


ULMII ULMI OLMH ULMm VLMH OLMH OLMH OLMH OLMH ULMH
0-6 6-12 12-24 24-42 42-60 0-6 6-12 12-24 24-42 42-60
Fig. 1-6. Root growth and various soil factors found at different depths (in inches) in an experimental Pineapple orange grove on acid, sandy soil after 13 years of differential fertilization with superphosphate. The symbols 0 L M H represent zero, low, medium,and high rates of application. Fig. 1 (upper left)total soil phosphorus; Fig. 2 (upper right) concentrations of small "feeder" roots found; Fig. 3 (center left) soil pH; Fig. 4 (center right) exchangeable potassium; Fig. 5 (lower left) total copper; Fig. 6 (lower right) total manganese. The L.S.D. bars indicate the required difference for significance at the 5% level between any two treatments or depths.


III


6.5.

6.0.

5.5
p H
5.0.

4.5.

AA


2a 15.

i10I


o,


mill loll 11.1


25v





SMITH: PHOSPHATE FERTILIZATION


were composited, screened to remove the fibrous "feeder" roots, and thoroughly mixed by rolling on a canvas cloth, and portions were saved for laboratory analyses. Rootlets smaller than about 1/16 inch in diameter were sorted out, dried, and weighed. In addition to pH, total amounts of P, Cu, Mn, and Zn were determined on certain soil samples after total digestion in sulfuric-nitric acid mixtures. Exchangeable K, Ca, and Mg were determined by neutral ammonium acetate extraction.

RESULTS AND DISCUSSION

Phosphorus status of soil-The values found for total P are shown in Fig. 1. The data are very consistent and show that while most of the applied P is held in the top foot of soil, there is a gradual accumulation throughout the top 5 feet. This is in agreement with the findings of Spencer (11) that superphosphate gradually distributes itself through the top few feet of soil. Actually, more total P was found than was applied to the plots receiving superphosphate for 13 years. This is doubtlessly due primarily to the fact that the lowhanging foliage interferes somewhat with the machine spreading of the superphosphate, and there would be a zone of relatively high P just outside the foliage line due to the deflection of particles. Sampling in this area showed an increase of 1900 lb. of P per acre through the 5-ft. column, whereas only about 1250 lb. of P had been applied. Thus, the sampling method may also exaggerate the other effects associated with differential phosphate fertilization. It is felt, however, that the trends would be indicative of the nature of the responses even though the magnitudes might differ somewhat from those shown.
Density of feeder roots-The distribution of feeder roots is shown in Fig. 2. The data are presented as the weight of roots found in a square foot of soil 6 inches deep taken from each depth zone. The total dry weights of feeder roots expressed as grams of roots per square foot column 5-ft. deep are as follows: No phosphate 23.8; low phosphate 21.4; medium phosphate 21.3; and high phosphate 16.3. It is of interest that Ford (3) also found 16.3 as an average weight of roots in commercial groves of this age category. These soils too, would have been high in phosphate


because the groves were grown before the general drop in applied phosphate in commercial groves.
While the data in Fig. 2 are less consistent than those for the concentration of P in Fig. 1, they clearly indicate that high-phosphate fertilization somehow causes a sharp reduction in the quantity of feeder roots in the top 12 inches of soil. In the 6 to 12-inch zone all 3 levels of applied phosphate significantly reduced root growth. It is probable that the effect on root growth is somewhat exaggerated in the area sampled because of the uneven distribution of applied phosphate. Even so, it is difficult to avoid the conclusion that applied phosphate has had no beneficial effect on root growth in this experimental grove. The depression of root growth below 12 inches is not statistically significant, hut the trend is still present to the 42-inch depth. Even to the 60inch depth there is no suggestion of increased root growth as a compensation for the reduction in growth at the shallower depths.
Since tree size, appearance, and yield records do not yet reflect the density of roots as measured here, it remains to be seen whether such a reduction is a definite handicap to the tree. No explanation is offered as to why superphosphate depresses root growth, but the effect is somewhat similar to that found with a high rate of ammonium ni.trate (4).
Soil pH-Increased acidity at all soil depths wvas associated with the use of superphosphate. Fig. 3 shows the pH values found at different depths in relation to treatment. In the two upper sampling depths there is a graduation in pH values corresponding to treatment. At the 3 lower depths, there was little or no difference among the pH values for the 3 rates of superphosphate, but those for the plots that received none were appreciably higher.
Superphosphate is not a simple material as it contains a mixture of phosphatic salts, gypsum, iron and aluminum oxides, silica, and trace quantities of several other substances. It is. mildly acidic and gives a pH reading of about 3 when mixed with water. The acidulating effect of superphosphate on most soils is of little or no practical significance because of the buffering action of the soil. However, with very sandy soils of low exchange








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


capacity and high rates of application, additional liming apparently is required to offset the acidifying effect of superphosphate.
The effect of superphosphate in lowering pH is particularly evident in the top 12 inches of the soil and corresponds to the area of maximal phosphate accumulation and maximal depression in root growth. Yet it appears doubtful that there is a simple cause and effect relation between pH and root growth. Previous studies (10) in which the pH was varied in this same general range, but without superphosphate as a variable, showed no depression in root growth due to lowered pH. Likewise, studies with different levels of phosphate in solution cultures did not show any adverse effect of high phosphate on root growth (2). Thus, while it is not yet established what causes the depression in root growth, it is apparent that superphosphate does not have a beneficial effect on soil reaction.
Effect of phosphate level on exchange K, Mg, and Ca-Tbere was practically no effect of phosphate treatment on the extractable quantities of the three base elements (K, Mg and Ca). The only difference of consequence was the tendency for more K to be retained in the upper depths where the greatest amount of phosphate had accumulated in the soil (Fig. 4). Mg values were virtually identical at all depths in all treatments and the respective total pounds per acre in 5 ft. of soil were no phosphate 340; low phosphate 321; medium phosphate 349; and high phosphate 330. Ca showed a slight, but irregular and nonsignificant, increase with values of 1176, 1090, 1307, and 1290 lb. per acre for the same respective treatments. This Ca trend was not accentuated in the upper soil depths where the phosphate accumulation was the greatest.
Effect of phosphate level on the total amounts of Cu, Zn, and Mn-There was no significant effect of phosphate level on the total amounts of any of these metals found in the soil. The concentrations of Cu and Mn are shown in Fig. 5 and 6. Zn showed a mean value of 19 p.p.m. in the top soil and about 8 p.p.m. in all lower depths regardless of treatment. These results are in harmony with the results found in a topsoil sampling 5 years previously (8). Both Zn and Mn show increases as a result of continued use of these elements


in the fertilizer. No Cu was applied during the interval, and Cu status of the soil is virtually unchanged.
GENERAL DISCUSSION
Several studies (1, 5, 7, 8, 11, 12) have shown that phosphate accumulates in Florida citrus groves. Remo i val of this element by the citrus crop is not large, being about 0.5 lb. of P per ton of fruit (9). Application of superphosphate does not markedly increase the absorption of phosphorus by the tree in ordinary acid, sandy Florida grove soil (7). The evidence thus far fails to show any beneficial effect of applied phosphate on citrus in this State except in a few cases, such as on muck soil or very light sands where the content of native phosphate is very low.
Wander (12), studying soil factors in relation to presence or absence of liming, noted that a phosphate differential existed in the topsoil and concluded that the greater retention of Mg and Mn in the limed plots was due to the absorptive capacity of the accumulated calcium phosphate, The present results, in addition to previously published data (8), fail to show any relation between large phosphate accumulations and the retention of Ca, Mg, Mn, Cu, or Zn. Thus, it appears possible that the effect noted by Wander was not 'attributable to phosphate but to pH. Liming probably retarded the losses of phosphate, Mg and MR for the same reason rather than through the indirect method postulated.
It might be expected that phosphate accumulation would also result in greater Ca accumulations in the soil, particularly if there was a reversion to calcium phosphate. However, neither exchange Ca nor total Ca (7, 8) is appreciably changed. The work of Spencer
(11) offers an explanation since be found that most -of the phosphate accumulated in Florida sandy grove soils is in the form of iron and aluminum phosphates rather than calcium phosphate.
SUMMARY
Soil samples to a depth of 60 inches were taken in a Pineapple orange grove on an acid, sandy soil after 13 years of differential fertilization with superpliosphate. Data derived from these samples showed that (1) the largest increase in P was in the top 12 inches of soil, but some increase was noted at all





FEDER AND FELDMESSER: BURROWING NEMATODE


depths, (2) the total weight of "feeder" roots in the 60 inches was nearly one-third less in the high phosphate plots than where none was applied, (3) appreciable acidity wvas imparted to the soil by the superphosphate, particularly in the top 12 inches, and (4) there was somewhat more exchangeable K found as a result of increased phosphate but the exchanigeable Ca ansd Mg wer e unaffected ansd there were no differences in the total amount of Cu, Zn, or Mn regardless of treatment. None of these findings can be construed as being highly beneficial to the culture of citrus.
LITERATURE CITED
1. Bryan, 0. C. The accumulation and availability of phosphorus in old citrus grove soils. Soil Sd. 35: 245-259. 1933.
2. Chapman, H. D. and D. S. Rayner. Effect of various maintained levels of phosphate on the growth, yield, composition, and quality of Washington navel oranges. Hilgardia 20: 325-358. 1951.
3. Ford, H. W. The influence of rootstock and tree age on root distribution of citrus. Proc. Amer. Soc. Hort. Sci 63: 137-142. 1954.


4. - ,W. Reuther and P. F. Smith. The
effect of nitrogen on root development of Valencia Orange trees. Proc. Amer. Soc. Hort. Sd. (MS aubmitted for publication).
5. Peech, M. Chemical studies on soils from Florida citrus groves. Fla. Agr. Exp. Sta. Tech. Bull. 340. 1939.
6. Reitz, H. J., et al. Recommended fertilizers and nutritional sprays for citrus. Univ. of Fla. Agr. Exp. Sta. null. 536. 1954.
7. Reuther, W., F. E. Gardner, P. F. Smith and W.* R. Roy. A progress report on phosphate fertilizer trials with oranges in Florida. Proc. Fla. State Hort. Soc. 61 : 44-60. 1948.
8. Reuther, W., P. F. Smith and A. W. Specht. Accumulation of the major bases and heavy metals in Florida citrus soils in relation to phosphate fertilization. Soil Sci. 73: 375-381. 1952.
9. Smith,' P. F. and W. Reuther. Mineral content of oranges in relation to fruit age and some fertilization practices. Proc. Fla. State Hort. Soc. 66: 80-86. 1953. 10. Smith. P. F., and W. Reuther. Preliminary report on the effect of nitrogen source and rate and lime level on pH, root growth, and soil constituents in a Marsh grapefruit grove. Proc. Soil Sci. Soc. Fla. 1S: 108-136. 1955.
11. Spencer, W. F. Phosphatic complexes in the soil. Ann. Rpt. Fla. Agr. Exp. Sta. p. 193, 1952; p. 218, 1953.
12. Wander, 1. W. The effect of calcium phosphate accumulation in sandy soil on the retention of magnesium and manganese and the resultant effect on the growth and production of grapefruit. Proc. Amer. Soc. Hort. Sd. S5: 81-9L. 1950.


STARTING AND MAINTAINING BURROWING NEMATODE-INFECTED CITRUS UNDER GREENHOUSE CONDITIONS


WILLIANM A. FEDER AND JULius FELDMESSER

Fruit and Nut Crops Section and
Nematology Section
Horticultural Crops Research Branch
Agricultural Research Service
United States Department of Agriculture

Orlando

The current nematode research program requires the use of large numbers of burrowing nematode-infected citrus seedlings as well as a large and reliable supply of burrowing nematodes. Large numbers of infected seedlings are needed for the chemical screening program and for various biological studies and other fundamental work. Obtaining sufficient burrowing nematodes from naturally infected grove trees requires a great deal of time and labor. A method of raising and maintaining burrowing nematode populations on citrus in the greenhouse was, therefore, devised.


Studies, which will be reported elsewhere, indicate that the burrowing nematode will infect and reproduce readily in citrus seedlings growing under normal greenhouse conditions in Florida. It was also found that grove subsoil, turned up while digging for nematode-infected roots, contained many small nematode-bearing root fragments, and that citrus seedlings planted into this soil in pots under greenhouse conditions were readily infected and supported a burrowing nemnato'de population.
These observations were utilized in guiding the construction of two drained concrete soil tanks. These concrete block tanks were constructed on a 4-inch thick, poured concrete slab and the soil-bearing portions had inside dimensions of 10' x 4' x 2' and 16' x 4' x 2', respectively. The bottom of the soilbearing portion of the tank is raised one block width above the concrete slab and is constructed of 94"' No. 9 expanded metal resting on cross bars of 2" x 2" x W' angle iron. The metal surfaces are all coated with red lead








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


primer and asphalt paint to redcle rusting and corrosion, The completed tank is shown in Fig. 1.


Fig. 1. Inside of soil tank shoving cross supports. expanded metal bottom, and a portion of the walls.

In filling the tank wvith soil a 2-inch lay' er t f 9. lime rock was first pouiredi onto the expanded metal bottom. Sterilized field soil wxas then placed onl the line rock layer to a depth of 4 inches. Finally, the remaining space in the tank was filled with the required number of yards of subsoil taken from beneath trees known to harbor the burrow'ving nematode in their roots. This soil was brought from the grove in closed metal garbage cans to avoid contamination of citrus plantings enroute. The soil in the tank wxas xx et clown and tampedi and allowed to settle for a fewv clays. Seedlings of Rough lemon and Duncan grapefruit and seeds of b)0th these varieties were then planted in the tank in rows, and the rows were marked with planting date and type of material planted. These plantings
w ere watered carefully to avoid water dam-


age and were cultivated and fertilized in a routine manner. It w'as found that the small root fragments, which seemingly contained the hulk of iiematodes found in the subsoil, did not wash clownl upon watering, but instead, some worked to the surface of the soil, if watering wxas excessive. It was necessary to push them below the surface when this occurredi. Water, which leached through the soil, wvas collected in large pans and examined periodically for the presence of burrowing nematodes. To date, no burrowing nematodes have been recovered from the leaching water.
After 6 weeks, burrowing - nematode - infectedi seedlings were harvested from the tank. These seedlings bore few to many lesions on the roots and all stages of the burrowing nematode were found within the lesions. The smaller tank holds about 1,300 growing seedlings when loaded to capacity, and the larger one about 2,100 seedlings. Seedlings usually are grown 3 months in the tank before they are harvested. This period is sufficient for them to overcome the initial shock of transplanting and to develop an adequate top and root system, Damping off occurs infreuquently andl is controlled by applications of wettable captan to the soil between the rows. In order to minimize trap-cropping, a few infected roots are cut up and buried after each
rwof seedlings is dug uip. In this manner, an active burrowving nematode population has been maintained in one tank since January 1956. This population has now survived a winter and a summer in the tank under normal greenhouse conditions. Approximately 800 infected seedlings have been harvested since January 1956.








GRIMM: DIEBACK INVESTIGATIONS


GORDON, R. GRIMM


PROCEDURES AND RESULTS
Temple orange and Glen Navel orange on Cleopatra mandarin rootstock, 32 and % inch in diameter, were used in transplanting tests to determine the effect of top pruning, the absence of fibrous roots, and defoliation. Transplanting experiments were begun in November and March at the U. S. Department of Agriculture experimental farm 7 miles west of Orlando, Florida. Each experiment was composed of eight treatments with eight trees each replicated four times, making 32 trees per treatment (table 1). Each treatment wag a combination of three separate operations; e.g., the trees for treatment I had branches, fibrous roots and leaves; those for treatment' 8 had their branches, fibrous roots, and leaves removed. Branched trees were pruned to leave 4-to-6-inch branches; the trees without branches were pruned to trunks approximately 16 inches high; all fibrous roots and all leaves remaining after top pruning were removed with pruning shears in the groups indicated. The trees were planted with a 5 x 5 foot spacing and the entire area was kept free of weeds.
Excellent, good, fair, and poor were used to describe the subsequent growth of the tree. An excellent tree had little or no dieback on the cut branches or main trunk and vigorous sprout growth; good and fair trees bad relatively increased amounts of dieback and relatively decreased sprout growth; poor trees either had died back far enough to make replacement desirable or were dead. Observations were continued until no further changes in growth habit were apparent.
Table I shows the numbers of excellent, good, fair, and poor trees within' each treatment for the November and March plantings. As a group, trees with fibrous roots present were distinctly better in both the November and'March plantings than those with fibrous roots removed. As a group, trees with branches present were better than trees with branches


Horticultural Crops Research Branch
Agricultural Research Service
United States -Department of Agriculture

Orlando

INTRODUCTION
Dieback of transplanted citrus trees refers to a progressive dying of a pruned branch or trunk from the cut surface toward the root. It has been recognized in Florida for as long as groves have been planted. Usually the losses from this disease have been minor, but within the past few years they have increased sufficiently to warrant investigation. Large acreages have been planted at all seasons of the year, and it has become apparent that losses of young trees from dieback have increased disproportionately with the increased acreage planted.
A study of the nature and cause of dieback was started by reviewing the methods of transplanting citrus trees. No general agreement was found among growers or nurserymen as to the best method of transplanting. Practices in top pruning the trees varied considerably. Methods of handling,. watering, and subsequent care also varied. A diversity of opinion prevailed on the importance of fibrous roots and of the leaves at the time of transplanting.
To determine the role of all of the various steps involved in transplanting on the incidence of dieback, controlled experiments were performed under field conditions. In con.
junction with these tests, laboratory isolations were made to determine the microorganisms associated with this disease.

I/The author wishes to acknowledge the cooperation and donation of citrus trees from Mr. C. F. Fawsett, Jr., of Orlando, Fla. and the following nurseries:Lake Garfield Nurseries Co., Bartow, Fla.; Glen St. Mary Nurseries Co., Winter Haven, Fla.; Grand Island Nurseries, Eustis, Fla.; and Ward's Nursery, Avon Park, Fla.


PRELIMINARY INVESTIGATIONS ON

DIEBACK OF YOUNG TRANSPLANTED CITRUS TREES'









FLORIDA STATE HORTICULTURAL SOCIETY, 1956


removed, and trees with leaves present were better than trees with leaves removed in the fall planting only. Statistical analyses of both experiments showed the comparisons discussed to be highly significant.
A third experiment of 3 x 2 x 2 factorial design was made to compare entire trees exposed to the sun for 11,4 and 213' hours with trees that were shaded and had their roots protected from drying by packing in wet sphagnumn moss from the time they were dug until transplanted. The influences of leaves and of no leaves and of a 3-hour delay in watering after planting in comparison with watering at planting were measured within each group. Treatments were made on 2'-inch Parson Brown orange trees on Rough lemon rootstock pruned to a 16-inch trunk and planted June 7, 1956. Each of the following treatments was


replicated three times with 5 trees each, making 180 trees:
1. Nto sun exposure, leaves on, watered at plant'rg
2. * , wa*erng delayed for3 hour.
3. off, watered at planting
4. w aterineg delayed for I hours
5. 1-1/4 hour eoposre . leaves on. watered at planting
6. *watering delayed for 3 hours
7. off, watered at planting
8. *watering delayed for 3 hour.
9. 2-1/2 hour exposure, leaves on. watered at planting 10. . watering delayed for 3 hours
11 of f. watered at planting
12. * , watering delayed for 3 hours
The trees exposed to the sun were laid on cultivated ground; the air temperature 3
inches above the surface was 930 F. and 112' on the ground surface. All trees were planted with a 5 x 5 foot spacing and arranged by treatment in a definite plot design. All were watered on the day of planting with 6 gallons of water at the times designated, and every 4 or 5 days thereafter during the next 6 weeks as weather conditions required.


Table 1. Distribution of trees by growth classes of Excellent, Good,
Fair, and' Poor following treatments at two planting seasons


November PlantineV March Plantint2J
Treatmnentsi./ E G F P E G F

Branches present
Fibrous roots present
1. Leaves present 24 7 0 1 16 5 5 6
2.ILeaves removed 6 11 7 8 17 4 4' 7

Fibrous roots removed
3. Leaves present 1 3 24 4 1 2 8 21
4. Leaves removed 0 3 10 19 Z 2 5 23

Branches removed
Fibrous roots present
5. Leaves present 5 2 10 15 11 2 9 10
6. leaves removed 0 2 7 23 6 6 7 13

Fibrous roots removed
7. Leaves present 1 3 6 22 2 1 7 22
8. Leaves removed 0 0 3 29 5 4 5 18

l/ Each treatment has a total of 32 trees. V Temple orange/Cleopatra mandarin 1/2-in, planted 11/9/55. Data taken
2/23/56.
2/Glen Navel orange/Cleopatra mandarin 5/8-in, planted 3/23/56. Data
taken 6/7/56.




GRIMM: DIEBACK INVESTIGATIONS


Table 2. 1'ean inches of dieback and new sprout growth 6 weeks after
transplanting Parson Brown orange trees, as influenced by
exposure, defoliation, and delay in initial watering


Treatment Dieback Sprout growth
in. in,
Exposure to the sun
0 hour 1.58 32.53
1 " 4.25*** 1o2*

21 5.12*** 3.85***

Leares present 3.02 18.99

Leaves removed 4.28* 16.16

Watering
at planting 3.59 17.63
delayed for 3 hours 3.71 17.97

*Indicate-- statistical significance at odds of 19:1
***Irdicates statistical significance at odds of 999:1


The results are summarized in Table 2 in terms of average inches of dieback of the main trunk and average inches of total new sprout growth per tree for the respective treatments. Trees exposed to the sun for 1,h or 231 hours prior to planting had considerably more dieback and less sprout growth than trees that had been protected from drying with wet sphagnum moss. Statistically the differences are very highly significant. It should also be noted that trees without leaves at the time of transplanting had significantly more dieback than trees with leaves at the time of transplanting. Time of initial watering did not affect the amount of dieback or sprout growth of the trees in this experiment.
Preliminary observations on the effectiveness of various pruning paints for the control of dieback were made during February, March, April, and May on sweet orange trees with various amounts of top pruning and defoliation. De-Ka-Go, Carbolineum, and pastes of Zineb, Orthocide, and neutral copper were applied to the cut surfaces immediately after pruning and before the trees were dug at the nursery. The treated trees were planted at random with non-treated trees and comparisons were made in the same planting. Only


6 percent of the trees showed measurable dieback, and this seemed to occur regardless of the presence or absence of wound paint.
Several fungi and an unidentified bacterium have been isolated from trees affected with dieback. However, investigations to date have not shown any one organism to be consistently associated with dieback. Colletotrichum gloeosporioides was isolated from 60 percent of the trees; Diplodia natalensis, Phomopsis citri, Fusarium spp., and bacteria were isolated from 10 to 30 percent of the trees.
DIscussIoN
Field observations and experimental data indicate that dieback of transplanted citrus trees is largely a result of mishandling the trees at some point during transplanting.
Transplanting citrus trees involves many operations such as pruning, digging, transporting, planting, watering, and fertilizing and any one or all may be done carelessly enough to injure the tree. Environmental conditions at the time of operations, such as temperature, humidity, wind and water, and soil characteristics may also have direct influences on the success of transplanting.
The presence of healthy fibrous roots and their protection from drying at all times have






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


proved to be important for vigorous tree growth, which apparently provides the best defense against dieback of transplanted citrus trees.
The presence of leaves can have a marked influence in preventing or checking dieback of the tree. It is not uncommon for dieback to proceed down one side of a limb or trunk on which no leaves are present and to stop on the other side at the first leaf. Exactly how a leaf stops diehack is not known; it may be only by sustaining healthy tissue through the normal leaf functions, Even though the leaves are lost shortly after planting, they may be beneficial to the tree during transplanting. In the third experiment, trees with leaves during exposure to the sun lost their leaves 2 or 3 days later, yet they had significantly less dieback than trees without leaves.
From the data obtained thus far it would seem advisable to top prune trees only moderately, maintaining 4-to-6-inch branches, This was particularly true for fall-planted trees, which were larger and stronger, and had less dieback 4 months after planting. Incidental observations have shown that the advance of dieback down a branch is often checked temporarily and sometimes permanently at the crotch.
A causal organism of dieback cannot be entirely ruled out. However, the fact that a tree has less dieback because of the presence of


fibrous roots, leaves, and branches, coupled with the fact that at present nIo one organism has been isolated consistently from all dieback trees, suggests that good transplanting methods offer the best control of this disease. It is evident that during transplanting of citrus the entire tree, particularly the fibrous roots, should he protected from drying at all times. Once the tree has been set in the grove it should he watered at planting and again the second or the third day afterward; and, in Central Florida sandy soils, every 3 to 5 days thereafter for the first few weeks as weather conditions require.
SUMMARY
Dieback and new sprout growth of young transplanted citrus trees were measured in relation to (1) top pruning, (2) defoliation, (3) root pruning, (4) exposure of the entire tree to the sun before transplanting, and (5) delayed watering after transplanting. The preliminary results indicate that diehack may be a result of injurious transplanting operations. Healthy fibrous roots were shown to he very important for vigorous tree growth and to constitute one of the best defenses against diehack. The presence of leaves appeared to be beneficial in limiting the amount of dieback, especially in fall-planted trees.
Investigations to date give no definite indications that fungi or bacteria are primary causal agents of dieback.


THE POSSIBILITY OF MECHANICAL

TRANSMISSION OF NEMATODES

IN CITRUS GROVES


A. C. TARJAN
Florida Citrus Experiment Station
Lake Alfred
The somewhat phenomenal spread of the burrowing nematode, Radopholus .similis. (Cobb) Thorne, in recent years has been attributed to subsoil drainage (3), to the movement of the nematode itself, and to the activities of humans (4). This latter means of

Florida Agricultural Experiment Station Journal Series, No. 529.


dispersal of the organism has been implemented mainly by the widespread dissemination of infected citrus nursery stock and other cultivated plants. It generally has been assumed that various implements and mechanical devices also play a role in the spread of the burrowing' nematode as in the case of certain other plant pathogenic nematodes (1, 2, 5). Although shovels, cultivators, and mobile harvesting machinery have been implicated, it was suspected that bulldozers were mainly responsible. The "pull and treat" program (6) of the Florida State Plant Board,








TARJAN: TRANSMISSION OF NEMATODES


which is accomplished by the destruction of burrowing nematode infected citrus and subSequent soil treatment with D-D soil fumigant, uses bulldozers for elimination of designated trees. The machines enter the groves, fell the trees and place them in piles for burning. If infested soil and infected roots were capable of being picked up and transported, the bulldozers, with their undesired cargo, might be assigned on the following day to either clearing virgin land for future groves or pushing out old or undesirable trees to make way for a new planting. In either case it was assumed that nematode inoculum might, in this manner, be disseminated to noninfested land,
With the cooperation of Mr. Charles Poucher, Florida State Plant Board, Lake Alfred, and the various contractors involved in clearing infested grove sites, a study was undertaken to determine (1) if bulldozers and cultivators were carrying soil and debris infested with nematodes, (2) the relative kinds and frequency of occurrence of these nematodes, and (3) whether clods of soil and debris infested with burrowing nematodes might be suitable inoculurn for infecting potted citrus plants. The vast majority of the sites visited were groves affected by spreading decline, but in a few cases noninfested groves were also inspected. Soil, including roots when available, was scraped off bulldozer tracks and was obtained also from various locations on the "dozer" body. Samples thus obtained were stored in pint jars, returned to the laboratory, and processed for nematodes.
During the course of this study, 63 samples were collected from 23 different groves in Lake, Polk, and Orange Counties. Genera of nematodes identified are listed in Table I while the relative abundance of nematodes in each of the samples is shown in Table 2.
Nematode genera with saprozoic or predatory feeding habits comprise the longest list in Table 1. There were additional genera of this group that were not identified principally because only spear-bearing nematodes were of primary int rest in this study, The bulb and stem nematodes, Ditylenchus spp. were the most numerous among the plant parasites found. Although many species of this genus are not parasites of higher plants, it has long


been suspected that other species are capable of inflicting serious root damage. Likewise, in the "Suspected Plant Parasite" group, the genus Dorylahnus probably contains species that are plant parasites as well as those which are predatory in feeding habit,
Data in Table 2 shows that most of the samples obtained yielded from 26 to 75 nematodes and that in no case did a sample fail to yield living nematodes. This is especially significant when it is taken into account that the major part of this survey was conducted in the winter and spring months of 1956 during an extended drought. Occasionally a sample consisted of only a small number of apparently desiccated roots and soil which was scraped off the body of the bulldozer, while at other times the sample was found packed under pressure in crevices in the tracks and had to be forcefully pried out. In one case, the machine operator' had finished for the day and in an attempt at disinfestation had sprayed the tracks with diesel fuel, a substance which has been assumed to be nematocidal. The soil sample, obtained about one hour after the spraying, yielded numerous active, apparently healthy nematodes when processed in the laboratory the next day.
Ironically, the only time that Radopholus similis was obtained was from a sample taken from a machine pushing out apparently healthy grapefruit trees for purposes of replanting with orange.
The imposing list of plant parasites shown in Table I disproves the conception that such nematodes cannot possibly survive in soil clods or debris exposed to air and sun. Where, in the case of certain plant parasites, adequate moisture is needed to prevent desiccation, matter containing adequate moisture can be found tightly packed on the bulldozer tracks, In one case, a bulldozer being transported by truck was intercepted about two miles from the grove site in which it had been working. As expected, numerous nematodes were obtained from the soil samples collected from the machine.
Although the foregoing data proved that certain machinery is capable of disseminating nematodes, the question remained whether inoculum thus translocated was capable of instituting an infection at a new location. Con-






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


sequently tests were conducted on potted seedlings simulating actual conditions as closely as possible.
Thirty 9-month-old grapefruit seedlings growing in autoclaved soil in 46 oz. cans were divided into five lots of six plants each. These were placed evenly in large flats of autoclaved soil, so that only the upper fifth of the can projected above the soil. This was done


to maintain as constant a soil temperature as possible within the cans. Inoculum consisted of finely cut citrus feeder roots which were moderately infected with burrowing nematodes. In simulating the physical state of potential inoculum as it had been observed on the bulldozers, various combinations of infected roots, mashed citrus fruit, clay, and soil were mixed and shaped by hand into


Table 1. Ge Plant Parasites


Tylenchulus (1) a/ Radopholus (1)

Tylenchorhynchus (2) Criconemoides (1) Tylenchus (6) Ditylenchus (18) Meloidogyne (1) Dolichodorus (4) Hemicycliophora (1) Pratylenchus (12)

Trichodorus (3) Hoplolaimus (2) Rotylenchus (3) Belonolaimus (1)

Tylenchidae (2) _/


nera of nematodes found in soil collected from bulldozers
Suspected Plant Parasites Saprozoiti


Aphelenchoides (31) Paurodontus (1)

Dorylaimus (11) Xiphinema (3) Tylencholaimus (3) Pseudhalenchus (5) _/ Belondira (1) Nothotylenchinae (1) _


es and Predators


Rhabditis (17) Diplogaster (5)

Acrobeles (8) Cephalobus (2) Tripylidae (1) b Diplogasteroides (2)

Rhabditolaimus (1) Monhystera (2)

Alalus (1) Prismatolaimus (1)

Acrobeloides (2) Discolaimus (2)

Mononchus (2) ilsonema (2) Eucephalobus (2) Plectus (1) Aporcelaimus (1)

Chiloplacus (1) Cervideflus (1) Aphelenchus (10)


a/ Numeral indicates frequency of occurrence. b_/ Identified only to family or sub-family. c/ New genus-technical description currently being prepared.





TARJAN: TRANSMISSION OF NEMATODES


Table 2. Relative number of nematodes recovered
from soil samples.


No. of Nematodes Frequency in Sanples
151 or more 12
76-150 13
26-75 22
11-25 8
10 or less 8
none 0


small clods. All of these inoculum combinations were either placed on or partially imbedded in the soil contained in the cans, some of which had been watered immediately prior to inoculation. This was done to approximate the condition where infested material had either fallen from a bulldozer to the ground or had been pushed into the ground by the machine tracks. Watering the soil in some of the cans simulated rainfall prior to inoculation. After the inoculum was introduced, water was applied to those cans which had not been pre-wetted. One flat was placed in a room provided with artificial illumination, a constant temperature of approximately 78' F., and a relative humidity which averaged about 80 percent during hours of illumination and 95 to 100 percent in total darkness. Two flats were placed outside exposed to sunlight, while another flat was placed in the partial shade of a slat house. A control flat containing plants which had received combinations of nematode-free citrus roots, citrus pulp, clay and soil was placed outside exposed to weather conditions.
Plants were harvested and screened for burrowing nematodes by the root incubation technique (7) approximately 10 weeks after this experiment was initiated. It was found that only plants which had been protected from exposure to direct sunlight, i.e. those placed in the constant temperature room and those placed in the slat house, became infected with burrowing nematodes. It did not appear to make any difference whether the plants were watered prior to or after inoculation, whether the inoculum rested on or was inserted in the soil, and whether the inoculum


was combined with clay, crushed citrus fruit, soil, or any combination of these.
These results, although derived from tests with potted seedlings, indicate that situations could arise in the field where nematodeinfected inoculum might be carried into noninfested land, come into contact with the soil in a shaded area prior to or following a rain, and could institute an infection of host plants growing in the immediate vicinity.
SUMMARY
A survey was undertaken in which soil and root samples were obtained mainly from the tracks of bulldozers employed in eradicating citrus groves afflicted with spreading decline. This survey was conducted mainly during the winter and spring months when the citrus area had received a minimum rainfall. Sixty three soil and root samples were collected from twenty-three groves in Polk, Lake, and Orange Counties. Fourteen different genera of known plant parasitic nematodes including Radopholus similis, the burrowing nematode, were identified. Experiments were conducted in
which burrowing nematode infected citrus
roots in combination with clay, crushed citrus fruit, and soil were introduced into pots containing 9-month-old citrus seedlings. After inoculation, these plants were either exposed to sunlight or placed in shaded areas. Only in the latter case did plants incur burrowing nematode infections. It is concluded that mechanical equipment such as bulldozers are capable of transmitting nematodes which, under the proper conditions, can institute infections of citrus.
LITERATURE CITED
1. de Carvalho, J. Cj 1953. Ditylenchus destructor em Tuberculo-Semente Importado da Holanda. Rev. Inst. Adolfo Lutz. 13: 67-74.
2. Courtney, W. D. and H. 13. Howell. 1952. Investigations on the Bent Grass Nematode, Anguina Agrostis (Steinbuch. 1799) Filipjev, 1936, U. S. Dept. Agr. P1. Dis. Rptr. 36 (3): 75-83.
3. DuCharme, E. P. 1955. Subsoil Drainage as a Factor in the Spread of the Burrowing Nematode. Fla. State Hort. Soc., Proc. 68: 29-31.
4. Simanton, W. A. 1956. How Has Spreading Decline of Citrus Spread? Sunshine State Agr. Res. Rpt.
1 (3): 5, 7.
5. Steiner, G., A. L. Taylor, and Grace S. Cobb. 1951. Cyst-forming Plant Parasitic Nematodes and their Spread in Commerce. Helm. Soc. Wash., Proc. 18 (1) : 13-18.
6. Suit, R. F., E. P. DuCharme, and T. L. Brooks. 1955. Effectiveness of the Pull-and-Treat Method for Controlling the Burrowing Nematode on Citrus. Fla. State Hort. Soc., Proc. 68: 36-38.
7. Young, T. W. 1954. An Incubation Method for Collecting Migratory Endo-parasitic Nematodes. U. S. Dept. Agr., Pl. Dis. Rptr. 38 (11): 794-795.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956

TRANSMISSION OF T.RISTEZA VIRUS BY

APHIDS IN FLORIDA


PAUL A. NORMAN
Entomology Research Branch
THEODORE J. GRANT
Horticultural Crops Research Branclh
Agricultural Research Service
U. S. Department of Agriculture

Orlando
The mild tristeza virus was transmitted from temple orange trees to Key lime test plants by two species of aphids in preliminary experimental work (16). The green citrus aphid (Aphis spiraecola Patch) gave positive transmissions to 9 of 128 test plants and the melon aphid (A. gossypii Clover) to 1 of 26 plants. Higher ratios of infection have heen obtained in recent tests with the combined use of controlled sources of inoculumn in several varieties of citrus seedlings, multiple-branched Key lime test plants, larger numbers of aphids per plant, and timely observations to detect initial symptoms. This report presents results obtained with this improved technique. It incriminates the black citrus aphid (Toxoptera aurantii (Fonse.) ) as a vector, and describes tests with other insects and mites, so far negative, as vectors. Studies of Meyer lemon trees as sources of inoculum are also discussed.
METHODS
In order to establish tristeza virus in plants of different citrus varieties, two Key lime plants (T, and T.) were selected as standard sources of the virus inoculum. These plants had been infected in March 1953 as a result of aphid transmissions from a stunted Temple orange tree on a red lime (Rangpur type) rootstock (16). Green citrus aphids were transferred to these plants after they had fed on the Temple orange for 116 hours, 75 to the T. plant for a 1-hour transmission feeding period and 30 to the T, plant for 23 hours' feeding. Both these Key lime plants have been used in other pathological investigations (8) and the reactions on the Key lime are considered typical of the mild tristeza virus in Florida.


Leaf pieces from the T,~ and T. sources were used to inoculate greenhouse-grown citrus seedlings. The Valencia and Florida sweet seedlings were considered to be nucellar, and the Temple oranges were sexual seedlings selected for characteristics of the parent variety. Presence of the tristeza virus in these plants was confirmed by retransmission with leaf-piece transfers to Key lime plants. The infected Valencia and Florida sweet seedlings were transplanted to a field and the infected Temple orange plants were kept in pots in a screen-house. Individual plants were rechecked by leaf-piece inoculations into Key lime plants for proof of continued presence of the virus in the young growth at the time of each acquisition feeding by aphids.
In the previous tests (16), in the present tests with the black citrus aphid, and in studies of Meyer lemon as a source of virus, small Key lime plants 8 to 12 inches high with single stems and 25 to 150 aphids were em. ployed. In the other tests healthy Key limes 18 to 20 inches high were cut back or the tops bent over to stimulate rebranching, and colonies of 300 to 700 aphids were used.
Pathological investigations had indicated that the optimum time to observe initial symptoms of vein clearing associated with the mild tristeza virus was 20 to 40 days following tissue inoculation. In insect-inoculated Key lime plants 30 to 60 days following infestation was found to be the optimum period. Thereafter the symptoms might diminish, especially under summer conditions in the greenhouse. Initial Symptoms did not always occur on all branches. The branches showing symptoms were tagged so that they could be observed frequently and used for testing retransmission by means of leaf inoculations into Key lime plants.
Isolated aphid colonies of single species were placed on young, succulent growth of healthy citrus seedlings and allowed to feed for 24 hours, since previous tests with other species (3, 5) had indicated that such feeding would free them of tristeza virus. The youing shoots with the aphids were then trans-






NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION


ferred to the infected seedlings that bad been Previously tissue-inoculated and tested, and the aphids were allowed to move over voluntarily. After a 25-hour period to acquire the virus, aphids on shoots from the infected seedlings were placed on the multiple-branched Key lime test plants in separate cages at the laboratory. Again the aphids were allowed to move over voluntarily. 'At the end of 24 hours counts per unit of leaf area were used as a basis for estimating the total number of aphids present on each test plant. Representative aphid specimens were collected for positive identification. The test plants were sprayed twice with 0.04 percent nicotine sulfate before they were transferred to, the greenhouse.
TESTS WITH GREEN CITRUS AND
MELON APHIDS
The results given in table 1, from tests carried out in March and April 1956, show that the green citrus aphid transmitted the virus from three varieties of infected citrus seedlings to Key lime plants. All test plants infested with melon aphids became infected. The proportion of successful transmissions by both species was much higher than in the previous tests (16).
Toblo 1-7ro.i.ioo f tttvsby ophid. f- -1 ,e io cto.
-edliog. to .ultipl-boohed Koy Ii. pl.ot,.

S.-o of Iooe-l- Nbr .,' Aphi. p-r N1ob- of Toot Phot.
Tost Plant Infested 1ofected Or- oit,., -ohid.
V.1.ooi. 300 3 1
1.00 1. 2
rP.'Id. -,ot 300 1. 3
T.pl. 400 2 1
Ikolop aphids
T.pl. 700 6 6

In these tests initial symptoms of tristeza were detected on one or more branches of the test plants 5 to 6 and, in one case, 8 weeks after inoculation. New young leaves of infested branches showed distinct vein clearing and a veinlet pattern that frequently faded as the growth matured. After the initial veinclearing symptoms disappeared, some leaf cupping and deficiency signs remained, Presence of the virus in all aphid-infected plants was confirmed by tissue transmissions to additional Key lime plants.


TESTS WITH THE BLACK CITRUS APHID
One positive transmission of tristeza virus was obtained in five tests with the black citrus aphid. In this test 25 alate adults and nymphs, all reared from one adult, were given an acquisition feeding period of 48 hours on an infected Valencia orange scion grown on a potted Key lime rootstock in the greenhouse. The transmission feeding period was 4 hours. Presence of the virus in the aphid-infected Key lime test plant was confirmed by leaf-tissue transfers. The identity of the aphid species was confirmed by Louise M. Russell, of the Entomology Research Branch, This is the first record of positive transmission of tristeza virus by this species.

MEYERt LEMON AS A SOURCE
OF TRISTEZA VIRUS
Meyer lemon trees are present in dooryards or small plantings in most citrus areas. Some Meyer lemon trees have been found to carry tristeza virus (11, 17, 20), but investigations in Texas (4, 18) indicate that its spread from this host is not common. Because of the wide interest in Meyer lemon as a host, tests were made to transmit the virus from it. Three aphid species were used as vectors. Colonies of 5 to 50 apterous adults were employed. In 16 tests with the black citrus aphid and 21 tests with the melon aphid no transmissions were ohtained. In 107 tests where the green citrus aphid was used, 2 transmissions were secured.
In the first positive transmission a Meyer lemon tree at Minneola, Fla., was the source of inoculum. Thirty apterous adult green citrus aphids fed for 42,12 hours on this tree and 42 hours on the test plant. Scattered but distinct clearing of veins occurred on the young leaves of the Key lime test plant 5 months later. These symptoms became less evident as the leaves matured, and subsequent new growth showed no further symptoms. While these transmission tests were being carried out, budwood from the Meyer lemon branch that the aphids had fed on was brought to the greenhouse and side-grafted into 5 Key lime plants. All these plants showed strong vein- and veinlet-clearing symptoms, which were evident for a longer period and were more distinct than those observed on the Key lime plant infected as a result of aphid inoculation.





40 FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Meyer lemon scion on one of the graftinoculated Key lime plants was allowed to develop, and subsequently green citrus aphids were fed on it for 24 hours and then transferred to two Key lime plants for another 24 hours. One plant, on which 75 aphids fed, showed no symptoms, but the other, on which 50 aphids fed, developed transitory leaf symptoms 4 months later. This limited symptom expression of tristeza suggested that either the source of inoculum contained only a very mild tristeza-virus strain or the aphids had sorted out and transmitted only a portion of the virus strain, mixture.
In order to obtain further information, leafpiece transfers and scion grafts were made. The Key limes inoculated with tissue from the Meyer lemon at the end of 2 months showed striking vein- and veinlet-clearing symptoms. The Key limes inoculated with tissues from the aphid-transmitted source showed only slight deficiency symptoms and a tendency for slight cupping of some leaves. Three months after the inoculations observations were made for the presence of stem pits. Two plants tissue-inoculated from the Meyer lemon source had averages of 28 and 100 pits per 10 centimeters of stem; two of three plants tissue-inoculated from the aphid-infected Key lime source had no pits, and one plant had 1 pit per 10 centimeters of stem. These results show that a milder form of tristeza virus was transmitted from the Meyer lemon by the aphids than was transmitted by tissue grafts from the same source.

TESTS WITH OTHER INSECTS AND MITES
Tests were also made with other insects and mites found on citrus in Florida. The sources of inoculum were tristeza-infected Key lime seedlings. Thus far there have been no positive transmissions. The species tested as vectors, with the number of Key lime plants infested, were as follows: green peach aphid (Myzus persicae (Sulz.) ) 4, citrus mealybug (Pseudococcus citri (Risso) ) 49, leafhopper Homnalodisca triquetra (F.) 35, blue sharpshooter leafhopper (Oncometopia undata
(F.) ) 7, big-footed plant hug (Acanthocephala femorata (F.) ) 14, southern green stink bug (Nezara viridula (L.) ) 29, stink bug Euschistus obscorus (P. de B.) 7, citrus red mite (Metatetranychus citri (MEG.) ) 8.


TEST PLANTS As A MEASURE
of ViRus TRANSMISSION
Tristeza of citrus was first recognized as a disease of sweet orange on sour orange rootstock. This scion-rootstock combination was used in initial studies, which showed that the disease is caused by a virus and can be transmitted by tissue grafts (1, 6) and by Aphis citricidus (Kirk) (1, 3, 13, 15). As information advanced, West Indian, Mexican, and Key lime plants were employed as means of detecting this virus (9, 10, 14, 19).
The primary symptoms of vein and veinlet clearing and stem pitting on the Key lime plants are useful. Improvements in the production and detection of symptoms on the test plants have been sought as means of obtaining further information on virus transmission. In the present investigations the use of standardized sources of inoculum, multibranched Key lime plants, large aphid populations, and observations at critical periods have given high ratios of virus transmission under early-spring conditions. The recovery from initial symptom expression in the summer suggests that the Key lime plants are not as good indicators of tristeza virus under high-temperature conditions. Temperatures appear to affect not only the occurrence of vein clearing on the leaves, but also stem-pitting symptoms, as noted by Grant and Higgins (8).
The intensity of symptoms on the test plants also varies with the virus strain. Recent pathological investigations indicate that the mild tristeza virus in Florida may be a mixture of strains (8). By use of the aphid-transmitted mild-virus source plants T, and T, and with leaf-piece transmissions to Key lime plants and successive selections of leaf pieces and transmissions to other Key lime plants, evidence was obtained of virus strains that cause many stem pits and some that cause few to no pits. Apparently the tristeza virus strains could exist in varying mixture levels in infected plants. Work in South Africa (12) and Brazil
(7) has shown that aphids have transmitted a mild foim of the virus from trees known to be carrying the severe form. In the present study of Meyer lemon as a virus source, the two transmissions obtained by means of aphids produced notably milder symptom expression on Key lime plants than those obtained by tissue transmission.





NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION


TRANSMsISSION OF TRISTEzA VIRUS
IN CITRUS GROVES
The green citrus aphid is the most abundant aphid on Florida citrus. It usually limits its feeding to seasonal growth flushes of succulent terminals which vary with the citrus variety and rainfall conditions, and its feeding curls the tender foliage. The black citrus aphid. appearing later in the season, feeds on more mature leaves. The melon aphid, although less prevalent on citrus than the green citrus aphid, is also found on young growth.
Recent studies in California (5) indicate that in four districts where measurements were taken the yearly average number of aphids of all species flying to a single orange tree ranged from 185,725 in the coastal area to 956,238 in the area around Covina and Azusa called the intermediate district.' The respective figures for the melon aphid alone were 3,200 and 35,600. Since the melon aphid is the demonstrated vector of tristeza virus in southern California, it is not surprising that the disease spread most rapidly in the intermediate district. Green citrus aphids made uip more than 85 percent of the aphids caught flying to the orange trees, but neither this species nor the black citrus aphid has been shown to carry the tristeza virus in California.
We do not have comparable data for aphid populations in Florida. However, our studies show that all three species are potential vectors of the tristeza virus.
Each tristeza-infected tree serves as a reservoir from which the aphids can obtain the virus. There are two types of reservoirs(A) an infected tree on a nontolerant rootstock, as sour orange, which shows decline symptoms and produces delayed, weak flushes of newv growth; and (B) a tree on a tolerant rootstock which has apparently healthy growth but carries the tristeza virus. The latter is a more dangerous source of the virus, because the succulent flushes of new growth are suitable for aphid feeding and transmission of the virus at the time other normal, healthy trees are flushing. The visibly diseased trees (type A) seem to be less dangerous sources of inoculumn because of their 10-day to 2-week delay in producing new flushes of growth that are less vigorous.
In California Dickson et al (5) reported that the rate of spread of tristeza in the groves


seldom exceeded two new infections each year from each diseased tree. They noted, however, that the most rapid spread was generally in th intermediate area where most orchards were ruined commercially about five years after the disease was first reported in them. This area had the largest number of flying aphids. .
In Florida the visible spread of the disease has been greatest in a Temple orange grove where all trees were reported as being on sour orange rootstock. Actually some were growing on tristeza-tolerant rootstocks and it is believedi that these trees have served as more favorable reservoirs of virus for aphid transmission than the visibly diseased trees on sour orange rootstock.
The more infected trees available, the greater is the chance for aphids to acquire the virus and transmit it to other trees. In Florida the number of visibly diseased trees is not always a reliable measure of the number of infected trees, for frequently there are mixtures of rootstocks.
Surveys made by the State Plant Board of Florida (2) show a widely scattered distribution of tristeza-infected trees. These trees serve as sources of virus, and as aphid infestations are not usually controlled by present spraying practices, the number of infected trees in the State may be expected to increase.
SUMMIARY
The green citrus aphid was found to transmit the tristeza virus from infected Valencia and Florida sweet seedlings as well as from the Temple orange variety previously reported. The black citrus aphid was shown for the first time to be a vector of the virus. Seven other insects and one mite species did not transmit the virus.
Improved techniques have given high ratios of transmission by the melon and green citrus aphids. The techniques utilize controlled sources of inoculum in several varieties of citrus seedlings, multiple-branched Key lime test plants, 300 to 700 aphids per test, and timely observations to detect initial symptoms.
Transmissions nf virus by the green citrus aphid from Meyer lemon produced notably






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


milder symptom expression on Key limes than
those obtained by tissue transfers to Key
limes from the same Meyer lemon source.
REFERENCES CITED
1. Bennett, C. W., and A. S. Costa. 1949. Tristeza disease of citrus. Jour. Agr. Res. 78 (8): 207-237.
2. Cohen, M., and L. C. Knorr. 1953. Present status of tristeza in Florida. Proc. Fla. State Hort. Soc. 66: 20-22.
3. Costa, A. W., and T. J. Grant. 1951. Studies on transmission of the tristeza virus by the vector Aphis citricidus. Phytopathology 41 (2) : 105-113.
4. Dean, H. A., and E. 0. Olson. 1956. Preliminary studies to determine possibility of insect transmission of tristeza virus in Texas. Jour. Rio Grande Valley Hort. Soc. 10: 25-30.
5. Dickson, R. C., Metta McD. Johnson, R. A. Flock, and Edward F. Laird, Jr. 1956. Flying aphid populations in southern California citrus groves and their relation to the transmission of the tristeza virus. Phytopathology 46 (4) : 204-209.
6. Fawcett, H. S., and J. M. Wallace. 1946. Evidence of the virus nature of citrus quick decline. Calif. Citrogr. 32 (2): 50, 88, 89.
7. Grant, T. J., and A. S. Costa. 1951. A mild strain of the tristeza virus of citrus. Phytopathology 41(2): 114-122.
8. Grant, T. J., and Richard P. Higgins, 1956. Occurrence of mixtures of tristeza virus strains in citrus. Submitted for publication in Phytopathology.
9. Grant, T. J., A. S. Costa, and S. Moreira. 1951. Studies of tristeza disease of citrus in Brazil. V.


Further information on the reactions of grapefruits, limes, lemons, and trifoliate hybrids to tristeza. Calif. Citrogr. 36: 310, 311, 324-329.
10. Knorr, L. C., and W. C. Price. 1954. Diagnosis and rapid determinations of tristeza. Fla. Agr. Expt. Sta. Ann. Rpt., pp. 196-197.
11. McClain, R. L. 1956. Quick decline (tristeza) of citrus. Calif. Dept. Agr. Bul. 45(2): 177-179.
12. McClean, A. P. D. 1954. Citrus vein-enation virus. So. African Jour. Sci. 50(6): 147-151
13. McClean, A. P. D. 1950. Virus infections of citrus in South Africa. Farming in So. Africa 25 (293) 262; 25(294): 289.
14. McClean, A. P. D. 1950. Possible identity of three citrus diseases. Nature, (London) 165: 767.768.
15. Meneghini, M. 1946. Sobre, a natureza e transmissibilidade da doenca "tristeza" dos citrus. Biologico 12: 285-287.
16. Norman, Paul A., and Theodore J. Grant. 1953. Preliminary studies of aphid transmission of tristeza virus in Florida. Proc. Fla. State Hort. Soc. 66: 89-92.
17. Olson, Edward 0., and Bailey Sleeth. 1954. Tristeza virus carried by some Meyer lemon trees in South Texas. Proc. Rio Grande Hort. Inst. 8: 84-88.
18. Sleeth, Bailey. 1956. Occurrence of tristeza in two citrus variety plantings. Jour. Rio Grande Valley Hort. Soc. 10: 31-33.
19. Wallace, J. M., and R. J. Drake. 1951. Newly discovered symptoms of quick decline and related diseases. Citrus Leaves 31: 8, 9, 30.
20. Wallace, J. M., P. C. J. Oberholzer, and J. D. J. Iiofmeyer. 1956. Distribution of viruses of tristeza and other diseases of citrus in propagative material. 'U. S. Dept. of Agr. Plant Disease Rptr. 40(1): 3-10.


PHYSIOLOGIC RACES OF THE BURROWING


NEMATODE IN RELATION TO CITRUS SPREADING DECLINE


E. P. DUCHARME' AND W. BIRCIFIELD'

The burrowing nematode, Radopholus sirnilis (Cobb) Thorne, is now known to parasitize more than 125 different species of plants. Some species show no evident effects of the parasite, whereas other species such as rough lemon suffer severely. Many of the susceptible species are grown as ornamentals around homes and, if .parasitized by burrowing nematodes, may be a source of infection for citrus growing close by. If all the burrowing nematodes that parasitize these plants are alike, then any infected plant could spread the in. fection to nearby citrus. On the other hand, should some colonies of burrowing nematodes be so specialized that they do not feed on citrus, then their presence on host plants would not be a threat to adjacent groves. Because of the extensive host range of the burFlorida Agricultural Experiment Station Journal Series No. 540.
'/Florida Citrus Experiment Station, Lake Alfred. 2/Florida State Plant Board, Gainesville, Florida.


rowing nematode, it is important to know whether physiologic races of burrowing nematodes occur in nature and whether there are races that do not parasitize citrus. A physiologic race is generally understood to be identical with the species in morphological respects but to differ from it in some aspect of its physiology, such as parasitism.
In Florida, clumps of banana, Musa nana and M. sapientuin, are often planted in and about citrus groves bordering lakes, marshes, irrigation ponds and drainage ditches. The first evidence indicating the existence of a physiologic race of burrowing nematodes that differs from the burrowing nematodes causing spreading decline came from such a clump of banana plants. The banana roots were heavily parasitized with burrowing nematodes whereas the citrus roots were not. Roots from this location were examined four times during the following year. Each time the citrus roots were free of burrowing nematodes although the citrus roots were intermingled with the para-





DUCHARME AND BIRCHFIELD: PHYSIOLOGIC RACES


sitized banana roots. Attempts to infect the roots of sour orange seedlings with burrowing nematodes from this location were not successfuil. The burrowing nematodes from this location, although they would not feed on citrus, could not be' distinguished morphologically from those causing spreading decline. In this discussion burrowving nematodes that parasitized banana but not citrus wvill be designated as the "banana race."
Clumps of banana plants in or next to 39 citrus groves and other clumps in 30 locations where there was no citrus were examined. for presence of burrowing nematodes. hI the 39 locations next to groves, the citrus and banana plants were close enough for root contact. Among these places examined, burrowing nematodes had parasitized banana but not citrus in 9 locations, both banana and citrus in 4, and only citrus roots in 3. No burrowing nematodes were found in the remaining 23 locations. Of the 30 isolated clumps of banana, 13 were parasitized by burrowing nematodes and 17 were not. None of the parasitized banana plants appeared to be diseased, whereas all infected citrus had symptoms of spreading decline. These observations indicated the existence of three physiologic races of burrowing nematodes, separable by their ability to parasitize either banana or citrus or both.
Experiments were conducted under controlled conditions to test the hypothesis derived from observations made in the field that at least three strains of burrowing nematodes exist. In the first experiment, sour orange seedlings planted in sterile soil maintained at temperatures of 715' to 78' F. did not become parasitized when inoculated with the banana race of burrowing nematodes. In another experiment, nematode-free banana plants and rough lemon seedlings planted side by side in the same container were inoculated with collections of the banana race and the race causing citrus spreading decline. The inoculated test plants were grown for six months with the soil temperature maintained at 715' to 78' F. The burrowing nematodes from banana infected the banana test plants, but not the rough lemon seedlings although the roots of both plants were intermingled. In contrast, the burrowing nematodes from a grove affected by spreading decline readily parasitized the rough


lemon roots and attacked the banana roots as well.
in another studx', nematode-free sour orange seedlings and banana plants growing in steamsterilized soil were cross-inoculated with burrowving nematodes from the same sources used in the preceding experiment. The soil temperature was maintained at 75' to 78' F. The burrowing nematodes from banana reinfected banana but not the sour orange seedlings, and those from a spreading decline affected grove parasitized both the sour orange and banana test plants. The results of these experiments confirmed the existence of twvo of the three physiologic races found in the field.
Burrowing nematodes that cause spreading decline are physically like those of the banana race. The average length and width of female nematodes from both races was almost identical and there wxas no significant difference in the physical proportions. No morphologic character was found that could be used to distinguish one physiologic race from the other. The two physiological races of the burrowing nematode (fladopholus similis) that have been found in nature have been separated only by differences in parasitic activity on citrus and banana. The existence of a possible third race, found in the field on citrus only, was not studied in the laboratory experiments undertaken.
it is likely that other physiological races of this nematode can be detected by using additional species of host plants. Burrowing nematodes collected from several kinds of ornamental plants failed to parasitize citrus in exploratory tests, possibly because they may be similar to the banana race. On the other hand, we know that the physiologic race causing spreading decline will infect Persea aniericana Mill., (avocado); Malpighia glabra L., (Barbados cherry); Hedychittin coronarium Koenig, (ginger lily); and Musa paradisiaca var. sapientum Kuntze, (common banana in Florida). At present it is not known how many physiological races of the burrowing nematode are involved in the spreading decline disease of citrus, but the existence of such races could explain some of the variation that occurs in the severity of disease expression among affected groves. In the search for resistant citrus rootstocks, it will be necessary to test prospective plants against different populations Of





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


burrowing nematodes from numerous locations.
Since one of the physiological races parasitized both citrus and banana, it becomes necessary to determine which race is present before deciding whether or not infected banana or other plants should be considered potential reservoirs of infection for citrus. Until


there is some practical way to distinguish these races, it is necessary for growers to take utmost precaution to avoid introducing any burrowing nematodes by planting infested ornamentals in or next to citrus groves. The existence of physiologic races of burrowing nematodes does not minimize the gravity of the spreading decline problem.


HARRY W. FORD
Florida Citrus Experiment Station
Lake Alfred
The purpose of this paper is to report the evaluation of certain rootstock material that seemed to show resistance to spreading decline. Spreading decline caused by the burrowing nematode Radopholus similis (Cobb) Thorne (7) generally affects all citrus rootstocks used commercially in Florida. Between 1951 and 1955, a total of 54 trees were found that appeared healthy although surrounded by decline trees. The trees were reported by Experiment Station personnel, extension workers, production managers, growers, and inspectors of the Florida State Plant Board. Most trees were eliminated as possible burrowing nematode resistant candidates after a preliminary inspection. A few trees showed potentialities worthy of intensive study for burrowing nematode resistance.
METHODS
The feeder roots of each tree recommended for study were sampled for the presence of the burrowing nematode by the root incubation technique suggested by Young (10). A feeder root distribution pattern was compiled for comparison with a representative standard for healthy trees. The method of root sampling is described in mother papei (4). Trees were accepted as candidates for the test program if the root profile compared favorably with that of a healthy tree even though burrowing nematodes were found associated with the roots, Forty-four of the 54 candidates were eliminated by this test.
Florida Agricultural Experiment Station Journal Series No. 551.


Ten trees were entered in the test program. The sweet orange scions of two trees were suspected as the source of the tolerant factor and were therefore included in the test program and coded sweet oranges E and F. Two trees were seedling sweet oranges and were coded sweet oranges C. and H. One tree was a seedling of Cleopatra mandarin and coded Cleopatra 1. The rootstocks of four of the trees appeared to be rough lemon and were coded rough lemon. The abbreviated designations were RL-A, RL-B, RL-C, and RL-D. The rootstock of the last candidate was unidentifiable as a common citrus species and was coded Clone X.
In order to obtain test material, roots of the desired tree were severed and both cut ends of each root lifted above the surface of the ground and tied to stakes. Five to 40 percent of the severed roots of rough lemon and five to 12 percent of sweet orange stocks produced sprouts. The sprouts were permitted to grow until eight to 15 expanded leaves were present. The sprouts were removed and cut into leaf bud cuttings by severing the stem above and below the bud with pruning shears. Henceforth the term cutting will be used in this report to indicate a rooted leaf bud cutting in which the bud has developed into a leafy shoot. The propagating procedure is contained in a separate report by Ford (3).
Root sprouts of promising candidates have been topworked to older citrus trees to obtain seed to determine if the nematode tolerant factor is seed transmitted.
The following tests were performed to evaltiate the material: I. A candidate rootstock clone was first evaluated by comparing the growth of six cuttings planted in sub-soil in-


CITRUS ROOTSTOCK SELECTIONS TOLERANT

TO THE BURROWING NEMATODE






FORD: CITRUS ROOTSTOCK SELECTIONS


fested with the burrowing nematode and six cuttings in non-infested citrus grove sub-soil. Separate 1.25 gallon containers were used for each cutting. The containers were placed in a water cooled temperature tank that maintained the soil temperature at 78' F. The plants in each container of decline soil were inoculated three times with burrowing nematodes obtained from different commercial groves. The cuttings were permitted to grow for three to six months depending on rate of growth and time of year.
II. Six Clone X cuttings were planted in containers filled with steam sterilized soil. Two hundred hand picked burrowing nematodes were placed on the roots of each plant and permitted to develop for six months.
II1. Six months old cuttings of RL-A, RL-B, and Clone X were budded with Parson Brown, Valencia, and grapefruit scions by using a patch bud technique (2). Three to six months after budding, the plants were tested for growth and nematode infestation in the temperature tank.
IV. Sweet orange E and sweet orange F were budded on susceptible rough lemon seedlings to determine if nematode tolerance in the roots could be induced by the scion of a budded tree.
V. Twelve cuttings of RL-A, RL-B, and


Clone X were grown in decline sub-soil to determine the influence of N and K on the population of burrowing nematodes. Two levels of N and K in factorial combination were applied as nutrient solutions twice weekly for four months. The following concentrations in ppm were used: N, 25 and 200; K, 0 and 300. Also, 24 cuttings of Clone X were divided into two groups. One group was planted in burrowing nematode infested soil and the other in non-infested soil. Each group was sub-divided into two groups of six plants each to which two levels of N were applied. Nitrogen at 25 and 210 ppm in the nutrient solution was applied twice weekly.
VI. The ability of the nematode to penetrate the feeder root, lay eggs and reproduce was determined by an aceto-osmic staining procedure developed by Tarjan and Ford (8). Rooted leaf-bud cuttings of clones RL-A, RLB, and Clone X were planted in'sterilized soil in separate petri dishes with a one half inch square of No. 41 Whatman filter paper under the root tip. Twenty-five female burrowing nematodes in 0.3 ml. of water were placed on the root tip and covered with a layer of soil. The inoculated roots were stained and cleared, after two to 26 days at 78 F. under artificial light, so that nematodes and eggs could be seen inside the roots.
VII. The number of eggs in the cortex and


Table 1. Root distribution of the parent tree of selected rootstock clones as comared to susceptible rough lemon .


Rootstock clone Feeder roots in indicated 10 inch depth zones
0-10 10-20 2C-30 30-40 40-50 50-60 Total Clone X - 9.2 11.2 16.0 12.6 8.8 5.9 63.7
Rou-h lemon B 1.9 .9 6.0 .4 3.6 1.6 20.4

flcuh lemon C 3.0 1.2 1.9 .5 .2 .1 6.9

Roug-h leaon P 3.9 2.2 4.4 3.3 .9 .3 15.0

Rourh lemon (Check) /,.7 2.1 5.3 4.3 3.7 2.0 22.1


a Mean of 4 satnples to a depth of 5 feet expressed as rrams dry weight in a
coltn one foot square.
b ean o^ 120 trees 25 years old in soil not infested with spreadin decline.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


stele of the feeder root of Clone X as compared to RL-A was determined by comparing single roots from a cutting of each clone placed together in a petri dish. Fifty female burrowing nematodes were placed between the two roots and incubated for four days after which the roots were stained and cleared.


VIII. From October 1955 to January 1956, fruit samples were collected from the Parson Brown scion of Clone X and compared with Parson Brown on rough lemon. Measurements were made of internal fruit quality. Appearance and palatability were evaluated by a panel.


Table 2. Growth and R. similis population of cuttings from selected rootstock clones after 3-4 months in temperature tanka


Clone Soil Shoot Growth Fresh wt. Fresh wt. Number
Condition cm. Shoot Roots R. similisb
(grams) (grams) p-er cutting

Rough lemon A Infested 45 28 21 117 ;es1
Non infested 48 30 26

RoW4h lemon 'P Infested 47 34 25 201 113
Non infested 51 37 31

ou-h lemon C Infested 39 32 23 123 + 75
lon infested 44 35 28

Rough lemon D Infested 43 46 61 352 *. 203
Non infested 51 55 66

Seet Orange Lc Infested 29 9 7 25 . 11
Non infested 38 12 12

Seet Orange Fc Infested 29 16 13 37 +t 16
Non infested 35 22 16

Sweet Orange Gd Infested 4 4 4 39 + 21
Non infested 9 7 5

Sweet Orange I'd Infested 5 3 2 4]. t 1S
.on infested 7 4 3
c
Cleopatra I Infested 10 2 1 24 :L 7
seedlinE 17on infested 24 5 3

Clone X Infested 28 45 !9 3 � 3
Yon infested 27 37 3?

a1ean of 6 plants froi separate containers.


U Incubated in fruit jars for 43 hours. The scion of a tree being tested as a potential rootstock. d Parent plant a seedling tree. e Standard deviation of the mean.





FORD: CITRUS ROOTSTOCK SELECTIONS


Table 3. Growth and R. silis population of clone X cuttings in steam sterilized soil inoculated with 200 .R. similis per plant.a


Treatment 3 months 6 months
Shoot growth Shoot rtob Number'~ Shoot growth ShOOtatoNumlbervw
Cm. Root R. similis cm. Root R. similis
________ er -cuttii, per cutting

Inoculated 21 .9 2 t2 49 .9 1�1t

Untreated 19 .9 47 .8


a Mean of 6 plants from separate containers. b Fresh weight of shoot divided by fresh wei ght of roots. C Plants removed from containers and roots incubated in fruit jars for 48 hours.


RESULTS
In Table 1 feeder root measurements of the parent trees of four rootstock candidates growing in decline soil are compared with the root density of trees on ordinary rough lemon in non-infested soil. Rough lemon B had a root density comparable to a healthy tree to a depth of five feet while Clone X had three times the root density of ordinary rough lemon.
The growth and burrowing nematode infestation of cuttings taken from 10 candidate rootstock clones is shown in Table 2. Shoot growth of RL-A and RL-B was reduced seven percent by the presence of the burrowing nematode. Both rough lemon clones supported a population of burrowing nematodes comparable to spreading decline susceptible rough lemon. There was no reduction in shoot length or root weight of Clone X whven grown in burrowing nematode infested soil and the population of burrowing nematodes was reduced to a very low level in all replicates of the test.
Nematode survival and plant growth when 200 hand picked burrowing nematodes were placed on the roots of six individual cuttings of Clone X in sterilized soil are shown in Table 3. After six months, the burrowing nematode population bad disappeared from the roots of 50 per cent of the cuttings and one to three nematodes were found on the roots of the remaining plants. There was no


depression of growth by the burrowing nematode.
The effect of a budded scion on nematode survival and plant growth of RL-A, RL-B, and Clone X is presented in Table 4. Growth comparisons between grafted combinations of the different clones are not entirely valid because all of the tests were not performed at the same time. Growth of grapefruit and Parson Brown scions on RL-A was reduced 10 and 18 percent respectively. The Valencia bud on RL-B was taken from the parent tree of RL-B so that the budded combination was genetically the same as the original tree in the field. This combination showed a 10 percent reduction in growth. The growth of cuttings of Clone X budded with Parson Brown from the original parent tree was not reduced in decline soil and the burrowing nematode population completely disappeared. Studies of Ruby Red grapefruit and Temple budded on Clone X were in progress only two months when this manuscript was written. The burrowing nematode population consisted of two to four adult females. No larvae were present indicating that the nematode population was not increasing. Sweet orange E and sweet orange F when budded on susceptible rough lemon were retarded in growth 65 percent by the nematodes so that the results are not reported. Unbudded cuttings of sweet orange E and F were also reduced in growth (Table 2). The data indicate that the two sweet orange clones






FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Ia
Table 4 Growth and Rl. sinilis population of budded rootstock cuttings.


Graft com- Scion Soil Duration Shoot growth Fresh wt. Nwiber b
bination Condition (months) cm. of plant 11. similis
Rootstock (grams) p~er cuttinF

Rough lemon A Grapefruit. Infested 3 13 21 75 & 47
Non infested 14 28

Rough lemon A Parson Brown Infested 3 35 97 156 �L 81
Non infested 43 124

Rough lemon B Valencia C Infested 3 26 - 84 & 23
Non infested 29

Clone X Parson Brownc Infested 4 29 112 0
Non infested 30 103

Clone X Ruby Red Infested 2 -- 2�t1

Clone X Temple Infested 2 -- 4 t 1


a Mean of 6 plants fron separate containers. b Incubated in fruit jar for 48 hours.

cCombination genetically the same as original tree found in the field.


do not have nematode tolerant characteristics that originate in the top of the trees as originally suspected.
The effect of N and K nutrition on nematode infestation of the host has attracted the attention of several workers (1, 5, 6). Oteifa
(5) found that nutrition was of considerable
importance in determining the development tii~e of root knot nematodes Meloidogyne incognita.
Nitrogen and K levels had no significant effect on the burrowing nematode population of RL-A, RL-B, and Clone X so that the results are not reported. The growth of Clone X cuttings was modified, hy increased N and K, from that reported for citrus in sand culture
(9). Additional studies are in progress to evaluate the -effect of nutrition on growth of Clone X cuttings.
The effect of N level on growth of Clone X in infested as compared to non-infested citrus grove sub-soil is shown in Table 5. Shoot growth was not affected by the burrowving nematode infested soil condition at either of the two N levels.


Studies of burrowing nematode activity by staining in sitit indicated that reproduction of burrowing nematodes was depressed in the cortex of the feeder roots of Clone X cuttings as compared with the cortex of RL-A, RL-B3 or ordinary rough lemon cuttings. Occasionally nematodes penetrated the stele of Clone X and after 21 days there was an increase in the nematode population. There was no indication of an exit of nematodes from the stele. No burrowing nematodes penetrated the stele of RL-A, RL-B or rough lemon under the conditions of this experiment. Eighty-five tests were made on the rough lemon clones. Apparently there is a difference between species from the standpoint of burrowing nematodes entering the stele. Nematodes were found in the stele of pumnmelo, for example.
A detailed comparison was made between Clone X and RL-A by placing female burrowing nematodes between single roots from each clone. The results of this test are shown in Table 6. There were 60 times more eggs in the cortex of RL-A than in the cortex of Clone X. In the cortex of RL-A eggs were scattered





FORD: CITRUS ROOT


throughout the tissues while ill thle cortex of Clone X all eggs that could be found were close to the body of the nematode. When nematodes penetrated the stele of Clone X, a condition that occurred in 11 percent of the samples, considerably more eggs were found per nematode.
A panel of Experiment Station personnel preferred the external fruit appearance of Parson Brown on rough lemon to that of Parson Brown on Clone X. However the panel preferred Parson Brown on Clone X for eating quality. juice characteristics of Parson Brown on Clone X and rough lemon are shown in Table 7.
DISCUSSION
RL-A was secured from the rootstock of a Valencia orange tree in Lake Alfred that had been in spreading decline infested soil for four years prior to 1951. Dense foliage covered the tree with leaves of normal size which was in marked contrast to adjacent trees with symptoms of spreading decline. The grove was pulled before the burrowing nematode was

Table 5. Effect of NT on FgIro,.tht cuttings in infested ax
temperature tanks


STOCK SELECTIONS 49

identified as the cause of spreading decline.
IRL-B, the rootstock of an 18 year Valencia tree from a grove in southern -Polk County was transplanted into spreading decline soil in 1941. Thus the feeder roots have been infested with the burrowing nematode for at least 14 years. The tree was considerably larger than surrounding decline trees even though some feeder root damage was detected. Below five feet the root. density fluctuated considerably during a one year period.
The results of growing plants of RL-A and RL-B under controlled conditions in infested soil and inoculation of individual roots in petri dishes indicate that the two rough lemon clones are reasonably tolerant to the damage of the burrowing nematode. The number of burrowing nematodes and the damage within the root cortex of the two tolerant clones are comparable to susceptible rough lemon. The nature of the tolerance of these rough lemon clones is not understood; however, the rapid rate of shoot growth and development of new feeder roots is probably an important factor.

mid R. sinilis population of Clone i. id non infested soil after 3 months in


IreatmentO Soil Sboot growth Shoo0ts atioc 'Number d
Condition CM. Root R. similisd
-per cutting'

LowNY Infested 26 1.3 6�t3

N'on infested 23 1.3


High N7 Infested 29 1.0 3 t. 2

Non infested 27 .

Significance N.S. 1.S. r S .


a Ilean of 6 plants from separate containers. b 25 P.pm and 210 ppm of Nq respectively applied twice weekly. CFresh weight of shoots divided by fresh weight of roots. d Roots incubated in fruit jars for 48 hours.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Table 6. Number of R. sinilis and eggs found in feeder roots of Clone XC a
and Rough lemon A cuttings four days after nematode inoculation.



Rootstock Corte Steleo
a. R 5lL- Lggs smli ggs

Rough lemon A 10.1 97.2 -Clone XC 5.2 1.6 3 9

Significance **

L.S.D. at .05 3.1 21.2


Fifty female burrowing nematodes placed between a feeder root of Clone XC
and a feeder root of Itough lemon A in a petri dish.
b Mean of 35 replicates in which the nematodes invaded the cortex. c The mean of /4 replicates in which the nematodes invaded the stele.

* Statistical significance at 5 percent level.
**.Statistical significance at 1 percent level.


It is conceivable that the burrowing nematode could damage RL-A and RL-B under poor grove management practices. This possibility will have to be evaluated under field conditions. At the present time RL-A and RL-B are propagated by cuttings although an evaluation of seed propagation is in progress. It is essential that the seed produce a very high percentage of nucellar plants as assurance that the rootstock will be genetically the same as the original parent. Tests for susceptibility to tristeza and xyloporosis are in progress.
Clone X, a rootstock that has not been identified, is resistant to the burrowing nematode found in citrus groves. The clone is not completely immune because nematodes penetrated the feeder roots and in 50 percent of the plants one to four nematodes survived three to six months. In every test conducted with cuttings of Clone X, the rate of growth in nematode infested soil was equal to or better than in non-infested soil. Laboratory studies indicated that the resistant factor was confined to the root cortex and had a detrimental effect on the eggs laid by the nematode.
The 25-year-old parent tree of Clone X was discovered in a grove near Davenport,


Florida in 1954. The tree was 16 feet high and yielded six hoxes. Root samples taken at the periphery of the tree over an 18 month period were devoid of burrowing nematodes. Feeder roots from the four adjacent trees were always found to harbor the nematode. With the exception of an area nine feet square near the southeast corner of the tree, feeder roots of adjacent rough lemon trees did not penetrate the dense root system of Clone X. The resistance of the feeder roots to the burrowing nematode and the dense nature of the root system suggests that the stock may also be of value as a biological harrier against the spread of the burrowing nematode.
Fruit of Clone X are not available at the present time so that all progeny have been obtained from leaf bud cuttings. The clone is more difficult to propagate and grows slower than rough lemon. The leaves appear to be resistant to anthracuose caused by Colletotrichurn gloeosporioides Penz but susceptible to sour orange scab caused by Elsinoe 'Fawcetti Bitancourt and Jenkins. In containers, the roots were more frequently damaged by excess water than roots of rough lemon.
The reaction of Clone X to other diseases






FORD: CITRUS ROOTSTOCK SELECTIONS


such as tristeza and xyloporosis is unknown at present. The stock should be evaluated in the field for general horticultural characteristics before being recommended for use in Florida citrus groves.
SUMMARY
Between 1951 and 1955 a total of 54 trees were found that appeared healthy although surrounded by decline trees. Most trees were eliminated as potential burrowing nematode resistant candidates after a preliminary inspection. Ten trees were entered in the test program.
The results of growing cuttings of candidate clones in spreading decline infested soil and inoculation of individual roots in petri dishes indicated that two rough lemon clones were tolerant to the burrowing nematode even though a high population of burrowing nematodes was found on the roots. Growth of plants was reduced 10 to 18 percent.
A third rootstock, that has not been identified, was found to be resistant to the burrowing nematode infecting citrus groves. Plant growth was not reduced in infested soil and the population of burrowing nematodes always decreased and frequently disappeared. The resistant factor was found to be confined


to the root cortex and had a detrimental effect on the eggs laid by the nematode. The
absence of information on general horticultural
characteristics, mineral nutrition, tristeza and
xyloporosis, indicate that field tests must be
evaluated before this clone can be recommended for planting in Florida citrus groves.
LITERATURE CITED
1. Chitwood B. G. and B. A. Oteifa. 1952. Nematodes parasitic on plants. Ann. Rev. Microbiol. 6:151-184.
2. Ford. Harry W. 1956. Unpublished data.
3. Ford, Harry W. 1957. A method of propagating 'citrus rootstock clones by leaf bud cuttings. Proc. Amer. Soc. Short. Sci. (In press).
4. Ford, Harry W., Walter Reuther, and Paul F. Smith. 1957. Effect of Nitrogen on root development of Valencia orange trees. Proc. Amer. Soec. Hort. Sei. (In press).
5. Oteifa, B. A. 1953. Development of the root knot nematode Meloidogyne incognita as effected by potassium nutrition of the host. Phytopath. 43: 171-174.
6. Oteifa, Bakir A. 1955. Nitrogen source of the host nutrition in relation to infection by a root-knot nematode Meloidogyne incognita. Plant Disease Reporter 39 (12): 902-903.
7. Suit, R. F., and E. P. DuCharme. 1953. The burrowing nematode and other parasitic nematodes in relation to spreading decline of citrus. Plant Disease Reporter 37(7). 379-383.
8. Tarian, A. C. and H. W. Ford. 1957. A modified aceto-osmium staining method for demonstration of nematodes in citrus root tissues. Phytopath. (In press).
9. Webber, J. H., and Batchelor, L. D. 1948. The Citrus Industry. Vol. I. Univ. of Calif. Press. Berkeley, Calif.
10. Young, T. W. 1954. An incubation method for collecting migratory endo-parasitic nematodes. Plant Disease Reporter. 38(11): 794-795.


Table 7. Juice characteristics of Parson Brown on Clone X compared to
Parson Brown on rou-h lemon, 1955-56.



Rootstock Date Juice by Soluble Acid Soluble Mgs. Vitamin
Weight Solids % Solids to C/I00111s.
% Acid
Ratio

Clone X Oct. 7 52.0 9.2 1.10 8.3 69.2

Rough lemon Oct. 7 50.7 9.4 1.21 7.7 58.4

Clone X Yov. 8 54.6 10.3 1.05 9.8 55.0

Rough lemon Yov. 8 50.9 10.1 1.27 7.9 55.0

Clone X Dec. 13 50.0 11.4 .97 11.7 63.1

.ough lemon Dec. 13 54.7 10.7 .94 11.4 60.0

Clone X Jan. 3 53.8 11.8 .81 14.6 66.1

Rough lemon Jan. 3 58.8 11.4 .88 13.0.6





FLORIDA STATE HORTICULTURAL SOCIETY, 1956

THE NEW 4-H CLUB PROGRAM FOR CITRUS

PRODUCTION TRAINING


JACK T. MCCOWN
Florida Agriculhiral Extension Service
Gainesville
Agricultural progress in America during recent decades has been astounding. Looking at agriculture * ral history it can be seen that this progress is closely associated with the emphasis agriculture has placed on developing its youth. Major agricultural enterprises have had specific programs to inspire youth. This is a part of the citrus industry that is lacking today. Realizing that many boys do not have the opportunity to study citrus the Agricultural Extension Service is expanding its citrus youth program to meet this need, This paper will outline the Extension, Service's citrus youth program in order that you may become better acquainted with its aims and objectives. The Extension Citrus Advisory Committee which plays an important part in developing this program, has outlined a 5-year project for 4-H Club boys wishing to become more intimately acquainted with the industry. The 5-year program as outlined below will meet all requirements for a 4-H Club project. Upon completing each year's requirements, the youth may continue his work toward the following year's requirements without waiting foran end of a calendar year.
The requirements for the first year are:
1. Map a 10-acre bearing grove showing the location of (1) healthy trees, (2) missing trees, (3) dead trees, (4) diseased trees, (5) young resets.
2. When the map is completed, it should show the total number of trees in the blocks, the number of healthy trees, and the number of diseased, dead and missing trees.
3. Be able to identify citrus fruits that have been injured by (1) rust mites, (2) scale,
(3) melanose.
4. Plant a citrus seedbed either as an individual home project, or in a cooperate , ive club project. Discuss size and location of your seedbed with your local leader, or Extension Agent. (Minimum size of seedbed to be determined.) '


5. Keep neat and accurate records in a record book, showing the work that has been done, and write a story about your citrus activity.
SECOND YEAR'S REQUIREMENTS
1. At least 6 months after completion of the first year map, make another map showing the location of (1) healthy trees, (2) missing trees, (3) dead trees, (4) diseased trees, (5) young resets.
2. When the map is completed, it should show the total number of trees in the block, the number of healthy trees and number of diseased, dead and missing trees. Refer to your first year map and copy the comparable figures and set them down below the first year's figures, Note whether the general condition in the grove is (1) improved, (2) worse, (3) the same. Mention the progress of the grove in the story at the end of the year,
3. Be able to identify early, midseason and late oranges, two kinds of g apefruit and one kind of tangerines. It is not necessary to, identify by variety, but the club member should be able to examine the fruit and determine whether it is early, midseason or late.
4. When the seedbed is between 12 and 18 months old, line out the seedlings. Discuss location of nursery and its size with the local leader or Extension Agent.
5. Be able to identify 5 pests of citrus (may be insects, diseases or both).
6. Keep neat and accurate records and write a story on the, second year's citrus activity.
THIRD YFAB's REQUIREMENTS
1. About 9 months after making the second map, make a third one the same way.
2. Determine the number of skips in the 10-acre plot due to missing, dead, or diseased trees. From this figure, calculate the percentage of trees missing, The percentage of crop loss in the grove would be about the same. Knowing what price per box the fruit brought, calculate the financial loss to the grower.





MeCOWN: CITRUS PRODUCTION TRAINING


3. Bud the nursery, The 4-H Club member should demonstrate to the local leader or the Extension agent his ability to bud and properly care for the nursery. The budded trees should be properly labeled. Certified budwood should be secured if possible, If certified budwood is used, the buds should be selected and the budding done under direct supervision of the leader and the State Plant Board representative.
4. Be able to -identify and know the approximate harvest season-whetber early, midseason or late-of the following citrus fruits: Oranges-Parson Brown, Hamlin, Navel, Pineapple, Jaffa, Valencia, Lue, Girn Gong. Grapefruit-Duncan, Marsh Seedless, Foster Pink, Thompson Pink, Red; Tangelos - Orlando, Minneola, Thornton; Miscellaneous, one variety of lemon, Persian (Tahiti) lime, MerCott.
5. Be able to identify four insects and three diseases that are of economic importance in citrus production.
6. Keep neat and accurate records and write a story of the year's activities.

FoURTH YEAR's REQUIREMENTS
1. Be able to identify leaf symptoms of the following mineral deficiencies in citrus: nitrogen, magnesium, zinc, manganese and iron.
2. The club member should be able to demonstrate his ability to stake out a grove for planting.
3. Sell or plant out the nursery trees. Learn to plant nursery trees in the grove by planting under the supervision of the club leader or Extension agent. Keep a record of bow these trees are cared for the first year. Include dates for each operation, including amount of water per tree, banking, planting cover crop, analysis and amount of fertilizer, insect and disease control.
4. Be able to identify five citrus insects and four diseases and tell how they can be controlled.
5. Explain what is meant by the "on tree" price growers get for citrus. Keep a record of 11 on tree" prices for one season from October I to June 15 for oranges and grapefruit. (Contact the same grower, grove caretaker, or cash buyer once each week and ask him the "on tree" price. Record this information, in table form in the record book, showing if it is early, midseason or late fruit prices.)


FIFTH YEAR'S REQUIREMENTS
1. Keep the following record on a bearing grove from September 1 to August 31. Fertilization: date, analysis, number of pounds per tree, method of application. Actually be on band and watch the entire operation for at least one application. Know bow to correct or prevent nitrogen, magnesium, manganese, zinc and iron deficiencies.
Spraying: Date, what is being sprayed for, materials used in the spray, approximate gallonaige or pounds of dust per tree.
Cultivation: Date, kind (disc, plow, acme).
Cover crop: Date planted, kind and seeding rate per acre (if not volunteer), Know why cover crops are needed in Florida citrus groves. Observe harvesting operations and spend at least half a day with a picking crew.
2. Know what "top working" means and how it is done.
3. Draw a floor plan of a fresh fruit packing house, single strength, sectionizing plant or concentrate plant , and know the fundamentals of their operation.
4. Keep neat and accurate records and write a story of the year's activity.
By providing this type of program we should achieve many objectives, First of all, the youth, through his association as a 4-H Club member would develop his leadership abilities. (2) Such a program would inspire the boy's interest in citrus through a closer 'association with many segments of the industry. (3) Provide the citrus industry with better trained personnel upon completion of this project. (4) Prepare some of these young men to achieve a better job by becoming better skilled. (5) Inspire a desire in some to further their educational training by attending college.
Now comes the question of what course of action must be taken in order that we may achieve these aims and objectives. A 4-H Club member who enrolls in a citrus project will through his local leader or county agent's leadership be made aware of the requirements necessary to carry on a project for 5 years. He will also be instructed in the procedure of keeping records, as a project record book will be provided outlining each. year's work. Upon completion of a year's project, several boys will be selected from each county to attend the annual junior Citrus Institute.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


This Institute is held at 4-H Camp Cloverleaf for the purpose of putting a final touch to the citrus project work for the year. Attending the Institute will he an award for the boy doing the best project work in his county. The junior Citrus Institute this past year was jointly sponsored by the Chilean Nitrate Educational Bureau of Orlando and Dolomite Products Inc., of Ocala. In addition to the junior Citrus Institute, we are preparing to promote additional interest among the club members in citrus by providing fruit judging contests and similar activities at the various county fairs throughout the state. At this time the ho)y will also he given the opportunity to participate in insect, disease and other identification contests.
It is important that the citrus industry take part in developing this program. Men in the industry can be of help by showing an interest


and taking an active part in local project work. We may also inspire the youngsters through encouragement and recognizing a job well done, In some instances financial aid may be necessary for clubs to develop local projects. Examples would include: nursery projects, small groves for demonstration purposes, tours and training schools. Organizations and individuals may help by making available funds for this purpose. We feel that the program outlined will be successful. However, greater goals may be achieved if we realize the importance of such a youth program and show an interest by putting forth a concerted effort to insure success. The young people of Florida are a part of the citrus industry. Let us prepare them to accept its future responsibilities in order that our industry may continue to he a leader among the various American agricultural enterprises.


FIELD OBSERVATIONS OF SEVERAL METHODS OF MANAGING CLOSELY

SET CITRUS TREES


FRED P. LAWRENCE
Florida Agricultnral Extension Service
Cainesville
ROBERT E. Nonnis
Florida Agricuiltutral Extension Service
Tavares
You will note from your program that the title of this presentation is "Field Observations of Several Methods of Managing CloselySet Citrus Trees." That title sounded simple enough when it was submitted to the program chairman but now that we have had more time to contemplate we are not so sure. For instance, how close is close? To help answer, this question wve turned to Webster's Collegiate dictionary only to find more confusion than enlightenment. We were reminded first of all that it depends how you pronounce the word. If you put a "z" in the pronunciationdloze-it means to "shut up" and considering the small amount of actual data we have, that might not be a bad idea. There are many other meanings, of course, but Definition No.


25, having the parts near together, is the one that seems most appropriate for our use.
Applying this definition,, consider first the citrus tree spacings of the various producing areas of the world. In Italy and other Mediterranean countries citrus trees are usually spaced l0'xI0' or l0'x12' which results in 300 to 450 trees per acre. The Japanese orchards average 240 to 300 trees per acre. Egypt's predominant spacing is 12'x18'; Peru 18'x18'; Brazil 21'x24'; California 22'x22' and Florida 25'x25'.
The planting distance in a given area depends upon such things as variety, species of rootstock used, type and fertility of the soil, the length of the growing season, and, to a large extent, upon the attitude of the individual doing the planting. To illustrate the latter point it might be well to point out that quite a number of California growers, according to an article in the October '55 issue of Citrograph, are turning to what they call hedgerow plantings and some groves are planted as closely as 8xlO which gives some 490 trees per acre.




LAWRENCE AND NORRIS: FIELD OBSERVATIONS


All of these plantings, or at least a major portion of them soon reach a point where the limbs and branches of the various trees interlock and overlap and unless special management practices of pruning are applied the bearing surface of such trees diminishes and naturally the production declines in proportion.
Accordina to the best estimates available Florida has 497,400 acres of bearing trees, 333,690 acres or 67% of which are 16 years of age or older. A grcat many of these groves are planted on spacings of 15x3O, 20x24, 25x25 and similar distances and if we apply definition No. 25 to the word close we vill find that most of these trees have their parts near together; hence we can apply the term closely planted and in need of some form of pruning.
Time will not permit our discussing the varied and many methods of pruning employed in the various citrus producing areas of the world-or even all of those practiced in Florida-so we will confine our remarks to some field observations of several methods of managing closely-set citrus trees; to narrow it down even more we propose to discuss briefly the following practices:
1. Hedging
2. Heading back
3. Thinning by tree removal
4. Topping-a form of rejuvenation pruning
In fairness to those who may read this paper in the printed proceedings we should state that from this point on our talk will be illustrated with color slides and we shall attempt to present, as clearly as possible, a word picture of these various methods of pruning.
Despite the difficulties associated with crowded groves, very little pruning of any nature has been undertaken in Florida either to prevent or to correct the situation. This has probably been due to the fact that earlier experiments suggested that pruning was an operation that contributed very little to over-all fruit production. In instances of moderate to severe pruning, a loss of fruit was noted without any apparent compensating effect on quality or fruit size.
On the basis of these earlier experiments,. recommendations were made that pruning


should be confined to the removal of dead wood and occasional broken limbs. This
recommendation, plus the fact that pruning is an expensive operation, has also brought about the situation that pruning in Florida until comparatively recently has been confined to the insid of the tree and to the removal of dead wood.
Insofar as the records show, no effort has been made to limit the size of citrus trees in Florida or to control crowding by judicious pruning of the periphery of the tree until some growers began to hedge tho periphery of their trees in the late 40's.
1. Hedging of citrus is a form of pruning clesigned to facilitate grove management practices and to improve the quality of fruit pro-duced. It is a practice that is becoming increasingly popular among Florida citrus growers as a way to alleviate the problem of overcrowding which ultimately results in a loss of production.
Hedging provides a means by which the bearing surface of trees is reduced in area without greatly reducing their 1 hearing ability. Indeed, in the case of some varieties, especially tangerines, hedging actually increases the per cent pack-out of fresh fruit in the first crop following the pruning operation by increasing fruit size. Fruit color and textures also are often improved because of increased sunlight and more effective insect and disease control.
One of the most valuable advantages of hedging, and the primary reason for its use in the first place, is to open the tree middles by removing interlocking branches. This allows for the movement of tractors, discs, spray and dust equipment and trucks through the grove without damage to the trees and fruit or to the equipment and operator. It speeds up grove operations generally, thereby reducing cultural costs.
If you would like additional information on hedging or plans for a hedging machine we suggest you obtain Experiment Station Bulletin 519 by D. S. Prosser and Extension Service Circular 115 by R. E. Norris.
2. Heading Back-This term and the type operation it implies is seldom used in Florida citrus; however, it is used rather extensively in the California lemon industry as well as throughout most of the other citrus producing






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


It required 3 men 5 days to run all brush from the 10 acres through the chipping machine. It took 4 men 3 days to haul out all limbs above 4 inches in diameter. It should be pointed out that this grove bad a problem of no place to haul and burn the brush so it had to be disposed of in place.
To dispose of the trees in the manner described the owner figured the total cost, of the operation at $1.50 per tree.
Of particular interest in the group of slides shown on this operation is the one showing how rapidly the remaining trees are filling in. Based on the progress the trees have made this year, it is believed that the grove will be back to normal production next year.
Some comments on similar operations:
Block B-Red grapefruit on rough lemon stock 10 years old was planted 1232x30 on Lakeland fine sand. Every fourth tree on the diagonal was sawed off flush with the ground with a pulpwood saw, dragged out and burned. The following year there was no noticeable reduction in crop. At 12 years of age (next year) the grower plans to remove every other tree on the diagonal-thus reducing the spacing to 25x3O at which time he will begin a program of hedging. Based on previous experience the grower feels there will be very little per acre loss in production-if any.
Block C-Twenty-five year old Valencias on rough lemon stock were planted 15x3O on Eustis fine sand. The trees were very crowded so every other tree was "buckhorned," bulldozed and replanted. The year before moving the production on the block was 4400 boxes. Fifty trees were removed and the following year the production dropped to 3960 boxes. The plan is to move 50 trees per year until the operation is completed. After the third year it is anticipated that the loss of 50 trees per year will not result in any loss of total crop produced.
Some figures on this operation:
It took 2 men 32 day to saw and re-sdw 20 trees; one man 12 to whitewash (by hand) 20 trees; one man one day to remove (by drag) the brush from 20 trees; four men, a bulldozer, a flat truck and a water wagon one day to push, haul 32 mile and re-plant 20 trees. The total cost of labor for this operation exclusive of equipment was $2.60 per tree.


areas of the world, It consists of removing a portion of the tree at regular intervals in order to retain a rather constant size of the tree. There are certain advantages and disadvantages to this method of pruning but since it appears to be of little value under present Florida conditions we will pass over it.
3. Thinning by tree removal-Tbis is a practice that has long been contemplated by Florida growers but one that has seldom been practiced. Numerous Florida groves planted during the last 30 years were spaced 15x30, or a similar distance, with the idea of removing every other tree. Few growers, however, have actually removed these trees and many have practiced little or no heading back or pruning of any kind.
Only in recent years have some few growers actually thinned their groves by removing trees in the closely-spaced rows. We regret that we do, not have more yield and cost data to present on these operations but the practice is not general and accurate data is scarce. We do have slides of one complete operation to show and some yield and cost data on the one operation:
The grove, consisting of a 10 acre block of Hamlins budded on rough lemon root, was planted in 1939 with a tree spacing of 15x25. The soil type is deep phase Lakeland fine sand. The trees were never beaded back or hedged and as a result the limbs were interlocked badly and many of the lower branches were dying as a result of sbading.,During the last 5 years production decreased, very markedly so during the past two seasons, which, as you know, were dry. During January and February 1956 every other row was removed by sawing the limbs off with a power saw and running all wood under 4 inches in diameter through a chipping machine. The stumps were treated with a tree killer (without success) on two occasions and as a final effort the stumps were sawed level with the ground and a chopper run down the row to remove all suckers.
The crop has not yet been harvested but the owner estimates his crop loss at 25% over the previous year's yield.
Some figures on the operation:
The rows were 21 trees long-2 men cut 2 rows per. day. Two men could trim the large limbs and stack the brush on 5 rows per day.





LAWRENCE AND NORRIS: FIELD OBSERVATIONS


Grove A-Cut back every other row in January 1947 just after the fruit was picked. The trees were whitewashed immediately. They started to sprout out in about six weeks and grew very vigorously the first year. The second year they put on only a few scattered fruit. The third year the growth was very dense and possibly because of the large trees on two sides, tended to grow upright but produced better than a box average of fruit. By the fourth year it was obvious that although the trees had good big broad leaves and were growing vigorously, they would soon be back like the old trees so it was decided to cut back the trees on both sides of the row. Some trees bore as much as 8 boxes of fruit the fourth year. These trees (as you can see by the slides) now have the characteristic appearance of budded trees and are yielding 10 boxes per tree. The new wood is quite thorny and some pruning to thin and shape is necessary,
Grove B-The initial operation was begun in February 1947. In this block it was noted that trees cut below 5 feet did not appear to come back as rapidly as did ones cut at a greater distance from the ground. Those trees topped above 5 feet were more difficult and expensive to handle in the original operation and did not respond any faster. It now appears that the trees cut 10 feet and higher will never "head-out" low and will ultimately be right back like they were originally; whereas the trees cut at 5 to -10 feet take on the characteristics of budded trees and will apparently remain relatively "low-headed" - provided they are hedged to prevent inter-locking. Of special interest in Grove B was one particular tree that yielded 16 boxes the fifth year. All trees in Grove B are currently pr ' oducing an average of 10 to 12 boxes of fruit.
In summary we again wish to point out that the contents of this paper are purely the results of field observations with no thought of making recommendations at this time. However, it seems logical that in many instances of closely-spaced trees high production can be maintained or regained through one of the forms of pruning outlined in this paper:
1. HedLyina:
A comparatively new method of pruning which is rapidly being adopted by Florida growers to relieve the. adverse ef-


The re-set trees began bearing the second year at the rate of about 1,4 box per tree average and in the third year they were yielding a box average. The fourth year's yield will probably be between three and four boxes.
And nowthe last practice to consider4. Topping, a form of rejuvenation pruning: Rejuvenation pruning is a term used by horticulturists to describe the objective of reinvigorating trees by stimulating more and better shoot growth and fruitfulness. This pruning must be severe enough to remove sufficient foliage to stimulate new growth over much of the tree.
When enough of the top is cut off, a growth response usually occurs throughout the woody framework. In order to produce, from pruning, an invigorating effect in a large old tree, it is necessary to make many small cuts or remove some of the large branches.
The method we have chosen to report on is that of removing the complete top of old seedling trees at varying heights from ground level to eighteen feet. This, too, is a new practice in Florida and although again, facts and figures are not abundant, we have some slides that are at least interesting. This practice might well be described as an act of desperation brought on in many groves by increased overlapping of limbs which resulted in a marked increase of pest and disease and a gradual dying of lower limbs. In some old seedling groves it is 10 to 15 feet from the ground to the first limb. The tops are sparse, the foliage is small, production is down and the cost of picking (usually from a 40 foot ladder) is such that it makes the operation very expensive.
During the last ten years many growers have been experimenting with various met ods of pruning to try to alleviate this condition. From these various methods of pruning we will discuss only the one wherein the -entire top of the tree is removed, The data presented is from two different blocks of old seedling trees owned by two different growers. Both growers topped only a few trees in 1947. Grower A started by topping trees in every other row at a relatively constant height of roughly 5 feet from the ground. Grower B topped about 20 trees in a block. These trees were topped from 1 foot to 15 feet in height.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


time) to prove or disprove the value of the operation. It would appear from the limited operations we have observed that if a grower has access to additional land and in instances of healthy trees a new grove that will bear heavily in 4 to 5 years can be established at an economic
figure.
4. Topping, a form ot rejuvenation pruning.
It is too early to make positive statements relative to this operation; however, it appears that by topping two or more rows per year (beginning on the outside row) this could raise production and reduce cost of harvesting in old
canopied groves.
Advantages:
a. Reduces height of tree.
b. Greatly improves tree vigor.
c. Increases vield and size of fruit.
d. Produces increased cover crop growth.
Disadvantages:
a. Complete loss of crop for two years.
b. An expensive operation.
c. New trees quite tborny.
d. If trees are not whitewashed and cuts
coated with water repelling paints the trees will be weak and soon rot away.


fects of crowding and shading found in most Florida groves 15 years old and older.
Advantages:
a. Increased effectiveness of pest control.
b. Decreased damage to trees and equipment.
c. Faster more economical grove operations.
d. Decreased dead wood.
e. Increased "pack-out" of fresh fruit.
f. Better sizes and better color of fruit.
g. More attractive appearance of grove.
Disadvantages:
a. Usually a reduced yield for at least
one ye r .
b. A fairly costly operation (varies; from
712c to 78c per tree)'/
2. Heading back:
We have not observed enough of this
type of pruning in Florida to offer any
comments.
3. ]'binning by tree removal:
As we have pointed out there are now
quite a number of growers who have recently turned to this method of relieving a crowded condition but very few have adequate records (because of length of '/Agricultural Extension Service Circular 115.


cations are made during the drier part of the year.
EXPERIMENTAL METHODS
The experiment to be described was begun in January, 1949, and was terminated with the 1955-56 crop. The trees used were Valencia oranges on sour orange rootstock planted on single beds in 1940, The soil in the experimental area was classified Parkwood loamy fine sand with pH ranging from 6.8 to 8.3 in the surface and with pH values above 6.8 in all depths to 42 inches. The surface samples contained carbonates equivalent to about 14 percent calcium carbonate and organic matter
r
or approximately 3 percent. The soil also contained 12 to 30 percent clay plus silt (particles less than 0.05 mm. in diameter) in various layers, thus being much finer in texture than soils used for citrus in Central Florida. In


HERMAN J. REITZ
Florida Citrus Experiment Station
Lake Alfred

Several years ago, considerable interest was expressed in the relative value of various systems of timing fertilizers, Partly as a result of this interest, several experiments were initiated to resolve this question. Some of the experiments conducted in Central Florida have been reported recently (3, 4). This paper presents the results of an experiment conducted at the Indian River Field Laboratory near Fort Pierce. The results agree with the other Florida data cited above in indicating that time of application of fertilizer is a relatively minor consideration, if the a h pp
Fla. Agri. Expt. Sta. Journal Series No. 546.


TIMING FERTILIZATION OF CITRUS IN

THE INDIAN RIVER AREA






REITZ: TIMING FERTILIZATION


this soil, the trees were known through measurement to have 75 percent of their fine root system in the upper 19 inches from the crown of the bed.
The seven experimental treatments consisted only of variations in the time of application of mixed fertilizers during the year. During each calendar year, every tree in the experiment received the same amount and analysis of fertilizer. The yearly total rates and analysis used were changed several times during the course of the experiment, as shown in Table 1. Rates were increased up to 1953 to achieve a greener, more dense foliage, and increased further after 1953 to achieve greater


Table 1. Amounts and analyses of fertilizer used
In the experiment
Year Analysis(a) Annual Rate,
per tree
Pounds
1949 3-6-8-3-0-1 16
1950 3-6-8-3-0-1 20
1951 4- 6-8-5-0-i 20
1952 5-6-8-5-o-.' 30
1953 6-6-8-5-0-0 30
1954 8-4-10-7-0-0 24
1955 B-4-10-7-0-0 24
(8)s.P205-K2o.Mg04Mo.Cu0 respectively.


yield, as was indicated might he possible by an adjacent experiment involving different rates of fertilization. The changes in analysis were influenced by trends in Central Florida fertilizer practice during the period. The timing treatments were as follows:

Treatment 1:
All fertilizer applied February 15th.
Treatment 2:
One-half total fertilizer applied February 15th and one-half June 15th.
Treatment 3:
All fertilizer applied May 1st.
Treatment 4:
One-half fertilizer applied May 1st and
one-half October 15th.
Trreatmnent 5:
All fertilizer applied October 15th.


Treatment 6:
One-half fertilizer applied June 15th and
one-half applied December 15th.
Treatment 7:
One-third fertilizer applied February 15th,
one-third June 1st, and one-third November
1st.
The schedule was adhered to within practical limits. All the treatments were replicated four times, at first using six trees per plot. Later it became recognized that several of the trees were affected by crinkle scurf and that additional trees were non-typical of the Valencia variety. These trees were then discarded and the results quoted are based upon the typical trees remaining in the plots insofar as this was permitted by the records.
RESULTS
Plot Observations-At the beginning of the experiment in January, 1949, the trees were somewhat small for trees nine years of age and also were showing the symptoms of low fertilization level. In August, 1949, a severe hurricane struck the grove and caused about 90 percent defoliation on all trees and almost complete loss of the fruit crop. Throughout 1950 and 1951, the foliage on all trees was light green and sparse, but this condition improved 'slowly throughout the period and was fairly satisfactory by the end of 1952. Through 1953 to the end of the experiment, all trees had satisfactory foliage conditions except when modified by treatments as noted below.
The most conspicuous changes in tree appearance were brought about by application of all fertilizer in October. In the last four years of the experiment, all trees so treated were notably earlier in blooming and coming into growth in the spring than other trees. The extreme example of this was observed January 7, 1954, when approximately one-third of all trees so treated were in full bloom from leafless inflorescenses while the trees in other treatments were completely without bloom. Twig growth on these trees was also early in development, and the twigs were long and had many leaves per twig. These leaves in most years did not become dark green-as did leaves from other treatments, and in some years the trees became conspicuously nitrogendeficient and sparse of foliage during the post-





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


with the fruit. It was coincidental that the severity of the leaf symptoms observed was greatest in the year that was picked for this study, so the differences found are doubtless greater than would have been found in other years.
The analytical results for nitrogen are presented in Fig. 1. These results correlate with the appearance of the trees. For example, the trees fertilized only in January and those fertilized three times per year maintained a reasonably good green color of leaves and relatively high nitrogen level tbrdughout the entire period. The trees fertilized in October only appeared nitrogen deficient during the months of May, June, and July, and at that time had extremely low levels of nitrogen in the leaves. Also, leaves from trees fertilized in October only increased in nitrogen content and improved in appearance during the summer although no nitrogen bad been applied; after the fall fertilization, the nitrogen content of these leaves greatly increased so that they were equivalent in nitrogen content to those of the January only plots and the plots receiving three applications. The trees fertilized in May only paralleled in nitrogen content the trees fertilized in October only, up to the point when in May the fertilizer was applied. After this application, the leaves increased markedly in nitrogen content but did not reach the level attained by the leaves in the January only or the three application treatments. This parallels the observation that while the trees fertilized in May only bad generally very dark green color, this was due


bloom and early summer season. In late summer, some greening of foliage occurred even before fertilization, presumably due to breakdown of organic matter in the soil. Trees given one-half the fertilizer in May and one-half in October were similarly but less conspicuously affected.
Trees given all fertilizer in May were at the opposite extreme in appearance compared with trees fertilized only in October. These trees bad limited spring growth, in number of twigs or length of twigs, and this spring growth became dark green slowly. The bloom was sometimes very late, not reaching a peak in 1954 until about April 9, and not then being profuse or conspicuous. The general leaf color in the post-bloom period was fairly dark green due to the color of the old leaves and the absence of new flush. In the early suminer period, the characteristic appearance of these trees was dull grayish green, the foliage was thin, and there were numerous dead twigs in the trees. During the late summer and fall the trees were of average foliage appearance, but this was generally the case with nearly all of the trees except possibly those fertifized only in October.
The general appearance of trees in all of the other treatments was not outstanding in any respect and the trees were fairly green throughout the year.
I Tree Size-The circumference of the trunks of the trees in the experiment was measured first in August, 1950, and again in January, 1956. The averages showed that the increase in trunk circumference was smaller for the trees receiving all the fertilizer in October than for any other treatment. However, differences in neither the actual trunk circumferences nor in the increases during the period were large enough to be of statistical significance, indicating that the timing of fertilization bad doubtful effect on tree size.
Leaf Analysis-Leaf samples were taken for mineral analysis on a number of occasions dur-, ing the course of the experiment, beginning in 1952. In one series, samples of leaves from fruit-bearing twigs were collected from four of the treatments at approximately monthly intervals from March, 1953, to May, 1954. This less commonly used type of sample was selected because it was desired to study the nutritional status of leaves most closely associated


Fig. 1. Nitrogen analysis of leaves from fruiting twigs of selected treatments.





REITZ: TIMING FERTILIZATION


to thle appearance of thle 01l1 leaves an(I that the appearance of the spring flush leaves of 1953 remained poor. It is also notable that as the 1954 flush of growth came out on trees fertilized in May only, the new leaves were lowest in nitrogen. It is assumed that data for trees receiving two applications per year would be intermediate between the extremes given here.
Among other major elements, the most conspicuous differences were in potassium and calcium. The treatment receiving all fertilizer in October was conspicuously high in potassium and lowv in calcium throughout the greater part of the year. The May only treatment was just the reverse. Differences in magnesium were erratic and differences in phosphorus were of small magnitude.
As already noted, during 1954 and 1955 there was very little difference in appearance of the trees regardless of treatment and this was reflected in leaf analysis. Table 2 shows


the analysis of spring flush leaves taken from iion-fruiting twigs onl two dates. This type of sample is more nearly the conventional sample taken in studies of leaf analysis. In most cases no significant differences were found. The most notable feature in Table 2 is the difference in analysis between 1954 and 1955. In 1954, leaves generally were low in nitrogen, phosphorus and potassium and high in calcium.
Fruit Qiiality-In each year except 1952-53, at least one sample of fruit was picked for juice analysis. Part of these results are presented in Table 3. Soluble solids in four of the six years for. which records are available were highest for fruit from the trees fertilized only in October; however, the two remaining years, the soluble solids level was lowest. This shift in relative level of soluble solids appeared to be of some consequence as it was supported by a significant interaction between years and treatment when subjected to analysis of va-


Table 2. Analysis of spring flush leaves taken from non-fruiting twigs July 26, 19514, and August 2, 1955 LEAF ANALYSIS

TREATMENT Nitrogen Phosphorus Potassium Calcium Magnesium
______19514 1955__1954 1955__1954_1955_1954_1955_1954 1955


Feb. 2.014 2.59 0.107 0.123 0.71 0.99 7.18 5.77 0.173 0.195
Feb. and June 2.06 2.74 0.103 0.124 0.61 0.95 7.52 5.59 0.151 0.183
May 2.17 2.514 0.109 0.123 0.68 0.89 7.31 5.89 0.176-0.198
May and Oct. 2.17 2.47 0.110 0.122 0.72 0.914 7.21 5.91 0.2142 0.194
Oct. 2.114 2.147 0.116 0.1114 0.73 0.914 6.74 6.02 0.194 0.206
June and Dec. 2.20 2.52 0.111 0.122 0.714 0.82 6.81 6.05 0'.219 0.186
Feb., June and Nov. 2.16 2.52 0.108 0.1214 0.67 0.98 7.02 5.71 0.2414 0.188

Statistical
significance~a) N.S. ** NoS. N.So N.S. N.S. * N.S. *

(a) N.S. - non-significant

* - significant at 5% level
- significant at 1% level
c - analysis run on composite samples only






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Table 3. Summary of fruit characteristics

JUICE ANALYSIS FRUIT SIZE
TREATMENT ____%_ci Ori Diameter, Avg. Wt.
0Brx Acd % Acid mm. grams


Feb.


Feb. and June May

May and Oct. Oct.


11.73 1.06 11.26


11.63


1-*07


11.70 1.03

11.48 1.09

11.63 1.07


June and Dec. 11.63

Feb., June, and Nov. 11.62


1.*06


1.06


Statistical


Significance (a):

Treatnents N.S.

Interaction *


N. S.

N. S.


(a) N.S. -non-significant

* -significant at 5% level

-significant at 1% level

riance by split-plot methods, using treatments as the main plots and years as the sub-plots as suggested by Pearce (2). This would be interpreted to mean that the treatments had a real effect on soluble solids but that the effect varied to some extent depending upon the season. No significant difference was discovered in acidity or ratio of soluble solids to acidity although the trees fertilized entirely or partly in October were among those giving fruit with highest acidity and lowest ratio. juice content was quite uniform and the differences were of no statistical significance in any case. Vitamin C was determined in only three years, but no differences of practical or statistical consequence were found. The interaction noted above for soluble solids ('Brix) was not significant for any ,other juice characteristic.


Fruit Size-One of the more noticeable effects of the treatments was the effect of the October treatment in producing fruit of larger than average size. This effect was noted strongly in the crops picked in 1952, 1954, and 1955. Measurements were taken of this characteristic by two methods, first, as the measured diameter of the fruit on the tree in 1951, 1952, 1954, and 1955, and second, as the average weight of the fruits which were sampled for fruit analysis in 1954, 1955, and 1956. The summary of both weight and diameter measurements is given in Table 3. Size differences were more noticeable in the diameter measurements. These measurements of diameter made in the field were largely done in the early years of the experiment while the weight measurements were done in the last three years of the experiment. Here again it


11.04 11-53

10.72 10-95 11. 05

11.14


70.5$ 71.

71.3 71.6 73.1 71.7 71.0


N. S.

N. S.


N.S.




REITZ: TIMING FERTILIZATION


is noted that the greater effects were obtained in the earlier years of the experiment than in the later ones. The significant interaction of fruit weight with years reflects relatively larger fruit in the October plots in 1954 than in 1955 and 1956.
External Characteristics af the Fruit
Studies were made on color and gra e o fruit, both in the field and to a limited. extent in the Citrus Experiment Station packinghouse at Lake Alfred. It was observed on many occasions that the color of fruit on trees fertilized in October only was outstanding in December and January; however, during February this difference diminished greatly so that when the fruit was mature enough to pick, the advantage had been completely lost. Packinghouse studies confirmed the field observation that little difference existed in the latter part of the season. The loss in the advantage for the October treatment was due to re-greening of fruit in that treatment and to improved color of fruit in other treatments.
When fruit was picked late in the season and judged for fruit color as well as coarseness, and later graded into United States grades, there was no advantage for any treatment over the other in any of these characteristics.
Yield-Yield results are given in Fig. 2. Although there were some obvious differences in average yield, the differences obtained were not statistically significant. Treatments involving application of fertilizer in October were lowest in average yield. The yield figures for these treatments include a great deal of late-bloom fruit which would be of no value for fresh fruit production unless it were handled separately. The yield from trees receiving all fertilizer in May was highest, but this high yield was the result of exceptional yield on two plots of the four replications and somewhat less than average yield on the remaining two. Yields from the other four treatments were intermediate between these extremes.

DiscussION
The results indicate that no large benefit in yield or fruit quality can be obtained under the conditions of this experiment by simply varying the time of application of fertilizers. Some smaller advantages or disadvantages can,


however, be assigned the individual treatments.
Applications made in October (before the end of the rainy season in this area) had several disadvantages. In addition to low yield, the trees bloomed dangerously early, showed nitrogen deficiency severely during post-bloom and early summer periods and set much latebloom fruit. Aside from larger fruit (of doubt20
19
1817
1E. -1951-56
15
LLi 14LLJ
cr 13' F- -1951-55
cr 12.
W
a- 11U)
UJ lox -1951-54
0 9.
M
_J 87
0
F_ 61.


Feb. Feb. May May Oct June Feb.
June Oct. Dec. June
Nov.
TREATMENT
Fig. 2 Accumulative yield by years during the last six years of the experiment. ful value for this variety), such treatments had no advantages.
Single annual application of fertilizer in May produced greatest average yield, but the result lacked statistical significance. The treatment bad nothing else to recommend it, and the tree condition in the post-bloom period would not be satisfactory to many growers.
The remaining four treatments prevented unfavorable tree condition and were satisfactory in all respects. Three applications per year bad no advantages over treatments using fewer applications, and hence cannot be recom-





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


in Central Florida (3, 4) have Hot shown is much difference as had previously been anticipated and it is probable that the effects spoken of above could be obtained only in the least fertile and coarsest textured soils.

SUMMARY
A fertilizer Aiming experiment using Valencia trees on sour orange rootstock planted on calcareous hammock soil was conducted over a seven-year period. The seven treatments involved one, two, or three applications per year, using a constant total amount of mixed fertilizer annually on all plots. Results indicate that applications made before the end of the rainy season (prior to November Ist) are undesirable; that three applications per year are unnecessarily expensive; and that satisfactory results can be obtained by using two applications, one after the end of the fall rainy season and a second before the beginning of the summer rainy season, or by a single application made in winter,
LITERATURE CITED
1. Martin, W. E. 1942. Physiological studies of yield, quality and maturity of Marsh grapefruit in Arizona. Ariz. Agr. Expt. Sta. Tech. Bul. 97.
2. Pearce C. 1953. Fruit experimentation with
ti trees an other perennial plants. Tech. Communication No. 23, Commonwealth Bureau of Horticulture and Plantation Crops, East Mulling, England. Section 25, p. 14.
3. Reuther, Walter, and Paul F. Smith. 1954. Eff ct of method of timing nitrogen fertilization on yield and quality of oranges. Proc. Fla. State Hort. Soc. 67: 20-26.
4. Sites, John W., I. W. Wander, and E. J. Des. zyck. 1953. The effect of fertilizer timing and rate of' application on fruit quality and production of Hamlin oranges. Proc. Fla. State Hort. Soc. 66:54-62.


mended. When all fertilizer was applied in February, quite satisfactory results were obtained and might be recommended. By comparison, February and June applications or December and June applications would perbaps reduce leaching loss if exceptional rainfall occurred after the single annual application and would reduce the hazard of excessive salt concentration if high rates of fertilization were used. Neither of these conditions was important in the experiment,
Similar conclusions might not be drawn if early orange varieties or grapefruit had been used in the experiment. The earlier coloring of the fruit, the larger fruit size, and the higher soluble solids frequently occurring in the treatments receiving October applications might be sufficient to justify their use for these varieties. Such comments are, of course, speculative in relation to the data presented here.
It is probable that fertilizer rate played an important role in the results. In later years, with higher rates, results were less pronounced than in earlier years with lower rates. Evidently striking results from timing experiments must depend upon attaining nutritional extremes at some period of the year (1). At high fertilizer rates, such extremes cannot be produced under the soil conditions existing in this experiment. Under other soil conditions, where less clay and organic matter is found in the soil, nutritional extremes may occur much more readily than was the case in this experiment. However, experiments performed





KNORR AND PRICE: GRAPEFRUIT STEM PITTING IS STEM PITTING OF GRAPEFRUIT A THREAT TO THE FLORIDA GROWER?


L. C. KNORR AND W. C. PRICE
Florida Citrus Experiment Station
Lake Alfred
Before attempting to answer the question raised in the title to this paper, it is necessary to consider two subsidiary questions. The first of these is this: What is stem pitting?
The term "stem pitting" was first used by Oberholzer, Mathews, and Stiemnie (16) in South Africa to designate a specific disease of grapefruit trees on rough lemon rootstock. Subsequently, the term came also to be used in a different sense: to designate a symptom, or set of symptoms, occurring in the wood of various kinds of citrus trees when infected with, or presumed to be infected with, one or another virus. This double usage has resulted in a certain amount of confusion.
The term stem pitting has been applied by others to the pitting that occurs under the bark of Key lime seedlings serving as indicator plants for tristeza virus (3). It has also been applied (1) to various types of pitting present in many varieties of citrus-for example, to the pitting in such varieties as trifoliate orange and sour orange, which varieties are found (5) to be free of pitting in Argentina where the stem-pitting disease abounds.
We are concerned with the disease of grapefruit known as stem pitting. According to Oberholzer, Mathews, and Stiemie (16), stem pitting is characterized by corrugations or longitudinal pits on the outer surfaces of trunks of affected trees; trees showing stem pitting of the trunk become stunted and bushy, giving rise to the name stunt bush; their foliage is sparse, small, mottled, and chlorotic; and their fruit are small with thick rind, high acid content, and low juice content. In severely affected trees, scaff I.old branches tend to grow downward at sharp angles, crowns are flat, and the rough-lemon rootstock suckers profusely.
According to McClean (12, 13), the symptoms described by Oberholzer et al. are secondFlorida Agricultural Experiment Stations Journal Series. No. 567.


ary ones that develop as affected trees mature, the important primary symptoms being those that are revealed by stripping off bark from the trunk and large limbs. In the surface of the underlying wood, there is to be found pits, shallowv grooves, or channels with their long axes paralleling the grain of the wood. The channels give the unaffected wood the appearance of ridges resembling loose strands of twine. Channelling is well-defined and characteristically present in the trunk and lower branches but may be lacking in twigs and young branches.
Oberholzer (17) in 1953 estimated that stem pitting had destroyed 40 per cent of the grapefruit groves in South Africa, and Oxenham and Sturgess (19) report that stem pitting, or dimples, of grapefruit, "is the most serious problem affecting the Queensland citrus industry," with most plantings becoming unproductive by the 15th year. This terrible destruction results apparently from injury to phloemn and xylem tissues in the scaffold of the tree, thus rendering tissues incapable of supplying either tops or roots with the water and food needed for growth and fruiting.
Oherhoizer, Mathews, and Stiemie (16) showed that stem-pitting disease is perpetuated by vegetative propagation and discovered that some sources of budwood carry a milder form of the disease than others. McClean (12, 13) proved the disease to be infectious and to be capable of transmission by grafting or by means of the brown citrus aphid', Toxoptera Icitricidus (Kirk.) (syn. Aphis citricidus Kirk.). He considered stem pitting to be caused by a virus that is widespread in citrus in South Africa, and he also reported that at least two

I/At this point it might Prove helpful to point out that a certain amount of confusion has arisen with respect to common names for Toxoptera (Aphis) citricidus (Kirk.), the highly efficient vector of tristeza in South America, South Africa, and Australia, and Toxoptera aurantii (Funsc.), the markedly inefficient vector that is present in Florida. In the American literature the common name f or T. citricidus is the brown citrus aphid, and for T. aurantii. the black citrus aphid (cf. "Common names of insects approved by the Entomological Society of America," Bul. Ent. Soc. of America 1 (4) : 1-14. 1955). In the literature of certain other countries however, the order is reversed: it is T. citricidus that is called the black citrus aphid (cf. "Common names of insects," Commonwealth Sci. & Ind. Res. Org. Australia. Ilul. 276, lip. 1956). and T. toxoptera the brown citrus aphid.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


strains of the virus exist. Bothi strains induce veinal flecking in West Indian (Key) lime seedlings and both stunt such seedlings rather severely, one more so than the other.
The second subsidiary question that must be considered is this: What is the relationship between stem pitting and tristeza? This is certainly not an easy question to answer, as will presently become evident. On the one hand, there are reasons for believing that these two diseases are caused by the same virus. McClean (18) has pointed out that the causal agents of both diseases are transmitted by Toxoptera citricidus and that both diseases are universal in South Africa. He thinks that it would be strange indeed for two distinct viruses to be transmitted by the same insect and also to be ubiquitous in the same crop. It is certainly tempting to regard the two diseases as specific host responses to the same virus but there may be good reasons for resisting such temptation.
Costa, Grant, and Moreira (8) suggested that stem pitting might be caused by the same virus as that which causes tristeza, or by a closely related virus, and McClean (18) concurred in this opinion. The virus responsible for stem pitting in South Africa is also believed to cause a die-back of lime in the Gold Coast, where at least two strains of the virus are reported to exist (8, 9), and to cause in South Africa (13) a severe decline of Tahiti lime on the tristeza-tolerant sweet-orange rootstock. Stem pitting has been reported to occur in Argentina (11), apparently having been introduced there simultaneously with tristeza. It is also known in the Belgian Congo (20).
McClean and van der Plank (14) postulated that the tristeza-virus complex has two components, a stem-pitting component and a seedling-yellows component. They postulate further that the stem-pitting disease is induced in grapefruit by the stem-pitting component whether the seedling-yellows component is present or not. It is not clear from the paper by McClean and van der Plank whether stempitting virus alone can cause decline of sweet orange on sour-orange rootstock or whether the seedling-yellows component must also be present. However, sour orange is thought to be more tolerant of stem-pitting virus alone than of the stem-pitting seedling-yel lows com-


Another reason for considering that tristeza and stem-pitting viruses are not identical is this: although tristeza virus is supposed to be universal in citrus of South Africa, many 25year-old grapefruit trees there do not have the stem-pitting disease (15). This could be interpreted to mean 1) that tristeza virus is different from stem-pitting virus despite being closely associated with it in nature, or 2) that some strains of tristeza virus are so mild that they do not cause stem pitting.
Stem-pitting disease of grapefruit does not occur in Florida, nor, to our knowledge, does it occur elsewhere in the United States. Tristeza is in Florida (7), however, and is reported to be spreading in some areas, such as Lake and Orange Counties (2). We know of a few grapefruit trees in Florida infected with tristeza virus that display a pitting of twigs and small branches comparable to the pitting that frequently develops in Key lime seedlings when infected by tristeza virus; these grapefruit trees, however, do not have the striations and channeling of wood of the trunk or large limbs, symptoms said by Oberholzer et al. to be the characteristic manifestations of stem - pitting disease; neither do these trees show any indications of decline nor deviations from normal fruiting. In Florida, we have examined a large number of grapefruit trees, many of which have been demonstrated to be carrying the virus of tristeza, but in none of these trees have we found the stem-pitting disease. Because of these observations, it seems safe to conclude that at present stem pitting occurs rarely, if at all, in Florida.
The virus, or virus complex, that causes seedling-yellows disease of grapefruit, sour orange, and Eureka lemon seedlings in Australia and South Africa also does not occur in Florida. When Florida tristeza virus is transmitted to these three species by budding from infected sweet-orange trees, it does not produce seedling yellows in them.
This certainly seems to be a paradox: although tristeza is not uncommon in Florida, neither the seedling-yellows component nor the stem-pitting component of the complex appears to occur here! How can this be explained?
One possible explanation is to assume that the seedling-yellows component is present in





KNORR AND PRICE: GRAPEFRUIT STEM PITTING


Florida but that bv itself it cannot produce seedling yellows, that seedling yellows develops only when the stem-pitting component is also present. If this is assumed, then it needs further to be assumed that only the seedlingyellows component of the complex, not the stem-pitting component, is present in Florida and that seedling-yellow virus by itself causes the mild form of tristeza to be found here. Although we do not have the experimental evidence necessary to rule out this possibility, wve prefer a simpler hypothesis.
Our hypothesis is that tristeza, stem pitting, seedling yellows, and the Cold Coast's lime die-back are cause 'd by a single virus that exists in the form of numerous strains. [It seems likely that this is about what Costa, Grant, and Moreira (3) had in mind when they suggested that tristeza and stem pitting are caused by the same virus.) It may further be supposed that naturally-infected trees can harbor two or more strains simultaneously and that one or another of these strains predominate, depending upon the species or variety of citrus in which they occur. The strain of virus predominating in sweet orange of South Africa is usually, though not always, one that will induce seedling yellows in grapefruit, Eureka lemon, and sour orange seedlings. We can designate it as the seedling-yellows strain. It apparently is not well adapted to the grapefruit. Consequently, when a mixture of strains is transmitted by Toxoptera citricidus from naturally-infected sweet orange to grapefruit, another strain better adapted to the grapefruit soon predominates; this may be a strain that causes stem pitting or another that is considerably less severe than the stem-pitting strain. Even when transmission is by grafting and when seedling yellows develops, the grapefruit tends to lose the component that causes seedling yellows while retaining the component that causes stem pitting (15); this observation can better be explained by assuming the stempitting and seedling-yellowvs components to be strains of the same virus than by assuming them to be distinct and separate entities.
It is -not necessary tq assume that strains of tristeza virus exist; their existence has been demonstrated in South America (4) and in the United States (18). It is necessary to assume only that the strains of tristeza virus commonly found in the United States cause


neither seed ling-yel lows disease nor stempitting disease.
Although there is no substantial body of experimental evidence on which to base a judgment of the validity of the hypothesis that tristeza seedling yellows, and stem pitting involve not a complex of viruses but a group of closely related strains, an experimental check of the hypothesis can readily be made in Australia or South Africa, where presence of a seedlingyellows factor is said to occur. Evidence is now available for the statement that a mild strain of tristeza virus will protect citrus from more severe forms of the virus (4, 6, 18). Consequently, a grapefruit seedling invaded by the stem-pitting component of the tristeza virus complex should be refractory to infection by the seedling-yellows component, whether introduced by means of grafting or by Toxoptera citricidus, if the twvo components are closely related strains but not if they are separate and distinct viruses. So far as we can learn from the literature, this test has not been made.
Let us now return to the main question of this paper: is stem pitting a threat to the Florida grower? We believe that it is a threat, but one that should not be taken too seriously so long as an efficient vector of tristeza like Toxoptera citricidtts is kept out of the state. If stem-pitting virus is a strain of tristeza virus, the possibility that it will arise by mutation of the mild strains of tristeza virus present in Florida is a virtual certainty. If an efficient vector of the virus, such as Toxoptera citricidiis, should feed on the tree in which the mutant arises, there will be a good possibility of spreading the virus to healthy trees in the neighborhood. In the absence of such a vector, the possibility of spread is very small indeed. Tristeza has been present in Florida for a good many years (10) and it is likely that the strains of virus in existence here are well adapted to the crop; they are more or less in equilibrium with the crop. This equilibrium is not likely to be upset except by some radical change, such as appearance of an efficient vector.
If stem pitting is caused by a separate and distinct virus that does not now exist in Florida, it should by all means be prevented from entering here. Quarantine measures -against importation of budwood is the most practical means by which to exclude it.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


REFERENCES TO THE LITERATURE
1. Bitters, W. P. N. W. Dukeshire, and J. A. Brusca. 1953. Stem pitting and quick decline symptoms as related to rootstock combination. California Citrog. 38: 154, 170-171.
2. Cohen. M. 1956. Injury and loss of citrus trees due to tristeza disease in an Orange County grove. Florida State fort. Soc. Proc. 69: 19-24.
3. Costa, A. S., T. J. Grant, and S. Moreira. 1950. Relatives of tristeza. A possible relation between tristeza and the stem-pitting disease of grapefruit in Africa. Citrus Leaves 30 (2) : 12-13, 35, 38.
4. Costa, A. S., T. J. Grant, and S. Moreira. 1954. Behavior of various citrus rootstock-scion combinations following inoculation with mild and severe 'strains of tristeza virus. Florida State Hort. Soc. Proc. 67: 26-30.
5. DuCharme, E. P., and L. C. Knorr. 1954. Vascular pits and pegs associated with diseases in citrus. U. S. Dept. Agr. P1. Dis. Reptr. 38: 127-142.
6. Grant, T. J., and A. S. Costa. 1951. A mild strain of the tristeza virus of citrus. Phytopathology 41: 114-122.
7. Grant, T. J., and H. Schneider. 1953. Initial evidence of the presence of tristeza, or quick decline, of citrus in Florida. Phytopathology 43: 51-52.
8. Hughes, W. A., and C. A. Lister. 1949. Lime disease in the Gold Coast. Nature 164: 880.
9. Hughes, W. A., and C. A. Lister. 1953. Lime dieback in the Gold Coast, a virus disease of the lime, Citrus aurantifolia (Christmann) Swingle. Jour. Short. Sci. 28: 131-140.


10. Knorr, L. C. 1956.' Suseepts, indicators, and filters of tristeza virus, and some differences between tristeza in Argentina and in Florida. Phytopathology 46: 557-560.
11. Knorr, L. C., E. P. DuCharme, and A. Banfi. 1951. The occurrence and effects of "stem pitting" in Argentine grapefruit groves. Citrus Mag. 14 (2): 32-36.
12. McClean, A. P. D. 1950. Possible identity of three citrus diseases. Nature 165: 767-768.
13. McClean, A. P. D. 1950. Virus infections of citrus in South Africa. III. Stem-pitting disease of grapefruit. Farming in So. Africa 25: 289-296.
14. McClean, A. ,P. D., and J. E. van der Plank. 1955. The role of seedling yellows and stem pitting in tristeza of citrus. Phytopathology 45: 222-224.
15. McClean. A. P. D. 1956. Tristeza and stempitting diseases of citrus in South Africa. FAO P1. Prot. Bul. 4: 88-94.
16. Oberholzer, P. C. J., I. Mathews, and S. F. Stiemie. 1949. The decline of grapefruit trees in South Africa. A preliminary report on so-called "stem pitting." Union So. Africa Dept. Agr. Sci. Bul. 297. 18p.
17. Oberholzer, P. C. J. 1953. Degeneration of our citrus clones. Farming in So. Africa 28: 173-174.
18. Olson, E. 0. 1956. Mild and severe strains of tristeza virus in Texas citrus. Phytopathology 46: 336-341.
19. Oxenham, B. L., and 0. W. Sturgess. 1953. Citrus virus diseases in Queensland. Queensland Dept. Agr. and Stocks. Pamphlet 154. 8p.
20. Steyaert, R. L., and R. Vanlaere. 1952. La "Cannelure" ou "Stem-Pitting" du Pamplemoussier au Congo Beige. Bul. Agr. du Congo Beige 43: 447454.


SEASONAL CHANGES IN THE JUICE CONTENT


OF PINK AND RED GRAPEFRUIT DURING 1955256


E. J. DESZYCK AND S. V. TING

Florida Citrus Experiment Station

Lake Alfred


Pink and red grapefruit in the early season does not always meet the minimum juice requirements as established by the Florida State maturity laws (3, 4). Because of the low juice content, harvest of these two varieties is often delayed, especially since the adoption of higher juice standards; these being raised approximately 10 percent during August 1 to October 15, and approximately 5 percent during October 16 to November 15. For the remainder of the season, the lower juice requirements defined by the Citrus Code of 1949 remain in effect. The relatively high juice required in the early season delays harvest of much of the pink and red grapefruit until the period of low


'/Cooperative publication by the Florida Citrus Experiment Station and the Florida Citrus Commission. Florida Agricultural Experiment Station Journal Series No. 565.


juice standards of November 16 to July 31 during each season.

Several factors influence juiciness of citrus fruit. Generally, juice content varies markedly with and during seasons; it is relatively low in the immature fruit and high in the fully ripened fruit late in the season. High rainfall and irrigation tend to raise juice volume, such factors accounting for variations from year to year. Still other factors are: location, variety, rootstock, age of trees, time of bloom, shape of fruit, and certain cultural deficiencies. Oil
(7) or arsenic (1, 2) sprays have not been found to affect significantly the amount of juice in the fruit.

The Florida Citrus Commission has been conducting a four-year survey of red and pink grapefruit to obtain a better understanding of the internal quality and maturity chacacteristics of these varieties. When the survey was begun in the fall of 1953, the soluble solids content in much of the fruit did not meet standards; however, since the juice re-





DESZYCK AND TING: SEASONAL CHANGES


SAMPLING PERIOD
Fig. 1. Seasonal changes in the average juice content of pink (P.S.) and red (R.R.) grapefruit of three sizes (96, 70, 54) grown on sour orange (S.O.) and rough lemon (R.L.) rootstocks during 1955-56.

quirements were raised in 1955, juice content became the limiting factor in maturity. Therefore, a study of juiciness was included during the 1955-56 season.
A preliminary report is here presented for the purpose of ascertaining the juice content of pink and red grapefruit of three sizes grown throughout the State during the 195556 season. Special emphasis was placed on its relationship to legal juice requirements. In addition to seasonal changes in juice content, the variations among samples during each sampling period as well as the daily increases in the juice are included.

ExPE11IMENTAL
For this survey, 137 groves were selected throughout the citrus area of Florida, including the Ridge section, and the East and West coasts. Of the total number, 68 groves were Ruby red and 41 pink seedless on rough lemon, and 20 groves were red and 8 pink on sour orange rootstock, Fruit sampling was similar to that used commercially; that is, each sam-


pie consisted of six fruit of one size picked from different trees. Three sizes (96, 70, and 54) were collected from tagged trees at intervals of 14-16 days during the 1955-56 season, extending from September to March. juice was expressed at the rate of 40 fruit per minute using a Food Machinery In-Line extractor (5) with a flush setting, 312 inch orifice tube, strainer tube of 3/32 inch openings, and a cup of six inches in diameter. The juice was then passed through a Chisholm-Ryder finisher of the tapered screw type equipped with 0.033 inch perforated screen, weighed and expressed as milliliters in each sample of six fruit. In compiling the data the average juice volume for each period of 14-16 days was used.





SqA7


---.








5.03 0.23 3,23 0.oOS 0 2 To~ U3 3
SAMPLING PERIOD
Fig. 2. Seasonal changes in the average juice content of two varieties of fruit of three sizes grown on two rootstocks during 1955-56,











































Juice Requirements Sampling Period
September October November December
.15-30 1-15 16-31 1-15 16-30 1-15 16-30

ml/6 fruit Perce
1110 (a)
and
above 7.7 32.1 46.5 ?6.8 85.0 81.1 96.3
1080 (b)
above 12.8 41.9 63.2. 84.5 85.0 86.9 97.3
1020 (c)
and
above 31.7 69.5 81.3 93.6 95.0 90.8 100.0
Below
1020 68.2 30.4 18.7 6.4 5.0 9.2 _O(a) Minimum Juice requirement for Aug. I - Oct. 15
(b) MiMm Juice requirement for Oct. 16-Nov. 15
(c) Minimum juice requirement for Nov. 16-July 31.


FLORIDA STATE HORTICULTURAL SOCIETY, 1956


to March. However, it is similar in the two varieties during the early season from September to January. On the average for-the season Ruby red fruit contains more juice than the pink variety.
The percentages of samples of size . 96 grapefruit meeting the legal juice requirements through December are listed in Table 1. Very little fruit can be picked under the 1955 juice standards, since only 7.7 percent of the samples attained sufficient juice (1110 ml.) at that time. During October I to 15, 32.1 percent of the fruit met the strict regulations. When the requirement is lowered to 1080 ml. during October 16 to November 15, 63.2 percent of the fruit met the standard during the first part of this period, and 84.5 percent during the latter part. Although the lower standard is restrictive, the majority of the samples acquired adequate juice. After November 15 when the requirement is lowered to 1020 ml. most of the fruit had enough juice for harvest. The size of the fruit appears to have no influence- on the time of attainment of the high juice standards effective through October 15 since approximately one-third of the samples of each size met the standards during the period.


RESULTS AND DiSCUSSION
In general the average juice content of pink and red grapefruit of three sizes on rough lemon and sour orange rootstocks gradually increased with the advance of the season ' with some exceptions (Fig. 1). Some irregularities were apparent for size 54 fruit on sour orange rootstock. In addition the juice volumes in the fruit of the three sizes decreased slightly during January and February (Fig. 2-A).

Rootstock apparently does not influence juice content in white varieties of grapefruit
(6). However in the pink and red varieties, significantly more juice is found in fruit grown on sour orange than on rough lemon rootstock during the latter part of the season (Fig. 2-11). This variation was first apparent in December for size 54 fruit, and during March for size 96. On the average for the season more juice was found in fruit on sour orange than on rough lemon rootstock.

The seasonal trends in the juice of two varieties and three sizes are shown in Fig. 2-C. The red variety contains significantly higher juice content than the pink grapefruit during the latter part of the season, January


Table 1. Percentage of grapefruit samples picked throughout the State attaining
juice standards from September to December, 1955 (size 96)





DESZYCK AND TING: SEASONAL CHANGES


Table 2. The average juice content and standard deviation for
grapefruit of size 70 for 13 sampling periods during
1955-56.


Sampling Period Jnuice Standard
(s1/6 frui t) Deviation

Sept. 15-30 1171 - 122.2
Oct. 1-15 1332 125.5
Oct. 16-31 1392 1.26.7
Nov. 1-15 1465 122.7
Nov. 16-31 .1495 114.7
Dec. 1-15 154 126.2
Dec. 16-31 1571 125.7
Jan. 1-15 1590 108.2
Jan. 16-31 1603 139.7
Feb. 1-15 1568 104.7
Feb. 16-29 1585 103.0
March 1-15 1604 109.7
March 16-31 160 110.7



The average juice content and the standard deviations for size 70 fruit for 13 sampling periods are shown in Table 2. The standard deviations are generally higher during the earlier part of the season than during the latter part with some exceptions. The average juice and the standard deviation can be helpful in ascertaining the range distribution about the mean, especially if used in the early season. For example, during September, the average juice content for size 70 fruit was 1171 ml. with a standard deviation of 122.2 ml]. Of the samples tested, approximately one-third fell between 1171-1293 ml., and one-sixth fell above 1293 ml. It is evident that with the juice requirement of 1380 ml., less than onesixth of the samples met this high requirement, and therefore fruit cannot be picked because of low juice volume.

The daily average increases in juice volume for one fruit of each size during sampling periods from October through December, are shown in Table 3. Large daily increases for all three sizes occurred during the October 8 sampling period, wvithi smaller amounts during the remaining periods. With sizes, the highest daily increase in juice was found for size 54, and the lowest for size 96. On the average the


juice increased by 0.6, 0.7, and 0.9 ml for sizes 96, 70, and 54, respectively. An estimate of the time of meeting juice regulations can be madle ly knowing the average daily increase in the juice. Of course, these values will vary with location, seasons, and other factors but can be useful as a guide to the time of barv esting.

SUMMARY AND CONCLUSIONS
A preliminary report of the juice content of seedless pink and red grapefruit of sizes 96, 70, and 54 grown on rough lemon or sour orange rootstocks is presented. The samples were collected twice monthly from 137 groves during the 1955-56 season. In general, the juice content increased with the advance of the season, increasing approximately one-third from September to March. In the latter part of the season, the red fruit contained more juice than the pink variety. Likewise, fruit on sour orange rootstock contained more juice than that grown on rough lemon. On the average, the red grapefruit on sour orange had th~e most juice while the pink variety on rough lemon had the least amount.
As far as meeting the high juice standards in effect from August 1 to October 15, approximately 8 percent of the fruit in September and 32 percent in October met the strict juice regulations. At the time of the medium juice requirements from October 16 to November 15, approximately 68 and 85 percent met


Table 3. Average daily increase in juice content per fruit
of grapefruit of three sizes (96, 70, and 54)
during October to December 1955.

Sampling Period Size
96 70 54 7
uI/fruit/day
Oct. 1-15 1.1 1.7 2.1
Oct. 16-31 0.5 0.5 0.8
Nov. 1-15 0.9 1.0 0.8
Nov. 16-30 0.1 0.3 0.4
Dec. 1-15 0.4 0.5 0.8
Dec. 16-31 0.4 0.2 0.4

Average 0.6 0.7 0.9







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


regulations in October and November, respectively. After November 15, most of the fruit met the low juice standards then in effect.
The variations in the juice content for each sampling period as well as the daily increases in juice volumes are presented.

LITERATURE CITED
1. Deszyck, E. J. and J. W. Sites. 1954. The effect of lead arsenate sprays on quality and maturity of Ruby red grapefruit. Proc. Fla. State Hort. Soc. 67: 28-42.


2. Deszyck, E. J. and J. W. Sites. 1955. Juice content in early Ruby red grapefruit. Proc. Fla. State Hort. Soc. 68: 47-49.
3. The Florida Citrus Code of 1949. Chapter No. 25149. State of Fla. Dept. Agr. Citrus & Vegetable Inspection Div.
4 General Laws of Florida, 1955. Minimum juice content for grapefruit. Chapter 29760, Senate Bill No. 562.
5. Gerwe, R. D. 1954. Extracting citrus juices. Proc. Fla. State Hort. Soc. 67: 173-176.
6. Harding. P. L. and D. F. Fisher. 1955. Seasonal changes in Florida grapefruit. U. S. Dept. Agr. Tech. Bul. 886.
7. Taylor, 0. C., G. E. Carman, R. M. Burns, P. W. Moore, and E. M. Naeur, 1956. Effect of oil and parathion sprays on orange size and quality. Calif. Citrograph 41: 452-454.


ample, this element is much less available at a soil pH of 6.0 or 7.0 than at more acid soil reactions.
Jones, Gall, and Barnette (6) reported that when zinc compounds are applied to the soil, they react to form three types of compounds:
(a) water soluble zinc compounds, (b) combinations formed by the reaction of soluble zinc compounds and the organic and inorganic colloidal , complex of the soil (replaceable zinc), and (c) combinations insoluble in water and not in combination with the colloidal complex of the soil (not replaceable). They found that when low concentrations of soluble zinc compounds react with the soil, the major portion of the zinc enters into combination with the colloidal complexes and may be replaced by a normal ammonium chloride solution. Under these conditions they found a near equivalence between the replaceable zinc of the soil and calcium removed from the colloidal complex. When high concentrations of soluble zinc compounds react with the soil, they found that the zinc is present not only in water soluble and replaceable forms but also in an insoluble form. They state that organic matter, clay, replaceable bases, carbonates and phosphates influence the fixation of zinc in the soil.
Jamison (4), however, reported little difference in the fixation of zinc in the presence and the absence of superphosphate in the soil. He states that the forces which retain zinc in these soils are far stronger than those holding zinc as phosphates or basic compounds ordinarily considered insoluble.


C. D. LEONARD, IVAN STEWART
AND GEORGE EDWARDS
Florida Citrus Experiment Station
Lake Alfred
Zinc foliage sprays have been used for more than 20 years for the correction and prevention of zinc deficiency or wrenching in Florida citrus groves. Such sprays are reasonably effective in controlling wrenching in most groves even though the zinc sources now used are very slowly absorbed and highly inefficient (7 . Sprays have the additional disadvantage of leaving a residue on the leaves which increases the scale population. Hence there is need for an effective and inexpensive method of supplying zinc to citrus trees by application of a suitable zinc fertilizer to the soil. The studies reported here were carried out in an effort to find such a method.
Soil application of zinc, chiefly as the sulfate, has been far less dependable than foliage sprays as a method of supplying zinc to citrus. Camp (3) reported in 1934 that in some cases no visible result was obtained from soil applications of zinc sulfate, whereas in others application of from 5 to 15 pounds per e
broadcast gave good responses. Even w re soil applications of zinc are effective absorption of zinc and correction of the zinc deficiency leaf pattern are relatively slow. The effectiveness of soil applications of zinc varies greatly with various soil characteristics; for exFlorida Agricultural Experiment Stations Journal Series, No. 559.


EFFECTIVENESS OF DIFFERENT ZINC

FERTILIZERS ON CITRUS





LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


Jamison (5) found that zinc applied as the sulfate leached from the soil faster where larger crystals or lumps were applied than where a fine powder was used. Most of the zinc from the fine source materials remained adsorbed in the surface three inches of soil while much of the zinc from coarse materials had penetrated into the deeper layers of soil or had leached. He attributed this difference to saturation with zinc of small local zones of soil beneath the lumps or large crystals.
Brown (2) mixed zinc sulfate thoroughly at the rate of 100 pounds per acre with five major citrus-producing soils which had been adjusted to pH levels of 4, 5, and 6. At pH's 4 and 5, the zinc content of the leaves of orange and grapefruit seedlings grown in these soils was very high, but in leaves of the plants grown in soil at pH 6 it was much lower. The uptake of zinc at different pH levels varied for the five soils, but with Lakeland soil at pH's 4, 5, and 6 the zinc contents of orange leaves were 202, 317, and 44 ppm, respectively.
LEACHING OF ZINC
The high uptake of zinc by citrus seedlings from different soils at pH 4 and 5 with which zinc sulfate had been mixed, as reported by Brown (2), shows that this material is an excellent source of zinc for citrus when distributed within the rooting zone of the trees. Since most of the zinc from finely-divided zinc sulfate becomes fixed near the soil surface (5), the poor results obtained from soil applications of this material in citrus groves appear to be due to its failure to leach downward into the rooting zone. In an effort to find a method of getting zinc deeper into the soil, two zinc chelates, zinc 1, 2 diaminocyclohexane tetraacetate (ZnDCTA) and the zinc chelate of
Table 1. Effect of soil pH on amount of radioactive
zinc leached through Lakeland soil from t.
zinc chelate.


;H of soil ZnDOTA ZnAlCA
cPm (a) cp

4 901 0
5 3230 0
6 2776 0
7 3153 12

(a) Counts per minute


an aromatic polycarboxylic acid (ZnAPCA) were tagged with radioactive zinc-65 and leached through Lakeland soil adjusted to pH's of 4, 5, 6, and 7. Counts made on the leachates showed that ZnDCTA was very effective in solubilizing zinc, and its effectiveness showed marked increases as the soil pH rose from 4 to 7 (Table 1). ZnAPCA was highly ineffective as a solubilizer for zinc.
Zinc sulfate and several zinc chelates were tagged with zinc-65 and leached through pots of Lakeland soil at pH 5.4. Counts on the leachates indicated that much more zinc in ZnEDTA remained soluble than in zinc sulfate (Table 2). Increasing the amount of
EDTA applied with the same amount of zinc (varying the molecular ratio of zinc to EDTA) increased the amount of zinc leached. Addition of non-ionic or anionic wetting agents also substantially increased the solubility of the zinc in this chelate, but addition of a cationic wetting agent reduced it. Zinc gluconate and zinc naphthenate were relatively ineffective as solubilizers for zinc. Zinc sulfate, with or without a wetting agent, was extremely ineffective in these leaching trials. These results show the great fixing power of the Lakeland soil for zinc.
The distribution of the zinc in the soil was determined by taking three cores of soil from each pot with a special soil sampling tube with

Table 2. Aoumt of radioactive zine fre different
oure. leached through pot. of Lakeland
soil at PH 5.4.

Zinc Soure Other Material CPm (a)
Zn EDTA 214
Zn EDTA 1 . PR-5i 498
Zn WTA 5 g. TR-51 876
0 Cationic wettig egent 81
Anionic vetting agent "6U No-ionic batting agent 687 Zn tarA (1:2) (b) 740
" (1:5) (b) 1621
Zn glucoote 14
Zn Naphthenete 2
Zn sO4l2O I
ZoS4 P2o 3 Sg. FR-51 .

(a) Counts par minute
(b) Molecular ratio of zinc to ETL






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


a narrow slit in the side and making radioactive counts directly on the soil at depths of one to six inches. These counts showed that most of the radioactive zinc applied in the form of zinc sulfate remained in the top few inches of soil, while that applied as ZnEDTA was much more uniformly distributed (Fig. 1). The total of the counts for the six-inch layers sampled was considerably greater for zinc sulfate than for ZnEDTA at pH's of 5 and 6, indicating much greater fixation of zinc from the sulfate. There was little difference in the total counts for these two zinc sources at pH's of 4 and 7. Radioactive counts made on the leaves of citrus seedlings grown in the pots showed a close correlation between the movement of zinc through the soil and the amount of zinc uptake by the plants.
FIELD EXPERIMENTS
Since the pot studies reported above showed considerably more leaching of zinc and greater uptake of zinc by citrus seedlings from chelated zinc than from zinc sulfate, field experiments were carried out in several commercial


Fig. I Residual concentrations a
leaching of ZnEDTA and Zi adjusted to different pH le


I000-


PH 4






Zn SO, ZnEDTA








24624


citrus groves to compare the effectiveness of chelated zinc with zinc sulfate. Two such experiments are reported below.
In December, 1952, a field plot experiment was started in a grove of 8-year-old Pineapple orange trees growing on Lakeland sandy soil with a pH of about 6.0. This grove was sprayed with zinc until 1951. The linear fourtree plots were completely buffered by other trees from adjoining plots, and replicated three times in randomized blocks. Zinc sulfate monohydrate, containing 36 percent zinc, was applied at rates of 100, 164, and 828 grams of zinc per tree per application. Each rate was applied once a year to one series of plots, and three times a year to another series. Three zinc chelates, ZnEDTA (zinc ethylenediamine tetraacetate), ZnHEIDA (zinc hydroxyethyl iminodiacetate), and ZnEDTA-OH (zinc hydroxyethyl ethylenediamine triacetate), were applied once a year at rates of 12.5, 25, 50, and 100 grams of zinc per tree. These chelates were also applied at rates of 12.5 and 25 grams of zinc per tree three times a year until 1955, when the use of ZnHEIDA was disf Zn65 following application and i SO,4 to pots of Lakeland sand


Depth, Inches


11 800N W)
800
C
60


C
0 4000
2OO-




LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


continued. In September, 1955 the 12.5-gram rate for ZnEDTA and ZnEDTA-OH applied three times a year was changed to 50 grams, and the 25-gram rate was changed to 100


grams. All materials were broadcast by hand under the spread of the trees. Leaf samples taken in August, 1955 (1955 summer flush) and in August, 1956 (1956 spring flush and


Table 3. Effect of soil application of zinc compounds on
the zinc content of leaves of Pineapple orange
trees on acid soil.


(b)
Source of Zinc gin. Zn No. prm zinc in leaves
applied , Applications Summer Spring Summer
per tree(a) per year Flush Flush Flush
per apple. 1955 1956 1956
1S4 H20 100 1 33 28 30
164 1 29 28 27
328 1 44 44 35
100 3 35 30 29
164 3 42 42 37
328 3 48 53 42

Zn EDTA 12.5 1 28 21 24
25 1 29 21 21
50 1 33 25 24
100 1 33 26 27
12.5 3 34 31 26
25 333 38 29

Zn HEIDA 12.5 1 29 -
25 1 34 -
50 1 35 -
100 1 37 -
12.5 3 32 -
25 3 33 -

Zn EDTA-OH 12.5 1 32 26 28
25 1 29 25 26
50 1 29 28 24
100 1 32 33 25
12.5 3 31 28 26
25 3 30 29 27

Check None - 31 23 24

(a)All applications broadcast.

(b) 1955 summer flush sampled in August, 1955. 1956 spring flush and sinner
flush sampled in August, 1956.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


summer flush separately) were analyzed for total zinc by the polarographic method of Barrows, Drosdoff, and Gropp (1).
The highest zinc contents were found in the leaves from trees that received the higher amounts of zinc sulfate (Table 3). Zinc sulfate applied three times a year resulted in higher zinc content of the leaves than the same amount of zinc per application applied


once a year. Application of 100 grams of zinc per tree as the sulfate and in the chelate form showed about equal effectiveness in increasing zinc in the leaves. The lower rates of application of the chelates showed little advantage over the untreated checks. These field results do not bear out the increased availability of zinc shown by the chelates in the pot experiment reported above. In the pot experi-


Table 4, Effect of amount and method of application
of' zinc chelates on the zinc content of
Pineapple orange leaves. (a)


. . Tretmnt . . .
Chelate Other Materal Gm. Zn How "1_)
.Applied Applied Spring Sumer
.,.- __ ._ . . Pii tee I Plush Flush

Zn ED_& -328 &2d 26 29
N 5 lb. soda ash 100 Chunks - 25
N 5 N W 328 N - 26
S5" WS 100 - 23
" 5" 328 - 25
3 oz. AP-78 (c) 100 - 25
8oz." " (C) 328 - 23
328 Sme piles 25 30
" 5 lbs soda ash 328 " N 39 25
N 5 " " 100 N N - 26
N 100 * " - 23

Zn EDTA-OH 328 Band 29 25
10 Th l~b soda ash 328 a28 24
-N " - 5 .100 Chunks - 25
" "I 5 U U N 328 - 29
" 5 "W 100 - 25
N 5 Nfl 328 - 28
" N 3 oz. AP-78 (c) 100 N - 23
" " 8 g) I28 " - 28
W- N 328 Piles 23 27
S "' 100 - 30
5 " 5bs soda ash 328 N 32 23
N N of " ]90 0 - 25

Check None 23 25


(aj Each treatment applied one time*
1956 flushes, sampled in August, 1956a
(c) Anionic wetting agent (ntara Chemical Company)*





LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


ment, ZnEDTA was more effective than zinc sulfate in penetration of soluble zinc through the soil and also in bringing about uptake of zinc by citrus seedlings.
A second experiment was started in the fall of 1955 in another part of the same Pineapple orange grove. It consisted of about 70 different zinc treatments, including sprays and soil applications, each applied to tl ree individual trees, Some of these treatments were applied in the spring of 1956. Three methods of soil application were used: (a) broadcast in a band 3 to 4 feet wide, (b) applied in hardened chunks made by mixing the zinc sources with water and drying, and (c) in small piles of loose material distributed around the trees. In some treatments, the zinc sources were mixed with soda ash (NaCO,) to raise the soil pH, wettable sulfur to lower the pH, or with a wetting accent. Zinc sulfate was also applied in mixtures with calcium, chloride. Foliage sprays of zinc sulfate neutralized with hydrated lime were applied for comparison with the soil treatments.
In this experiment two zinc chelates (ZnEDTA and ZnEDTA-OH) were tested at a rate much higher than in the first experiment, but were again found to be relatively ineffective as sources of zinc regardless of the method of application (Table 4). A small increase in zinc in the spring flush leaves was brought about by mixtures of chelated zinc and soda ash applied in small piles, when compared with the cbelates applied alone. However, none of the cbelate treatments brought about any substantial increase in the zinc content of the summer flush leaves, when compared with the untreated checks. These results are in general agreement with those obtained in the first experiment.
Five pounds of zinc sulfate applied broadcast twice a year showed only a small increase in zinc uptake oVer similar application once a year, and the addition of wettable sulfur showed no advantage over zinc sulfate alone (Table 5). When applied in chunks, addition of wettable sulfur gave a small increase over application of zinc sulfate alone.
Zinc sulfate applied as a foliage spray in January, 1956 gave a progressive increase in the zinc content of the 1956 spring flush leaves as the concentration of the spray was increased from three to 12 pounds of zinc sul-


fate per yy) gallons. However, the sprays gave no increase in zinc content of the 1956 summer flush leaves when compared with the untreated checks. This failure of the sprayed zinc to move in substantial amounts into the newer flush tends to explain why such sprays must be repeated everv year or two in most groves.
Application of zinc sulfate to the soil in small piles is comparable to the use of hardened chunks in that both methods give a high concentration of zinc over numerous small local soil zones. The work of Jamison (5) indicates that this should induce greater total movement of zinc down through the soil. In this experiment, application of zinc sulfate in small piles, either alone or with wettable sulfur ' gave slightly lower zinc levels in the leaves than similar amounts applied broadcast or in chunks. However, when five pounds of zinc sulfate was mixed with five pounds of calcium chloride and applied in small piles, it gave a very striking increase in the zinc content of th leaves. The 1956 spring flush leaves contained 170 ppm. of zinc. This is nearly three times as high as that obtained from a foliage spray at 12 pounds of zinc sulfate per 100 gallons, and is four times greater than that obtained from any other soil treatment. The younger 1956 summer flush leaves contained 82 ppm of zinc, which is twice as much as the highest level from any other treatment. Several extra samples of leaves were taken and analyzed to verify these unusually high values. In the spring flush they approach the high leaf zinc levels reported by Brown (2) for citrus seedlings grown in pots of soil in which zinc sulfate had been mixed at the rate of 100 pounds per acre.
It would appear that the high concentration of soluble calcium supplied by the calcium chloride replaced most of the zinc fixed by the soil in exchangeable form, or by saturating the exchange complex with calcium, prevented fixation of zinc in exchangeable form. This would permit more of the zinc to leach downward into the root zone where it could be taken up by the trees,
It was not possible to prepare hardened chunks by mixing zinc sulfate and calcium chloride with water even when cement was added, but satisfactory chunks were made by mixing five pounds each of zinc sulfate, cal-





78 FLORIDA STATE HORTICULTURAL SOCIETY, 1956


eium chloride, and wettable sulfur with water. Application of these chunks, however, showed no advantage over similar chunks containing only zinc sulfate and wettable sulfur, and both of these treatments gave leaf zinc levels


far below those given by the mixture of zinc sulfate and calcium chloride applied in piles. This may be due to the slow breakdown of the chunks, but it may also be due in part to lowering of the soil pH by the sulfur. Various


Table 5. Effect of amount and method of application of
zinc sulfate on the zinc content of Pineapple
orange leaves,


TrrEtnt M (b)
Zinc sulfate Other Material No* of Oneo Zn. How Spring Sumer
Lbs/tree Lb/tree times applied applied Flush Flush
applied per tree I
(a) .

2 1 328 Band - 21
2 2 656 N 32
2 5 W S 1 328 9 26 28
5 1 820 N 38 33
5 2 1640 N 42 35
5 5 W S 1 820 a 32 29
5 5 W S 2 1640 33 33

5 1 820 Chunks - 30
5 2 1640 " - 35
5 5 Ws 1 820 3 38 35
3 5 WS 2 1640 X 40 1
5 5 VS
150 ml Ethomeen T-15(o)l 820 - 30
5 5 WS
5 CaC12 1 820 36 35


5 1 820 Sm. piles 26 28
5 '5 W S 1 820 ' N 31 26
5 5 OaCl 1 820 " " 170 82
311 2l 1 ea(?)21o - Foliage 31 22
6 g. 1 1 - Spray 44 23
12"" 4 " "" 1 - 60 24

(Plots) Check - None - 23 25


(a) Where 2 applications are shown, they were made
one being made in Apr. 1956.
(b) 1956 flushes, sampled August, 1956.


about 6 mos. apart, the second


(c) Cationic vetting agent (Armour Chemical Division, Armour & Co*)





WENZEL AND MOORE: GRAPEFRUIT UTILIZATION


mixtures of zinc sulfate and calcium chloride are being studied further as a possible source of zinc suitable for soil application to citrus trees.
SUMMI ABY
A study was made to compare the effectiveness of soil application of different zinc sources to citrus trees growing on acid soil. Zinc sulfate and chelated forms of zinc were tagged with radioactive zinc-65 and leached through pots of Lakeland soil adjusted to different pH levels to study their leaching properties. Counts made on the leachates indicated that ZnEDTA and ZnDCTA (zinc 1, 2 diaminocyclohexane tetraacetate) were much more effective in carrying zinc through the soil than was zinc sulfate. Virtually none of the zinc sulfate was leached through the pots.
In a field experiment with Pineapple orange trees, zinc sulfate and three zinc chelates were about equal in increasing the zinc content of the leaves when each wvas applied once a year at 100 grams of zinc per tree per application. The highest zinc contents were found in the leaves from trees that received two pounds of zinc sulfate per tree per application.
In a second field experiment, a single application of five pounds zinc sulfate per tree, applied broadcast , in hardened chunks made by mixing it with water, or in small piles scattered around the trees gave a slightly higher zinc content of both spring and summer flush leaves than foliage sprays applied at the rate of three pounds of zinc sulfate per 100 gallons. Foliage sprays at 6 and 12 pounds of zinc sulfate per 100 gallons substantially in-


,creased the zinc content of the spring flush over that obtained with the three-pound rate, but failed to increase the zinc content of the summer flush leaves. A mixture of five pounds zinc sulfate and five pounds calcium chloride, applied in small piles beneath the trees, increased the zinc content of the spring flush leaves to 170 ppm, and that of the younger summer flush leaves to 82 ppm. Both figures are unusually high for mature citrus trees growing in the field.
LITERATURE CITED
1. Barrows, Harold L., Matthew Drosdoff, and Armin H. Gropp. 1956. Rapid Direct Polarographic Determination of Zinc in Plant Ash Solutions. Agricultural and Food Chemistry 4: 850-853.
2. Brown. J. W. 1955. Absorption of Zinc by Citrus from Various Soil Types. Thesis, University of Florida3. Camp, A. F. 1934. Studies on the Effect of Zinc and Other Unusual Mineral Supplements on the Growth of Horticultural Crops. Fla. Agr. Exp. Sta. Annual Report, page 67.
4. Jamison, Vernon C. 1943. The Effect of Phosphates upon the Fixation of Zinc and Copper in Several Florida Soils. Proc. Fla. State Hort. Soc. 56: 26.11.
5. Jamison, Vernon C. 1944. Citrus Nutrition Studies. Fla. Agr. Exp. Station Annual Report. page 192.
6. Jones. H. W., 0. E. Gall. and R. M. Barnette. 5936. The Reaction of Zinc Sulfate with the Soil. Fla. Agr. Exp. Station Dul. 298.
7. Stewart, ivan. C. D. Leonard. and George Edwards. 1955. Factors Influencing the Absorption of Zinc by Citru s. Proc. Fla. State Hort. Soc. 68: 82-88.
ACKNOWLEDGEMENT
The authors express their appreciation to the Minute Maid Corporation and to its representatives for their cooperation and for permitting the use of the grove in which the field experiments reported here were carried out. Appreciation is also expressed to the Dow Chemical Company and to Geigy Agricultural Chemicals for supplying the zinc chelates used.


-INCREASED UTILIZATION OF GRAPEFRUIT

THROUGH IMPROVEMENT IN QUALITY OF PROCESSED PRODUCTS'


F. W. WENZEL AND E, L. MOORE Florida Citrus Experiment Station

Lake Alfred
Increased utilization of grapefruft is needed because the present supply is in excess of de'/Cooperative publication by the Florida CDitrus Experiment Station and Florida Citrus Commission. Florida Agricultural Experiment Station Journal Series No. 564.


mand. The average financial return to grapefruit growers has been small during recent years. During the 1955-56 season 48 percent of the grapefruit crop used was for processed products, such as canned grapefruit juice, canned grapefruit sections, and frozen concentrated grapefruit juice. Obviously, large amounts of these products are being bought by consumers, but improvements in the quality of some of the products packed could and







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


should be made. Better quality in processed grapefruit products should lead to increased demand and subsequently to increased utilization of grapefruit.
This paper will discuss briefly (a) utilization of Florida grapefruit for processed products, (b) factors which affect the quality of processed grapefruit products, and (c) past and current investigations of the Florida Citrus Experiment Station and the Florida Citrus Commission concerning factors upon which the quality of processed grapefruit products depends,

UTILIZATION OF FLORIDA GRAPEFRUIT
There has been a gradual increase in the production of Florida grapefruit from about 18 million boxes for the 1936-37 season to a peak production of about 42 million boxes during the 1953-54 season; for the past twvo seasons approximately 35 and 38 million boxes


have been produced. During the same time production of Florida oranges has increased from 19 million boxes in 1936-37 to over 91 million boxes during the 1955-56 season. It may be seen from the figures in Table 1 that the utilization of grapefruit by the Florida citrus processing industry has gradually increased over the years. For example, about 38 percent of the grapefruit used in the 1936-37 season went into processed products compared to 48 percent during 1955-56. The maximum utilization occurred in 1945-46 when 69 percent was processed. The use of oranges for processing has increased from 3 percent during the 1936-37 season to about 37 percent in 1946-47 and to 71 percent in 1955-56. This, it is evident that currently almost 50 percent of the grapefruit and over 70 percent of the oranges grown in Florida are being used for processed products. This is in marked contrast to the situation in and prior


TAEI
Utilization of Florida Grapefruit - Fresh and Processed 1, 2 Fresh fruit Fruit Fresh and
sales processed processed
Season Processed
Thousands Thousands Thousands % Of total
of bores of boxes of boxes
1936-37 3-1,233 6,759 17,992 37.6

1941-1.2 8,956 10,143 19,099 53.1

1946-47 10,414 15,866 26,280 60.4

1951-52 19,172 13,678 32,850 41.6

1952-53 17,305 25,035 32,340 4.6.5

1953-54 20,451 20,089 .40,54.0 49.6

1954-55 19,26.3 15,660 34,923 44.8

1955-56 19,925 18,661 38,586 48.4
1 Figures above for boxes for 1953-54 and previous seasons from Florida Citrus Fruit1955 Annual ~zSwmr, prepared by Paul E. Simler and J. C. Townsend, Jr., with the
cooperation of Florida Crop and Livestock Reporting Service, Orlando, Florida,
Florida Citrus Cormission, Lakeland, Florida, Florida Department of Agriculture,
Nathan Mayo, Commissioner, and Agricultural Marketing Servioe, U.S. Department of
Agriculture.
2 Figures above for boxes for 1954-55 and 1955-56 from Annual Reports, Citru's and
Vegetable Inspection Division, Florida Department of Agriculture, Winter Haven,
Florida.








TABLE 2
Quantity of Florida Grapefruit Used for Packs of Major Processed Products prior to the 1952-53 Season 1, 2 Processed 1936-37 1941-42 1946-47 1951-52
grapefruit Boxes % Boxes % Boxes % Boxes %
product
Canned juice 3,057,179 51.9 5,683,874 58.0 7,5a4,708 49.0 6,812,089 56.3
Canned blinded juice 90,367 1.3 1,123,932 11.5 4,273,355 27.7 2,736,950 22.7
Canned sections 2,701,714 45.8 2,852,107 29.2 3,453, W 22.4 2,290,301 19.0
Canned citrus salad 49,205 0.8 122,694 1.3 140,357 0.9 238,054 2.0
Totals 5,898,4 5 100.0 9,782,607 100.0 15,452,247 100.0 12,077,394 100.0
Figures above for field boxes furnished by and used through the courtesy of the Florida Canneral
Association, Winter Haven, Florida.
2 Figures above do not include utilization of grapefruit for other processed products, such as processed
grapefruit concentrate.


TABLE 3
Quantity of Florida Grapefruit Used for Peaks of Major Prosessed Products front the 1951-52 Season through the 1955-56 Season lp 2 Processed 1951-52 1952-53 1953-54 1954-55 1955-56
grapefruit Boxes % Boxes % Boxes % Boxes % BOX03 %
product


WENZEL AND MOORE: GRAPEFRUIT UTILIZATION


to 1936, when most of the oranges and grapefruit from Florida were sold as fresh fruit. In view of these facts, it is time that more emphasis be placed by growers and processors on the production and use of citrus fruits having internal quality necessary for the production of processed products of good quality.
The quantity of grapefruit, used for the production of the more important processed grapefruit products is shown in Table 2 for some seasons prior to the 1952-53 season. Statistics presented in Table 3 show that the four products that have been the best outlets
-for grapefruit during the past five seasons have been canned grapefruit juice, canned grapefruit sections, canned blended juice, and frozen grapefruit concentrate. Perhaps it


should be pointed out, since both seedless and seedy grapefruit are produced, that during the 1955-56 season 75 percent of the seedy grapefruit was sent to commercial canneries but the corresponding amount of seedless fruit was 32 percent.
During the last five years utilization of grapefruit (Table 3) for canned juice has varied from less than 7 to more than 11 million boxes, while that for blend has varied only slightly; these two products in 1955-56 provided an outlet for about 11.8 million boxes or 66.4 percent of the total grapefruit used by processors in the major processed products,
Since the 1946-47 season, the pack of canned grapefruit sections and citrus salad


Canned juice


6,812,089 50.6 8,338,569 56.2 11,459,550 58.0 8,226,991 53.8 9,585,095 53.8


Canned blended juice 2,736,950 20.4 2,371,543 16.0 2,797,251 14.1 2,074,358 13.6 2,236,437 12.6
Canned sections 2,290,301 17.1 2,553,104 17.2 3,111,999 15.7 3,367,o6i 22.o 3,179,466 17.8


Canned citrus salad 238,054 1.8


289,489 1.9 379,666 1.9 326,837 2.1 295,622 1.7


Frozen concentrate 1,084,986 8.1 1,159,173 7.8 1,682,141 8.5 1,065,480 7.0 2,128,620 12.0
Frozen blended 268,231 2.0 133,785 0.9 358,429 1.8 224,586 1.5 365,110 2.1
concentrate
Totals .13,430,611 100.0 3.4,845p663 100.0 19t789,056 loo.0 15,285,333 100.0 17,790,350 100.0
Figures above for field boxes furnished by and used through the courtesy of the Florida Canners' Association,
Winter Haven, Florida.
2 Figures above do not include utilization of grapefruit for other processed products, such as processed grapefruit
concentrate, frozen grapefruit sections, chilled grapefruit sections and salad, or chilled grapefruit juice.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


has ranged from approximately 4 to 6 million cases (24/2's). During the 1955-56 season almost 33' million boxes of grapefruit were used for canning about 5,'' million cases of grapefruit sections and salad, which corresponded (Table 3) to 19.5 percent of the total grapefruit used. Through the use of grapefruit of suitable quality and good processing procedures, canned sections of excellent quality may be obtained. Such a product has always met with good consumer acceptance, and it is believed that the increased sale of canned grapefruit sections, both in this country and in foreign countries, would provide a means for the utilization of some of the excess grapefruit now available. Since Florida produces over 70 percent of the world crop of grapefruit, it would seem that the potential possibilities for export of canned grapefruit sections should be very great. It is difficult to understand why in recent years the grapefruit section pack continues to be only approximately double what it was in the 1930-31 season.
The largest production o! frozen concentrated grapefruit juice occurred during the 1955-56 season, when over 2,2' million gallons were produced from about 238 million boxes of fruit. In contrast to this, during the same season over 70 million gallons of frozen concentrated orange juice were produced. Thus, it is evident that the acceptance and use of frozen grapefruit concentrate by consumers has been far below that of frozen orange concentrate. There was a sharp drop in production during the 1950-51 season of frozen grapefruit concentrate to only about 188,000 gallons caused by poor acceptance of the 1.6 million gallons of this product packed in the previous year. The size of the frozen grapefruit concentrate pack has just in recent seasons reached and during 1955-56 exceeded what it was six years ago in its second season.
About 179% million boxes of grapefruit were used in 1955-56, by the processing industry for the production of the major grapefruit products listed in Table 3. Canned grapefruit juice provided an outlet for 53.8 percent of this fruit and 17.8 percent was used for the canning of grapefruit sections. In the production of the canned blended juice and frozen grapefruit concentrate packs, 12.6 and 12.0 percent of fruit were Used, respectively.


Canned citrus salad and frozen concentrated blended juice together accounted for 3.8 percent. The utilization figures given in Tables 2 and 3 are only for the more important products listed and, therefore, are slightly less than the actual total amounts of grapefruit used for processing. Some fruit also was used for products such as concentrated processed grapefruit juice, chilled grapefruit juice, and chilled grapefruit sections and salad. Thus during the 1955-56 season, 544,070 boxes and 262,099 boxes of grapefruit were used for chilled sections and juice, respectively.
QUALITY OF PIROCIESSED GRAPEFRUIT PRODUCTS
The meaning of the term, quality, depends upon both the person using the term and the products to which the term is applied. For example in speaking of fresh grapefruit, growers and shippers place considerable emphasis on the external appearance of fruit, provided it meets maturity standards for internal quality, while processors are chiefly concerned with the internal characteristics of the fruit. Thus, the concentrator is more interested in the total soluble solids in the juice than he is in having fruit free of external blemishes. In packing unsweetened canned grapefruit juice, the use of fruit containing juice of low acidity and high Brix/acid ratio is extremely important, while fruit with a greater acid content, provided that it is not excessive, may be used for the pro. duction of sweetened processed grapefruit products.
The definition of quality for processed citrus products should be based upon the desires and opinions of consumers, because the demand for these products depends to a great extent upon such desires. Of course, the price that consumers have to pay for these products is another factor and perhaps the major one which influences total demand; also, today ease of use or convenience is becoming continually of greater importance to the housewife. Recently, Florida Citrus Mutual has reviewed (22) some of the consumer surveys (5, 7, 24) which have been made during recent years to determine the characteristics of processed grapefruit products which consumers considered to be acceptable and of good quality. The canned grapefruit juices used for one of these surveys (4, 5) were packed in the pilot plant at the Citrus Experiment Station. Other reports on consumer surveys (4, 6) con-









WENZEL AND MOORE: GRAPEFRUIT- UTILIZATION


recently completed has shown that the discoloration or browning of canned grapefruit sections during storage is related to the acidity in the canned product, which is dependent upon the acid content of the grapefruit used. In general, browning occurred during storage more frequently in the canned sections with the greater acidities.
The effect of cultural practices on the quality of canned grapefruit sections has been subject to investigation during the past three seasons. Discussion of the data obtained when canned grapefruit sections were processed commercially from fruit grove plots that were treated with fertilizer containing various amounts of potash has been reported (27). It was found, as is generally known, that the time at which grapefruit are harvested is a factor affecting the quality of canned sections; also that when grapefruit were picked at the same time from trees which had received fertilizer containing 0, 3, and 10 percent potash ., the firmness of the canned sections decreased with increase in the amount of potash. A similar study using arsenated and unarsenated grapefruit will be completed this season.
Research has been done on various problems concerning the production and storage of frozen concentrated grapefruit juice. Data on changes that occur in this product during storage, such as gelation, clarification, sugar hydrate formations and the very slight- loss of ascorbic acid have been published in various articles (2, 8, 13, 14, 15, 18, 25). Thermal stabilization of grapefruit juice for the production of frozen concentrate has been found necessary to prevent the occurrence of gelation and clarification in this product during storage and distribution. Atkins, Rouse and others (1, 2, 3, 19, 20) have reported results obtained from several investigations of this process for the production of frozen grapefruit concentrate of good quality. During storage at 0' F. or lower, undesirable flavors may develop in frozen grapefruit concentrate. Such off-flavors are usually described as being similar to tallow, castor oil, or cardboard. Results of the study since 1953 of this problem were recently reported (17). Oxidative changes are believed to be involved in the development of these off-flavors and it has been found that the maintenance of a sufficiently high peel oil


corned with this problem have also been published. Very briefly and in general, most of the results from these surveys have indicated that most consumers prefer grapefruit products that have a typical grapefruit flavor, are moderately sweet and not excessively bitter. Therefore, these three characteristics may be used as an indication of quality in canned grapefruit juice and other grapefruit products. Characteristics other than these also influence the quality of such products. For example, canned grapefruit sections of good quality should also be firm and uniform in size and appearance; discoloration and undesirable flavors in sections, caused by poor storage conditions, are not desirable. Likewise frozen concentrated grapefruit juice should show no tendency to gelation, should reconstitute easily and ihen be free from indications of separation or clarification.
To improve the quality ot processed citrus products, both growers and processors should consider factual information that has been made available through past research investiaations concerning the factors that affect the quality of these products. They should also be aware of current research projects, the ultimate practical object of -which is the profitable utilization of the entire grapefruit crop either by improvement in the quality of the major processed products that are now packed, thereby causing better acceptance and more demand, or by the development of new processed products or by-products that will provide other outlets for this fruit. Some of these research investigations, that have been completed or are in progress, at the Citrus Experiment Station will be discussed briefly. Principal emphasis concerning processed products has been placed on the factors affecting the quality of canned grapefruit sections, canned grapefruit juice and frozen concentrated grapefruit juice.
An investigation on the effect of storage temperature on quality of canned grapefruit sections was discussed by Huggart, Wenzel and Moore (9). Results indicated that for maintenance of original good quality in canned sections, the products should be held at 70' F. or lower. Marked changes in color, flavor and firmness that result in lower quality in this product occurred at storage temperatures of 80' F. or above. Another study (10)




Full Text

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of the FLORIDA STATI: I-IORTICULTURAL SOCIETY VOLUME 69 Published by the Society

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FLORIDA STATE HORTICULTURAL SOCIETY , 1956 I SIXTY-NINTH ANNUAL MEETING of the FLORIDA STATE I-IORTICUL TURAL SOCIETY held at ORLANDO, FLORIDA November 7, 8 and 9 1956

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II FLORIDA STP.,..TE HORTICULTURAL SOCIETY, 1956 FLORIDA STATE: HORTICULTURAL SOCIETY Executive Committee SECRETARY . Dn . ERNEST L. SPEN CER Bradenton PUBLICATION SECRETARY RALPH P. THOMPSON" Winter Haven 1956 PRESIDENT R. A. CARLTON W e st Palm Beach TREASURER R. R. REED Tampa EDITING SECRETARY W. L. TAIT Wint e r Haven CITRUS C. A. ROOT SECTIONAL VICE-PRESIDENTS VEGETABLES Winter Gard e n KROME MEMORIAL RoY 0. NELSON South Miami . ' ; PROCESSING DR . R. D. GERWE Lakeland M EMBER.S-AT-LARGE L ou is F. RAUTH D e lra y B e ach ORNAMENTAL Dn. T. J. SHEEHAN Gainesville HowARD A. THULLBERY , L a ke \ V al e s Dn . F . S . JAMISON, Gainesvill e F R ANKL. HOLLAND, Wint e r H ave n J. A n THUR LEWIS, Miami E . S. REASONER, Bradenton

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 FLORIDA ST ATE: I-IORTICUL TURAL SOCl~TY Executive Committee 1 9 5 7 SECRETARY Dn . ERNEST L. SPENCER Bradenton P)'lESIDENT ROBERT E. NoRms Tavares PUBLICATION SECRETARY RALPH P. THOMPSON ,vinter Haven TREASURER R. R. REED Tampa EDITING SECRET ARY w. L. TAIT ,vint e r Haven CITRUS SECTIONAL VICE-PRESIDENTS VEGETABLES CHARLES D. KIME, JR . Waverly KROME MEMORIAL DR. PAUL L. HARDING Orlando PROCESSING DR. JAMES M. BONNELL Plant City !\fEMBERS-AT-LARGE NORMAN C. HAYSLIP Ft. Pierce ORNAMENTAL s. A . ROSE Gainesville R. A . CARLTox, \Vest Palm Beach FRED J. WESEMEYEH, Ft. Myers , FRANK L. HOLLAND, Winter Haven Dn. GEORGE D. RUEHLE , Homestead DR. R. D. GEnWE, Lakeland III

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IV FLORIDA STATE HORTICULTURAL SOCIETY, 1956 eonj,titution Article I-NAME-This organization shall be known as the Florida State Horticultural So ciety. Article II-OBJECTIVE-The objective of this Society shall be the advancement and de velopment of horticulture in Florida. Article III-YEAR-Th e year shall begin January 1 and close December 31. Article IV-CLASSIFICATION OF MEM BERSHIP-There shall be three classifications of membership, all of which carry voting privileges: A-Annual B-Sustaining C-Patron Nothing in this article shall be construed as operating against or cancelling the privil eges of Life Members accept ed as Life Members prior to th e adoption of this constitution. Article V-ELIGIBILITY FOR MEMBER SHIP-Any individual, firm or partnership in terested in the development an d advancement of horticulture in Florida shall be eligible for membership. Article VI-DUES-Dues shall be paid an nually according to classification at rate as prescribed in By-laws. Article VII-ANNUAL MEETING The Society shall hold an annual meeting each year in accordanc e with the By-laws unless pre vented from doing so by causes beyond its control. Article VIII SECTIONS The Society shall be divided into sections representing various horticultural interests as provided in the By-laws. Article IX-OFFICERS-The officers shall consist of a President, a Vice President from each section , a Secretary, a Publication Sec retary, an Editing Secretary, and a Tr eas urer, which officers shall be elected by a majority vote of the membership present at the annual meeting and shall assume their respectiv e of fices at th e beginning of the new year . Article X-SUCCESSION-In th e abse nce of th e Pr es ident or his inabilitv to serve tem porarily the Vice President of 'the Citrus See ton shall serve inst ea d. If the po s ition of Presid en t is vacated, the Executiv e Committee shall d es ignate his successor. Article XI-EXECUTIVE COMMITTEE The Executive Committee shall consist of not more th a n 15 persons including the immediate Past Pr es ident and all Officers above named , the others to be e l ec t ed at same tim e and in same manner as prescribed in Article IX. The Pr eside nt shall be c hairman of the Exec utive Committee. Th e Executive Committee shall hav e authority to ac t for the Society be tween annual meeting s . Article XII-MEETINGS OF THE EXEC UTIVE COMMITTEE-The Executive Com mitt ee shall meet upon call of th e Chairman at such time and place as may be approved by a majority of the Committee. A majority of the Committee shall constitute a quorum. The Committee may b e canvassed by mail and vote by ballot in lik e manner. Articl e XIII COMMITTEES Th e Presi dent shall with the approval of the Executive Committee appoint a ll standing or special committees as provid e d in the By-laws . Article XIV-DUTIES OF OFFICERS The Pr eside nt shall be the official head of the Society to preside at a ll Executive Committee meeting s and at th e general session of the annual meeting. H e shall be dir ec tl y respon sibl e to the Executive Committee and may be removed from office for cause by an affirma tive vot e of a majority of the full Executive Committ ee. Th e Vice Presidents shall be membei s of the Executiv e Committee. The Vice President of the Citrus Section shall assume th e duties of the President in the temporary abs ence of the Presid e nt. The Vice Pr esi dents of th e various sections shall preside over the particular sec tions of which the y are representatives at the annual meeting.

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 V The Secretary shall record all records of all meetings of the Executive Committee and shall be responsible except as may otherwise be designated in the By-laws for . recording and keeping proceedings of the annual meeting. He shall likewise issue and mail out statem e nts of dues to the membership, notices of meetings and perform such other
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VI FLORIDA STATE HORTICULTURAL SOCIETY, 1956 the nomination of Vice President for that sec tion. Such nominations by the committee how ever shall not preclude nominations from the floor. Program Committee-The Vice Presidents of the various sections shall constitute a Program Committee of which the President shall be the Chairman and the Secretary and Treasurer shall be ex officio members. Auditing Committee The President with the approval of the Executive Committee shall appoint an auditing committee which commit tee shall confer with the Treasurer in prepar ing an audit to be presented by the Treasurer at the annual meeting. The President shall appoint such other committees as may be deemed advisable and approved by the Exec utive Committee. DEPOSITORY The Executive Committee shall have au thority to select a depository or establish a trusteeship for funds of the Society as it may deem in the best interest of the Society. All Patron Membership dues and all donations, unless otherwise specified by donor, shall be invested by the Treasurer in United states Government bonds. The earnings from these bonds shall be left as accrued values or re invested in the United States Government bbnds unless it is ordered by the Executive Committee of the Society that such earnings can be made available for operating expense. APPROVAL OF BILLS All bills before being paid shall be approved by the President, Secretary or Treasurer, and vouchers drawn to pay such bills shall be signed by the President or in his absence the Vice President of the Citrus Section and coun tersigned by the Treasurer. HONORARY MEMBERS Any individual who has rendered especially meritorious service to the Society and to the advancement of horticulture in Florida may be designated by a two-thirds vote of the full Executive Committee and approved by a ma jority vote of the Society as an Honorary Member of the Society. Such honorary mem bers shall not be required to pay dues. AMENDMENTS These By-laws may be amended at any an nual meeting by an affirmative majority vote of the membership present when such amend ments have been approved and recommended by a majority of the Executive Committee. . These By-laws shall take effect immediately upon adoption by the membership at the an nual meeting in October, 1951.

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 VII of the FLORIDA STATE: 1956 VOLUME LXIX PRINTED 1957 CONTENTS Officers for 1956 ___________________________________________________ . ___ ------------------------------______________________________ II Officers for 1957 ________________________________________________ -------------______________ _______ -------------------------------III Constitution and By-Laws ____________________________________ . __________________ ________________ ______________________ IV President's Annual Address, R. A. Carlton, West Palm Beach_________________________________________________ 1 Plant Research in the Atomic Age, George L. McNew, Boyce Thompson Institute for Plant Research, Inc., Yonkers, N. Y ..... _______________________________________________________ 4 The Mediterranean Fruit Fly Eradication Program in Florida, Ed L. Ayers, Plant Commissioner, State Plant Board of Florida, Gainesville, and G. G. Rohwer, Area Supervisor, U. S. Department of Agriculture, Lake Alfred .. : .. ______ .______________________ 12 A ward of Honorary M em bersh i ps _______________________________________________________________ ---------------,-------------15 CITRUS SECTION Injury and Loss of Citrus Trees Due to Tristeza Disease in an Orange County Grove, Mortimer Cohen, State Plant Board of Florida, Gainesville________________________________________ 19 Effect of Phosphate Fertilization on Root Growth, Soil pH, and Chemical Constituents at Different Depths in an Acid Sandy Florida Citrus Soil, Paul F. Smith, U. S. D. A. Horticultural Statioi1, Orlando ___________________________________________________ c____________ 25 Starting and Maintaining Burrowing Nematode-Infected Citrus Under Greenhouse Conditions, William A. Feder and Julius Feldmesser, U. S. D. A. Horticultural Station; Orlando -------------------------------------------------------------------------------_ ___ _____ .. ___________ 29

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VIII FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Preliminary Investigations on Dieback of Young Transplanted Citrus Trees, Gordon R. Grimm, U. S. D. A. Horticultural Station, Orlando___________________________________________________ 31 The Possibility of Mechanical Transmission of Nematodes in Citms Groves, A. C. Tarjan, Florida Citrus Experiment Station, Lake Alfred____________________________________________ 34 Transmission of Tristeza Virus by Aphids in Florida, Paul A. Norman and Theodore J. Grant, U. S. D. A. Horticultural Station, Orlando________________________________________________ 38 Physiologic Races of the Burrowing Nematode in Relation to Citrus Spreading Decline, E. P. DuCharme, Florida Citrus Experiment Station, Lake Alfred, and W. Birchfield, State Plant Board of Florida, Gainesville,______________________________________ 42 Citrus Rootstock Selections Tolerant to the Burrowing Nematode, Harry W. Ford, Florida Citrus Experiment Station, Lake Alfred __________ --------------------------------------------44 The New 4-H Club Program for Citrus Production Training, Jack T. McCown, Florida Agricultural Ext_ension Service, Gainesville __ ~-------------------------------------------------------52 Field Observations of Several Methods of Managing Closely-Set Citrus Trees, Fred P. Lawrence, Florida Agricultural Extension Service, Gainesville, and Robert E. Norris, Florida Agricultural Extension Service, Tavares.___________________________________ 54 Timing Fertilization of Citrus in the Indian River Area, Herman J. Reitz, Florida Citrus Experiment Station, Lake Alfred __ ----------------------------------------------------------------58 Is Stem Pitting of Grapefruit a Threat to the Florida Grower? L. C. Knorr and W. C. Price, Florida Citrus Experiment Station, Lake Alfred_____________________________________ 65 Seasonal Changes in the Juice Content of Pink and Red Grapefruit During 1955-56, E. J. Deszyck and S. V. Ting, Florida Citrus Experiment Station, Lake Alfred________ 68 Effectiveness of Different Zinc Fertilizers on Citrus, C. D. Leonard, Ivan Stewart and George Edwards, Florida Citrus Experiment Station, Lake Alfred_______________________ 72 Increased Utilization .of Grapefruit Through Improvement in Quality of Processed Products, F. W. Wenzel and E. L. Moore, Florida Citrus Experiment Station, Lake Alfred _____________ -----------------------------------------------------------------------------------------------79 Long Range Relationships Between Weather Factors and Scale Insect Populations, Robert M. Pratt, Florida Citms Experiment Station, Lake Alfred_____________________ 87 Notes on the Use of Systox for Purple Mite Control on Citrus, Roger B. Johnson, Florida Citrus Experiment Station, Lake Alfred __________________ ------------------------------------93 Pr.igress Report on Greasy Spot and Its Control, W. L. Thompson, John R. King and E. J. Deszyck, Florida Citrus Experiment Station, Lake Alfred________________________________ 98 Use of 1, 2-Dibromo-3-Chloropropane on Living Citrus Trees Infected with the Burrowing Nematode, Julius Feldmesser and William A. Feder, U. S. D. A. Horticultural Station, Orlando ________________ . ---------------------------------------__ _____________________ 105

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 PROCESSING SECTION Rapid Determination of Peel Oil in Orange Juice for Infants, R. W. Kilburn and L. W. IX Petros, Florida Citrus Canners Cooperative, Lake \Vales -------------------------------107 Effects of Finisher Pressure on Characteristics of Valencia Orange Concentrate, 0. W. Bissett and M. K. Veldhuis, U. S. Citrus Products Station, Winter Haven _ _____________ _ _ 109 A Study of the Degrees Brix and Brix-Acid Ratios of Grapefruit Utilized by Florida Citrus Processors for, the Seasons 1952-53 Through 1955-56, E. C. Stenstrom and G. F. Westbrook, Citrus and Vegetable Inspection Division, Stat e Department of Agriculture, Winter Haven __ _ _______ ----------------:-------------------_____ __ 113 Diacetyl Production in Orange Juice by Organisms Grown in a Continuous Culture System, Lloyd D. Witter, Metal Division, Research and Development Department, Continental . Can Co., Inc., Chicago , Ill. __ ____ __ _ _ __ _ _____ __________ _ ________ __ _ __ __________ __ _ 120 Standardization of Florida Citrus Products , Arthur R . Pobj e cky, Southern Fruit Distributors, Inc., Orlando . _ __ _ __ _ ______ __ __ _ _ ____ _ __ _ ____ __ _____ __ __ _ _ _ _ _ ____ _ __ ----------------------------------125 Citrus Vitamin P, Boris Sokoldf, Isidor Chainelin, Morton Biskind, William C. Mar tin, Clar _ ence Saelhof, Shiro Kato, Hugo Espinal, Taekyung Kim, Maxwell Simpson , Norman Andr ee and Georg e Renninger , Southern Bio-Research Laboratory, Flodda South e rn College, Lakeland _____ __ ____ __ : _ ___ __ _ _ ____________ _ __ __ ____ __ _ _ _______ ____ 128 Vacuum Cooling of Florida Vegetables, R. K. Showalter and B. D. Thompson,, Florida Agricultural Experim e nt Station, Gainesville -----------------------------------------------~---132 Th e Quality Control of Chilled Orange Juice from the Tree to the Consumer, Leo J. Lister, Halco Products , Inc ., Fairvilla , and Arthur C. Fay , H . P. Hood and Sons, Boston, Mass. ---------------------------------------------------------------------------136 Hydrocooling Cantaloupes, K. E. Ford, Georgia Experiment Station, Experiment, Georgia ------------------------------------------------------------------------------------------138 The Sloughing Disease of Grapefruit, W. Grierson and Roger Patrick , Florida Citrus Experiment Station, Lak e Alfred ___ _ _ _ ___ _ __ ___ _______________ _ _ ___ __ _ __________________________________________ 140 Effect of Variety and Fresh Storage Upon th e Quality of Frozen Sweet Potatoes, Maurice W. Hoover and Victor F. Nettles, Florida Agricultural Experiment Station, Cain esville __ _____ -------------------_ __ _____ __ __ __ ------------------__ _ ___ __________ _____ __ 142 Storage Studi es on 42 Brix Concentrated Orange Juices Processed from Juic es Heated at Varying Folds. II. Chemical Changes with Particular Reference , to Pectin; A. H. Rouse, C. D. Atkins and E. L. Moore, Florida Citrus Experiment Station, Lak e Alfred ----------------------------------------------------------------------------------------------145 Purification of Naringin , R. Hendrickson and J. W. Kesterson, Florida Citrus Experiment Station, Lak e Alfred ________ _____ ___ _ _________ ---------------------------------------149 Sectionizing Marsh Seedless Gr a pefruit, Gray Singleton, Shirriff,Horsey Corporation, Ltd., Phnt City --------------------------------------------------------------------------------------152 An Effective High Pressure Cleaning System for Citrus Concentrating Plants, D. I. Murdock a nd C. H . Brokaw, Minute Maid Corporation, Orlando ____ __ _ _ ___ ____ ________ _ ____ 154

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X FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Some Studies on the Use of Sodium Nitrit e as a Corrosion Inhibitor in the Canning Industry, J. R. Marshall, Tampa Laboratory of Research and Technical Department, American Can Co., Tampa ________ __ __ ______ ___ ----------------------------159 Reducing Losses in Han 1 esting and Handling Tangerines ; W. Grierson, Florida Citrus Experiment Station , Lake Alfred _ __ _ __ _ _ _______________ _ ___ _ _ _ __ ___________ -------------------------165 Quality of Canned Grapefruit Sections from Plots Fertilized with Varying Amounts of Potash, F. W. Wenzel, R. L. Hnggart, E. L. Moore, J. W. Sites, E. J. D e szyck, R. W. Barron, R. W. Olsen, A. H. Rous e and C. D . Atkins, Florida Citrus Experiment Station, Lak e Alfred________ ___ ___ __ __ _ _____ _ __ _ _ ___ __________ _ ___ _ __ _ _______ _ ____ ____ _ _ 170 Storage Studi e s on 42 Brix Concentrated Orange Juices Processed from Juices Heated at Varyirig Folds . I. Physical Changes and Retention of Cloud, E. L. Moore, A. H. Rouse and C. D. Atkins, Florida Citrus Experiment Station, Lake Alfred _ _ ___ _ 176 Effect of Thermal Treatment and Concentration on P e ctinesterase ,' Cloud and Pectin in Citrus Juices Using a Plate Typ e Heat Exchanger, C. D. Atkins, A. H. Rouse and E. L. Moore, Florida Citrus Experiment Station, Lake Alfred _ _ _ _ _ __ __________ __ _ _ __ _ __ __ 181 Distribution and Handling of Frozen Fruits, Vegetables and Juices, George J. Lorant, Birds Eye Laboratories, Albion , New York _ __ _ ___ _ _ __ ______ ___ _____ __ _ ___ _ ___ _ __ __ _________ __ _____ __ _ _ ____ 185 Dried-Citrus-Pulp Insect Problem and Its Possible Solution with Insecticide-Coated Paper Bags, Hamilton Laudani, Dean F. Davis, George R. Swank and A. H. Yeomans, Stored-Products Insects Laboratory, Savannah, Georgia _ ------"~---------'---191 VEGETABLE SECTION Progress Report on Cantaloupe Varieties, B. F. Whitner , Jr. Central Florida Experiment Station, Sanford _______________ ____ ____ . --------------------------------------------------195 Phytotoxicity of Fungicides to Cantaloupes, Robert A. Conover, Sub-Tropical Experim e nt Station, l-fomestead ----------_ _ ____ __ -------------------------------------198 Irrigation of Sebago Potatoes at Hastings, Florida, Donald L. Myhre, Florida Agricultural Experiment Station, Potato Investigations Laboratory, Hastings __________ _ _ ________ 200 Use of Certain Herbicides in Fields of Growing Tomatoes Progress Report, John C. Noonan, Sub-Tropical Experiment Station , Homestead ______ _ ___ _ ________ _ __ _ ______ _ ____ ____ _____ _ 204 Crop Production in Soil Fumigated with Crag Mylone as Affected by Rates, Application Methods and Planting Dates, D. S. Burgis and A. J. Overman, Gulf Coast Experiment Station, Bradenton -------------------------------------------------------207 Breeding Objectives and the Establishment of New Breeding Lines of Southernpeas, A. P. Lorz, Florida Agricultural Experiment Station, Gainesville ___ _ _____________ _ _ __ ___ ---210 Factors Influencing Consumer Preference of Southern Peas ( Cowpeas), Maurice W. Hoover, Florida Agricultural Experiment Station, Gainesville _ __ _ __ __ _________ __ _____ __ _____ _ 213 Outlook for the Production of Southern Field Peas for Freezing , James Montelaro, Minute Maid Corporation, Plymouth _ _ __ _ __ _ _______ _ ________ _ ___ __ __________ _ _ _ _ ______ _ ______________ __ ___ _ _____ 216

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 XI Insect Problems in the Production of Southern Peas ( Cowpeas), John W. '-" 1 ilson, Central Florida Experiment Station, Sanford, and W. G. Genung, Everglades Experiment Station, Belle Glade _-----------------217 Influence of Nitrog en, Phosphorus, Potash and Lime on the Growth and Yield of Strawberri es, R. A. Dennison and C. B. Hall, Florida Agricultural Exp er iment Station, G a inesville .... __ -----..... . ---------------------224 Lim e-In duced l'vianganese Defici e nc y of Strawberries , C. B. Hall and R. A. Dennison, Florida Agricultural Exp e rim e nt Station, Gainesville . . 228 Cucumber Fungicides for th e West Coast of Florida, Grov e r Sowell, Jr., Gulf Coast Experim ent Station, Brad en ton -. ------------------------230 Not es on Current D eve lopments of Gray Mold, Botrytis Cinerea Fr. of Tomato and Its Control, R. S. Cox , Everglades Exp eri ment Station, B e ll e Glade, and N. C. Hayslip, Indian River Field Laboratory, Ft. Pierce __ ----------------235 Evaluation of Control Methods for Blackheart of Celery and Blossom-End Rot of Tomato es, C. M. Geraldson, Gulf Coast Experiment Station, Bradenton .----------236 Control of Dise ases in the Cel ery Seedbed, R. S. Cox, Everglades Experim e nt Station, Bell e Glade 242 The Assay of Streptomycin as it Relates to th e Control of Bacterial Spot, Grover Sowell, Jr. , Gulf Coast Experiment Station, Bradenton .. . . -244 Control of Pole B ean Rust with Maneb-Sulfur Dust , Robert A. Conover, Sub-Tropical Experim en t Station, Homestead 247 Fungicidal, Herbicidal and N ema tocidal Eff ec t s of Fumigants Applied to Vegetable Seedbeds on Sandy Soil, A. J. Overman and D. S. Burgis, Gulf Coast Experi~ ment Station, Bradenton 250 Variety Tests of Commercial Typ es and New Breeding Lines of Southernp ea, L. H. Halsey, Florida Agricultural Experim e nt Station, Gainesville ................ . 255 R esu lts of Differ ent Seeding and Fertilizer R a tes for Potato es at Hastings, E. N. McCubbin, Florida Agricultural Experiment Station, Potato Investigations Laboratory, Hastings ..... _ 259 Production of Spinach for Processing on Muck Soils of Central Florida, M. M . Hooper , Vegetable Grower, Apopka 261 KROME MEMORIAL SECTION Th e Concept, Duti es, an d Op era tions of the Florida Avocado and Lime Commission, C. F. Ivins , Florida Avocado and Lime Commission, Homestead . .. ....... .. ............ ... _ 262 Not es on Tropical Fruits in Central America , Wilson Popenoe, Escuela Agricola Panam er icana , Tegucigalpa, Honduras 267 Marketing of Lim e s and Avocados in Florida , Harold E. Kendall, South Florida Grower s Association, Inc., Goulds ..... ...... . . 270

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XII FLORIDA STATE HORTICULTURAL SOCIETY, 1956 The Sub-Tropical Fruit Program of Dade County, John D. Campbell, County Agricultural Agent, Homestead :--: 272 Some Observations on Lim e and Avocado Grove Cultural and Maintenance Practices in Dade County, Norman E. Sutton, Grove Management, Inc., Goulds ...... . . .. . ------274 Future of Florida Minor Tropical Fruit Industry in Doubt, Nixon Smiley, Miami Herald Farm and Garden Editor and Director, Fairchild Tropical Garden, Miami ........ -.. --275 . Krome Memorial Avocado Variety Committee Report, F. B. Lincoln , Chairman, Homestead --.. --.. .. . .. . . . .. ............... . ....... . ..... .... 27 6 Pollination and Floral Studi es of the Minneola Tangelo, Margaret J. Mustard, S. John Lynch and Roy 0. Nelson, Division of Research and Industry, University of uiami, Coral Gables ... _ ..... ...... .. . ...... -.. .. .. .. 277 Changes In Physical Characters and Chemical Constituents of Haden Mangos During Ripening at 80 F. , Mortimer J. Soule, Jr., and Paul L. Harding, U. S. D. A. Horticultural Station, Orlando . . ........... --282 Further Rooting Trials of Barbados Cherry , Roy 0. Nelson and Seymour Goldweb e r, Division of Research and Industry, University of Miami; Coral Gables .... . .... _ .. .... 285 Research on Sub-Tropical Fruits as a R e sult of Mediterranean Fruit Fly Eradication Program, Geo. D. Ruehle, Suh-Tropical E~periment Station, Homestead ...... .. ...... . 287 Some Effects of Nitrogen , Phosphorus and Potassium Fertilization on the Yield and Tr ee Growth of Av~cados, S. John Lynch and Seymour Goldweber, Division of Research and Industry, Univ e rsity of Miami, Coral Gahles -289 A Comparison of Three Clon es of Barbados Cherry and th e Importance of Improv e d S e lections for Commercial Plantings, R. Bruce Ledin, Sub-Tropical Experiment Station, Homestead . ...... . . ...... . .. .. .. 293 Rare Fruit Council Activiti es , 1956, William F. Whitm an, Salvatore Mauro, Seymour W. Younghans, :Miami Beach . .. ... _ ... .. .. . 297 Some Notes on a We e vil Attacking Mahogany Trees, F. Gray Butcher and Seymour Goldw e ber , Division of Research and Industry , University of Miami, Coral Gables .......... --.. . ....... .... ....... ... .. ..... .. .. . .. .. . . .... ..................... .. 303 Response of Lychees to Girdling, T. W. Young: Sub-Tropical Experiment Station, Hom es tead .. .................... . ... . . ................. .. ............ . . . . ..... ....... --305 Some Aspects of the Lyche e as a Commercial Crop, Gordon Palmer, Florida Lychee Grow er s Association , Osprey .. .. ......... . -----.. . ........... .. . ........... . ............ 309 The Effects of Longtime Avocado Culture on the Composition of Sandy Soil in . Dade County, John L. Malcolm, Sub-Tropical Experiment Station, Homestead ..... .. ...... 313 Rooting of Peach Cuttings Under Mist as Affected by Media and Potassium Nutrition, Mario Jalil, Escu e la Agricola Panamericana, Honduras, and Ralph H. Sharp e, Agricultural Exp e riment Station, Gainesville .. ..... ... ... . ................ . . ... . ... . . .............. . ....... 324

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Some Effects of Nitrogen, Phosphorus and Potassium F e rtilization on the Growth , Yield, and Fruit Quality of Persian Limes, Seymour Goldweber, Manley Boss and S. John Lynch , Division of Res ea rch and Industry , University of Miami, XIII Coral Gables ____ _ ___ -. _____ __ _ _____ __ -_________________ ____ _ _ ------------------------------------328 ORNAMENTAL SECTION Mist Propagation of Roses, S. E. McFadden , Jr., Department of Ornamental Horticulture, Universit y of Florida, G a inesville __ _ __ __ __ _ _ _______ ____ ----------------------------333 Gladiolus Botrytis Control, R. 0. Magie , Gulf Coast Experiment Station, Braden337 Some Notes on Philodendron Hybrids , Erdm an West and H. N. Mill e r, Florida Agricultural Experiment Station, Gain esv ille _ _ __ _________ __ ---------------------------------------343 F e rtilization of Gladiolus, S. S. \,Voltz, Gulf Coast Experiment Station, Bradenton---------347 Studies on th e Nutritional Requirements of Chrysanthemums, S. S. \Voltz, Gulf Coast Exp e riment Station, Bradenton . . -___ -------------------------352 Virus Ring Spot of Peperomia Obtusifolia and Peperomia Obtusifolia var . Variegata, M. K. Corbett, Florida Agricultural Experiment Station, Gainesville. 357 How to Landscape ~ur Outdoor Space for Living, Thomas B. Mack, Florida Southern College, Lakeland --------------__________ -----• ---360 Regional Performance of Hemerocallis in Florida , Eunice T. Knight, Apopka-----363 . The Palm Society, Dent Smith, The Palm Soci e ty, Daytona Beach-----------366 Comparison of Happiness Rose Production on Four Rootstocks, S. E. McFadden, Jr., Department of Ornam e ntal Horticulture, University of Florida, G a inesville ______ 368 Florida Nursery Law , Paul E. Frierson , State Plant Board of Florida , Gainesville ___ ---370 Research in th e Ornamental Field in Control of Mcditerraneaii Fruit Fly , E. W. Mc• Elwe e, Florida Agricultural Exp e rim e nt Station , Gainesville ____ --------------379 The Florida Flower and Nursery Industry, Cecil N. Smith, Florida Agricultural Ex perim e nt Station , Gainesville -------------------------------------380 The Downward Movement of Phosphorus in Potting Soils as Measured by P", Daniel 0. Spinks and William L. Pritchett, University of Florida, Gainesville ____ ___ __ . .. .. .. 385 Twelve Bauhinias For Florida, R. Bruce Ledin, Sub-Tropical Experiment Station, Homestead -----------------------------388 P es ticides and Plant Injury , S. H. Kerr, Florida Agricultural Experiment Station, Gainesville ------------______ _ . _ .... . . . -------------.. -------------------------398 The Effect of Parathion as a Corm and Soil Treatment for Gladiolus, E. G. Keis• heim e r, Gulf Coast Experiment Station, Bradenton---------------403 The Genus Solandra in Florida, R. D. Dick ey, Florida Agricultural Experiment Station, Gainesville -----------------------------------465

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XIV FLORIDA STATE . HORTICULTURAL SOCIETY, 1956 Studies on Chemical Weed Control in Plumosus Fern, C. C . Helms, Jr., J. M. Crall and E. 0. Burt, Waterm e lon and Grape Investigations Laboratory, Leesburg ....... .. .. ... .. 407 Fungicides and Plant Injur y, Albert P . Martinez, St:ite Plant Board of Florida, Ga in es vii le _ ... _ . ... . . ......... .. . . . ... .... ..... ....... .. . .. . .......... ... . . .................. . . .. 413 The Hunting Billbug a Serious Pest of Zoysia, E. G. Kelsheimer, Gulf Coast Experi• ment Station, Bradenton 415 ANNUAL REPORTS Necrology . .. ...... ........ .. .. . ... ........ ..... -... .......... ... .... ...... .. . .. ........... .. .. . .... 419 Report of Executive Committee . ........................ . ...... . . ... ..... .. .... . ..... . .... .. ... . ... ... ... ... . . ........... . .. . . 421 General Business Meeting .... ... ......... .. . . . . . .. ... .... . ... ...... ... . . 421 RPsolutions ......... ... ............. ... . ... .. . . . . . .. ....... .. .. 421 Report of Treasurer . ... ...... .. . . . . . . ... -.. . . ..... .. . . . . . . -. . .. -..... . . . . . . ... ... ... . 422 List of Members . ............ ... . .. . . . -__ .. 423 433

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1 THE PRESIDENT'S ADDRESS R. A. CARLTON West Palm Beach One of the duties imposed upon the Presi dent of this Society is an annual address on the activities of your Society and the general state of Horticulture in Florida. I am glad to report that your Society is now the third larg est Horticultural Society in the United States and the seventh oldest society. It is exceeded in . membership by the Wisconsin and Michigan Horticultural Societies in that order. The oldest society is in Ohio and was organized in 1847. The Wisconsin Society which has the largest membership has received State aid since 1879 which may account in some measure for the size of its membership. In the preparation of this address it was natural to reflect upon the changes that have occurred in the activities of the Society in the more than 30 years in which I have been a member, and more or less active in the So ciety's functions. When I became a member, the horticultural crops of the State were strug gling along on an unbalanced program of nu trition, and your Society was struggling in about the same manner. Colonel Bayard F. Floyd had been Secre tary since 1917 and most of the Presidents and Executive Committeemen of those days insisted on the Colonel running it as a one man show, and imposed upon . him the com plete responsibility for the program, arrange ments for the meetings, and everything else requiring much work and time. I recall that some of the young upstarts in the Society about 25 years ago, myself included, became somewhat critical of some of the Colonel's best efforts at program and meeting arrange ments. As usual, everybody thought something should be done but nobody wanted to do any work. This state of mild criticism prevailed until about 1939 when the speaker and some others approached the Colonel about forming a Vegetable Section of the Society. The Colonel was quite agreeable and cooperative but flatly declined to accept any responsibility for a program for such a section. Being brash and bold, I accepted this responsibility and during the next five years I learned how easy it is to talk too much. Anyway, during those years working with Colonel Floyd I gained a deep appreciation of the problems he had faced through the years and sincerely re gretted any criticism I ever had of his efforts. His untimely death in 1945 prevented the Society from ever awarding him any honorari um, if it had been possible for the Society to accord him anything commensurate with the services he had rendered. It affords me great pleasure to report that during the past year your Society operated under a new deal compared to the years out lined above. This year it was a pleasant ex• perience to see how all your General Officers . worked together as a team to develop the pro gram and arrangements for this meeting. The Chairman of each Section readily accepted the responsibility of developing the program for his Section, and the Executive Committee men from the Society at large were most help ful to the General Officers in arranging the many details of this meeting. I wish to express my sincere appreciation for the help and co operation I have received from one and all. Some of my foregoing remarks have empha sized the fact your Society has been most for tunate in the selection of a Secretary. This good fortune still prevails in Dr. Ernest L. Spencer. He has all the attributes of other good secretaries with an additfonal one of getting more work out of other people without making anybody mad. During the past two years your Society created a Fellowship in Virology at the Uni versity of Florida; This Fellowship was awarded to Mr. Robert Bozarth, a graduate of Everglades High School in 1948 and the Col lege of Agriculture, University of Florida, in 1952. He is presently directing his study on the viruses of gladiolus. When these viruses have been . isolated they will be identified by symptoms, host reaction, cross protection, and by the use of the Spinco Ultra Centrifuge at tempts will be made to purify and crystallize the viruses. These studies will aid in the de veloping of practical and economical control measures that can be applied by the growers. Realizing full well the complex field involved in research on crop viruses, the recipient of

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2 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 this Fellowship expressed his problems well I thought and I quote, "To use a bit of double talk, we are experimenting with experiments to carry on the experiment." This certainly in dicates he knows what he is up against. During April a major outbreak of the Medi terranean fruit fly occurred in Dade County, Florida and since that time this insect has been found in some 26 counties. The reoccurrence of this insect in the State had been expected by many due to the increase in air travel to the State from all parts of the world, and the reduced inspection service at ports of entry. Many of us who remembered the hectic days of the eradication campaign in 1929 were ap palled by prospects of a similar experience. However, time had wrought many changes in techniques of control, insecticides and bait at tractants used in eradication of this insect. No one could fail to be impressed by the fact that with the discovery of an outbreak of this insect today, this spot, and many miles of area surrounding would be thoroughly sprayed within a matter of hours. Respraying of such areas would occur almost in the twinkling of an eye, in opinion of some of us, who were constantly faced with wash jobs on our cars. A full report will be made to the Society at this meeting on the status of the control pro gram of this insect. I feel the control agencies have done a remarkably good job on this prob lem and should be congratulated on avoiding much confusion and hysteria that usually ac companies a control and eradication program of this magnitude. Your Societv has been much concerned in recent years ~ith the control and eradication of spreading decline in citrus. I do not have figures later than June 1st, 1956, but at that time inspection had been made on 4,421 grove properties_ comprising approximately 18,000 acres. Infested groves were 960, comprising about 7,500 acres. Inspection had been made of 2,243 nurseries of which 306 were found to be infested. Beginning July 1st, 1955, the State Plant Board started its program of pull ing trees from infested grove properties and treating the soil to eradicate spreading decline. As of June 1, 1956, 200 grove properties com prising 1440 acres had been pulled and treated at a cost per acre of approximately $305.00. This total cost may be broken down with $89.00 cost to push and bum trees, and $150.00 to remove roots and do a thorough job of treating the soil. The State. Plant Board expects to complete the removal of all infested acreage by July 1, 1957, and treat the acreage from which trees and roots have been re moved. This clearly indicates fine progress in the control and eradication of this production problem. Despite the dual threats of fruit fly and spreading decline and other problems, the citrus industry continues to set new records of production with an estimated 138,000,000 boxes of fruit to be harvested in the coming season. Except for the war years, the citrus section never had it so good, due in a large measure to its hand maiden the Processing Section which utilized 71 percent of last sea son's crop . The Processing Section is diligent ly making every effort to improve quality and increase consumer demand for its products. Much progress is being accomplished as re flected in increased consumption of all pro cessed citrus products. In the field of the Krome Memorial Section of your Society, much progress may be noted. Nutritional sprays of zinc, manganese and iron chelates have revolutionized the produc tion picture on the limestone soils of Dade County where much of the commercial acreage of subtropical fruits are planted. Mechanical improvements in land preparation and devel opment on this unusual soil has also contrib uted to increased acreage. Two lime concen trate plants in Dade County are contributing much to stabilizing the market for Persian limes. Some 6500 acres are now planted to this fruit crop in Dade County. New mango varieties are encouraging in creased plantings of this fruit. This is one fruit immigrant that the longer it stays with us the better it gets. New variety developments are a far throw from the the first Mulgoba tree that fruited successfully in West Palm Beach around the turn of the century. Some of you have heard the beloved Dr. David Fairchild tell the Society of his hopes and fears of the early plantings of mangos in Florida. The annual Mango Forum and exhibit is a state-wide organization and I believe is a fitting example of Dr. Fairchild's fondest hopes for this fruit in the western world. Lychees have r _ eached commercial produc tion and a growers association was formed in

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CARLTON: PRESIDENT'S ADDRESS 3 1951. This association is actively working on production and marketing probl e ms . In the realm of the Vegetable Section, U.S.D.A. Truck Crop statistics reveal th e Florida growers brought 385,000 acres of vegetable crops to the point of harvest l a st season, with shipments of 155,000 carlot equivalents. Acreage of vegetable crops has increased 21 percent and volume of shipments 42 percent in the past fiv~ years. In the same five year period returns on vegetables at the F.O . B . level have increased 31 percent. To matoes continu e to be the most important vegetable crop grown in the State with the value of last year ' s crop exceeding the valu e of all animal products sold in the State. Last season 4.6 percent of the State's tomato pro duction was shipped as vine-ripen e d a nd this supply resulted in much attention being di rected toward this new development from a marketing st a ndpoint. A study is now being made by Agricultural Economics Department of the College of Agriculture on the m a rket outlook for vine-ripened tomatoes . The Chair man of this year's Vegetable Section of your Society is a successful vine-ripened tomato grower. I predict that the marketing of vine ripened tomatoes is here to stay and that Flori da will soon develop this activity into a major enterprise. Last season Florida harvested 37,700 acres of sweet corn, which was a crop not grown commercially in the State 15 years ago, The State now furnishes a continuous supply of this crop to the markets from October until July. Notable advanc e s have been made by all phases of the vegetable industry in mechani zation of production and harvesting processes . One of the newest harvesting machines to come to my attention is for tomatoes. This machine has an overall width of 365 feet. Such developments are resulting in larger growing operations. The Ornam e ntal Section of your Society is a phase of horticulture that has increased phenomenally in recent years. The gladiolus in dustry has expanded since 1940 from 4,500 acres producing 5,000,000 dozen blooms to 11,600 acres producing 20,000,000 dozen blooms. The growing of chrysanthemums h a s jumped from 5 acres in 1950 to 230 acres with a large part of this e nterprise located in Martin Count y . Last s e ason 46 growers har vested 3,500,000 bun c hes of pompous and 72,000 doz e n standard blooms valued at $3,500,000.00. This is a good example of a hot house enterprise being adapted to production in the open under Florida's climate. A sizeable industry has developed on the woody peat soils of Highlands County in the production of calladium bulbs. This enter prise has meant much to the economy of that area. The importance of large ornamental nursery business in the State is well known. The eternal light of your Society is its pub lished proceedings . Volume 68, relating to the 1955 meeting cont a ins 400 pages. In the 69 years of the Societ y' s existence its proceedings have reported the best history of Florida ' s horticulture both practical and technical. Several years ago an index was published of volumes 5 through 37 of the proceedings. Three years ago your Executive Committee de cided to compile an index of volumes 38 through 68 and this was completed this sum mer and now publi s hed and available to mem bers. This work of indexing the proceedings was done with the int e nt of encouraging mem bers to better use their proceedings as refer ence material for any ph a se of horticulture in which they might be interested. I realize that I, and possibly many other members, .have not used th e ir proceedings in the past as we should h a ve, and possibly this was due in part to a lack of an index which would permit us to refer quickly and efficient ly to any per s on or subject covered in th e pro ceedings. The Society has grown too large and com plex for any member to attend the sessions and hear all the papers which might be of interest and value to them. Study of the proceedings is the only way then in which the Society may be of the most value to you . I would be remiss in duty if I didn ' t urge every member here to use and appreciate the work and knowledge . recorded in your Society's proceedings. I am not one to sermonize, but if I were, an appro priate text might be found in Matthew 5:15: "Neither do men light a candle and plac e it under a bushel , but upon a candlestick; and it giveth light unto all who are in the house."

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4 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 PLANT RESEARCH IN THE ATOMIC AGE GEORGE L. McNmv Boyce Thompson Institute for Plant Research, Inc. Yonkers, N. Y. When your fine secretary invited me to ap pear on this program last June, I demurred long enough to prove my modesty and the_n hastened to accept before he changed his mind. As usual, I always enjoy a hip to your unique state. It is a particular honor and pleasure to appear before such a venerable and respected society as yours to discuss cer tain new aspects of agricultural research. At the very outset we should come to an understanding that nothing I am going to say in the next hour will revolutionize Florida's agriculture. You will probably not find a single item to help you increase soil fertility, sup press insects or aileviate plant diseases. After all you have one of the better, if not the best, ag;i~ultural research services in the United States to provide such information. Since it would be foolhardy for me to attempt to com pete with such talent in your own fine institu tions, I will spend this hour discussing selected items of research behind their research. Per haps we can take a stroll behind the scenes to see what sort of principles of life and living processes are being investigated in order to provide a jumping off place for future research in agriculture. THE CHALLENGE OF THE MODERN ERA Our newspapers like to refer to this as the atomic age. Perhaps this is fitting because it is an era of change, growth and violent adjust ments. To many of our citizens it has become an era of frustration, uncertainty and worry as , we face a violently explosive international .situation and see our economy shaken and un stable on the rapidly shifting sands of techno logical change and social unrest. Although we know that atomic violence hangs over our heads by day and night, I would not have us live in fear and trepida tion. There is another side to this whole pic ture that we should never forget. The same forces that threaten us can be diverted to our peacetime use and civilized progress, It is this story of progress through research in the com mon great cause of humanity that we will in spect here today. THE NEW ERA IN RESEARCH The opportunities in research were never more promising of glorious success than to day. Scientists have behind them a mass of knowledge to be used as a foundation and new research tools that were undreamed of three decades ago. For the first time in the history of science man can trace the meta bolism of a living thing by use of radioactive, unstable atoms. You can label a part of a tissue as it grows; a molecule in process of digestion, or even the parasite or pest that attacks the crop. The tissue, the molecule, the parasite, or the insect then becomes so conspicuously unique that it can be traced wherever it goes and yet it behaves exactly the same as all of its less conspicuous brethren. The physical chemist has given the biologist a host of other relatively simple tools to help in manipulating and , sepa,rating the labelled molecules. By use of paper partition chroma tography one can separate out all the amino acids, ketones, aldehydes, acids, growth hor mones, etc., then identify them and measure their concentration. , Assays that would have taken many months to perform can now be done in 48 hours. Best of all, however, the new techniques reveal related but previously unknown compounds to whet the curiosity and initiative of the investigator. No less sig nificant is the use of elution column chroma tography, ultracentrifuges, electrophoresis equipment and a host of other devices to sep arate and purify components with biological activity. If there is any question about the identity and concentration of any material there are spectrophotometric devices to substantiate one's opinions and guide his research. For example, just think of this fact. One of our scientists tells me that we can now make a complete amino acid analysis of a single female house fly in two days. If we find an undescribed amino compound we can elute it and get a complete fingerprint of its characteristic bonds within two hours by use of infrared absorp tion. You can do all this if the miserable old

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McNEW: PLANT RESEARCH 5 flv had as much as a few micrograms of the chemical in her body. This example could be multiplied a hun dred-fold by choice of other devices and tech niques-the physical chemist who pulls two closely related viruses apart in an electrophore sis apparatus by minute differences in their surface charges or by differences in their mass or density in an ultracentrifuge, or the X-ray crystallographer ,vho plots the arrangement of invisible and active atoms one to another in a crystal lattice that one barely sees under the most powerful microscope. This is a great era in which to live. Every scientist worthy of the name should thrill to the opportunities be fore him to understand the universe. For many decades the botanist and horti culturist have been interested in the outside of plants. They did a necessary job of describ ing the organs and determining the relation of one plant to another. We learned how to change these external appearances by breed ing, altering their nutrition, or exposing them to chemicals. However, no one knew exactly what had been done or why plants reacted the way they do. Today a new viewpoint is com ing into plant research. \Ve are more interested in what a plant does than what it looks like. The activities going on inside of millions of . tiny cells in each tissue arouses one's imagination. There is a beehive of activity in one of these cells-with a volume of less than one-billionth of a cubic inch-that would put the best man-made factory to shame. For ex ample, if one provides the leaves of a plant with labelled C''O,, within five minutes there may be detected 57 new organic compounds in the tissue. Within a couple of hours some of the very complex new molecules are being secreted from the roots. One must admit that the dynamics of cell operations are tremend ous. The activities of these cells are of interest to men because anyone who can control the cell can change the tissue and thereby regulate the entire plant to our selfish purposes, One can make cells grow faster, change their shape, inactivate them completely, change their heredity; render them more nutritious or make th~m immu~e to disease_ by use of the appro priate chemicals, Therefore the scientist who will take the time and effort to understand cell functions should be able to uncover basic principles of life which he can exploit in mak ing plants more serviceable to man. By the same token, the man who would control in sects, diseases and weeds has an obligation to study them carefully to determine their strengths and weaknesses. By so doing, the biologist can orient the ef1 forts of the chemist in developing new types of chemicals to solve many problems in. plant culture. The examples we will consider here today lie in this general area on the frontiers of science. They are chosen from work of various scientists at Boyce Thompson Institute, not because thev are the only work in the area or even superio~ to that of ~thers but because of my familiarity with them. FUNGICIDAL BuLI,ETS Men have been at war with, the fungi since time eternal. You people here in Florida need not be reminded that tremendous quantities of chemicals must be applied to plants to prevent fungous diseases. You contribute a substantial share of the 125 million dollars spent each year in the United States on control of plant diseases. In spite of this terrific investment we are only partially successful in reducing the rav ages by fungi. According to our best estimates they still destroy 7% of our potential agricultur al productivity. This amounts to about 2.8 billion dollars a year. To get down to brass tacks it means that every man, woman and child in the United States pays $24.20 a year in tribute to the fungi. Each family would be horrified if it entered $96 a year in its house hold budget as the cost of plant diseases but such are the facts. Obviously we need better methods of con trolling diseases. Some people may make their contribution by breeding resistant plants, im proving crop rotations etc., but we have elected to see what can be done in improving fungi cides. There are several good fungicides but we need more and the only way we are going to get them is invent them. We have decided to learn all we can about the ones now avail able so we can develop better ones. Here are a few examples of recent developments. Sulfur operates in a unique fashion. The particle of sulfur deposited on a leaf or fruit volatilizes and reaches the spore in the vapor phase. By use of radioactive sulfur (S:i:;) Drs.

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6 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Miller and McCallan have shown that the sul fur atom is taken up by the spore and is almost immediately reduced to hydrogen sullide. It is released within a couple of minutes from the spore and, contrary to previous conceptions, the H,S does not act as a fungicide in destroy ing the spore. Please note that facts such as these could be determined only by using iso tope tracer techniques. Once these facts were out in the open our scientists began to wonder how sulfur could destroy a spore without entering into cell re actions. Biochemical studies have shown that the spore suffers irremedial damage when it gives up two hydrogens to reduce each sulfur. For each molecule of sulfur reduced, the spore releases a molecule of carbon dioxide. By the time the spore has reduced 15,000 to 25,000 parts of sulfur per million units of body weight it succumbs. The search in this area goes on to determine what organic acid in the spore is undergoing decarboxylation. Insofar as we know, sulfur is unique among the fungicides in its ability to destroy a spore solely by robbing it of ma terials. All other fungicides enter the spore and react with vital cell constituents. Sulfur is a hit and run bullet that bleeds the spore to death. The organic fungicides are far more fas cinating. They can be designed in a wide variety of forms with only minor differences in configuration. By trial and error, chemists have learned that there is a rigid requirement of chemical structure to attain effective fun. gitoxicity. Why does a minor change in chemi cal structure affect the fungicidal activity so drastically? It is becoming increasingly clear that the changes either influence the ability to penetrate the fungous body, to enter into certain vital cell reactions and disrupt them, to change resistance to the cell's detoxification mechanisms or to modify the stability and per sistence of the molecule. Most of you "know that there are two quin one fungicides on the market under the trade names of Spergon ( chloranil) and Phygon ( dichlone). Many of you may have heard me say in years past that dichlone was about 20 times as fungicidal as chloranil. This appears to be tru e when one measures their effect on spore germination but it is contrary to what one would expect from their chemical attributes. Dr. Owens has cast much light in this area by recent studies on the effect of several dozen quinones and hydroquinones on enzyme systems. He found that there was a very close correlation between fungitoxicity and ability to inhibit sulfhydryland amino bearing enzymes. An exception was observed in comparing benzoquinone and naphthoquin one analogues. He was finally able to show that benzoquinone appeared to be less active than naphthoquinone because it was detoxi fied more readily by entering into extraneous reactions. Dark-colored spores secrete sub stances that inactivate much of the benzo quinone before it can penetrate and destroy the spore. . Most of us have wondered what roles are played by the halogens on the organic mole cules so commonly used as insecticides, fungi cides and herbicides. Dr. Burchfield has care fully studied the effect of placement of two types of chlorine in the symmetrical triazines, a new class of fungicides developed by Dr. Schuldt in cooperation with chemists of the Ethyl Corporation. These compounds have the following structure: 6(chloroanilino)-2,4-dichloro-4-triaz:l.ne The two chlorines on the triazine nucleus were found to be essential for reaction with sulfhydryl-bearing enzymes and related com pounds. If they are replaced with other groups the molecule becomes impotent because it can not react in the cell environment. The chlorine on the anilino group serves a multiple function. When placed ortho to the nitrogen it activates the chlorine on the triazine nucleus. One might describe it as a booster charge because of its effect on electron density at the vital part of the molecule. Therefore, if the chlorine is substituted at this point activity may be in creased several-fold, depending upon the species of fungus affected. This booster effect declines as the chlorine is pushed farther away into the meta or para

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McNEW: PLANT RESEARCH 7 positions on the phenyl ring. In spite of this diminishing effect the parachloroanilino com pound is much more active than its meta ana logue. This has been shown to be due to its_ greater ability to penetrate the spore wall of certain fungi. The concepts on spore penetration have changed drastically in the last three years. We are leamincr that certain groups such as the parachlorophenyl, or the long alkyl chain of 14 to 17 carbon atoms alter the lipoid solu bility of a molecule enough to regulate com pletely the ability to penetrate the waxy and oily layers in the fungous wall. Merely by changing the length of the carbon chain in the 2-position of the imidazoline nucleus it is possible to render the molecule safer for use on plants and more destructive for spores at the same time. Glyodin was developed by Drs. Wellman and McCallan merely by lengthening the carbon chain from eleven atoms where it rendered the molecule violently injurious to the plant and relatively weak for the fungus to 17 carbon_ atoms where the reverse situation held. In studies employing radioactive molecules, Dr. Miller has been able to show that fungi cides not only penetrate the spore wall at un believably fast rates but may also change the permeability of spore membranes. If spores are placed in a suspension containing 2 p.p.m. of glyodin they will accumulate up to 6000 p.p.m. of their own body weight within 2 to 5 minutes. Interestingly enough, such a spore destroyed by this organic chemical will take up just as much mercury or silver fungicide as a normal living one. Likewise, he found that mercury and silver did not interfere with each other although it had been assumed that heavy metals might be expected to occupy similar reaction sites. The spores actually took up more mercury after they had been exposed to silver than comparable untreated spores. This was traced to a change in the semi permeable membranes of the spore. Silver af fects the spore so its cell constituents are lost more readily and external chemicals penetrate more actively. By patient studies such as these we are cataloguing the effects of changes in chemical structure on the activities of various. types of molecules. The ultimate goal of course is to define all the characteristics of a fungicide so we can design one that will penetrate the fungous body, enter into a vital reaction with an enzyme or metabolite, but not be detoxi fied by extraneous reactions. This is a big order but it is not an impossible one._ Vmus MULTIPLICATIONS AND PATHOGENESIS One of the great areas of knowledge to be developed is the nature of virus infections in plants. In spite of the monumental stride~ for ward in the past thirty years, the riddle of how viruses multiply and cause disease remains un solved. The presence of virus protein does not necessarily cause disease symptoms. Investi gators have isolated and identified heavy weight proteins from apparently normal plants so removal of proteins from normal pathways of metabolism does not e~p~ain the disease conditions. As a matter of fact nu cleic acid may be combined with proteins without inciting symptoms as witnessed by the research on recovery of tobacco from ring spot done by Dr. Price, a former member of our staff, now with the Citrus Experiment Station. On the assumption that there is some physio logical disturbance other than the abnormal use of protein, Dr. Porter has been investi gating the biochemical changes in plants dur ing the incipient stages of infection before disease symptoms appear. The first reaction of a plant to the tobacco mosaic virus appears to be an abnormal synthesis of amino acids. By use of paper chromatography he has been able to demonstrate a net increase in alanine, threonine, aspartic acid, lysine, gamma amino butyric acid, asparagine and serine within 72 to 96 hours. After attaining this peak concen tration they began to decrease so they were present in subnormal concentrations after 192 hours. Glutamine followed the same pattern except that it attained a much higher peak and within a shorter period after inoculation of the virus. Apparently there is some mechan ism of nitrogen assimilation triggered by the virus before it begins to multiply much less create symptoms. As soon as the virus begins to multiply, the concentration of amino acids declines. The mechanism by which these changes are implemented is imperfectly un derstood and obviously justifies much more investigation if we are to understand the physiological basis of pathogenesis by viruses.

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8 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Within the past five years the scientific world has come to understand much more about the virus particle itself. Dr. Magdoff has been studying the physical properties of southern bean mosaic virus by X-ray diffrac tion. Interest is being directed primarily to ward the spatial relationship of nucleic acid to the protein and to the packing of subunits of the virus in crvstals. We now know that viruses may be degraded by removing nucleic acids and can be restored to activity by re combination of these two components, so studies of this sort become extremely im portant. There is no more exciting area of research than these on virus proteins. The v e ry basis of life is involved in the studies on ribonucleic acid and protein synthesis. In due season, as techniques are perfected on viruses, one may expect such studies to be extended to the mechanisms of heredity. Far in the future the redesigning of chromosomes by chemical methods far more advanced than the primitive use of colchicine today to induce polyploidy. THE MECHANISM OF ACQUIHED RESISTANCE OF INSECTS TO INSECTICIDES One of the serious problems facing the agriculturist is the tendency of insects to ac quire resistance to insecticides. For example, greenhouse operators have found that red spider mites develop resistant populations within a few months to two vears after a new chemical is introduced. In ' the past decade they have run through five new chemicals that were found only by a tremendous invest ment in funds and research time. The mites are so tiny that we have not had the courage to begin a study of them. There are equally interesting cases of resistance in houseflies, mosquitoes, flea beetles, lice, etc., that can be used. Currently our people are working on the resistance of houseflies to chlorinated hy drocarbons since they present an excellent subject for study on the comparative biochem istry of resistant and susceptible populations. By use of pure culture techniques to avoid microbiological contaminants, paper chroma tography to separate and measure cellular compon e nts such as amino acids, and use of Geiger counters to follow the pathway of metabolism of unstable atoms such as S" " we are obtaining considerable information on what happens when an insect becomes resist ant. Dr. Moorefield has continued studies which he began while he was a student at the Uni versity of Illinois. The flies resistant to DDT have a new type of enzyme known as dehydro chlorinase. This material makes it possible for the insect to detoxify the chemical by remov ing HCl from the molecule. The enzyme does not require a metallic constituent to activate it and appears to be a specific sulfhydryl type of material. Within the past year, Dr. Moore field has shown that the ability to produce this enzvme is latent in the larvae of an ordin.i ary pop~1lation of DDT-susceptible insects but probably does not occur uniformly in all in dividuals. When larvae are exposed to DDT only those with exceptional ability to generate this enzyme mature. Because of this, the re sistant adults have demonstrable quantities of dehydrochlorinase while comparable suscepti ble insects do not. It is perfectly obvious that we need to know more about the metabolic processes of insects which permit them to detoxify chemicals or develop alternate metabolic pathways to es cape the lethal effects of insecticides. Since sulfhydryl compounds allegedly play such an important role, Dr. Cotty and Dr. Hilchey have been studying sulfur metabolism. Con trary to ordinary beliefs that animals must ob tain their sulfur from organic materials in plants, these investigators have demonstrated that insects can convert sulfates "into sulfur amino acids . By use of paper chromatography to separate the various acids and measure their concentrations and by feeding sulfates and other materials labelled with sss they have been able to trace the process in aseptically reared cockroaches and houseflies. The sul fates are converted into methionine and the methionine is changed into cystine through an intermediate cystathionine. The cystathionine seems to serve as a unidirectional regulant since cystine cannot be converted back into methionine. The cystine may be converted into taurine and excreted as such. Preliminary evidence indicates that some re sistant houseflies have exceptional ability to synthesize glutathione but further research along these Jines will be re<1uired to establish the point.

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McNEW: PLANT RESEARCH 9 THE PROCESSES OF ABSCISSION FORMATION One of the very vital processes in plants is the abilitv to shed leaves and blossoms. The process depends upon the formation of an abscission layer of cells at the base of the leaves or blossoms but beyond this knowledge very little is known. We know that many plant disease agents produce a biochemical change that causes diseased leaves to fall so one may assume that chemical messengers are involved in abscission cell formation. Since we know so little about the chemical stimuli we have very imperfect control over defoliation of cotton to facilitate picking or removal of leaves from nursery stock to improve its storage qualities. Neither do we know how to prevent shatter ing of foliage from forage legumes, or loss of leaves from diseased plants and blossoms from cut flowers such as the rose. Sometime ago we set out to design a new type of heterocyc!ic sulfur fungicide. We failed completely insofar as making a fungicide was concerned but we did notice that some of the compounds had ability to cause the leaves to drop from beans. Over a period of two years we have synthesized a variety of related compounds and succeeded in developing a new class of defoliants that can be applied either through the roots or directly to the foliage. The remarkable thing about these new materials is that they cause a simple physio logical defoliation without burning or distort ing the leaves. As a matter of fact they dupli cate the natural processes of leaf shedding almost precisely. A couple of days after the material is added to soil the innermost leaves begin to change color. Some members of the series cause the leaves to take on a red tinge, then become yellow and finally drop from the plant. Defoliation proceeds steadily out ward and upward until the entire plant is de foliated. If the plant is held for several weeks it completes its dormant period. New buds break forth and the plants resume normal growth. These materials offer such a wonder ful opportunity to study the biochemistry of defoliation that we were prompted to organ ize a study of defoliation by natural processes, freezing and chemicals. Dr. Plaisted has found that within a matter of a couple of days after a defoliant is applied to cotton, the number of free amino acids in the petiole increases from three to about twelve. A similar phenomenon has been ob served in the leaves of deciduous trees in the fall and Dr. Weinstein found that rose petals undergo an increase in soluble nitrogen after cutting. This promising lead suggested that the first stage in abscission formation is the stim ulation of amino acid production and that these amino acids would facilitate formation of new cells in the abscission layer. Unfortunately the story on abscission will not prove so simple. A careful study of the total nitrogen balance indicates that the amino acids are the result of senescence in which proteolysis occurs rather than the incitants of a . new process. However, we do have one fas cinating lead in Dr. Plaisted's work. He has found an active principle in shattered blos soms that causes abscission of foliage in nor mal healthy plants. Studies are underway to isolate this factor and learn more about its be havior. The significance of this research to date is that we are building up a set of ex perimental procedures for regulating and studying this vital, but very seriously neglected field. THE REGULATION OF PLANT GROWTH If studies such as those described on the fungicides, viruses, insecticides and foliage abscission seem far-fetched, unrealistic and not likely to ever produce significant practical re sults, I would like for you to bear with me a moment while we outline the consequences of another basic research program. About 25 years ago the Institute assigned Dr. Zimmer man and Dr. Hitchcock to a study of how plants grow. They were free to study any aspect of plant growth and differentiation that appealed to them. Their attention was grad ually focused on methods of altering the nor mal balance of growth hormones or chemical stimuli in plants by adding chemicals to the plant. From this research there came knowledge on the use of ethylene gas to anaesthetize cells or regulate maturation 'processes in cells, and root-inducing substances that have hcen use ful in plant propagation. Interest in indole and

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10 FLORIDA STATE HORTICULTURAL SOCIETY, '1956 naphthalene compounds led to a study of other types of acids, especially chlorinated de rivatives of benzoic acid and eventually to aryloxy acids such as 2,4-D. By 1941 they had described the selective growth regulant ability of 2,4-D and opened the doors to a new era in weed control and the development of specific growth regulants. There is no need to dwell upon how the American public grasped the opportunity to remove broadleafed weeds from lawns, road sides, wheatfields, pastures and cornfields. Within ten years, consumption of 2,4-D ex ceeded 25 million pounds a year. Even more important was the contagious enthusiasm of dozens of chemical companies to hunt for other classes of regulants and selective herbi cides and of scores of experiment stations to employ weed specialists to study the chemical control of weeds. An entire new profession sprang up within a decade. A national society and four regional weed control conferences were organized so thousands of scientists meet annually to discuss progress and plan for the future. This probably has been the most pro gressive and dynamic branch of agricultural science in the past two decades. Peculiarly enough, 2,4-D came into exist ence because someone was interested in growth processes. These men were not as-. signed to work on weed control. There is good reason to believe that they might never have discovered such a material had they been told that they were to study weed control because they would have had no background, either from experience or literature knowledge to suggest that selective growth regulants should have been used. If ever there was an example to show how science makes its big steps for ward, this is one. Science needs depth and breadth of under standing. The men of science must dig be neath the surface to find more than meets their eyes. If research projects are defined so speci fically that scientists must follow narrow, rigidly prescribed objectives, their effective ness will be minimized because it is these big steps forward that clear the way for the work men of science to build a new house of knowl edge . Let us look at four rooms in the 2,4-D house to see what has happened since 1941. The 2,4-D molecule has three significant features. These are the two chlorines on the benzene ring: Cl the oxygen linkage between the ring and acid groups, and the free carboxyl group. Explora tory research has indicated that the oxygen link may be replaced with nitrogen to give a weaker class of regulant but so far nothing of practical significance has developed in this area. Study soon showed that the halogens played very dominant roles. The chlorine para to the oxygen was found to be indispensable but the ortho chlorine could be eliminated or replaced by a methyl group to give a compound only slightly less effective. However, when a third chlorine was added to one of the free positions a gamut of effects was obtained. A chlorine in the 3-position to give the 2,3,4,-trichloro compound has very little effect on regulant ability. When added in the 6-position so both positions ortho to the oxygen are blocked, the compound is essentially inactive. When the chlorine is added in the 5-position to give 2,4,5-trichlorophenoxyacetic acid there is . a slight diminution of regulant activity for some plants and an increase in the caustic or lethal effect on others. This new compound will destroy raspberries and woody plants that are very resistant to 2 , 4-D. This was the first major step forward and has been tremendously im portant in brush control on ranges and farm pastures. The next step came from a study of the car boxyl grouping. McNew and Hoffman found in 1946 that the acid group could be converted ,to a salt, amide or ester without destroy ing activity. In other words the 0=y OH group could be changed without destroying regulant ability provided a free carbonyl ( C=O) grouping remained. This fact was ex ploited fully in the next few years by three lines of development. The volatility of the ma terial was reduced so it would be less hazard

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McNEW: PLANT RESEARCH 11 ous for use around valuable susceptible plants by converting it to metallic or other salts. The acid was rendered readily dispersible in water by converting it to the very soluble triethano lamine salts. Finally, it was converted to one of the esters which were more effective in the arid western areas than the salts because of their volatility and lipid solubility proper ties. The third change came from further studies in the Institute laboratories on 2,4-dichloro phenoxyethanol and its sulfate ester. Dr. King found that these materials were essentially in active on plants normally susceptible to 2,4-D. Thus the replacement of the free carbonyl group by a hydroxyl group was fatal to the herbicidal activity. The project might have died at this point had he not noticed that the ethyl sulfate ester, since named Crag Herbicide I, would prevent germination of weed seeds when it was sprayed on the soil . He showed that the compound was activated into a herbi cide by ordinary soil but not by steam steri lized soil. It remained for Dr. Vlitos to show that Bacillus ceretts var. mycoides, a common soil bacterium, produces a sulfatase enzyme that removes the sulfate radicle. Other bacteria in the soil oxidize the resultant ethanol deriva tive to 2,4-D acid. Thus soil microorganisms can generate 2,4-D in the soil in sufficient quantities to kill weeds. This is a safer, more selective type of compound than 2,4-D. By extending this principle to other analogues of the phenoxy-ethanol series a . whole comple ment of new compounds is being evolved that can be used to destroy weeds in fields of such sensitive crops as tomato. The fourth development came from study ing the effect of increasing the length of the carbon chain in the acid. Dr. Wain of England has confirmed earlier observations by Syner holm and Zimmerman that 2 , 4,-dichloroary loxy compounds with an even number of car bon atoms in the side acid are more toxic than the compounds with an odd number. This has been shown to be due to the ability of plants to metabolize this part of the molecule by re moving two carbons at a time to convert the material back to 2,4-D. Because of this 2,4dichlorophenoxybutanol may be converted into 2,4-D by some plants. Peculiarly enough, the legumes such as peas and alfalfa do not have this ability so the butanol derivative does not hurt them even as it destroys wild mustard and other weeds growing in pea or alfalfa . fields. These four developments within the first decade of the 2,4-D era show what can be done by the ingenuity, curiosity and alertness of scientists once they are given a new tool to work with. Of course these four achievements stand out like brilliant gems of intellectual at tainment but one must remember the tens of thousands of hours of patient research and hundreds of ideas that failed. They are the overhead that must inevitably be paid for every advance in research. SUMMARY We have foraged far afield in our discussion here today. Some of you may be confused by the complexity of the details as to chemical structures or the nature of cell activities. You have my humble apologies for overburdening you . However, the details are not too import ant. They are nothing more than illustrations of the basic principles we have been eluci dating. If you can leave here with a positive impression as to the general principles in volved we will feel that all the hours spent in preparation and travelling down here were well spent. Let us look at these principles. Principl e l. The scientific agriculturist is turning his attention from exterior considera tions to a study of cell metabolism. This new trend is absolutely necessary if we are to make systematic progress in the future. Remember, the person who can control the operation of cells can determine the fate of the individual plant, the disease agent, the insect, etc. Principle 2. It is possible to design mole cules to do almost fantastic things to a cell. Although our knowledge is in a most primi . tive state there is a great gleam of light shin ing down upon us. It is possible to design mole cules that fit like the key in the lock of cell morphology and physiology. Molecules can be made to penetrate one type of tissue and not another, to change cell permeability, to enter into different metabolic pathways, and even to differ in their stability and reactiveness. Re member that the future will see new kinds of molecules in the garden. They will take the place of insects, diseases and weedy plants . and make plants rebel at their own genetics .

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12 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Principle 3. The type of basic research that must be pursued in this great development does not come easily. It takes time, patience and many, many dollars. It is necessary that every one of us understands this and encour ages it. Men must be encouraged to seek basic principles of life processes so investigators such as themselves can use intelligence in creating new processes of farming and new products. The scientist who operates from a sound set of basic principles is efficient, ef fective and adaptable. Without these principles he must experiment by blind probing. Even tually blind research becomes too expensive to support because of the low, rate of progress. Principle 4. There never was a time when biologists had better research tools at their disposal than today. The things that can be done in a ~ most routine fashion simply were not dreamed of twenty years ago. There is a certain measure of hazard to the tremendous technological strides of our lifetime but the long range view is that more good will come from it than harm. People will be fed better, clothed warmer, and housed more satisfactori ly because of scientific progress. We are con fident that the future is brighter for having knowledge of the atom even though it may do great damage in the hands of a moron or a moronic society. Before every scientist there is an opportunity to serve as never before. There are available , new tools, more money, and more challenge than ever before. If this nation and its demo cratic processes are to continue strong, healthy and progressive its security will come through skillful use of every mental and physical re source at our command. Therefore it is not only a privilege to be a scientist in such a great era; it is a moral obligation to serve skillfully and progressively with the long range viewpoint uppermost in our minds. THE MEDITERRANEAN FRUIT FLY ERADICATION PROGRAM IN FLORIDA En L. AYERS, COMMISSIONER State Plant Board of Florida Gainesville G. G. ROHWER, AREA SUPERVISOR U. S. Department of Agriculture Lake Alfred Modern warfare against a major agricultural insectenemy in Florida has come into its own in the present Mediterranean Fruit Fly Erad ication Program. The combination of aircraft and improved chemical control procedures, supported by an intensive inspection program, has beaten the fly back and should effect com plete eradication within a matter of months. More than 25 .years ago this same insect in vaded Florida and was eradicated after a long and expensive fight that exhausted 18 months in time and $7,500,000 in state and federal appropriations. That was a campaign that created a great deal of criticism with its poli cy of destroying all host fruits and vegetables. In addition, the arsenic used in spraying host plants did much damage to those plants and trees. That was modern warfare in those days utilization of the best known methods of erad icating a fly that had seriously affected fruit and vegetable production in other parts of the world. Regardless of procedures followed the outcome was the successful eradication of the Medfly, the only time in agricultural history that this insect had been eradicated from any country. . The present campaign against the Medfly began only a few days after a Miami resident reported to the Dade County Agent's office that larvae had been found in a backyard planting of grapefruit. Tentative identification of the larvae as that of the Medfly was made by state and federal laboratories, ~ind the posi tive identification followed the receipt by these same laboratories of fly specimens trapped in the Miami area. The early weeks of the campaign could not have been much different from those of the

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AYERS: MEDITERRANEAN FRUIT FLY 13 first fight, for the methods were very similar. Until research men could formulate an effec tive program, the eradication plan moved along the old lines of destruction of host fruits and vegetables and the ground spraying of host plants and trees. Todav however the modern idea is the use of ~hemical co~trol procedures tested and approved in other campaigns against the same flv. In this instance, the testing ground was Hawaii, where the Medfly is only one of three major fruit fly threats. The Florida fight has offered the first complete test for these chemicals and procedures. Within two weeks after the initial find a network of traps had been cast over the state in an effort to delimit the infestations; and the malathion spray formula, involving a protein hydrolysate bait, had been given its first test in the heavily infested areas of Miami. When fly catches disclosed that the infes tations were more widespread in Florida than at first thought, spraying took to the air with the employment of aircraft equipped for this purpose. These aerial applications marked the real break with the past and the time-con suming procedure of destroying host fruits and vegetables was discarded. The spray mixture of malathion, an organic phosphate, and a protein hydrolysate bait proved successful under Florida conditions. Malathion, used in the form of 25 percent wettable powder, was selected for the pro aram because it possesses the lowest mam ~alian toxicity of any effective toxicant avail able for Medfly control. The theory of aerial application of insecti cides has been applied to the program and proved an unqualified success as evidenced by the fact that the Medfly apparently has been eradicated from almost half the state's 27 in fested counties within the space of six months and insecticidal treatments discontinued. To accomplish this malathion bait sprays, through October, have been applied to 750,000 acres one or more times. The repeat treatments to this acreage have accounted for the treatment of more than 5,000,000 acres. Dieldrin sur face treatments have been applied under host plants to 28,000 acres. During the early months malathion was utilized at the rate of one-half pound of toxicant per acre , but this dosage has been cut to approximately three-tenths of a pound in recent months. The attractant first used in the mixture was an enzymatic protein hydrolysate from brew er's yeast or casein, employed at the rate of one pound per acre. Later a less expensive attract ant, an acid hydrolysate of corn protein in liquid form was used at the rate of one quart per acie. Only one pint of this liquid attractant now is used, mixed with three-tenths of a pound of actual malathion and enough water to compose one liquid gallon of mixture. This spray is applied at the rate of one gallon to an acre. In the early stages of the campaign the spray was applied at 10-day intervals in order to kill each new generation of the fly. This schedule was set up on the basis of a normal life cycle of approximately 30 days. In a breakdown of this cycle, roughly 10 days each are allotted to the larval and pupal stages, and the period required before the female fly be comes sexually mature enough to lay eggs. The eggs hatch in one to two days. The purpose of the 10-day spray schedule was to kill the immature fly in the pre-ovi position period. The us e of dieldrin for the treatment of soil surfaces is designed to kill the larvae leaving the fruit to enter the ground to pupate, and also kill adult flies emerging from the soil. Dieldrin granular 30-40 mesh is applied at the rate of 50 pounds of 10 percent material per acre, or approximately five pounds actual dieldrin per acre. The material is ap plied to the soil under host fruits. When the infestations persisted in some limited areas after several months of spraying field inspections disclosed that some adult flies were appearing in traps after the 30-day life cycle period. Some of this occurrence was attributed to heavy showers, but research proved that the fly larvae were still alive and active in over-ripe guava drops 19 days after the first spray. Larval development was de layed to approximately 21 d~ys in over-ripe mango drops and as long as 25 days in some mummified grapefruit, sour orange, and tan gerine shiners. This prolongation of one stage in the reproduction process meant a greatly extended life cycle which had to be . com pensated for through extending the bait spray treatments.

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14 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Spray applications have b ee n cut to seven day intervals in recent months and the possi bility of flies escaping the poison spray re duced to an infinitesimal point. Effectiveness of the spray has been attested to by recent findings which disclose an exceptional drop in the fly populations in the state . Twelve coun tie s hav e been released from the a e rial spray program, and two others are scheduled for release in the next two we e ks. In addition , four of these counties no longer are subject to fumigation regulations for fruits and vege t a bl e s originating in those counties. The decrease in fly finds is more than en couraging in the light of tr a pping reports. During the summer months when the fly ap parently was making most headway, the field total never exceeded the August figure of 18,000 traps. Finds at that time wer e numbered at more than 2,000 flies. That was listed. as encouraging in the light of 5,000 finds from 4,000 traps in June. But even more progress is not e d in the latest figures which disclose less than 600 finds from 48,000 trap s, Effectiveness of the trapping operation was increased by the improvisation of a new type of trap designed by a research entomologist with the program. This trap is a horizontal plastic model open at opposite ends. The principal attractant used in the trapping op e ration is oil of angelica seed , which is mixed with a poison, thre e percent DDVP ( Dimethyl Dichloro Vinyl Phosphate). Chlor dane or DDT powder is dusted in the dry traps to kill ants that might remove th e flies. One of the important parts of the program, the roadblock, has been discontinued as a re sult of the sharp drop in fly infestations. The system of roadblocks w a s established in the first weeks of the program and con tinued until last month when vehicular in spections were considered no longer necessary. Check points were set up around h e avily in fested areas to protect other parts of the state from equally as heavy infestations. In five months of operation the roadblock inspectors checked more than 4,000,000 ve hicles and confiscated many tons of host fruits, v e getables and plants. This was of inestimable value to the eradication program, since it was established beyond a doubt that the fly moved to other points in the state along well-traveled highways. This movement parall e led that of vehicular traffic. It is impossible to estimate how far and how fast the insect would have traveled without roadblocks to halt that pro gress. Complete eradication of the Medfly is the aim of the program and must be accomplished in order to protect the agricultural interests of Florida and of the United States. The use of dieldrin for soil applications and of malathion for foliar treatment has per mitted Florid a to move practically all fruit and vegetable crops to date . That is in sharp con trast to the first eradication program in which host fruits and vegetables were destroyed. In. short , the present program is eradicating the fly and p e rmitting the marketing of com modities under almost normal circumstances. In this, fumigation has played an extremely important r ole and will continue to play that role until th e Medfly has been completely eradicated. ED B ( ethylene di bromide) is used to fumig a te citrus and other host fruits and MB ( methyl bromide) many host vege tables. Both g a ses are used in specially con structed or modified gas-tight fumigation houses equipp e d with special air circulation and gas volitization equipment, At the end of October more than 175 fumigation chambers had been approved for use in the Medfly pro gram in conn e ction with fumigating material regulated on account of the Mediterranean Fruit Fly Quarantine. In addition, 37 fruit processing plants had so modified their pro cessing procedures to permit them to handle the regulated fruit without endangering fur ther spr e ad of the Medfly. Presence of th e Medfly in other countries is marked by increased cost and reduced pro duction. This is especially true in lands around the Mediterranean Sea where the European and Mediterranean Plant Protection Organiza tion has s e t up a committee to study the fly and its control. Last meeting of this body was held in September of this year at Bonn, Ger many. Sin c e no e radication program has been devised in that part of the world, the emphasis was on fumigation and physical controls . Germany, incid e ntally, is vitally interested in the fly, since the pest has been prevalent there since 1954. The Medfly was first dis covered there in 1936, but did not appear in damaging proportions until last year. Imported fruit is believed to be the cause for the in

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AWARD OF HONORARY MEMBERSHIPS 15 festations, since the winters in Germany are considered severe enough to eliminate local incidences of the fly. Nevertheless, the peach crop in Germany has been infested in particu lar cases to 100 percent, enough to affect the national economy . Apricots, apples, pears, and tomatoes also have been infested in that coun try. Peaches grown in Egypt also have been 100 percent infested when no control is applied; certain parts of Brazil no longer export citrus, and Spain ships only early varieties of citrus which must be marketed before ripening prop erly. Reports of this kind emphasize the fact that the Medfly must be eradicated from Florida. Although the program is many months away from that successful conclusion, there is every reason to believe that eradication will be ac complished within the space of one year. The program is being financed by state and federal governments, with each appropriating an equal half of the over-all eradication fund of $10,000,000. That is a small figure on the basis of the present day dollar value when compared with the cost of the first fight. The cooperation of personnel of the Florida Department of Agriculture, State Experiment Stations, other civilian and military govern mental agencies and the general public has been of inestimable value to the eradication program. AWARD OF HONORARY MEMBERSHIPS LLOYD STANLEY TENNY Lloyd Stanley Tenny was born near Hilton, N.Y. eighty years ago this month and was reared on a farm. He received his A.B. Degree from the University of Rochester in 1902, served as Assistant Pathologist with the U. S. Department of Agriculture from 1902 to 1904, as Assistant Pomologist 1904 to 1907 and as Pomologist for the U.S.D.A. until 1908 when he returned to Cornell for further study. From 1911 to 1913 Mr. Tenny was with Cornell's Agricultural Extension Department, being ad vanced to Professor of Extension. He was the first state leader of county Agricultural Agents in New York and helped organize the first Farm Bureaus. Mr. Tenny was Secretary-Manager of the Florida Growers & Shippers League from 1913 to 1916, Secretary of Florida East Coast As sociates 1916-17, and Secretary-Treasurer of the Coral Reef Nurseries from 1917 to 1918. Mr. Tenny was Vice President of the East ern Fruit and Produce Exchange of Rochester, N. Y., and of the North American Fruit Ex change of New York City and president of the Southern States Produce Distributors from 1918 to 1921. The Bureau of Agricultural Economics called him as Assistant Chief 1921 to 1926 and as Chief in 1928. He was Vice President of the California Vineyardists As sociation in 1928-29; President of the Federal Fruit Stabilization Corporation of California 1929-30; and General Manager of the Chicago Mercantile Exchange from 1929 to 1943 when he retired. He is now living in Henderson ville, North Carolina. Few men have so profoundly influenced Florida Agriculture in five short years as did Mr. Tenny. He was one of the BIG FIVE ( consisting of P . H. Rolfs, H. Harold Hume, W. , J. Krome, Wilmon Newell and Lloyd S. Tenny) who played a tremendous part in Florida Horticulture. Mr. L. B. Skinner (for years President of this Society) brought Mr. Tenny to Florida to organize the Grower ' s and Shipper's League in 1913. Soon thereafter Dr. E. W. Berger took to his office samples of Citrus Canker because Mr. Tenny had been a Pathologist. Mr. Tenny recognized it as a very serious threat and "sold" the Florida authori ties on the idea that eradication would be cheaper in the long run than control. How right he turned out to be!!! Soon, the eradication of Citrus Canker was made the number one objective of the Grow er's and Shipper's League because Florida had no department in its government which could undertake it, no funds and no law. Just imagine!!! Mr. Tenny threw himself into the fight with all of his tremendous energy, skill, knowledge and resourcefulness. He whipped together an organization, raised the finances and together with others of the BIG FIVE drew up and secured the passage of the "FLORIDA PLANT ACT OF 1915." Having

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16 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 secured the law that was necessary, he helped the others select the "PLANT COMMISSION ER" Dr. Wilmon Newell; the " State Nursery Inspector" and the "Port Inspection Depart ment," which in cooperation with the U.S.D.A. was responsible for the inspection of all plants entering the State from foreign countries. Having helped make the Plant Board a go ing concern, Mr. Tenny turned his attention to the task for which he had been brought to Florida, that of getting better rail rate sched ules for Florida growers and shippers. It is not too much to say that but for the timely arrival of Mr. Tenny the Florida citrus industry might very easily have been wiped out by Citrus Canker. Like all other members of the BIG FIVE, Mr. Tenny was a giant. The Florida State Horticultural Society takes pleasure in making Mr. Lloyd Stanley Tenny an Honorary Member and regrets that the state of his he~lth requires that .it be in ab sentia. ARTHUR FORREST CAMP Dr . Arthur Forrest Camp came to Florida from California in 1923, and during the en suing thirty-three years has compiled a record of service to horticulture equalled by fewsurpassed by none. . He graduated from the University of Cali fornia with honors in 1920; and was awarded his Doctor's Degree in 1923 by Washington University, St. Louis, Missouri, and immedi ately staited on a career that was to be de voted not only to horticultural advancement in Florida but to advancement on an interna tional scale. From 1923 to 1929 Dr. Camp served in several important research positions with the Florida Experiment Station at Gainesville, and in 1929 was made Horticulturist In Charge, Department of Horticulture. This same year he was made an agent of the U.S.D.A., and played an outstanding part in the eradica tion of the Mediterranean fruit fly. In 1930 he returned to the Experiment Station and served as head of the Horticulture Department until 1936 when he became Horticulturist In Charge, Citrus Experiment Station. Since 1944 Dr. Camp has served as Vice-Director , Agriculture Experiment Stations, in charge of the Citrus Experiment Station. He personally carried on research until 1944, and under his guidance the Citrus Experiment Station has grown in both size and stature until it now occupies and enjoys an outstanding position in the field of horticultural research. Dr. Camp has over one-hundred publications on citrus and other tropical and sub-tropical crops. Some of these publications, especially those dealing with the fertilization and nutri tion of citrus have been and are being used as guideposts in production management. His development of a coordinated system of spray ing and fertilizing citrus is in a large measure responsible for the tremendous per-acre pro duction citrus growers now enjoy as com pared to the 1930s. The development of such a program has been worth untold millions to the citrus industry, as it has enabled growers to maintain a rather uniform per-box cost over the last twenty-five years while per-acre costs have gone steadily upward. As an agent of the Florida Citrus Commis sion, Florida Citrus Mutual and the Florida State Plant Board , Dr. Camp has been called upon for fact-finding trips to South and Cen tral American countries, Spain, Japan, Cali fornia, and Texas. His reports following these trips enabled the various agencies to formulate plans to protect and promote citrus in Florida. He is considered the citrus industry's outstand ing. spokesman on technical subjects, and has been called on many times to state the indus try's case before legislative committees of both the State and Federal governments. Dr. Camp has done consulting work on Citrus production, marketing and processing in many foreign countries for governments, companies, cooperatives, and individuals including Cuba, Jamaica, Haiti, Honduras, Nicaragua, Costa Rica, Guatemala, Argentina, Brazil, Paraguay, Peru, Surinam, Bermuda, Mexico, Sweden, Spain, and Japan, He was made an Honorary Citizen of Argentina in recognition of assistance given the citrus in dustry in that country. Dr. Camp was instrumental in setting up and carrying out research into the tristeza problem, a new disease that posed a threat to Florida citrus and one that decimated many groves in South America . Thanks to this work tristeza no longer poses the threat that it once did. Dr. Camp is an honorary member of the Kiwanis Club and Gamma Sigma Epsilon,

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AW ARD OF HONORARY MEMBERSHIPS 17 and a member of the Florida State Horticul tural Society, American Society for Horticul tural Science, American Association for the Advancement of Science. He is in American Men of Science, Who Knows-and What and Who's Who in American Education. He is a grove owner, and the president of the Haines City Citrus Growers Association. It is with tremendous pleasure that the Florida State Horticultural Society recognizes the great service that Dr. Camp has rendered to the horticulture of the State of Florida and other countries and his leadership in the field of citrus research that has been largely re sponsible for the enviable position the Florida Citrus Industry holds today. HAROLD G. CLAYTON It is a great privilege to present to the membership of this Society a distinguished na tive Floridian who has, by unanimous vote of the Executive Committee, been designated to receive an Honorary Membership in the Society. Harold G. Clayton was born February 27, 1892, at Ocala, Fla. He grew up and attended public schools in Tampa; received B.S. Degree in agriculture from University of Florida in 1914; received M.S.A. Degree from same in stitution in 191.6. After a brief period of farm work he was made County Agent in Manatee County, in March 1917. He entered military service in World War I on May 15, 1918 and served until December 6, 1918. Early in 1919 he returned to county agent work and in October 1919 he was made District Agent with the Agricultural Extension Service at Gainesville. He continued as District Agent until November 1934, at which time he was asked by the Director of the Extension Service to assume administrative direction of the Agricultural" Adjustment Administration, later the Production and Marketing Administration, and now Agricultural Stabilization and Con servation Committee. He served in this posi tion until July 1, 1947. During this period he continued to hold a cooperative appointment with Extension Service. On July 1, 1947 he was made Director of the Florida Agricultural Extension Service, the position he held until May 31, 1956 when he retired. H. G. Clayton married the former Miss Harriet Ray, of Tampa. The Claytons have one child, Peggy, who is now Mrs. Peggy Clayton May, and two grandchildren. As Secretary to the State Agricultural Ad justment Administration Committee, a mem ber of the State Defense Council, Chairman of the State USDA War Board during World War II, he rendered outstanding service to Florida agriculture by arranging for the pro curement and proper distribution of vital agricultural supplies and by stimulating farm people to extraordinary effort in war crop production, in buying U.S. War Bonds, in salvage drives, and in other activities con nected with the war effort. Through his knowledge of Florida agricul ture, his careful study and understanding of the functions of all agencies concerned with agriculture, and his persistent efforts to work in close harmony with all agencies and groups, he has been instrumental in bringing about effective working relationships between these agencies and groups for the maximum service to Florida agriculture and the solution of major agricultural problems. While serving as district agent, he was ac tive in promoting 4-H Club work and in co operation with the state 4-H Club agents he helped to start the state's 4-H camping sys tem, which today is outstanding in the Nation. From 1947 he served as Administrator to the State Soil Conservation Board. He was appointed to this position by two different boards since the State Soil Conservation Board was completely reorganized by the 1953 Legislature. He served as Chairman of the State Seed Certification Advisory Committee. He was a member of the Farmers Home Administration State Advisory Committee, He was a member of the State Agricultural Stabilization and Conservation Committee, He collaborated with Florida Forest Serv ice and Soil Conservation Service in a weather modification evaluation study. During his service as Director of the Flori da Agricultural Extension Service the number of county agents increased from 61 to 66. (Florida has one county which is not classi fied as an agricultural county.) The number of assistant county agents has increased from 18 to 54; the number of home .demonstration

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18 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 agents from 41 to 52, and the number of as sistant home demonstration agents from 9 to 22. The total staff of specialists has been in creased from 14 to 33. Mr. Clayton's wide knowledge of and service to horticulture in Florida is reflected again by the fact that this increase in . specialists' services covers every phase of horticulture in our state. Mr. Clayton has for many years been a faithful member of this Society and a regular attendant and keen observer at its meetings; learning the needs, problems, views, of people actually engaged in various horticultural enter prises; using his knowledge and his ability to strengthen and direct the Agricultural Exten sion Service for the common good. Always modest-never once grasping for spotlight or for front page-devoted to Florida, her horticulture, her agriculture, her farm youth-never asking for anything for himself other than an opportunity to serve others always trying to see the other fellow's point of view. A person whose soundness of judgment has been recognized by those at the highest levels in our state government and institutions. A man who has by both precept and example rendered outstanding service to this Society and to Florida horticulture. Always a gentle man-a person of highest character-who has in every way measured fully to the highest standards of honorary membership in this dis tinguished Society.

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COHEN: TRISTEZA DISEASE 19 INJURY AND LOSS OF CITRUS TREES DUE TO TRISTEZA DISEASE IN AN ORANGECOUNTYGROV~ MORTIMER COHEN State Plant Board Gainesville Suon after the discovery of tristez a in Florida , it became apparent that careful study over an extended period of tim e would be necessary to assess accurately the amount of damage done by this disease and to make predictions regarding future losses. In July 1952, th e refore, a large grove near Winter Garden in which many trees with tristeza had been found, was mapped tree-by-tree , by a group of Plant Board inspectors. In the mapping, trees were rated on the following scale: 0-Healthy 1 -Slight decline 2 -Moderate decline 3 -Severe decline X-Dead or missing R-Replant tree Infected trees in this grove are of mature size and are not stunted . The large size of the trees and the observable spread of disease in the planting are taken to indicate that the disease was brought in by natural means, probably by aphids, rather than through in fected budwood. This is in contrast to the situation in other parts of the state where the majority of infected trees apparently had tristeza virus introduced with th e original bud. 1 /The Information reported in this p aper Is no t due to the effort s of a s ingle individual but i s the result of the cooperative work of many individuals now or formerly on the Plant Board st a ff . Among the people whose efforts have materially aided in the coll e ction and assembly of the data presented in the pap e r are : J. N . Busby, K. E. Bragdon, A . C. Cr e ws, L. W . Holley, Dr . L. C. Knorr, Mrs. Enid Matherly, John Perry, C. R. Roberts, Mrs. Jean Smith , Howard Van Pelt. This grove has been mapped twice a year since July 1952, the last mapping having been completed in July 1956. The entire area included in the study is shown in Figure 1, which also provides a graphic comp a rison between th e condition of the grove in July 1952 and in July 1956. The entire grove are a consists of about 80 acres. Approximately 20 acres, planted entirely to Temple oranges on sour orange stock, a re not included in our statistical summary because many trees in that portion of the grove showed signs of de cline from water damage in 1954 and it was desired to restrict the study, as much as possible , to the effect of tristeza only. The remaining 60 acr e s consists of 4169 trees, of which 88 per cent are Temples on sour orange rootstock , mainly 26 to 30 years old. Also in the grove are 297 Valencia trees on sour orange stock, about 200 trees on grape fruit stock, and a small number for which th e rootstock is undetermined. Properties owned by 4 different individuals are included in this 60 acre block. It should be stressed that this is not a n e glect e d planting but that normal practices of cultivation and fertilization are being follow e d. Figure 1 shows only trees rated 2, 3, X or R, that is , tre e s in definite decline, missing or replanted. Tre e s rated 1, those in slight de cline, are not included, because slight symp toms are som e time s due to transient causes and not to tristeza. This map contrasts trees affected in July 1952 (shown as O's) with the large number of additional trees affected by July 1956 (shown as X's). The many trees which went into serious decline in the 4-year int e rval betw ee n the 2 mappings can be clearly se e n. All portions of the grove were not affected e qually. Some of the older areas planted with Temple orange on sour orange stock were the most severely affected

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Fii . 1. Spread of disea s e in an orang e g rove near Winter Garden from July 1952 to JuJy 1956. Map sh ow s tr ee s in moderate or s ev e re decline, dead, mi s s i ng or repl an t e d . Trees with s li g ht symptom s of decline are not shown. All tre e s a re of the Templ e or a nRe var i ety e x cept for the ind i cated block of V a l e nc i as . X "' 0 0 X 0 0 r 1x 0 X 0 0 Ji 0 X X 0 0 X X I I X 0 0 0 X X 0 0 X 0 N 0 0 0 0 0 X 0 0 X 0 I 0 X X X 0 X 0 0 X X 0 X X X X 0 X 0 X X X X 0 X 0 X X X Q I IX X X X 0 X X X X 0 0 0 0 X X 0 X X 0 0 X X 0 X 0 O O O 0 X 0 X X 0 0 X O 0 X X 0 X 0 -~ 0 0 X X X 0 X 0 X X X .( X 0 X 0 0 0 0 0 X X X X X X 1. X X X X X X X X X X X X 0 X X X X X Y. 0 0 X X 0 0 X X X X X X 0 X X X X 0 > X X X X X 0 X X X X X 0 0 X X X ' 0 0 0 X 0 0 00 X X X 0 X X O OX X X 0 X X X X X O 0 0 000 X X X X X X O X X XX X X 0 X X X X X 0 X X X 0 X XX OX X X 0 0 0 0 0 0 X X 0 X 0 XO 0 0 -,,'Ixxxxxxox 0 0 0 X :( X X 0 X X X X X X X X X O 0 .f!",c.," X X X X X 0 X X X X X X X X X X 0 X 0 X X X X X X O X 0 0 ,:>'it"& .. 0 X X XO X X X 0 0 X X X 0 X X X X XX 0 0 0 X 0 0 0 0 X X <)'Q-., X X X XX X X 0 X X X 0 X X 0 0 X X 0 X X X X X X X X X X X X 0 X 0 X X I X XO X 0 X 0 Y. X X X X X X X X X X X X X X X X X X X X 0 0 X X X XX X X 0 X X 0 X 0 X 0 X X XX X X XO X 0 0 0 X X 0 X X X X X X ,0 0 0 X 0 0 X X I O X X X X 0 X X 0 X 0 X X X 0 X X X 0 X X X X X C XX X X 0 XX X 0 X X 0 0 X 0 0 0 X 0 0 " 0 XX X X O O X 0 X o o 0 . 0 "' X 0 X X X X X 0 X X 0 y X 0 X 0 X X X X X l 1 X X X 0 X X X X 0 X x x o X X XX OX X X X 0 X X X l X X X X X X X X X . X X X X X 0 I 0 0 XO X X X oo x oo x X X X X O XX X 0 I X X X X o o xxo X XX X 0 X X X X X X X X 0 X X X 0 X X X XX XX X 0 X X X X O 0 IX X 0 0 X 0 X X X X X X X X X X X X X 0 X 0 X X u X X X X xo xxx xx X 0 X X X X X X 0 ' X X X X X X 0 xoxxxx 0 0 0 X X 0 X X X X 0 X X X X 0 0 X 0 0 X X 0 X XX X X X X X X X X X 0 XX xxxxo xx x I X 0 0 oxxoooox 0 X X X X 0 XO O 0 X X X X X X X X XO X X X X X 0 0 0 X X X X XO X X X X X O X X X 0 X X X X 0 X O O 0 o xxxx x X O X X X I X 0 XX X 0 X xxooo xxo X X X 0 0 0 0 X X X xooo x x oo 0 I X X X 0 X x o xxoxoo X X O XX X X O O X X X 0 0 X X X XX X X I XI I I.X IX x ox XX 0 X XI X I. I O X 0 XXX XX 0 XX X 0 0 0 X 0 XIX X x o xxxxxxx 0 X X O 0 xoxx X xoo 0 X X X X ll X 0 XX X X X X 0 0 0 0 0 o x x x xxox xxxx oxo X XX X X X X 0 0 X X X r. XX 0 X X X XO X X XX X XX X 0 0 0 I X X X X X 0 X O X X X l 0 X X X X X X X x X i X l 0 X 0 B&rn X X 0 0 0 0 0 X 0 X XO X X 0 X X 0 MA P : 0 Tree:, i n d ec lin e, de ad , mi s ain g or rep lan t ed i n J u l r , 1 952 X A d d it i on al a f fe ct ed by Ju ly, 1 956 t,,j 0 "':l t"" 0 ::d ...... t:J > en t-3 > t-3 t_:rj P:1 0 ::d t-3 ...... n c:::: t"" t-3 c:::: ::d > t"" en 0 n ...... t_:rj t-3 ~ '"< ...... co C)l en

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COHEN: TRISTEZA DISEASE 21 hut the eastern portion of the area studied was not as badly affected as the middle por tion. Trees in the Valencia _orange block, which is thoroughly infected with psorosis as well as tristeza, were not as severely injured, on the average, as trees in the Temple blocks. The western-most planting consists of Temple trees which are approximately 8 years old. A relatively low proportion of these trees showed symptoms of decline. . nc. 2 TTi.EI.5 RATtO 2, 3, X AJ'D ft IN AN O~.lGF. CC\lNIT 6Rr"IVI rROH JULY 1"'52 TO JUL\' 1"5'• Most striking is the relative absence of disease in all trees on grapefruit rootstock. These are located in some of the rows direct ly south of the Valencia block. This situation is discussed below. 't.~lR, " T!'J:U l~CO lCOO 9C() ""' 700 600 2C'O 100 r.ryc_:.;,;Ar:E ()f A:.L TJ>.::?:! ,o :o The increase in the number of trees in de cline from 1952 to 1956 did not come about abruptly, but was the result of a steady trend, as is shown diagrammatically in Figure 2 where the number of trees in classes 2, 3, X and R at each mapping is indicated by a line graph. Trees in class 1, those in slight decline, are not included in this graph. The Jtrtr DEC, JULY 1"~2 llJH fli, AUG, ~:Al!, AUC, .JAN, JLTLY i,~._ 1'!55 ll,5~ TABLE 1 DISEASED, MISSING, AND REPLANT TREES IN AN ORANGE GROVE NEAR WINTER GARDEN NUMBER OF TREES CLASS OF DECLINE PERCENTAGE DEAD OR TOTAL OF ALL DATE SLIGHT MODERATE SEVERE MISSING REPLANTS AFFECTED TREES July 1952 285_ 186 22 19 107 619 14.8% Dec. 1952 360 173 160 27 100 820 19.6 July 1953 241 201 267 30 135 874 .20.9 Feb. 1954 452 264 235 37 137 1125 26.9 Aug. 1954 444 298 220 137 213 1312 31.4 Mar. 195~ 1540 307 66 7 346 2266 54.3 Aug. 1955 393 209 227 127 365 1321 :n.6 Jan. 1956 433 196 251 175 327 1382 33.1 July 1956 .385 158 220 269 479 1511 36.3

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22 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 total number of trees in classes 2, 3, X and R increased from 334 in July 1952 to 1126 .in July 1956. Thus 27 per cent of all trees in the grove were in definite decline or missing, dead, or replanted by July 1956. If this rate of increase of diseased trees continues for the next 4 years, July 1960 will see 46 per cent of all trees in the grove in this category of seriously affected trees. It is interesting also to compare the num ber of trees in all classes during the succes sive mappings from 1952 to 1956 as shown in table I. The major increase in "total trees affected" during this period is in replant trees and trees dead or missing, but the num ber of trees in intermediate stages of decline has also remained at a higher level than was observed during the first two mappings. In March 1955, a three-and-one-half-fold in crease over the previous reading in the num ber of trees in slight decline was recorded. The count occurred after a relatively dry win ter. The transient nature of this apparent de cline is indicated by the fact that most of these trees were again rated as healthy in the subsequent 3 mappings. If one projects the data in Table 1 to July 1960, and in cludes also trees showing slight symptoms of decline, it will be found that 57 . 8 per cent of all trees in this grove will have been af fected by the end of 4 more years, provided the present rate of increase in the number of trees in decline continues. What is the evidence that these trees are suffering from tristeza disease? Numerous trees have been examined for the presence of honeycombing-that pattern of tiny holes in the bark below the bud union which has proven to be quite reliable in Florida as a field test for the presence of advanced tris teza in trees on sour orange rootstock. A high proportion of the trees examined have shown this symptom. A more specific method for determining if plants are suffering from tristeza disease is the histological examination of the bark from the bud union of suspect trees as described by Schneider ( 1). Bark samples collected at random from 33 trees in decline in the grove were examined using this method. Of the 33 trees examined, 30 were found to be positive for tristeza. Six of the histologically tristeza positive trees were indexed on key lime seedlings, and all 6 were found, by the transmission test also, to be carrying the tristeza virus. It is interesting to contrast the results of these histological tests with similar tests made on trees in the 20-acre area previously men tioned as having been excluded from the study because its trees had suffered from water damage . Bark samples from 11 trees in decline in the water-damage area were examined and IO of these were found to be negative for tristeza. . It is quite clear, therefore, that, in the 60 acres under study, tristeza was the major cause of decline. On the basis of this evi dence it can be estimated that upwards of 90 percent of the diseased trees studied were injured by tristeza disease. When trees in this grove once begin to deteriorate, they do not recover, but con tinue to decline and eventually die. This can be seen by observing the fate of trees found in decline when the grove was first mapped in July 1952. Figure 3 summarizes the in formation on all the trees rated as being in slight, moderate, or severe decline in July 1952. Of a total of 483 trees in all categories in 1952, 294 were dead, missing or replanted by July 1956, and 396 trees or 82 . percent were more seriously in decline than in 1952. As might have been expected, more of the trees at first judged to be in slight decline Rating ln July 1 1/~ G or fr te.s t(.ite
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COHEN: TRISTEZA DISEASE 23 proved to have been affected by a temporary condition , and a higher proportion of these trees showed recovery. If the 203 tr ee s which were found to be in moderate or severe de cline are consid e red alone, it is seen that 189 trees or 93 percent were more seriously in decline in 1956 than in 1952. The fact that trees in decline generally do n ot improve but continue to decline further is an additional indication that tristeza is re:1ponsible for the condition of the grove. It is enlightening , in this connection, to com pare the fate of trees in that area of, the grove which was affected by water damage with trees from an area in which tristeza was the prime dise a se factor. In a portion of the water damage area in August 1954 , 274 trees were rated as showing some degree of decline. Two years later only 22 percent of these trees showed any det e rioration; some of these, no doubt, were suffering from triste za. On the other hand, in a comparable area in another part of the grove where no wat e r damage had been noted and where 180 trees were in decline in August 1954, 52 percent of the trees had deteriorated by July 1956 . When tristeza was first found in Florida, most pathologists expected to see a repetition of the damage done in South America. One of the warnings issued by pathologists was to avoid planting citrus on grapefruit root stock because it , lik e sour orange rootstock , had been found in South America to make a combination non-tolerant to tristeza. After extensive examination of Florida citrus groves, however, State Plant Board inspectors have not been able to find any trees on grape fruit rootstock which were in decline be cause of tristeza infection. \Vhen th e grove in this study was examined, it was found th a t the bud union on about 200 trees h a d a con figuration which indicated that the rootstock was grapefruit rather than sour orang e . These trees have been watched since 1952 and it is of intere s t to examine Figure 4 which is a map of the portion of the grove containing the trees on grapefruit rootstock. Figure 4 shows both the rootstock and tree condition in August 1955. Trees on grap e fruit rootstock are mixed in with trees on sour orange rootstock thus providing an excellent comparison of the behavior of trees on these two rootstocks under identical environmental conditions . Ev e n a c asual e xamination of l-" L O. 4 cor :Dl Tl ()l,i OF ti v.,;S 1N A PLANTI NG OI i NI Xi:.D S:. U H OWIGi: AN D GIL\Pl.fl! U l? ROO T STOC KS AUCUS1' 1 9SS f. o otsto~k: Q-c.,.•~rnd.t. Li O.,,bt.t\'1 Trff Conditiori: H-.l.t.h7 l Slight. O.Cllne 2 Moderate 0.C:Uae J S.r1ou• Dkl1n• X DNd or JU .. 111, .. ...,... Figure 4 will reveal that very few of the trees on grapefruit rootstock are in decline while a very high proportion of the adjoining trees on sour orange rootstock are diseased. Bark samples were taken from 9 of the grapefruit trees which did show some sign of decline, and were examined microscopically. None of the specim e ns was found to have histological indications of tristeza. These observations do not prove that citrus trees on grapefruit rootstock cannot be in jur e d by tristeza in Florida , since these trees may eventually show tristeza injury, but it is very apparent that grapefruit cannot be con sider e d to be in the same class as sour orange insofar as susceptibility to tristeza in Florida is concerned. On(; of the purposes for undertaking the study of the grove near Winter Garden was to explore the possibilities for predicting fu ture outbreaks of tristeza in Florida. To carry out this aim, two small plots containing 58 trees in all were set up for special study of trees on sour orange rootstock. Trees in one plot had Valencia orange tops , and Temple orange tops were used in the second plot. Bark samples have be e n taken periodically from tree s in these plots and prepared for microscopic examination . In the course of this study, 6 previously healthy trees in these plots have developed histological symptoms of tristeza. These histological symptoms were evident from six months to 2 years before ther e was any visual indication in th e field

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24 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 that these trees were diseased. This confirms the observations made by Schneider ( 1) on trees with quick decline disease in California. Thus, a toor actually is available for short time prediction of future deterioration of citrus trees from tristeza disease. Since it is obvious that histological symp toms of tristeza must be preceded by en trance of the virus into a tree, a number of healthy-appearing trees were indexed on key lime seedlings to determine if any of them were carrying the virus of tristeza. In this way it was hoped the interval between the introduction of the virus and the first ap pearance of histological symptoms could also be approximated. This phase of the work has produced most surprising results. So far, 21 trees in this grove which are histologically normal have been checked by transmission test for the presence of tristeza. Of these, 15 trees or 71 percent have been found to be positive for tristeza. Furthermore, 4 out of 5 trees on grapefruit rootstock which were similarly indexed proved to be carrying tris teza virus although, as previously mentioned, there is no indication, in Florida, that trees on grapefruit rootstock are injured by this disease. If the foregoing sampling of the trees in this grove can be considered repre sentative it must be concluded that about three quarters of the healthy-appearing trees in this grove are carrying the virus of tristeza. The most surprising aspect of this project is that only one of the trees tested has so far shown histological signs of tristeza disease, although a few of these trees are known bv indexing to have been carrying the virus f~r almost 3 years, and most of the trees are known to have been infected for almost 2 years. It should be mentioned that similar virus-carrying susceptible trees, which appear healthy and do not show histological signs of tristeza, ' have been found elsewhere in Orange county, and a few have been found in other counties in the state ( 2). The signi ficance of this finding is not fully under stood. It may be that the virus has an ex tremely long incubation period before it be gins to affect the phloem of the host tree. (Phloem breakdown is one of the earliest fea tures of the histological picture of a tree in decline with tristeza disease). Another citrus virus disease with an incubation period of many years is already known-psorosis disease -but it has not been suggested previously that 'this might also be the case with tristeza. A second possibility is that an additional fac tor as yet unknown, in addition to the virus indexed, must be present before the disease can begin to run its course. In any case, this matter is being studied actively, and con tinued observation of these trees certainly should throw more light upon the problem. The above considerations should not ob scure the central fact that tristeza disease in Florida has caused serious losses to citrus. Although this paper describes conditions in a single grove only, many other groves in Orange county and elsewhere have been damaged by tristeza. At present, many of the factors involved in producing an outbreak of this disease are not understood and cannot be predicted. Growers who plant groves on sour orange rootstock, the only rootstock used in Florida on which trees are definitely not tolerant to tristeza, are risking the life of their planting. Is it wise, therefore, to continue the use of this dangerous rootstock where other rootstocks can do the job safely? LITERATURE CITED 1. Schneider, Henry. 1954. Anatomy of bark of bud union, trunk, and roots of quick-decline-affected sweet orange trees on sour orange rootstock. HiJ 4 gardia 22: 567-581. 2 . Cohen, Mortimer. 1956. Incidence of tristeza virus in Florida in trees not yet showing field symptoms. Phytopath. 46: 9 (abstract).

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SMITH: PHOSPHATE FERTILIZATION 25 EFFECT OF PHOSPHATE FERTILIZATION ON ROOT GROWTH, SOIL pH, AND CHEMICAL CONSTITUENTS AT DIFFERENT DEPTHS IN AN ACID SANDY FLORIDA CITRUS SOIL 1 PAUL F. SMITH Horticultural Crops Research Branch Agricultural Research Service United States Department of Agriculture Orlando In recent years, certain studies ( 4, 10) have been made to explore the i:elation be tween fertilization practices and root devel opment of citrus in the sandy soils of Florida. Those reports were concerned primarily with the effect of nitrogen sources and rates a~d methods of timing on the density of roots ~n the top 5 feet of soil, where the. changes m chemical composition were relatively small. With adequate liming, nitrogen appears to have little or no permanent effect on soil composition ( 10) . The present studies involved deep_ sampli~g in a long-term phosphate expenment m which there has been a large permanent change in the phosphorus status of the soil because of the accumulation of applied phos phate. Previous reports . ( 7, 8) describin_g the results from this expenment for the first 6 vears, failed to show any beneficial response in tree growth, yield, or fruit quality to ap plied phosphate. No additional data on these factors are presented here, but the results through the 13th year are still essentially the same. The present report is concerned with the density of small roots, soil pH, and cer tain chemical constituents in the soil in rela tion to the rate of phosphate fertilization. EXPERIMENTAL METHODS Pineapple orange trees on Rougl~ lemon stock were planted on a virgin plot of ground in a random block experiment in 1942 and certain plots have never received any phos1/This study wns made possible by the ge!'ero'!s cooperation of Loren H. Ward of Orlando, Flonda, m whose grove the experiment lies. The technic~l a~ sistance of G. K. Scudder. Jr.. and G. Hrnc1ar 1s gratefully acknowledged. phate. The soil is a transitional type between Lakeland and Eustis fine sands, previously identified as Lakeland (7, 8). The plan fol lowed is to apply 0, 1, 3, and 8 units of P 2 0.,, respectively, to different plots for each 4 units of nitrogen used . There are six 12tree plots for each phosphate level. The P.0, comes from 20 percent superphosphate, and compensatory amounts of gypsum are given so that all plots receive the amount of CaSO, carried by the highest level of superphosphate. The highest rate of P 2 0, was the usual com mercial rate at the time the experiment was started, but current recommendations ( 6) call for a drastic reduction. The experimental rates of P,0, described above will be referred to as none, low, medium, and high in discussing treatments. All trees have regularly received 3 applica~ tions a year of a mixed fertilizer containing little or no organic material and no super phosphate. The current mixture is 10-0-10-3 (Mg0) 0.5 (Mn0)-0.5 (Zn0)-0.1 (B,0 a ) ap plied at the rate of 24 lb. per tree per year. Copper also was included for the first 10 years but omitted since. Zinc was applied in spray form only once and that was in the spring of 1954. For the first 9 years the appropriate quantities of superphosphate and gypsum were also applied 3 times a year and to the same area as covered by the mixed fertilizer. From the 10th year on, these materials have been applied all in one spring application. No attempt has been made to compensate for the calcium carried as the phosphate salts, but a relatively high rate of dolomitic limestone has been regularly applied to all plots. In July 1955 eight 2-inch cores of soil were taken from each plot. The most uniform trees were selected, and in most cases only one core was taken per tree. The cores we~e t3:ken at the tree-drip line and to a depth of 5 feet: The samples were taken by depths of 0-6 in., 6-12 in., 12-24 in., 24-42 in., and 42-60 in. The 8 cores of soil for the respective depths

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26 500 400. PPM300. p 200. 100 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 5.0 I LSD t 0.05 (I) ... 02.0. 0 0:: en 1.0 ::E (!) t 0.05 o~-----.__. ..... _ ...... __ _ OLMH OLMH OLMH OLMH OLMH 6.5 6.0 5.5 pH 5.0. 4.5. 25 2 15 PPM 10 Cu 0 I LSD @ 0.05 20 I LSD. o.o, 5 O OLMH OLMH OLMH OLMH OLMH 80 60 P 40. PM MN20. o.~~~~~--,:0-:~~~rn-~T.Tr OLM OLMH OLMH OL LMH 0-6 6-t2 12-24 24-42 42-60 Fig. lwG. Root growth and various soil factors found at different depths (in inches) in an experimental Pineapple orange grove on acid, sandy soil after 13 years of differential fertilization with superphosphate, The symbols O L M H represent zero, low, medium,and high rates of application. Fig. 1 (upper Ielt) total soil phosphorus; Fig. 2 (upper right) concentrations of small "feeder'' roots found; Fig. 3 (center left) soil pH; Fig. 4 (center right) exchangeable potassium; Fig. 5 (lower left) total copper; Fig. 6 (lower right) total manganese. The L.S.D. bars indicate the required difference for significance at the 5% level between any two treatments or depths.

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SMITH: PHOSPHATE FERTILIZATION 27 were composited, screened to remove the fibrous " feeder" roots , and thoroughl y mix e d by rolling on a canvas cloth , and portions were saved for laboratory analyses. Rootlets smaller than a bout 1/16 inch in diam e t e r were sorted out, dried , and weighed. In addition to pH, total amounts of P, Cu, Mn , and Zn were de termined on certain soil sampl e s a fter total digestion in sulfuric-nitric acid mixtur e s. Ex changeable K, Ca, and Mg w e re determined by neutral ammonium acetate e xtraction. RESULTS AND D1scuss10 N Phosphorus status of soil-The values found for total P are shown in Fig. 1. The data are very consistent and show that whil e most of the applied P is held in the top foot of soil, there is a gradual accumulation throughout the top 5 feet. This is in agreement with the findings of Spencer ( 11) that superphosphate gradually distributes itself through the top few feet of soil. Actually, more total P was found than was applied to the plots r e ceiving superphosphate for 13 years. This is doubt lessly due primarily to the fact that the low hanging foliage interferes somewhat with the machine spreading of the superphosphate, and there would be a zone of r e lativ e ly high P just outside the foliage line due to the deflec tion of particles. Sampling in this area showed an increase of 1900 lb. of P per acre through the 5-ft. column, whereas only about 1250 lb. of P had been applied. Thus, the sampling method may also exaggerate th e other effects associated with differential phosphate fertili zation. It is felt , however, that the trends would be indicative of the nature of the re sponses even though the magnitudes might differ somewhat from those shown. Density of feeder roots-The distribution of feeder roots is shown in Fig. 2 . The data are presented as the weight of roots found in a square foot of soil 6 inches deep taken from each depth zone. The total dry w e ights of feeder roots expressed as grams of. roots per square foot column 5-ft. deep are as follows: No phosphate 23.8; low phosphate 21.4; medium phosphate 21.3; and high phosphate 16.3 . It is of interest that Ford ( 3) al s o found 16.3 as an average weight of root s in com mercial groves of this age cat e gory. These soils too, would have been high in phosphate because the grov e s were grown before the general drop in applied phosphate in com mercial groves. While the data in Fig. 2 are Jess consistent than those for th e concentration of P in Fig. 1 , they cl e arly indicate that high-phosphat e fertilization som e how causes a sharp reduc tion in the quantity of feeder roots in the top 12 inches of soil. In the 6 to 12-inch zon e all 3 levels of appli e d phosphate significantly re duced root growth. It is probable that th e effect on root growth is somewhat exagg e rated in the area sampled because of the uneven dis tribution of applied phosphate. Even so, it is difficult to avoid the conclusion that applied phosphate has had no beneficial effect on root growth in this exp e rimental grove. Th e de pression of root growth below 12 inches is not statistically significant, but the trend is still present to the 42 inch depth. Even to the 60inch depth there is no suggestion of increased root growth as a compensation for the reduc tion in growth at the shallower depths. Since tr e e size, appearance, and yield records do not yet reflect the density of roots as measur e d h e r e , it remains to be se e n whether such a reduction is a definite handi cap to the tr ee . No explanation is offered as to why superphosphate depresses root growth, but th e effect is somewhat similar to that found with a high rate of ammonium ni trate (4). Soil pH-Increased acidity at all soil depths was associat e d with the use of superphosphate. Fig. 3 shows the pH values found at differ ent depths in r e lation to treatment. In the two upper sampling depths there is a grad uation in pH v a lues corresponding to treat ment. At th e 3 lower depths, there was little or no differ e nc e among the pH values for the 3 rates of superphosphate, but those for the plots that r e ceived none were appreciably higher. Superphosphate is not a simple material as it contains a mixture of phosphatic salts, gyp sum, iron and aluminum oxides, silica , and trace quantiti e s of several other substances. It is mildly acidic and gives a pH reading of about 3 wh e n mix e d with water. The acid ulating e ff e ct of superpho s phate on most soils is of little or no practical significanc e b e cause of th e buff e ring action of the soil. How ever, with very sa ndy soils of low exchang e

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28 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 capacity and high rates of application, addi tional liming apparently is required to offset the acidifying effect of superphosphate. The effect of superphosphate in lowering pH is particularly evident in the top 12 inches of the soil and corresponds to the area of maxi mal phosphate accumulation and maximal de pression in root growth. Yet it appears doubt ful that there is a simple cause and effect re lation between pH and root growth. Previous studies ( 10) in which the pH was varied in this same general range, but without super phosphate as a variable, showed no depres sion in root growth due to lowered pH. Like wise, studies with different levels of phosphate in solution cultures did not show any adverse effect of high phosphate on root growth ( 2) . Thus, while it is not yet established what causes the depression in root growth, it is ap parent that superphosphate does not have a beneficial effect on soil reaction. Effect of phosphate level on exchange K, Mg, and Ca-There was practically no effect of phosphate treatment on the extractable quantities of the three base elements (K, Mg and Ca). The only difference of consequence was the tendency for more K to be retained in the upper depths where the greatest amount of phosphate had accumulated in the soil ( Fig. 4). Mg values were virtually identical at all depths in all treatments and the respec tive total pounds per acre in 5 ft. of soil were no phosphate 340; low phosphate 321; me dium phosphate 349; and high phosphate 330. Ca showed a slight, but irregular and non significant, increase _ with values of 1176, 1090, 1307, and 1290 lb . per acre for the same respective treatments. This Ca trend was not accentuated in the upper soil depths where the phosphate accumulation was the greatest. Effect of phosphate level on the total amounts of Ctt, Zn, and Mn-There was no significant effect of phosphate level on the total amounts of any of these metals found in the soil. The concentrations of Cu and Mn are shown in Fig. 5 and 6. Zn showed a mean value of 19 p.p.m. in the top soil and about 8 p.p.m. in all lower depths regardless of treat ment. These re~ults are in harmony with the results found in a topsoil sampling 5 years pre viously ( 8). Both Zn and Mn show increases as a result of continued use of these elements in the fertilizer. No Cu was applied during the interval, and Cu status of the soil is vir tually unchanged. GENERAL D1scuss10N Several studies (1, 5, 7, 8, 11, 12) have shown that phosphate accumulates in Florida citrus groves. Removal of this element by the citrus crop is not large, being about 0 . 5 lb. of P per ton of fruit (9). Application of super phosphate does not markedly increase the ab sorption of phosphorus by the tree in ordin ary acid, sandy Florida grove soil (7). The evidence thus far fails to show any beneficial effect of applied phosphate on citrus in this State except in a few cases, such as on muck soil or very light sands where the content of native phosphate is very low. Wander (12), studying soil factors in re lation to presence or absence of liming, noted that a phosphate differential existed in the topsoil and concluded that the greater reten tion of Mg and Mn in the limed plots was due to the absorptive capacity of the accumulated calcium phosphate, The present results, in ad dition to previously published data ( 8), fail to show any relation between large phosphate accumulations and the retention of Ca, Mg, Mn, Cu, or Zn. Thus, it appears possible that the effect noted by Wander was not attribu table to phosphate but to pH. Liming probably retarded the losses of phosphate, Mg and Mn for the same reason rather than through the indirect method postulated. It might be expected that phosphate ac cumulation would also result in greater Ca accumulations in the soil, particularly if there was a reversion to calcium phosphate. How ever, neither exchange Ca nor total Ca (7, 8) is appreciably changed. The work of Spencer ( 11) offers an explanation since he found that most of the phosphate accumulated in Florida sandy grove soils is in the form of iron and aluminum phosphates rather than calcium phosphate. SUMMARY Soil samples to a depth of 60 inches were taken in a Pineapple orange grove on an acid, sandy soil after 13 years of differential fer tilization with superphosphate. Data derived from these samples showed that ( 1) the largest increase in P was in the top 12 inches of soil, but some increase was noted at all

PAGE 46

FEDER AND FELDMESSER: BURROWING NEMATODE 29 depths, ( 2) the total weight of "feeder" roots in the 60 inches was nearly one-third less in the high phosphate plots than where none was applied, ( 3) appreciable acidity was im parted to the soil by the superphosphate, par ticularly in the top 12 inches, and ( 4) there was somewhat more exchangeable K found as a result of increased phosphate but the ex changeable Ca and Mg were unaffected and there were no differences in the total amount of Cu, Zn, or Mn regardless of treatment. None of these findings can be construed as being highly beneficial to the culture of citrus. LITERATURE CITED 1. Bryan, 0. C. The accumulation and availability of phosphorus in old citrus grove soils. Soil Sci. 35: 245-259. 1933. 2. Chapman, H. D. and D. S. Rayner; Effect of various maintained levels of phosphate on the growth, yield, composition, and quality of Washington navel oranges. Hilgardia 20: 325-358. 1951. 3. Ford, H. W. The influence of rootstock and tree age on root distribution of citrus. Proc. Amer. Soc. Hort. Sci. 63: 137-142. 1954. 4. -----, W. Reuther and P. F. Smith. The effect of nitrogen on root development of Valencia orange trees. Proc. Amer. Soc. Hort. Sci. (MS sub mitted for publication). 5. Peech, M. Chemical studies on soils from Florida citrus groves. Fla. Agr. Exp. Sta. Tech. Bull. 340. 1939. 6. Reitz, H. J., et al. Recommended fertilizers and nutritional sprays for citrus. Univ. of Fla. Agr. Exp, Sta. Bull. 536. 1954. 7. Reuther, W., F. E. Gardner, P. F. Smith and W. R. Roy. A progress report on phosphate fertilizer trials with oranges in Florida. Proc. Fla. State Hort. Soc. 61: 44-60. 1948. 8. Reuther, W., P. F. Smith and A. W. Specht. Ac cumulation of the major bases and heavy metals in Florida citrus soils in relation to phosphate fertiliza tion, Soil Sci. 73: 375-381. 1952. 9. Smith, P. F. and W. Reuther. Mineral content of oranges in relation to fruit age and some fertilization practices. Proc. Fla. State Hort. Soc. 66: 80-86, 1953. 10. Smith, P. F., and W. Reuther. Preliminary re port on the effect of nitrogen source and rate and lime level on pH, root growth, and soil constituents in a Marsh grapefruit grove. Proc. Soil Sci. Soc. Fla. 15: 108-116. 1955. 11. Spencer, W. F. Phosphatic complexes in the soil. Ann. Rpt, Fla. Agr. Exp. Sta. p. 193, 1952; p, 218, 1953. 12. Wander, I. W. The effect of calcium phosphate accumulation in sandy soil on the retention of magnesium and manganese and the resultant effect on the growth and production of grapefruit. Proc. Amer. Soc. Hort. Sci. 55: 81-91. 1950, STARTING AND MAINTAINING BURROW ING NEMATODE-INFECTED CITRUS UNDER GREENHOUSE CONDITIONS WILLIAM A. FEDER AND JULIUS FELDMESSER Fruit and Nut Crops Section and Nematology Section Horticultural Crops Research Branch Agricultural Research Service United States Department of Agriculture Orlando The current nematode research program requires the use of large numbers of burrow ing nematode-infected citrus seedlings as well as a large and reliable supply of burrow ing nematodes. Large numbers of infected seedlings are needed for the chemical screen ing program and for various biological studies and other fundamental work. Obtaining suf ficient burrowing nematodes from naturally infected grove trees requires a great deal of time and labor. A method of raising and main taining. burrowing nematode populations on citrus in the greenhouse was, therefore, de vised. Studies, which will be reported elsewhere, indicate that the bu~rowing nematode will infect and reproduce readily in citrus seed lings growing under normal greenhouse con ditions in Florida. It was also found that grove subsoil, turned up while digging for nematode-infected roots, contained many small nematode-bearing root fragments, and that citrus seedlings planted into this soil in pots under greenhouse conditions were read_ily infected and supported a burrowing nematode population. These observations were utilized in guid ing the construction of two drained concrete soil tanks. These concrete block tanks were constructed on a 4-inch thick, poured con crete slab and the soil-bearing portions had inside dimensions of 10' x 4' x 2' and 16' x 4' x 2', respectively. The bottom of the soil bearing portion of the tank is raised one block width above the concrete slab and is con structed of '•" No. 9 expanded metal resting on cross bars of 2" x 2" x }4'' angle iron. The metal surfaces are all coated with red lead

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l 30 FLORIDA STATE HORTICULTURAL SOCIETY , 1956 primer and asphalt paint to reduc e rusling and corrosion. The completed tank is hown in Fig. 1. Fig. 1. Inside of soil tank showing cross support5, expanded metal bottom, and a portion of the walls~ In filling the tank with soil a 2-inch layer of W' lime rock was first poured onto the ex pand ed metal bottom. Sterilized field soil was then placed on the lime rock layer to a depth of 4 inches. FinalJ y, the r ema ining space in the tank was filled with th e required num ber of yards of subsoil taken from beneath tre es known to harbor the burrowing nem atode in their roots . This so il was brought from th e grove in closed metal garbage cans to avoid contamination of citrus plantings enroute. The soil in the tank was wet down and tamp ed and allowed to settle for a few d ays. Seedlings of Rough lemon and Duncan grapefruit and seeds of both these varieties were th en planted in the tank in rows , and th e rows were marked \vith planting date and type of material planted. These plantings wer e watered caxefully to avoid water damage and were cultivated and fertilized in a routine manner. It was found that the small root fragments , \ hich see mingl y contained the bulk of nematodes found in the subsoi l , did not wash clown upon watering, but in stead, some worked to th e surface of the soil, if watering was excess iv e. It was n ece ssary to push th e m b e low th e surface when this oc c urr ed. Water , which l eac h e d through the soil, was co ll ec t ed in l a rg e pans and examined periodically for the presence of burrowing nematodes. To date, no burro,.,ving nematodes have been recovered from the leaching water. After 6 we ks, burrowing nematode in fected seed lin gs were harvested from the t ank. These seedlings bor e few to many lesions on the roots and a ll stages of th e bunowing nematode were found within the lesions. The sma ll er tank holds about 1,300 growing seed lings when loaded to capacity, and the larger one about 2,100 seed lings. Seedlings usually are grown 3 months in th e tank before they are harvested. This period is sufficient for them to overcome the initial shock of trans planting and to develop an adequate top and root system. D amping off occur infre quently and is con trolled b y a pplications of wettable ca ptan to th e soil between the rows. In order to minimize trap-cropping, a few infected roots are cut up and buried after eac h row of seedlings is dug up. In this manner, an active burrowing n e matode population has been maintained in on tank since January 1956. This population has now survived a winter and a summer in th e tank under normal greenhouse cond itions . Approximately 800 in fected seedlings have been harvested since J an u ary 1956 .

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GRIMM: DIEBACK INVESTIGATIONS 31 PRELIMINARY INVESTIGATIONS ON DIEBACK OF YOUNG TRANS PLANTED CITRUS TREES 1 GORDON R. GRIMM Horticultural Crops Research Branch Agricultural Research Service United States Department of Agriculture Orlando INTRODUCTION Dieback of transplanted citrus trees refers to a progressive dying of a pruned branch or trunk from the cut surface toward the root. It has been recognized in Florida for as long as groves have been planted. Usually the losses from this disease have been minor, but within the past few years they have increased suf ficiently to warrant investigation. Large acre ages have been planted at all seasons of the year, and it has become apparent that losses of young trees from dieback have increased disproportionately with the increased acreage planted. A study of the nature and cause ~f dieback was started by reviewing the methods of trans planting citrus trees. No general agreement was found among growers or nurserymen as to the best method of transplanting. Practices in top pruning the trees varied considerably. Methods of handling, watering, and subse quent care also varied. A diversity of opinion prevailed on the importance of fibrous roots and of the leaves at the time of transplanting. To determine the role of all of the various steps involved in transplanting on the inci dence of dieback, controlled experiments were performed under field conditions. In con• junction with these tests, laboratory isolations were made to determine the microorganisms associated with this disease. 1 /The author wishes to acknowledge the cooperation and donation of citrus trees from Mr. C. F. Fawsett, Jr., of Orlando, Fla, and the following nurseries: Lake Garfield Nurseries Co., Bartow, Fla.; Glen St. Mary Nurseries Co., Winter Haven, Fla.; Grand Island Nur series. Eustis, Fla.; and Ward's Nursery, Avon Park, Fla. PROCEDURES AND RESULTS Temple orange and Glen Navel orange on Cleopatra mandarin rootstock, }i and ~, inch in diameter, were used in transplanting tests to determine the effect of top pruning, the ab sence of fibrous roots, and defoliation. Trans planting experiments were begun in Novem ber and March at the U. S. Department of Agriculture experimental farm 7 miles west of Orlando, Florida. Each experiment was com posed of eight treatments with eight trees each replicated four times, making 32 trees per treatment ( table I). Each treatment was a combination of three separate operations; e.g., the trees for treatment I had branches, fibrous roots and leaves; those for treatment 8 had their branches, fibrous roots, and leaves removed. Branched trees were pruned to leave 4-to-6-inch branches; the trees without branches were pruned to trunks approximately 16 inches high; all fibrous roots and all leaves remaining after top pruning were removed with pruning shears in the groups indicated. The trees were planted with a 5 x 5 foot spacing and the entire area was kept free of weeds. Excellent, good, fair, and poor were used to describe the subsequent growth of the tree. An excellent tree had little or no dieback on the cut branches or main trunk and vigorous sprout growth; good and fair trees had rela tively increased amounts of dieback and rela tively decreased sprout growth; poor trees either had died back far enough to make re placement desirable or were dead. Observa tions were continued until no further changes in growth habit were apparent. Table I shows the numbers of excellent, good, fair, and poor trees within each treat ment for the November and March plantings. As a group, trees with fibrous roots present were distinctly better in both the November and March plantings than those with fibrous roots removed. As a group, trees with branches present were better than trees with branches

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32 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 removed, and trees with leav es present were better than trees with leav es r emoved in the fall planting only. Statistical analyses of both experiments showed the comparisons dis cussed to be highly significant. A third experiment of 3 x 2 x 2 factorial de sign was made to compare en tir e trees ex posed to the sun for l tmd 2Jf hours with trees that were shaded and h ad their roots protect ed from drying b y packing in wet sphagnum moss from the tim e they were dug until transplanted. The influ ences of l eaves and of no l eaves and of a 3-hour delay in watering after planting in comparison with watering at planting were measured within each group. Treatments were made on )~-inch Parson Brown orange trees on Rough l e mon rootstock pruned to a 16-inch trunk and planted June 7, 1956. E ach of the following treatm e nts was replicat ed thr ee tim es with 5 trees each, making 180 tr ees: 1. No sun e~oirnre, le av es on, wat . ~red at plant!r . g 2. " " " " -..Jte.inf; delayed .for 3 hour, ). " " oft, watered &t planting 4. 11 , wat~ri l"lg delayed for 1 hour! 5. l-t/4 h-,ur e xposure , leaves on, watered at planting 6. " " " " " , watering delayed for 3 hciurs 7. " off. waterl!'Ci at plantir B. " , watering d"hyed for ') h ou rs 9. 2-1/2 hour exp o~J1Jr• , leaves watered at planting 1 0 , " " " " ", va~ring_ dfl!l~yed for J hOYrs 11. off, watered at planting 12., 11 , vaterlng dehyed for ) hours Th e tr ees exposed to the sun were laid on cultivated ground; the air temper a ture 3 inches above th e surface was 93 F. and 112 " on the ground surface. All trees were pl a nt ed with a 5 x 5 foot spacing and arrang ed by treatment i n a definite plot design. All were watered on th e day of planting with 6 gallons of water at th e times designated, and every 4 or 5 da ys thereafter during the next 6 weeks as weather conditions required. Table 1. Distribution of trees by growth classes of Excellent, Good, Fair, and Poor following treatments at two planti.ng seasons Treatznentsl/ November ~lantingY March ~lsmt1ng2/ E G F p E G F p Branches present Fibrous roots present 1. Leaves present 24 7 0 l 16 5 5 6 2. Leaves removed 6 11 7 8 17 4 4 ' 7 Fibrous roots removed 3. Leaves present 1 3 24 4 1 2 8 21 4. Leaves removed 0 3 10 19 z 2 5 23 Branches removed Fibrous roots present 5. Leaves present 5 2 10 15 11 2 9 10 6. leaves removed 0 2 7 23 6 6 7 13 Fibrous . roots removed 7. Leaves present 1 3 6 22 2 1 7 22 8. leaves removed 0 0 3 29 5 4 5 18 1/ Eaeh treatment has a total of 32 trees. ?J Temple orange/Cleopatra mandarin 1/2-in. planted 11/9/55. Data taken 2/23/56. 1/ Glen Navel orange/Cleopatra mandarin 5/8-in. planted 3/23/56. Data taken 6/7 /56.

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GRIMM: DIEBACK INVESTIGATIONS 33 Table 2. M?.an inches of dieback and new sprout growth 6 weeks after transplanting Parson Brown orange trees, as influenced by exposure, defoliation, and delay in inHial watering Treatment Dieback S12rout growth in. ino Expos11re to the sun 0 hour 1.58 32053 1 n 4.25*** 17002*** 2 n 5.12*** 3.85*** Le<'l.ires present 3.02 18099 L:-.e.ves removed 4.28* 16.16 Waterfog at planting 3.59 17.63 delayed for 3 hours 3.71 17.97 *Indicate~ statistical significance at odds of 19:1 ***Indicates statistical signifi_cancl:l at odds of 999 :1 The results are summarized in Table 2 in terms of average inches of dieback of the main trunk and average inches of total new sprout growth per tree for the respective treatments. Trees exposed to the sun for u; or 2)f hours prior to planting had considerably more dieback and less sprout growth than trees that had been protected from drying with wet sphagnum moss. Statistically the dif ferences are very highly significant. It should also be noted that trees without leaves at the time of transplanting had significantly more dieback than trees with leaves at the time of transplanting. Time of initial watering did not affect the amount of dieback or sprout growth of the trees in this experiment Preliminary observations on the effective ness of various pruning paints for the control of dieback were made during February, March, April, and May on sweet orange trees with various amounts of top pruning and de foliation. De-Ka-Go, Carbolineum, and pastes of Zineb, Orthocide, and neutral copper were applied to the cut surfaces immediately after pruning and before the trees were dug at the nursery. The treated trees were planted at random with non-treated trees and compari sons were made in the same planting. Only 6 percent of the trees showed measurable dieback, and this seemed to occur regardless of the presence or absence of wound paint. Several fungi and an unidentified bacterium have been isolated from trees affected with dieback. However, investigations to date have not shown any one organism to be consistently associated with dieback. Colletotrichum gloeo sporioides was isolated from 60 percent of the trees; Diplodia natalensis, Phomopsis citri, Fusarium spp., and bacteria were isolated from 10 to 30 percent of the trees. DISCUSSION Field observations and experimental data indicate that dieback of transplanted citrus trees is largely a result of mishandling the trees at some point during transplanting. Transplanting citrus trees involves many op erations such as pruning, digging, transporting, planting, watering, and fertilizing and any one or all may be done carelessly enough to injure the tree. Environmental conditions at the time of operations, such as temperature, humidity, wind and water, and soil characteristics may also have direct influences on the success of transplanting. The presence of healthy fibrous roots and their protection from drying at all times have

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34 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 proved to be important for vigorous tree growth, which apparently provides the best defense against dieback of transplanted citrus trees. The presence of leaves can have a marked influence in preventing or checking dieback of the tree. It is not uncommon for dieback to proceed down one side of a limb or trunk on which no leaves are present and to stop on the other side at the first leaf. Exactly how a leaf stops dieback is not known; it may be only by sustaining healthy tissue through the normal leaf functions. Even though the leaves are lost shortly after planting, they may be beneficial to the tree during transplanting. In the third experiment, trees with leaves during exposure to the sun lost their leaves 2 or 3 days later, yet they had significantly less die back than trees without leaves. From the data obtained thus far it would seem advisable to top prune trees only mod erately, maintaining 4-to-6-inch branches. This was particularly true for fall-planted trees, which were larger and stronger, and had less dieback 4 months after planting. Incidental observations have shown that the advance of dieback down a branch is often checked tem porarily and sometimes permanently at the crotch. A causal organism of dieback cannot be en tirely ruled out. However, the fact that a tree has less dieback because of the presence of fibrous roots, leaves, and branches, coupled with the fact that at present no one organism has been isolated consistently from all die back trees, suggests that good transplanting methods offer the best control of this disease. It is evident that durin'g transplanting of citrus the entire tree, particularly the fibrous roots, should be protected from drying at all times. Once the tree has been s e t in the grove it should be watered at planting and again the second or the third day afterward; and, in Central Florida sandy soils, every 3 to 5 days thereafter for the first few weeks as weather conditions require. SuMMAHY Dieback and new sprout growth of young transplanted citrus trees were measured in re lation to ( 1) top pruning, ( 2) defoliation, ( 3) root pruning, ( 4) exposure of the entire tree to the sun before transplanting, and ( 5) de layed watering after transplanting. The pre liminary results indicate that dieback may be a result of injurious transplanting operations. Healthy fibrous roots were shown to be very important for vigorous tree growth and to constitute one of the best defenses against dieback. The presence of leaves appeared to be beneficial in limiting the amount of die back, especially in fall-planted trees. Investigations to date give no definite in dications that fungi or bacteria are primary causal agents of dieback. THE POSSIBILITY OF MECHANICAL TRANSMISSION OF NEMATODES IN CITRUS GROVES A. C. TAHJAN Florida Citrus Experiment Station Lake Alfred The somewhat phenomenal spread of the burrowing nematode, Radopholus similis . (Cobb) Thome, in recent years has been at tributed to subsoil drainage ( 3), to the move ment of the nematode itself, and to the ac tivities of humans ( 4). This latter means of Florida Agricultural Experiment Station Journal Series. No. 529. dispersal of the organism has been imple mented mainly by the widespread dissemina tion of infected citrus nursery stock and other cultivated plants. It generally has been as sumed that various implements and mechan ical devices also play a role in the spread of the burrowing ' nematode as in the case of certain other plant pathogenic nematodes ( 1, 2, 5). Although shovels, cultivators, and mobile harvesting machinery have been im plicated, it was suspected that bulldozers were mainly responsible. The "pull and treat" program ( 6) of the Florida State Plant Board,

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TARJAN: TRANSMISSION OF NEMATODES 35 which is accomplished by the destruction of burrowing nematode infected citrus and sub sequent soil treatment with DD soil fumi gant, uses bulldozers for elimination of desig nated trees. The machines enter the groves, fell the trees and place them in piles for burn ing. If infested soil and infected roots were capable of being picked up and transported, the bulldozers, with their undesired cargo, might be assigned on the following day to either clearing virgin land for future groves or pushing out old or undesirable trees to make way for a new planting. In either case it was assumed that nematode inoculum might, in this manner, be disseminated to non infested land. With the cooperation of Mr. Charles Pouch er, Florida State Plant Board, Lake Alfred, and the various contractors involved in clear ing infested grove sites, a study was under taken to determine (I) if bulldozers and cul tivators were carrying soil and debris. infested with nematodes, ( 2) the relative kinds and frequency of occurrence of these nematodes, and ( 3) whether clods of soil and debris in fested with burrowing nematodes might be suitable inoculum for infecting potted citrus plants. The vast majority of the sites visited were groves affected by spreading decline, but in a few cases noninfested groves were also inspected. Soil, including roots when avail able, was scraped off bulldozer tracks and was obtained also from various locations on the "dozer" body. Samples thus obtained were stored in pint jars, returned to the laboratory, and processed for nematodes. During the course of this study, 63 samples were collected from 23 different groves in Lake, Polk, and Orange Counties. Genera of nematodes identified are listed in Table I while the relative abundance of nematodes in each of the samples is shown in Table 2. Nematode genera with saprozoic or preda tory feeding habits comprise the longest list in Table I. There were additional genera of this group that were not identified principally because only spear-bearing nematodes were of primary interest in this study. The bulb and stem nematodes, Ditylenchus spp. were the most numerous among the plant parasites found. Although many species of this genus are not parasites of higher plants, it has long been suspected that other species are capable of inflicting serious root damage. Likewise, in the "Suspected Plant Parasite" group, the genus Dorylaimus probably contains species that are plant parasites as well as those which are predatory in feeding habit. Data in Table 2 shows that most of the samples obtained yielded from 26 to 75 nema todes and that in no case did a sample fail to yield living nematodes. This is especially signi ficant when it is taken into account that the major part of this survey was conducted in the winter and spring months of 1956 during an extended drought. Occasionally a sample consisted of only a small number of apparent ly desiccated roots and soil which was scraped off the body of the bulldozer, while at other times the sample was found packed under pressure in crevices in the tracks and had to be forcefully pried out. In one case, the machine operator had finished for the day and in an attempt at disinfestation had sprayed the tracks with diesel fuel, a substance which has been assumed to be nematocidal. The soil sample, obtained about one hour after the spraying, yielded numerous active, apparently healthy nematodes when processed in the laboratory the next day. Ironically, the only time that Radopholus similis was obtained was from a sample taken from a machine pushing out apparently healthy grapefruit trees for purposes of re planting with orange. The imposing list of plant parasites shown in Table I disproves the conception that such nematodes cannot possibly survive in soil clods or debris exposed to air and sun. Where, in the case of certain plant parasites, adequate moisture is needed to prevent desiccation, matter containing adequate moisture can be found tightly packed on the bulldozer tracks. In one case, a bulldozer being transported by truck was intercepted about two miles from the grove site in which it had been working. As expected, numerous nematodes were ob tained from the soil samples collected from the machine. Although the foregoing data proved that certain machinery is capable of. disseminating nematodes, the question remained whether inoculum thus translocated was capable of in stituting an infection at a new location. Con

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36 FLORIDA STATE HORTIC~LTURAL SOCIETY, 1956 sequ en tly tests were conducted on potted seedlings simulating actual conditions as clos e l y as possible. Thirty 9-month-old grapefruit seedlings growing in auto clav ed soil in 46 oz. cans were divid ed into five lots of six plants eac h. These were placed evenly in l arge flats of au to clav ed soil, so that only th e upper fifth of the can projected abov e the so il. Thi s was done to maint ain as constant a soil t e mp era ture as possible within the c ans . Inoculum consisted of finely cut citrus feeder roots which were moderately infected with burrowin g nema t ode s. In simulating th e physical stat e of p o tential inoculum as it had been obs e rved on . the bulldozers , various combinations of in fected roots, mashed citrus fruit, cl ay, and soil were mixed and shaped b y h and into Table 1. Genera of nematodes found in soil collected from bulldozers Plant Parasites Tylenchulus (1) !/ Radopholus (1) Tylenchorbynchus (2) Criconemoides (1) Tylenchus (6) Ditylenchus (18) Meloidogyne (1) Dolichodorus (4) Hemicycliophora (1) Pratylenchus (12) Trichodorus (3) Hoplolaimus (2) Rotylenchus (3) Belonolaimus (1) Tylenchidae (2) !l/ Suspected Plant Parasites Aphelenchoides (31) Paurodontus (1) Dorylaimus (11) Xiphinema (3) Tylencholaimus (3) Pseudhalenchus (5) J;/ Belondira (1) Nothotylenchinae (1) !l/ !/ Numeral indicates frequency of occurrence. Ef Identified only to family or sub-family. J;/ New genus-technical descriRtj)on currently being prepared. Saprozoltes and Predators Rhabditis (17) Diplogaster (5) Acrobeles (8) Cephalobus (2) Tripylidae (1) !l/ Diplogasteroides (2) Rhabditol.aimus (1) Monhystera {2) Alaimus (1) Prismatolaimus (1) Acrobeloides (2) Discolaimus (2) Mononchus (2) 1lilsonema (2) Eucephalobus (2) Pleotus (l} Aporcelaimus (l} Chiloplacus (1) Cervidellus (1) Aphelenchus (10)

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TARJAN: TRANSMISSION OF NEMATODES 37 Table 2. Relative n1ll!lber of n emat odes recovered from soil samples. No, of N e matodes 151 or mo re 76-150 26-75 11...25 10 or less none Frequency in S'1.l'lr, les 12 13 22 8 8 0 sma ll clods . All of these inoculum combin at ions were either placed on or parti a lly im b ed ded in the soil contained in the cans some of which had been watered immediately prior to inoculation. This was don e to approximate th e condition where infest ed materi a l had e ither fallen from a bulldozer to the ground or ha_cl b een push ed into th e ground by the machme tracks. wat er ing the soil in some of t~e cans _ simulated rainfall prior to inocula tion. After the inoculum was introduced water was applied to thos e cans which had not been pre-wett ed . One flat was plac ed in a room provided with artificial illumination, a constant t e mperatur e of approximately 78 F. , and a rel a tive humidity which averaged about 80 percent during hours of illumination and 95 to 100 p er cent in total d arkness . Two flats were plac ed outside ex posed to sunlight, while another flat was placed in th e partial shade of a slat house. A control flat containincr plants which had r ece ived combinations of nematode-free citru s roots, citrus pulp, clay a nd soil was placed outside expose d to weath er conditions. Plants were harv este d and screened for bur rowing nematodes by th e root incubation technique (7) approximately 10 weeks after this experiment was initiated. It was found that only plants which had been protected from exposure to direct sunlight, i .e. those placed ,in the constant temp era ture room and those placed in th e slat hous e, becam e in fected with burrowing nematodes . It did not appear to make any differ ence whether the plants were water ed prior to or after inocula tion, wh e th e r the inoculum r este 'cl on o r was inserted in the soil, and wheth e r the inoculum was combined with clav cru s hed citrus fruit, soil, or any combinatio;/ of these. These results, although d erived from t e sts with potted seedlings, indicat e that situations co uld aris e in th e field wh e re nematode infected inoculum might be carried into non infested land, come into contact with th e soil in a shad ed area prior to or following a rain, an d could institute an infection of host plants growing in th e imm ed iate vicinity. SUMMARY A survey was und e rtaken in which soil and root samples wer e obtained mainly from the t~acks of bulklo~ers e mplo yed in eradicating citrus grov es afflict ed with spreading decline. Tl_1is surv ey w~s co nd ucted mainly during the wmter and sp rmg months when the citrus area had rec e iv ed a minimum rainfall. Sixty three soil and root sampl es wer e collected from tw e nty-thr ee groves in Polk, Lake, and Orange Counties. Fourteen different genera of known plant para s itic nem a todes includ ing Raclopho lu s simili s, the burrowing nematode, were identified. Experiments wer e conducted in which burrowing nematode infect e d citrus roots in combination with cla y, crushed citrus fruit, and soil were introduced into pots con taining 9-month-old citrus see dlings. After inoculation , these plants were ei ther expose d to sunlight or plac ed in shaded areas. Only in th e latter case did plants incur burrowing nema tod e infections. It is con clud ed that mechanical e quipm e nt such as bulldozers are c,ipable of transmitting n e matodes which, under th e proper conditions, can institut e in fections of citrus. LITERATURE CITED 1. de Carvalho, J. C1 1953 . Dityl enc hus des tr uctor !:t.TA~~ifi1t~:tet 3 t~ 6 \~f 4 ~rtado da Roland a. Rev. 2. Courtn ey, W. D. and H. D. Howell. 1952. In vestigatio n s on the Dent Grass Nematode, An g uina Agrost i s (St ei nbuch, 1 799) Filipjev, 19a6, U . S. D ep t . Agr. , Pl. Di s. Rptr. 36 (3), 75-83. 3. DuCharme, E. P. 1955. Sub so il Draina ge as a Factor in th e Spread of the Burrowing Nematode. Fla. State Hort. Soc., Proc . 68 : 29-31. , 4. Sima!'ton, W. A. 1 956. How Has Spread,in g De cline of Citru s Spread? Sunshine State Agr. R es. Rpt. l (3): 5, 7 . ~ Steiner, G.,. A. L. Taylor, and Grace S. Cobb. 19ol. Cyst -fo rmmg Plant Parasiti c Nematod es and their Spread in Comm erce. Helm . Soc. Wash . Proc 1 8 (1): 13-1 8. ' . Suit, R : F., E. P. DuCharme, a nd T. L . Brooks. l 9aa. Effe ct 1v e11ess of the Pull-and-Treat Me t hod for Controlling the llurrowin g Nematode on Citrus Fla State Hort. Soc., Proc. 68 : 36-38. 7. Y_oun g, _T. W. 195 4. An l'ncubation Method f~r Collectmg M11,ratory Endo -para s it ic Nematodes U S Dept, Agr., Pl . Dis. Rptr . 38 ( 11) : 794 795. . . .

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38 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 TRANSMISSION OF TRISTEZA VIRUS BY APHIDS IN FLORIDA PAUL A. NonMAN Entomology Research Branch THEODORE J. GRANT Horticultural Crops Research Branch Agricultural Research Service U. S. Department of Agriculture Orlando The mild tristeza virus was transmitted from Temple orange trees to Key lime test plants by two species of aphids in preliminary experimental work ( 16) . The green citrus aphid (Aphis spiraecola Patch) gave positive transmissions to 9 of 128 test plants and the melon aphid (A. gossypii Glover) to 1 of 26 plants. Higher ratios of infection have been obtained in recent tests with the combined use of controlled sources of inoculum in several varieties of citrus seedlings, multiple-branched Key lime test plants, larger numbers of aphids per plant, and timely observations to detect initial symptoms. This n:port presents results obtained with this improved technique. It in criminates the black citrus aphid (Toxoptera aurantii ( Fonsc.) ) as a vector, and describes tests with other insects and mites, so far neg ative, as vectors. Studies of Meyer lemon trees as sources of inoculum are also discussed. ., METHODS In order to establish tristeza virus in plants of different citrus varieties, two Key lime plants (T 1 and T2) were selected as standard sources of the virus inoculum. These plants had been infected in March 1953 as a result of aphid transmissions from a stunted Temple orange tree on a red lime ( Rangpur type) rootstock ( 16). Green citrus aphids were transferred to these plants after they had fed on the Temple orange for 116 hours, 75 to the T1 plant for a 1-hour transmission feeding period and 30 to the T 2 plant for 23 hours' feeding. Both these Key lime plants have been used in other pathological investigations ( 8) and the readions on the Key lime are consid ered typical of the mild tristeza virus in Florida. Leaf pieces from the T 1 and T, sources were used to inoculate greenhouse-grown citrus seedlings. The Valencia and Florida sweet seedlings were considered to be nucellar, and the Temple oranges were sexual seedlings selected for characteristics of the parent varie ty. Presence of the tristeza virus in these plants was confirmed by retransmission with leaf-piece transfers to Key lime plants. The in fected Valencia and Florida sweet seedlings were transplanted to a field and the infected Temple orange plants were kept in pots in a screen-house. Individual plants were re checked by leaf-piece inoculations into Key lime plants for proof of continued presence of the virus in the young growth at the time of each acquisition feeding by aphids. In the previous tests ( 16), in the present tests with the black citrus aphid, and in studies of Meyer lemon as a source of virus, small Key lime plants 8 to 12 inches high with single stems and 25 to 150 aphids were em ployed. In the other tests healthy Key limes 18 to 20 inches high were cut back or the tops bent over to stimulate rebranching, and col onies of 300 to 700 aphids were used. Pathological investigations had indicated that the optimum time to observe initial symp toms of vein clearing associated with the mild tristeza virus was 20 to 40 days following tis sue inoculation. In insect-inoculated Key lime . plants 30 to 60 days following infestation was found to be the optimum period. Thereafter the symptoms might diminish, especially under summer conditions in the greenhouse. Initial symptoms did not always occur on all branches. The branches showing symptoms were tagged so that they could be observed frequently and used for testing retransmission by means of leaf inoculations into Key lime plants. Isolated aphid colonies of single species were placed on young, succulent growth of healthy citrus seedlings and allowed to feed for 24 hours, since previous tests with other species ( 3, 5) had indicated that such feed ing would free them of tristeza virus. The young shoots with the aphids were then trans

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NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION 39 ferred to the infected seedlings that had been previously tissue-inoculated and tested, and the aphids were allowed to move over voluntarily. After a 25-hour period to acquire the virus, aphids on shoots from the infected seedlings were placed on the multiple-branched Key lime test plants in separate cages at the labor atory. Again the aphids were allowed to move over voluntarily. 'At the end of 24 hours counts per unit of leaf area were used as a basis for estimating the total number of aphids present on each test plant. Representative aphid spec imens were collected for positive identifica tion. The test plants were sprayed twice with 0.04 percent nicotine sulfate before they were transferred to , the greenhouse. TESTS WITH GREEN CITRUS AND MELON APHIDS The results given in table 1, from tests carried out in March and April 1956, show that the green citrus aphid transmitted the virus from three varieties of infected citrns seedlings to Key lime plants. All test plants infested with melon aphids became infected. The proportion of successful transmissions by both species was much higher than in the previous tests ( 16) . ,eedliD(• to multiple-branched Key phnt,. So\ll'ce or Iaoeuhm Number or J.phia, per Number of Tut flapt.f Va1-ncia P'lorlo.a , ... t TaQple Test Plant Infested 11\ftC:lid Grun citrus aphids JOO 400 JOO 400 l.:tlOP aphids 700 In these tests initial symptoms of tristeza were detect e d on one or more branches of the test plants 5 to 6 and, in one case, 8 weeks after inoculation . New young leaves of in fested branches showed distinct vein clearing and a veinlet pattern that frequently faded as the growth matured. After the initial vein clearing symptoms disappeared, some leaf cupping and deficiency signs remained. Pres ence of th e virus in all aphid-infect ed plants was confirmed by tissue transmissions to ad ditional Key lime plants. TESTS ~ ' ITH THE BLACK CITRUS APHID One positive transmission of histeza virus was obtained in five tests with the black citrus aphid. In this test 25 alate adults and nymphs, all reared from one adult, were given an ac quisition feeding period of 48 hours on an infected Valencia orange scion grown on a potted Key lime rootstock in the greenhouse. The transmission feeding period was 4 hours. Presence of the virus in the aphid-infected Key lime test plant was confirmed by leaf-tissue transfers. The identity of the aphid species was confirmed by Louise M. Russell, ~f the Entomology Research Branch. This is the first record of positive transmission of tristeza virus by this species. MEYER LEMON As A SouRCE OF TmSTEZA Vmus Meyer lemon trees are present in dooryards or small plantings in most citrus areas. Some Meyer lemon trees hav e been found to carry tristeza . virus ( 11, 17 , 20), but investigations in Texas ( 4, 18) indicate that its spread from this host is not common . Because of the wide interest in Meyer lemon as a host, tests were made to transmit the virus from it. Three aphid species were used as vectors. Colonies of 5 to 50 apterous adults were employed. In 16 tests with the black citrus aphid and 21 tests with the melon aphid no transmissions were ob tained. In 107 tests where the green citrus aphid was used, 2 transmissions were secured. In the first positive transmission a Meyer lemon tree at Minneola, Fla., was the source of inoculum. Thirty apterous adult green citrus aphids fed for 42 hours on this tree and 42 hours on the test plant. Scattered but distinct clearing of veins occurred on the young leaves of the Key lime test plant 5 months later. These symptoms became less evident as the leaves matured, and subsequent new growth showed no further symptoms. While these transmission tests were being car ried out, budwood from the Meyer lemon branch that the aphids had fed on was brought to the greenhouse and side-grafted into 5 Key lime plants. All these plants showed strong veinand veinlet-clearing symptoms, which were evident for a longer period and were more distinct than those observed on the Key lime plant infected as a result of aphid inoculation.

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40 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 The Meyer lemon scion on one of th e graft inoculated Key lime plants was allowed to de v e lop , and subsequ e ntly green citrus aphids were fed on it for 24 hours and then trans ferred to two Key lime plants for anoth e r 24 hours. On e plant, on which 75 aphids fed, showed no symptoms, but the other, on which 50 aphids fed, developed transitory leaf symp toms 4 months later . This limited symptom expression of tristeza suggested that either the somce of inoculum contained only a very mild tristeza-virus strain or the aphids had sorted out and transmitted only a portion of the virus strain• mixture. In order to obtain further information, leaf pi e ce transfers and scion grafts were made. The Key limes inoculated with tissue from the Meyer lemon at the end of 2 months showed striking veinand veinlet-clearing symptoms. The Key limes inoculated with tis sues from the aphid-transmitt e d source showed only slight deficiency symptoms and a tenden cy for slight cupping of some l e aves. Three months ft e r the inoculations observations were made for the pr e sence of stem pits. Two plants tissu e -inoculat e d from th e Meyer l e mon so urce had averages of 28 and 100 pits per 10 centim e ters of stem; two of three plants tissue-inoculated from the aphid-infected Key lime sourc e had no pits, and one plant had 1 pit per IO centimeters of stem. These results show that a milder form of tristeza virus was transmitted from the Meyer lemon by the aphids than was transmitted by tissue grafts from the same source, TESTS Wrnr OTHER INSEC T S AND MITES Tests were also made with other insects and mites found on citrus in Florida. The sources of inoculum were tristeza-infected Key lime seedlings. Thus far there have been no positive transmissions. The species tested as vectors, with the number of Key lime plants infested, were as follows: green peach aphid ( M yzus p ers icae ( Sulz.) ) 4, citrus mealybug ( Psemlococcus citri (Risso) ) 49, leafhopper I-! omalodisca triquetra ( F.) 35, blue sharp shooter leafhopper ( Oncometopia imdata (F.) ) 7, big-footed plant bug (Acanthocepha la femorata (F.) ) 14, southern green stink bug (Nezara viridula (L.) ) 29, stink bug Euschistus obscurus (P. de B.) 7, citrus reel mite ( M etatetranychus citri ( McG.) ) 8. TEST PLANTS As A MEASUHE of Vrnus TRANSMISSION Tristeza of citrus was first recognized as a disease of sweet orange on_ sour orange root stock. This scion-rootstock combirrntion was used in initial studies, which showed that the disease is caused by a virus and can be trans mitted by tissue grafts ( 1, 6) and by A phis citricidus (Kirk) (1, 3, 13, 15). As informa tion advanced, West Indian, Mexican , and Key lime plants were employed as means of de tecting this virus (9, 10, 14, 19). The primary symptoms of vein and veinlet clearing and stem pitting on the Key lime plants are useful. Improvements in the pro duction and detection of symptoms on the test plants have been sought as means of ob taining furth e r information on virus transmis sion. In the present investigations the use of standardized sources of inoculum, multi branched K ey lime plants, large aphid popula tions, and observations at critical periods have given high ratios of virus transmission under ea rly-spring conditions. The recovery from initial symptom expr ess ion in the summer sug gests that the Key lime plants are not as good indicators of tristeza virus under high-temper ature conditions. T e mperatur es appear to af fect not only the occurrence of vein clearing on the leaves, but also stem-pitting symptoms, as noted by Grant and Higgins ( 8). The intensity of symptoms on the test plants also varies with the virus strain. Recent patho logical investigations indicat e that the mild tristeza virus in Florida may be a mixture of strains ( 8). By use of the aphid-transmitted mild-virus source plants T1 and T2, and with l ea f-piece transmissions to Key lime plants and successive selections of leaf pieces and trans missions to other Key lime plants, evidence was obtain e d of virus strains that cause many stem pits and some that cause few to no pits. Apparently the tristeza virus strains could exist in varying mixture levels in infected plants. Work in South Africa ( 12) and Brazil (7) has shown that aphids have transmitted a mild form of the virus from trees known to be carrying the severe form, In the present study of Meyer lemon as a virus source, the two transmissions obtained by means of aphids produced notably milder symptom expression on Key lime plants than those obtained by tissue transmission.

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NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION 41 TRANSMISSION OF TmsTEZA Vmus IN CITRUS GROVES The green citrus aphid is the most abundant aphid on Florida citrus. It usually limits its feeding to seasonal growth flushes of succu lent terminals which vary with the citrus variety and rainfall conditions, and its feeding curls the tender foliage. The black citrus aphid, appearing later in the season, feeds on more mature leaves. The melon aphid, although less prevalent on citrus than the green citrus aphid, is also found on young growth. Recent studies in California ( 5) indicate that in four districts where measurements were taken the yearly average number of aphids of all species flying to a single orange tree ranged from 185,725 in the coastal area to 956,238 in the area around Covina and Azusa called the intermediate district. The respectiv'e figures for the melon aphid alone were 3,200 and 35,600. Since the melon aphid is the demonstrated vector of tristeza virus in southern California, it is not surprising that the disease spread most rapidly in the inter mediate district. Green citrus aphids made up more than 85 percent of the aphids caught flying to the orange trees, but neither this species nor the black citrus aphid has been shown to carry the tristeza virus in , California. We do not have comparable data for aphid populations in Florida. However, our studies show that all three species are potential vec tors of the tristeza virus. Each tristeza-infected tree serves as a reservoir from which the aphids can obtain the virus. There are two types of reservoirs ( A) an infected tree on a nontolerant root stock as sour orange which shows decline symptoms and produc~s delayed, weak flushes of new growth; and ( B) a tree on a tolerant rootstock which has apparently healthy growth but carries the tristeza virus. The latter is a more dangerous source of the virus, be cause the succulent flushes of new growth are suitable for aphid feeding and transmission of the virus at the time other normal, healthy trees are flushing. The visibly diseased trees ( type A) seem to be less dangerous sources of inoculum because of their 10-day to 2-week delay in producing new flushes of growth that are less vigorous. _ In California Dickson et al ( 5) reported that the rate of spread of tristeza in the groves seldom exceeded two new infections each year from each diseased tree. They noted, how ever, that the most rapid spread was generally in the intermediate area where most orchards were ruined commercially about five years after the disease was first reported in them. This area had the largest number of flying aphids. In Florida the visible spread of the disease has been greatest in a Temple orange grove where all trees were reported as being on sour orange rootstock. Actually some were growing on tristeza-tolerant rootstocks and it is be lieved that these trees have served as more favorable reservoirs of virus for aphid trans mission than the visibly diseased trees on sour orange rootstock. The more infected trees available, the great er is the chance for aphids to acquire the virus and transmit it to other trees. In Florida the number of visibly diseased trees is not always a reliable measure of the number of infected trees, for frequently there are mixtures of rootstocks. Surveys made by the State Plant Board of Florida ( 2) show a widely scattered distribu tion of tristeza-infected trees. These trees serve as sources of virus, and as aphid infesta tions are not usually controlled by present spraying practices, the number of infected trees in the St~te may be expected to in crease. SUMMARY The green citrus aphid was found to trans mit the tristeza virus from infected Valencia and Florida sweet seedlings as well as from the Temple orange variety previously reported. The black citrus aphid was shown for the first time to be a vector of the virus. Seven other insects and one mite species did not transmit the virus. Improved techniques have given high ratios of transmission by the melon and green citrus aphids. The techniques utilize con trolled sources of inoculum in several varieties of citrus seedlings, multiple-branched Key lime test plants, 300 to 700 aphids per test, and timely observations to detect initial symp toms. Transmissions of virus by the green citrus aphid from Meyer lemon produced notably

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42 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 milder symptom expression on Kef limes than tho se obtained by tissue transf ers to Key limes from the same Meyer lemon source. REFERENCES CITED 1. Bennett, C. W., and A. S. Costa. 1949. Tri steza disease of citrus. Jour .. Agr. Re s. 78 ( 8): 207-237. 2. Cohen, M., a nd L. C. Knorr. 19 53. Present status of tristeza in Florid a. Proc. Fla. State Hort. Soc. 66: 20-22. 3 Costa, A. W., and T. J. Grant. 1951. Studies on tr a~smiss ion of the tristeza virus by the vector Aphis citricidus. Phytopathology 41 (2): 105-113. 4. Dean, H . A., and E . ,o_.. _ Olson. _ 19 56. Prelim_in':ry st udi es to determine poss1b1hty of 1n _seet transm1ss1on of tristeza virus in Texas. Jour. R10 Grande Valley Hort. Soc. 10: 25-30. 5 Dickson R. C. Metta McD. Johnson , R. A. Flock, and. Edward F. Laird, Jr. 1956. Flying ap hid populi: tions in southern Californ~a citrus grov~s and ~heir relation to the transmission of the tr1steza virus. Phytopathology 46 (4): 204-209. 6. Fawcett, H . S., and J. M. Walla_ce . 1946: Eviden~e of the virus nature of citrus quick dechne. Cahf. Citrogr. 32 (2): 50, 88, 89. 7. Grant, T. J., and A. S. Costa. 1951. A mild strain of the . tristeza virus of citrus. Ph ytopatho logy 41(2): 114-122. 8 . Grant, T. J., and Richard P. Higgins, 1956. Oc currence . of mixtur es of tristeza virus strains in citrus. Submitted for publication. in Phytopathology. 9. Grant, T. J., A. S. Costa, and S. Moreira. , 1951. Studies of tristeza disease of citrus in Brazil. V. Further information on the reactions of. grap ef rui~s. limes, lemons , and trifoliate hybrids to tr1steza. Cahf. Citrogr. 36: 310, 311, 324-329. 10. Knorr, L. C., and W. C. Price. 1954. Diagnosis a nd rapid determinations of tristezn. Fla. Agr. Expt. Sta. Ann. Rpt., pp. 196-197. 11. McClain, R. L . 1956. Quick decline (triste za) of cit ru s. Calif. Dept. Agr. Bui. 45(2): 177-179 . 12. McCl ean, A. P. D. 19 54. Citrus vein-enation vi rus. So. African Jour. Sci. 50(6): 147-151 13. McClean, A. P. D. ~95~ . Virus jnfections o: citr us in South Africa. Farmmg m So. Africa 25 (293) , 262; 25(294): 289. 14. McClean. A. P. D. 1950 . Possible identity of three citrus diseases. Nature, (London) 165: 767 .768 . 15. Meneghini , M. 1946. Sohre , a na~ureza e_ tra~s missibilidade d a
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DUCHARME AND BIRCHFIELD: PHYSIOLOGIC RACES 43 s itized banana roots. Attempt s to infect th e roots of sour orange seedlings with burrowing nematodes from this location were not succ e ss ful. The burrowing nematod e s from this loca tion, although they would not feed on citru s, could not be distinguished morphologicall y from those causing spr e ading decline. In thi s discussion burrowing nematodes that parasit ized b~~ana but not ,,citrus will be d e signat e d as the banana race. Clumps of banana plants in or n e xt to 39 citrus groves and oth e r clumps in 30 loc a tions where th e re was no citrus wer e e xamin e d . for pr e sence of burrowing n e matod es . In th e 39 locations next to groves, the citrus and banana plants were close enough for root con tact. Among these places examined , burrow ing n e matod e s had parasitiz e d banana but not citrus in 9 locations, both banana a nd citrus in 4, and only citrus roots in 3. No burrowing nematodes were found in the r e maining 23 locations. Of the 30 isolat e d clumps of banana, 13 were parasitiz e d by bur rowing nematodes and 17 were not . None of the parasitized banana plants appeared to b e diseased, wh e reas all infected citrus had s y mptoms of spreading d e cline. These ob s e rvations indicated the existenc e of thr ee physiologic races of burrowing n e matod e s. separable by th e ir ability to parasiti ze eith e r banana or citrus or both. Experiments were condu c t e d under con trolled conditions to test th e hypothesis de rived from observations mad e in th e field that at least three strains of burrowing nematod e s e xist. In the first exp e riment , sour orange seed lings planted in st e rile soil maintained at temp e ratures of 75 to 78 F. did not becom e parasitized when inoculated with th e banan a race of burrowing nematodes. In another e periment , nematode-free banana plants and rough l e mon se e dling s plant e d side b y side in the same cont a iner were inoculated with col lections of the ban a na race and the race causing citrus spreading decline . Th e inocu lated test plants were grown for six months with the soil temperature maintained at 75 to 78 F. The burrowing nematodes from banana infect e d the banana test plants, but not the rough lemon seedlings although th e roots of both plants w e r e intermingled. In contrast , th e burrowii1g nematodes from a grove affected by spreading decline readily parasitized the rough l e mon roots and attack e d the banana roots as w e ll. In anoth e r study , nematode-fr ee sour orang e s e edlings and ban a na plants growing in steam st e rilized soil w e r e cross-inoculated with bur rowing n e matod es from the same sourc e s used in the pr e c e ding e xperiment. The soil tem p e rature was maintained at 75 to 78 F. The burrowing nematodes from banana reinfected banana but not the sour orang e seedlings , and those from a spr ea ding d e clin e affected grove parasitized both the sour orange and banana te s t plants. Th e results of thes e exp e riments confirmed the ex istenc e of two of th e three physiologic races found in . the field. Burrowing n e matodes that cause spr e ading decline ar e physically like thos e of the banana race. Th e averag e length and width of female nematod es from both races was almost identi cal and there wa s no significant difference in th e physical proportions. No morphologic character was found th a t could be us e d to distinguish one physiologic race from the oth e r . Th e two ph y siological races of the bur rowing n e matode (Radopholu-s similis) that h a ve been found in nature have b e en separated cnl y by differeni;es in parasitic activity on citrus and banan a . The e xistence of a possible third rac e , found in th e field on citrus only, was not studied in the laboratory exp e riments undertak e n. It is lik e ly that other physiological races of this nematode can be d e tected by using addi tional sp e cies of host plants. Burrowing nema todes collected from several kinds of orna mental plants failed to parasitize citrus in ex ploratory tests, possibly becaus e they may b e similar to the ban a na rac e . On the other hand, w e know that th e ph y siologic race causing spreading declin e will infect P e r s ea am e ricarw Mill., (avocado); Malpighia glabra L. , (Bar b a dos ch e rry) ; H e dychimn coronarium Koen ig , ( ging e r lily) ; and Musa paradisiaca var. sapient11m Kuntze, ( common banana in Flori d a ) . At present it is not known how many ph y siological races of th e burrowing nematod e are involved in the spreading decline diseas e of citrus, but th e existenc e of such races could expbin some of the variation that occurs in the sev e rity of disease e xpression among af f e cted grov e s. In the search for r e sistant citrus rootstocks , it will be nec e ssary to test prospec tiv e plants against diff e rent populati o ns of

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44 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 burrowing nematodes from numerous loca 0 tions. Since one of th e physiological rac es para sitized both citrus and banana, it becomes necessary to determine which race is present before deciding whether or not infect ed ban ana or other plants should be considered po tential r ese rvoirs of infection for citrus. Until there is some practical way to distingui s h thes e races , it is nec essa ry for growers to take ut most precaution to avoid introducing any bur rowing nematodes by planting infest e d orna mentals in or next to citrus groves. Th e exist ence of physiologic races of burrowin g nema todes do es not minimize th e gravity of the spreading decline problem. CITRUS ROOTSTOCK SELECTIONS TOLERANT TO THE BURROWING NEMATODE HAHHY w. FORD Florida Citrus Exp erime nt Station Lake Alfred Th e purpose of this pap e r is to report the evaluation of certain rootstock mat e rial that seemed to show resistance to spreading d cline. Spreading decline caused b y the bur rowing nematod e Radopholus simili s (Cobb) Thorne (7) gen era lly affe c ts all citrus root stocks us ed commercially in Florida. B e tween 1951 and 1955, a total of 54 trees were found that appeared healthy although surrounded by decline trees. Th e trees were report ed by Ex p e riment Station p e rsonnel , ex tension workers, production managers, growers, and inspectors of the Florida State Plant Board. Most trees were eliminated as possible burrowing nema tode resistant candidates after a pr e liminary inspectio n , A few trees showed potentialities worthy of intensiv e study for burrowing nema tode resistance. METHODS The feeder roots of each tree recommended for study were sampled for the pr esen ce of the burrowing nematode by the root incuba tion technique suggested by Young ( 10). A feeder root distribution pattern was compiled for comp a rison with a repr esen tative standard for healthy trees. The method of root sampling is described in another pap e 1 ( 4). Trees were accepted as candidates for th e test program if the root profile compared favorably with that of a healthy tr ee even though burrowing nematod es were found associated with the roots. Forty-four of the 54 candidates were eliminated by this test. Florida Agricultural Experiment Station Journal Series No . 55 1. Ten tre es were entered in the test program. The sw eet orange scions of two trees were sus pected as the source of the tolerant factor and were th erefo re included in the test program and coded sweet oranges E and F. Two trees were se ed ling sw ee t orang es and were coded swe et oranges G and H. On e tree was a seed ling of Cl eo patra mandarin and coded Cleo patra I. The rootstocks of four of the tr ee s ap peared to be rough lemon and were coded rough lemon . The abbreviated designations were RL-A, RL-B, RL-C, an d RL-D. The rootstock of the l ast candidat e was unidenti fiable as a common citrus s pecies and was coded Clone X. In order to obtain test material, roots of the d es ir e d tree were sev ere d and both cut ends of each root lifted above the surface of the ground and ti ed to stakes . . Five to 40 per c e nt of the severed roots of rough lemon and five to 12 percent of sweet orange stocks pro duced sprouts. The sprouts were p e rmitted to grow until eight to 15 expanded leav es were present. The sprouts were removed and cut into leaf bud cuttings by severing the stem above and below tq e bud with prunin g shears. Henceforth the t erm cutting will be used in this report to indic a te a rooted leaf bud cutting in which the bud has dev e loped into a leafy shoot. The propagating procedure is con tained in a separat e report by Ford ( 3). Root sprouts of promising candidates hav e been topworked to older citrus trees to obtain seed to determine if the nematode tolerant factor is seed transmitted. The following tests were performed to eval uate the material: I. A candidate rootstock clone was first evaluated by compiring the growth of six cuttings plant ed in sub-soil in

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FORD: CITRUS ROOTSTOCK SELECTIONS 45 fested with the burrowing nematode and six cuttings in non-infested citrus grove sub-soil. Separate 1.25 gallon containers were used for each cutting. The containers were placed in a water cooled temperature tank that maintained the soil temperature at 78 F. The plants in each container of decline soil were inoculated three times with burrowing nematodes ob tained from different commercial groves. The cuttings were permitted to grow for three to six months depending on rate of growth and time of year. II. Six Clone X cuttings were planted in containers filled with steam sterilized soil. Two hundred hand picked burrowing nema todes were placed on the roots of each plant and permitted to develop for six months. III. Six months old cuttings of RL-A, RL-B, and Clone X were budded with Parson Brown, Valencia, and grapefruit scions by using a patch bud technique ( 2). Three to six months after budding, the plants were tested for growth and nematode infestation in the tem perature tank. IV. Sweet orangy E and sweet orange F were budded on susceptible rough_ lemon seed lings to determine if nematode tolerance in the roots could be induced bv the scion of a budded tree. V. Twelve cuttings of RL-A, RL-B, and Clone X were grown in decline sub-soil to determine the influence of N and K on the population of burrowing nematodes. Two levels of N and K in factorial combination were applied as nutrient solutions twice weekly for four months. The following concentrations in ppm were used: N, 25 and 200; K, 0 and 300. Also, 24 cuttings of Clone X were di vided into two groups. One group was planted in burrowing l}ematocle infested soil and the other in non-infested soil. Each group was sub-divided into two groups of six plants each to which two levels of N were applied. Nitro gen at 25 and 210 ppm in the nutrient solu tion was applied twice weekly. VI. The ability of the nematode to pene trate the feeder root, lay eggs and reproduce was determined by an aceto-osmic staining procedure developed by Tarjan and Ford ( 8). Rooted leaf-bud cuttings of clones RL-A, RL B, and Clone X were planted in sterilized soil in separate petri dishes with a one half inch sr1uare of No. 41 Whatman filter paper under the root tip. Twenty-five female burrowing nematodes in 0.3 ml. of watel' were placed on the root tip and covered with a layer of soil. The inoculated roots were stained and cleared, after two to 26 days at 78 F. under artificial light, so that nematodes and eggs could be seen inside the roots. VII. The number of eggs in the cortex and Table 1. Root distribition of the parent tree of selected root stock clonp,s as coml)ared to susceptible roueh lemon, Rootstock clone Feeder roots in indicated 10 inch depth zones 0-10 10-20 20-~0 30-:\P tJ0-20 20-6:> Clone X 9.2 11,2 16.0 12.6 8.8 5.9 Rough lemon B 1.9 .9 6,0 E.4 3.6 1.6 Ilcui.:;h lemon C 3.0 1,2 1.9 .5 .2 .1 Rouch_ lemon n .3. 9 2.2 4,1. .3 .3 .9 .3 b Rowh lemon ...........__ __ (Ched:) I 7 2,1 5 .3 4,3 3.7 2.0 a Mean of 4 sa,ri~les to a depth of 5 feet expressed as !'Tarns dry wei::-:ht in a col1.L'7l!l. one foot squ.
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46 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 stele of the feeder root of Clone X as com pared to RL-A was determin ed by comparing single roots from a cutting of each clone placed tog e th er in a petri dish. Fift y female burrowing nematodes were placed b e tw een the two roots and incubated for four days after which the roots were stain ed and cleared. VIII. From October 1955 to January 1956, fruit samp] es were coll ec ted from the Parson Brown scion of Clone X and compar ed with Pai '.so n Brown on rough lemon . Measure ments were made of int erna l fruit quality. Ap pearanc e and palatability were evaluat e d by a panel. '.l'able 2, Growth and E,. similis population of cuttincs from selected root stock clones after 3-4 months in temperature tank~ Clone Rouch lemon .".. Rough lemon B .~ ourh lemon C Rough lem,on D Sweet Orange i: c S t ,-_ F'c wee -1.1.ange _ Sweet Orance Gd Sweet Oranre 1:d C Cleoi: , atra I se
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FORD: CITRUS ROOTSTOCK SELECTIONS 47 Table 3. Growth and R. s:unilis population of Clone X cuttings in steam sterilized _soil~ated with 200.E. silnilis per plant.a Treatment 3 months 6 months Shoot growth Shootratiob Number Shoot growth Shoo:tratioDNumberc Root R, silnilis Root R. similis c:m. c:m. ner cuttin1:1 ner cutt-:i,.,,. Inoculated 21 .9 2 :t. 2 49 .9 1 Untreated 19 .9 47 .8 a Mean of 6 plants from separate containers. b Fresh weight of shoot divided by fresh weight of roots. c Pl.ants removed from containers and roots incubated in fruit jars for 48 hours. RESULTS In Table I feeder root measurements of the parent trees of four rootstock candidates grow~ ing in decline soil are compared with the root density of trees on ordinary rough lemon in non-infested soil, Rough lemon B had a root density comparable to a healthy tree to a depth of five feet while Clone X had three times the root density of ordinary rough lemon. The growth and burrowing nematode in festation of cuttings taken from 10 candidate rootstock clones is shown in Table 2. Shoot growth of RL-A and RL-B was reduced seven percent by the presence of the burrowing nematode. Both rough lemon clones supported a population of burrO\ , ving nematodes com parable to spreading decline susceptible rough lemon. There was no reduction in shoot length or root weight of Clone X when grown in burrowing nematode infested soil and the population of burrowing nematodes was re duced to a very low level in all replicates of the test. Nematode survival and plant growth when 200 hand picked burrowing nematodes were placed on the roots of six individual cuttings of Clone X in sterilized soil are shown in Table 3. After six months, the burrowing nematode population had disappeared from the roots of 50 per cent of the cuttings and one to three nematodes were found on the roots of the remaining plants. There was no depression of growth by the burrowing ne matode. The effect of a budded scion on nematode survival and plant growth of RL-A, RL-B, and Clone X is presented in Table 4. Growth com parisons between grafted combinations of the different clones are not entirely valid because all of the tests were not performed at the same time. Growth of grapefruit and Parson Brown scions on RL-A was reduced 10 and 18 per cent respectively. The Valencia bud on RL-B was taken from the parent tree of RL-B so that the budded combination was genetically the same as the original tree in the field. This combination showed a 10 percent reduction in growth. The growth, of cuttings of Clone X budded with Parson Brown from the original parent tree was not reduced in decline soil and the burrowing nematode population com pletely disappeared. Studies of Ruby Red grapefruit and Temple budded on Clone X were in progress only two months when this manuscript was written. The burrowing ne matode population consisted of two to four adult females. No larvae were present indi cating that the nematode population was not increasing. Sweet orange E and sweet orange F when budded on susceptible rough lemon were retarded in growth 65 percent by the nematodes so that the results are not reported. Unbudded cuttings of sweet orange E and F were also reduced in growth (Table 2). The data indicate that the two sweet orange clones

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48 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 4 Growth and E• population of budded rootstock cuttings~ G raft comScion Soil bination Condition R ootstock Rough lemon A Grapefruit, Infested Non infested Rough lemon A Parson Brown Infested N on infested Rough lemon B Valencia 0 Infested Non infested Clone X ' Parson Brown Infested Non infested Clone X Ruby Red Infested Clone X Temple Infested a Yiean of 6 plants from separate containers. b Incubated in fruit jar for 48 hours. Duration Shoot growth Fresh wt. Number b (months) cm. of plant Jl. sim.ilis {!:!ams l :12er cutting 3 13 21 75 t. 47 14 28 3 35 97 156 :t. 81 43 124 3 26 84 z 23 29 4 29 l12 0 JO 103 2 2 t. l 2 4 c Combination genetically the same as original tree found in the field . do not have nematode tolerant characteristics that originat e in the top of the trees as orig inally suspected. The effect of N and K nutrition on nema tode infestation of the host has a ttracted the attention of several workers ( 1 , 5, 6). Oteifa ( 5) found that nutrition was of considerable importance in determining th e development time of root knot nematodes Meloidogyne in cognita. Nitrogen and K levels had no significant e fect on the burrowing n emato de population of RL-A, RL-B , and Clone X so that the r esu lts are not reported. The growth of Clone X cut tings was modified, by incr ease d N and K, from that reported for citrus in sand culture ( 9). Additional studies are in progress t o eva luate the effect of nutrition on growth of Clone X cuttings. The effect of N level on grow th of Clon e . X in infested as compared to non-infested citrus grove sub-soil is shown in Table 5. Shoot growt h was not affected by the burrowing ne matode infest ed so il condition at either of the two N levels. Studies of burrowing nematode activ it y by staining in sit u indic a t ed that reprodu ction of burrowing nematodes was depressed in the cortex of th e feeder roots of Clone X cuttings as compared with th e cortex of RL-A , RL-B or ordinary rough l _ emo n cuttings. . O casion a lly nematodes penetrated the st e le of Clon e X and after 21 days there was an in crease in the nematod e population. Th ere was no indic at ion of an exit of nematodes from the stele. No burrowing nematodes penet rated the stele of RL-A, RL-B or ro ugh lemon under the conditions of this experiment. Eight y -fiv e tests were made on the rough lemon clon es. Ap parently th ere is a diff e renc e between specie s from th e s tandpoint of burrowing nematodes entering the stele. Nematodes were found in the st e l e of pumm e lo , for exam ple. A d e t ailed comparison was m ade betw een Clone X and RL-A by placing female burrow ing nematodes between single roots from ea ch clone. The results of this test are shown in Table 6. Th e r e were 60 tim e s more eggs in the cortex of RL-A than in the cortex of Clone X. In th e cortex of RL-A eggs were scattered

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FORD: CITRUS ROOTSTOCK SELECTIONS 49 throughout the tissues while in the cortex of Clone X all eggs that could be found were close to the body of the nematode. When ne matodes penetrated the stele of Cl one X, a condition that occurred in 11 percent of the samples, considerably more egg s wer e found per n e matode. A panel of Experiment Station personnel preferred the external fruit app ea rance of Par son Brown on rough lemon to that of Parson Brown on Clone X. However the p ane l pre ferred Parson Brown on Clone X for eating quality. Juice characteristics of Parson Brown on Clon e X and rough lemon are sh own in Table 7. DISCUSSION RL-A was secured from the rootstock of a Valencia orange tree in Lake Alfred that had been in spreading decline infested soil for four years prior to 1951. Dense foli ag e covered th e tree with leaves of normal size which was in marked contrast to adjacent trees with symp toms of spreading decline. The grove was pulled before the burrowing nematode was id e ntified as th e cause of spreading decline. . RL-B, th e rootstock of an 18 year Val en cia tre e from a grove in southern• Polk County was transplanted into spreading declin e soil in 1941. Thus th e feeder roots h ave be en in fested with the burrowing nematode for at least 14 yea rs. The tre e was considerably larg er than surrounding decline trees even though som e feeder root d a mage was d e tected. B e low fiv e feet the root• density fluctuated considerably during a on e year period. The results of growing plants of RL-A and RL-B under controlled conditions in infested soil and inoculation of individual roots in petri dish es indicate that the two rough l e mon clon es are reasonably tolerant to the damage of the burrowing nematode. The number of burrowing nematodes and the d ama ge within th e root cortex of the two tolerant clon es are comparabl e to susceptibl e rough lemon. The nature of the toler a nce of these rough l e mon clones is not understood; how ever , th e rapid rate of shoot growth and development of new feed er root s is probably an important factor. Table 5. Effect of Non ~ro,th and R. similis population of Clone~ cuttincs in inf~ste:l. and r.on infested soil after 3 months in temperature tank~ Trea.tmentb Soil Shoot growth Shoo:tratioc Condition cm. Root Low N Infested 26 1.3 Non infested 23 1.3 High N Infested 29 1.0 Non infested 27 .8 Significance N,S, N,S, a Hean of 6 plants from separate containers. b 25 ppm and 210 ppm of N respectively applied twice weekly, c Fresh weight of shoots divided by fresh weight of roots. d Roots incubated in fruit jars for 48 hours. r-!umber d Ii, similis er cut.tin . 6 . 3 3 . 2 N,S.

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50 FLORIDA STATE HORTICULTURAL SOCIETY; 1956 Table 6. Number of B,. similis and eggs found in feeder roots of Clone X a and Rough lemon A cuttings four days after nematode inoculation . Cortexb Stele 0 Rootstock g. simllis Eggs g. similis Eggs Rough lemon A 10.1 97.2 Clone X 5.2 1.6 .3 9 Significance * ** t.s.D. at .05 .3.1 21.2 'l. Fifty female btn-rowing nematodes placed between a feeder root of Clone X and a feeder root of Rough lemon A in a petri dish. b Mean of .35 replicates in which the nematodes invaded the cortex. c The mean of 4 replicates in which the nematodes invaded the stele. * Statistical significance at 5 percent level. Statistical significance at l percent level. It is conceivable th at the burrowing nematode could damage RL-A and RL-B under poor grove management practices. This possibility will have to be evaluated under field condi tions. At the present time RL-A and RL-B are propagated by cuttings although an evalu a tion of seed propagation is in progress. It is essential that the seed produce a very high percentage of nucellar plants as assurance that the rootstock will be genetically the same as the original parent. Tests for susceptibility to tristez a and xyloporosis are in progress . Clone X, a rootstock that has not been iden tified, is resistant to the burrowing nematode found in citrus groves. The clone is not com pletely immune because nematodes penetrated the feeder roots and in 50 perc ent of th e plants one to . four nematodes survived thr ee to six months. In every test conducted with cuttings of Clone X, the rat e of growth in ne matode infested soil was eq ual to or better than in non-infested soil. L abora tory studies indicated that the resistant factor was con fined to th e root cortex and h ad a detrimental e ffect on the eggs laid by the nematode. The 25-year-old parent tr ee of Clone X was discovered in a grove near Davenport , Florida in 1954. The tree was 16 feet high and yielded six boxes. Root samples taken at the periphery of the tree over an 18 month period were devoid of burrowing nematodes. Feeder roots from the four adjacent trees were al ways found to harbor the nem atode. With th e exception of an area nine feet square near th e southeast corner of the tree, feeder roots of adjacent rough l emo n trees did not penetrate th e dens e root system of Clone X. The re sistance of the feeder roots to the burrowing nematode and the dense nature of th e root system suggests that the stock may a lso b e of value as a biological barrier against th e spread of the burrowing nematode. Fruit of Clone X are not available at th e present time so that all prog eny hav e been obtained from leaf bud cuttings. The clone is more difficult to propagate and grows slower than rough lemon. The leaves appear to be r es istant to anthracnose caused by Colletotri chum gloeosporioides P enz but susceptible to sour orange scab caused by Elsinoe 'Fawcetti Bitancourt and J e nkins. In containers, the roots were more frequently damag ed by excess water than roots of rough lemon. The r eact ion of Clon e X to other diseases

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FORD: CITRUS ROOTSTOCK SELECTIONS 51 such as tristeza and xyloporosis is unknown at present. The stock should be evaluated in the field for general horticultural characteris tics before being recommended for use in Florida citrus groves. SUMMARY Between 1951 and 1955 a total of 54 trees were found that appeared healthy although surrounded by decline trees. Most trees were eliminated as potential burrowing nematode resistant candidates after a preliminary in spection. Ten trees were entered in the test program. The results of growing cuttings of candi date clones in spreading decline infested soil and inoculation of individual roots in petri dishes indicated that two rough lemon clones were tolerant to the burrowing nematode even though a high population of burrowing nematodes was found on the roots. Growth of plants was reduced 10 to 18 percent. A third rootstock, that has not been identi fied, was found to be resistant to the burrow ing nematode infecting citrus groves. Plant growth was not reduced in infested soil and the population of burrowing nematodes al ways decreased and frequently disappeared. The resistant factor was found to be confined to the root cortex and had a detrimental ef fect on the eggs laid by the nematode. The absence of information on general horticultural characteristics, mineral nutrition, tristeza and xyloporosis, indicate that field tests must be evaluated before this clone can be recom mended for planting in Florida citrus groves. LITERATURE CITED 1. Chitwood B. G. and B. A. 0teifa. 1952. Nem atodes parasitic on plants. Ann. Rev. Micro biol. 6 :151-184. 2. Ford. Harry W. 1956. Unpublished data. 3. Ford, Harry W. 1957. A method of propagating 'citrus rootstock clones by leaf bud cutting's. Proc .1 Amer. Soc. Hort. Sci. (In press). 4. Ford, Harry W., Walter Reuther, and Paul F'. Smith. 1957. Effect of Nitrogen on root development of Valencia orange trees. Proc.. Amer. Soc. Hort. Sci. On press), 5. Oteifa, B. A. 1958. Development of the root knot nematode Meloidogyne incognita as effected by potassium nutrition of the host. Phytopath. 48: 171-174. 6. 0teifa, Bakir A. 1955. Nitrogen source of the host nutrition in relation to infection by a root-knot nematode Meloidogyne incognita. Plant Disease Re porter 39 (12): 902-908. 7. Suit, R. F., and E. P. DuCharme. 1963. The burrowing nematode and other parasiticnematodes in relation to spreading decline of citrus. Plant Disease Reporter 37 (7). 379-383. 8. Tarjan, A. C. and H. W. Ford. 1957. A modified aceto-osmium staining method for demonstration of nematodes in citrus root tissues. Phytopath. (In press). 9. Webber, J. H .. and Batchelor, L. D. 1948. The Citrus Industry. Vol. I. Univ. of Calif. Press. Berke ley, Calif. 10. Young, T. W. 1954. An incubation method for collecting migratory endo-parasitic nematodes. Plant Disease Reporter. 38 ( 11) : 794-795. Table 7. Juice characteristics of Parson Brown on Clone X compared to Parson Brown on rough lemon, 1955-56, Rootstock Date Juice by Soluble Acid Soluble Mgs. Vitamin \./eirht Solids cf Solids to C/lOOMl.s. p cf p 'f, Acid Ratio Clone X Oct, 7 52,0 9.2 1,10 8,3 (R.2 Rough lemon Cct. 7 50.7 9.4 1.21 7.7 58.4 Clone X l:ov, 8 54.6 10,3 1,05 9.8 55.0 Rou2;h lemon l'ov. 8 50,9 10.1 1,27 7.9 55.0 Clone X Dec, 13 50,0 11,4 .97 11.7 63,1 !lough lemon r:ec. 13 5/+o 7 10.7 ,94 11.4 60.0 Clone X Jan, 3 53.8 11.8 .81 14,6 6(,1 Rour,h lemon J:i.n. 3 58.8 11,4 .88 13.0 61,.,6

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52 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 THE NEW 4-H CLUB PROGRAM FOR CITRUS PRODUCTION TRAINING JACK T. McCowN Florida Agricultural Extension Service Gainesville Agricultural progress in America during re cent decades has been astounding. Looking at agricultu_ral history it can be seen that this progress is closely associated with the em phasis agriculture has placed on developing its youth. Major agricultural enterprises have had specific programs to inspire youth. This is a part of the citrus industry that is lacking today. Realizing that many boys do not have the opportunity to study citrus the Agricul tural Extension Service is expanding its citrus youth program to meet this need. This paper will outline the Extension Service's citrus youth program in order that you may become better acquainted with its aims and objec tives. The Extension Citrus Advisory Com mittee which plays an important part in de veloping this program, has outlined a 5-year project for 4-H Club boys wishing to become more intimately acquainted with the industry. The 5-year program as outlined below will meet all requirements for a 4-H Club project. Upon completing each year's requirements, the youth may continue his work toward the following year's requirements without wait ing for an end of a calendar year. The requirements for the first year are: 1. Map a 10-acre bearing grove showing the location of ( 1) healthy trees, ( 2) missing trees, ( 3) dead trees, ( 4) diseased trees, ( 5) young resets. 2. When th e map is completed, it should show the total number of trees in the blocks, the number of healthy trees, and the number of diseased, dead and missing trees. 3. Be able to identify citrus fruits that have been injured by ( l) rust mites, ( 2) scale, ( 3) melanose. 4. Plant a citrus seedbed either as an individual home project, or in . a cooperative club project. Discuss size and location of your seedbed with your local leader, or Ex tension Agent. ( Minimum size of seedbed to be determined.) 5. Keep neat and accurate records in a record book, showing the work that has been done, and write a story about your citrus ac tivity. SECOND YEAR'S REQVIREMENTS 1. At least 6 months after completion of the first year map, make another map show ing the location of (I) healthy trees, ( 2) missing trees, ( 3) dead trees, ( 4) diseased trees, ( 5) young resets. 2. When the map is completed, it should show the total number of trees in the block, the number of healthy trees and number of diseased, dead and missing trees. Refer to your first year map and copy the comparable figures and set them down below the first year's figures. Note whether the general con dition in the grove is ( 1) improved, ( 2) worse, ( 3) the same. Mention the progress of the grove in the story at the end of the year. 3. Be able to identify early, midseason and late oranges, two kinds of grapefruit and one kind of tangerines. It is not necessary to iden tify by variety, hut the club member should be able to examine the fruit and determine whether it is early, midseason or late. 4. When the seedbed is between 12 and 18 months old, line out the seedlings. Discuss location of nursery and its size with the local leader or Extension Agent. 5. Be able to identify 5 pests of citrus (may be insects, diseases or both). 6. Keep neat and accurate records and write a story on the . second year's citrus ac tivity. THIRD YEAR'S REQUIREMENTS 1. About 9 months after making the second map, make a third one the same way. 2. Determine the number of skips in the IO-acre plot clue to missing, dead, or diseased trees. From this figure, calculate the per centage of trees missing. The percentage of crop loss in the grove would be about the same. Knowing what price per box the fruit brought, calculate the financial loss to the grower.

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McCOWN: CITRUS PRODUCTION TRAINING 53 3. Bud the nursery. The 4-H Clnb mem ber should demonstrate to th e local leader or the Extension ag e nt his ability to bud and properly care for the nursery. The budd e d trees should be properly lab e l e d. Certified budwood should be secured if possible. If c e rtified budwood is used, th e buds should be selected and the budding don e under direct supervision of th e leader and the State Plant Board representativ e . 4 . Be able to id e ntify and know the ap proximate harvest season-wh e ther e a rly, mid season or late-of the following citrus fruits: Or a nges-Parson Brown, Hamlin , Navel, Pin e apple, Jaffa, Valencia, Lue Gim Gong. Grape fruit-Duncan, Marsh Seedless, Foster Pink, Thompson Pink, Red; Tangelos Orlando, Minneola, Thornton; Misc e Uan e ous, on e vari e ty of lemon, P e rsian (Tahiti) lime, Mer cott. 5. Be able to identify four insects and thr e e diseases that are of economic import ance in citrus production. 6. Keep neat and accurate records and write a story of the year's activities. FOURTH YEAR'S REQUIREJ\IENTS 1. Be able to identify leaf symptoms of the following mineral deficiencies in citrus: nitro gen, magnesium, zinc , manganese and iron. 2. The club member should be able to demonstrate his ability to stake out a grove for planting. 3. Sell or plant out the nursery trees. Learn to plant nursery tre e s in the grove b y plant ing under the supervision of th e club lead e r or Extension ag e nt . Keep a record of how these trees are cared for the first year. In clude dates for each operation, including amount of water per tree, banking, planting cover crop, analysis and amount of fertilizer, insect and disease control. 4. Be able to identify five citrus insects and four diseases and tell how they can be con trolled. 5. Explain wh a t is meant by th e "on tr e e" price growers get for citrus. Keep a record of "on tree" prices for one season from October 1 to June 15 for oranges and grapefruit. ( Con tact the same grower, grove car e taker, or cash buyer once each week and ask him the "on tree" price. R e cord this information _ in table form in the record book, showing if it is early, mi
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54 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 This Institute is held at 4-H C a mp Cloverl e af for the purpo s e of putting a fin a l tou c h to the citrus project work for the y e ar. Attending the Institute will . b e an award for th e boy do ing the best proje c t work in his count y . Th e Junior Citrus . Institute this past ye ar was jointly sponsor e d by the Chilean Nitrate Edu cational Bureau of Orlando a nd Dolomite Products Inc., of Ocala. In addition to the Junior Citrus Institute, w e ar e prep a ring to promote additional inter e st among the club m e mbers in citrus by providin g fruit judging contests and similar activities at th e various county fairs throughout the st a te. At this time th e boy will a lso b e given th e oppor tunity to participat e in insect, dis ea se and other identification conte s ts . It is important that th e citrus industry take part in d e vdoping this program. Men in the industry can b e of help by showing an inter e st a nd t a king an active part in local project work. We may also inspir e the y oungsters through encourag e ment and r e cognizing a job well done. In some instances financi a l aid may b e n e c e ssary for clubs to develop local proj e cts. Examples would include: nursery projects , small groves for demonstration pur poses , tours and training schools. Organiza tions and individuals may h e lp by making a vailabl e funds for this purpos e . We fe e l that the program outlin e d will be successful. How e ver , gr e ater goals ma y be achieved if w e rea lize th e importanc e of such a youth program and show nn inter e st by putting forth a con certed effort to insure succe s s. Th e young peopl e of Florida are a part of th e citrus in dustry . Let us prepare them to acc e pt its fu ture r e sponsibiliti es in order that our industry may continu e to b e a leader among th e various American agricultural enterpris e s. FIELD OBSERVATIONS OF SEVERAL METHODS OF MANAGING CLOSELY SET CITRUS TREES F1mo P. LAWRENC E Florida Agricultmal Extension Ser v ice Gainesville ROBEnT E. Nonm s Florida Agricultural Extension S e rvice Tavares You will not e from y our program that th e title of this presentation is "Fi e ld Observa tions of Several Methods of Managing Closely S e t Citrus Tre e s." That title sounded simpl e enough when it was submitted to the program chairman but now that w e have had mor e tim e to contemplat e we are not so sure. For instance, how close is clo se ? To help answer this que s tion we turned to W e bst e r's Coll e gi a te dictionary only to find more confusion than enlightenment . We were reminded first of all that it depend s how you pronounce the word. If you put a "z" in the pronunciation clo z e-it means to " shut up " and considering the small amount of a ctual data we have, th a t might not be a bad idea. Th e re ar e m a n y other meanings , of course, but Definition No. 25, ha v ing th e pa r t s n e ar tog e th e r , i s the one that s ee ms most appropriate for our use. Applying this definition, consid e r first the c itrus tree spacings of th e various producing ar e as of th e world. In Italy and oth e r Medi t e rranean countri e s citrus tr ee s ar e usuallv spaced lO'xlO' or 10'xl2' which results in 300 to 450 trees per a cre. Th e Jap a nes e orchards averag e 240 to 300 tr ee s p e r acr e. Egypt's predominant spacing is 12'xl8' ; Peru 18'xl8'; Brazil 2l'x24' ; California 22'x22' and Florida 25'x25'. The planting distanc e in a given area de p e nds upon such things a s vari e ty, species of rootstock us e d, type and fertility of the soil, th e length of the growing season, and, to a large e xtent, upon the attitud e of the indi vidual doing the planting. To illustrate the l a tter point it might be w e ll to point out that quite a numb e r of California growers, accord in g to an article in the October '55 issue of Citrograph, a re turning to what th e y call h e dgerow pl a ntin g s and som e groves are planted as clo s el y a s 8xl0 which giv e s som e 490 tr ee s per acre .

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LAWRENCE AND NORRIS: FIELD OBSERVATIONS 55 All of these plantings, or at least a major portion of them soon reach a point where the limbs and branches of the various trees inter lock and overlap and unless special man agement practices of pruning are applied the bearing surface of such trees diminishes and naturally the production declines in propor tion. According to the best estimates available Florida has 497,400 acres of bearing trees, 333,690 acres or 67% of which are 16 years of age or older. A great many of these groves are planted on spacings of 15x30, 20x24, 25x25 and similar distances and if we apply defini tion No. 25 to the word close we will find that most of these trees have their parts near together; hence we can apply the term close ly planted and in need of some form of prun ing. Time will not permit our discussing the varied and many methods of pruning em ployed in the various citrus producing areas of the world-or even all of those practiced in Florida-so we will confine our remarks to some field observations of several methods of managing closely-set citrus trees; to narrow it down even more we propose to discuss briefly the following practices: l. Hedging 2. Heading back 3 . Thinning by tree removal 4. Topping-a form of rejuvenation prun ing In fairness to those who may read this paper in the printed proceedings we should state that from this point on our talk will be illustrated with color slides and we shall at tempt to present, as clearly as possible, a word picture . of these various methods of pruning. Despite the difficulties associated with crowded groves, very little pruning of any nature has been undertaken in Florida either to prevent or to correct the situation. This has probably been clue to the fact that earlier ex periments suggested that pruning was an op eration that contributed very little to over-all fruit production. In instances of moderate to severe pruning, a loss of fruit was noted With out any apparent compensating effect on quality or fruit size. On the basis of these earlier experiments, recommendations were made that pruning should be confined to the removal of dead wood and occasional broken limbs. This recommendation, plus the fact that pruning is an expensive operation, has also brought about the situation that pruning in Florida until comparatively recently has been con fined to the inside of the tree and to the re moval of dead wood. Insofar as the records show, no effort has been made to limit the size of citrus trees in Florida or to control crowding by judicious pruning of the periphery of the tree until some growers began to hedge tho periphery of their trees in the late 40's. 1. Hedging of citrus is a form of pruning designed to facilitate grove management prac tices and to improve the quality of fruit pro -duced. It is a practice that is becoming in creasingly popular among Florida citrus grow ers as a way to alleviate the problem of over crowding which ultimately results in a loss of production. Hedging provides a means by which the bearing surface of trees is reduced in area without greatly reducing their bearing ability. Indeed, in the case of some varieties, especial ly tangerines, hedging actually increases the per cent pack-out of fresh fruit in the first crop following the pruning operation by in creasing fruit size. Fruit color and textures also are often improved because of increased sunlight and more effective insect and disease control. One of the most valuable advantages of hedging, r,nd the piimary reason for its use in the first place, is to open the tree middles by removing interlocking branches. This al lows for the movement of tractors, discs, spray and dust equipment and trucks through the grove without damage to the trees and fruit or to the equipment and operator. It speeds up grove operations generally, thereby reduc ing cultural costs. If you would like additional information on hedging or plans for a hedging machine we suggest you obtain Experiment Station Bulle tin 519 by D. S. Prosser and Extension Serv ice Circular ll5 by R. E. Norris. 2. Heading Back-This term and the type operation it implies is seldom used in Florida citrus; however, it is used rather extensively in the California lemon industry as well as throughout most of the other citrus producing

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56 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 areas of the world. It consists of removing a portion of the tree at regular intervals in order to retain a rather constant size of the tree. There are certain advantages and disadvan tages to this method of pruning but since it appears to be of little value under present Florida conditions we will pass over it. 3. Thinning by tree removal-This is a prac tice that has long been contemplated by Florida growers but one that has seldom been practiced. Numerous Florida groves planted during the last 30 years were spaced 15x,'30, or a similar distance with the idea of re moving every other t;ee. Few growers , how ever, have actually remov e d these trees and many have practic e d little or no heading back or pruning of any kind, Only in recent years have some few grow_ ers actually thinned their groves by removing trees in the closely-spaced rows. We regret that we do , not have more yield and cost data to present on these operations but the prac tice is not general and accurate data is scarce. vVe do have slides of one complete operation to show and some yield and cost data on the one oper a tion : The grove, consisting of a 10 acre block of Hamlins budded on rough lemon root, was planted in 1939 with a tree spacing of 15x25. The soil type is deep phase Lakeland fine sand. The trees were never headed back or hedged and as a result the limbs were inter locked b a dly and many of the lower branches were dying as a r e sult of shading. During the last 5 y ea rs production decreased, very mark edly so during the past two seasons, which, as you know, were dry. During January and February 1956 every other row was removed by sawing the limbs off with a power saw and running all wood under 4 inches in diameter through a chipping machine. The stumps were treated with a tree killer ( without suc cess) on two occasions and as a final effort the stumps were sawed level with the ground and a chopper nm down the row to remove all suckers. The crop has not yet been harvested but the owner estimates his crop loss at 25% over the previous year's yield. Some figures on the op era tion: The rows were 21 trees long-2 men cut 2 rows per day. Two men could trim the large limbs and stack the brush on 5 rows p e r day. It required 3 men 5 days to run all brush from th e 10 acres through the chipping ma chine. It took 4 men 3 days to haul out all limbs above 4 inches in diameter. It should be pointed out that this grove had a problem of no place to haul and burn the brush so it had to be disposed of in place. To dispose of the trees in the manner described the owner figured the total cost of the operation at $ 1.50 per tree . Of particular int e rest in the group of slides shown on this operation is the one showing how rapidly the remaining trees are filling in. Based on the progress the trees have made this year, it is believed that the grove will be back to normal production next year. Some comments on similar operations: Block B-Red grapefruit on rough lemon stock 10 years old was planted 12}h30 on Lakeland fine sand. Every fourth tree on the diagonal was saw ed off flush with the ground with a pulpwood saw, dragged out and burned. The following year there was no noticeable reduction in crop. At 12 years of age ( next year) the grower plans to remove e very other tree on the diagonal-thus reducing the spacing to 25x30 at -which time he will begin a . program of hedging. Based on pre vious exp e rience the grower feels there will be very little per acre loss in production-if any. Block C-Twenty-five year old Valencias on rough lemon stock were planted 15x30 on Eustis fine sand. The trees were very crowded so every other tree was "buckhorned ," bull dozed and replanted. The year before moving the production on the block was 4400 boxes. Fifty trees were removed and the following year the production dropped to 3960 boxes. The plan is to move 50 trees per year until the operation is completed. After the third year it is anticipated that the loss of 50 trees per year will not result in any loss of total crop produced. Some figures on this operation: It took 2 men Jf day to saw and re-saw 20 trees; one man }f to whitewash (by hand) 20 trees; one man one day to remove (by drag) the brush from 20 trees; four men, a bull dozer, a flat truck and a water wagon one day to push, haul J~ mile and re-plant 20 trees. The total cost of labor for this operation ex clusive of e quipm e nt was $2 . 60 per tree.

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LAWRENCE AND NORRIS: FIELD OBSERVATIONS 57 The re-set trees began bearing the second year at the rate of about }i box per tr e e aver age and in the third year they were yielding a box averag e . The fourth year ' s yield will probably be between three and four boxes. And now . the last practice to consider4. Topping, a form of rejuvenation pruning: Rejuvenation pruning is a term us e d by hor ticulturists to describe the objective of re invigorating trees by stimulating mor e and better shoot growth and fruitfuln e ss. This pruning must be severe enough to r e move suf ficient foliage to stimulate new growth ov e r much of th e tr ee . When enough of the -top is cut off, a growth response usually occurs throughout the woody fr a mework. In order to produce, from pruning, an invigorating effect in a large old tree, it is necessary to make many small cuts or remove some of the large branches. The method we have chosen to report on is that of removing the complete top of old seedling tre e s at varying heights from ground level to e ighteen feet. This, too, is a new practice in Florida and although again, facts and figures are not abundant, we have some slides that are at least interesting. This prac tice might well be described as an act of desperation brought on in many groves by in creas e d overlapping of limbs which resulted in a marked increase of pest and disease and a gradual dying of lower limbs. In some old seedling groves it is 10 to 15 feet from th e ground to the first limb. The tops are sp a rse, the foliage is small, production is down and th e cost of picking ( usuall y from a 40 foot ladd e r) is such that it makes the operation v e r y ex pensive. During the last ten years many growers have been experimenting with various meth ods of pruning to try to alleviate this condi tion. From these various methods of pruning we will discuss only the one wherein the en tire top of the tree is removed. The data pre sented is from two different blocks of old seedling trees owned by two differ e nt grow ers. Both growers topped only a few trees in 1947. Grower A started by topping trees in every other row at a relatively constant height of roughly 5 feet from the ground. Grow e r Il topp e d a bout 20 trees in a block. These trees were fopp e d from 1 foot to 15 fe e t in height. Grove A-Cut back every other row in January 1947 just after the fruit was picked . The trees were whitewashed immediatel y . They started to sprout . out in about six weeks and grew very vigorously the first year. The second year they put on only a few scattered fruit. The third year the growth was very dense and possibly because of the large trees on two sides, tended to grow upright but pro duced better than a box average of fruit. By the fourth year it w a s obvious that although the trees had good big broad leaves and were growing vigorously, they would soon be back like the old tre e s so it was decided to cut back the trees on both sid e s of the row. Some trees bore as much as 8 boxes of fruit th e fourth year. Thes e trees ( as you can see b y the slides) now have the characteristic ap pearance of budd e d tr ee s and are yielding 10 boxes per tree. The new wood is quite thorny and some pruning to thin arid shape is neces sary. Grove B-The initial operation was begun in February 1947. In this block it was not e d that trees cut below 5 feet did not appear to come back as rapidly as did ones cut at a greater distance from the ground. Those trees topped above 5 feet were more difficult and expensive to handle in the original operation and did not respond any faster. It now appears that the trees cut 10 feet and higher will never "head-out" . low a~d will ultimately be right back like they were originally; whereas the trees cut at 5 to 10 fe e t take on the char acteristics of budded tre e s and will apparent l y remain relatively "low-h e aded" provided they are hedged lo prevent inter-locking. Of special inter e st in Grove B was one particular tree that yielded 16 boxes the fifth year. All trees in Grove B are curr e ntly pr , oducing an average of 10 to 12 box e s of fruit. In summary we again wish to point out that the contents of this paper are purely the re sults of field observ a tions with no thought of making recommendations at this time. How ever, it seems logical that in many instances of closely-spaced tr e es high production can be maintained or regained through one of the forms of . pruning outlined in this paper: I. Hedging : A comparativ e ly n e w method of pnm ing which is rapidl y b e ing adopted by Florida grow e rs to r e lieve the . adverse e f

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58 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 fects of crowding and shading found in most Florida groves 15 years old and older. Advantages: a. Increased effectiveness of pest control. b. Decreased damage to trees and equip ment. c. Faster more economical grove operations. cl. Decreased dead wood. e. Increased "pack-out" of fresh fruit. f. Better sizes and better color of fruit. g. More attractive appearance of grove. Disadvantages: a. Usually a reduced yield for at least one year. b. A fairly costly operation ( varies from 7lk to 78c per tree) 1 / 2. Heading back: We have not observed enough of this type of pruning in Florida to offer any comments. 3. Thinning by tree removal: As we have pointed out there are now quite a number of growers who have re cently turned to this method of relieving a crowded condition but very few have adequate records (because of length of 1 /Agricultural Extension Service Circular 115. time) to prove or disprove the value of the operation. It would appear from the limited operations we have observed that if a grower has access to additional land and in instances of healthy trees a new grove that will bear heavily in 4 to 5 years can be established at an economic figure. 4. Topping, a form ot re1uvenation pruning. It is too early to make positive state ments relative to this operation; how ever, it appears that by topping two or more rows per year (beginning on the outside row) this could raise production and reduce cost of harvesting in old canopied groves. Advantages: a. Reduces height of tree. b. Greatly improves tree vigor. c. Increases yield and size of fruit. cl. Produces increased cover crop growth. Disadvantages: a. Complete loss of crop for two years. b. An expensive operation. c. New trees quite thorny. d. lf trees are not whitewashed and cuts coated with water 1epelling paints the trees will be weak and soon rot away. TIMING FERTILIZATION OF CITRUS IN THE INDIAN RIVER AREA HERMAN J. REITZ Florida Citrus Experiment Station Lake Alfred Several years ago, considerable interest was expressed in the relative value of various sys-_ terns of timing fertilizers. Partly as a result of this interest, several experiments were in itiated to resolve this question. Some of the experiments conducted in Central Florida have been reported recently ( 3, 4). This paper presents the results of an experiment con ducted at the Indian River Field Laboratory near Fort Pierce. The results agree with the other Florida data cited above in indicating that time of application of fertilizer is a relatively minor consideration, if the appliFla. Agri. Expt. Sta. Journal Series No. 54G. cations are made during the drier part of the year. EXPERIMENTAL METHODS The experiment to be described was begun in January, 1949, and was terminated with the 1955-56 crop. The trees used were Val encia oranges on sour orange rootstock planted on single beds in 1940. The soil in the ex perimental area was classified Parkwood loamy fine sand with pH ranging from 6.8 to 8.3 in the surface and with pH values above 6.8 in all depths to 42 inches. The surface samples contained carbonates equivalent to about 14 percent calcium carbonate and organic matter of approximately 3 percent. The soil also con tained 12 to 30 percent clay plus silt (parti cles less than 0.05 mm. in diameter) in various layers, thus being much finer in texture than soils used for citrus in Central Florida. In

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REITZ: TIMING FERTILIZATION 59 this soil, the trees were known through measurement to have 75 percent of their fine root system in the upper 19 inches from the crown of the bed. The seven experimental treatments con sisted only of variations in the time of appli cation of mixed fertilizers during the year. Dur ing each calendar year, every tree in the ex periment received the same amount and analysis of fertilizer. The yearly total rates and analysis used were changed several times during the s;ourse of the experiment, as shown in Table 1. Rates were increased up to 1953 to achieve a greener, more dense foliage, and increased further after 1953 to achieve greater Table 1. Amounts and analy1es of fert111zer used 1n the experiment Year Analys1ola) Annual Rate, per tree 1949 3-6-8-3-016 1950 3-6-8-3-0-! 20 1951 4-6-8-5-0-! 20 1952 5-6-8-5-0JO 1953 6-6-8-5-0-0 30 1954 8-4-10-7-0-0 24 1955 8-4-10-7-0-0 24 yield, as was indicated might be possible by an adjacent experiment involving different rates of fertilization. The changes in analysis were influenced by trends in Central Florida fertilizer practice during the period. The tim ing treatments wer e as follows: Treatment 1: All fertilizer applied February 15th. Treatment 2: One-half total fertilizer applied Febru ary 15th and one-half June 15th. Treatment 3: All fertilizer applied May 1st. Tr ea tment 4: One-half fertilizer applied May 1st and one-half October 15th. Treatment 5: All fertilizer applied October 15th. Treatment 6: One-half fertilizer applied June 15th and one-half applied December 15th. Treatment 7: One-third fertilizer applied February 15th, one-third June 1st, and one-third November 1st. The schedule was adhered to within prac tical limits. All the treatments were replicated four times, at first using six trees per plot. Later it became recognized that several of the trees were affected by crinkle scurf and that addi tional trees were non-typical of the Valencia variety. These trees were then discarded and the results quoted are based upon the typical trees remaining in the plots insofar as this was permitted by the records. RESULTS Plot Observations-At the beginning of the experiment in January, 1949, the trees were somewhat small for trees nine years of age and also were showing the symptoms of low fertilization level. In August, 1949, a severe hurricane struck the grove and caused about 90 percent defoliation on all trees and almost complete loss of the fruit crop. Throughout 1950 and 1951, the foliage on all trees was light green and sparse, but this condition im proved ~lowly throughout the period and was fairly satisfactory by the end of 1952. Through 1953 to the end of the experiment, all trees had satisfactory foliage conditions ex cept when modified by treatments as noted b e low. The most conspicuous changes in tree ap pearance were brought about by application of all fertilizer in October. In the last four y e ars of the experiment, all trees so treated w e re notably earlier in blooming and coming into growth in the spring than other trees. The extreme example of this was observed Janu ary 7, 1954, when approximately one-third of all trees so treated were in full bloom from leafless infloresc e nses while the trees in other treatments were completely without bloom. Twig growth on these trees was also early in development , and the twigs were long and had many leaves per twig. These leaves in most years did not become dark green -as did leaves from other treatments, and in some ye ars the trees became conspicuously nitrogen deficient and sparse of foliage during the post

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60 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 bloom and early summer season. In late sum mer, some greening of foliage occurred even before fertilization , presumably due to break down of organic matter in the soil. Trees given one-half the fertilizer in May and one-half in October were similarly but less conspicuously affected. Trees given all fertilizer in May were at the opposite extreme in appearance com pared with trees fertilized only in October. These trees had limited spring growth, in num ber of twigs or length of twigs, and this spring growth became dark green slowly. The bloom was sometimes very late, not reaching a peak in 1954 until about April 9, and not then be ing profuse or conspicuous. The general leaf color in the post-bloom period was fairly dark green due to the color of the old leaves and the absence of new flush. In the early sum mer period, the characteristic appearance of these trees was dull grayish green, the foliage was thin , and there were numerous dead twigs in the trees. During the late summer and fall the trees were of ~verage foliage appearance, but this was generally the case with nearly all of the trees except possibly those fertilized only in October. The general appearance of trees in all of the other treatments was not outstanding in any resp e ct and the trees were fairly green throughout the year. Tree Size-The circumference of the trunks of the trees in the experiment was measured first in August, 1950, and again in January, 1956. The averages showed that the increase in trunk circumference was smaller for the trees receiving all the fertilizer in October than for any other . treatment. However, dif ferences in neither the actual trunk circum ferences nor in the increases during the period were large enough to be of statistical signi ficance, indicating that the timing of fertiliza tion had doubtful effect on tree size. Leaf Analysis-Leaf samples were taken for mineral analysis on a number of occasions dur ing the course of the experiment, beginning in 1952. In one series, samples of leaves from fruit-bearing twigs were collected from four of the treatments at approximately monthly in tervals from March, 1953, to May, 1954 . This less commonly used type of sample was select ed becaus e it was desired to study the nutri ticmal status of leaves most closely t1ssociated with the fruit. It was coincidental that the severity of the leaf symptoms observed was greatest in the year that was picked for this study, so the differences found are doubtless greater than would have been found in other years. The analytical results for nitrogen are pre sented in Fig. 1. These results correlate with the appearance of the bees. For example, the trees fertilized only in January and those fertilized three times per year maint ai ned a reasonably good green color of leaves and relatively high nitrogen level throughout the entire period. The trees fertilized in October only appeared nitrogen deficient during the months of May, June, and July, and at that time had extremely low levels of nitrogen in th e leaves. Also, leaves from trees fertilized in October only increased in nitrogen content and improved in appearance during the sum mer althou _ gh no nitrogen had been a?plied; after the fall fertilization, the nitrogen con tent of these leaves greatly increased so that they were equivalent in nitrogen content to those of the January only plots and the plots receiving three applications. The trees fertil ized in May only paralleled in nitrogen con tent the trees fertilized in October only, up to the point when in May the fertilizer was ap plied. After this application, the leaves in creased markedly in nitrogen content but did not reach the level attained by the leaves in the January only or the three application treatments. This parallels the observation that while the trees fertilized in May only ha
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REITZ: TIMING FERTILIZATION 61 to the appearance of the old leaves and that the appearance of the spring flush l eaves of 1953 remained poor . It is also notable that as the 1954 flush of growth came out on trees fertilized in May only, the new leav es were lowest in nitrogen. It is assumed that data for trees receiving two applications p e r year would b e intermediate between the extremes given here. Among other major elements, the mo s t con_ spicuous differences were in potassium and calcium. The treatment receiving all fertilizer in October was conspicuously high in potas sium and low in calcium throughout the greater p ar t of the year. Th e May only treat ment was just the reverse. Differences in magnesium were erratic and differences in phosphorus were of small magnitude. As already noted, during 1954 and 1955 there was very littl e differenc e in appe a rance of the trees regardless of tr ea tment and this was reflected in leaf analysis. Table 2 shows Table 2. Analysis of spring non-fruiting twigs July 26, the analysis of spring flush leaves taken from non-fruiting twigs on two dates. This type of sample is more nearly the conventional sample t a ken in studies of l ea f analysis. In most cases no significant differences w ere found. The most notable feature in Table 2 is the dif ference in analysis between 1954 and 1955. In 1954, leaves g e nerally were low in nitro gen, phosphorus and potassium and high in calcium. Fruit Quality-In each year except 1952-53, at least one sample of fruit was picked for juice analysis. Part of these results are pre sented in Table 3. Soluble solids in four of the six years for_ which records are available were highest for fruit from the trees fertilized only in Octob er; however, the two remaining years, the soluble solids lev e l was lowest. This shift in relative level of soluble solids app ea red to be of some consequence as it was supported by a significant interaction between years and treatment when subjected to analysis of vaflu.sh leaves taken from 1954, and August 2, 1955 LEAF ANALYSIS TREATMENT Nitrogen Phosphorus PotassiUJ11 Calcium Magnealum 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955 Feb. 2.04 2.59 0.107 0.123 0.71 0.99 Feb. and June 2.06 2.74 0.103 0.124 0.61 0.95 May 2.17 2.54 0.109 0.123 o.68 o.89 May and Oct. 2.17 2.4, 0.110 0.122 o. 72 0.94 Oct. 2.14 2.47 0.116 0.114 0.73 0.94 June and Dec. 2.20 2.52 0.111 0.122 0.74 0.82 Feb., June and Nov. 2.16 2.52 0.108 0.124 0.67 0.98 •statistical Significance (a) N.S. iHIN.S. N.S. N.S. N.S, (a) N.S, non-significant * significant at 5% level * significant at 1% level C analysis run on composite samples only , 7.18 5.77 0.173 0.195 7.52 5.59 0.151 0.18.3 7.31 5-89 0.176_0.198 7.21 5.91 0.242 0.194 6.74 6.02 0.194 0.206 6.81 6.05 o.219 0.186 7.02 5.71 0.244 0.188 * N.S. C

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62 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 ----------Table 3. Summary of fruit characteristics ----JUICE ANALYSIS FRUIT SIZE TREATMENT ----0 Bri:x % Acid Feb. 11.73 1.06 F'eb. and June 11.63 1.07 May 11.70 lo03 May and Oct. 11.48 1.09 Oct. 11.63 1.07 June and Dec. 11.63 1.06 F'eb., June, and Nov. 11.62 1.06 Statistical Signif1canee(a): Treatment!! N.S. N.S. Inters.ction -11-1! N.S. (a) N.S. non-significant * significant at 5% level .significant at 1% level riance by split-plot methods, using treatments as the main plots and years as the sub-plots as suggested by Pearce ( 2). This would be in terpreted to mean that the treatments had a real effect on soluble solids but that the effect varied to some extent depending upon the season. No significant difference was discov ered in acidity or ratio of soluble solids to acidity although the trees fertilized entirely or partly in October were among those giving fruit with highest acidity and lowest ratio. Juice content was quite uniform and the dif ferences were of no statistical significance in any case. Vitamin C was determined in only three years, but no differences of practical or statistical consequence were found. The in teraction noted above for soluble solids ( 0 Brix) was not significant for any 1 other juice characteristic. 0 Bri:x Diameter, Avg. Wt. % Acid mm. grams 11.26 70.5 187 11.04 71.5 196 11.53 71.3 187 10.72 71.6 200 10.95 73.1 203 11.05' 71.7 193 11.14 71.0 193 N.S. * * N.S. N.S. * ------------Fruit Size-One of the more noticeable ef fects of the treatments was the effect of the October treatment in producing fruit of larger than average size. This effect was noted strongly in the crops picked in 1952, 1954, and 1955. Measurements were taken of this characteristic by two methods, first, as the measured diameter of the fruit on the tree in 1951, 1952, 1954, and 1955, and second, as the average weight of the fruits which were sampled for fruit analysis in 1954, 1955, and 1956. The summary of both weight and diam eter measurements is given in Table 3. Size differences were more noticeable in the diame ter measurements. These measurements of diameter made in the field were largely done in the early years of the experiment while the weight measurements were done in the last three years of the experiment. Here ~gain it

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REITZ: TIMING FERTILIZATION 63 is noted that the greater effects were obtained in the earlier years of the experiment than in the later ones . The significant interaction of fruit weight with years reflects relatively larger fruit in the October plots in 1954 than in 1955 and 1956. Ext e rnal Characteristics uf th e Fruit Studies were made on color .and grade of fruit, both in the field and to a limited extent in the Citrus Experiment Station packing house at Lake Alfred. It was observed on many occasions that the color of fruit on trees fertilized in October only was outstanding in December and January; however, during February this difference diminished greatly so that when the fruit was mature enough to pick, the advantage had been completely Jost. Packinghouse studies confirmed the field ob servation that little difference existed in the latter part of the season. The loss in the ad vantage for the October treatment was due to re-greening of fruit in that treatment and to improved color of fruit in other treatments. \Vhen fruit was picked late in the season and judged for fruit color as well as coarse ness, and later graded into United States grades, there was ilo advantage for any treat ment over the other in any of these character istics. Yield-Yield results are given in Fig '. 2. Al though there were some obvious differences in average yield, the differences obtained were not statistically sigaificant. Treat ments involving application of fertilizer in October were lowest in average yield. The yield figures for these treatments include , a great deal of late-bloom fruit which would be of no value for fresh fruit production unless it were handled separately. The yield from trees receiving all fertilizer in May was high est, but this high yield was the result of ex ceptional yi e ld on two plots of the four replications and somewhat less than average yield on the remaining two. Yields from the other four treatments were intermediate be tween thes e extremes. DISCUSSION Th e r es ults indicate that no large benefit in yield or fruit quality can be obtained under the conditions of this experiment by simply varying the time of application of fertilizers. Some smaller advantages or disadvantages can, however, b e assigned the individual treat ments. Applications made in October ( before the end of the rainy season in this area) had sev eral disadvantages. In addition to low yield, the trees bloomed dangerously early, showed nitrogen deficiency severely during post-bloom and early summer periods and set much late bloom fruit. As . ide from larger fruit ( of doubt20 19 17 15 W 14 w ~I er 12 UJ CL II en W 10 X 0 9 CD ...J 8 ;: 7 0 t6 5 4 3 2 -1951-56 -1951-55 -1951-54 -1951-53 -1951-52 -1951 o..._~--~-------""'--~'--""""'--""""'---Feb . Feb . Moy Moy Oct. J\Jne Feb. June Oct. Dec. June Nov. TREATMENT F'ig . 2 Accumulative yield by years during the last six years of the expe riment. ful value for this variety), such treatments had no advantages. Single annual application of fertilizer in May produced great es t average yield, but the result lacked statistical significance. The treat ment had nothing else to recommend it, and the tree condition in the post-bloom period would not be satisfactory to many growers . The remaining four treatments prevented unfavorable tree condition and were satisfac tory in all respects. Three applications per year had no advantag es over treatments using few er applications, and hence cannot be recom

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64 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 mended. When all fertilizer was applied in February, quite satisfactory results were ob. tained and might be recommended. By com parison, February and June applications or December and June applications would per haps reduce leaching loss if exceptional rain fall occurred after the single annual applica tion and would reduce the hazard of excessive salt concentration if high rates of fertilization were used. Neither of these conditions was important in the experiment. Similar conclusions might not be drawn if early orange varieties or grapefruit had been used in the experiment. The earlier coloring of the fruit, the larger fruit size, and the higher soluble solids frequently occurring in the treatments receiving October applications might be sufficient to justify their use for these varieties. Such comments are, of course, speculative in relation to the data presented here. It is probable that fertilizer rate played an important role in the results. In later years, with higher rates, results were less pronounced than in earlier years with lower rates. Evi dently striking results from timing experi ments must depend upon attaining nutritional extremes at some period of the year ( 1). At high fertilizer rates, such extremes cannot be produced under the soil conditions existing in this experiment. Under other soil conditions, where less clay and organic matter is found in the soil, nutritional extremes may occur much more readily than was the case in this experiment. However, experiments performed in Central Florida ( 3, 4) have not shown as much difference as had previously been anti cipated and it is probable that the effects spoken of above could be obtained only in the least fertile and coarsest textured soils. SUMMARY A fertilizer timing experjment using Valen cia trees on sour orange rootstock planted on calcareous hammock soil was conducted over a seven-year period . The seven treatments in volved one, two, or three applications per year, using a constant total amount of mixed fertilizer annually on all plots. Results indicate that applications made before the end of the rainy season (prior to November 1st) are un desirable; that three applications per year are unnecessarily expensive; and that satisfactory results can be obtained by using two applica tions, one after the end of the fall rainy season and a second before the beginning of the summer rainy season, or by a single applica tion made in winter. LITERATURE CITED 1. Martin, W. E. 1942. Physiological studies of yield, quality and maturity of Marsh grapefruit in Arizona. Ariz. Agr. Expt, Sta . . Tech. Bui. 97. 2. Pearce, S. C. 1953, Fruit experimentation with fruit trees and other perennial plants. Tech. Com munica t ion No. 23, Commonwealth Bureau of Horti culture and Plantation Crop s , East Malling, England. Section 25, p, 14. 3. Reuther, Walter, and Paul F. Smith. 1954. Ef fect of method of timing nitro g en fertilization on yield and quality of oranges . . Proc. Fla. State Hort. Soc. 67: 20-26. 4. Sites, John W., I. W. Wander, and E. J. Des zyck. 1953. The effect of fertilizer timing and rate of application on fruit quaJity and production of Hamlin oranges. Proc. Fla. State Hort. Soc . 66:54-62 ,

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KNORR AND PRICE: GRAPEFRUIT STEM PITTING 65 IS STEM PITTING OF GRAPEFRUIT A THREAT TO THE FLORIDA GROWER? L. C. KNonn AND W. C. PmcE Florida Citrus Experiment Station Lake Alfred Before attempting to answer the question raised in the title to this paper, it is necessary to consider two subsidiary questions. The first of these is this: What is stem pitting? The term "stem pitting" was first used by Oberholzer, Mathews, and Stiemie ( 16) in South Africa to designate a specific disease of grapefruit trees on rough lemon rootstock. Subsequently, the term came also to be used in a different sense: to designate a symptom, or set of symptoms, occurring in the wood of various kinds of citrus trees when infected with, or presumed to be infected with, one or another virus. This double usage has re sulted in a certain amount of confusion. The term stem pitting has been applied by others to the pitting that occurs under the bark of Key lime seedlings serving as indicator plants for tristeza virus ( 3). It has also been applied (I) to various types of pitting present in many varieties of citrus-for example, to the pitting in such varieties as trifoliate orange and sour orange, which varieties are found ( 5) to be free of pitting in Argentina where the stem-pitting disease abounds. We are concerned with the disease of grapefruit known as stem pitting. According to Oberholzer, Mathews, and Stiemie ( 16), stem pitting is characterized by corrugations or longitudinal pits on the outer surfaces of trunks of affected trees; trees showing stem pitting of the trunk become stunted and bushy, giving rise to the name stunt bush; their foliage is sparse, small, mottled, and chlorotic; and their fruit are small with thick rind, high acid content, and low juice con tent. In severely affected trees, scaffold branches tend to grow downward at sharp angles, crowns are flat, and the rough-lemon rootstock suckers profusely. According to McClean ( 12, 13), the symp toms described by Oberholzer et al. are secondFlorida Agricultural Experiment Stations Journal Series, No . 567. ary ones that develop as affected trees mature, the important primary symptoms being those that are revealed by stripping off bark from the trunk and large limbs. In the surface of the underlying wood, there is to be found pits, shallow grooves, or channels with their long axes paralleling the grain of the wood. The channels give the unaffected wood the ap pearance of ridges resembling loose strands of twine. Channelling is well-defined and characteristically present in the trunk and lower branches but may be lacking in twigs and young branches. Oberholzer ( I 7) in 1953 estimated that stem pitting had destroyed 40 per cent of the grapefruit groves in South Africa, and Oxen ham and Sturgess ( 19) report that stem pit ting, or dimples, of grapefruit, "is the most serious problem affecting the Queensland cit rus industry," with most plantings becoming unproductive by the 15th year. This terrible destruction results apparently from injury to phloem and xylem tissues in the scaffold of the tree, thus rendering tissues incapable of supplying either tops or roots with the water and food needed for growth and fruiting. Oberholzer, Mathews, and Stiemie ( 16) showed that stem-pitting disease is perpetu ated by vegetative propagation and discovered that some sources of budwood carry a milder form of the disease than others. McClean ( 12, 13) proved the disease to be infectious and to be capable of transmission by grafting or by means of the brown citrus aphid', Toxoptera citriciclus (Kirk.) ( syn. A phis citricidus Kirk.). He considered stem pitting to be caused by a virus that is widespread in . citrus in South Africa, and he also reported that at least two 1 ; At this point it mi1?ht prove h e lpful to point out that a certain amount . of confusion has arisen with ' respe"ct to common names for Toxoptera (Aphis) citricidus (Kirk.), the highly efficient vector of tristeza in South America, South Africa, and Aus tralia, and Toxoptera aurantii (Fonsc.), the mark• edly inefficient vector that is present in F1orida. In the American literature the com1119n name for T. citricidus is the brown citrus aphid, and for T. aurantii, the black citrus aphid ( cf . "Common names of insects approved by the Entomological Society of America," Bui . Ent. Soc . of America 1 (4): 1-34. 1965). In the literature of certain other countries however, the order is reversed: it is T. citricidus that is called the black citrus aphid (cf. "Common names of insects," Commonwealth Sci. & Ind. Res. Org. Australia, Bui. 27 5, 32p. 1955). and T. toxoptera the brown citrus aphid.

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66 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 strains of the virus exist. Both strains induce veinal flecking in West Indian (Key) lime seedlings and both stunt such seedlings rather severely, one more so than the other. The second subsidiary question that must be considered is this: What is the relationship between stem pitting and tristeza? This is cer tainly not an easy question to answer, as will presently become evident. On the one hand, there are reasons for believing that these two diseases are caused by the same virus. Mc Clean ( 13) has pointed out that the causal agents of both diseases are transmitted by Toxoptera citricidus and. that both diseases are universal in South Africa. He thinks that it would be strange indeed for two distinct viruses .to be transmitted by the same insect and also to be ubiquitous in the same crop. It is certainly tempting to regard the two dis eases as specific host responses to the same virus but there may be good reasons for re sisting such temptation. Costa, Grant, and Moreira ( 3) suggested that stem pitting might be caused by the same virus as that which causes tristeza, or by a closely related virus, and McClean ( 13) con curred in this opinion. The virus responsible for stem pitting in South Africa is also be lieved ta cause a die-back of lime in the Gold Coast, where at least two strains of the virus are reported to exist ( 8, 9), and to cause in South Africa ( 13) a severe decline of Tahiti lime on the tristeza-tolerant sweet-orange root stock. Stem pitting has been reported to oc cur in Argentina ( 11), apparently having been introduced there simultaneously with tristeza. It is also known in the Belgian Congo ( 20). McClean and van der Plank ( 14) postulated that the tristeza-virus complex has two com ponents, a stem-pitting component and a seedling-yellows component. They postulate further that the stem-pitting disease is induced in grapefruit by the stem-pitting component whether the seedling-yellows component is present or not. It is not clear from the paper by McClean and van der Plank whether stem pitting virus alone can cause decline of sweet orange on sour-orange rootstock or whether the seedling-yellows component must also be present. However, sour orange is thought to be more tolerant of stem-pitting virus alone than of the stem-pitting seedling-yellows com plex. Another reason for considering that tristeza and stem-pitting viruses arc not identical is this: although tristeza virus is supp0t,ed to be universal in citrus of South Africa, many 25year-old grapefruit trees there do not have the stem-pitting disease ( 15). This could be interpreted to mean 1) that tristeza virus is different from stem-pitting virus despite being closely associated with it in nature, or 2) that some strains of tristeza virus are so mild that they do not cause stem pitting. Stem-pitting disease of grapefruit does not occur in Florida, nor, to our knowledge, does it occur elsewhere in the United States. Triste za is in Florida ( 7) , however, and is reported to be spreading in some areas, such as Lake and Orange Counties (2). We know of a few grapefruit trees in Florida infected with tris teza virus that display a pitting of twigs and small branches comparable to the pitting that frequently develops in Key lime seedlings when infected by tristeza virus; these grapefruit trees, however, do not have the striations and channeling of wood of the trunk or large limbs, symptoms said by Oberholzer et al. to be the characteristic manifestations of stem pitting disease; neither do these trees show any indications of decline nor deviations from normal fruiting. In Florida, we have examined a large number of grapefruit trees, many of which have been demonstrated to be carrying the virus of tris teza, but in none of these trees have we found the stem-pitting disease. Because of these ob servations, it seems safe to conclude that at present stem pitting occurs rarely, if at all, in Florida. The virus, or virus complex, that causes seedling-yellows disease of grapefruit, sour orange, and Eureka lemon seedlings in Aus tralia and South Africa also does not occur in Florida. When Florida tristeza virus is trans mitted to these three species by budding from infected sweet-orange trees, it does not pro duce seedling yellows in them. This certainly seems to be a paradox: al though tristeza is not uncommon in Florida, neither the seedling-yellows component nor the stem-pitting component of the complex ap pears to occur here! How can this be ex plained? One possible explanation is to assume that the seedling-yellows component is present in

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KNORR AND PRICE: GRAPEFRUIT STEM PITTING 67 Florida but that by itself it cannot produc e se e dling y ellows, that seedling y e llows d e vel ops only when the stem-pitting component i s also present. If this is assumed , th e n it ne e ds further to be assumed that onl y th e see dling yellows component of the compl e x, not the stem-pitting component, is present in Florida and that seedling-yellow virus by it se lf causes the mild form of tristeza to be found here . Al though we do not have the experim e ntal e vi dence n e cessary to rule out this possibility, we prefer a simpler hypothesis. Our hypothesis is that tristez a , st e m pitting , seedling yellows, and the Gold Coast's lime die back are caused by a singl e virus that ex ists in the form of numerous strains. [It seems likely that this is about what Costa, Grant , and Moreira (3) had in mind wh e n th ey sug gested that tristeza and stem pitting a r e caused by the same virus.] It may furth e r be sup posed that naturally-infected trees can harbor two or more strains simultaneously and that one or another of these strains pr e dominat e , depending upon the species or v a riety of citrus in which they occur. The strain of virus pre dominating in swe e t orange of South Africa is usually, though not always, one that will in duce seedling yellows in grapefruit , Eureka lemon, and sour orange seedlings. vVe can designate it as the seedling-yellows strain . It appar e ntly is not well adapted to the grape fruit. Consequently, when a mixture of strains is transmitted by Toxoptera citricidus from naturally-infected sweet orange to grap e fruit, another strain better adapted to the grap e fruit soon predominates; this may be a strain that caus e s stem pitting or another that is consid erably less s e vere than the stem-pitting strain . Even when transmission is b y grafting and when s e edling yellows develops , the grapefruit tends to los e the component that causes seed ling yellows while retaining the component that causes stem pitting ( 15); this observation can better be explained by assuming th e stem pitting and seedling-yellows components to be strains of the same virus than by assuming them to be distinct and separate entiti e s. It is not n e c e ssary to_ assum e that s trains of tristeza virus exist; their exist e nc e has been demonstrated in South Am e rica ( 4) and in the United States ( 18). It is necessary to as sume only that the strains of trist e za virus commonly found in the United States cause neither seedling-y e llows disease nor st e mpitting diseas e. . Although there is no substantial body of ex perimental evid e nce on which to base a judg ment of the validity of the hypothesis that tris teza seedling yellows, and stem pitting involv e not a complex of viruses but a group of closely related strains, an experimental check of th e hypothesis can readily be made in Australia or South Africa, wh e re presence of a seedling yellows factor is said to occur. Evidence is now available for the stat e ment that a mild strain of tristeza virus will protect citrus from mor e severe forms of the virus ( 4 , 6, 18). Cons e quently, a grapefruit se e dling invaded b y th e stem-pitting component of the tristeza virus complex should be refractory to infection by the seedling-yellows component, whether in troduced by means of grafting or by Toxoptera citricidus, if the two components are closely related strains but not if they are separate and distinct viruses. So far as we can learn from the literature, this test has not been made. Let us now return to the main question of this paper: is st e m pitting a threat to the Florida grower? We believe that it is a threat, but one that should not be taken too seriously so long as an efficient vector of tristeza lik e Toxoptera citricidus is kept out of the stat e . If stem-pitting virus is a strain of tristeza virus , the possibility that it will arise by mutation of the mild strains of tristeza virus present in Florida is a virtual certainty. If an efficient vector of th e virus , such as Toxoptera citrici dus, should fe e d on the tree in which the mu tant arises, there will be a good possibility of spreading the virus to h e althy trees in th e neighborhood. In the abs e nce of such a vector, the possibility of spre a d is very small indeed. Tristeza has been present in Florida for a good many years ( 10) and it is likely that th e strains of virus in existence here are w e ll adapted to the crop; they are more or less in equilibrium with th e crop. This equilibrium is not likely to be upset except by some radical change, such as app ea ranc e of an efficient vec tor. If stem pitting is caused by a separate and distinct virus that does not now exist in Flori da , it should by all means be prevented from entering her e. Quar a ntine measures against importation of budwood is the most practical means by which to exclude it.

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68 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 REFERENCES TO THE LITERATURE 1. Bitters, W. P .. N. W. Dukeshire, and J. A. Brusca. 1953. Stem pitting and quick decline symp. toms as related to rootstock combination. California Citrog. 38: 154, 170-171. 2. Cohen, M. 1956. Injury and loss of citrus trees due to tristeza disease in an Orange County grove. F'lorida State Hort. Soc. Proc. 69: 19-24. 3. Costa, A. S., T. J. Grant, and S. Moreira. 1950. Relatives of tristeza. A possible :relation between tristeza and the stem-pitting disease of grapefruit in Africa. Citrus _ Leaves 30 (2): 12-13. 35, 38. 4. Costa, A. S., T. J. Grant, and S. Moreira. 1954. Behavior of various citrus rootstock-scion combina tions following inoculation with mild and severe ' strains of tristeza virus. Florida State Hort. Soc. Proc. 67: 26-30. 5. DuCharme, E. P., and L. C. Knorr. 1954. Vas cular pits and pegs associated with diseases in citrus. U. S. Dept. Agr. Pl. Dis. Reptr. 38 : 127-142. 6. G1 ant , 'I'. J., and A. S. Costa. 1961. A mild strain of the tristeza virus of cit-rus ~ Phytopathology 41: 114-122. 7. Grant, T. J., and H. Schneider. 1953. Initial evidence of the presence of tristeza, or quick decline, of citrus in Florida. Phytopathology 43: 51-52. 8. Hughes, W. A., and C. A. Lister. 1949. Lime disease in the Gold Coast. Nature 164: 880. 9. Hughes, W. A., and C. A. Lister. 1953. Lime die back in the Gold Coast, a virus disease of the lime, Citrus aurantifolia (Christmann) Swlni:tle. Jour. Hort. Sci. 28: 131-140. 10. Knorr. L. C . 19&6 . Su:;ccpb;, indicators, and filters of tristeza virus. nnd some differences be tween tristeza in Argentina and in Florida. Phyto pathology 46: 557-560 . 11. Knorr, L. C., E. P. DuCharme, and A. Banfi. 1951. The occurrence and effects of ••sten1 pitting" in Argentine grapefruit groves. Citrus Mag. 14 (2): 32-36, 12. McClean, A. P. D. 1950. Possible identity of three citrus diseases. Nature 165: 767-768. 13. McClean, A. P . D. 1950. Virus infections of citrus in South Africa. III. Stem-pitting disease of grapefruit. F'arming in So. Africa 25: 289-296. 14. McClean, A .. P. D., and J. E. van der Plank. 1955. The role of seedling yellows and stem pitting in tristeza of citrus. Phytopathology 45: 222-224. 15. McClean. A. P. D. 1956. Tristeza and stem pitting diseases of citrus in South Africa. FAO Pl. Prat. Bui. 4: 88-94. 16. Oberholzer, P. C, J., I. Mathews, and S. F. Stiemie . I 949. The decline of grapefruit trees in South Africa . A preliminary report on so-called "stem pitting." Union So. Africa Dept. Agr. Sci. Bui. 297. 18p. 17. Oberholzer. P. C. J. 1953. Degeneration of our citrUs clones. Farming in So. Africa 28: 173-174. 18. Olson, E. 0. 1956. Mild and severe strains of tristeza virus in Texas citrus. Phytopathology 46: 336-341. 19. Oxenham, B. L., and 0. W. Sturgess. 1953. Citrus virus diseases in Queensland. Queensland Dept. Agr. and Stocks. Pamphlet 154. Sp. 20. Steyaert, R. L., and R. Vanlaere. 1952. La "Cannelure" ou "Stem-Pitting'' du Pamplemoussier au Congo Beige. Bui. Agr. du Congo Beige 43: 447454. SEASONAL CHANGES IN THE JUICE CONTENT OF PINK AND RED GRAPEFRUIT DURING 1955-'56' E. J. DESZYCK AND s. V. TING Florida Citrus Experiment Station Lake Alfred Pink and red grapefruit in the early season does not always meet the minimum juice re11uirements as established by the Florida State maturity laws ( 3, 4). Because of the low juice content, harvest of these two varieties is often delayed, especially since the_ adoption of high er juic.e standards; these being raised approx imately 10 percent during August 1 to October 15, and approximately 5 percent during Octo ber 16 to November 15. For the remainder of the season, the lower juice requirements de fined by the Citrus Code of 1949 remain in effect. The relatively high juice required in the early season delays harvest of much of the pink and red grapefruit until the p~riod of low 1 /Cooperative publication by the Florida Citrus Experiment Station and the Florida Citrus Commis sion. Florida ' Agricultural Experiment Station Journal Series No, 565, juice standards of November 16 to July 31 during each season. Several factors influence juiciness of citrus fruit. Generally, juice content varies markedly with and during seasons; it is relatively low in the immature fruit and high in the . fully ripen ed fruit late in the season. High rainfall and irrigation tend to raise juice volume, such fac tors accounting for variations from year to year. Still other factors are: location, variety, rootstock, age of trees, time of bloom, shape of fruit, and certain cultural deficiencies. Oil ( 7) or arsenic ( 1, 2) sprays have not been found to affect significantly the amount of juice in the fruit. The Florida Citrus Commission has been conducting a four-year survey of red and pink grapefruit to obtain a better understand ing of the internal quality and maturity chac acteristics of these varieties. When the survey was begun in the fall of 1953, the soluble solids content in much of the fruit did not meet standards; however, since the juice re

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DESZYCK AND TING: SEASONAL CHANGES 69 ,. 17 e--oPS/RL .. -.oAR/AL -R/so. Od . 23 Now.23 Oee . 23 Jon23 ... . 23 SAMPLING PERIOD Fig. 1. Seasonal changes in the average juice con• tent of pink (P.S.) and red (R.R.) grapefruit of three sizes (96, 70, 54) grown on sour orange (S,O.) and rough lemon (R.L . ) rootstocks during 1955-56. quirements w e r e raised in 1955 , juice content . became the limiting factor in maturity. Th e r e for e , a study of juiciness was included during the 1955-56 s e ason. A preliminar y report is here presented for th e purpose of ascertaining the juice cont e nt of pink and red grapefruit of three siz e s grown throughout the Stat e during the 195556 season. Sp e ci a l emphasis was placed on its rel a tionship to le g al juice requir e ments. In ad dition to seasonal changes in juic e content, th e variations among samples during each sam pling period as well as the daily increas e s in th e juice are included. ExPEHIMENT AL For this survey, 137 grov e s w e re sel e ct e d throughout the citrus area of Fl o rida, includin g the Ridge section, and the East and West coasts. Of the total number, 68 groves w e r e Ruby red and 41 pink seedless on rough lemon , and 20 groves w e re red and 8 pink on sour orange rootstock. Fruit sampling was similar to that used commerciall y ; that is, each sampie consist e d of six fruit of one siz e pick e d from diff e r e nt trees. Thr e e sizes (96, 70 , and 54) were collected from tagged trees at in tervals of 14-16 days during the 1955-56 sea son, ext e nding from S e pt e mber to : M a rch . Juice was expr e ssed at the rat e of 40 fruit per minute using a Food Machinery In-Lin e e tractor ( 5) with a flush setting, J~ inch orifice tube, strain e r tube of 3/32 inch openings, and a cup of six inches in diam e ter. The juic e was then passed through a Chisholm-R y d e r fin isher of th e tap e red scr e w type equipp e d with 0.033 inch perforated screen, weighed and e pressed as milliliters in e ach sampl e of six fruit. In compiling the data the average juice volume for e ach period of 14-16 days was us e d. A OltZS Nod5 OK . U .k111,U SAMPLING PERIOO Fig. 2. Seasonal changes in the average juice con tent of two varieties of fruit of three sizes grown on two rootstocks during 1955-56 .

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70 FLORIDA STATE HORTICULTURAL SOCJETY, 1956 RESULTS AND DISCUSSION In general the average juice content of pink and red. grapefruit of three s izes on rough lemon and sour orange rootstocks gradually increased with the advance of the season, with some exc e ptions ( Fig. l). Some irregularities were appar en t for size 54 fruit on sour orange rootstock. In addition the juic e volumes in the fruit of the three sizes decreas ed slightly dur ing January and February (Fig. 2-A). Rootstock apparently does not influ e nce juice content in white varieties of grapefruit ( 6). However in the pink; and red varieties, significantly more juice is found in fruit grown on sour orange than on rough lemon rootstock during the latter part of the season ( Fig. 2-B). This variation was first apparent in December for size 54 fruit, and during March for size 96. On the average for the season more juice was found in fruit on sour orange than on rough lemon rootstock. The seasonal tr e nds in the juice of two varieties and three sizes are shown in Fig. 2-C. The red variety contains significantly higher juice content than th e pink grapefruit during th e latter part of th e season, January to March. However , it is similar in th e two varieties during the ea rly season from Septem b e r to January. On th e average forthe season Ruby red fruit contains mor e juice than the pink variety. The percentages of samples of size 96 grapefruit meeting the legal juice require ments through Decemb e r are list e d in Tabl e l. Very little fruit can be picked under th e 1955 juice standards, since only 7.7 p ercen t of the samples attained sufficient juic e ( lllO ml.) at th a t time. During October l to 15, 32.1 per cent of the fruit m e t the strict regulations. When the r eq uirem en t is lowered to 1080 ml. during October 16 to November 15, 63 . 2 per cent of the fruit met the standard during the first part of this period, and 84.5 percent dur ing the latt er part. Although th e lower stand ard is restrictive, th e majority of the samples acquired adequate juice. Aft er November 15 when the r eq uirement is lowered to 1020 ml. most of the fruit had enou gh juice for harvest. The size of the fruit appears to have no influ e nce on the time of attainment of the high juice standards effective through Oct~b t: r 15 s ince approximately one-third of the samples of each size met the standards during the period. Table 1. Percentage o! grapefruit 1amples picked throughout the State attaining juice atandarda !rom September to December, 1955 (size 96) Juice ml/6 fruit lllO (a) and above 1080 (b) &11d above 1020 (c) and above Below 1020 September 1~30 12.8 31.7 (a} Minimum juice requirement for Aug. 1 Oot. 15 (b) Minimum Juice requirement tor Octo 16-Nov. 15 (c) Minimum juice requirement tor Nov. 16-Jul7 31. Sampling Period October November 1-15 16-31 1-15 16-30 32.1 46.5 76.8 85.0 41.9 63.2 84.5 85.0 69.5 81.3 93.6 95.0 30.4 18.7 6.4 5.0 December 1-15 16-30 81.l 96.3 86.9 97.3 90.8 100.0 9.2 -0

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DESZYCK AND TING: SEASONAL CHANGES 71 Table 2. The anrage juice content and standard deviation tor grape!rui t of eize 70 for 13 sampling period• during 1955-56. Sampling Period Juice Standard (ml/6 fruit) Deviation Sept. 15-30 un 122,2 Oct. 1-15 1332 125.5 Oct. 16-31 1392 126.7 No'f. 1-15 1465 122.7 Ncr,, 16-31 1495 114.7 Dee, l-15 1541 126.2 Dee, 16-31 15n 125.7 Jan. 1-15 1590 108.2 Jan. 16-31 1603 139.7 :feb, 1-15 1568 104,7 Feb, 16-29 1585 103,0 March 1-15 1604 109,7 March 16-31 1609 110,7 The average juice content and the standard deviations for size 70 fruit for 13 sampling periods are shown in Table 2. The standard de viations are generally higher during the earlier part of the season than during the latter part with some exceptions. The average juice and the standard deviation can be helpful in as certaining the range distribution about the mean, especially if used in the early season. For example, during September, the average juice content for size 70 fruit was 1171 ml. with a standard deviation of 122.2 ml. Of the samples tested, approximately one-third fell between 1171-1293 ml., and one-sixth fell above 1293 ml. It is evident that with the juice requirement of 1380 ml., less than one sixth of the samples met this high requirement, and therefore fruit cannot be picked because of low juice volume. The daily average increases in juice volume for one fruit of each size during sampling periods 'from October through December, are shown in Table 3. Large daily increases for all three sizes occurred during the October 8 sampling period, with smaller amounts during the remaining periods. With sizes, the highest daily increase in juice was found for size 54, and the lowest for size 96. On the average the imce increased by 0.6, 0.7, and 0.9 ml for sizes 96, 70, and 54, respectively. An estimate of the time of meeting juice regulations can be made by knowing the average daily increase in the juice. Of course, these values will vary with location, seasons, and other factors but can be useful as a guide to the time of har vesting. SUMMARY AND CONCLUSIONS A preliminary report of the juice content of seedless pink and red grapefruit of sizes 96, 70, and 54 grown on rough lemon or sour orange rootstocks is presented. The samples were collected twice monthly from 137 groves during the 1955-56 season. In general, the juice content increased with the advance of the season, increasing approximately one-third from September to March. In the latter part of the season, the red fruit contained more juice than the pink variety. Likewise, fruit on sour orange .rootstock contained more juice than that grown on rough lemon. On the aver age, the red grapefruit on sour orange had the most juice while the pink variety on rough lemon had the least amount. As far as meeting the high juice standards in effect from August 1 to October 15, ap proximately 8 percent of the fruit in Septem ber and 32 percent in Octqber met the strict juice regulations. At the time of the medium juice requirements from October 16 to Novem ber 15, approximately 63 and 85 percent met Table 3. 1-rerage dally increase 1n juice content per fruit of grapefruit of three sizes (96, 70, and 54) during October to December 1955, Sampling Period Size 96 70 54 ml/fruit/day Oct. 1-15 1,1 1,7 2.1 Oct. 16-31 0,5 0,5 o.8 No\', 1-15 0.9 1.0 0,8 Ncr,, 16-30 0.1 0.3 0.4 Dee, 1-15 0.4 o.5 o.s Dec, 16-31 0.4 0,2 0,4 Average 0,6 0.7 0.9

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72 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 regulations in October and November, respec tively. After November 15, most of the fruit met the low juice standards then in effect . The variations in the juice content for each sampling period as well as the daily increases in juice volumes are presented. LITERATURE CITED 1. Deszyck, E. J. and J. W. Sites. 1954. The effect of lead arsenate sprays on quality and maturity of Ruby red grapefruit. Proc. Fla. State Hort. Soc. 67: 38-42. 2. Deszyck, E. J . and J. W. Sites. 1955. Juice con tent in early Ruby red grapefruit, Proc. Fla. State Hort. Soc, 68: 47-49. 3. The F'lorida Citrus Code of 1949. Chapter No. 25149. State of Fla. Dept , Agr, Citrus & Vegetable Inspection Div. 4 General Laws of Florida. 1955. Minimum juice content for grapefruit. Chapter 29760, Senate Bill No. 562. 5. Gerwe, R. D. 1954. Extracting citrus juices. Proc. Fla. State Hort. Soc. 67: 173-176. 6. Harding, P. L. and D. F. Fisher. 1955. Seasonal changes in Florida g rapefruit. U . S. Dept. Agr. Tech . Bui. 886. 7. Taylor, 0. C ., G. E . Carman, R. M. Burns, P. W. Moore, and E . M. Naeur, 1956. Effect of oil and parathion sp1ays on orange size and qua1ity. Calif. Citrograph 41: 452-454. EFFECTIVENESS OF DIFFERENT ZINC FERTILIZERS ON CITRUS C. D. LEONAHD , IVAN STEWART AND GEORGE Eow ARDS Florida Citrus Experiment Station Lake Alfred Zinc foliage sprays have been used for more than 20 years for the correction and preven tion of zinc deficiency or Frenching in Florida citrus groves. Such sprays are reasonably ef fective in controlling Frenching in most groves even though the zinc sources now used are very slowly absorbed and highly inefficient (7). Sprays have the additional disadvantage of leaving a residue on the leaves which in creases the scale population. Hence there is need for an effective and inexpensive method of supplying zinc to citrus trees by application of a suitable zinc fertilizer to the soil. The studies reported here were carried out in an effort to find such a method. Soil application of zinc, chiefly as the sul fate, has been far less d e pendable than foliage sprays as a method of supplying zinc to citrus. Camp (3) reported in 1934 that in some cases no visible result was obtained from soil appli cations of zinc sulfate, whereas in others ap plication of from 5 to 15 pounds per tree broadcast gave good responses. Even where soil applications of zinc are effective absorp tion of zinc and correction of the zinc defi ciency leaf pattern are relatively slow. The effectiveness of soil applications of zinc varies greatly with various soil characteristics; for exFlorida Agriculturnl Experiment Stations Journal Series, N'o. 559 . ample, this element is much less available at a soil pH of 6.0 or 7.0 than at more acid soil reactions. Jones, Gall, and Barnette (6) reported that when zinc compounds are applied to the soil, they react to form three types of compounds: (a) water soluble zinc compounds, (b) com binations formed by the reaction of soluble zinc compounds and the organic and inorganic colloidal complex of the soil ( replaceable zinc), and ( c) combinations insoluble in water and not in combination with the colloi dal complex of the soil ( not replaceable). They found that when low concentrations of soluble zinc compounds react with the soil, the major portion of the zinc enters into combination with the colloidal complexes and may be re placed by a normal ammonium chloride solu tion. Under these conditions they found a near equivalence between the replaceable zinc of the soil and calcium removed from the colloi dal complex. When high concentrations ot soluble zinc compounds react with the soil, they found that the zinc is present not only in water soluble and replaceable forms but also in an insoluble form. They state that or ganic matter, clay, replaceable bases, carbon ates and phosphates influence the fixation of: zinc in the soil. Jamison ( 4), however, reported little dif ference in the fixation of zinc in the presence and the absence of superphosphate in the soil. He states that the forces which retain zinc in these soils are far stronger than those holding zinc as phosphates or basic compounds ordin arily considered insoluble.

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LEONARD, STEW ART AND EDWARDS: ZINC FERTILIZERS 73 Jamison (5) found that zinc applied as the sulfate leached from the soil faster where larger crystals or lumps were applied than where a fine powder was used. Most of the zinc from the fine source materials remained adsorbed in the surface three inches of soil while much of the zinc from coarse materials had penetrated into the deeper layers of soil or had leached. He attributed this difference to saturation with zinc of small local zones of soil beneath the lumps or large crystals. Brown (2) mixed zinc sulfate thoroughly at the rate of 100 pounds per acre with five major citrus-producing soils which had been adjusted to pH levels of 4, 5 , and 6. At pH's 4 and 5, the zinc content of the leaves of orange and grapefruit seedlings grown in these soils was very high, but in l eaves of the plants grown in soil at pH 6 it was much lower. The uptake of zinc at different pH levels varied for the five soils, but with Lakeland soil at pH's 4, 5, and 6 the zinc contents of orange leaves were 202, 317, and 44 ppm, respective ly. LEACHING OF ZINC The high uptake of zinc by citrus seedlings from different soils at pH 4 and 5 with which zinc sulfate had been mixed, as reported by Brown (2), shows that this material is an ex cellent source of zinc for citrus when distrib uted within the rooting zone of the trees. Since most of the zinc from finely-divided zinc sulfate becomes fixed near the soil surface ( 5), the poor results obtained from soil applica tions of this material in citrus groves appear to be due to its failure to leach downward into the rooting zone. In an effort to find a method of getting zinc deeper into the soil, two zinc chelates, zinc 1, 2 diaminocyclohexane tetra. acetate (ZnDCTA) and the zinc chelate of Table 1. Etfoot or pR on ...,,,,,t or •l.Do leached through Lakeland n-a,. tvo zillc chelateo, pH or ecil ZtiDCT.l Znl.R:4 era (a) Cfll 4 901 0 5 1230 0 6 2716 0 7 3153 12 (a) Counto per llimlte an aromatic polycarboxylic acid ( ZnAPCA) were tagged with radioactive zinc 6S and leached through Lakeland soil adjusted to pH's of 4, 5, 6, and 7. Counts made on the leachates showed that ZnDCT A was very ef fective in solubilizing zinc, and its effective ness showed marked increases as the soil pH rose from 4 to 7 ( Table 1). ZnAPCA was highly ineffective as a solubilizer for zinc. Zinc sulfate and several zinc chelates were tagged with zinc-65 and leached through pots of Lakeland soil at pH 5.4. Counts on the leachates indicated that much more zinc in Zn EDT A remained soluble than in zinc sul fate ( Table 2). Increasing the amount of EDTA applied with the same amount of zinc ( varying the molecular ratio of zinc to EDT A) increased the amount of zinc leached. Addi tion of non-ionic or anionic wetting agents also substantially increased the solubility of the zinc in this chelate, but addition of a cationic wetting agent reduced it. Zinc gluconate and zinc naphthenate were relatively ineffective as solubilizers for zinc. Zinc sulfate, with or with out a wetting agent, was extremely ineffective in these leaching trials . These results show the great fixing power of the Lakeland soil for zinc. The distribution of the zinc in the soil was determined by taking three cores of soil from each pot with a special soil sampling tube with Tabb 2. !a:nmt ot radioacthe abc h'ca dU'f•NDt ISOUl"CH leeched through pats ot Lakela.ncl 0011 at J>ll ~.~. Zinc SOUl"Ce Ot.he:zMater!al era (a) Zn EMA 2U Zn EDT! l gm. 1'11-~l 498 Zn EDTA. ' gm. 1'11-51 8?6 Cation.tc wttug egent . 111 hionic vetting agent 6~ Non-ionic wtting agent !HI Zn ID!'A (l 12) (b) 71.1:, (115) (b) 1621 Zn gluconate u Zn NaJ:Cthenate 2 Zn 50 4 11;io 1 Zn 50 4 2:zo S gm, l'R-51 11 (a) Counts per llinute (b) Molecular ratio ot dnc to mT.&.

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74 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 a narrow slit in the side and making radio active counts directly on the soil at depths of one to six inches. These counts showed that most of the radioactive zinc applied in the form of zinc sulfate remained in the top few inches of soil, while that applied as ZnEDT A was much more uniformly distributed (Fig. 1). The total of the counts for the six-inch layers sampled was considerably greater for zinc sulfate than for ZnEDT A at pH's of 5 and 6, indicating much greater fixation of zinc from the sulfate. There was little difference in the total counts for these two zinc sources at pH's of 4 and 7. Radioactive counts made on the leaves of citrus seedlings grown in the pots showed a close correlation between the movement of zinc through the soil and the amount of zinc uptake by the plants. FIELD EXPERIMENTS Sin'Ce the pot studies reported above showed C<}usiderably more leaching of zinc and greater uptake of zinc by citrus seedlings from che lated zinc than from zinc sulfate, field experi ments were carried out in several commercial citrus groves to compare the effectiveness of chelated zinc with zinc sulfate. Two such ex periments are reported below. In December, 1952, a field plot experiment was started in a grove of 8-year-old Pineapple orange trees growing on Lakeland sandy soil with a pH of about 6.0. This grove was sprayed with zinc until 1951. The linear four tree plots were completely buffered by other trees from adjoining plots, and replicated three times in randomized blocks. Zinc sulfate monohydrate, containing 36 percent zinc, was applied at rates of 100, 164, and 328 grams of zinc per tree per application. Each rate was applied once a year to one series of plots, and three times a year to another series. Three zinc chelates, ZnEDTA (zinc ethylenediamine tetraacetate), ZnHEIDA ( zinc hydroxyethyl iminodiacetate), and ZnEDTA-OH (zinc hy droxyethyl ethylenediamine triacetate), were applied once a year at rates of 12.5, 25, 50, and 100 grams of zinc per tree. These chelates were also applied at rates of 12.5 and 25 grams of zinc per treeJ three times a year until 1955, when the use of ZnHEIDA was disFig. I Residual concentrations of Zn 65 following application and leaching of Zn EDTA and Zn S0 4 to pots of Lakeland sand adjusted to different pH levels. 1000 PH 5 PH 4 Zn S0 4 PH 6 PH 7 ,n 800 U) C: N Q) ::::, 600 C: ::e ... Q) a. 400 en C: ::::, 0 0 200 2 Depth, Inches

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LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS 75 continued. In September, 1955 the 12.5-gram rate for ZnEDTA and ZnEDTA-OH applied three times a year was changed to 50 grams, and the 25-gram rate was changed to 100 grams. All materials were broadcast by hand under the spread of the trees. Leaf samples taken in August, 1955 ( 1955 summer flush) and in August, 1956 ( 1956 spring flush and Table 3. Effect of soil application of zinc compounds on the zinc content of leaves of Pineapple orange trees on acid soil. Source or Zinc gm. Zn No. I?m . (b) zinc in leaves applied (a) Applications Summer Spring Summer per tree per year Flush Flush Flush ~r a:12P1. 1222 1226 1226 Zn so 4 J 100 1 33 28 30 164 1 29 28 27 328 1 . 44 44 35 100 3 35 30 29 164 3 42 42 37 328 3 tz.8 22 1.2 Zn EDTA 12.5 l 28 21 24 25 1 29 21 21 50 1 33 25 24 100 1 .3.3 26 27 12.5 .3 34 31 26 22 2 22 28 22 Zn HEIDA 12.5 1 29 25 1 34 50 1 35 100 1 37 12.5 3 32 2 Zn EDTA-OH 12.5 1 32 26 28 25 1 29 25 26 50 1 29 28 24 100 1 32 33 25 12.5 3 .31 28 26 22 2 20 22 2:z Check None 31 23 24 (a)All applications broadcast. ( b \955 summer flush sampled in August, 1955. 1956 spring flush and sUlllller flush sampled in August, 1956.

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76 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 summer flush separately) were analyzed for total zinc by the polarographic method of Bar rows , Drosdoff, and Gropp ( 1). Th e high est zinc contents were found in the leaves from trees that received the higher amounts of zinc sulfate ( Table 3). Zinc sul fate applied three times a year resulted in higher zinc content of the leav es than the same amount of zinc per application applied once a year . Application ofl00 grams of zinc per tree as the su lfate and in the chel ate form showed about equal effectiveness in increa s ing zinc in the l eaves. The low er rates of ap plication of th e chelates show ed little advan tage over the untreated checks. Thes e field r sults do not bear out th e increased availability of zinc shown by the c helates in the pot ex periment . reported above. In the pot experiTable 4. Etf'ect of' amount and method or application of ' zinc chelates on the zinc content of Pineapple orange leaves. (a) , Zp H)TA 5 l.bs soda ash 5 " " II " 5 " \E " 5 II 3 oz. AP-?8 (c) II 8 OZo II (c) " " 5 lbs soda ash " 5 II " " II Zn EDT~OH " II 10 lbs soda ash =w H 5 h Ii" i' " II 5 . . " " 5 " \E II n 5 " n " 3 oz. AP-78 (c) II 8 QZ9 " (g) " " " " II 5 lbs soda ash II i " II Check (a) Each treatment applied one time. Gmo Zn Applied J28 100 328 100 328 100 328 328 328 100 100 328 328 100 328 100 328 100 J28 .328 100, 328 l.QO None How Fe Zinc ..U,) Applied Spring Sum.er II II a II 26 Smo piles 25 " " 39 " . a " Band II Chunks " " n " Piles II " II 29 28 23 .32 29 25 26 23 25 25 23 30 25 26 23 25 24 25 29 25 28 23 28 27 30 23 25 23 25 (b) 1956 flushes, sampled in August, 1956. (c) Anionic vetting agent (Ant.are. Chemical Compa!l1')o

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LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS 77 ment, ZnEDTA was more effective than zinc sulfate in penetration of soluble zinc through the soil and also in bringing about uptake of zinc by citrus seedlings. A second experiment was started in the fall of 1955 in another part of the same Pineapple orange grove. It consisted of about 70 different zinc treatments, including sprays and soil ap plications, each applied to three individual trees. Some of these treatments were applied in the spring of 1956. Three methods of soil application were used: (a) broadcast in a band 3 to 4 feet wide, ( b) applied in harden ed chunks made by mixing the zinc sources with water and drying, and ( c) in small piles of loose material distributed around the trees. In some treatments, the zinc sources were mixed with soda ash (Na2CO,) to raise the soil pH, wettable sulfur to lower the pH, or with a wetting agent. Zinc sulfate was also applied in mixtures with calcium chloride. Foliage sprays of zinc sulfate neutralized with hydrated lime were applied for comparison with the soil treatments. In this experiment two zinc ch elates ( Zn EDT A and ZnEDTA-OH) were tested at a rate much higher than in the first experiment, but were again found to be relatively ineffec tive as sources of zinc regardless of the method of application ( Table 4). A small increase in zinc in the spring flush leaves was brought about by mixtures of chelated zinc and soda ash applied in small piles, when compared with the chelates applied alone. However, none of the chelate treatments brought about any substantial increase in the zinc content of the summer flush leaves, when compared with the untreated checks. These results are in general agreement with those obtained in the first experiment. Five pounds of zinc sulfate applied broad cast twice a year showed only a small increase in zinc uptake over similar application once a year, and the addition of wettable sulfur showed no advantage over zinc sulfate alone ( Table 5). When applied in chunks, addition of wettable sulfur gave a small increase over application of zinc sulfate alone. Zinc sulfate applied as a foliage spray in January, 1956 gave a progressive increase in the zinc content of the 1956 spring flush leaves as the concentration of the spray was increased from three to 12 pounds of zinc sulfate per 100 gallons. However, the sprays gave no increase in zinc content of the 1956 sum mer flush leaves when compared with the untreated checks. This failure of the sprayed zinc to move in substantial amounts into the newer flush tends to explain why such sprays must be repeated every year or two in qiost groves. Application of zinc sulfate to the soil in small piles is comparable to the use of hard ened chunks in that both methods give a high concentration of zinc over numerous small local soil zones. The work of Jamison (5) in dicates that this should induce greater total movement of zinc clown through the soil. In this experiment, application of zinc sulfate in small piles, either alone or with wettable sul fur, gave slightly lower zinc levels in the leaves than similar amounts applied broad cast or in chunks. However, when five pounds of zinc sulfate was mixed with five pounds of calcium chloride and applied in small piles, it gave a very striking increase in the zinc content of the leaves. The 1956 spring flush leaves contained 170 ppm. of zinc. This is nearly three times as high as that obtained from a foliage spray at 12 pounds of zinc sulfate per 100 gallons, and is four times greater than that obtained from any other soil treatment. The younger 1956 summer flush leaves contained 82 ppm of zinc, which is twice as much as the highest level from any other treatment. Several extra samples of leaves were taken and analyzed to verify these unusually high values. In the spring flush they approach the high leaf zinc levels reported by Brown ( 2) for citrus seedlings grown in pots of soil in which zinc sulfate had been mixed at the rate of 100 pounds per acre. It would appear that the high concentra tion of. soluble calcium supplied by the cal cium chloride replaced most of the zinc fixed by the soil in exchangeable form, or by satur ating the exchange complex with calcium, pre vented fixation of zinc in exchangeable form. This would permit more of the zinc to leach downward into the root zone where it could be taken up by the trees. It was not possible to prepare hardened chunks by mixing zinc sulfate and calcium chloride with water even when cement was added, but satisfactory chunks were made by mixing five pounds each of zinc sulfate, cal

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78 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 cium chloride, and wettable sulfur with water. Application of these chunks, however, showed no advantage over similar chunks containing only zinc sulfat e and wettabl e sulfur, and both of these treatments gave leaf zinc lev e l s far below those given by the mixture of zinc sulfate and calcium chloride applied in piles. This may be due to the slow breakdown of the chunks , but it may also be due in part to lowering of the soil pH by the sulfur. Various Table 5 Etf'ect ot amount and method of application of zinc sul.f'ate on the zinc content ot Pineapple orange leaves. Zinc sul.tate Lbs/tree 2 2 2 5 5 5 5 5 5 5 5 5 5 5 5 5 3/100 galo 6 II II 12 " " (Plots) Treayne~ 5 5 5 5 other Material Lbs/tree ws ws ws ws 5 ws 5 W S l'foe ot times applied (a) 1 2 1 1 2 1 2 1 2 1 2 150 ml Ethom.een T-15(c)l 5 W s 5 CaCl2 5 W s 5 CaCJ.i 1 1 l 1 1 Ca(0H) 2 /100 gal. l 2 " l 4 " 1 Check Gm.so Zno applied per tree 328 656 328 820 1640 820 1640 820 1640 820 1640 820 820 820 820 820 None Bow applied pm sine (b) Spring Summer nuh nuah B&J3d Clnmka 26 38 42 32 33 38 4D Sm. piles 26 " 31. " " 170 Foliage 31 Spr&1' 44 60 23 21 32 28 33 35 29 33 30 35 35 4l 30 35 28 26 82 22 23 24 25 (a) Where 2 applicationa are shown, the, were made about 6 110110 apart, the second one being made in Apr. 19560 (b) 1956 flushes, sampled Auguat, 1956. (c) Cationic wetting agent (Armour Chemical Din.sion, Armour & Co 0 )

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 79 mixtures of zinc sulfate and calcium chloride are being studied further as a possible sourc e of zinc suitable for soil application to citrus trees. SUl\Il\IAHY A study was made to compare the effective ness of soil application of different zinc sources to citrus trees growing on acid soil. Zinc sulfate and chelated forms of zinc were tagged with radioactive zinc-65 and leached through pots of Lakeland soil adjusted to dif ferent pH levels to study their leaching prop erties. Counts made on the leachates indi cated that ZnEDTA and ZnDCTA (zinc 1, 2 diaminocyclohexane tetraacetate) were much more effective in carrying zinc through the soil than was zinc sulfate. Virtually none of the zinc sulfate was leached through the pots . In a field experiment with Pineapple orange trees, zinc sulfate and three zinc chelates were about equal in increasing the zinc content of the leaves when each was applied once a year at 100 grams of zinc per tree per application . The highest zinc contents were found in the leaves from trees that received two pounds of zinc sulfate per tree per application. In a second field experiment, a single ap plication of five pounds zinc sulfate per tree, applied broadcast, in hardened chunks made by mixing it with water, or in small piles scat tered around the trees gave a slightly higher zinc content of both spring and summer flush leaves than foliage sprays applied at the rate of three pounds of zinc sulfate per 100 gal lons. Foliage sprays at 6 and 12 pounds of zinc sulfate per 100 gallons substantially increased the zinc content of the spring flush over that obtained with the three-pound rate, but failed to increase the zinc content of the summer flush leaves. A mixture of five pounds zinc sulfate and five pounds calcium chloride, applied in small piles beneath the trees, increas ed the zinc content of the spring flush leaves to 170 ppm, and that of the younger summer flush leaves to 82 ppm. Both figures are un usually high for mature citrus trees growing in the field. LITERATURE CITED 1. Barrows, Harold L., Matthew Drosdoff, and Armin H. Gropp. 1956. Rapid Direct Polarographic Determination of Zinc in Plant Ash Solutions. Agri cultural and Food Chemistry 4: 850-853. 2. Brown, J. W. 1955. Absorption of Zinc by Citrus from Various Soil Types. Thesis, University of Flori .. da. 3. Camp. A. F. 1934. Studies on the Effect of Zinc and Other Unusual Mineral Supplements on the Growth of Horticultural Crops. F'la. Agr . Exp. Sta. Annual Report, page 67. 4. Jamison, Vernon C. 1943 . The Effect of Phos phates upon the Fixation of Zinc and Copper in Sev eral Florida Soils. Proc. Fla. State Hort. Soc. 56: 26-31. 5. Jamison, Vernon C. 1944. Citrus Nutrition Studies. Fla. Agr . Exp . Station Annual Report, page 192. 6. Jones. H. W., 0. E. Gall , and R. M. Barnette. 1936. The Reaction of Zinc Sulfate with the Soil. Fla. Agr. Exp. Station Bui. 298. 7. Stewart, l'van, C. D. Leonard, and George Ed wards. 1955. Factors Influencing the Absorption of Zinc by Citrus. Proc. Fla . State Hort . Soc . 68: 82-88. ACKNOWLEDGMENT The authors express th . eir appreciation to the Minute Maid Corporation and to its rnpre sentatives for their cooperation and for per mitting the use of the grove in which the field experiments reported here were carried out. Appreciation is also expressed to the Dow Chemical Company and to Geigy Agricultural Chemicals for supplying the zinc chelates used. INCREASED UTILIZATION OF GRAPEFRUIT THROUGH IMPROVEMENT IN QUALITY OF PROCESSED PRODUCTS 1 F. w. WENZEL AND E. L. MOORE Florida Citrus Experiment Station Lake Alfred Increased utilization of grapefruit is needed because the present supply is in excess of de1 /Cooperative publication by the Florida Citrus Experiment Station and Florida Citrus Commission. Florida Agricultural Experiment Station Journal Series No. 564. mand. The average financial return to grape fruit growers has been small during recent years. During the 1955-56 season 48 percent of the grapefruit crop used was for processed products, such as canned grapefruit juice , canned grapefruit sections, and frozen con centrated grapefruit juice. Obviously, large amounts of these products are being bought by consumers, but improvements in the quality of some of the products packed could and

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80 FLORI.DA STATE _ HORTICULTURAL SOCIETY, 1956 should be made. Better c1uality in processed grapefruit products should lead to increased demand and subsequently to increased utiliza tion of grapefruit. This paper will discuss briefly (a) utiliza tion of Florida grapefruit for process ed prod ucts, ( b) factors which affect the quality of processed grapefruit products , and ( c) past and current investigations of the Florida Citrus Experiment Station and the Florida Citrus Commission conc e rning factors upon which the quality of processed grapefruit products depends . UTILIZATION OF FLORIDA GRAPEFf\UIT There has been a gradual increas e in th e production of Florida grapefruit from about 18 million boxes for the 1936-37 season to a peak production of about 42 million boxes dur ing the 1953-54 season; for the past two sea sons approximately 35 and 38 million boxes have been produced. During the same tim e production of Florida oranges has increased from 19 million boxes in 1936-37 to over 91 million boxes during the 1955-56 season. It may be seen from the figures in Tabl e 1 that the utilization of grapefruit by th e Florida citrus processing industry has gradually in creased over th e yea rs. For exa mple , about 38 pe rcent of the grapefruit used in the 1936-37 season went into processed products com pared to 48 perc en t during 1955-56. The maximum utilization occurred in 1945-46 when 69 percent was processed. The use of oranges for processing has increased from 3 percent during the 1936-37 season to about 37 percent in 1946-47 and to 71 percent in 1955-56 . This, it is evident that currently al most 50 percent of the grapefruit and over 70 percent of the oranges grown in Florida are being used for processed products. This is in marked contrast to the situation in and prior Tm.Bl Season 1936-37 1941-42 1946-47 1951-52 1~2-5.3 l95J-S4 1954-SS 19S5-S6 Utilization ot !'lorida Grapefruit !'rash and Prooeased l, 2 F:reah fruit Fruit Fresh and salee processed prooeaaed Thousands Thouaands Thousands of boxes ot boxes ot boxes 11,233 6,759 17,992 8,956 10,14.3 19,099 10,414 15,866 26,280 19,172 1.3,678 32,BS0 17,.305 15,0.35 .32,340 20,451 20,089 40,540 19,26.J lS,660 34,923 19,925 18,661 J8,S86 Processed % ot total 37.6 5.3.1 6o.4 41.6 46.5 49.6 44.8 48.4 l figures aboTe for boxes for 195.3-54 and previous seasons from Florida Citrus Fruit 1955 Annual &immar7, prepared b7 Paul E. Shuler and J. c. Towsend, Jr., with the cooperation of Florida Crop and Livestock Reporting Service, Orlando, norida, norida Citrus Camaiasion, Lalcal.and, Florida, Florida Department of Agriculture, Nathan Mqo, Coaniaaioner, and J&ricultural Marketing Service, u.s. Department of Agriculture. 2 Figures above tor boxea tor 1954-55 and 1955-56 frm Annual Reports, Citrus and Vegetable Inspection Division, Florida Department of .Airiculture, Winter Hann, Florida.

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 81 TABLE 2 Quantity ot Florida Grapetruit Used tor Packa ot Major Prooesaed Produota prior to the 1952-53 Seaeon 1 , 2 Processed 1936-37 1941-42 191/,-47 1951-52 grapetrui t Boxes Boxes % Boxes :l Boxes produot Canned Juice J,057,179 51.9 5,683,874 58.0 7,584,708 49.0 6,812,089 56.J Canned blended juice 90,367 1.5 1,123,932 ll.5 4,273,355 27.7 2,736,950 22.7 Canned sections 2,701,714 45.8 2,852,107 29.2 3,453,827 22.4 2,290,301 19.0 Canned ci true salad 49,205 o.s 122,694 1.3 140,357 0.9 238,054 2.0 Totals 5,89B,.4h5 100.0 9,782,607 100,0 15,452,247 100.0 12,077,394 100.c, 1 Figures above for field boxes furnished by and used throu,ih the courtesy of the Florida Canners• Aaoooiation, Vinter Haven, Florida, 2 F!EUres above do not include utilization of grapefruit tor other procened produota, suoh u grapefruit oonoentrate, to 1936, when most of the orang es and grape fruit from Florida were sold as fresh fruit. In view of these facts, it is time that more em phasis be placed by growers and processors on the production and use of citrus fruits hav ing internal quality necessary for th e produc tion of processed products of good quality. The quantity of grapefruit used for th e pro duction of th e more important processed grapefruit products is shown in Table 2 for some seasons prior to the 1952-53 season . Statistics presented in Table 3 show that the four products that have been the best outlets for grapefruit during the past five seasons have been canned grapefruit juice , canned grapefruit sections, canned blended juice, and frozen grapefruit concentrate. Perhaps it should be point ed out, since both seedless and seedy grapefruit are produced, that during the 1955-56 season 75 percent of the seedy grapefruit was sent to commercial canneries but the corresponding amount of seedless fruit was 32 percent. During the last five yea rs utilization of grapefruit (Table 3) for canned juice has varied from less than 7 to more than 11 mil lion boxes, while that for blend has varied only slightly; these two products in 1955-56 provided an outlet for about 11.8 million boxes or 66.4 percent of th e total grapefruit used by processors in the major process ed products. Since the 1946-47 season, the pack of canned grapefruit sectio ns and citrus salad TABLE .3 ~tit;r ot norida Gra~tnlit Used tor Paaka ot Major Proo•ued Produota .trom tbe 1951-52 Seuon tbrougb tho 1955-56 Season l, 2 Prooessed 1951-52 1952-5.3 1953-5!! 1954-55 1955-56 grapetnlit Boxes Boxes % Boxes % Boxea % Boxes produot Canned Juioe 6,812,089 S0.6 8,.3.38,569 56.2 ll,459,550 58.0 8,226,991 5.3.8 9,585,095 5.3.8 Canned blended juioe 2,7.36,950 20,4 2,.371,54) 16.0 2,797,251 14.l 2,074,.358 l).6 2,2.36,4.37 12.6 Canned Hotiona 2,290,.301 17.1 2,55.3,104 17,2 .3,lll,999 lS.7 .3,.367,061 22.0 .3,179,466 17.8 Canned oi true salod 2.38,054 l.8 289,489 l.9 .379,686 l.9 .326,857 2.l 295,622 l.7 h-ozen concentrate l,084,986 8.l l,l59,l7.3 7.8 l,682,141 8.5 l,065,480 7,0 2,128,620 12.0 J'rozen blended 268,2.31 2.0 1)),785 0,9 .358,429 l.8 224,586 l.5 .365,UO 2.l concentrate Totals l.3,4.30,6ll 100.0 14,845,66.3 100.0 19,789,056 100.0 15,285,.3.3.3 100.0 17,790,.350 100.0 l l'icur•• al>ove tor !ield boxes turniahod b;r and used tbrougb tbe courtea;r or tbo Florida Ce:nnera I Aaaooiation, Wintv HaYen, Florida. 2 l"icurea above do not include utilization or g:rapefrui t tor other prooeasod produots, auob aa prooooaed il"&pefrui t oonoontrato, trozon g:r•~t aections, obillod grapotnlit ooctiona and aalod, or cbilled gr~tnlit Juico.

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82 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 has ranged from approximately 4 to 6 million cases (24/2's). During the 195 . 5-56 s e ason al most 3Jf million boxes of grapefruit were us e d for canning about 5)f million cases of grape fruit sections and salad, which corresponded ( Table 3) to 19.5 percent of the total grape fruit used. Through the use of grapefruit of suitable quality and good processing pro cedures, canned sections of excellent quality may be obtained. Such a product has always met with good consumer acceptance, and it is believed that the increased sale of canned grapefruit sections, both in this country and in foreign countries, would provide a means for the utilization of some of the excess grape fruit now available. Since Florida produces over 70 percent of the world crop of grape fruit, it would seem that the potential possi bilities for export of canned grapefruit sec tions should be very great. It is difficult to understand why in recent years the grapefruit section pack continues to be only approxi mately double what it was in the 1930-31 season. The largest production oi frozen concen trated grapefruit juice occurred during the 1955-56 season, when over 2Jf million gallons were produced from about 2J~ million boxes of fruit. In contrast to this, during the same sea ~on over 70 million gallons of frozen con centrated orange juice were produced. Thus, it is evident that the acceptance and use of frozen grapefruit concentrate by consumers has been far below that of frozen orange con centrate. There was a sharp drop in produc tion during the 1950-51 season of frozen grapefruit concentrate to only about 188,000 gallons caused by poor acceptance of the 1.6 million gallons of this product packed in the previous year. The size of the frozen grape fruit concentrate pack has just in recent seasons reached and during 1955-56 exceeded what it was six years ago in its second season. About 17~ .. million boxes of grapefruit were used in 1955-56, by the processing industry for the production of the major grapefruit products listed in Table 3. Canned grapefruit juice provided an outlet for 53.8 percent of this fruit and 17.8 percent was used for the canning of grapefruit sections. In the produc tion of the canned blended juice and frozen grapefruit concentrate packs, 12.6 and 12.0 percent of fruit were used, r e sp e ctively. Canned citrus salad and frozen concentrated blended juice togeth e r accounted for 3.8 per cent. The utilization figures given in Tables 2 and 3 are only for the more important products listed and, ther e fore, are slightly less than th e actual total amounts of grapefruit used for processing. Some fruit also was used for products such as concentrated processed grape fruit juice, chilled grapefruit juice, and chilled grapefruit sections and salad. Thus during the 1955-56 season, 544,070 boxes and 262,099 boxes of grapefruit were used for chilled sec tions and juice, respectively. QUALITY OF PROCESSED GRAPEFRUIT PRODUCTS The meaning of the term, quality, depends upon both the person using the term and the products to which the term is applied. For ex ample in speaking of fresh grapefruit, growers and shippers place considerable emphasis on the external appearance of fruit, provided it meets maturity standards for internal quality, while processors are chiefly concerned with the internal characteristics of the fruit. Thus, the concentrator is more interested in the total soluble solidg in the juice than he is in having fruit free of external blemishes. In packing un sweetened canned grapefruit juice, the use of fruit containing juice of low acidity and high Brix/acid ratio is extremely important, while fruit with a greater acid content, provided that it is not excessive, may be used for the pro• duction of sweetened processed grapefruit products. The definition of quality for processed citrus products should be based upon the desires and opinions of consumers, because the demand for these products depends to a great extent upon such desires. Of course, the price that consumers have to pay for these products is another factor and perhaps the major one which influences total demand; also, today ease of use or convenience is becoming con tinually of greater importance to the house wife. Recently, Florida Citrus Mutual has re viewed ( 22) some of the consumer surveys ( 5, 7, 24) which have been made during recent years to determine the characteristics of pro cessed grapefruit products which consumers considered to be acceptable and of good qual ity. The canned grapefruit juices used for one of these surveys ( 4, 5) were packed in th e pilot plant at the Citrus Experiment Station. Other reports on con s umer surveys ( 4, 6) con

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 83 cerned with this problem have also been pub lished. Very briefly and in general, most of the results from these surveys have indicated that most consumers prefer grapefruit products that have a typical grapefruit flavor, are mod erately sweet and not excessively bitter. Therefore, these three characteristics may be used as an indication of quality in canned grapefruit juice and other grapefruit products. Characteristics other than these also influence the quality of such products. For example, canned grapefruit sections of good quality should also be firm and uniform in size and appearance; discoloration and undesirable fla vors in sections, caused by poor storage con ditions, are not desirable. Likewise frozen concentrated grapefruit juice should show no tendency to gelation, should reconstitute easi ly and then be free from indications of sepa ration or clarification. To improve the quality ot processed citrus products, both growers and processors should consider factual information that has been made available through past research investi gations concerning the factors that affect the quality of these products. They should also be aware of current research projects, the ulti mate practical object of which is the profit. able utilization of the entire grapefruit crop either by improvement in the quality of the major processed products that are now packed; thereby causing better acceptance and more demand, or by the development of new processed products or by-products that will provide other outlets for this fruit. Some of these research investigations, that have been completed or are in progress, at the Citrus Experiment Station will be discussed briefly. Principal emphasis concerning processed prod ucts has been placed on the factors affecting the quality of canned grapefruit sections, canned grapefruit juice and frozen concen trated grapefruit juice. An investigation on the effect of storage temperature on quality of canned grapefruit sections was discussed by Huggart, Wenzel and Moore ( 9). Results indicated that for maintenance of original good quality in canned sections, the products should be held at 70 F. or lower. Marked changes in color, flavor and firmness that result in lower quality in this product occurred at storage temper atures of 80 F. or above. Another study ( 10) recently completed has shown that the dis coloration or browning of canned grapefruit sections during storage is related to the acidity in the canned product, which is dependent upon the acid content of the grapefruit used. In general, browning occurred during storage more frequently in the canned sections with the greater acidities. The effect of cultural practices on the quality of canned grapefruit sections has been subject to investigation during the past three seasons. Discussion of the data obtained when canned grapefruit sections were processed commercially from fruit grove plots that were treated with fertilizer containing various amounts of potash has been reported ( 27). It was found, as is generally known, that the time at which grapefruit are harvested is a factor affecting the quality of canned sec tions; also that when grapefruit were picked at the same time from trees which had re ceived fertilizer containing 0, 3, and 10 per cent potash, the firmness of the canned sec tions decreased with increase in the amount of potash. A similar study using arsenated and unarsenated grapefruit will be completed this season. Research has been done on various problems concerning the production and storage of froz en concentrated grapefruit juice. Data on changes that occur in this product during stor age, such as gelation, clarification, sugar hy drate formations and the very slight loss of ascorbic acid have been published in various articles ( 2, 8, 13, 14, 15, 18, 25). Thermal stabilization of grapefruit juice for the produc tion of frozen concentrate has been found necessary to prevent the occurrence of gela tion and clarification in this product during storage and distribution. Atkins, Rouse and others (1, 2, 3, 19, 20) have reported results obtained from several investigations of this process for the production of frozen grape fruit concentrate of good quality. During stor age at o F. or lower, undesirable flavors may develop in frozen grapefruit concentrate. Such off-flavors are usually described as being simi lar to tallow, castor oil, or cardboard. Results of the study since 1953 of this problem were recently reported ( 17). Oxidative changes are believed to be involved in the development of these off-flavors and it has been found that the maintenance of a sufficiently high peel oil

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84 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 level in grapefruit concentrate helps to pre vent either the development or the detection of these undesirable flavors. Two investiga tions were instigated, during the 1955-56 season, at the request of the Quality Advisory Committee of the Florida Canners' Associa tion to determine factors that affect the qual. ity of frozen grapefruit concentrate. The first of these studies was the determination of most of the chemical, physical and other characteris tics of 28 packs of commercial frozen grape fruit concentrate that were collected from 11 Florida plants. The purpose of the second study was to obtain data that might indicate the relationship between the quality of raw grapefruit juice and that of the frozen grape fruit concentrate produced from it. Fruit from different localities were obtained and 11 lots were processed in the pilot plant. Data obtained from these two investigations were presented recently ( 28) and similar studies are again planned for this season. The effect of fruit maturity on the quality of frozen grapefruit concentrate is also being studied intensively. The presence of the bitter glucoside, naring in, is the chief cause of bitterness in processed grapefruit products. Kesterson and Hendrick son ( 11) found no significant difference in the amount of naringin in juices extracted from different varieties of Florida grapefruit and also reported that most of the naringin was in the albedo, rag and pulp of the fruit. The degree of bitterness in canned grapefruit juice or frozen concentrate is dependent upon the juice extracting and finishing procedures used, since the quantity of pulp, rag, and albedo in the processed product is determined by these procedures. A method for the estimation of naringin was devised by Ting ( 23) that is based on the enzymic hydrolysis of it by a glycosidase. With further modifications, this method may provide the processor with a laboratory procedure for determining, and thereby controlling, the degree of bitterness in processed grapefruit products. Some work also has been started by Olsen ( 16) to develop uses for grapefruit in products different from those that have been previously discussed, with emphasis on the utilization of grapefruit of high acid content. A canned pasteurized grapefruit product has been made from very sour grapefruit juice by the addition of sugar and a small amount of peel oil and when this product is mixed with an equal volume of water, a very palatable grapefruit drink is obtained. A clarified grapefruit con centrate of good quality has been prepared and the preparation of either a still or car bonated grapefruit drink from this product is being investigated. Canned blended fruit juices of various types are being consumed in larger quantities yearly and, therefore, the use of grapefruit juice in various types of blends may be investigated during this season; sev eral packs for storage studies may be pro cessed. From this discussion it should be evident that a great amount of research has been and is being done at the Citrus Experiment Station on problems related to the quality of processed grapefruit products. Now let us consider what the grower and processor can do to improve the quality of processed grapefruit products. One of the major problems that confronts the processor in his attempt to make products of uniform and acceptable quality is the great variation throughout the entire packing season in the internal quality of grapefruit that he has to use. This wide variation in fruit exists because of many factors, such as differences in varie ties, maturity, cultural practices, rootstock, soil and weather conditions. Sites and Camp (21) discussed some of these factors in relation to the use of citrus fruits, chiefly oranges, for the production of frozen citrus concentrates. Wen zel and Moore ( 26) reported on the character istics of concentrates made from different varieties of citrus fruits, including grapefruit. In general the flavor of processed products made from seedy grapefruit is better than that in products made from seedless grapefruit. Other factors causing wide variations found in the quality of grapefruit sold for processing are the use of fruit from packing houses which is not suitable for fresh shipments, the fact that only a portion of the grapefruit crop is arsenated, the increased production and use of pink grapefruit, and the tendency for grapefruit trees to bloom and set fruit at dif ferent times during the same season. Since such great variation exists in the quality of fruit throughout a season, processed products of variable quality will result if such fruit is used at random. If products of acceptable,

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 85 uniform, and improved quality are to b e packed , the processor must eliminate th e grapefruit, which he receives from either pack ing houses or groves, that is not suitable for use in the specific type of process e d produ c t that is being p a cked. Also for the compl e te utilization of the grap e fruit crop, culled fruit that cannot b e either sold as fr e sh fruit or used in proc e ss e d products, will have to b e diverted to some other use , such a s the pro duction of citrus by-products as r e c e ntly sug gested by Kesterson, Hendrickson and New hall in a report ( 12) to a Grapefruit Stud y Committee of Florida Citrus Mutual. If such culled fruit cannot b e profitably used for some other purpose, th e n it will be better to return it to the grower to be discarded rather than to impose it upon consumers as canned grapefruit juice or frozen grapefruit conc e trate of poor and unacceptable quality. Grow ers should realize that some of the grapefruit that is being produced c a nnot be made into canned grap e fruit juice, canned sections or frozen concentrate of good quality. It is sug gested that growers find out mor e about the intern a l quality of grap e fruit th a t , is ne e d e d by processors for the production of products of good quality; then using inform a tion av a il able about the relation of cultural practices and other factors to the internal quality , do what they can to produce fruit that will b e suitable and desirable for the production of one or two specific processed products. Much mor e information is needed b e fore such characteristics as flavor or degree of bitterness in grapefruit may be subject to control by the grower through cultural or other practic e s. However, grow e rs can control to some extent the acidity in grapefruit by ar senation; also fertilizer constituents, such as potash, have an effect on this characteristic. Ther e fore, growers can do something about the production of grapefruit with a low acid content or high Brix/acid ratio, which is de sirable for producing processed products of good quality and especially those that will not be sweetened by the addition of sugar. It is realized that problems are encountered wh e n arsenation is used, but such treatment pro vides the principal methotl for th e production of less tart or sweeter grapefruit e ither early in the season or during mid-season. Regardless of the cultural practic es used, it i s very import a nt that growers do not harve s t the crop until the fruit h a s reach e d its optimum ma turity and a desirable Brix/acid ratio obtain e d for th e specific use for which it is intended. Sinc e the int e rnal qu a lity of the fruit is on e of the major factors that determines the qual ity of process e d product s , processors should obtain and us e only the kind of grapefruit th a t is needed to produce products of good quality. During the p a st season most of the conc e trators, who packed fro z en grapefruit con centr a te, made an effort to obtain fruit of better internal quality than that previously us e d; this was done following recommenda tions of the Quality Advisory Committee of the Florida C a nners' Association and surely was a step in the right direction. Some incentive to the grower for the pro duction of grap e fruit of good quality would be provided if processors found it economical ly possible to pay for grapefruit on the basi s of its internal quality, as they are now doing for th e procur e ment of oranges of high solid s content for frozen orange concentr a te. Processing procedures and techniques deter• min e to som e extent the quality of all pro cess e d citrus products. For exampl e , the de gree of bitterness in canned grap e fruit juic e or frozen conc e ntrate may be varied by juice extr a cting and finishing procedures. During the past season some processor s have d e creased the bitterness in packs of canned grapefruit juice and frozen conc e ntrate b y voluntarily making changes in extracting and finishing procedures, even though such changes resulted in a decrease in the yield of juice . Such efforts are to be comm e nded and should result in an increased demand for thes e products of better quality. Thermal stabiliz a tion of grapefruit juice used in the production of frozen concentrate has been found to be necessary to prevent gelation and clarification in this product during distribution and stor age. Adjustment of the a mount of peel oil in frozen concentrate is also necessary for d e sirabl e intensity of flavor and to help prevent the occurrence or the detection of "oxidiz e d" off-fl a vors that may occur during frozen stor age . Unsweetened cann e d grapefruit juice and unsw ee tened frozen concentrate s hould b e mad e only from fruit th a t is fully mature and from juice whi c h has a Brix/ acid r a tio within the range that h a s been s hown b y various sur

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86 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 veys to be acceptable to consumers. When sweetened products are packed from low ratio fruit, excessive amounts of sugar should not be added since dilution of the flavor in the product will result. All processed grape fruit products should be stored under condi tions which will minimize changes in flavor that occur if the temperature and time of stor age are too great. Storage of canned grape fruit juice and sections at temperatures lower than 80' F., if possible, is advisable and frozen concentrate should be stored at 0 F. or lower. It is hoped that this brief discussion will help growers to understand some of the prob lems involved in the production of processed grapefruit products of good quality and to realize that the production of products which will be acceptable to most consumers depends to a great extent on the internal quality of the grapefruit which the processor uses. SUMMARY Statistics presented show that canned grape fruit juice, canned blended juice, canned grapefruit sections, and frozen grapefruit con centrate are the principal products into which Florida grapefruit are processed. About 48 per cent of the grapefruit crop was used during the 1955-56 season in these and other pro cessed grapefruit products. Research investigations concerned with fac tors, such as bitterness, acidity, flavor and stability, that affect the quality of processed grapefruit products are briefly discussed. In order that improvement may be made in processed grapefruit products, it is suggested that growers produce fruit of such internal quality that most of it can be processed into products of good and acceptable quality; also, if possible, that grapefruit which will not be sold as fresh fruit should be produced with internal quality suitable for use in one or two specific processed products. It is suggested that processors use only fruit of such internal quality that will result in the production of products of good and acceptable quality; that processing procedures which affect quality be carefully controlled and that processed prod ucts be stored at all times under optimum conditions for maintenance of their initial good quality. Complete utilization of the Florida grape fruit crop should be possible through the sale of fresh fruit and processed grapefruit prod ucts of good quality, together with the diver sion to the production of citrus by-products or other uses of all fruit that cannot be used for these purposes because of poor internal quality. LITERATURE CITED 1. Atkins, C. D., and A. H. Rouse. 1953. Time temperature relationships for heat inactivation of pectinesterase in citrus juices. . Food Technol. 7: 489-491. _ 2. Atkins, C. D., A. H. Rouse, R. L. Huggart, E. L. Moore. and F. W. Wenzel. 1953. Gelation and clarification in concentrated . citrus juices. III. Effect of heat treatment of Valencia or . ange and Duncan grapefruit juices ' prior to concentration. Foo
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PRATT: LONG RANGE RELATIONSHIPS 87 22. Steele, Herman F. 1956. Summary of con Sumer surveys. Florida Citrus Mutual Mimeo. Re port Feb. 28. 23 . Ting, S. V. 19 5 5. Application of en z ymic hydro lysis in the analy s is of naringin in gr a pefruit prod uct s. Fla. Agr. Exp . Sta . . Citrus Station Mimeo. Report 56-9. 24 . U. S. Dept. A g riculture. Bure a u of Agricultural E conomics, Washington, D.C. 19 5 0 . Consumers use of a nd opinions about citrus products. 25. Wenzel, F. W. , E. L. Moore , A. H. Rouse and C. D . Atkins. 1951. Gelation and cl a rification in con centr a ted citrus juic e s. I. Introduction and present s t a tu s . Food Tech no I. 5: 454-457. 26. Wenzel, F. W., and E. L . Moore. 1955. Ch a acteristics of concentrates m a de from diff e rent varieties of citrus fruits. Food T e chnol. 9: 293-296 . 27. Wenzel. F . W., R. L. Hu g g a rt, E. L. Moo r e, J . W. Sites, E . J . Deszyck , R . W . Barron, R. W . Ol s en , A. H . Rou s e . and C. D. Atkins. 1956. Quality of canned grap e fruit sections from plots fertilized with var y in g amounts of potash. Proc. Fl a . State Hort. Soc . 69: 170-175. 28. Wenz e l, F. W .. R. W. Ol se n , E. L. Moor e , R . L. Huggart, C. D . Atkins, A. H. Rouse, S. V. Ting, E. C. Hill, E. J. D e s z yck, R. Patrick, and R. W. Barron. 1956. Investi ga tions concerning f a ctors affecting the quality of froz e n grapefruit concentrate. Fla. A g r . Exp. Sta., Citru s Station Mim eo. Report 57-3 . LONG RANGE RELATIONSHIPS BETWEEN WEATHER FACTORS AND SCALE INSECT POPULATIONS ROB E RT M. PnA TT Florida Citrus Experiment Station Lak e Alfred Forecasts of scale infestations can be based in part on annual and seasonal cycles, but to forecast the lev e l the population will reach at any given time, it is necessary to know some thing of the factor~ which cause deviations from the long term a verage population . The abundance of scales and other ins e cts and mites is regulated by many interacting climatic and biological factors. The total ef fect of these can be determin e d only by field ob se rvations . Methods of d e t e rmining the populations of scales and other insects and mites have b e en described previously ( 1). A continuous record for nearly six years is now available. It is not possible to evaluate all of many individual factors separat e ly on the basi s of field records , but some can b e isolated in the laboratory, and others are of sufficient im portance to be recognized even in the presen c e of other influences. Certain climatic factors which have b e en found to have an influence on the population of Florida red and purple scales are discussed here. FLORIDA RED SCAL E The population of Florida red scale, Chry somphalus aonidium (L.), reaches a peak som e time in July e ach year. This is followed by a declining . tr e nd that continu e s into Sep t e mber. In the five years for which a conFlorida Agri c ultur a l Experimen t St a tion Journ a l S er ies , No. 563. tinuous record is available, there have b ee n two years in which the population was almost constant at a low level from October through February. In the other three years, the av e age infestation has increased sharply in Octo b e r and re a ched a high level by the middle of Novemb e r. Obviously, it is advantageous to citrus growers to know as far ahead as possible whether such a fall red scale outbreak will occur. It has be e n known for several years that when the red scale activity index ( 1) in creased to a high level in August, a high pop ulation in October and Nov e mber would fol low. This observation was us e d successfully in forecasting th e severe outbre a k that occurred in . the fall of 1955. The ecological factors in volved in this pattern w e re not known. Since the trend was discernible as early as the first week in August, obviously, the factors respon sible had to have occurred before this tim e . A critical examin a tion of a graph showing p e cent of l e aves infested show e d that in th e years when fall outbreak s occurred, a higher population lev e l occurred as early as mid-July, s o the clim a tological data from the months preceding that date were examined. Among the factors considered w e re rainfall ( Table 1) and temp e r a tures, as r e fl e cted by monthly summation of Heating Degree Days (Table 2). Note that in measuring the amount of cold weather in degree days, a low value indic a tes warm weather and a high value indicates cold weather, Red scale infestations were comput e d for comparison a s the ma x imum infestation in October or November, and as the av e rage

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88 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 1 Rainfall 1951-56* Year December Jamary February March April 1950-51 2.56 1.36 2 .53 1.68 4.96 1951-52 1.94 .49 5.96 4.,n .84 1952-53 .59 3.51 2.99 3.61 4.90 195.3-54 4.10 1.38 1.50 2.23 3.85 195Ai-55 1.39 2.25 1.75 .91 2.67 1955-56 1.08 1.89 .99 .38 2.30 *Compiled !l'Olll Weekly Weather am Crop Summary. percent of leav es infested, August through December (Table 3). To seek a basis for comp aris on, the years of the record were divided into two groups, one including the three years ( 1951, 1954, 1955) in which a fall outbreak occurred, and one including two years ( 1952, 1953) in which red scale populations were negligible in the late s umm er and fall. The climatological data for these two groups of years were then exa mined for diff eren ces. The months were considered individually and in various com binations. Inspection of the population data an d the climatological records indicated that the great est difference in temperature and rainfall between th e two groups of years oc curred in March, but that the most consistent relationship betw een climatic factors and sca l e population was for the period, Januar y through March. Where a substantial differ enc e between th e two groups of years was found, th e coefficient of correlation between the weather factor and scale population was computed. These comparisons are summar ized in Table 4. The correlation between the highest level of activity in August and the average infesta tion, August through December, is significant. The correlations between the cold weather factor ( degree days, January through March) and both the August activity and fall average population is highly significant. The n egat ive correlation between the total rainfall, Januar y through March, and August activity is not significant, but between rain Table 2 Heating Degree ~s 1951-56* Year December J'anuar:r February March April 1950-51 253 189 153 68 40 1951-52 71 122 151 45 23 1952-53 207 174 88 18 21 195.3-54 145 118 124 146 2 195Ai-55 275 2~ 123 78 4 1955-56 147 309 S6 80 15 *Computed b.r subtracting the daj_cy' mean temperature !l'Olll 65 F. am summing for the period. Data f'l'OJl J\ygrothermograph stations at Iske Alfred, Merritt Islam, Tavares, Lutz. am Avon Park.

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PRATT: LONG RANGE RELATIONSHIPS 89 FACTORS IN FALL RED SCALE POPULATION Fig. 1. Factors in Fall Red Scale Population. Cl) Ill :i:: 12 6 I 5 z
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90 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 4 Correlations between Red Scale am Weather 1951-55 Comparison August Activity**/Popuation*** Degree Ihzy's, Jan.-Mar./August Activity Degree Days, Jan.-Mar./Popuation Rain, Jan.-Mar./A:ngust Activity Rain, Jan.-Mar./Popuation Correlation Coefficient Significance* 19 : 1 99 : 1 99 : l n.s. 19 .: l *Required for significance at the 19 : l level .878. Required for significance at the 99 : l level .959. **Maxilmlm activity level during the month. ***Average percent of leaves infested, August through December. from March through June has been found, and there does not appear to be any relationship between populations in this period and those occurring in the fall. PURPLE SCALE Purple scale, Lepidosaphes beckii ( N ewm.), is regarded as the major scale pest of citrus in Florida. An examination of the annual popula tion cycles for the last five years reveals that there is but little difference from year to year. This suggests that differences in the weather from year to year have less influence on the population level at any given season than is the case for other pests, such as red scale. There is, however, a well defined annual cycle. The population reaches a peak sometime in July, the exact time apparently being determined by the time of the onset of the rainy season. Following the summer peak of infestation, the population declines rapidly until mid-September. This reduction has been attributed to a disease, Chytridiosis ( 2, 3). After September, there is a more or less regu lar increase in population through the time when counts on old leaves are ended in May, and until a peak of infestation on new leaves is reached again in July. There is some year-to-year variation in the magnitude of the population. Examination of the population data revealed a small, but con sistent, difference at the end. of December which permitted dividing the record into two Table 5 lurple Scale Intestations in December, May, am Percent Leaves Infested Max. Date of Year 4th Week-Dec. 4th Week-Ha;r Peak 1951-52 8.5 22.5 10.9 1st Week 1952-53 ll.l. 27.3 14.3 lat Week 1953-54 8.3 29.2 18.3 1st Week 195A,-55 u.s 28.8 17.2 2m Week 1955-56 8.6 23.6 18.8 3rd Week

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PRATT: LONG RANGE RELATIONSHIPS Table 6 91 Relation Between Degree Da)-a in December am Jamar.r to l\lrple Scale Poplll.ation the following December Degree Ila.Ya Percent leaves Infested in following December Year Dec.+Jan. lat Week 1950-51 w. 9.2 1951-52 19.3 10.8 1952-5.3 .381 8 .3 1953-54 26.3 12.4 1954,-55 517 7.7 groups of years. In one group ( 1951, 1953, 1955), the infestation was between 8 and 9 percent. In the other years ( 1952, 1954), it was over 11 percent. These general relation ships persisted until the following July (Table 5), with the following exceptions: in May, 1954, the population was higher than would have been expected from . the preceding De . cember population, and the July population was proportional to that occurring . in May. In 1956, the July peak was higher than would have been expected from the December and May levels. To find climatic factors correlated with the purple scale population in December, the records were examined in the same way that was used for red scale. A preliminary exam ination of the records indicated that there were no differences in the summer and fall months that showed any consistent relationship with the scale population at the end of the year so attention was given to the records of the pre vious winter ( see Tables 1 and 2) . No general relation between rainfall and population was found, but it was determined that there was a fairly constant inverse rela tionship between the amount of cold weather in December and January and the purple scale population the following December (Table 6). That is, the warmer this period, the higher the scale population. With the limited data available, a significant correlation (r= -.878: required for 19 : l -.878) was found only between the tempera ture factor and the population in the third week of December, but it is not considered 2m Week .3rd Week 4th Week Av. 8.9 8.5 8.5 8.8 11 .3 11.5 11.1 11.2 8 .3 8.2 8 .3 8 .3 12.3 12.1 12.8 12.4 7.6 8 .3 8.6 8.1 that there is anything critical about this par ticular time. Obviously, there is a very high correlation between the population in the third week and in the fourth week. With exceptions noted above, the popula tions in May and July are proportional to those in December, and therefore to the De cei_nber-January temperature factor . In 1954, the scale population was low through March, as expected, but the increase in population in April and May was rapid and a high level was reached. The peak popula tion in July was proportionately high. Examination of weather records indicated that the only unusual occurrence was an un seasonable cold spell early in March (see Table 2). This was accompanied by a brief reduction in scale population and followed by an increasing trend. A significant correlation (r=.939) was found between the degree days in March and the change of scale population between that at the encl of December and that at the peak of population in July. There was also a significant correlation ( r= .878) be tween the lowest March weekly mean tem perature and the change in scale population from the end of December to the end of May. In 1956, the scale population at the encl of May was relatively low, and in propo1tion to the population at the end of December, but the average infestation increased rapidly in June and July. When the peak was reached the third week in July, the population was at a record high level. There are indications that this was a result of the prolonged drought, but the evidence is not considered conclusive.

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92 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 There was, however , a s ignificant correlation (r= -.890) betwe en th e rainfall in the peri od, January through March, and th e ratio be tween the May and July populations. In April of 1953, th ere was a brief decline in purple scale population at a time when a strongly increasing tr e nd was to b e expec t e d. This coincided with an extensive rainy period. There was a highly significant negativ e corre lation between the amount of rain in March and April ( see Table 2) a nd the population change in the same period (r= -.993: .95 9 required for significance at 1%). From the foregoing, it ma y be concluded th a t the purple scale population at the end of the calendar year is proportional to the temp era tures in the preceding Dec em ber and Janu ary (inversely correlated with the number of degree days) and that this general rela tion s hip will persist through the peak of in festations the following July, but the antici pat ed general trend may be modifi ed by sub sequ en t weather conditions which have more imm ediate effects ( Fig. 2). If th e r e is a late cold spell, the population following will be high er. If there is a wet s pring , it will be lower, but if the spring is exceptionally dry, it will be higher than expecte d. FACTORS IN PURPLE SCALE POPULATION 500,. (/) 300• ><( 0 lAJ 200• ILi a: (!) ILi "' it) .,. co 0 II') II') II') II') II') I0011t I I I I I iin "' it) II') II') in in en en en en en 0 DEC.-JAN; 30 2 2 :e. 6,. 4,. 2 2 2,. 2 :c.Si6 .. 4,. 2. 01 ILi C'" a. (/) ILi 6,. u. z 4,. 2,. i .,-N .,, . II') II') Ill II') II') II') en en en en End of DEC. "' .,, .,. II') co II') II') II') II') II') en en en en en End of MAY Fig. 2. Factors in Purple Scale Population. .-.."' If) .,. II') co II') II') II') II') II') en en en en en At peak in JULY

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JOHNSON: SYSTOX USE 9::l Su.l\IMARY The population level of red scale in the fall months has been found to be correlated with the amount of cold weather in the period, January through March, and is negatively cor related with the rainfall in the same period. When the index of red scale activitv has re~che? a high level in August, a high popu lation m October and November has followed. The population of purple scale in Decem ber is correlated with the amount of warm weather in the previous December and Jan uary. The purple scale population in May and July is proportional to that in December un less there is a spring drought or a late cold spell, in which case, the populations will be higher than indicated, or unless there is abun dant spring rain, in which case, the purple scale population will be lower. LITERATURE CITED 1. Pratt, Robert M. 1952. Forecasting citrus insect infesta~ions. Fla. Grower 60 ( 11) :21. 2. Fisher, F. E., W. L. Thompson and J T Griffiths. 1949. Progress report on th.; fungus dis~ eases of scale insects attacking citrus in Florida. Fla. Ent. 32 :1-11. 3. Muma, Martin H. 1955. Factors contributing to the .natural C'on . trol of citrus insects and mites in Florida. Journal Econ. Ent . 48:432-438. NOTES ON THE USE OF SYSTOX FOR PURPLE MITE CONTROL OF CITRUS ROGER B. JOHNSON' Florida Citrus Experiment Station Lake Alfred Systox has been shown to be effective against the purple mite, M etatetranychus citri McG., under Florida conditions. Spencer and Selhime ( 1) reported in 1954 that Systox at dosages of 1 pint or 1 quart per 100 gallons controlled citrus red mite ( purple mite) as well as oil emulsion, ovotran, aramite or EPN. Thompson et al. (2) also reported in 1954 that the average period of control with Systox was 6 weeks, but that control for as long as 13 weeks had been obtained with Systox as compared to only 8 weeks with DN Dry Mix or 3 quarts of an 84 percent oil emulsion . In addition, Systox has been used by growers in both ground and air applications with re portedly satisfactory results at dosages that were sometimes very low. Since Systox is an expensive material, it is important that it be used efficiently. For this reason, experiments were conducted in 1955-1956 to obtain in formation on the effect of date of application, dosage and thoroughness of application on the interval of control of purple mite with Systox. Systox is the trade name of an emulsifiable spray concentrate containing 21.2 percent of O,O-diethyl-0-2 ( ethylmercapto) -ethyl thi ophosphate. The active ingredient, known as Florida Agricultural Experiment Stations Journal Series, No. 562. demeton, is reported to be about as toxic to warm blooded animals as parathion and is more readily absorbed through the skin. This means that the same precautions used in handling parathioi1 must also be employed with Systox. TIMING OF SYSTOX SPRAYS Jeppson et al. ( 3) demonstrated that the longest periods of control in California fol lowed application of Systox during November and December although no application was made in January or February. These authors also reported that control tended to decrease progressively from March through September. Johnson and Thompson ( 4) reported that con trol in Florida decreased from January to May, but had made no applications prior to January. A grove of thinly-foliated Valencias about 8 to 10 feet in height at Haines City, Florida was used for an experiment to determine ef fects of date of application. This grove was divided into three blocks, each 6 by 20 trees in size. Each block or replicate was divided into four plots. One plot in each replicate was sprayed in October, a second in December, a third in February, and the last in April. A different dosage or material was applied to each of three subplots of 10 trees each. De tails of these applications are presented in Table 1. Control following the October application is shown in Fig. 1. Control is considered satis

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94 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 1 Data on the application of sprays in experiment to determine effect . or time of application or Systox on purple mite control. Date or Application Spra7 Do~ !'respray Population Material per 100 gallons Oct. 27, 1955 S,-Stox 1/2 pint Systox \1int DR Dry Mix 2 .3 lb. Dec. 22, 1955 Systox 1/2 pint l pint DR Dry Mix 2/.3 lb. Feb. 16, 1956 Systox 1/2 pint S,.stox 1 pint Ovotran l lb. Apr. 4, 1956 Systox 1/2 pint Systox 1 pint OVotran 1 lb. factory until the population exceeds 100 mites per 100 leaves. Systox at )f pint per 100 gal _ lons gave control for a period of 63 to 71 days, or about two weeks lon ge r than DN Dry Mix No. I. Systox gave somewhat better results at the dosage of I pint, but, although both dos ages of Systox were significantly better than DN Dry Mix No. I, th e re was no significant difference between the two Systox treatments. Control of purple mite with )f or I pint of Systox as well as% pound of DN Dry Mix No. I in Dec ember sprays is shown in Fig. 2. Systox at )f pint controlled purple mite for 63 to 76 days while DN Dry Mix No . 1 gave con trol for only 35 to 53 days. There was no significa nt difference between )f and I pint of Systox, but both dosages were significantly better than DN Dry Mix No. L Control of purple mite with February sprays is show n in Fig. 3. Systox at )f pint as well as ovotran at I pound controlled purple mite for 60 to 7 4 days. Although mite counts were not continued long enough to determine the in terval of control with I pint of Systox, mite populations where this dosage was us ed re mained low eve n 73 days aft er app lication. per I?!r 100 lMves acre Mites Eggs 2.7 pints 100 80 5.2 pints 100 80 2.9 lbs. 100 80 2 .3 pints 550 (,CJO 4.0 550 690 2.8 lbs. 550 690 1.9 pints 650 780 4.9 650 780 6.o lbs. 650 780 1 .3 pints 1090 540 2.9 1090 540 .3 .3 lbs. 1090 540 In Fig . 4 is shown purple mite control with sprays applied in April. In this applic a tion, Systox at Jf pint controlled purple mite for only 20 to 35 days while ovotran as well as I pint of Systox both controlled for 35 to 48 days. The results of this experiment, presented in Figs. 1 through 4, show that S ystox was ef fec tive against purpl e mite from late October through February, that a dosage of pint of Systox per 100 gallons can be superior to DN Dry Mix No. I in late October and December, and that )f pint of Systox can eq ual I pound of ovotran in February. These data also show that Systox was relatively ineff ective in April. Data pres en t ed in Table I show that during the interv a l from October through February when control was satisfactory the dosag e of )f pint of Systox per 100 gallons was equiva l e nt to 2.7 to 1.9 pints per acre. Since th e low er rate p er acre was as effective against a high mite population as the high er rate against a low population, it can be concluded that about 2 pints per acre of tr ees 8 to 10 feet high will give satisfactory results from Octo ber through February. Larger amounts should be needed on larger trees.

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JOHNSON: SYSTOX USE 95 ... ., .. ,. .. , I FIG.3 ' iDN. Dry Ml1 i I ..,,, I .,..,,. •,, SJSIOI, pt. TT 9t 109 Oct. 27, 1955 s,1101, pt. Mu. Saft Po ulallo• ~1 , ool--'!!!.!.'-"-"'-'-''-""'<==----1t------'t5 .! E :, ,,. ,...,sr1to1,lpt. z EFFECT OF DOSAGE Three experiments were conducted to de termine whether dosages of )$ or )4 pint of Sys tox per 100 gallons would give as satisfactory control as Jf pint. The first of these tests was started when sprays were applied November 15, 1955 to sparsely foliated trees 8 to 10 feet in height in a grove of Valencias at Haines City, Florida. Mite populations when sprays were applied were at the low level of 105 mites and 308 eggs per 100 leaves. Under these conditions, dosages of Systox from Ji to 1 pint per 100 gallons gave satisfactory control. However, data presented in Table 2 show differences between treatments. Dosages of )4 pint (0.6 pint per acre) or )f pint ( 1.4 pints per acre) of Systox as well as DN Dry Mix No. 1 con trolled purple mite for 85 to 105 days. The dosage of ~t pint ( 2.2 pints per acre) gave be tween 105 and 127 days of control while con trol with 1 pint ( 3.5 pints per acre) exceeded 127 days . ., > ., ., ..J 0 2200 l flO.t 't" , ON Dry MIi I __ J I / pt . DAYS AFTER SPRAYING Dec. 22,1955 FIG. 4 923 DAYS AFTER SPRAYING Apr. 4,1956 In a second experiment, Systox was applied at dosages of 1, and )4 pint per 100 gallons to heavily foliated Temple orange trees at Haines City, Florida. This application was made on Decemb e r 19, 1955 when prespray mite pop ulations averaged 580 mites and 550 eggs per 100 leaves. Under these conditions, intervals of control were as follows: 52 to 73 days with )$ pint of Systox (0.5 pint per acre), 73 to 91 clays with J{ pint of Systox ( 1.0 pint p e r acre), and 121 to 145 clays with both aramite 15-W at 2 pounds and ovotran at 1 pound. Although all periods of control in this test were length ened by the effects of a period of natural mor tality in March and early April, this test dem onstr a ted the inferiority of dosages of Systox as low as )$ to Ji pint per 100 gallons under the conditions of this test. A third test was started when sprays were applied April 3, 1956. Prespray mite popula tions averaged 210 mites and 890 eggs per 100 leaves. Under these conditions, the inter vals of control with dosages of )$ or Ji pint of

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96 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 2 Control ot purple llite vith 4 do11&gu ot Syatox applied to TaJ.encias on Novamber 15, 1955. BaiDe• Cit,-, norida 2 Material am l>oeage per 100 gallona. 1 Lin purple llitea and eggs per 100 leaves on irdicated dates (days atter application on November 15, 1955.) libT. 21 Dec. l Jan. 3 Feb, 8 Feb. 28 (~) (+16) (+49) ( -+85) ( +105) S79tox, 1/4 pint Hite• I 9 0 2) 49 ll8 Egge I 137 9 53 136 500 S711tox, 1/2 pint M!.tu I 0 0 8 17 120 Egp I 67 14 34 131 550 578tox, 3/4 pint HI.tell I 0 0 15 23 82 Egp I 98 21 51 108 33'2 sntox, 1 pint HI.tea I 0 0 3 9 44 Eggs I 76 18 14 68 180 DN Dey Mix, 2/3 lb, Mites I 1 1 21 51 182 Eggs I 92 72. 72. 145 652 ImJ I HI.tea (1911) nad nsd nad nad nad (9911) nad nsd nsd nad nad 1 AU apra:ys incluied 5 lbs. of vettable sulfur per 100 gallona, 2 Anrage pre-apre:y mite population 105 mite• am 308 eggs per 100 leaves. Table 3 Control or Purple Mite vith 4 doesges ot S;yatox applied to Valencia Orange• on April 3, 1956, Haine• Cit;y, norida Material and l Dosage per 100 Gall.01111 Lin purple aite• and eggs per 100 leavea on indicated datea 2 (dayw after application on . AFil 3, 1956). Aprll 6 (+l) 17 +14) A~23 <20) Ma:,2 (+29) Syatox, 1/8 pint Mites I 38 60 J2 447 Eggs I 362 50 244 143 S,..tox, 1/4 pint HI.tea I 24 44 15 215 Egp I 482 '9 81 114 Mites I 17 19, 5 98 Eggs I 316 63 31 84 Syatox, l pint Mites I 22 16 2 25 Eggs I 774 167 64 24 Ovotran, 1 pow,d Mites I 36 20 20 Eggs I m 82 76 55 Mar. 21 (+127) 171 . 986 291 1024 l66 673 77 IP, , 326 1298 llJ nad LSD Mites (19:1) 152 (9911) 221 1 Iu apra,a included !iii Z, 2 lba per 100 gallona I Neutro oop 53•, 1.4 lba; and wettable IIUlf'lzr, 5 lba. 2 Anrage pre-11pra7 mite popal.ation 205 mite• and 890 eggs per 100 leaves.

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JOHNSON: SYSTOX USE 97 Table 4. :i:tteot ot tboroughnesa ot application on Control or Purpoe Mite vith 87eto1. l&lm .utred, norida. Material(•) and 1'7peot Mite DoMp / 100 pllou Application Stap s,-,tox, 1/2 pint Iuide 1'oliage Mites I :Egge I S:,atox, 1/2 pi.nt Olrtaide 1'ollage Mites I Egge I S,.atox, 1/2 pint .lll 1'oliap MitH I Egge I DI! Dry Mix, 2/J lb. Olrtaide Poliage M1tea I Egge I Systox lasted only 20 to 29 days. Furthermore, mite populations 29 days after spraying (Table 3) were significantly higher where these dosages of Systox were used than where 1 pint of Systox or 1 pound of ovotran had been used. There was no significant difference be tween J~ and pint of Systox. The results of these three dosage experi ments do not prove that dosages of Systox low er than Jf pint per 100 gallons will give un satisfactory control of purple mite. They do indicate, however, that control of purple mite with J~ pint of Systox per 100 gallons may be satisfactory under some conditions but in ferior to higher dosages or other acaricides under other conditions. EFFECT OF THOROUGHNESS OF APPLICATION One test was carried out to determine wheth~r thorough coverage of all leaf sur faces would give better control of purple mite than ordinary brushing sprays of the type commonly used for rust mite control. The re sults of this test, presented in Table 4, show no superiority in purple mite control with a thorough application to all foliage over a brushing spray to outside foliage only. Both types of application were superior to a brush ing spray with DN Dry Mix No. I. DeOftlber 1955-March, 1956, Number ot Mi tH am Egge per 100 :X...•• D!,I• Bef!lre f-b•!!! .lt'tej {+) ST<~ December 8 1 12~~, l-3l + l l• l t•eJl 290 298 ll3 483 711 872 299 455 1031 1494 399 85 0 15 1?9 1049 137 33 62 501 300 rn 1 9 90 959 :m 29 48 -'01 310 uo l4 88 800 815 448 130 2'16 1914 SUMMARY Systox w as found to be effective against purple mite from late October through Febru ary, but relatively little value in April. A dos age of Jf pint of Systox per 100 gallons of spray was superior to DN Dry Mix No. 1 in late October and December, and equal to 1 pound of ovotran in February. Both Systox dosages were relatively ineffective in April. A dosage of pint of Systox _ per 100 gallons applied in October was as effective as % pound of DN Dry Mix No. I. The same dosage, how e ver, ,yas of only slight value when applied in December and April. . Brushing-type applications of Systox were as effective as full-coverage sprays. Either type of Systox application was superior to brushing-type DN Dry Mix spra ys . LITERATURE CITED \} .. ;;::{t/ 1. Spencer, Herbert and A. G. Selhime. New miti cides for the citrus r e d mite (purple mite). Fla. State Hort . Soc. Proc. 67: 1954 . > 2. Thompson, W. L . , R. B. Johnson , and J. W. Sites. The status of the purple mite and its control, Fla. State Hort. Soc. Proc. 67: 1954. 3. Jeppson, L. R., M. J. Jesser, and J. 0 . Com plin. Seasonal weather influence on efficiency of Systox applications for control of mites on lemons in Southern California. Jour, Econ. Ent. 47 (3): 620525 , 1954. 4. Johnson, R. B. and W , L. 'I'hompson. Progress r epo rt on research with miticides. Fla. State Hort. Soc. Proc. 68: 1955.

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fl3 FLORIDA STATE HORTTCULTURAL SOCIETY. JD~fj PROGRESS REPORT ON GREASY SPOT AND ITS CONTROL -\'\;ll E. J. D1-:szyu; Florida Citrns E.r111,,-i11ll'11f Statio11 Lak<' .\lfnd Greas\ spot, a cliseas<' of citrus. has lw<'ll present i11 Floricla for 111a11\ \ ears ( I). h11t was a rni11or problem u11til about I !-J-H. B\ I !-J,50 tlw dislase \\ as pn\,dent ill 111a11\ groves in tlH l'l'ntral part of thl' stall. l)uri11'..'; the past .5 \l'ars. it l1c1s IH[omt ol l'l"d with gteasy spot.

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THOMPSON, ET AL: GREASY SPOT CONTROL 99 as August, but are usually not very noticeable until October. As winter progresses, greasy spot becomes more severe and reaches a peak in February or March. In 1954 , the severity of greasy spot increased about 30 percent be tween December 2 and January 25. Experi ments conducted on the east coast during the 1955-56 season showed that severity of greasy spot increased 15 percent from October 17 to November 29 and 40 percent from October 17 to March 8. Although a marked reduction of greasy spot resulted from the fungicidal sprays, the percentage incre ase in severity in sprayed plots was comparable to the increase in the checks. Injury: The principal injury caused by greasy spot is a premature leaf drop. Som e times approximately 85 percent of the infected leaves drop during the fall and winter months. Heavy leaf drop is more common on young trees, but mature trees may also lose a high percentage of leaves. The number of leaves dropped is proportional to the severity of greasy spot. Cause: In 1948, Thompson (6) reported that greasy spot was more severe in un sprayed plots than in plots where rust mite Phyllocoptruta oleivora (Ash.) were kept at a low level with sulfur sprays. In 1952, Sho icki Tanaka and Shunici Yamada (5) reported from Japan that greasy spot was caused by a fungus M ycosphaerella Horii (Hara.). Fisher ( 3) also found a fungus associated with greasy spot. In later work Fisher ( 2) , Grif fiths ( 4) and Thompson ( 8) found that greasy spot was less severe where summ e r copper sprays and other fungicides had been applied, which further indicated that the in jury was caused by a fungus. It has not been determined whether rust mites and some species of sucking insects are a contributing factor. Leaves k e pt free of rust mites with Aramite were less severely affected by greasy spot than mite-infested leaves ( 10). Areas around purple scale, red scale, and white fly are sometimes discolored. This injury may ii lso be greasy spot. Control: Earlier work showed that greasy spot was more abundant in unsprayed plots and in plots sprayed post-bloom with copper oil without subsequent rust mite control than in plots rec e iving a complete spray program (IO). In later work, Fisher (2) Griffiths (4) and Thompson ( 8) ( 10) found that a sum mer copper application reduced greasy spot. Thompson (10) found that 0.75 pound of a neutral copper ( 53 % metallic copper) was as effective as 1.5 pounds per 100 gallons. It was also found that two summer applications were more effective than one. Captan and Ziram showed promise, especially with two applications ( 10). It was also found that greasy spot was less abundant where summer applications of oil emulsion were made than in unsprayed checks ( 3) ( 4) ( 8) ( 10). Timing of the summer copper application has been an important factor in the d e gree of control (3) (4) (10). In 1954, a copper spray applied on June 10 was effective in one grove, but an application on June 15 in a nearby grove was not effective. All copper sprays ap plied during July were effective. August ap plications vvere effective in one of four ex periments and September applications were of little value in two experiments ( 10). Purple mites in the fall and winter months were more abundant following copper sprays applied in September than after earlier appli cations. Fall scale infestations were no higher following either a summer application of copper-oil or copper-parathion than where copper was omitted ( 10) . In 1954, there was no significant difference in the soluble solids and acid where copper was added to summer sprays than where it was omitted ( 10). External fruit quality of Hamlin oranges was affected as a result of a summer copper application. Winston et al. ( 11) reported that "star melanose" was associated with Bordeaux mixture sprays . Later, Thompson (7) reported that "star melanose" developed as a result of applying sprays containing copper on melan ose-infected oranges. In general, "star melan ose" on grapefruit has not been as severe as on oranges, but Fisher ( 2) reported that fruit quality in July and August sprayed plots was low due to copper blackening and enlarging melanose lesions already present ori the fruit when sprayed. The discoloration of blossom end russeting on oranges following a summer copper spray was also a factor that lowered grade.

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100 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 EXPEHIMENTS IN 1955 Methods: In 1955 , two similar experi ments were conducted to determin e th e mini mum concentration of copp er necessary to control greasy spot, the timing of _one and tw~ applications of fungicides, the_ effec t of funp cidal sprays on subsequent mite and scale festations and the effect on internal and ex ternal fruit quality. Near the town of Dunde_e in C en tral Florida a young, red grapeirmt grove was selected for one of these experi ments. For the other experiment , a red grape fruit grove was selected near Wabasso on the East Coast. In each experiment, th e tr ea ments were randomized and replicated three times. Each plot consisted of four tr ees at Dunde e and two trees at Wabasso. All neces sary sulfur sprays were applied for rust mite control. Parathion and wettabl e sulfur were combined with the fungicides in all July sprnys except where an oil emulsion was t ested for control o f both scale insects and greasy spot. Wher e a second fungicide spray was applied, the scalicide was omitted. All sprays were ap plied with high-pressure , hand-gun sprayers. R eco rd s of greasy spot severity were ob t ained from samples of fifty l eaves from each tree. From twigs selected at random in gathering samples, th e fourth leaf from. t~e t~rmin al was picked. _ L eaves were class1hed m th e laboratory into four grades, b~sed _o n the severity of greasy s pot. The seventy of greasy spot in each plot was then computed by multi plying th e number of leaves in the light grade by one, th e medium grade by two, and the severe grade by three. Products were added and then divided by the number of sampled leaves in each plot. Thus, the higher the rating, . the greater th e severity of the disease. Comparison of Materials: In this article, amounts of copper are designated as metallic copper and applied in the form of a n e tral copper. In th e 1955 experiments, ~he amount of copper per 100 gallons was vaned from 0.16 to 0.53 pound. In the Dundee ex periment , applications of 0.39 and 0.,53 pound of copper per 100 gallons resulted in the highest degr ee of control and were mor e ef fective than 0.16, 0.21 or 0.27 pound (Tabl e 1). In the Wab asso experiment, all copper sprays were about equally effective and sig nificantly reduc e d the severity of greasy spot. Some of th e low er concentrations of copper applied in two different sprays at an interval of six weeks were more effective than one application of the higher concentrations (Table 2). For example, at Dundee two apTable 1. Greasy Spot Control with Varying Amounts ot Copper. S:e.tg: Dates Dundee Wabasso July l July 9 n n " " " " It n ft a " ft Treatments No treatment Copper II n " " Pounds * " Per 100 ~al. 0.16 0.21 o.27 o.39 0.53 L.S.D. 19tl L.S.D. 99tl * .Amounts of copper presented as metallic copper. Mean rating or Greaez S:egt Dundee 54.5 35.8 41.7 .3.3.8 25.2* 22.3* Wabasso 218.7* 145.2 .. . 133.3* 140.2 102.2** 142.8* 60.5* 80. 9**

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THOMPSON, ET AL: GREASY SPOT CONTROL 101 plications of 0.16 pound of copper per 100 gal lons on July 1 and August 19 were as effec tive as a single application at 0.39 pound on July 1. The highest degree of control from copper alone resulted from a July application of 0 . 27 pound followed by 0.16 pound on August 19. In the Wabasso experiment, where two copper applications were made, results were similar to those obtained at Dundee (Table 2). Control with oil emulsion was variable. At Dundee, 1.3 percent oil or 0.7 percent oil plus 1 pound of 15 percent parathion per 100 gal lons were as effective as a single application . of 0.39 pound of copper per 100 gallons. The most effective control from combinations in volving oil was obtained with a July oil ap plication followed in August with 0.27 pound of copper . plus 5 pounds of wettable sulfur per 100 gallons. At Wabasso, neither concen tration of oil was effective. Furthermore, where the copper spray followed the oil apTable 2. Comparison or One vs. Two Fungicidal Applications for Greasy Spot Control. Plots Materials* Amounts per Mean Rating or 100 gallons Grea& Soot Julz Aue:ust Dundee Wabasso 1 No treatment 54.5 218.7 2 Copper 0.16 lb. 35.8 145.2x 3 " 0.16 lb. 0.16 lb. 21.
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102 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 plication, control was only equal to the July application of 0.16 pound of copper. Th e r e is no explanation why th e oil was not effective in th e Wabasso grove, ex cept that it may have been applied too early in the summer. How ever, in both locations, a July application of 0.16 pound of copp e r combined with oil emulsion and followed in August with 0.16 pound of copper plus wettable sulfur resulted in a high degree of control. Another very e fective program at Wabasso was a June ap plication of 0 . 27 pound of copp e r plus 5 pounds of wett a ble sulfur per 100 gallons and followed in Jul y with oil e mulsion. One application of Captan at 2 pounds per 100 gallons was as effective at Dundee as one application of 0.16 pound of copper, but not as e ff e ctive as 0.39 pound. At Wabasso, one application of 2 pounds of Captan per 100 gallons was not effective and two applications were no more effective than on e application of 0.16 pound of copp e r. Ziram applied at 2 pounds per 100 gallons was not effective in eith e r experiment, but two applications at 1 pound was as effective as a single application of 0 ." 39 pound of copp e r. Nabam applied at 2 quarts plus 1 pound of zinc sulfate per 100 gallons was as effective as 0.39 pound of copper at Dunde e . At Wabas so, Ferbam was not effective at 2 pounds p e r 100 gallons. Timing of Sprays: As stated previously, it has been observed that control of greasy spot vari e d in different groves even when the dos age of copper and time of application were similar. In 1955 at the Dundee grove, the summer flush of growth came out between the July 1 and the August 19 a pplication s. Where 0.27 pound of copper w a s used, th e August spray was mor e effective than one appli e d in July . Where a s little as 0.16 pound of copper followed . the Jul y application , th e re was a marked increase in the degr e e of con trol. In another experim e nt in a 40-year-old grapefruit grove , various amounts of copper were applied between June 21 and September 12. In this grove , there was little or no growth after the spring flush and there was no dif ference in the degree of greasy spot control, r e gardless of th e conc e ntration of copper or the timing of the application, Som e control of greasy spot may be ex pect e d from a post-bloom application on spring growth, but not enough to d e pend upon wher e greasy spot is sev e r e . On April 19, 1955, several different neutral copper compounds wer e combined with lim e -sulfur to determine whether thes e mixtures would cause a leaf drop a nd bum. On Dec e mber 21, leaf sam ples w e re grad e d for th e severity of greasy spot. Greasy spot was as severe where 1 g a lon of lime-sulfur was used as in the un treated check , but less severe in three differ ent plots where either 3.0 pound s of copper sulfat e, 1.0 pound of copper oxide, or 1.5 pounds of basic copper sulfate was mixed with 1 gallon of lim e -sulfur per 100 gallons. A mix ~ ture of basic copper sulfate and wettable sul fur was not as effective as any of the lim e sulfur-copper mixtures. Unfortunately, the limes ulfur-copp e r combination caused burn and leaf drop and it is not recommended in eith e r a spring or summer spray, but this ex periment did demonstrate that, if the copp e r adheres to the leaves for a long period of tim e , greasy spot will be less severe on t . he spring flush of growth than on untreated trees. Effect on Fruit Quality: In 1955, sum mer copper sprays w e re applied on Pine apple oranges at the Citrus Experiment Sta tion. This grove had received a post-bloom copper spray and the fruit was not severely affected with melanose. The amounts of cop per per 100 gallons were 0.16 pound, 0.27 pound, 0.39 pound and 0.53 pound, respec tively. Dates of application varied betwe e n Jun e 28 and August 8. There was very little discoloration wher e copper was used in amounts betw e en 0.16 pound and 0.39 pound per 100 gallons. Howev e r , where 0.53 pound was used , there was a definite discoloration of melanose lesions. Fi e ld observations were made at the In dian River Field Laboratory wh e re different amounts of copp e r had been applied on Val encia oranges. The concentrations of copp e r sprays were the same as at the Citrus Experi ment Station. Where 0.16 pound per 100 gal lons was applied, either in one or two ap plications, there was no adverse effect. How ever, with 0.27 or 0.39 pound, there was a mod e rate amount of discoloration. When 0.53 pound of copp e r was us e d, melanos e lesions wer e very dark , resulting in a d e finite grad e lowering factor. The timing of sprays was not a factor since there was as much discoloration

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THOMPSON, ET AL: GREASY SPOT CONTROL 103 following 'a July 1 spray as there was when the application \Vas made as late as August 8. On grapefruit, a low percentage of melanose lesions had a darker color than normal, but it was not a grade-lowering factor. Summer copper-oil applications darkened corky lesions more than the wettable• sulfur-copper com binations, but the grade was not affected where fruit was originally free of melanose lesions. Even though there was a minimum amount of discoloration of lesions and wind scars in this experiment, a summer copper-oil spray is not recommended where the crop is to be sold on the fresh fruit market. Compared to untreated trees there was no significant difference in the amounts of either soluble solids or titratable acid in pink grape fruit and Pineapple oranges where summer copper sprays had been applied. Effect On Subsequent Mite and Scale In festations: Purple mite, Metatetranychus citri, was more abundant in September 1953 following an August copper spray than following earlier applications ( 10). On De cember 21, 1955, in the Dundee grove, there was no difference in the percentage of in fested leaves between plots sprayed with copper-wettable sulfur in either July or Au gust and where the copper was omitted in the wettable-sulfur spray. In all plots where oil was used, alone or in combination with cop per, the mite population was not as high as where copper-wettable sulfur-parathion had been used. \1/hen infestations were low in the spring, scale control has been as satisfactory where fungicides have been included in the summer scalicide sprays as where they were omitted. DISCUSSION Timing of fungicidal applications appears to be one of the most important factors in greasy spot control and more knowledge is necessary about the life cycle of the fungus before definite recommendations can be made. In Florida, at the present time, it is not known when or how long the leaves are susceptible to infection. There are usually two to four flushe~ of growth that need protection between February or March and August. If a post bloom copper is applied for melanose con trol, that application will protect the spring foliage from greasy spot infection for a certain period. If the second flush develops in May or early June, then a July copper spray of about 0.4 pound per 100 gallons may be more effective than an August application. For instance, in 1954, July applications were more effective than August applications in three of four experiments. This does not mean that each summer the copper spray should be applied in either July or August, but where only one summer copper is to be applied, it should be delayed until after the summer flush is out. Two low-dosage summer copper sprays can be used to advantage where no post-bloom copper is applied. If parathion is used as a scalicide and it is necessary to spray in June or early July, add the equivalent of 0.16 pound of metallic copper, in the form of a neutral copper, per 100 gallons. In four to six weeks follow with 0.2 pound of copper plus wettable sulfur. If oil is used as a scalicide, then follow that application in four to six weeks with a low-dosage of copper. The ap plication following the scalicide spray is not necessarily an extra operation because a sulfur spray for rust mite control is usually neces sary following a June or July scalicide spray. Since oil was not effective at Wabasso in the one experiment conducted there, it is sug gested that 0.2 pound of copper be added to the summer oil and followed in four to six weeks with the same amount of copper in a wettable sulfur spray. The oil-copper combination should not be applied on oranges to be sold on the fresh fruit market. However, there has been no in jury other than the effect on corky tissue where wettable sulfur or oil emulsion has been supplemented with neutral copper. The grade of both oranges and grapefruit was not af fected when fruit was free of melanose lesions and blossom-end russeting when the copper spray was applied. The organic fungicides tested have not been as effective as copper, especially with one ap plication. Even though single, applications of the organic fungicides Captan and Ziram have not been as effective as copper and are more expensive, there may be a place for these materials. On oranges, where the crop is grown for the fresh fruit market, two appli cations of one of these organic fungicides may be used.

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104 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 SUMMARY Gr easy spot, a disease of citrus, causes a premature leaf drop. Symptoms are raised, yellowish-brown to black spots most prevalent on the undersides of leaves. Greasy spot infection was reduced with a July or August application of 0.4 pound of copper per 100 gallons, but two applications one in July at 0.27 pound and a second in August at 0.16 pound-were more effective. A July oil emulsion spray was as effective in Central Florida as one copper spray, but was not effective on the East Coast. Very effec tive treatments were either July oil followed in August with 0.27 pound of copper or June copper followed in July with oil. Also effec tive were either two applications of Captan at 2 pounds, or Ziram at 1 pound per 100 gallons. Summer copper sprays did not affect soluble solids or acid in the juice of Pineapple oranges or red grapefruit. Melanose lesions were noticeably darkened and enlarged where 0.4 pound of copper per 100 gallons was applied on oranges, but there was very little adverse effect following either one or two applica tions of 0.16 pound of copper. Subsequent purple mite infestations were no higher in December where copper was in cluded in the summer scalicide spray than where it was omitted. In 1955, scale infestations were at a low level when the scalicides were applied and the addition of copper to the summer sprays did not affect scale infestations by October. LITERATURE CITED 1. Fawcett and L ee. 1926. Citrus diseases and their control. 2. Fisher , Fran. 1954. Rept , Fla. Agri. Expt. Sta. Ann. 3. Fisher. Fran. 19 55. Fla. Agri. Expt. Sta . Ann. Rept. 4. Griffith s , J. T . 1955. Greasy spot and factors related to its intensity and control in Florida citrus groves. Citrus Industry, Vol. 36 No. 5. 5. Tanaka, Shoichi and Shunichi Yamada. Studies on the greasy spot (black melanose) of citrus. R e print from Bui. No. 1 Horticultural Division National Tokai-Kinki Agri. Expt. Sta. Okitsu, Japan. 6. Thon1pson, W. L. 1948. Greasy spot on citru s leaves. Citrus Industry, Vol. 29 No. 4. 7. Thompson, W. L. 1949. The relationship of tim ing post-bloom sprays to certain fruit blemishes on oranges. Citrus Industry, Vol . 30 No. 4. 8. Thompson, W. L. 1954. Fla. Agri. Expt, Sta. Ann. Rept, 9. Thompson , W . L . 1955. Fla. Agri. Expt, Sta. Ann. Rept. 10. Thompson, W. L. 19 55. Greasy Spot Control, Citrus Industry. Vol. 36 No. 5. 11. Winston, J. R. , John Bowman and Walter . J . Bach. 1927. Citrus mel a nose and its control. U.S.D.A. Bui. 1474.

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FELDMESSER AND FEDER: NEMAGON USE 105 us~ OF 1,2-DIBROM0-3-CHLOROPROPANE ON LIVING CITRUS TREES INFECTED WITH THE BURROWING NEMATODE JULIUS FELDMESSEH AND \VILLIAM A. FEDEH N e matology Section and Fruit and Nut Crops Section Horticultural Crops Research Branch Agricultural Research S ervice United States Department of Agriculture Orlando Part of an eight-year-old grove planted to Valencia orange on Rough lemon rootstock heavily infected with the burrowing nematode, RadoJJholus similis (Cobb) Thorne , reported to be the causative agent of spreading decline of citrus ( 2), was made available to the au thors for fumigation experiments in May 1955 1 It was decided to use 1,2-dibromo-3-chloropro pane in this grove since this is readily avail able commercially and has been reported to be non-toxic to citrus in nematocidal applications ( 1). All treatments were made with an emul sifiable concentrate containing 50% by weight of this chemical'. METHODS Pre-treatment root samples were taken and ten plots were set up and fumigated in the first week of June 1955. During this time, maximum air temperatures averaged 95 F. and the soil temperature at the six-inch level was 82 F . Relative soil moisture was 1.86 % at the six-inch level. Three plots of twenty trees each, numbers 1, 6, and 7, were treated with a tractor-drawn pressure applicator delivering a continuous flow of fumigant through nine inj ec tion points ten inches apart and ten inches beneath the 1 /The authors wish to express their thanks to Mr. H. 0. Estes and Mr. R. J. Estes, Altura s , Florida, o_wners of the grove. for their wholehearted coopera tion; and to Dr. A. F. Camp, Vice-Director-in-Charge, and to Dr. R. F. Suit, Pathol og ist, Citrus Experi ment Station. Lake Alfred, for their intere st in this project and for their help in securing the experi ment a l area. 2 / 1, 2-dibromo-3-chloropropane was made ava ilable by the Shell Chemical Company under the name "Nemaa-on.'• surface at the rate of one gallon, t\;VO gallons , and four gallons of Nemagon per acre, re spectively. Each of three plots of twenty trees each, numbers 3, 4, and 5, was drenched with 1,000 gallons of water which contained the 50 % emulsifiable concentrate adjusted so that each plot received amounts equivalent to one gal lon, two gallons, and four gallons of 1 , 2-di bromo-3-chloropropane per acre, respectively . The plots w e re then harrowed with a disk harrow and an additional 1,000 gallons of water was added to each plot. In four plots, numbers 9, 10, 11, and 12, areas twenty by thirty feet around single tre es were treated with hand injection apparatus . The 50% emulsifiable concentrate was applied on twelve-inch centers, ten inches deep. Single trees in two plots were treated with amounts equivalent to 13.8 gallons of 1,2-dibromo-3chloropropane per acre (roughly equal to 10 p.p.m. by volume in the soil four feet deep) and single trees in the other two plots were treated with amounts equivalent to 27;6 gal lons of 1,2-dibromo-3 chloropropane per acre ( roughly equivalent to 20 p.p.m.). Two plots, numbe1's 2 and 8 ( twenty trees each), were set aside as untreated controls. RESULTS Pre-treatment root samples were collected June 4 , 1955, and post-tr ea tment root samples were collected Sept e mber 29, 1955, November 21, 1955 , : March 9, 1956, and June 6, 1956 ( Table 1). Each sample consisted of approxi mately 100 grams of root material. Sampl es were incubated according to the technique de vised by Young ( 3), and nematode counts were made ov e r a period of several weeks after collection. On each of the sampling dates, ob servations were made on the condition of treated trees: amount of new growth, chlorosis or the lack of it, wilt symptoms, etc. At no time during the one-year observation period were there any indications of respons e to treatment in trees in plots 1, 3, 4, 5, 6, and 7 that caused them to differ in any way from

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106 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table l. Numbers of Radopholus similis individuals occurring in one set of pre-treatment root sa.'llples and four sets of post-treatment root samples taken over a one-year period from a planting of Valencia onRougb lemon rootstock treated with 50% emulsifiable concentrate 1,2-dibromo-J cbloropropane Post Treatment Plots and TreatJllents Pre-treatment Sept. 29 Nov. 21 Mar. 9-19 June 6 Jul. 9 (June 4,12222 Oct. 12,12.2.2 Dec. 12, 1 2.22 12,26 1226 1.1 gal./ acre, pressure rig 11 2. Control 146 3. l gal./acre, drench 4 4. 2 gal./acre, drench 48 5. 4 gal/acre, drench 31 6. 2 gal./acre, pressure rig 5 7. 4 gal./acre, pressure rig 17 8. Control J 9. 13.8 gal./acre, band injected 115 10. 27.6 gal./acre, band injected 272 11. 27.6 gal./acre, band injected 19 12. lJ.8 gal./acre, band injected 449 *No roots encountered the trees in check plots 2 and 8. Nematode counts indicate that no significant differences existed between the check plots and the treatment plots. The trees in both the check and treatment plots showed slight symptoms of chlorosis and wilt throughout the observa tion period. New growth was sporadic and was observed in trees in all of these plots. The trees in plots 9, 10, 11, and 12 began to show signs of chemical injury such as defolia tion and branch and root die-back by Septem ber 1955 and were judged to be dead or dy ing by March 1956. The data indicate that the three lower dos age rates of 1,2-dibromo-3-chloropropane that are tolerated by living citrus trees cause neith24 18 148 :32 125 766 252 25 68 117 84 :35 2 252 128 24 17 l 188 53 14 0 492 80 26 0 66 28 139 429 96 37 0 0 0 27 0 0 0 28 7 0 16 0 0 0 40 er significant reductions of burrowing nema tode populations nor favorable growth re sponses, and that the higher dosage rates that do approach the levels at which nematode eradication might be expected are not tolerated by living citrus trees. Intermediate rates of ap plication will be tried in other experiments. LITERATURE CITED 1. McBeth, C. W., and G. B. Bergeson. 1955. 1,2dibromo-3-chloropropane-a new nematocide. Plant Dis. Reptr. 39(3): 223-225. 2. Suit, R. F., and E. P. Ducharme. 1953. The burrowing nematode and other parasitic nematodes in relation to spreading decline of citrus. Plant Dis. Rptr. 37(7): 379-383. 3. Young. T. W. 1954. An inoculation method for collecting migratory endo-parasitic nematodes. Plant Dis. Rptr. 38(11): 794-795.

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KILBURN AND PETROS: PEEL OIL 107 RAPID DETERMINATION OF PEEL OIL IN ORANGE JUICE FOR INF ANTS 1l.'1 J f ;' R. w. KILBURN AND L. w. PETROS Florida Citrus Canners Cooperative Lake Wales Mechanically extracted orange 1mce con tains a moderate amount of essential oil from the peel of the fruit. The characteristic flavor of orange juice is due in part to this essential oil. Excessive peel oil is removed from the juice by vacuum distillation or centrifuging during the processing of canned orange juice. The deoiling process is controlled to leave a desirable amount of oil in the juice. The amount of oil in canned orange juice produced for infants is considerably lower than the level considered desirable in regular canned juice. Removal of almost all of the oil improves digestibility, justifying the sacrifice of aroma. The concentration of peel oil in citrus juice is measured by the modified Clevenger method ( 2) by inspectors of the Department of Agri culture for determining grade. More rapid methods of analysis have been developed by various workers. The turbidimetric method of Burdick and Allen ( 1) has been extensively used. This method was tested and found to give unsatisfactory results for the low oil in orange juice for babies. The solubility of oil in the a~etone distillate, noted by Burdick and Allen as being of no consequence at the levels normally encountered in canned juice, was the cause of difficulty. A study was made of modification of the t:urbidimetric method at low oil concentration. Attempts were made to minimize the effect of oil solubility by descreasing the acetone con centration in the distillate. Turbidimetric measurements of oil in several acetone-water mixtures are summarized in Fig. 1. Solubility effect decreased in dilute acetone but 100% Figure 1 LIIIHr ,_ISSIOH o, MIX!lft OF STIAJI DISTIWD 0RNGt OIL IN WATER '"' OIIGMIC SOI.YPff SOWTION 100-"'1:l"O::::--------=-----,,-----,,-"'I !10 eo ;;: 70 }60 .. ,0 [ IOJl~P\"'pw,ol g 20 ........,__,..__, .o• .~o, .o• .0,--,..........._.oe .oo .,.,.........__,10 .11 .12 j OIL BY YOLLM: IN MIXTIRE transmission was reached at oil concentrations too high to be useful. Wolford, Patton and McNary ( 3) en countered the same difficulty with the tur bidimetric method during their studies of citrus waste disposal. Their modified proced ure substituted ethyl alcohol for acetone as the organic solvent. This modification was re ported to give satisfactory results at concen• trations below .005%. The high excise tax on ethyl alcohol makes it desirable to use other organic solvents if .010 . 008 t .006 ! .004 . 002 Figure 2 COMPARISON OF CLEVEN:;ER ANO TURBIDIMETRIC METH:0S FOR OIL IN ORANGE JUICE FOR BABIES Turbtdllrlftrlc Method••-• .... .., , 10 II TIME IN l
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108 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 possible. The turbidity of peel oil in 10% isopropanol was tested with the result shown in Fig. I. The sensitivity is higher with this solvent than is the case with acetone; also the limiting solubility is lower. The preliminary re sults looked satisfactory so the distillation pro cedure was set up to give 10% isopropanol in the diluted distillate. A distillation ratio of two to one was also used to improve accuracy at low oil levels. EXPERIMENTAL PROCEDURE Apparatus. The distillation apparatus con sists of a 500 ml. boiling flask, a Kjeldahl trap and a West type condenser in the vertical posi tion for convenience. Light transmission of the turbid distillate is measured on a B&L Mono chromatic photoelectric colorimeter with a 435 mu filter. U.S.P. isopropanol is used. A 750 watt electric heater was found to be the most convenient heat source. Procedure. 100 ml. of juice and 5 ml. of isopropanol are added to the flask. The trap and condenser are connected and 20 ml. dis tilled into a 50 ml. graduate. The distillate is mixed, made up to 50 ml. by addition of water then mixed again. The turbid solution is poured into a tube and the light transmis sion measured against a distilled water blank. The transmission reading is converted to oil concentration from a standardization curve. A 10% solution of isopropanol should be checked for turbidity occasionally. Presence of turbidity indicates an unsatisfactory purity of alcohol. DiscussmN Standardization of the procedure. The pro cedure was standardized by a method selected as most likely to give good correlation with the Clevenger method. A series of dilutions of steam distilled orange oil in isopropanol was prepared. 5 ml. of solution, containing a known amount of oil, was added to 100 ml. of water in the boiling flask and distilled according to the procedure. The light transmission of the distillate was plotted against the volume of oil added to the flask ( the same value as the % "recoverable'' oil by volume) . A series of runs established the relationship over the range .002% to .03% oil by volume. This meth od of standardization automatically corrects for incomplete recovery by distillation. The graph of the data on semi-log paper was a straight line, indicating a uniform re covery by distillation, as well as conformity to Beer's law, over the selected range. Com parison of this graph with the dilution graph shown in Fig. I, indicates an 84% recovery of oil by distillation. This checks with the value obtained by Burdick and Scott ( 1). Comparison with the Clevenger Method. The modified turbidimetric method was used for routine testing of canned orange juice for babies. Samples were checked for oil every thirty minutes without difficulty because the entire determination takes. about seven min utes. The USDA inspectors also ran oil by the Clevenger method on composites of samples taken over a period of several hours. The data obtained, permits an indirect comparison• of the two methods. Results of the two meth ods for a typical day of operation is shown in Fig. 2. Results throughout the season exhibit similar agreement. The Clevenger method gen erally gives slightly lower results. Su11-1MARY A modified turbidimetric method for esti mation of peel oil in orange juice, based on distillation with isopropanol, gives satisfactory results on juice with low oil content. LITERATURE CITED. 1. Burdick, E. M., and Allen, J. S. Analytical Chemistry 20, 539-41 (1948). 2. U. S. Department of Agriculture, U. S. Stand ards for Grades of Canned Orange Juice, Production & Marketing Administration. 3. Wolford, R. W., Patton, V. P., and McNary, R. R. Food Technology 6, 418-21 (1952).

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. BISSETT AND VELDHUIS: VALENCIA CONCENTRATE 109 EFFECTS OF FINISHER PRESSURE ON CHARACTERISTICS OF VALENCIA ORANGE CONCENTRATE 0. W. BISSETT AND M. K. VELDHUIS U. S. Citrus Products Station 1 Winter Haven In processing citrus juices in the laboratory pilot plant a screw type finisher was modified so that it could be more precisely controlled and adjusted, and its operation made more uniform over reasonable variations in rate of juice feed and pulp content . Tests were made on Valencia orange juice to determine the ef fect of different finisher settings on juice yield, pectinesterase activity, pectin, flavon oids, and cloud stability of unheated and heated concentrates. While it would not be possible to adapt the settings directly to other finishers, the re sults illustrate some of the effects that could be expected ,vith variations in fishing prac tices. Extracting and finishing equipment must act together and the method of opera tion of one will markedly affect the method of operation of the other. However, certain prin ciples will apply to all units. Olsen, Huggart, and Asbell (8) extracted Pineapple orange juice at low and high pres sure. Pulpy cutback juice and 55 Brix concen trates were prepared from each and subse quently blended in various proportions in preparation of 42 Brix products. An increasing tendency toward gelation was observed with high pressure extraction over that of low pres sure and with increased concentration of coarse pulp in the cutback juice. Rouse (9) reported increasing pectinesterase (PE) activity with increasing pulp content in Valencia orange juice. Rouse and Atkins ( 10) found that PE was completely inactivated in a shorter time in an orange juice of 5 % pulp content than in. one of 10% pulp content. It was the purpose of this investigation to study the effect of varying the finisher pres1 / 0ne of the. laboratories of the Southern Utiliza tion Research Branch, Agricultural Research Service, U. S. Department of Agriculture. sure and heat treatment temperature in the preparation of Valencia orange juice for con centration. EXPERIMENTAL Equipment A standard Brown Citrus Machinery Cor poration" extractor using the same settings as in commercial practice was used in connection with a Model C Chisholm-Ryder' finisher mod ified as described below. This finisher has a horizontal screw operating in a cylindrical screen 5 inches in diameter and 9 inches in length. The pulp passes out through a conic a l annular orifice having a clearance normally fixed by an adjustment at the end of the screw shaft. With a fixed orifice, the relation ship between juice and pulp produced de pends to a l arge extent on the rate of feed. This particular finisher was modified by re placing the screw adjustment with an air actuated diaphragm , and air at constant pres sure was supplied to one side of the dia phragm. This maintained a constant pressure on the end of the shaft, but left it free to move horizontally and vary the size of the orifice in accord with the rate of feed and the amount of pulp present. The effective diameter of the diaphragm was about 5 inches, so air pres sures of 5, 6, 7, and 8psig . gave loadings on the end of the shaft of about 100, 120, 140, and 160 pounds. A new drive was inst a lled which reduced the speed of the screw to 200 RPM from a previous 262.5 RPM. This modi fied finisher duplicated the operation of com mercial finishers very well. It was noted that the pulp from this finisher contained fewer particles of coarse pulp than that from larger machines used in processing plants. Preparation of Sam11les Fifty boxes of Valencia oranges were de livered to the laboratory immediately after picking. The fruit was mechanically random ized into four lots of 1100 to 1200 pounds and stored at 40 F. until processed, The juice 2 /Thc mention of trad e products does not imply that they are preferred by the Department of Agri culture over similar products not mentioned.

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110 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 of the four lots was ex tracted separately using finisher settings of 5, 6, 7, and 8 psig. dia phragm pressures re spe ctively. The juice from each lot of fruit was divided into four por tions consisting of controls and portions heat treated to 150 , 170, and 190" F . The juice was heated in a small tube heat exchang er in 6 seconds, held at the temperature for 5 seconds and cooled to 60 " F. in 3 seconds in an annular ice water cooler. Each portion was concentrated to 55 Brix at 75 F. in a falling film evaporator, cut back to 42 ' Brix with un heated juice, canned, and frozen at o F. Analytical Methods PE was determined by a modified method previously described by Bissett , Veldhuis, and Rushing ( 1); total pectin by that of Mc Cready and McComb (7); soluble pectin by that of McComb and McCready (6); flavon oids by the Davis method ( 2); cloud both in itially and after storage at 40 F. by the meth od of Loeffler ( 5); and visual cloud stability by the method described by Guyer et al ( 4). Viscosities were recorded as the number of seconds required for 100 spindle revolutions Table I. Materials balance durino extraction and finishlno Finisher Peel Finisher Juice Total settinos waste waste yield recovery pslo. . . ,. 5 40.0 7.5 51.7 99.2 6 39.8 7.1 532 100.1 7 39.8 6.5 525 98.8 8 39.4 6.4 53.3 99.1 of a Stormer' instrument using a 26-gram ac tivating weight. Brix was measured by both spindle and refractometer ; acid ( as anhydrous citric) was titrated with standard alkali; and suspended solids were determined by the method used by the U. S. Department of Agriculture in grading canned grapefruit juice. EXPERIMENTAL RESULTS AND DISCUSSION Yields from each lot of fruit are shown in Table 1. As the extractor settings remained constant, the yield of peel remained practically the same for all four lots. The percentage of finisher wastes (pulp and rag) decreased, and the juice yields increased with increases in finisher settings. The yields of juice increased from 51.7% to 53.3 % which is' equivalent to an increase from 5.3 to 5.45 gallons per 90pound box of fruit. The analyses of the single strength juice from each lot of fruit are presented in Table 2. The data do not indicate appreciable differ ences in Brix, acid, initial cloud, peel oil, total pectin, or flavonoids of the juices processed at the four finisher settings. Small increases were observed in the suspended solids, PE, and soluble pectin with increased finisher pressure. The analyses of the 42 Brix products are presented in Table 3. The PE data follow the expected trend of reduced activity with in creased treatment temperature, but do not in dicate a change with increased finisher pres sure. There was a slight increase in soluble Table 2. Analyses of single strength juice Finisher Brix at 20 C. settings Spindle Refrac tometer psig. 5 12.90 13.05 6 13.20 13.00 7 13.35 13.30 8 13.30 13.10 Acid Suspended Initial solids cloud % •fo light transmission 1.10 14 24.0 1.07 15 24.5 1.10 15 22.0 1.09 16 23.5 Oil % 0.066 0.064 0.050 0.056 PEu./ml. xl0 4 43.8 38.3 49.6 47.3 Pectin Flavonoids total soluble ppm ppm ppm 1138 165 380 1100 165 377 1200 185 405 1025 189 388

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BISSETT AND VELDHUIS: VALENCIA CONCENTRATE 111 Tobit 3 . Analrsu of 42 Brix conctnlratu Fini1h1r Treatment PEu./ml. Soluble Flavonoid1 Visco,lty Weeks stltin91 temp . xl04 per pectin in 12• Brix HC./100 stable 12• Brix ,,v . ot40"F. (visual) p1i9 . "F. ppm ppm 5 control 45 . 8 666 363 82.1 5 6 control 40 . 7 662 380 87.9 I 190 5 . 1 836 373 96 . 8 >5 7 control 42.4 701 375 139.3 u ::; !. 2 .., u a: .., .. 0 T 14 21 21 42 DAY$ STORED AT F. Fig. 1. Cloud stability at 40 F. of concentrates prepal'ed from juice with finisher setting of S psig. 100 i ~. .. .. .. i 0 .. ..J ~6 a: 0 :, 0 ..., u ... ~2 u C .., .. 0 +11o•r \_ 190"F 7 14 21 21 42 DAYS STORED AT 40• F . Fig. 3. Cloud stability at 40 F . of concentrates prepared from juice with finisher settinir of 7 psig. values with increased finisher pressure, or heat treatment. Increases in viscosities of the concentrates with increased finisher pressures are pronounced while the use of heat treat ments did not influence th e viscosities of the products. Visual evaluation for cloud stability in 40 F. storage showed that only three sam ples retained their cloud for as much as one week. Of th ese, the product of 6-pound fin isher se tting and 170 F. heat treatment was found unstable after two-week storage and the product of 5and 6-pound settings and 190 F. heat tr ea tment remained stable for five weeks. The loss of cloud during 40 F. storage, as indicated by increased light transmission is shown in Figs. 1, 2 , 3, and 4. In all controls cloud loss was very rapid. Heat treatment at 150 F . provided cloud stability for only a few days while 170 F. tre a tment provided only slight additional stability. The use of 190 F. heat treatment of juices processed at 5and 6-pound finisher settings effectively stabilized the cloud for five weeks or longer , while similar heat treatments of juices prot ., ., 3 C :, 3 u 10 I 42 OAYS STORED AT 40•~ Fig . 2. Cloud stability at 40 F . of concentrates prep~u-ed from juice with finisher setting of 6 1>sig. i z 0 :ta .. i .,, .. 0 z ..., ... 0:6 C ... ::, 0 ..., u I DAYS STORED AT 40• f. Fig. 4. Cloud stability at 40 F. of concentrates prepared from juice with finisher settinir of 8 pslg.

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112 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 cessed at 7an
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STENSTROM AND WESTBROOK: BRIX~ACID RATIOS .113 A STUDY OF THE DEGREES BRIX AND BRIX ACID RATIOS OF GRAPEFRUIT UTILIZED BY FLORIDA CITRUS PROCESSORS FOR THE SEASONS 1952-53 THROUGH 1955-56 E. C. STENSTROM AND G. F. WESTBROOK Citrus & Vegetable Inspection Division State Department of Agriculture \Vinter Haven In February of 1956, our Division was a$ke
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114 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Figure 1, 12,0 12,0 Degrees Brix 1952-53 __ _ ll,O 1951-52 ___ _ 11,0 10,0 Brix-acid ratio 8,0 8,0 1,324 2,934 2,777 3,2S? 1,693 April 1,275 Mey 7,0 728 (One tholl.!land boxes, 5 year average) Oct, Dec, Jan, Feb, Mar, June data that we can determine what time of the season the grapefruit utilized reaches its high est Brix level, together with appropriate ra tios. A further bit of information is included here, also. As a result of the optional com pliance provision of the regulation previously mentioned, close records were maintained on the fruit received for concentrating during the period March 18 to July 1, 1956 . Some 3700 lo a ds were processed under this . pl a n, and only a negligible portion failed to meet the mini mum Brix of 9.5 degrees. However, some 20% were below the specified 7.5 to 1 ratio level, princip a lly because of inadequat e screening by fruit procurement departments. Neverthe less, the average ratio . of the unsweetened grapefruit concentrate packed during this period was more than 9.0 to 1, as evidenced by our inspection records ( 3) . In attempting to evaluate the factual in formation we have presented here; it is neces sary to make several assumptions: ( 1) That weather conditions will be no more unusual than those of the past five years. Hurricanes, freezes, and droughts may seriously affect the quality and movement of the grapefruit crop. ( 2) That cultural practices will remain es sentially the same. Certain spray and other cultural practices may cause additional vari ables. ( 3) That fruit will be harvested at about the same periods as in the past. Changes in fruit utilization intervals would be most significant. As can be seen from the tables, there is an ample supply of fruit meeting 9.5 degrees Brix with a minimum of 7.5 to 1 ratio any month from February through June. Since eva poration facilities are relatively idle during .February and March, it is convenient for pro cessors to concentrate grapefruit juice dur ing these two months. However , those desiring to pack unsweetened juice will find it much less difficult if they can delay their operations until April or May, for the percentage of 9.0 to 1 ratio fruit has risen sharply by that time,

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TABIE 11 Peroent ot IPad• Meeting varioua De~NH Brix-Ratio eombinationo, $0&1011 1952-~ JANllldlf btt:ffl!; BRll l .s 0,9 2,3 4.3 7,0 5.7 7.5 27.7'/, ,O l.S 2,8 4. 7 6,2 4.6 4,1 23.9% .s 1,2 1.6 3.9 4.5 2,1, 2,8 16,1,% ,o o.a 1.0 1.3 1.2 1,2 1.6 1 .1% .s o,s 0.3 o,6 o.6 o. 7 1.0 3. 7% .0&11p o,4 o.4 o.8 o.6 o,8 1.0 4,0% 1ut.\L 6,0% 9,7% 17.3% 23.7% 20,3% 23.0% 100,0 , 1,3 , 1.7 : g:~ : o.~ r 6,6:,( 1.7 2,4 1.3 o.8 0,3 0,9 8.2% FEBRUARY DIDREES BRll 3.3 3,2 2.2 1.1 0,7 o.6 12.4% 4.3 4.2 4.7 4.1 3,9 4.4 2.0 2,3 1,1 1.0 1.0 0,7 19.1% 18.9% 11,0&0p 1DT.,L :-9.0 i,.s 14.U: o,6 9.0 23,8%, 1.4 7 .l 23.2%: 3.0 4.9 17. 7%: 2.4 3.1 9, 7%: 1.6 2.1 5.7%, 1.6 1,8 5,8%: 1.5 34.8% 100.0 ,12.1 ,: DECJEMBE 1 1952 9,0 o.s 1.4 1,9 2,2 1.9 1.6 1,4 10.9% J.11.RCH DEG REE.. ~ BRIX 9.S o.s 1.5 2.8 J,O 2,6 1,1 1.8 1o.o 1.3 2.6 ),6 ).3 2,J 1.4 1,8 16,3% ro.s o.ll 1.8 3. 7 3.1 1.5 1.1 1.4 lJ.4 % 1PT\I s.o,: 25,3% 23.5% 20,)% 11.8% 5,3% J.8% 11,b&Op fuflL 2 .3 6,o:t 6, 1 1 15.1% 9.4 24.4,; 6,9 20,9~ 5.0 14.9%, 2,1 8,9% l.9 9,8 % 34.0 % 100,0 ------j~.,c-!E!s=wu_::;JlR',;;,L,.,..lJl..,---------:-:-------,,0:,:,;EC"'ilE"'~~ \:;Y BR"""'IX.------------:-:------mnE"'d""'li':",&.;.U"'t!Ei,,, ~,.,..-::,, -_ -_ -_ -.,,. -,.. -re--_-_.... -'T --r-rr: .. -, .. -,,, -,,,, -r -_ RATIO -9.0 9.0 9.~ 10.0 ro.s 11,0&Up IDTlL ,-9.o 9.o 9.S ro.o 10.s 11,0&Up 'tbT,L :-9.o 9.0 9,5 . 10,0 ro.5 11.o&tlp TOT.\L 'IOT : .L 23,17> 15.1% 18,()1, 14.8J; 12.11, 16,9% 100,0 :31.5:1. 17,8% __ 16,3:f. lJ.81, 8,81, 11.81, lQO,O :19. 25( 20,3\l'. 2J.0 :0: 15.7'/. (fl 1-3 t"1 z (fl 1-3 :;d 0 > z t:J t"1 (fl 1-3 tJj ::0 . 0 0 tJj ::0 H n H t:J ::0 > 1-3 H 0 (fl ...... ...... 01

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TABL& 2• Percent cf Loads Meeting Various De~ees Brix•R:itio Combinations, See.son ~54 CX:TOBffi DEGREES BRIX NOVEMBER DECREF..'l BR IX 11.ffiUp TClrAL : 9.0 9.0 9.5 10.0 10.5 6.~i 0,2 0.3 0.3 O,U% : 6.5 1,1 1,8 0,8 0,4 0.2 4.3% : 7,C 17.8 C.l 5.3 1.7 0.3 7.5 27.0 6.5 2.7 1,4 0.3 a.a 10. 5 3. o 1.0 0.2 c.4 33.6% , 7 .6 o.4 o,4 2,0 4.9 4,3 1,9 7.6 8,1 5.4 2,1 6.6 5,6 3.6 1.5 3.5 2,5 1,6 1.0 2.0 1.1 o.s o,4 1.1 o.6 0.5 0.2 0.2 38,1% : 7,9 8.5 4.0 l.J o.j 0,1 9.C&Up 1.8 0.7 0.2 O.l 14, 7% : 5.8 5,7% : 2.6 2,8% : 1,5 TCTAL 61.1% 20. 7~ 11.3% 4,5% 1.3% 1,1% 100.0 JANUARY DEGREES BRIX RATIO -9.0 9.0 9.5 10,0 10.5 11,'1 &Up TOTAL : 6.o -1 u.5 1.0 1.1 2.0 1,9 2.0 8,5% , 6,5 1.2 2.2 4,2 4,0 3,2 3,9 18. 7% : 7 .o 2,5 3,3 5,3 4, 7 3,0 4.0 22. 8% : 7.5 3,1 3.1 3,9 3,3 2.0 2,5 17,9% ,8.0 2,4 2.1 2,4 2.3 1.6 1.5 12,3% : 8.5 2,h 1. 7 1. 7 1.3 1.1 1.0 9,2% 9,C&Up 4,0 1.8 1,3 1,1 0,9 1,5 10.6% TOTAL 16.1% 15,2% 19,9% 18,7% 13,7% 16,4% 100.C ~7 ~9 ~4 L3 2~ 1.1 2.2 2.2 2.2 4,3 1,8 2.8 2,6 2.6 6,0 1.9 2.4 2,4 2.5 4,1 1.6 1. 7 2.1 1.6 3.4 3,8 5,6 6,5 4,5 7 .1 FEBRUARY DEGREES BRIX -9,0 9,0 9,5 10.0 10.5 0.2 o. 7 1.0 1,4 1,3 1,0 1,6 2,6 3.1 2,6 2.0 2.1 3,2 4,1 2.6 1.5 2.2 4,2 4.9 2.6 1.7 1.6 2.8 3.5 2.2 1.2 1.1 1.8 2. 7 1. 7 2.6 2.5 2.5 2.4 2.0 o. 7 a:5 a:5 1.3 o.6 1.0 2.2 1.4 1,5 2,5 1,4 1,9 2. 7 1.8 1.8 10.8 6. 7 9.3 o:4 0.3 1.2 0.7 1. 7 1.8 1.9 1.7 1.6 1.6 8.1 6.1 11.0 & Up o.4 1.7 1,3 o.8 0,7 0.2 0.1 11.0 & Up _Tor_AL_l_2 __ l"-'-%--ll= lcc;%..;le.<5c.c.• 9'--'%~17c:c•:::::4%::....:,15e..::•c::,l%c:.....=2::.;8•c_:4,:_%_=.;100==a;:__.,_: --=-:20:..:•.::,&f,:..:1=2.=-<$:=16,2% 12!~_% l? _ ,4i 23,2% TOTAL 1.2% 14,8% 32,1% 26,0% 15,1% 6,8% 4.0% 100.0 TOTAL 6,5% 14,8% 18.6% 18,9% 14.6% 10,5% 16.1% 100.0 100.0 : -9,0 4,1 3.8 3,5 , 2.3 : 2.5 0.2 0.8 1.4 1.5 1.4 1.5 3.1 0.5 0.9 1.5 1.5 1. 7 1.6 3.0 DECEiJBFit DEGREES !RIX 9,5 10.0 10.5 0.5 0.9 4.9 5,3 4,0 6.7 7,6 4.0 6.1 4.5 2.1 3,6 2.4 1.4 1.3 1.0 0.3 0.7 0.7 0.3 MAROI DEGREES BRIX 9.5 10.0 10.s 11.0 & Up 1.5 2,8 2.1 1.2 o.8 o.6 o.6 11,0 &Up 9,9% 10. 7% 16.4% 19,3% 15.6% 28.1% JUNE TCJ!'AL 2,9% 18.4% 28.8% 21,6% 15,2% 6,9% 6.2% 100.0 TOTAL 6.1& 12,5% 16.5% 16,3% 14,2% 11.u 23,0% 100.0 TClrAL '-::i:j t-< 0 !:d ..... t:1 :,,. r.n 1--3 :,,. 1--3 ttj ::i:: 0 !:d 1--3 ..... (") q t-< 1--3 q !:d :,,. t-< r.n 0 (") ..... ttj 1--3 ..... co i:..n 0)

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T.ABU: 3• Percent of l<,~ds Meeting V'1rioua D 8 4:rees Brix-Ro.t1o Com!Hcationa, scns Il.o & 02 6.o-1 o.6 0.2 0.2 1.6,t : 0.5 1.s 2~1i 4.IJ% , ---r.-r -2.0 4.6 6.5 J.s 5.6 J.4 1.1 0,8 14,4% : 2.5 7,9 7.4 4.S 4,5 26.5% : 0.2 2,1 7.0 9,4 5,7 5,0 7.0 lJ,O 15.0 9.4 J.6 1.2 0.4 42.6%: 6.6 8.8 9,5 8.0 5,1 2.5 40.5% : J,l 5,0 8.0 6,6' 5.2 J,2 7-5 9,3 11.2 6,4 1,9 o.8 o.J 29,9% : 3,3 4,2 4,8 3,4 2. l 1,0 18.8% : 1,7 3,7 4.4 4.4 3.0 1.6 8.0 2.3 4,0 2,1 o.8 0.1 9,3% : 1,2 1.3 1.8 1,5 0,5 0.3 6.6,: : o.6 1,3 1,7 1,7 1,1 0.7 8,5 0.5 0.$ 0,8 0.1 1.9%: 0,4 0,3 o.s 0.3 0.2 1,7% : o.6 0,5 o.6 0.7 0,5 0.4 9,C&Up O,J 0.2 0.3 0.1 0.9% 0,3 0,4 0,4 0.1 1.2% : 0.,3 0,4 0.3 0,5 o.6 0.5 TOTAL 25,4% 34,4% 24,6% 10,5% 3,L% 1,7% 100.0 11,8% 17,5% 24,9% 21. 2% 13. 9% 10. 7% 100.0 6.5% 13.0% 22. 0% 24,li% 18,1% 16.0% JANUARY FEBRUARY lWll'.ll n .. nirnrn m:rx !l&WE'I BRIX llmtEES Ill!IX RAT10 -9,ci 9.0 9,5 10.0 10.s lI.o &Up Tim!: : -9,0 9,0 9.5 m.o Io.; II.o & Up TWAL: -9.0 9.o M 10.0 IOo5 11.0 & 02 6.o -1 0.9 1,5 2.2 3,8 3 , , 7 6.2 18,3%: o.6 1,0 1.5 1.6 1,J 4,8 10.8% : 0.5 o.s o.s o.s 1.2 J,1 6,5 1,7 2,6 4,1 s.o 5.'? 7 . 5 26.6% : 1.1 1,5 2,7 3,4 3,3 9,4 21.4% : 0.9 0.8 102 2.5 2.3 ~-7 7.0 1.2 2,4 3,9 Sol 4.9 6.1 23,6% : 1.2 1,5 2,5 4.1 .3.9 7.6 20,8% : 1.1 1 , 4 2e2 .3.2 3,0 8,7 7-5 1 . 2 1.6 3.0 .3.0 3.0 2.9 14.n: , 1,6 1. 7 2.9 4.2 3.2 5,4 19,0% : 1,7 1,6 2 .3 3.1 2.8 6.1 a.a 0.8 0,9 1,7 l,9 1.4 1,3 8,0% : 1.2 1,5 2,5 3,2 2.3 3.6 14,3% : 1.8 1.8 2.2 2.5 1,9 4,7 8,5 o.s o.6 0.7 0,8 0,8 0,6 4,0% : 1.1 0,8 1,4 1.2 . 0.7 1,7 6.9% : 1,2 1.0 2,1 1,4 1.6 2,8 9,C&Up 0,6 0.7 o.a 0.9 1.0 o.a 4,8% : 0.9 1.0 1,1 1;1 o.6 2,1 6.8% : 2,4 2.5 2.8 .3.0 2,4 3o4 TOTAL 6.9,t 10.3% 16.4% 20.5% 20.5% 25.4% 100.0 7,7% 9,0% lli,6% 18,8% 15,.3% 34.6% 100.0 9,6% 9,6% 1.3,6% 16,5% 15.2% 35,5% AIBIL MAY JUNE ll= BRIX n.o &U2 T1'i'AI: ; DEGREES BRIX : DEGREES !RIX RATIO -Y,0 9,() 9,5 m.o 10.5 -9,0 9,0 9,5 10.0 10.5 U,O & Up TOrAL : -9.li 9.0 M 10.0 10.5 11.0 & il2 6.o -1 c.5 o.J o.s o.8 0.3 1.9 4,3% I 0.1 0.3 0.2 0.3 o.3 ~ -o::, 1,5% : o,4 o.4 0~6 6.S 1.1 1.1 1,5 1.5 1.4 3.3 9,9% ' 0.2 o.J 0,3 0.4 o.s 0.9 2.6% : 0,3 0,4 0.3 o.8 7.0 1.9 1.s 1.9 2.2 Jol 6.S 17,)$ I 1 .3 0,6 0,6 1.3 1,4 2,1 7.J% : o.s o.i. 0,2 o.8 o.s 1.2 7.5 J,.3 1,6 2.9 2,J 2.0 5,7 17,8% : 2.1 0.9 1.4 2.0 1,4 4.4 12.2%: 0.9 o.6 0.6 1,3 2,0 2.0 8.c, 2.4 2,1 2,6 2,7 1,9 4,1 15,8% I 2,9 2.0 2.J 2,.3 1,9 J.6 15.0,: ' 1.6 1.2 1.3 1,9 2,0 2.6 8,5 1,9 2.0 1,7 2.2 l,J .3,5 12,6% : 2,9 1,6 2.6 2.1 1,.3 J,2 13,7% I 1,4 1.6 1,9 1.8 2.4 .3,2 9,(.Up 5,4 3. 8 J,6 J.8 2.4 3,5 22,5% I 10.1 8.2 a.s 8.J 5.6 1.0 47,71, I 15,0 6,6 9,1 9,5 7.9 14,6 TOI'AL 16,5% 12.4% 14.7% iS,5% 12,4% 28,5% 100.0 ' 19,6% 13.9% 15.9% 16.7% 12.L:C 21,5% 100.0 : 19,4% 10,1.% 1.3,6% 16.1% 15,5% 25.()% TOi'AI: 7,7% 29.4,: 31.1,: 18,8% 7.1,: 3,3% 2,6% 100.0 TO!'AI, 6. :. . ~ 14,4..; 19 , 6% 17,6% l4o9% 10,1% 16.5% 100.0 TOTAL 1,1& 1,8% 3c6% 7.61, 10,6% 12.)% 62,7 100.0 '(fl t--3 l:
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wu:4, hroent fl LOada lloet1ng Var1oua. Degree, Brix-Ratio Combinat1 .. 1955-56 OCTOBER "%j N0V.:tIBER DECEl :Bfill t"' De rees Brix ~rf• Bri~~7!ti--------Ml9----~-@aBr~ 2 -__ 0 RATIO .0 9.0 9. 10.0 10. 11.0 & .92• 0o0 :\c llo rTotal : -9._0___.9 9. 10.0 10_. _ll.0 & Up Total !::d .0-1 o. 0.2 0.3 0.5 1 . 5-5% , o.e 2.0 1.2 10.6% ..... 6.5 1.9 4.8 2.2 1.9 0.1 10. 7.5 ti 8~2 7.; 3.5 1-4 0.2 28. TCJrAL 28.21.24.6'26.]1, 12.BS 6.8% 1.3 "/. 100.0 7 -4"/. 8.6"/. 15,3 "/. 20.p"/. 18.51, 29,7% 100.0 4.41, 5.6"/. u.C/$ 16.6% 20-4 % 42.0,i 100.0 f-3 : t:".1 l,!AltCH 0 RAT !::d .0-1 11. 0 o. 1. n. ,, 0.3 0. 2 6,5 1.0 l4.1 26./.i% : 0.7 o.6 1.2 2.1 2:9 22 .2%, o.6 0.5 1.0 1.8 2.1 9.9 15. APRIL ~'iAY Jtr.lE t"' Degrees Brix Defees Brix De~raos Brix 'C/l RATIO -9.0 9.0 9.5 10.0 10.5 u.o & !:!E T otal ,-9,0 9.0 Total I -9,0 9 .0 9 .5 10.0 10. 5 ll.O & Up Tr,t:il 9.10,0 10~-ll .O & Up 0 6.0-1 0.3 0 . 3 0.5 o.6 0.7 3.7 6.)1, : 0,1 0.2 0.5 0.7 l,O 2.8 5 ,31,; -o~o-:I; 0.4 0.5 1.0 1.9 4.5 % 6.5 o.6 0,5 0.7 1.3 1.3 8.l 12.51, I 0-4 0.4 o.6 0.9 1,4 4.7 8.4%, o.4 0.3 o.8 l ,5 1.3 4.1 _ 8.4% n 7.0 o.8 0.7 1.3 l,5 1.9 10.5 16.7% , 0,7 . 0.7 1.3 l,7 1.7 6.2 12.3%, 1.0 0.7 1.7 2.7 2. 3 5.9 14.31, ..... t:".1 7.5 0.7 1.0 1,3 2.1 2.3 10.2 17.6 "/. : 1,7 1.0 1.9 1.8 2.2 s.2 16.81,, l,2 0.9 1.3 2,4 3.0 7.0 15.81, f-3 8.o 0,7 1.0 1.7 2.1 1,7 1.a 15,0"/. : 1.2 1.0 2,4 2.2 2.5 6.9 16.2%, 1.0 1.0 1,5 2,1 2.6 7.4 15.6% 8.5 o.6 o.6 1.0 1.5 1.5 6.2 11.4% : 0.7 0.9 1.6 1.8 2,l 6.o 13,1"/.: 0.7 o.a 1.5 2 .0 2,2 .9 13,1% 9.0 & )%>2,2 l.8 2.0 2-4 2.9 9,4 20.7% , 2.2 2.4 3.5 4,5 4.8 10.5 27.gt,,, 2.9 2.2 3.0 4.4 4.3 11.5 28;31I-' TCJrJJ. 5,915,9% 8,5 % ll,51, 12.3 % 55.91, 100.0 , 1.Q
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STENSTROM AND WESTBROOK: BRIX-ACID RATIOS 119 and percentage-wise is more than four times as great in May as in February. Now, it is true that the bulk of the crop has normally been harvested earlier ( 4), so fruit procure ment departments would have to arrange for suitable supplies in advance with appropriate additional two months, sugar content would remain rather constant while ratio would con tinue to increase ( 5). In practice, the econom ics of such a policy might be variable, of course, and will not be considered here. The real problem then, seems to be in ob taining fruit of suitable ratios, but this should not be an insurmountable one. Those opera tors who control a major portion of their sup ply should keep a regular check on the de velopment of their blocks. Enough data should be available to enable field production men to project the probable ratio curve after the first few months. Operators depending picking dates. . In the interest of efficiency, if for no other reason , it behooves concentrators to use fruit with the highest Brix obtainable. From the Brix-ratio graphs ( Fig. 1) we can see that this point has generally been reached in March of each of the years studied. However, if selected high Brix crops were held for an Tu.ble S1 Partial summary of tabulated data showing percentages meeting certain minimum ratios at 9.5 degrees Bru level. Percent of loads with 7.5 to l ratio October November December Janua::z Febru!!!Z April 1955-56 19.2 21.9 27.9 25.3 L0.7 53.l 56.1 62.9 195L-55 13.7 16.9 22.7 24.6 37.2 L5.l L6.2 57.9 1953-54 6.5 20.9 27.6 29.4 L5.7 L9.J 57.9 59.0 1952-53 9.1 26.5 31.7 25.o )2.9 Lo.3 44.) L4.o Averages 12.1 21.6 27.5 26.1 39.1 47.0 51.l 56.o Percent of loads with 8.0 to 1 ratio October November December Janua!Z Februa!;l April 1955-56 6.8 1.0 11.6 11.8 2).8 34.4 Lo.2 48.8 1954-55 4.) 5.6 9.3 12.7 21.5 30.8 33.3 48.7 1953-54 1.9 9.4 13.7 17.7 30.5 36.0 43.9 L9.8 1952-53 2.6 12.4 16.6 11.4 17.5 24.0 35.3 39.3 Averages 3,9 8.6 12.8 13.4 23.3 31,3 )8.2 46.7 Percent of loads with 8.5 to l ratio October November December Janua!:l lebrua!:l March April 1955-56 2.6 2.2 4.9 5.o 11.2 21.2 26.9 34.8 1954-55 1.3 1.5 4.1 6.4 9.9 19.5 22.0 38.6 1953-5L 0.1 3.6 5.5 9,9 19.2 24.9 32.5 Lo.2 1952-53 o.6 5.4 7.4 6.1 9.0 12.6 25.8 32,9 Averages 1.3 ).2 5.5 6.9 12.3 19.6 26.8 36.6 Percent of . loads with 9.0 to l ratio . October November December Jc..nua!:l Febru~ March April 1955-56 . 1.3 o.6 2.4 2.0 4.5 11.0 16.7 23.3 1954-55 o.4 o.5 1.9 3.5 4.9 . 11.6 13.3 29.4 1953-54 0.3 1.4 2.3 L.8 11.0 16.9 23.7 32.1 1952-53 . 0.1 2.1 ).1 ).2 L.1 6,9 17,3 26,l Averages 0.5 1.2 2.4 3.4 6.1 ll.6 17,8 27.7 June 62.1 6L.3 L5.l 40.3 53.0 L8.4 58.2 40.2 3L.o 45.2 June 34.8 5o.L 33.9 21.0 )6.5 June 23.2 Ll.l 27.7 20.4 28.1

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120 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 largely on purchased fruit will have to insist on very rigid requir e ments as to acceptable lots. In eith e r case, fi e ld men will have to know . within v e ry close limits the actual Brix and ratio that may be expected before picking crews move into a block for harv es ting. REFERENCES 1. F'lorida Citrus Commi s sion. Amendment No . 5. Regulation No. 19, March 7, 1956. 2 . Citrus & Vegetable In spe ct.ion Division. Aver a ge a cid and solids content, by week , of fruit r e ceived at proces s ing plants, 1949-50 through 195656. (Mimeographed reports) 3. -----Unpubli s hed data , 1956. 4. ----AnnuRI Reports, 1949-50 through 1955-56 . 5. Harding, P . L., and D. F. Fisher. Seasonal changes in Florid a grnpe[ruit . USDA Tech . Bui. 886, April 1945. DIACETYL PRODUCTION IN ORANGE JUICE BY ORGANISMS GROWN IN A CONTINUOUS CULTURE SYSTEM LLOYD D. WITTER M eta l Division , Res e arch & D eve lopment Department Conti11e11tal Can Company, Inc. Chicago, Illinois I N TRODUCTION The development of an off-flavor and odor during the manufacture of frozen orange juice concentrate has resulted in severe economic losses to a number of citrus concentrate pack ers. This off-flavor is reminiscent of "butter milk" and is a result of the accumulation of diacetyl, a ' metabolic product of certain bac teria. Other than the work by Kilburn and Tuthill (II), former studies on the growth characteristics of these organisms and their production of diacetyl in orange juice has been limited to static batchwise cultures. Kilburn and Tuthill ( 11) used the continuous culture method to show the relationship between data obtained by plate count, microsopic count, and diacetyl analysis, and thereby validated the use of the latter analysis as a quality control tool in the citrus industry. It was considered appropriate to supple ment this applied investigation with a more basic approach to the characteristics involved in the formation of diacetyl in orange juice in a continuous culture system. This technique manages a unique separation of the rate of diacetyl production by a given organism from that organism's rate of growth. Batchwise in vestigations \ ar e necessarily a summation of growth and ' m~fabqFc product formation and the latter cani1ot be studied separately. In the continuous culture system the vessel or fermentor in which the test organisms are growing and forming metabolic products is supplied , with fresh sterile rnedium at a con stant rate. A constant volume is maintained in the fermentor by having an overflow rate that is constant as well as equal to the input rate of the fresh medium. By appropriate adjust ment of the flow rate through the fermentor, a constant microbial population density of ac tively growing organisms can be maintained. J\t this constant population the rate of product formation can be studied without being af fected by variations in the number of or ganisms. THEORY OF PnoDUCT FonMATION IN A CONTINUOUS CULTURE SYSTEM To assist the reader, the following nomen clature will be _ used in the development of equations: a =diacetyl concentration at time t (in p.p.m.) a.= diacetyl concentration . at zero time (in p.p.m.) k = growth rate constant (in reciprocal hours) k'=reaction rate constant for diacetyl for mation ( in p ' .p.m. formed per hour by one million organisms per ml or a population density of one.) R . medium flow rate (in ml per hour) t = time ( in hours) V = capacity of the fermentor ( in ml) x = bacterial population density at time t ( in million organisms per ml)

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WITTER: DIACETYL IN ORANGE JUICE 121 x,,= bacterial population density at zero time Equations applicable to the behavior of a population density with time in a continuous culture system were derived by Monod (14) using a differential material balance of the system. By a slightly different approach, Golie ( 8) arrived at the same basic equation of dx dt = Rx kx-v Equation ( 1) states that the rate of change of bacterial population in the fermentor with time is equal to the rate of bacterial density increase less the rate at which the bacteria are being washed from the fermentor. Inte gration of equation ( 1) yields. ...L1n2. : k ..,!. t Xo V Hence, when the rate of medium flow ( R) divided by the capacity (V) of the fermentor is equal to growth rate constant ( k), the population density of the bacteria in the fer mentor will remain constant. Monad ( 14) pre sented a rigorous proof of this fact. Under these conditions the bacteria were being washed from the fermentor in the overHow at a rate commensurate with their rate of re production in the fermentor. Although the characteristics of a bacterial population in a continuous culture system, as discussed above, have received a good deal of attention (6, 16), only a limited description of product formation by bacteria in this sys tem has been made. Maxon (13) in his micro biological process report on continuous fer mentation presented a detailed treatment of product formation in cases where the sub strate concentration was rate-limiting. How ever, in this investigation of the rate of diace tyl production in orange juice, as in many other fermentations where the substrate con centration might be excessive, the rate-limiting factor in the system would be the enzyme con centration or bacterial population density . . In attempting to develop an expression for the product concentration and rate of product formation in a continuous culture system, it was assumed that the rate of product forma tion was proportional to the bacterial popula tion density and that this was rate-limiting. Further, it was assumed that product concentration in the overflow from the fermentor was representative of the instantaneous product concentration within the fermentor, which from a practical standpoint, as shown by Mac Donald and Piret ( 12), was not too difficult to realize. \Vith these assumptions, a differen tial material balance of the fermentor gives the following expression: Ra k'xdt = Tdt In equation ( 3) the terms, R, V, and k 1 are constants, but the population density, x, in a gener:il solution is a variable with time. How ever, the variation of the population density with time is described by the exponential form of equation ( 2). Hence, substituting for x in equation ( 3) from equation ( 2) and rear ranging gives the basic expression da + R k'x e(k-R/V)t dt' v• o This differential equation is first order and linear with respect to a, and has the solution: . , .-ft" v,,,,,. , . ..,,,. . . f ;.. , .. :] which upon integration and simplification be comes a = k'x 2 e(k-R/V)t k 09 -Rt/V When t=O, then a=a 0 and the constant of integration becomes C k 1 x 0 k Substituting into equation ( 6) for the constant of integration, C, as given in equation ( 7), the final expression obtained is: a k'xoe-Rt/V (ekt l) •o e -Rt/V k \Vhen equation ( 8) was used in the calcu lation of experimental results the unknown was the reaction rate constant for diacetyl formation , k'. Implicit in this constant are the experimental conditions such as temperature, medium, etc., but most important, the organ ism being tested. A comparison of the k' values of two different organisms tested under essentially the same conditions was a com parison of their ability to produce diacetyl

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122 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 under these conditions. Further, if the k' value of an organism was known , the level of diace tyl concentration for any bacterial population density in the continuous culture system coiild be estimated. Determination of k': Under experimental conditions the population density was held es sentially constant with x 0 equal to x. Also under these conditions the diacetvl concen tration is constant and a. is equal t~ a. To ob tain constant x and a values, conditions were adjusted such that k is equal to R/V. Hence, substituting into equation ( 8) for x ., a 0 , and k gives a : k'xe-Rt/V / RIV ( eRt V 1 ) "' ae -Rt/V which simplified and solved for k' gives k' = aR xV The units of k' are expressed as p. p.m. of diacetyl formed per hour by a population den sity of one ( a million organisms per ml). EXPERIMENTAL METHODS The . continuous culture system employed did not vary appreciably in general set-up from those already described in the literature (2, 4, 6, 7, 15), except for possible simplifi cation. The fermentor consisted of a 500 ml flask with a side arm overflow. Both the fer mentor and a sterile medium supply flask were immersed in a 30 C. constant temperature bath and equipped with magnetic stirrers to insure adequate agitation. The flow rate of sterile orange juice was controlled by a Sigma motor pump which delivered by positive dis placement as low as 4.7 ml per hour. Growth in the fermentor was followed by plate counts and direct counts. A number of direct counting methods have been developed specifically for the determination of organ isms in orange juice ( 9, 18, 21) and these along with some 25 other staining procedures were examined for possible use. The procedure finally adopted was as follows: With the use of a standard loop, 0.01 ml of th e sample to be counted was evenly spread over an area of 1 sq. cm. that had previously be e n ruled off on a clean slide. The smear was ai r dried and lightly fixed with heat, A drop ( approximately 0.01 ml) <:>f stain solution ( consisting of 1 ml 10% tannic acid, 2 ml 0.001% aqueous methylene blue, and 1 drop of acid alcohol) was placed over the fixed smear and examined through a coverslip which is sealed to the slide with wax. This wax seal prevents the evaporation of the stain solution. The medium dark contrast oil immersion objective of a phase microscope and 15X oculars were used in counting. The oculars co _ ntained a grid on which a field corresponding to l/400th of a sq. mm. on the smear was ruled off by previ ously viewing a haemocytometer under the same conditions. The dilution factor for count ing was 4 x 10•. From th e number of different methods available in the literature for the quantitative determination of diacetyl ( 5, 17, 19), several of which were specifically used for the detec tion of diacetyl in orange juice ( 3, 10), the procedure of Westerfeld (20) was finally chosen and used without modification. To pre pare the sample of orange juice for the diace tyl test, a distillation was perfoi med. Distilla tion was not carried out for the purpose of concentration as done by Hill, Wenzel and Barreto ( 10) and by Byer ( 3), but to physi cally separate the diacetyl from the orang e juice. The single strength juice used for this study contained an unknown substance which inhibited the development of the diacetyl test. It was shown by a series of experiments that this inhibition was not due to the juice mask ing the color of the test, to the presence of an unknown constituent in the juice competing with diacetyl for the guanidinyl groups of creatine, or to the juice having sufficient buf fering capacity to prevent obtaining the re quired alkalinity. An attempt to remove the inhibiting factor by treatment with Norite charcoal was unsuccessful, hence, distillation was employed . A standard curve relating diacetyl concen tration and optical density readings was con structed using known amounts of purified diacetyl. The two organisms used in this investiga tion, Lactobacilltts No. 802 and Lactobacilltts No. 805, were both originally isolated from orange juice and for neither organism was th e species established. Both organisms were capa ble of growth in orange juice with the produc

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WITTER: DIACETYL IN ORANGE JUICE 123 tion of a t y pical "buttermilk" off-odor and off flavor. To start a continuous culture system expe r iment, th e fermentor was inoculated with an actively growing culture of th e organism to be t es t ed. This culture was allowed to grow batchwise in the fermentor for five to eight hours before starting to add fresh sterile single strength orange juice. The fresh juic e was added continuously and at a constant rate to the fermentor, although the rate was sometimes purposely changed during the course of an experiment to some other constant value. While a run was in progr ess, dir ect counts, plate counts, and diacetyl t es ts were made. The overflow of juice was collected and the volume measured at various times to deter mine the flow rate, R. When the run was com pletecl-g enera lly from 50 to 80 hours after the start-the population density and diacetyl concentration were plotted against time to give a graphical picture of the ex p e riment. The rate of diacetyl production was also cal culated. Each experiment differed slightly in detail, but all of them followed the genera l pattern described. RESULTS AND D1scuss10 N Three representative graphs of thre e typical experiments are given in Figs. 1, 2, and 3. In these thr ee experiments, as well as ip all other e xperiments performed during th e course of this investigation, when the rate of delivery of fre s h juice was altered, an alteration in the population density and the diacetyl conceniii z LIJ C GROWTH ANO OIACETYL FORMATION BY 2 . 5 LACTOBACILLUS ,i.eo2 IN A CONTINUOUS CULTURE SYSTEM. 0 :ii 1.5 a: a: I .,J LO~ . 5 LIJ 0 ' BO ti .,J 0 i t... Q

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124 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 sufficiently to dilute the organisms from the . fermentor at a rate greater than they were being reproduced and both the population density and the diacetyl concentrat . ion dropped. However, it is important to note that these variables were kept constant for something over 30 hours. In Figs. 2 and 3, the flow rate was purposely changed and the curves re sponded as would be expected. For those portions of these experiments where the population density: and the diacetyl concentration remained constant, values of k' were calculated using equation (10). Using all of the data available, k' values were calcu lated and averaged for both test organisms. The average k' value for Lactobacillus No, 805 was 2.5 and that of Lactobacillus No . 802 was 0.015. The reaction rate constant k' is the proportionality factor which relates the rate of diacetyl production by a given organism to its population density, while the constant ratio of k' / k relates the concentration of diacetyl to the population density under equilibrium con ditions. The average k' values given merely express an order of magnitude of diacetyl formation, since at the high population densi ties used experimentally, the value of k varies slightly with the population density, as dis cussed by Adams and Hungate ( 1). Since k was considered a constant in the integration of equation ( 4), a true variation in k in turn caused a pseudo variation in k', although the magnitude of the error was not great. At the lower population densities that would be met in commercial operations (less than one mil lion organisms per ml) , both k and k' would be constant. Experimentally, however, it was very difficult to adequately balance the con tinuous culture system at these lower levels. The results of these experiments again em phasize the lack of validity in using either plate or direct counts as the sole criterion for predicting potential off-flavor in concentrated . orange juice. Organism No. 805 produced dia cetyl at about 167 times the rate of organism No. 802, while growing at a rate that is rough ly 67% the rate of the latter. Disregarding dilu tion, ten thousand No. 805 organisms per ml would produce 0.1 p . p.m. diacetyl (an unac ceptable level) in four hours while it would r c <1uirc one millio11 No. 802 organisms per ml a p e riod of eight hours to produce this same level of diacetyl concentration. SUMMARY Two organisms previously implicated in the spoilage of orange juice were grown in the continuous culture system and their rates of diacetyl production were determined. One of the test organisms, Lactobacillus No. 802, pro duced diacetyl at the rate of 0.015 p.p.m. per hour, per one million organisms per ml. The other test organism, Lactobacillus No. 805, pro duced diacetyl at a rate 167 times as great as the first, or 2.5 p.p.m. of diacetyl per hour, per one million organisms per ml. The relationship of product formation to population density in a continuous culture system was mathematically defined and a method for calculating the diacetyl concen tration and rate of diacetyl formation was derived. ACKNOWLEDGMENT The author wishes to thank V. S. Troy, J. M. Berry, and J. F. Folinazzo for their as sistance and helpful suggestions and other members of the research staff who reviewed this manuscript and assisted in its preparation for publication. LITERATURE CITED I. Adams, S . L. and R. E. Hungate. Continuous fermentation cycle times: prediction from growth curve analysis. Ind. En,r. Chem., 42, 1815-1818 (1950). 2. Bilford. H. R., R. E. Seal!, W. H. Stark, and P. J. Kolachov. Alcoholic fermentation of molasses: rapid continuous fermentation process. Ind. Eng. Chem., 34 1406-1410 (1942) . ' 3. Byer, E. M. Visual detection of either diacetyl or acetylmethyl-carbinol in frozen concentrated orange juice. Food Technol., 8, 173-174 (1954). 4. Elsworth, R. and L. R. P. Meakin. Laboratory and pilot plant equipment for the continuous culture of bacteria with examples of its use. Chem. and Ind., . 926927, July 24, 1954 . 5. Englis, D. T., E. J. Fisch, and S. L. Bash. De termination of diacetyl. Anal. Chem., 25, 1373-1375 (1953). 6. Finn , R. K . and R. E. Wilson. Population dyna mics of' a cOntinuous )lropagator for microorganisms. J. Ag. & Food Chem . , 2, 66-69 (1954). 7. Gerhardt, P . Brucella suis in aerated broth cul ture: continuous culture studies. J. Bact., 52, 283-292 (1946). 8. Golie, H. A. Microorganisms production: theoreti cal c onsi
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POBJECKY: FLORIDA CITRUS STANDARDIZATION 125 14. Monod. J. La technique rle culture continue, theorie et applications. Ann. Inst. Pasteur, 79, 390-410 ( 1950). 15. Moyer, H. V. A continuous method for culturing bacteria for chemic a l study. J. Bact., 18, 59-67 (1929). 16. Novick. A. and L. Szilard. Experiments with the chemostat on spontaneous mutations of bacteria. Proc. Nat'I Acad. Sci .• 36, 708-719 (1950) . 17. Roe, H. R. and J. Mitchell . Determination of small concentrations of carbonyl compounds by a differential pH method. Anal. Chem., 23, 17 58-1760 (1951). 18. Stevens, J. W. and T. C. Manchester . . Methods for direct count of microorganisms in citrus products. J. Assoc. Off. Agr. Chem., 27 :2, 302-307 (1944) . 19. Stotz, E. and J. Raborg. A colorimetric deter mination of acetoin and diacetyl. J. Biol. Chem., 150, 25-31 (1943). 20. Westerfeld. W. W. A colorimetric determination of blood acetoin . J. Biol. Chem., 161, 495-502 (1945). 21. Wolford , E. R. A dire ct microscopic method modified for estimation of microorganisms in California frozen citrus concentrate. Bur. of Agr. and Ind. Chem. Bulletin, AIC-365 ; U. S. D. A. (1953). STANDARDIZATION OF FLORIDA CITRUS PRODUCTS ARTHUR R. PonJECKY Southern Fruit Distributors, Inc. Orlando Members and friends of the Florida State Horticultural Society, I will present my topic in the hope that it will not only benefit our great citrus industry but also the ultimate con sumers of our products. Because standardiza tion has been such an important factor in the development and growth of our processed citrus industry a brief history of its standards is in order. The depression brought on the fir~t need for standards. The United States Department of Agriculture was petitioned to . issue a Fed eral standard for Canned Grapefruit sections. This standard enabled a canner to have his warehouse stocks graded and certified by Fed eral Inspectors. Banks used these . certificates to establish a fair loan value. As other citrus products were introduced Federal Standards were issued on them. With the rapid expansion of canned citrus , many buyers changed from the early practice of buying on samples and started to buy on a grade basis. In 1940, another use was made of the standards. Several Florida Canners re quested the U. S. Department . of Agriculture to furnish inspectors to their plants on a con tinuous basis. These Federal Inspectors would observe the fruit used, the entire processing of the product and the overall sanitation of the entire operation. With this added information, they were able to do a much better job of grading the finished product. The Canner was then allowed to indicate on his label that his product was packed under Federal Inspection along with the official grade assigned the product. This was the start of Grade Labeling. To put our taxpayers at ease, this inspection was not a handout; the canner reimbursed the government for all Inspectors' salaries and ex penses for the services rendered. The War Department made full use of the Federal Standards during the War that fol lowed. They carried on their vast purchasing program by paying for all processed citrus on a grade basis. At the close of the war, the majority of Florida citrus canners were having all of their products inspected. To the credit of our industry this was being done entirely on a voluntary basis with the canners paying the cost of inspection. In 1948, I realized that the existing Federal Standards needed some drastic changes. At an industry meeting I suggested that the indus try incorporate Brix-acid ratios into the stand ards to eliminate the extrem e ly tart juice that was canned in some seasons. For example, canned grapefruit juice with a Brix of 9.5 and an acid of 2.00% was in the Fancy Grade, even though the Brix-acid ratio was below 5 to 1. Canned orange juice with ratios below 8 to 1 also fell into Fancy Grade. The Florida Citrus Industry gave my suggestion ' unani mous backing. However, the Federal Govern ment was not able to make these revisions without the approval of the other citrus pro ducing areas. During this delay, another seg ment of the industry was heard from. Frozen orange concentrate had been introduced and the concentrators wanted the new found "Cinderella" protected at a ny cost. This com bination of events coupled with Fuller War ren's ambition to be governor, climaxed in Mr. Warren realizing his life's ambition and in the birth of "The Florida Citrus Code of 1949." This Law is unique in many ways. It not only requires that all fresh fruit meet the ma

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126 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 turity laws in the code, but also all citrus prod ucts processed in Florida must meet its re quirements or be labeled SUBSTANDARD. The code also authorized the Florida Citrus Commission to establish State Grades on all processed citrus. The Commissioner of Agri culture has the responsibility of Inspection and Compliance with the law. The inspection is being carried out at present by Federal In spectors under a joint agreement with the Florida Department of Agriculture. The Citrus Commission has adopted the Federal Stand ards as State Standards. Here I wish to em phasize that whereas in other citrus producing areas the use of these standards is voluntary in Florida because of its laws they are com pulsory. Standards can be classified into three parts. If a product is to be properly labeled, it must be described, this is a "Standard of Identity.'' To protect the consumer the containers must be properly filled, this is a "Standard of Fill.'' Once established, these two are seldom changed so we will concern ourselves with the third part-that is, "Standards of Quality." The standard for Canned Grapefruit has best stood the test of time. Fancy Grapefruit sections have not changed in the past thirty years. I see no need for any changes in the near future. Because of the high labor cost involved, canners try only to pack Fancy quality. However, some fruit due to its na ture, does not hold up as well during process and consequently some of the segments be come broken and soft. This is graded as Choice instead of Fancy. Since both of these grades have the same nutritive value , con sumer should choose based on the use intend ed for the canned grapefruit. purchased. The Standard for Canned Grapefruit Juice has had many revisions. There are separate re quirements for the two styles ; that is sweet ened and unsweetened. The sweetened style requires a minimum Brix of 11.5 and a minimum Brix-acid ratio of 9 to 1. The un sweetened style a minimum Brix of 9.0 and a sliding scale of ratios starting at 8 to I at a Brix of 9.0 down, to a ratio of 7 to I at a Brix level of 10.5 or higher. We all agree that a 7 to I Brix-acid ratio is too tart and so it would seem advisable to raise this level and at the same time simplify the standard by doing away with the sliding scale. We have con.;e a long way in improving our canned grapefruit juice from the high acid product of the past. But I feel that to move forward w e must have an examination of conscience. Our maturity laws are based on Brix-acid ratios. This allows some crops of fruit to be harvested ' as early as September and October. The native Floridian or Florida cracker doesn't eat grapefruit until a much later elate. So we live under two sets of maturity standards, a brix-acid ratio for the "Yankees" and a taste test for ourselves. The unfortunate part is that only a very small part of our crop is picked during this early period; statistics will hear me out on this. The only argument that can be advanced for this early harvest is that it helps the market on fresh fruit by extending the ship ping season. Most growe rs will bear me out that for many years, they haven't realized any of this better market price. It is my honest opinion that if the grapefruit season was post poned until November it would not only elim inate some of the undesirable fresh fruit going to market and to canneries but it would also create a better economical return to the grow er and processor. It is sound logic that the few crops now be ing picked early would taste better if they re mained on the trees longer. This would en courage more consumers to eat grapefruit in fresh form thus helping the fresh market. By eliminating the very small percentage of early grapefruit being canned in September and October the overall quality of canned sweet ened grapefruit juice would be improved. Our best quality unsweetened grapefruit juice is canned in the late spring when grapefruit reaches its optimum sweetness. Canners would be . encouraged to carry over large in ventories of premium quality unsweetened juice if they knew . that they did not have to compete with the low price now created by the canning of the early packing house elim inations. Buyers would also remain more active through September and October with this add e d confidence in our market. I am cer tain that all of this would add up to improved quality in both fresh grapefruits and canned grapefruit juice, with a better economical re turn to all segments of the industry. The Standard for Canned Orange Juice has also had many revisions. Sweetened Orange Juice requires a minimum Brix of.10.s and a minimum Brix-acid ratio of 12 to 1. Unsweet

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POBJECKY: FLORIDA CITRUS STANDARDIZATION 127 cned orang e juice a minimum llrix of 10 . 5 and a sliding ratio scale of 10 to 1 if th e Brix i s less th a n 11.5 and down to 9 to 1 if th e B r ix is above 11.5. Here again we all agr e e th a t the 9 to 1 ratio at any Brix level is too tart and so it should be raised and the sliding scale, which only . serves to confus e our production personnel, be done away with. Again we c a n help the quality of both fr e sh orang e s and canned orange juice by holding back slightly on our picking schedul e . There is one other important factor in orange juic e th a t I must dwell on. This factor is color. Many of our northern friends associ a te the word or a nge with the orange color . Th e deep orange color of synthetic beverages to which artificial color has been added, strength ens thi s delusion . The color of Florida orang e juice v a ries from yellow to yellow-orange in color. This variation in color depends on the variety of orange and to a lesser degree on th e growing season. Consumers should be in formed th a t this lack of ornnge color in no way detracts from the health-giving qualiti e s of Florida orange juice-actually in many in stance s the vitamin level on the pale colored earl y v a ri e tifs i s even higher than the l a ter varieties. Th e sugg e stions I have made on Cann e d Grapefruit Juice and Orange Juice would of course al s o benefit the quality of canned blended juice. Canned tangerine juice can be improv e d by changes in th e methods of process and stor age. Som e in the industry would like to r e classif y tangerines and call them orange s . I wish to remain old-fashioned in this respect. To m e thos e zipper-skinned fruit mother put in our stockings at Christmas are still tang e ines. Our latest product, orange juice in c a tons, still is in search of an official n a me. Be cause of the varied methods of production it had been verv difficult to establish a Standard of Identity. However, steps have been tak e n to have the Federal Food and Drug Admin istration issue a Standard of Identity and this should e nabl e packers to properly l a bel this it e m. I . h a v e s aved Frozen Orange Concentrat e for the very l a st. My reason is, that the Florida citrus code and Federal Standards h a ve done much to promote the .popularity of this product. The code prohibits th e addition of sugar to Florida Orange Conc e ntrate-this protects the consumer from any possible adulteration that might arise by the substitution of sugar for natural fruit solids. The code establishes a minimum fruit solids value in the finished con centrate which assures the consumer that after the addition of thre e parts water the recon stituted orange juice is of the same strength as the freshly extract e d orange juice. The minimum Brix-acid ratio of 12 to 1 is much higher than the minimum of 8 to 1 allowed in fresh fruit and the pr e sent 9 to 1 allowed in canned orange juice. And here I wish to clinch my previous arguments against the early harvesting of Florida citrus. In spite of the rigid controls the concentrators have im posed on themselves . They were able to pro duce seventy million gallons of frozen orang e concentrate during the past season. To do this, they utilized fifty million boxes of oranges out of a ninety-two million box crop. This entire production was accomplished during a four months production period, in most plants, and the growers enjoyed the best returns on record. Consumers may now ask this question: If your industry is so highly standardized why the variations in quality? Th e re are many rea sons. Primarilv the differences in the varieti e s of fruit we gr~w; diff e r e nces in the processing and blending of fruit; and differences in the packers as well. Stand a rds will never change these, but standards can a nd must assure you a satisfactory product. Many of our quality problems arise after our products leave our warehouses. Prolonged storage at high tem peratures will alt e r the quality of all canned citrus products . Many handlers and consum e rs still fail to realize that frozen orange concen trate is a perishable product and must be handled as such. In conclusion any industry that has enjoyed the tremendous growth of ours has a right to be proud of th e products it produces. How ever, to continue forward we must not rest on past performanc e s. It is with this thought that I wish to re-emphasize that the only real important chang e we can make to furth e r improve our product s is to change our ma turity laws . To do this the standards must b e rigid enough to d e la y the picking of fruit until November or such tim e that we ourselves are satisfied with th e fl a vor of the fruit we harvest.

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128 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 CITRUS VITAMIN 'P' (Citrus Bio-Flavonoids) Boms SOKOLOFF, M.D., IsrnoR CHAMELIN, Sc.n, MORTON BISKIND, M.D., WILLIAM C. MARTIN, M.D., CLARENCE SAELHOF, M.D., PHD., SHIRO KATO, M.D., ;Huco EsPINAL , M.D., WITH TECH NICAL ASSISTANCE OF T AEKYUNG KIM, MAXWELL SI!-f PSON, NORMAN ANDREE AND GEORGE RENNINGER South e rn Bio-Research Laboratory Florida Southern College Lakeland Twenty years ago in 1936, Dr. Alb~rt Szent-Gyorgyi announced the discovery of a Capillary Permeability factor, vitamin P, iso lated by him and his associates from red pep per and lemon. At first he believed that vita min p was a single chemical substance. How ever several months after his announcement, he r~ctifiecl his statement admitting that vita min P is a compound of several flavonoids. Immediately after the discovery of vitamin P, the California Fruit Growers Exchange em barked on an extensive investigation of vita min P. The California scientists isolated sev eral flavonoids present in citrus fruit and synthesized some, like methyl-chalcone hes peridin. Th e results of the clinical trials with their flavonoid compounds were not very en couraging, and somewhat disappointing. By 1946-47, the whole problem of vitamin P reached a critical state. The work of Szent Gyorgyi seemed to b e discredited and con troversial. The vitamin nature of vitamin P was denied by some workers, its therapeutic value questioned, and some workers even claimed that vitamin P or flavonoids are neither absorbed nor assimilated by the or ganism (Clark) . It was under these highly unfavorable conditions that the Southern Bio Research Laboratory in 1947 began the in vestigation on citrus vitamin P. We visualized two possible roads of attack ing this problem. One, to follow the steps of California and to try i s olating various citrus flavonoids, or to return to the original concept of Szent-Gyorgyi and to work with vita min P as a flavonoid complex. We chose the second approach and decided to work and to investigate the flavonoid compound we ex tracted from citrus wastes. This compound, composed of the flavonoids naturally present both in grapefruits and oranges, we called citrus vitamin P, or C.V.P. It is water soluble, and it contains several flavonoids, apparently forming one or two complex flavonoid mole' cules, as flavonoids tend to do so easily. It was this compound that we have been inves tigating experimentally and clinically for the last nine years. THE BIO-ASSAY FOR VITAMIN p The chemical tests on flavonoids are of a limited significance. The boro-citrate test, the Lawrence test and others give an indication of the chemical nature of a flavonoid but they do not disclose the biological activity of the compound. Thus, our second problem was to work out a reliable bio-assay. Ambrose and DeEds offered a method of testing capillary permeability by applying chloroform to the skin of rabbits and injecting trypan blue dye. Although this method has some merit, it is not sufficiently exact for any quantitative test. Gradually we elaborated a bio-assay technique which we believe is accurate and dependable. This method is based on the dlscovery of Dr. M. J. Shear of the National Health Institutes that the polysaccharide isolated from Serratia marcescens induces an extensive hemorrhage in the tumors of animals. ( 1) Th e bacterial polysaccharide preparation supplied to us by Dr. Shear and labeled P-25 is well standardized . A dose of 0.5 mg. in jected in a rat, 150 grams weight and bearer of a tumor two inches in diameter, kills the animal in 67 hours. Death is caused by a pro fuse capillary bleeding and a destruction of numerous capillaries of the tumor. Our tests with citrus vitamin P have demon strated its biological a ctivity. Table I gives the data pertaining to one of our tests . When 3 mg. of the citrus vitamin P com pound were injected one hour before the in

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SOKOLOFF, ET AL: CITRUS VITAMIN P 129 jection of bacterial polysaccharide, the animals lived an average of 20 hours in s tead of an average of 7 hours without vitamin P. When, however, th e dose of vitamin P was increas e . cl to 10 mg., 66 % of the animals survived and 33% lived an average of 45 hours, (2) Rat Nos. r;1 .. A, m" 171-B, fo 171...C, m. 171 .. D, mo l7l•E, mo 174--A, fo 174-B, mo 174-C, mo l 74-D, mo 174-E, mo 174-F, mo 177 .. 1.., fo l'7'7•B, mo 177--C, fo 1'77•D, mo 1'7'7-'E, mo l77•F.P m. 1'77•H, m. 178--A, n:.o Controls l78•B, mo 178-C, f. lriS-D, mo 178-'E, f. 178-F, fo 178 ... H, m. (*) TABLE I THE PRO'!'ECTIVE ACTION OF CITRUS VI TAMI M P AGAINST THE HEMORRHAGEwI.NDUCING ACTIVITY OF BACTERIAL POLYSACCHARIDE, F-25 (~) TREA 'Ill!E:NT Citrus Result: p .. 25 Vita.min P D~6th or survival Oo5 mgo 3 mgo Death in 17 hreo Oo5 ill5. 3 mgo Death in 22 hrs o 25 mino 0.,5 mg. 3 r.1g~ Dea.th in 18 hrso o.s mgo 3 mg. D'!ath in 19 hrs. 10 min. Oo5 mgo 3 mgo Dea.th in 20 hrs. 40 min. Oo5 nig o 3 mg. Death 111 19 hrso Oo45 mg 3 mgo Death in 24 hrso 30 mino Oo5 mgo 10 %1'.lgo Death in 36 hrs o Oo5 ~ 10 mgo Survived Oo5 mgo 10 mgo Death in 52 hrso Oo5 ~ 10 mg. Surviveid 0.5 mg" 10 mgo Survived Oo5 lllgo 10 mgo Dea.th in 66 hrs o Oo5 mg. 10 mg• Survived o.4 mgo lO mgo Survived Oo45 mg 10 mgo Survived o.s mg. 10 mgo Survived Oo5 mg. 10 mgo Death in 26 hr::.• Oo5 mgo 10 mg. Survived Oo5 Illgo None Deuth in 6 hrso 25 mino Oo5 mgo None, Death in 7 hrs. 35 mino Oo5 mg. None Death in 9 hrs. Oo5 mg. None Death in 7 hrso 30 mino 6.5 mg. none Death in 8 hrso 20 mino Oo5 mg. :Mone Death in 7 hrs o 15 mlno P ls a preparation of Shce.r bacterial polysaccbarideo

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130 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Rechecking our results, we found that a dose of 12 mg. gave a complete protection to all animals receiving the deadly dose of 0.5 mg. of bacterial polysaccharide. Thus this dose served us during all our further investigations as the basis of our bio-assays. During the following years, we had the opportunity to test various citrus flavonoids isolated by us or produced by Californians or some other companies. \Ve found that water insoluble hesperidin gave no protection against capillary hemorrhage tested by this method, even when given in a dose ten times larger than our protective dose of 12 mg. Taking the index 1.0 ( corresponding to 12 mg.) as a de parting point for the tests of other flavonoids, we found that methyl-chalcone hesperidin showed a very mild capillary activity with an index of 0.1. The synthetic phosphorylated hesperidin exert,ed an activity about 0.15. Ru tin gave an index of 0.2. On the other hand, the lemon infusion prepared by the California Fruit Growers Exchange has a relatively high index of 0.3, or approximately three times less capillary activity than our Florida citrus vita-• min P compound. (Table II) '!'~LE II CCMFAJU.TIVE .lCTIVTl'Y OF VARIOUS FU.VONOID CCMP0UIIDS J.GilNST Hl!MORRIWlE-fRODUCING BACTERIAL POLYSACCHARIDB T!le m1nlma.1 clou, ot flavo• Index ot Compounds nolds protecting an1m3.la 'b1olog1oal trom death by 0.5 ag. ot aot1T'1t7 Bactr. Polyaaocharlde (*) vlt&I:1ln f compound (c,v.P.) l2 "'6• 1.0 Wate r--insoluble hesperidln 120 ll'(!t 0 Callt'ornia meth7lchalcone hesperldln 12u ""'" 0.1 Phoaphorylated he:i ... peridln, N.n.c. 80 '11,t,1 0.15 Lemon Intudon,, co:icnt. Cc.litorn!a 35 "'6• 0.3 Rutln 60 mg. 0.2 Rats, British bri,ed, avera.ge weight 150 gm., bearers of Crocker carcinolnll, two ln Having asserted and proved to our own satisfaction that the Florida citrus vitamin P compound is biologically superior to the ones produced by Californians, we embarked on the clinical investigations with this compound. THE PHYSIOLOGY OF THE CAPILLARY SYSTEM The medical profession fully realizes the important role which capillary dysfunction plays in many diseases. Stefanini and Dame shek ( 3) in their recent book on hemorrhagic disorders point out capillary fragility as the cause of abnormal bleedings. One must clear ly visualize that the essential exchange of body fluids takes place in the capillaries and that the role of the large blood vessels is actually limited to transporting blood to the capillaries. The peculiar paradox of the human organism is that the capillaries are easily injured by numerous bacterial and chemical agents or by metabolic disturbances. We know by now that increased capillary fragility is a common phenomenon, much more so than we thought ten or fifteen years ago. The work of Griffith ( 4), Beard wood ( 5), Greenblatt (6) and many others indicate that the capillaries are abnormally fragile, and therefore might bleed easily in numerous di seases such as arteriosclerosis, hypertension, and particularly so in diabetes (7). When a stroke (apoplexy) occurs, this means that some capillaries of the brain tissue became over-fragile and broke down causing bleed ing, often fatal. In many bacterial infections and in almost all virus infections, capillary fragility, localized or generalized, is present. ( 8, 9, 10). The inflammation of the mucous membrane itself, when one has a sore throat, or swollen gums, or pneumonia, or any other infectious disease is closely associated with the injury to the capillary system. Even in heart failure, with sudden death or coronary thrombosis, one might blame capillary injury for the tragic accident. For in such cases, the so-callecl intimal capillary, which is located in the wall of the larger coronary vessels is al:i normally fragile and might suddenly break down and bleed .. If the bleeding is profuse, man dies at once. When the bleeding is very small, a bloocl clot is formed and coronary oc clusion, known as coronary thrombosis, Jakes place. (11, 12, 13, 14). Older people more frequently have increased capillary fragility than younger ones, and the danger to their lives from capillary bleeding is higher. ( 15, 16, 17).

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SOKOLOFF, ET AL: CITRUS VITAMIN P 131 CLINICAL INVESTIGATIONS The clinical investigations, in which ninety two physicians associated with various hospi tals took part, and the results of which were reported in sixty-three papers published in medical and scientific journals, have demon strated the therapeutic value of the Florida citrus vitamin P compound, isolated by us from citrus waste, in the following conditions where increased capillary fragility or capillary bleeding was evidenced. Radiation erythema (18; 19, 20) Tuberculous hemoptysis (21, 22) Habitual. Abortion ( 23, 24, 25, 26, 27, 28) Erythrohlastosis Fetalis (29, 30) Bleeding Gastric and Duodenal Ulcers ( 31, 32, 33) Cerebral Hemorrhage: Stroke (34, 35) Retinitis (36, 37, 38) Dental Diseases and Surgery ( 39, 40) Hemorrhagic Cystitis ( 41) Hemorrhagic Diathesis (3, 42, 43) Increased Capillary Fragility ( 44, 45) Altogether about 9,000 case histories were collected during the last seven years. To conclude: The experimental and clinical studies on Florida citrus vitamin P compound extracted from citrus waste, have supplied the evidence of its therapeutic value in increased capillary fragility and capillary bleeding. In directly, the data so collected confirms the original findings of Szent-Gyorgyi and his as sociates concerning vitamin P. REFEnENCES (1) Shear, M. J. et al, J. Nat. Inst., 44 :4, 81, 1943. (2) Sokoloff, B. Eddy, W. H., and Redd, J. B.: J. Clin. Inv., 30:395, 1951. (3) Stefanini, M. and Dame shek. W.: The Hemorrhagic Disorders, Grune & Strat ton, 1956, New York. (4) Griffith, J. W., Jr., and Lin dauer, M.A.: Am. Heart J., 28:758, 1944. (5) Beard wood, J. T., Roberts. E., and Trueman, R.: Proc. Amer. Diabetes Assoc., 8 :241, 1948. (6) Greenblatt, Robert B.: Obst. & Gynec .• 2: 53-534, November 1953. (7) Loewe. Walter H.; Eye, Ear, Nose & Throat Monthly, 34:108, 1955. (8) Biskinc, M. S. and Martin, W. C.: Am. ,T. Dig. Dis., 21 :177, 1954. (9) Diskind, M. S. and Martin, W. C.: Am. J. Dig. Dis., 22:41-45, 1955. (10) Sokoloff, Boris: Am. J. Dig. Dis., 22 :1, 1955. (11) Wartman, W. B.: Am. Heart J., 15: 459, 1938. ( 12) Winternitz, M., Thomas, B., and Lecompte, P.: The Biology of Arteriosclerosis, Springfield, Charles Thom as, 1938. ( 13) Paterson, J. C.: Arch. Path., 29: 345, 1940. (14) Sokoloff, B., Martin, W. C., Saelhof, C. C.: .T. Am. Geriatr. Soc. (in press). (15) Ibid. (16) Mar tin, W. C.: Intern. Record of Med. & Gen. Prac. Clin ics, Vol. 168, No. 2, February 1955. (17) Perry, D. J. and Linden; L.: Science Newsletter, April, 1953. (18) Arons, I., Freedman, J., and Weintraub, S.: Brit. J. of Radiology, 27 :696-98, 1954. (19) Sokoloff, B., and Eddy, W. H.: Capillary Fragility & Stress, Mono. FSC 3 :33-65, 1952. (20) Martin, William P. Proc. Meet., Buffalo Gen. Hospital. May, 1952. (21) Jones, Lelan.d W. and Croce, Pietro: Capil. Frag. & Stress, 3 :19-21, 1952. (22) Sokoloff, B., and Eddy, W. H. Bio-Flavon oids in Capillary Fragility, Mono. 2, FSC, 1952. (23) Papers of the Royal Committee on Population, Vol. IV Reproductive Wastage: Abortion, Stillbirth, and In fant Mortality. London, 1950, His Majesty's Stat. Off. pp, 3-52. (24) Moore. Robert Allan: Pathologic Anato my in relation to the Causes, Pathogenesis, and Clin ical Manifestations of Disease. Saunders Co.. 1952. (25) Greenblatt, R. B., and Suran, R. R.: .Am. J. Obst. & Gynec .. 57 :294, 1949. (26) Taylor, Finis A.: West. J. of Surg., Obst., and Gynec., Vol. 64, pp, 280-283, May 1956. ( 27) His kind, Leonard: Journal-Lancet, Vol. 75, No. 6, p, 272, Minneapolis, June 1955. (28) Javert, Carl T.: Obst. & Gynec., Vol. 3, No. 4, April 1954. (29) Rogers, George C., and Vieming, John M.: West. J. Surg., Obstet., and Gynec., 63 :586, 1955. (30) Jacobs, Warren M.: Surg., Gynec., & Obstet., August 1956, Vol. 102. 233-236, 1956. (31) Gray, H. K., Shands, W. C. M., and Thuringer, C.: Ann. Surg., 139: 731, 1954. (32) Ivy, A. C., Grossman, M. I., and Bacharach, W. H.: Peptic Ulcer, New York, Blakiston Co., 1950. ( 33) Weiss, S. and Weiss, B.: Bull. Int. Cong. of. Gastroenterology, London, July 1956. ( 34) Alvarez, Walter C.: J.A.M.A .. 157 :1199, 1955. (35) Sokoloff, B., Biskind, M., Martin, W. C. and Chamelin, l'.: Trav. XXth Intern. Congress Physio logy, August 1, 1956, Brussels. (36) Shepardson, H. C .. and Crawford. J. W.: Calif. & West. Med., 35: 111, 1931. (37) Wagener, H. P.: .Proc. Am. Diabetes Asso., 5:203, 1945. (38) Loewe, Walter R.: Eye, Ear, Nose & Throat Monthly, Vol. 34, No. 2, Febru ary 1955. (39) Puckett, John B.: Dental Digest, June 1956. (40) Wellensiek, Ellen K.: Texas Dental Journal, June 1956. (41) Saelhof, Clarence C.: Am. J. Dig. Dis., 22 :204-6, July 1955. (42) Sokoloff, Boris and Eddy, Walter H.: Cnpillary Frag. & Stress. Mono. FSC. 3:14-16, 1952. (43) Sokoloff, ll. and Eddy, W. H.: Capillary Frag. & Stress, Mono. FSC, 1952. (44) Martin, W. C.: Intern. Record of Med. & Gen. Prac. Clinics, Vol. 168, No. 2, February 1955. (45) Sokoloff, B., Biskind, M. S., Martin, W. C. and Saelhof, C. C.: Clin. Med .. Vol. 2, No. 8, pp. 787-792, August 1955. (46) Biskind, M. S. and Martin, W. C.: Am. J. Dig, Dis., 22 :41-45, 1955 1 ( 47) Biskind, M. S. and Martin, W. C.: Am. J. Dig. Dis., 21-177, 1954. ( 48) Finch. Frederick L.: Tri-State Medical Journal, Feb. 1956, Vol. III, No. 12.

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132 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 VACUUM COOLING OF FLORIDA VEGETABLES R. K. SHOWALTER AND B. D. THOMPSON 1 Florida Agricultural Exp e riment Station Gain e sville The first Florida shipments of vacuum cooled lettuce were m a de from Oneco during th e 1955-56 season. Although the vacuum cooling of lettuce has develop e d rapidl y in California and Arizona since the first com mercial shipments in 1948, the method has not been widely adapt e d in oth e r areas. Flori da growers and shipper s h a ve shown consid erable interest in vacuum cooling. The re ported advantages are the maintenance of better quality by more rapid precooling and th e reduction in packing a nd shipping costs through cheaper cont a iner s and the elimination of package and top ic e . Lettuce ha s not been grown in sufficient volume in concentrated areas in Florida to ju s tify the cost of establish ing a permanentl y locat e d vacuum cooler. The unit at Oneco was s e mi-portable and when th e lettuce season ended in Manatee . County it was moved to lettuc e production areas in other states. The results pres e nted here were obtained from prelimin a ry vacuum cooling studies with several vegetables to determine primarily the effects of the vacuum treatment on quality. Vacuum cooling h a s b ee n studied b y sev e ral investigators . Fri e dm a n ( 3) found that almost any fruit or v e g e t a bl e can b e vacuum cooled to some ext e nt , but th e re was a rapid temperature decreas e onl y in vegetables with a large ratio of surface a r e a to volume. Vac uum cooling was found e ff e ctive for pre packaged spinach, colesl a w , and salad mix after the bags were p a ck e d in master con tainers ( 2) . VACUUM COOLING PROC E SS The process by which the rapid chilling o c curs is based on ev a por a tive cooling. At normal atmospheric pr e s s ur e of approximate ly 30 inches, water boils at 212 F. If the pres1 /The authors wish to e xp res s appreciation to the City Products Corp. , th e V. B . Hook Co. and the P rine and Griffin farm s for m a king the equipment available for these studie s. They also wish to thank the growers and shippers wh o furnished vegetables and the companies who s u pp lied containers for the te s ts. sure over water is reduced to 0.18 inches ( vacuum of 29.82 inches) the water boils at 32 ' F. The water which "boils" or evaporates from th e vegetables cools them to a temper atur e corr e sponding to the t e mp e rature of th e w a ter. To secure the reduced pressure , v e getables are placed in a chamb e r and the required ,vacuum is obtained by a pump or a steam jet . The cooling of the vegetable is measur e d with a recording th e rmometer and th e v a cuum is released when the desired t e mperature is reached. Since vacuum cooling d e p e nds upon evaporation of water , one might think that considerabl e w e ight loss occurs. However, wilting is not severe and Friedman and Radspinner ( 4) reported weight losses of only 1 to 4.7 p e rc e nt. The lettuce vacuum cooled in fib e rboard c a rton s at Oneco was either pack e d dry in the field or washed and packed in the pack inghouse. The vacuum tub e ( 22 ft. long x 7 Jf ft. in diameter) was loaded with 240 car tons ea c h containing rn or 2 dozen h e ads of lettuc e . The vacuum pump , power e d by a di ese l engine, pulled the air from the tube containing the lettuce through . a s e cond tube of e qu a l size containing blocks of ice. The tub e of ic e condensed the evaporated mois ture before it reached the vacuum pump. Studi e s w e re made in a laboratory model va c uum cooler at Belle Glad e in May and Jun e 1956. The vacuum chamber, with a cap a city of about 4 cartons , was e vacuated b y an e l e ctric powered pump. Th e evaporated moisture was condensed by mech a nical re frigeration. VACUUM COOLING OF LE'ITUCE Data were obtained on th e weight loss, cooling rate, and quality of w e t and dry let tuce. Wetting the lettuce befor e vacuum cooling did not affect the cooling rate. Little diff e r e nc e in weight loss wa s found among 50 cartons of wet and dr y lettuce from five dif fer e nt lots as shown in Table 1. When the individu a l h e ads were weigh e d in one test, thos e with added water lost only 1.9 percent comp a red with 2.3 percent w e ight loss of the dry h ea d s . V a cuum cooling had no apparent detri m e nt a l effects upon the quality of the lettuce.

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SHOWALTER AND THOMPSON: COOLING VEGETABLES 133 Table l. Average Temperatures and Weight Losses of Wet and Dry Lettuce Vacuum Cooled in Commercial Unit at Oneco, Florida Dry Units Tested or Wet Number: Type Lettuce Wet 10 Fiberboard Cartons Wet 10 II II Wet 10 II II Dry 10 II II Dry 10 II " Wet 32 Single Heads Dry 30 Single Heads When held in storage at 37-40 for 8 days the quality was still good . The dry lettuce showed moderate wilting after 8 days and a weight loss of 4.1 percent compared with slight wilting and a loss of 1.4 percent for the wet lettuce. After 16 days storage th e outer leaves of both wet and drv lettuce were considerably wilted. Another lo't hydrocooled and top-iced for 16 days was very crisp. However, the top-iced h eads developed mor e reddish discoloration than the vacuum cooled heads. VEGETABLES IN VARIOUS CONTAINERS During March 1956, small quantities of vegetables were cooled in the commercial vacuum unit along with th e loads of lettuce. Prepackaged broccoli, spinach, radishes, salad mix, and coleslaw cooled a t different rates. The t e mperature of the broccoli decreased only 15 " in the same period that th e spinach and salad mix cooled 30-33 ( Table 2). In the commercial vacuum unit celery cooled from 61 to 45 at the s lowest rate for th e vegetables in bulk contain ers . In the laboratory vacuum unit two tests of similar cartons of cel erv cooled from 80' to 38 in 30 minutes and from 80 to 44 in 20 minutes. Fri e dman and Rad spinner ( 4) found that the initial temperature of celery had a marked effect on th e final t e mperature, while the initial t e mperature of lettuce h ad little effect on its final temperature. Th ey attributed the difference to the smaller sur face area-volume ratio of celery. In the celery Time in Vegetable Temp. Weight Vacuum Before After Loss Min. OF OF C1f /0 45 65 36 2.6 36 71 38 3.5 40 76 38 3.1 36 75 38 3.1 57 74 42 3.2 45 65 36 1.9 45 65 36 2.3 cooled to 38 at the base of the stalks, con siderable freezing injury of the leaves oc curred. Although the vegetabl es were vacuum cooled in film bags, fiberboard cartons, small baskets and wir e bound crates, the containers were not all compared in the same tests ., Fiberboard cartons and wirebound crates of sweet corn were vacuum cooled at the same time in one test (Test No. 3, Table 3), and there was littl e difference in rate of cooling and no differenc e in appearance of the corn. In another test bunched radishes in wooden baskets were vacuum cool ed with topped pre packaged radishes (Table 2). Some of the tops on the bunched radishes were severely wilted, but ther e was no change in appear ance of the prepackaged lot. The weight loss of the bunched radishes averaged 7 percent compared with 4 percent for the prepackaged ones. PREWETTING OF S,VEET CORN Sinc e succulence or moisture content is one of the import an t quality factors of. sweet corn, attempts were made to reduce the moistur e loss
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134 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 cooling. Dewey ( 1) also reduced the weight loss of sweet corn by adding water immedi ately prior to the vacuum treatment. He re duced the weight loss from 3.2 percent for dry broccoli to almost none for wet broccoli. EFFECT OF VACUUM COOLING ON QUALITY Quality evaluations of the dry and wet vacuum cooled and hydrocooled swe e t corn were made at harvest and after 2, 6, and 7 days' storage at 35 and 90-95 percent rela tive humidity. The vacuum cooled ears were packed. in fiberboard cartons and the hydro cooled ears in wirebound crates. The succu lence as measured by th e shear press, was lower after vacuum cooling dry than at har vest, and remained low er than the other treat ments at all storage periods ( Table 4). The kernels vacuum cooled wet were still more succulent after 7 days' cold storage than at harvest , although the husks had wilted very slightly. The hydrocooled ears , maintained the most succulence and the freshest husks. The husks in all treatments remained green. Slight denting of kernels was found only in the dry vacuum lot after 6 and 7 days' stor age. Small quantities of vacuum cooled and hydrocoole
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SHOW ALTER AND THOMPSON: COOLING VEGETABLES 135 Ta'.,le J. Aver3.3~ Temperatures a.1d Ueisht Losses of -,-Jet and Dry Sweet Corn Vacuum Cooled in La bo rat o rJ Jnit at B elle Glade, Florida. Test Dr:, Uni t s Containers : fo. e r Tested or '.-Je t ; Jo . Ears 1 Dry 2 Fiberboard Cart:>ns 2 Dry 2 II II 3 Dry 1 W ire bound C rate 3 Dry 1 Fiberboard Carton 4 .iet 1 Wire bound Crate 4 Dry 1 II " 5 ,/et 60 Ear s 5 Dry 60 .=;a.rs 6 './et 36 Ears 6 Dry 3 6 Ears and endfve was about the same after 11 days cold storage. SUMMARY The first Florida shipments of vacuum cooled lettuce originated from the semi portable installation at Oneco . A number of vegetables were vacuum cooled in the Spring of 1956 with the commercial lettuce cooling e quipment and a laboratory model at Belle Glade. The vegetables with a large ratio of surface area to volume cooled most rapidly , but sweet com and celery also cooled s a tis factorily. The bulk and prepackaged vegetable con tainers tested did not affect th e cooling proTi,:,e in Corn Temeerature (Cob) l/ eieht Vacu'..un 3e fore :After: Decrea s e Hi n. Dr DF O F . ; ;, 18 78 38 40 30 84 38 46 25 83 40 43 25 84 36 48 40 8 2 33 49 40 8 4 32 52 40 81 35 46 2 ,7 40 90 34 56 5.5 40 84 38 46 0 40 86 38 4 8 6.1 cess. Th e vacuum method did not result in objectionabl e wilting except for radish tops. Weight loss of sweet com was reduced by wetting before vacuum cooling. Vacuum cooled vegetables retained their freshness well during storage. LITERATURE CITED 1. Dewey , D . H. Evap o rati\ e Cooling of Fruita and Vegetables. Refrig, Engin . 60: 1281-1283. 1952 . 2 . Friedm an, B . A. V ac uum Cooling of Prepa c kag e d Spinac h, Coleslaw, and Mi x ed Sal a d. Proc. Amer. Soc. Hort. Sci . 58 : 279-2 8 7. 1951. 3 ..... ....... . ......... ,. .............. ... Vacuum Coolin g Upheld in Tests. W ei,; lern Grower a nd Shil)per 23 ( 8 ): 21-24, 31. 1952. 4. ........ ..... . ... ..... ........... ...... and W. A. R a dspinner. Vacuum C oo lin g Fresh Vegetabl es and Fruits. U .S. D . A. Agr. Mark et . ing Service Report No. 107. 195G. 'l'ab l e 4. Ch~nges in Quality of Florida Sweet Corn After Dry and 'de t Vac1.r..1m Coolinc and !ly drocoolin i . l.:etho d of : At Harvest 2 Day s C o ld Stora!"e:t 6 Days Cold Storage:t 7 Days Cold St a race? Precooling : Succulence =succul ence : ifusks : Kernels: Succulence: Husks : Kernels= Succulence : Husks =Kernels 1 ; ml. Juice ~ml. Juice ~C o ndition; Denting~ ml. Juice Condition; Denting: ml. Juice :conditfo n ;o e ntin g Dry Vacuum Cooled Wet Vacuum Cooled Hyd roco o le d 11.4 . 11.4 11. 4 11.2 15.7 is.6 S li Rh t Wilting Fresh Fresh t. ~let None 11.2 None 1.i..o None Cold stora,p:e t.?mr,erature 35 F. and relative humidity 90-95 percent. Slight il ilti ng Not Crisp Fresh Slight o n 10,2 2S% ears None lJ.O Mo ne Slight Slight on W ilti ng 50~ ear s Very tfone Slight

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136 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 THE QUALITY CONTROL OF CHILLED ORANGE JUICE FROM THE TREE TO THE CONSUMER LEO J. LISTER Halco Products, Inc. Fairvilla AND AnTHUR C. FAY H. P. Hood & Sons Boston, Mass. For a number of years, due to the com patability of citrus juice and milk, the citrus and dairy farmers looked for a suitable means of processing and packaging citrus juice for distribution by dairy route trucks. With the advent of chilled orange juice, this was ac complished. Cartoned, or chilled orange juice as it is commonly called, is a single strength orange juice, marketed in a waxed fiberboard carton. The juice is extracted and treated in such a manner as to retain most of the desirable flavor and aroma which is associated with freshly squeezed orange juice. It is highly perishable in nature, and must be stored or transported under adequate refrigeration in order to reach the consumer in a palatable state. During the past season (1955-56) more than 3,000;ooo boxes of Florida oranges were used iri production of this product. It is anti cipated that during the curr~nt 1956-57 sea son, an excess of 5,000,000 boxes will be util ized. It is the goal of the product control in the Chilled Orange Juice industry to present to the customer-the housewife, the institu tional dietician, or the restaurateur-orange juice of such quality, to have more uniformity in flavor and aroma, than juice extracted from fresh oranges themselves. The selection of the fruit to be extracted is the first and a very important step in qual ity control of chilled juice. This is accom plished in the groves, where the fruit is tested and tasted at regular intervals for maturity by . trained technicians and buyers. \Vhen the fruit in the groves reaches its peak of ma, turity, it is then selected for its quality. The maturity of the fruit is based for all practical purposes on the relationship of the per cent of soluble solids to the acid content, since it has been found that when certain ratios of sugars to acids are found in the fruit, the juice will also have best flavor, color, cloud, vitamin C, and all the other desirable quali ties. Once the particular crops are selected for picking, the steps from the groves to the pro cessing plant, the storage and extraction stages are very similar to that which is per formed in other types. of citrus juice plants. Extreme care is exercised in properly grading the fruit to be certain that no undesirable fruit enters the line for extraction into the juice. The juice flows into a stainless steel trough, which is connected to each extractor, and thence into a paddle type prefinisher. The overflow from the prefinisher passes into the screw type finisher. The type and amount of pulp or juice sacks in the finished product is governed by the size of the openings in the screens of the prefinisher. Prefinished juice flows into a surge tank where it is pumped to the blend tanks as pulpy juice is desired. The juice from the finisher surge tank is also pumped to the blend tanks. From this line a sample is taken every fifteen minutes and checked for brix-acid ratio and rapid peel oil determination ( Burdick Method). Through this method of checks, a constant ratio can be maintained by either increasing or reduc ing the flow of fruit in the bins. From the blend tanks, the juice is pumped through a plate type heat exchange for stabilization of enzymic and microbiological . action. Proces sing time and temperature are carefully con trolled so that no significant change in flavor will occur. After stabilization, the juice is rapidly cooled to 32 F. and pumped to a cold wall or refrigerated holding tank. The juice flows by gravity to a milk type filling machine where milk type cartons are filled, sealed, and hand packed in cases. The cases, closed bv an automatic sealer, are then con veyed tc; the cold room for storage and ulti mate _ loading onto a refrigerated truck.

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LISTER AND FAY: QUALITY CONTROL OF ORANGE JUICE 137 Samples are taken at regtilar intervals from the production line by a U.S. Department of Agriculture Inspector. These samples are tested for brix-acid ratio, carton fill tempera ture, and peel oil content. At present, there are no U.S.D.A. grade standards for chilled orange juice, only those regulations set by the Florida Citrus Commission and inforced by the U.S.D.A. Inspector. Plant Sanitation is the most important part of quality . control. Through laboratory tests such as mold counts, microscopic examina tions, insect counts, and platting , the cleanli ness of the equipment can be determined. After each day's operation, floors, walls, tanks, extractors, and all pipelines are thoroughly cleaned with a strong detergent and sanitized with hot water and chlorine solution. In less than twenty minutes from the time the orange rolls from the bins, it has been juiced, placed in a carton, cased, and in the cold room ready for shipment. The advent of mechanically refrigerated in sulated trucks has played an important part in expanding the geographical limits of the market for chilled orange juice. Fast trucks equipped with sleeping accommodations for the relief driver or the use of exchange driv ers at designated points enroute enable de livery from Florida to New England markets in approximately 36 hours. Control of tem perature is so important that spot checks are made, unknown to the drivers, by inserting a specially designed thermograph in on e of the cases after removing two of the quart pack ages. SAMPLING PnocEDUHE Upon arrival at the destination, spot checks of the temperature of the product in differ ent parts of the load are made; the thermo graph is sent to the laboratory together with six quart packages, two each are taken from a case in the rear, middle, and front of the load. One of each pair of samples is set aside for shelf life determination at 45 F. and is flavored each day for four days, then at less frequent intervals until the termination date stamped on the top of each package. . The three other paired samples are each subjected to th . e following tests, net weight of contents, microbiological counts for . bacteria, yeasts and molds, pH, brix-acid ratio, and flavor criticisms by two or more experienced per sons. One of the three samples from each shipment is analyzed for Vitamin C content. If flavor criticisms indicate a strong peel oil flavor, determination is made for the per centage of peel oil, otherwise this test is omitted. Standards of satisfactory. performance with plus or minus tolerances for each of these measurements have been mutually agreed to by the parties concerned, and close contact is maintained by phone between the Florida and New England laboratories if results indi cate an unfavorable trend in compliance with the standards. Deviations from standards call for prompt correction and not necessarily re jection unless it is believed the deviation will result in unfavorable customer reaction. DISTRIBUTION CHANNELS When a shipment arrives at the New Eng land plant, it is transferred directly to special ly refrigerated chests maintained at 30 F., providing the temperature and flavor at the time of unloading are found to be satisfac tory . The temperatures normally maintained for refrigeration of dairy products are not re garded as adequate for the handling of chilled orange juice. Each shipment is kept sufficiently isolated in the storage chest, and records kept of the disposition of each ship ment into the various channels of distribu~ tion so that it could be promptly located and withdrawn from the market if subsequent tests and especially the progressive flavor de velopment in the shelf life samples indicate that even a slight chance will be taken with customer satisfaction. Great care must be ex ercised to avoid excessive inventories, and to insure systematic turnover of the loads in the order of their receipt. Close contact between the laboratory and distribution is absolutely essential. Special icing of each case of orange juice on milk routes is necessary to maintain temperatures well below those normally re garded as satisfactory in handling dairy prod ucts. Route men have learned to pay critical attention to the termination date on the pack age and refuse to accept a product which is so near its termination date that the customer will not have time to use it. Routemen have learned the hard wav that the distribution of one bad lot of oran'ge juice can result in a greater drop in sales than they can build back in three or four months. The successful distribution of orange juic e depends upon rigid control of four things:

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138 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 ( 1) careful selection and skillful blending of fruit, ( 2) precision in processing, ( 3) abso lute control of temperatures below 35 F. from Florida to the customer's doorstep, and ( 4) thorough laboratory checking at the pro cessing and distribution end, coupled with unyielding determination to withdraw from the market any product which will jeopardize uninterrupted customer satisfaction. The distribution of orange juice on milk routes is a natural; it can be done if we face up to the problems of complete control from the tree to the customer's doorstep. HYDROCOOLING CANTALOUPES K. E. FORD Associate Agricultural Economist Georgia Experiment Station Experiment, Georgia The growth and prosperity of cantaloupe production in the Southeast depend on placing high quality melons on the market. Hydro cooling tests were conducted during June and July of 1955 and 1956 by workers of the Georgia Experiment Station in cooperation with the Georgia Coastal Plain Experiment Station at Tifton, Georgia. The purpose of the tests was to determine the effect on the marketability of cantaloupes of higher quality. Information on the rate of heat removal is essential to determine the possibility of hydro cooling cantaloupes. A pilot plant model of a hydrocooler was obtained from a local man ufacturer. This equipment was li~ited to pro cessing two Jumbo crates of cantaloupes at the time. The process involved was practically identical to that of the commercial models sold by this and other manufacturers to hydro cool peaches at rates ranging up to 600 crates or bushels per hour. Hydrocooling is known to slow the ripening process in other products, and if immature cantaloupes are so treated, they might not have the desired quality. Consequently, canta loupes for the 1955 tests were picked at three stages of maturity, namely: full slip, showing good color, and full ripe. Tests were made by size of melon and included sizes 36s 27s and Jumbos. ' ' In these preliminary tests three thermome ters were inserted into the cantaloupes at dif ferent positions and readings were recorded at two minute intervals for one hour to obtain Journal Series No. 303, Georgia Experiment Station. the rate of heat removal. Bulbs of the ther mometers were placed in the flesh at the stem end, in the cavity, and in the flesh at the blos som end. Results given are from the readings of the thermometers inserted in the flesh, which were practically identical for both posi tions. Full slip and full ripe cantaloupes were used for the 1956 tests. Information was ob tained on the effect of hydrocooling on the quality of cantaloupes in addition to the rates of heat removal. Crates of cantaloupes at each stage of maturity were hydrocooled and held in storage at 38 F. for eight days. Check crates were placed in the same storage with out hydrocooling. At the end of the storage RATE OF HEAT REMOVAL BY STAGE OF MATURITY PMR # 45 CANTALOUPES IN HYDROCOOLING TESTS TEMPERATURE (F) 4 0 15 30 45 60 TIME (MINUTES AFTER ST ART)

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FORD: HYDROCOOLING CANTALOUPES 139 period, refractometer readings were made of the cantaloupe juice. Such re ad ings are closely correlated with quality as rated by tast e . The Zeiss hand refractometer reads percentage of sucrose directly but the readings are more correctly percentag es of total soluble solids. Cantaloupes of th e PMR No. 45 variety were used for most of the te sts . This is the variety currently grown in practically every area from which cantaloupes are shipp e d in crates. Since the temperature in refrigerated rail cars and trucks is about 50 F. at the time of loading, this was considered to be the maxi mum temperature at which the cantaloupes should be removed from the hydrocooler . Low er temperatures would probably be de sira ble b eca use of the possibility of a rise between the . hyclrocooler and the refrig e rated carrier. Considering the initial temperatures of the cantaloupes, there was little difference in the rate of heat removal when maturity wa s the source of variation. Between 35 and 40 min utes were r equ ired to bring the temp erat ure down to 50 F. (see chart). Cantaloupes used for tests to prepare this chart were size 27s. A slightly shorter length of tim e was necessary to reduc e th e temperature to 50 F. in size 36s and the tim e for Jumbos was abo ut the same as for 27s. While additional testing is essential, per haps the most significant single finding in the 1956 tests was the relationship between hydro cooling and soluble solids in the cantaloupe juice after eight clays in storage. The soluble so lids content was higher at the end of the storage p erio d for cantaloupes which had been hvdrocooled than for those which wer e not hydrocool ecl prior to storage ( see tables) . The analysis of variance indicates that stage of ma turity was non-significant as a source of varia tion in th e soluble solids in the cant a loupe juice; how ever, treatment and maturity by treatment int era ction were highly significant. The temp era ture of the hydrocooled canta loupes was reduced to 40 F. within an hour. A much longer tim e was required for those cantaloupes placed in cold storage without PERCENT SOLUBLE SOLIDS IN PMR # 45 CANTALOUPES AFTER EIGHT DAYS IN STORAGE, BY STAGE OF MATURITY AT HARVEST AND BY TREATMENT BEFORE STORAGE MATURITY AND AVERAGE STANDARD COEFFICIENT TREATMENT DEVIATION OF VARIATION FULL SLIP HYDROCOOLED 8.42 0.533 6.33 NOT HYDROCOOLED 7 .82 1.474 18.84 FULL RIPE HYDROCOOLED 8.81 0.727 8.26 NOT HYDROCOOLED 6.96 1.415 20.33 ANALYSIS OF VARIANCE OF SOLUBLE SOLIDS IN PMR # 45 CANTALOUPES AFTER STORAGE SOURCE OF VARIATION DEGREES OF SUM OF MEAN FREEDOM SQUARES SQUARE REPLICATES 19 36.657 MATURITY I I .128 1.128 TREATMENT I 29.890 29.890** MATURITY BY TREATMENT INTERACTION I 7.750 7 .750*l RESIDUAL 57 63.084 1.107 TOTAL 79 138.509 **SIGNIFICANT AT THE 0.01 LEVEL.

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140 FLORIDA STATE HORTICULTURAL SOCIETY 1956 h ydrocooling. In the latter tr atment . th e r es piration process, during which the sugars continue to br eak down, occurr cl for a long e r period than in th e cantaloupes which were hydrocooled before torage. Undou bt ed l y, the respiration process had been greatly r e duc e d by the time the ca ntaloup es were removed from th e h_vdrocooler and p l aced i n storage. THE SLOUGHING DISEASE OF GRAPEFRUIT \IV . GHIERSO , AND ROGER PATI~ICK Florida Citrus Experiment Station Lake Alfred In 1955 , Grierson and le whall ( 1) reported that a distinctiv e and peculiar peel br eak down h ad b een not e d on r e el and pink grape fruit for thre e consecutive seasons and had caused oc casiona l severe loss es in bansit . This diseas was given th e name of sloughi n g because o l th e distinctive manner in wh i ch the dead diseased tissue separated from the healthy tis sue below , thus corresponding exacll_ to the dictionary cleHnition of s l oughing in its medi cal sense. CmmENT STAT Th e occurrence of sloughing in October 1956 marks th e fifth co ns ec utiv e season in which this dis ease has been obse rv ed. It ha s b ee n found in fiv e co unti es ( L ake, Polk , High l ands , Oran ge and Pin !la s) and uncon firm e d reports indicate that it may also be pr ese nt in other districts. The total q uantit_v ol fruit lost each vea r i s not high. However since s l oughing occu'rs only ear l y in the season' when prices are high , th e los s of a s ingl e car load in transit can cause a disproportionat e l y severe financial loss to th e individual s hipp e r. DES C HIPTIO N Th e I sions s tart as very faint discolorations that ultimat e l y deepen to c ho co J at brO\ n in co l or. Thi s injm y i s peculiar in th at th e dis co l ored peel does not dry up with age, but b eco m es soft and moist as the disease pro g r esses. Th e diseas cl tissu e do es not ex t end deep e r than th e albedo and in th e a dvan ced stages s li ght fing e r pr ess ur e will ca u se th e i11 jur ed portions to s lou gh off th e sound fl es h below. A c urious characteristic is tJ1at fruits afflict e d with s l oughing seldom succumb to P e nicillium ( blu e a nd g r een molds) or t o stern-encl rot, Ji' l o 1 icla Al?ricu l lural Experiment Stat i ons J o urnal Se rie s Na . 5 61. Figs. 1 , 2 and 3 s how th e progress ot th e disease. Fig. 1 was taken five clays from pick in g ( at which time about five percent ol th e fruit in this picking were a ff ec t ed). On most of these fruits s l oug hin g shows only as a dis co lor ed arna except for one fruit on which th e l es ions are far e nough advanc e d that the n ec rotic tissues ca n be "s l oughed off" by fing er pressur e. S eve ral of th ese fruits s ho w that s loughin g, lik e m e l anose, of t e n t e nds to follow a "tear sta in " patt e rn . Fig. I. Sloughing of Ruby Red Grapefruit, photo graphed five day s from picking a nd s ubseq u ent to degreening . Fig. 2 shows th e same fruit a t seven da ys from picking, the l es ion s are now quite moist and a r e b ginning to sl ip off easi l y und e r finger pressure. Fig. 3 , taken ten days from pi c king , shows the ex tr e m e stag of sloughing in whic h con siderab l e areas of th e p ee l are r ead ily separable from tJ1 e sound fl es h b e low . Th e cut sections show how the l es i ons do not p e n e bat e b ey ond th e a lb e do. Fig. 4 shows a very a dvanced case of slough in g photographed twenty-one days tr om picking. Th necrotic ti s u es were separa t e d from th e h ea lth y fl es h by fing e r pr ess ur e a l.on e.

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GRIERSON AND PATRICK: GRAPEfRUIT SLOUGII!Nl; 141 Fi g. 2. Th e same fruit as in Fi g. 1 , photographed tw o da ys lat e r. Tlw ,1 ll wdo a11d tlan do ,u n rt'dtt<.vd to a sn it mush. Dl'spitl' thi s tltc fle s h wmai11('(! plump. l w.dtll\ a1 , d \I ith I mgid jui ce ,l'sid('s. E Xl'EI\I . \IE:',;T . \L Sincl' s lo11 gh i11 g dews 11ot appt'ar u 11t il !om to tl'n ci,l\s aft1r pid:i11g it is 111, ap p arl' 11t in th e e;ro,. is s1•t 0111\ occ a .s ionalk i11 tltl' packingho11w a11d is 11s11,;11_, t 1 co 1111k;.,.c1 as a tra11sit or markd dis,•as, . Sin e<. ii is 11< it possi hl l' to pred ict ,, lw11 sloughing \\ ill occ m. it has 11ot l we 1, possihl(' to sd up s, stt• n1ati c perim e nls to s lu ththis dis t as e. :\II intormaF ig. 3. The same fruit as in Figs. 1 a nd 2, photo graph e d t e n days from picking . ( H e ld a t room tem p e r ature). tio11 !t : 1 s !,ad lo <.o m , !m m itl\ Ts li _ gati011 ol losses r l'portcd I l\ commercial packi11gho11s1 •s. Cult11ns ha\'!' l)('et1 mad1 of thl' various organism ., fo111HI i11 thl' necrotic il'sio11s. :\lost of thl'st• ar, 11mmal grove organisms . h11t a1 1~ that stt•n, at a ll 111111s11al havl' lwc11 used to ill
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142 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 3. It appears to be associated with fruit from young trees (but that is almost inevitable with a comparatively new variety such as Ruby Red grapefruit). 4. Sloughing is checked or controlled by cold storage. On two separate occasions, part of an affected picking has been held in cold storage. Only very minor evidence of slough ing was found in the cold stored fruit even when it was subsequently held at room tem perature. When a single crop has been shipped as a split load, half in cartons and half in wire bound boxes, sloughing appeared only in the fruit in the cartons. It is felt that this is prob r.bly a reflection of the difficulty of cooling fruit in cartons quickly. 5. Since it is usually discovered after pack ing it is generally attributed to some p a cking house problem such as over-heated degreening rooms, rough handling or ( on Western ship ments) cyanide fumigation . The ev idence so far available indicates very strongly that sloughing originates in the grove . This is p a ticularly apparent when fruit from several groves is handled in the packinghouse at the same tim e. 6. Sloughing tends to re-occur in fruit from certain groves. 7. Except in the fall of 1955, sloughing oc curred only during a period of high rainfall. In 1955 there was little rainfall during the sloughing season. However, it has been pointed out ( 2) that in the case of brown rot, h eavy dew can b e as damaging as actual rainfall, so moisture conditions cannot be eliminated as a pertin e nt factor. 8. The most promising line of approach at present seems to li e in the investigation of any possible correlations with othei; grove dis eases . For this reason the observations of production managers are of great interest. Corrective M easu r es . So little is known of the causes of this disease that it is not possible to recommend a remedial program . Two suggestions, how ever, may _ help to minimize losses from sloughing. If a grove is known to have pro duced fruit with sloughing in a previous sea son it could b e checked by picking samples in the period before the grove is expected to pass the maturity tests. Such samples should be degreened, and held at room temperature, and checked for any signs of incipient sloughing. Since sloughing is checked by refrigeration it is to be expected that prompt and effective pre-cooling, followed by the best available in transit refrigeration would minimize such losses. The best corrective measure, in the long run, is probably to help investigate the cause of the disease by reporting known instances of sloughing as promptly and fully as possible. One of the principal reasons for giving these reports is to encourage shippers to contact these authors when sloughing is encount e red . LITERATURE CITED 1. Grierson, W. n nd W, F. Newhall. 1955. "S lou g ing," a new disease of red grapefruit. The Citrus I'ndustry, 36 (10) : 16, 19. October. 2. Knorr , L. C .. H . J. Reitz and F . J . Reynolds. 1956. Occurr e nce and control of brown rot of citrus on the tree. a disease new to Florida. Citrus Maga zine, I 9 ( 1) : 6-8 , Septem her. EFFECT OF VARIETY AND FRESH STORAGE UPON THE QUALITY OF FROZEN SWEET POT A TOES MAURICE w. HoOVER 1 AND VICTOR F. NETTLES' Florida Agricultural Experim en t Station Gainesville Sweet potatoes are usually proc essed by _canning; however, an excellent product can 1 /Depar tment of Food Technology and Nutrition and 2 /Dcpa rtment of Vegetable Crops, Florida Agri cultur a l Experiment Station. Florida Agricultural Experiment Station Journal Series No. 54 3. be produced by freezing ( 1) ( 4). Normally better results are obtained when sweet pota toes are canned immediately after they are harvested without going through a curing process and ex tended storage ( 2). Best re sults are obtained with frozen sweet potatoes which are cured after harvesting ( 1). Th e purpose of this investigation was to determin e the effect of fresh storage and variety upon the quality of the froz e n product. The effect

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HOOVER AND NETTLES: SWEET POTATOES 143 of cooking method upon the carotene con tent, in preparing the potato 'for freezing, was also studied. MATERIALS AND METHODS The varieties of sweet potatoes used in this study were the Heartogold, Georgia Red, Goldrush, Unit No. 1 Porto Rico, and Early port. As soon as the potatoes were harvested, they were graded and cured at 85 F. for 10 days. After the sweet potatoes were cured, sam ples were placed in storage at 60 F. Potatoes for freezing were taken from storage at in tervals of three weeks over a period of 105 days (0, 21, 42, 63, 84, and 105 days). After removing the potatoes from storage, they were ,baked for about an hour at 350 F., cooled and frozen at zero. degrees F. Approximately three weeks after the potatoes were frozen, they were removed from the freezer, heated for about 20 minutes and evaluated subjectively for color, texture, and flavor. Scores ranged from one for those that were unacceptable to six for excellent. Each taste panel member gave a preference rating and, in this instance the lowest number represented first preference. For carotene analysis the potatoes were cut longitudinally and a quarter of each potato was dried at 65 F. after which they were ground through a 20 mesh screen. One gram of the oven dried sweet potato was boiled in 25 ml. of distilled water for five minutes. One hun dred ml. of 95 percent ethyl alcohol were added to the boiled material, and the contents ground in a Hamilton Beach Blender for five minutes. The blended material was filtered and the filtrate was transferred to a separatory funnel containing about 100 ml. of N-hexane. Distilled water was added to facilitate the transfer of the carotene from the alcohol frac tion into the N-hexane. The alcohol-water fraction was drawn off and the funnel stem dried by inserting a strip of gauze into the lower part of the funnel. Preliminary work in dicated that there was little, if any, advantage to running the material through a separation column. The carotene solution was transferred into a 250 ml. volumetric flask and made to yolume. About 25 ml. of the extract was fil tered into a 100 ml. erlenmeyer flask contain ing anhydrous sodium sulfate and the percent of light transmission through the carotene so lution was obtained with a Bausch and Lomb Spectronic 20 Colorimeter set at a wavelength of 450 mu. The carotene content of the pota toes was determined by comparing with a standard curve made with pure carotene con taining 90 percent beta and 10 percent alpha. The effect of cooking methods on the caro tene content was studied. In this phase of the study the potatoes were cooked ( 1) by baking in an oven for about one hour at 350 F.; (2) with steam under 10 pounds steam pressure for 30 minutes; and ( 3) with free steam for 40 minutes. RESULTS AND D1scuSSION There was a wide variation in the quality of frozen sweet potatoes among the different varieties. The Georgia Reel variety received the highest rating for color, texture, and flavor ( Table 1). It was also preferred by the panel over the other four varieties tested. Even though this variety was lowest in carotene con tent, its color was rated highest by the taste panel. It was bright yellow in comparison with the darker or duller orange color of the Hearto gold and Goldrush varieties. Although caro tene is the primary factor contributing to the color of frozen sweet potatoes, it does not seem to be the only thing affecting their color. There did not appear to be any difference in the quality of potatoes that could be at tributed to time in storage. Evidently, there fore, sweet potatoes may be cured and stored for at least 105 days at 60 F .without any appreciable decline in quality. This statement refers only to the potatoes that are sound and free from disease at the end of the storage period. Table 1. Subjective eva.luation or frozen sweet potatoes of five ditferent varieties. Color Texture Flavor Preference Variety (1 to 6) (1 to 6) (1 to 6) rank ( ~) Hea:rtogold 4.4 4.4 4.4 Georgia Red 4.9 4.9 5.2 Goldrush 4.5 4.3 J.9 Porto Rico J.6 4.& 4.9 Earlyport 2.5 J.2 J.J ( *) Lowest number indicates the variety most preferred. Significant differences were found in the carotene content of different varieties ( Table 2). The Goldrush and Heartogold varieties contained the largest amounts. The former con tained 43.3 mg. per 100 grams of dry potatoes and the latter contained 28.8 mg. The Porto Rico, Earlyport, and Georgia Red varieties

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144 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 2. Carotene content (mg. per 100 grams of dry potatoes) of frozen sweet potatoes stored fresh at 60F for different periods of time prior to freezing. Variety Days in Storage . . . 0 21 42 Heartogold 25.9 30.0 .32.2 Georgia Red 13.8 19.3 14.5 Goldrush .38.6 49.4 42.7 Porto Rico 16.J 18.2 16.1 Earlyport 15.3 15.9 17.1 -------Mean 21.9 26.5 24.5 L.S.D. for variety at .05 level 4.80 L.S.D~ for varietv at .01 level= 6.02 possessed 18.0, 17 . 2 , and 16.0 mg., respective ly, carotene per 100 grams of dry potatoes. There appeared to be a significant increase in the carotene content of the potatoes during the first three weeks of storage; however, there was considerabl e variation from one in terval to the next which lessens the probability or hypothesis that a true increase in carotene did occur in storage . A greater loss of carotene resulted when potatoes were cooked by baking than occurred when th ey were cooked with steam under pressure or with free steam (Tabl e 3) . Pota toes baked in dry heat alone lost 11.9 percent of the carotene, on dry weight basis. Those cooked with free steam lost 4.4 percent, and the ones cooked under steam pressure lost only 0.75 percent. Thus, it is evident that the use of dry heat in the preparation of sweet pota toes for freezing should be held to a minimum Table J . .. Effect of cooking m e thod s upon the carotene content of sweet potatoes of the Goldrush variety, on a dry wi~ht basis. f '.ethod o! cooking Con t ro l (raw) Steam (10 l bs . pressure) Free Steam Baked (J50f) Carotene (J!ll. per 100 gra.>:tS ) 47. 8 6 47.50 45.75 42.17 L.S.D. for carotene at .05 level l.5J L.s.D. for carotene at .Ol level 2.11 Percent l oss 0.75 ,.J 9 ll. 89 63 84 105 Mean .32.9 24 .3 28.0 28.8 16.6 15.8 15.9 16.0 46.1 41.7 41.6 . 43.3 21.0 16.6 19.s 18.0 19.2 17.9 17.8 17.2 27.1 23.3 24.6 that is consistent with maintaining good tex ture, appearance, and flavor. This point should also be considered when preparing sweet pota to samples for carotene analysis. It has been reported that it is not necessary to cook sweet potatoes in preparation for mak ing carotene analyses ( 3). This is true where fresh tissue is used rather than oven dried ma terial. Evidence obtained in this study indi cates, however, that the tissue should be cooked if the potatoes are to _ be dried prior to making the carotene determinatio11s. When the sweet potatoes were cooked, there was no sig nificant difference in carotene content between those with freshly cooked tissue and the ones that were dried in an oven at 65 C. SUMMARY AND CONCLUSIONS A study was made to determine the effect of variety and fresh storage upon the quality of frozen sweet potatoes. The influence of cooking methods upon the carotene content was also studied . Sweet potatoes of five varie ties were cured at 85 F. for 10 days followed by fresh storage at 60 F. for periods of time ranging from zero to 105 days before freezing. The frozen potatoes were reheated and graded by the taste panel for color, texture, and flavor. The carotene content was also deter mined.

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ROUSE, ET AL: ORANGE JUICE STUDIES 145 Sweet potatoes of the Georgia Red variety were preferred over the other varieties as a frozen product. However, a good frozen prod uct was produced with potatoes of the Gold rush, Porto Rico, and Heartogold varieties. Fresh storage up to 105 clays did not seem to affect the quality of frozen potatoes when good sound potatoes were used. The method of cooking the potatoes in preparation for freezing had a significant effect upon their c,irotene content. There was a greater loss of carotene from the potatoes when they were cooked with dry heat than occurred when steam was used. LITERATURE CITED 1. Hoover, Maurice W. and G. J. Stout. 1956. Studies relating to the freezing of sweet potatoes. Food Technol. 10: 250-253. 2. Huffington, Jessie M., E. R. McConnell, and P. B. Gottschall, Jr., 1956. Sweet potato varieties for canning: Influence of storage on quality. Proc. Amer. Hort. Soc. 67: 504-513. 3. Mitchell, H. L. 1949. Determination of carotene in sweet potatoes. Plant Physiol. 24: 323-326. 4. Woodroff, J. G. and Atkinson, Ida S. 1944. Pre serving sweet potatoes by freezing. Ga. Expt. Sta. Bui. No. 232. STORAGE STUDIES ON 42 BRIX CONCEN TRATED ORANGE JUICES PROCESSED FROM JUICES HEATED AT VARYING FOLDS. II. CHEMICAL CHANGES WITH PARTICULAR REFERENCE TO PECTIN' A. H. ROUSE, C. D. ATKINS AND E. L. rvloORE Florida Citrus Experiment Station Lake Alfred The purpose of this investigation was to determine some of the chemical changes, and especially the loss of pectin, that would occur in frozen orange concentrates during storage at 40 F. It was also desirable that similar in formation be obtained on heat-treated con centrates when the thermal treatment is ap plied either prior to concentration or at dif ferent stages of the concentration process. A total of 24 experimental packs of frozen con centrated orange juices, prepared from Pine apple and Valencia oranges, were used in this study. EXPERIMENTAL PROCEDURES P~eparation and Storage of Samples. ~ In preparing the 24 packs: of concentrates, single strength juice was used as the I-fold product and concentrates were removed from the pilot plant Model A thermocompressor type eva porator ( 1) at concentrations of 2-, 3-, and 4fold. Each of these four products was divided '/Cooperative research by the Florida Citrus Ex periment Station and Florida Citrus Commission. J<'lorida Agricultural Experiment Station Journal Series, No. 552. into three equal volumes and one of these was used as an unheated control; the other two volumes were heated in a tubular pasteurizer to 150 and 175 F., respectively, in 6 seconds and cooled in 14 seconds. All products were further concentrated in the pilot plant Model B evaporator (2) to 55 Brix, cut-back to 42 Brix with unheated juice, sealed in 6-oz. cans, and stored at -8 F. until the beginning of the 40 F. storage period. Further detailed infor mation on the preparation of these 42 Brix frozen orange concentrates is described in the first pa per in this series ( 6) . At the beginning of the 40 F. storage period, the 24 experimental packs were thawed for 1 hour in a Thermo-Rotor type. thawer with rolls submerged in water at 40 F. ,The speed of rotation of the rolls was 60 r.p.m. The thawed samples were pla98d directly in stor age at 40 F. and analyzed at periodic inter vals until an extreme degree of clarification de veloped in each sample. Methods of Analyses. Samples of 42 Brix concentrates were examined for gelation. ( 7), both prior to and after 40 F. storage, and then reconstituted with three volumes of dis tilled water. After three minutes of stirring, the juices were centrifuged for 15 minutes at 1700 r.p.m. in .. an InternationaL,Centrifuge,

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146 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Size 1, Type SB and the percentage pulp by volume noted. Subsequently, centrifuged juice will be referred to as serum. Other analyses were determined on either the reconstituted juices or serums. Pectinesterase activity ( 8) is expressed by the symbol (PE.u) g. which represents the milliequivalents of ester hydrolyzed per minute per gram of soluble solids (" Brix). This is multiplied by 1000 for easy interpretation. Hesperidin ( 3), the principal glycoside of orange, was determined initially and after the concentrates showed extreme clarification. These analyses were made on the reconstituted juices. Light transmittance ( 5), index of cloud, was determined on the serum by using a Lume tron colorimeter, Model No . 402-E; clarifica tion was considered to be extreme when values were 85 percent or greater. Pectin , as anhydro galacturonic acid, was measured by the rapid colorimetric method of Dische ( 4) as applied to citrus juices by Rouse and Atkins ( 8) with the modifications that the samples of recon stituted juices were not comminuted prior to centrifugation and that the sample used for analysis was 15 grams of serum. Previous tests had shown that the amount of pectin, ex pressed as milligrams per 100 grams of serum, was approximately the same as the water soluble pectic substances in the reconstituted juice and is a major factor that determines the amount of cloud or turbidity 1n the juice. EXPERIMENTAL RESULTS AND D1scusSION Pectinesterase activities in the 42 Brix Pine apple and Valencia orange concentrat e s, prior to storage at 40 F., are presented in Tables 1 and 2, respectively. Control or unheated sam ples varied very little in activity (14.6 to 17.1 units), while the activity of the heat-treated samples fluctuated ( 4.9 to 11.2 units) accord ing to thermal treatment and quantity of pulp in unheated cut-back juices added. Approxi mately 50 percent of the activity shown for the 42 Brix concentrates, which were stabil ized at 150 F., and 80 percent or more of that in the products stabilized at 175 F. was from the unheated cut-back juices. The total glycosides, expressed as hesperi din, in the Pineapple and Valencia orange con centrates, prior to storage, ranged from 28 to 37 mg./ 100 ml. of reconstituted juice. After the development of extreme clarification in the samples at 40 F. storage, the amount ot glycosides remained the same . Pulp (Tables 1 and 2), indicative of in soluble solids, varied from 5.0 to 7.0 percent and 4.5 to 5.5 percent for the Pineapple and Valencia orange concentrates, respectively. After extreme clarification, the corresponding pulp levels increased, varying from 7.5 to 8.5 percent and from 8.0 to 9.5 percent. Although the size of pulp particles influences the per centage of pulp, as determined by the centri fugal method, it is of interest to know that the water-insoluble solids in the products also T.&BLE l 5wmurT ot Qicioel. Properties in 42 Brix Pineapple Orang• Oonoentratea Stored at 40, l Semf!!•• e:1or to ator!f!• Saq)] '"• attar a:trclaritioatioD Concentration Thermal (P!,u,)1, Pulp b)' Peotin Ti.ae Pulp b)' Pectin vhen treatment aolu'bl• aolida Tolume in serum required volume atabilised o,. X 1000 mg,/loo,. da;ra mg,/lOOg, Control 15,8 6,o 9,4 1,5 8,0 4,3 1-told 150 10,9 5,0 10.3 10,0 8,0 5 ,0 175 7.9 5,0 10,3 9,5 8,0 6.3 Control 14,6 6,0 8,6 1,0 8.0 3,9 2-told 150 9,6 5,0 ll,3 7,0 8,0 5,3 ;15 7,0 5,0 11,3 9,0 7,5 5,2 Control 15,9 6,0 8,4 0,5 8,0 3,3 150 9,4 5,0 10,7 6,5 8,0 4,9 175 6,9 5.0 ll,2 7,0 8.0 6,0 Control 15,2 7.0 7.0 0,5 8,5 3,2 4-told 150 11,2 6,o 10.4 4,0 8,5 4.0 . 175 6,1 S,5 11.1 6,5 8,0 5,0 l on JuioH,

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ROUSE, ET AL: ORANGE JUICE STUDIES 147 TABLE 2 ot Cbaioal. PropertiH 1n 42 Briz Valencia llr&Dg• 0oncc:tratea Stored at 40'. 1 J.!'.ior to story• Sea2lu atter extrolaritication Concentration (PE.u.)g, Pulp hT llhen treatment soluble solids volume etabilbed o:r. 11000 j Control 16.6 5.5 1-told 1500 10.5 s.o 175 6,J s.o Control 17.l 5,0 2-told 150 7,5 4,5 175 5,3 4,5 Control 15,0 5,5 3-told 150 8,3 5,0 175 5,9 4,5 Control 14.7 s.o 4-told 150 8,8 5,0 175 4,9 4,5 1 .&naJT••• on noonetituted juicee, increased as did the apparent pulp content during storage. For example, the average water-insoluble solids found in the Pineapple and Valencia orange concentrates prior to storage were 61 to 52 mg./100 g. of recon stituted juices, respectively, whereas, after ex treme clarification had occurred, these average values for the corresponding juices increased to 80 and 74 mg./100 g. Time required for the 24 samples of con centrates to show an extreme degree of clari fication varied from 0.5 to 34 days, depending on the variety of fruit from . which it was pro cessed, thermal treatment, and fold at which it was stabilized (Tables 1 and 2). , As ex pected under similar conditions of processing, Valencia orange concentrat e s were more stable at 40 " F. storage than the Pineapple orange products; also the packs heated at 1and 2fold were more stable than those heated at 3and 4-fold. The amount of pectin in the heat-treated packs was greater than in the control packs because of the partial inactivation of pectinest erase, thereby preventing the destruction of pectin during concentration; also the quan tity of pectin was greater in the Valencia orange products (12.1 to 14.2 mg./100 g.) than in the Pineapple orange products (7.0 to 11.2 mg./ 100 g.) . There were not sufficient quantities of pectin in any of the products to cause semi-or solid gels during storage; how ever, all samples developed No. 2 gels, indiPectin TiM Pulp hT P.ctin in eenm, required volume in serum mg./lOOg. dqa j ag./100,. 12.1 4.0 8.5 5.1 .12.8 16.0 9 .o 4,9 12.J 34,0 8,5 ,8 12.3 2.0 8.0 5,2 13.S 13,5 9.5 4,6 1).6 27.0 8,5 4,5 12.1 2.0 8,0 5,3 14,2 12.0 8,5 5,5 13,9 16,5 9.0 S.3 12,6 1.5 8.3 4.9 13.8 7,0 9,0 4,6 14,2 9,5 9.5 5.0 cative of slight gelation, when stored at 40" F. Data in Tables 1 and 2 show that during stor age of the concentrates at 40 F., the pectin decreased 50 percent or more with subse quent increase in clarification. The gradual loss of pectin during storage and its relation ship to clarification, index of cloud , for the controls and heat-treated 1-, 2-, 3-, and 4-fold products is presented graphically in Figs. 1, 2, 3, and 4. As the pectin in the serum de creased during storage of the products at 40 " F., the apparent pulp content and the water insoluble solids increased, as previously men tioned. Formation of degraded pectic com pounds, such as insoluble pectinates and pec tates, through the action of pectinesterase on the water-soluble pectin, is the cause of these increases. The longer storage life at 40 F. of the Valencia packs was probably due to the greater amount of pectin found initially in the serum and to a higher degree of polymeriza tion of the pectin molecule; the latter was in dicated by a slower rate of change in viscosity as previously reported ( 9). No significant differences in flavor were ob served by the authors between the controls and the heat-treated samples; neither were flavor differences found when juices were heated at these different folds. However, a slight lowering of flavor quality was observed in both the Pineapple and Valencia orange packs after storage at 40 F. for 10 and 24 days, respectively .

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148 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 12 9 a, 6 0 .... a, e 3 Cl) .. 0 PINEAPPLE ORANGE JUICES Nont SliQht Otfinitt Extreme 5 ,o~---'----'-----'~--~-...... --~o .. C) ::, 12 ... z .. 0 !!:9 0 ---. 175F. Control " .. VALENCIA ORANGE JUICES 10 15 20 TIME, DAYS --_1_5p• F. 25 Non, Slight Otfinitt Edrtmt 30 z 0 ;: "' 0 .: ii: "' ..J 0 .... 0 .. .. 0: C) .. 0 Fig. 1. Relationship of pectin to clarification dur ing 40 F. storage of 42 Brix orange concentrates when juices to evaporator were heat treated at 1fold. 12 \ '\\ 9 \\ '\, . , a,6 ',, , ..!._75•F o ',._!i~F ., f ~l Control PINEAPPLE ORANGE JUICES Nont Slioht Definite Extreme ~o~---'----'-----'~--~-...... --~-~ ,--, g ,,\ ~ '\ . t;,,... z ' ' /:t \ . '. -\ "~:---f!.._S•F. -. 0 Control VALENCIA ORANGE JUICES 10 15 20 T1ME DAYS None SliQht Otfinilt Eatrtmt 25 30 z ... "' !2 "0: -o~ on ro . PINEAPPLE i.: 5 ORANGE JUICES ., 0 t---~---'-----'---~--...L---~--1 c3 0 .. C) ::, ~12 ... z .. 0 :!, 9 z ;: 0 ~6 0 .. ~:--,.. '' \ , ', ' ' " ' , Control VALENCIA ORANGE JUICES '10 15 20 TIME DAYS Nono Slloht Otfinitt ' Eatrtmt 25 30 .... 0 .. .. 0: C) .. 0 Fig. 2. Relationship of pectin to clarification dur ing 40 F. storage of 42 Brix orange concentrates when juices to evaporator were heat treated at 2-fold. 12 Nona 9 <' ' Slloht . '. \ \ \ Dollnlto \ \ ,;,6 \ 0 \ , '•-.175•F. '-----... !'o•F. .... Extremt z ,;, 0 E3 Control ;: Cl) PINEAPPLE 0 .. ORANGE JUICES .: 0 ii: 5 "' ,o ..J 0 0 .. ' ... (0 ,, None ::, '. 0 ~12 '\' .. \ ' .. ... 0: z ' ' C) .. ' ' Sllpt .. u 0 !!: 9 \ \ z \ Dtfinitt ;:: 0 , ~6 I 115• F ~---.-:-- •-. --. 150• F. [atremt 3 Control VALENCIA ORANGE JUICES 0 10 15 20 25 30 TIME DAYS Fig. 4. Relationship of pectin to clarification dur ing 40 F. storage of 42c Brix orange concentrates when juices to evaporator were heat treated at 4-fold.

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HENDRICKSON AND KESTERSON: NARINGIN 149 SUMMARY Storage of 42 Brix Pineapple and Valencia orange concentrates at 40 F. resulted in in creased gelation, clarification, and apparent pulp content, whereas pectin decreased. Total glycosides, as hesperidin, remained constant in these products during storage. The experi mental packs heated at 1and 2-fold were more stable than those heated at 3and 4fold; also all of the Valencia concentrates, control and heat-treated, were more stable than the Pineapple packs. LITERATURE CITED I. Atkins, C. D . , F. W. Wenzel, and E. L. Moore. 1950. Report on new technical strides in desii,:n of FCC evaporator. Food Inds. 22: 1353, 1466, 1467 . 2. Atkins, C. D . , F . W. Wenzel, and E. L. Moore. 1951. An evapora~ o r of improved desi gn for the concentration of citrus juices. Proc', Fla. State Hort. Soc., 64: 188-191. 3. Davis. W. B. 1947. Determination of fl ava nones in citrus fruits. Anal. Chem. 19: 467-478. 4. Dische, A. 1947. A new s pecific color reaction of hexuronic acids. Jour. Biol. Chem. 167: 189-198. 5. Huggart, R. L., E . L. Moore, and F. W . Wen zel. 1951. The measurement of clarification in con centrated citrus juices. Proc . Fla. State Hort. Soc. 64: 185-188. 6. Moore, E. L., A. H. Rouse, and C. D. Atkins. 1956. Storag e studies on 42 Brix concentr-ated orange juic es processed from juices heated at varying folds. I. PhysicRl changes an d retention of cloud. Proc. Fla. State Hort. Soc. 69: 176-181. 7. Olsen, R. W., R. L. Huggart, and . M. Asbell. 1951. Gelati<'n and clarification in concentrated citrus juices. II . Effect of quantity of pulp in concentrate made from seedy varieties of fruit. Food Technol., 5: 530-533. 8. Rouse, A. H. and C. D. Atkins. 1955. Pectin esterase and pectin in commercial citrus juices as determined by methods used at the Citrus Experi ment Station. Fla. Agr. Exp. Sta. Tech. Bui. 570. 9. Rouse, A . H., C. D. Atkins, and E . L . Moore . 1955. Chemical change s in processed citrus juices and concentrates during storage at 40 F. Univ. of Florida Citrus Exp. Sta. Mimeo Rept. 56-3, October 4. PURIFICATION OF NARINGIN R. HENDRICKSON AND J. \V . KESTEHSON Florida Citrus Experiment Station Lake Alfred The pharmaceutical usefulness and physio logical importanc e of naringin has long been overlooked, even though its characteristic bit terness is a nostalgic reminder of early medi cines. Prime interest has been centered on the tasteless glucoside of sw ee t oranges, hes peridin, which has been closely associated with all vitamin P investigations . _ Circumstantial evidence has pointed to the fact that naringin may have an even greater pharmacological activity as previously shown by Armentano ( 1) and recent work on antiviral activity ( 4). Sufficient evidence has been accumulated to encourage the pharmaceutical industry to ob jectively re-evaluate naringin. An investigation was therefore undertaken to find an improved naringin purification procedure for preparing a high purity product. As with many products, naringin has a much higher solubility in hot water than in cold and is the basis for an extraction and purifica tion techniqu e reported by Poore ( 7). Ac cording to this method, crude naringin is ex tracted from chopped grapefruit peel by add ing four parts of water and h ea ting to 90" C. Th e water extract is filtered off after five minF'lorida Agricultural Experim en t Station Journal Series No. 524 . utes and the clear extract concentrated to ap proximately one-ninth the original volume. The concentrated extract is allowed to crystal lize for two days in a cool place and then filtered. The isolated naringin crystals are then purified by the following technique. First dis solved in a small amount of hot water contain ing 20 percent alcohol, impurities are precipi tated by adding. an excess of neutral lead ace tate with the excess lead eliminated by passing hydrogen sulfide through the solution. After filtering, naringin is crystallized by concen~ trating the solution and allowing it to stand in a cool place. The naringin is further purified by dissolving it in small amounts of hot water, from which it will recrystallize upon cooling. The pronounced solubility of naringin in water above 50 C. has been shown by Pulley ( 8) who plotted its solubility at numerous tem peratures. The simplicity of recrystallizing na ringin from water can readily be seen from his plotted solubility curve which shows narin gin to be more than 10 percent soluble at 75 C. and less than 0 . 02 percent soluble at 6C. This decreased solubility of naringin at low temperatures may at times cause the pre cipitation of this substance in canned grape fruit sections and juice. N aringin may also b e recrystallized from water by adding an alkali, which greatly in creases its solubility followed by acidification, and is the basis of anoth e r extraction technique

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150 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 ( 3). The addition of acid forces the recrystal lization of naringin, but the compound thus obtained is yellow. It was found difficult to remove this color even when activated carbon is used. The need for an even better method of puri fying naringin became evident in the over 0 all investigation on the recovery of citrus gluco sides. Some of the results have been reported previously by the authors ( 6), but the opti mum methods of purifying crude naringin re quired further study. EXTRACTION TECHNIQUE AND DISCUSSION In the following investigation three differ ent samples of crude naringin were employed. Two samples used were purchased and ana lyzed 81 and 86 percent pure by the Davis test (5) while the third sample was only 29 percent pure. This last sample was typical of the crude naringin obtained in the alkaline ex traction of grapefruit peel by the Baier process ( 3). About 50 percent of the impurities in this product is a filter-aid which is added to fa cilitate the final extraction. All naringin samples and extracts were analyzed by the Davis test ( 5). The first hopeful sign of a new method to purify naringin occurred when an attempt was made to dissolve and filter a hot, highly con centrated solution of naringin in 99 percent isopropyl alcohol. Before the filtration was more than one-third complete the entire mass had become granular, stiff, and finally solidi fied. The product was crystalline, with the minute crystals being needle-shaped. , Upon stirring 30 g. of a purchased naringin sample ( 86 percent pure) in 150 ml. of boil ing isopropyl alcohol, a solution was obtained that filtered readily leaving a residue of 2.5 g. of which 0 . 5 g. was found to be naringin. The clear filtrate, when boiled, quickly seeded itself and within five minutes had crystallized into a solid mass. After diluting with 150 ml. more of isopropyl alcohol and stirring to a thin slurry, the naringin was filtered and dried at 85 C. There was an 87 percent recovery of a very white product which analyzed as being 95 percent naringin. The filtrate was found to have 1.0 percent naringin still in solution. When this trial was repeated with a few modi fications, such as stirring the initial solution longer, permitting the naringin to crystallize over a longer period of time, and washing the final product with more isopropyl alcohol, even better results were obtained. Recovery was im proved to 89 percent; the final product was exceedingly white and analyzed as being a 100 percent pure product by the Davis test. Effect of Recycling Alcohol. In repeated trials where attempts were made to conserve alcohol and improve the over-all recovery by re-using the filtrate of one run as the solvent for the second, the following results were ob tained. Initial recovery was 88 percent with the product being 99.5 percent pure; the fol lowing trial using the previous filtrate im proved the recovery to 95 percent with purity of the product dropping to 98 percent. Re using the filtrate a second time decreased the recovery to 91 percent and the product purity to 95 percent. The concentration of naringin in the filtrates continually increased to 2.4 per cent and failed to crystallize further during an extended holding time. Effect of Concentration. The possibility of a critical concentration ratio of solvent to naringin in this purification procedure was then investigated. Crude naringin of 86 per cent purity was dissolved in boiling isopropyl alcohol at four concentration levels; 30 g. per 600 ml., 30 g. per 300 ml., 30 g. per 150 ml., and 30 g. per 100 ml. These levels of con centration are respectively equivalent to 4.3 8.6, 17.2 and 25.8 g. of pure naringin per 100 ml. of isopropyl alcohol. Each sample was stirred for two minutes, filtered, and the fil trate heated to its boiling point to initiate crystallization. As soon as each sample began lo crystallize, it was allowed to cool and was filtered subsequently and washed. The sam ple with the lowest naringin concentration was an exception in that it failed to crystallize promptly and was allowed to cool to room temperature and stand overnight. By the next day the sample appeared to have crystallized as well as the others. Isolated similarly, it was found to be the equal of the other three trials, each of which yielded an 89-90 percent re covery of naringin having 98-99.5 percent purity. The trial having a concentration of 8.6 g. of naringin per 100 ml. of isopropyl alcohol appeared to be the more suitable for a large scale operation. At higher concentra tions, it is conceivable that recrystallization could begin before the initial filtration was

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HENDRICKSON AND KESTERSON: NARINGIN 151 complete. There is the further disadvantag e at higher concentrations that the voluminous character of the recrystallized naringin will so stiffen the mixture as to make handling too difficult. At lower concentrations, the higher cost of solvent and longer tim e required for recr y stallization would preclude . its industrial use. In a trial where crude naringin of 29 per cent purity was purified by this procedure us ing a ten to one solvent to naringin ratio , a product of 98 p e rcent purity was obtained . Th e recovery of available n a ringin was not as efficient as with samples of higher initial purity, being only 60 percent . The filtrate and washings contained 26 perc e nt of unrecover able naringin and constituted the greatest loss. The 14 percent naringin remaining in the ex tracted crude residue could be recovered with more efficient washing of this residue. A bet t e r recovery of purified naringin is possible when the crud e naringin samples have a high e r initial purity . It is quite possible in this cas e that the crude naringin recovered by th e Bai e r process ( 3) could b e isolated using s maller quantities of filter-aid which would improve th e purity of the crude product. Upon using purchased naringin of 86 percent purity under similar conditions, there was a 92 percent recovery of a 99.5 percent pure product. Only 5.5 percent n a ringin was lost in th e filtrate and washings, with another 1.9 percent lost in the extracted residue. In an other trial with a purchased product of 81 percent purity, 85 percent was recovered with 11.4 percent naringin being lost in the filtrate and 3 percent in the residue . Critical Eff e ct of Water. Another impor tant consideration in the purific a tion of naringin i s water. For ex a mple, naringin will crystallize from water as an octa-hydrate molecule having eight waters of cr y stallization, which product m e lts at 83 C. ( 2). When crystallized from certain other solv e nts, such as isopropyl alco hol, naringin h as two waters of crystallization and melts at 171 C. ( 2) . The physical ap pearance of the products und e r the micro scope is very similar , crystallizing as needles which . are usually found agglomerated in a rosette pattern. The drying of purified naringin is considerabl y simplified when the dihydrate mol e cule is form e d and is a distinct advan tage of this proc e ss over th e oth e rs previously mention e d , since the naringin can be dried more readily and at higher t e mperatur es . The octa-hydrate pi;oduct must be carefully dri e d at approximately 60 C. , a fter which the tem perature can be raised slowly to over 100 C., whereupon an equivalent dihydrate product will be obtained. In preparing a highly purified product, it is also important to consid e r the hygroscopic property of naringin. An exceedingly dry sam ple of naringin dihydrate, dried at 105-110 C. for two hours , was found to increase approxi mately six percent in weight in less than two l1ours when e xposed to average room temper ature conditions. The uptake of water is ex ceedingly rapid initially, and especially so ~vith a small sample having a large surface exposed. The solubility of naringin in isopropyl al cohol is influenced greatly by water of crystal lization and extraneous water. The octa-hy drate form of naringin is more than 30 percent soluble in commercial ( 99 percent) isopro panol, while the dihydrate is soluble only to the ext e nt of approximately 0 . 2 percent. Th e solubility of these same two naringin mole cules in water is just the reverse, the dihy drate being the more soluble. In view of this information , the solubility of naringin dihy drate in isopropanol was investigated to de termine the effect of extraneous water mixed with the alcohol. A series of isopropanol sam ples were made in which the water content was as follows: less than 1 percent, 2 percent, 3 percent, and 4 percent. After shaking each sample with an excess of naringin for 14 hours at 27 C . , the solubility of the dihydrate in each was respectively as follows: 0.15, 0.28, 0.40, and 0.50 percent. When each of the four isopropanol samples was r e fluxed for 15 min utes at approximately 82 C. with an exc e ss of naringin, the dihydrate crystals had the fol lowing solubility: 0.65 , 1.1, 1.6, and 2.5 per cent respectively. Relating this information back to th e isopropanol purification procedure, it can be shown that maximum yield of puri fied naringin is obtained by cooling the crys tallized naringin as close to room temperature as possible before . filtering and by making every effort to keep the isopropanol as anhy drous as possible. In a number of repeated ex traction trials, naringin recovery was improved one to thr ee percent by thoroughly drying

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152 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 crude naringin samples just prior to ex traction and keeping the isopropanol well enclosed at a ll tim es possible; SUMMARY Commercial purification of crude naringin was shown to be possible by the following method: Suffici e nt well dri ed crude narin g in is slurried for five to ten minutes with boiling hot anhydrous ( or 99 percent) isopropanol, to yield an 8.5 to 10 percent naringin solution. The dissolved naringin is filtered quickly from the insolubles and h ea ted further or seeded to initiat e crystallization of the naringin dihy drate. The crystallized naringin and solution is allow e d to cool to room t em perature, where upon it is filter e d and the pure naringin furth e r washed with isopropyl alcohol. The crystals are dried at 85' C., yielding a final product of 98 to 100 perc e nt purity. In establishing a new purification procedure, the effe cts of naringin concentration w ere measured and the n ece ssity of keeping _ th e process as anhydrous as possible was shown. It was found that solvent costs can be reduced by recycling th e extraction alcohol in subse quent purifications, but its effect was reflected in the final product purity. Solubility of narin gin in isopropyl alcohol a nd mixtures of it and water were ~easured at two t e mperatures. LITERATURE CITED 1. Armentano, L. The effect of flavone dyes on blood pressure. Fe it . ges. Experimentelle Medizin 102: 219 . 1939. 2. Asah ina, Y., and M. Inubuse. On the flavanone glucosides IV. N a ringin a nd hesp er idin. J. Pharm. Soc. Japan 49: 12 3 -34 . 1929 . 3 . Baier . W. E. Methods for re cove ry of naringin . U. S. Pat en t No. 2,421,063. May 27, 1947. 4. Cutting, W. C., R. H. Dreisbach and F. Mat sushima. Antiviral chemotherapy VI. Parental and other effe cts of flavanoids. Stanford Med. BuJI. 11: 227-9. 19 53 . , 5. Davi s . W. B. Determination of flav ano nes In citrus fruit s . Anal. Chem. 19: 4768. 1947. 6. Hendri cks on, R. and J . W. Kesterson. Recovery of citrus glucosides. Proc. Fla. H ort. Soc. 67: 199203. 19 54. 7. Poore, H. _ D. Recovery of naringin and pectin from .grapefruit residue. Ind . Eng. Chem. 26: 637-9 . 19 34 . 8. Pulley, G. N. Solubility of naringin in water. Ind. Eng. Chem. Anal. Ed . 8: 360. 1936. SECTIONIZING MARSH SEEDLESS GRAPEFRUIT GRAY SINGLETON Shirriff-Horsey Corporation, Ltd. Plant City In the early days of grapefruit sect ionizing the p ee ling was done with knives. Girls sliced off th e stem and stylar ends of the fruit, then the lateral pe e l was removed by strokes of the knife, from top to bottom. In peeling, a con siderable slice was cut from each s eg ment. About 1929 the first canners started using lye to remove the carpellary membranes after the albedo had been stripped by hand. This saved that part of th e fruit which had previ ously been lost in hand peeling. When lye peeling was started, th ere was a great protest from th e "green pe e l " canners who said that the ly e would poison _ those who ate lye peel sections. But, when they found that ly e peeling increased _. the yield about 30 per cent and decreased th e cost of operation considerably, they decided that th e ir fears about the toxicity of lye peeled fruit were unfounded, which, in fact, they were. Lye p ee led sections . are usually not of as high quality as were those produced by hand peeling. At time s the lye is too cool or too weak and fragm en ts of membrane are not re moved. Frequently, th e lye is too hot or too strong and "cuts " into the sections making them _ soft and of poor appearance and texture . During the p e riod when hand peeling was i11 vogue, the m ars h se ed less variety of grape fruit was preferred. Th e sections were mor e uniform becaus e no ragged pits were left where seed were remov ed. \Vhen lye p ee ling came in, marsh seedless fruit went out. Seeded fruit became the stand ard for sections. This change was caused by the fact that seeded fruit has a solid core , while marsh seedless has a hollow core. Ly e gets into this hollow core and destroys the m e mbran es which bind the carpels together. When the sectionizing girls pick up a marsh seedless fruit th a t has been lye peel ed, th e segments fall apart in hand and sh e _ throws them on the garbage b e lt. The fruit must b e firm if good sections are to be produc ed. The shift from marsh to seeded fruit in volved about four million boxes each year and

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SINGLETON: GRAPEFRUIT SECTIONIZING 153 was a serious blow to the marsh . Fruit for sectionizing brings a pr e mium ov e r fruit for juice. Some years ago we decided that we could sell more sections if we could ag a in g e t the smooth, firm sections that were produced when we us e d the hand pe e ling of marsh in stead of th e l y e peeling of the s e eded varie ties. The results of our inv e stigation were pub lished in the magazine Citrus Industry, May, 1953 . The present paper is given to r e port certain refinements in the process that have been made s ince the first work was done. In the laboratory work , marsh seedless fruit was dipped in water at 190 degr e es, Fahren heit, for from sev e n to nine minutes. The time required to soft e n the albedo vari e s with the size of the fruit and the thickness of the pe e l. When the p ee l was soft, the fruit was cooled in water a nd the albedo remov e d by hand . This is the standard procedure in pre paring grapefruit for lye p e eling. In the usual l ye peel method the whole fruit is run through the lye bath and rinse wat e r sprays in stainless steel bask e ts. This re moves that part ,of the carpellary membrane which is exposed. Instead of doing this , we separated the carp e ls so th a t all of the mem brane would be exposed to the action of the lye. This separation is easily and quickly done by unskilled labor. It is naturally slow for a few days, but good speed is att a ined within a week. In the laborator y we placed the separated carpels in wire baskets and dipped them in a solution of canner's alkali having a strength of 2 p e r cent and a t e mperature of 190 degr e es, Fahrenheit. The membrane )Was dissolved in a few seconds and the baskets wer e dipped in cold water to cool the sections and rin s e off the dissolved membran e . The sections were then clean and ready to pack. In this labora tory work we had no broken sections . This method worked equally well with marsh grapefruit, seeded grapefruit and Valencia oranges. Th e product was of b e tter appear ance than that produced by the old hand peeling or the regular ly e peel process. The next step was to place th e separated carp e ls in wire baskets and send them through the regular lye sprays and cold water rinse. This work e d well but was too slow for com mercial production. We next tri e d separating the carpels and dropping them on a LaPort e mat which car ried them through th e lye and rins e and dis charged onto a wide rubber belt, from which the sections were packed. This worked w e ll e xcept that too many of th e peel e d sections stuck in the meshes of the LaPort e mat and were mashed. Th e next step was to pass the sep a rated c a pels through the lye on a wir e mesh belt and discharge into a flum e of cold water whi c h served as a rinse. Th e flum e carried the s e tions to the packing room where they wer e discharg e d onto another wir e mesh belt from which they were packed. The flume was us e d because we had gotten so much better results in th e laboratory , wh e re the sections w e re dipp e d into cold wat e r, th a n we had b ee n a ble to get by the u s ual cooling sprays. The flume method worked much better than we had expected . It is w e ll known to all who h a ve worked with s e ctions that wh e n the fruit comes to the s e ctioniz e rs, fr e sh from the lye bath and rinse, it is soft and difficult to handle without excessive breakage. When th e lye peeled sec tions came from the flume th e y wer e firm and solid, with better texture th a n we had ever been able to get in any oth e r way. Even late in the s e ason th e flum e d sections were firm. We do not attempt to explain th e improv e ment in textur e , yield and appearanc e of th e se flumed sections except to off e r th e . following c omm e nts: 1. The wat e r used in th e flume was from a deep well a nd contained considerable calci um in s olution. 2. Using a 0.17 p e r cent solution o f calcium chloride in distilled water w e got re s ults simi lar to those given in the flume. 3. Soluble calcium in the flume w a t e r prob ably pr e cipitated insoluble calcium p e ctate in the outer layer of cells in the sections. 4 . L y e pe e l e d whole fruit , wh e n passed through the flume, showed little or no firming, probably because relatively few cells were ex posed to the w a ter. Th e development of chilled sections in gl a ss makes it imperative that we produce sections having better appearance than thos e we are now packing in tin. Hanel p e eling is one an swer, but at a heavy loss in yi e ld. Th e proc e ss outlin e d here ma y b e a better answer-in both g lass a nd tin.

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154 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 AN EFFECTIVE HIGH PRESSURE CLEANING SYSTEM FOR CITRUS CONCENTRATING PLANTS D. I. MURDOCK Staff Bacteriologist c. H. BROKAW Chief, Quality Control Department Minute Maid Corporation Orlando In the citrus juice concentrating industry, as with other food processors, there has been a considerable lag in improving cleaning meth ods compared to technological advances in processing. Recently, however, with the steady decrease in profit margins, there has been a growing impetus to improve cleaning practices. This change has emphasized reducing the amount of production time lost when the plant is shut down for clean-up. In the citrus con centrating industry this clean-up period usual ly occurs two or more times per week and it may require, depending upon the size of the plant, 4 or more hours. The biggest bottle neck in cleaning Minute Maid Corporation plants has been in the juice extraction room where fiber brushes and steam guns were formerly used to clean the juice extractors and the finishers. The use of fiber brushes was time consuming, and the steam gun was cum bersome besides having the tendency to "bake" citrus solids on the surfaces being cleaned. Steam guns also produce a considerable amount of vapor, especially during cold weath er when it is not uncommon for the whole juice room to be completely fogged, making it impossible to see what has , or has not, been cleaned . To alleviate this condition, Minute Maid in vestig~ted the possibilities of high-pressure equipment for cleaning the extractors. A small portable insecticide spray rig, shown in Fig. 1,. was obtained which consisted of a John Bean Model 33-K pumping unit, a 55-gallon drum, high-pressure hose, and a heavy-duty adjust able GunJet spray gun, a type commonly used to spray citrus trees. Th e pump delivers 3 gallons per minute at 300 pounds pressure, which is enough volume to operate one Gun Jet. The unit, which costs approximately $250., may be mounted on wheels for portable use. It is ideally suited for small cleaning operations, and for high-pressure cleaning of extractors was found to be more effective than any of the other methods investigated. For example, an In-line extractor (manufac tured by Food Machinery & Chemical Cor poration) could be cleaned approximately 5 minutes faster with a GunJet than with a steam gun in one study where both methods of cleaning were compared: (Table I , Fig. 2 and 3). High pressure cleaning using a Gun Jet, besides saving time, has numerous other ad vantages; namely, 1. Not hazardous-(Eliminates burns ob tained from the steam guns.) 2. Reduces humidity and resulting mold growth. 3. Can see what you are doing. 4. Results in better and more thorough clean-up than can be obtained by other stand ard methods. 5. Makes cleaning job easier. 6. Separate adjustment of handle of gun controls the type of spray needed for cleaning job. 7. Not bulky-easy to handle. Readily re moves material from cracks and crevices dif ficult to clean by other methods. 8. Eliminates tedious hand dressing . The small portable high pressure system proved to be so successful that a more perma nent installation was investigated. Heretofore, the detergent solution for steam guns was pre pared by adding the material to make-up vessels from 5-gallon buckets which were usually either full or completely filled. Such prepa ration of the solution, which was heated in a tank by manually opening and closing a steam valve, required one man's attention and re sulted in a variation of detergent concentra tion, and of temperature for each batch. To eliminate this situation, the Engineering Department of Minute Maid Corporation de veloped an automatic detergent mixing system.

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MURDOCK AND BROKAW: CLEANING SYSTEM 155 FIGURE I _ PO.RTR8LE-ij/(H-P.RESSVRE-CLERNING..f.NUl1 TFINX l 41 ~A,S(),t.,1N#/Vd',1N ---.~-..-,..-c, .... r~ KEY cl d.s-GHL ... BE.J:L!::!. !.•~-~-.!:J!5'PVHP/Mf f!!.ff1:•WIT"HJHP.BRlfi6S /-srRRTrON G;fSOL/N•N61N {ELECrRIC•c:!Qrfl..B~-~-StJ{fJJ"r/TUrEp) ~• ~ P,,,,E.S-SURE HOSE ..SY.STE,-.,•COM PR NY• GUNcJeT .... ... ruizr TlME :u,:;,utt.t:.i W c1.:::: .1 .. 1 F' .M.C !:'C'R/,CTO.~ wm lwtbo4 of Cleu101 ,o.ctrxtJ-aeto:a Cln.i:it'd 10 .\\ T~ in. ML'\, to c1e1r.~. &a.c:h t::ictr.cto:r " The unit which is shown in Fig. 4 can be built for approximately $2,000. It consists, essen tially, of a 500-gallon stock detergent solution tank, a similar size mixing tank, high pressure pump, high pressure hoses, and Gun Jets. ( Ca pacities of solution tanks are dependent upon the number of gallons of detergent required for cleaning. For efficient operation, the con centrate solution tank should provide stock solution for one or more clean-ups. The mixing tank, on the other hand, need only be large enough for heating, i e , 200-500 gallons. Deter gent tanks used in one installation are shown in Fig. 5.) The stock solution which for con venience, may be prepared one or more days in advance of plant clean-up , is made up at the rate of I pound of detergent per gallon of waler. The stock solution in the concentrate tank is diluted 16 to 1 with water by means of a flow control valve as it is pumped by a centrifugal pump into the mixing tank. The diluted solution in the mixing tank, which is used for cleaning purposes, is maintained at a constant level by an electrode limit switch . A steam jet heater, illustrated in Fig. 4, for heating the solution in the mixing tank can also be used for pre-heating the stock solu tion in the concentrate tank. In this installa tion the heater is designed to raise the tem perature of the stock solution in the concen trate tank to 212 F. within 30 minutes, and that in the mixing tank from 70 F. to 140 F.

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156 FLORIDA STATE HORTICULTURAL SOCIETY , 1956 at th e rat e of 150 ga ll o n s p e r minut e. Th e t emp e ratur e o f th e dilut e d so luti on i s co n troll e d b y a dir ec t ac tin g t e mp era tur e co ntrol va l v e, which ma y b e adjust e d to a n y d e sir e d t e mp e r at ur e . A hi gh pressur e pump i s us e d to pump th e d e terg e nt so luti on t hrou g h p i p e lin e s to va ri o u s l oca ti o n s in th e juic e room. High pressm e hos e s , w i th GunJ e ts attach e d , ar e c onn e c t e d to th e v a rious d e t e r ge nt outl e t s . Usua ll y t wo g un s are u se d for eac h lin e o f ex tractor s, and up t o 5 g un s m ay b e u se d w ith th e s y st e m , whi c h s uppli e s d e t e r gen t so luti o n a t th e rat e o f 20 g allon s p e r minut e . Th e g uns ar e op e rat e d a t a pump pr ess ur e b e tw ee n 2 00 to 300 pounds p e r squar e in c h , with a d e t e r ge nt so l u t ion t e mp e ratm e of approximat e l y 125 F . In addition to c l ean in g th e e xtracto r s , th e G unJ e ts a r e us e d v e r v e ff e ctiv e l y in cl e anin g t he fini s h e r s, as w e ll as e mploy e d in oth e r p a rt s o f th e pl a nt t o cl e an v a riou s t a nk s, e tc. It is a lso a v e r y e ff e ctiv e cl e an i ng tool for cl e aning " inacc e ssibl e" spots whic h cannot b e r e ached b y oth e r m e th ods of clea nin g. A c e bifugal pump d e s i g n e d t o d e li ve r 1 55 ga JJ ons p e r minut e at 55 pounds pressure , is also u s e d with th e s y st e m for " back-Hushing " th e e x a ctors with a d e t e r ge nt so luti on . ( D e t e rg e nt ba c k-flushin g i s th e pumping of a c l e an in g so luti o n b a c k thr o u g h th e juic e lin e s a nd up int o th e ex t rac t o r s . Thi s proc e dm e is ge n e ra ll y e mplo ye d in cl ea ning F. i \iI.C. e xh c t ors on l y, s inc e th e BrO\ n e xtra c tors , manufa c tur e d b y Brown C itrus M a ch in e r y Co rp ora ti on , u s e a built-in cl e aning syst e m for thi s purpos e . ) Our dis c u ssion so far has dealt w ith cl e an in g th e e quipm e nt w h e n the p l ant is s hut clown for thi s purpo se; that is , w ee kend o r Fig. 2 . ln lir : . e juic e extractor in s tallation . Cov e r s { A) a r e r e mov e d durin g cl ea ning process. ( Photo gra ph c ourt esy of Food M a chin ery & Che mi ca l Corporation).

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MURDOCK AND BROKAW: CLEANING SYSTEM 157 midweek type clean-up. The juice room equip ment in our p l ants is also cleaned while the r es t of th e pbnt is still in operat i on. This int e rmitt e nt " type of cl ea ning cons i sts of back flu s hin g th e ex tractors , h eade r lin es or ju ice trou g h , finishers, and fr es h juic e tank , eve ry four horns w ith chlorinated water of approxi mat e l y 25 p.p . m. from th plant service water supply , not necessarily through the high pre sme system. This operation requires usually 15 to 20 minutes , depending on whether or not th e finisher screens are changed. Chlorinated water back-flushing is a very e ffective m ea ns of contro llin g bacteria! con tamination. In one study where samp l es of juice w ere p l ated prior to a nd just after this type c l ean ing , a r e duction in total viab l e counts from 35 to 62 % was obtained. (Ta bl e II ). In observing cleaning practices used by our plants it wa quite evident that in order to TABIE Il EFFECT OP JlACK-fWSBING F .H . C. EX'1'RAC'1'0RS \.II'I'll CHLORINATED WATER CJl BACTERlA.L CONTAMINA!l'IOH SOORCE OF SAMPIE BEFCE.E rwsanro AFTm FWSRDiG DllC!lEASE APIT.R P'WSIOJW 3,110,000 1,185,000 Atter Finillhe r 1,020,000 66o ,ooo Rote: Rasu1ta expreued as tbe averas@ nl&bu ot m.Lcroorgan1ar.e per ml. 1'roc tvo teat run•. Ch1or1m.ted. vatu 20 )0 p.p.D, 62 35 minimize the time r eq uired , prop e r coord in ation and training of a ll individua l s invo l ved was n cessary. On e major factor responsible for this in e ffici e nc y in cleaning is the season al natur e of th e citrus industi y which results, in many cases, in a lm ost a comp l e t e change of production personnel at the beginning of each pack, with only the key e mploy ees b e ing re tained from year to year. Fig. 3. C leaning ex tr actor with GunJet , Note absence of fog or mist around s urac es being cleaned.

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158 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 FIGURE IV -tfffiH('-RE.S.SC/R&-CLE,
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MARSHALL: CORROSION INHIBITOR 159 Fig . 5 . In s tallation of high pressure cleaning sys t em s howin g mixing tank-l ef t , and concentrate s tock so luti o n ta r.. k right. High pr ess ur e pump is l ocated on floor wit h s t ea m and water co ntrol valves mount ed above tanks. Fig. 6. High pressure system can a l so be u se d for cleaning Brown ext ractor s. ( Photograph courtesy of Brown Citrus Machin e r y Corporation) . tion with high pressure system was found to be a very effec tiv e cleaning tool. S e veral of its advan t ages over other m et hods of cleaning are given. The importance of intermittent cleaning of th e extrac tors with ch lorin ated wa t er i s discussed along with th e need of em ploying train ed personnel to reduce cleaning tim e . SOME STUDIES ON THE USE OF SODIUM NITRITE AS A CORROSION INHIBITOR IN THE CANNING INDUSTRY J . R. MARSHALL 0 Tampa INTRODUCTION As the canned food industry and the can manufacturing industry have advanced techni cally, th ere has b een a trend toward r ed uced tin coating weights on all containe rs . Such reduction has resulted in millions of dollars in savings to the canning industry and to the consuming public . It a lso has set up a safe guard aga inst drastic c utba cks in tin plate availability in times of national e m e rg ency. The u se of e l ectro l ytic plate bearing only a small percentage of the tin used on the old tim e hot dipped plate h as been made possible •Tampa Laboratory of Research & Technical De partment of the American Can Company , Tampa, F ' la . for many it ems by exte nsiv e laboratory tests and subsequent industry ex perience. vVhere it has b ee n n ecessa r y to m a intain the internal tin coa ting weight at a high e r l eve l , the exterior tin coating we ight has been r educe d , in many instances, to the minimum by the use of dif ferentia l e l ectroplating . It is generally accepted that tmcl er good handling and storage condi tions, th e li g htest ex t e rnal tin coating performs satisfactorily; whereas, und e r improper condi tions , the heaviest tin coating weights are not sufficient to prevent outside rusting. ( 1). The presence of rust on th e outside of a can of food detracts from its sa l es va lu e. This fact i s especially true in th ese clays of mass merchandising when th e cons um e r has an op portunity to choose not on l y th e type and brand of product on the supermarket shelf, but

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160 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 g e nerally th e mo s t attractiv e container as w e ll. Another reason for rust pr e v e ntion is that speci fications for canned foods purchased by th e government, a rm e d forces, and other agenci e s stipulate that the cans shall be free from rust. The succ e ssful use of light e r electrolytic tin coatings on cans for civilian trade has led th e military s e rvic e s to mak e e xh a u s tive tests on the exterior rust resistance of such containers. Their tests included CTS, No. 25, No. 50 a nd 1.25 lb. plat e s . Two types of organic coatings w e re employed: that applied to the flat sheet of plate prior to can fabrication and that a plied to the fill e d container after proc e ssing. The cans w e re stored under Temperate, Desert, Arctic and Tropic climatic conditions. The test results indicated again that the ex ternal protection afforded th e steel base is not influenced in direct proportion to the tin coat ing used. Th e postcoating and the precoating of the plate with organic m a terials respectiv e ly gave the best protection against rusting. There was littl e differenc e in the degree of rusting among th e various tin coating weights in either the coated variables or the plain variables. ( 2) Normally , the lighter tin coating weights used to replace the heavi e r coatings can be expected to perform satisfactorily if good can handling and processing procedures ar e fol lowed. The s e processing techniques include the use of non-corrosive proc e ssing and cool ing waters, the use of recommended processing and cooling practices, the casing of dry clean cans which are warm enough to evaporate any traces of moisture, and clean, dry storage con ditions with uniform temperatur e s. Because of the economic a dvantages of lighter tin coat ings, it is to the advantage of the packer to use all precautions to assur e satisfactory per formance of the container. At best, howev e r, some packing procedures a re too corrosive to allow the satisfactory use of reduced tin co a ings without special precautions. In working with the various canners, it was found that grapefruit sections and pimi e ntos, both boiling water proc e ss items, required special handling precautions if the industry was to enjo y the advantage of the lighter tin coatings. Since the probl e m was mainly on e of exterior c a n corrosion , th e experimental work was dir e cted toward an additive for the process or cooling wate_r which would help correct th e condition. Sinc e there is always the possibility of contam i nation of the product, any a dditive used should be nontoxic. This stipulation narrowed the field and made ex periment a tion with sodium nitrite attractive. In ord e r to better understand the function of sodium nitrite as a corrosion inhibitor, we would like to cover briefl y some of the factors contributing to the external corrosion of metal contain e rs. CAUSE OF RusT Each corrosion problem may vary because of the nature of the materials and process in volved but the basic chemical reactions have much 'in common. External rusting of cans may b e considered a part of the general sub ject of corrosion of ferrous metals. Although many factors are involved in the corrosion of metals, only a few ( oxygen, mois ture, temperature , and presence of acids or salts) are of particular interest in connection with external corrosion of tin plate containers. Effective pr e vention of external rusting is sim ply the control of one or more of these primary factors through taking reasonable precautions to protect the cans during processing, cooling, and storage. Many theories have been advanced . regard ing the exact nature of the corrosion of iron. One expl a nation is given by Hildebrand (6) who indicates that the initial step in the forma tion of rust is the production of ferrous ions. These ions combine with oxygen to form ferric oxide. The production of ferrous ions is re tarded on pure iron by the polarization effect of hydrogen; however, their production is catalyzed by the pres e nce of impurities, vari ous salts and hydrogen ions. Although, as stated above, many ideas have been adv a nc e d to explain corrosion, it has been establish e d that metallic corrosion in a solu tion cap a bl e of conducting electricity is of an electroch e mical nature. ( 5). Two dis s imilar metals in electrical cont a ct and wetted by a conducting solution, form an electrolytic cell. The less noble of the two metals becomes the anode and corrodes; wh e r e as, the oth e r metal becomes th e cathode and is protected. Actual l y , when the exterior of a tinplate container is exposed to certain atmospheric conditions or to corrosive water in th e presence of oxygen, corrosion takes place at minute points where the iron is exposed. Small electrolytic cells are

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MARSHALL: CORROSION INHIBITOR 161 es tabli s h ed at these exposed points , and tbe co rrosion of iron occms preferentially to tl1 at of th e tin. The tin coa tin g or an overcoating of e nam e l r e tards rusting by protecting th e iron from physical contact with th e co rrosiv e water or atmospheric conditions. This situation is quit e different from th a t ex isting on th e insid e of th e co nt aine r vvhere, in most cases , as th e r es ult of the p r esence of little or no oxygen th e tin i s a no d i c to the iron and iliereby provide sac rificial protection and s uffi c i e nt she lf life for satisfactory merchandising. It has b ee n s hown that the formation of fer rous ion e ith e r b y e l ectroc h em ic a l ac ti o n or through solution b y weak acids , i s an esse nti a l step in th e formation o f rust. If m ea n s for stopping thi s part of the reaction a r e es t a b lish ed , then rustin g could be retarded or per haps prevented. During the past few yea rs , co nsid e rabl e work ha s been d o n e to d eve lop a prot ec tiv e oxide film on iron similar to that which oc c ur s naturall y on a luminum. It was found that a film could b e form e d on ferrous m e t a l in th e absence of excessive disso l ved oxygen with oxidizing mat e rials such as sodium nitrit e and c hrom a t e. (2) (3) Pr yo r and Cohen ( 9 ) con c lud ed that th e protective ac _ tion of th e a bov e anod i c inhibitors is based on the formation of protective film s of 2 gam m a Fe,O" maintain e d in co n s tant repair. The prot ec tiv e film in aer a t ed so lutions is formed primarily by reaction with dissolv ed oxygen; how eve r , in cl eae rat e cl so lutions th e inhibitors , du e to th e ir oxidizing c h arac t e r , r eac t direct l y with iron to form pro t ec tiv e films . EXPERI1IENT AL PRO CEDU HE In this work , the use of a l ong-k nown rust inhibitor " as applied to the cann in g industr y. Fig. 1. Tinp l ate strips immersed in Sodium Nitrite s olution o f indicated concentration s for period of 4 weeks at room. temper at ur e.

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162 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 To det er mine the desired concentration of sodium nitrite for the semi-commercial tests, strips of tinplate were immersed in solutions of sodium nitrite at concentrations of 0, 100, 200, 300, 400, 500 and 1000 ppm. The nitrite solutions and tinplate strips were placed in 500 ml. beakers and stored at room tempera ture. One strip was completely submerged and another was partially submerged and partially out of the water in each case. Above 200 ppm. no rust was encountered on the strips during a period of four weeks. Slight rust was ob served on the strips of tinplate in the un treated water in about 24 hours. Fig. ( 1) is a photograph of the results of this experiment. In the semi-commercial tests, sodium nitrite was added to the process water to a concen tration of 400 to 600 ppm. Periodically sodium nitrite was added to maintain the concentra tion. Both continuous type cookers and batch type retorts were used in studying the effec tiveness of sodium nitrite. The use of sodium nitrite in cooling water was not considered because the expense of such treatment would make it non-commercial, unless the water was recirculated which would bring in many tech nical problems. Our experience indicates that the protective film formed during processing gave adequate protection during cooling and normal storage. It has been reported that sodium nitrite in concentrations below 200 ppm . has caused pitting of ferrous metals. (7) Since the sodium nitrite concentration is being continually di luted in the cooker by the condensation of steam and the replacement of water carried out on the cans, the method shown in the appendix was developed for accurately deter mining its concentration. . Because excessive amounts of sodium nitrite do not give signi ficantly better re.suits, careful control of its concentration in the water will mean savings as well as preventing ineffectively low con centration from occurring, Sodium nitrite cannot be used in solutions having a pH lower than 6,5 because it decom poses chemically. In our te sts, all water was found to be in the pH range