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DOCUMENT
Bulletin 898 (Tech.)
r? .'
c-' Z9
Use of Methyl Bromide
and the
Economic Impact of Its Proposed Ban
on the
Florida Fresh Fruit and Vegetable Industry
T. H. Spreen
J. J. VanSickle
A. E. Moseley
M. S. Deepak
L. Mathers
i.rston Science
Library
AUG 12,1996
Universiy of Florida
S-, UNIVERSITY OF
. FLORIDA
Agricultural Experiment Station
Institute of Food and Agricultural Sciences
I -
I
THE USE OF METHYL BROMIDE AND THE ECONOMIC IMPACT OF ITS
PROPOSED BAN ON THE FLORIDA FRESH FRUIT AND VEGETABLE INDUSTRY
by
Thomas H. Spreen
John J. VanSickle
Anne Moseley
M.S. Deepak
Lore Mathers
Thomas H. Spreen and John J. VanSickle are Professors, Anne Mosely is Economic
Analyst, M.S. Deepak is Post Doctoral Research Associate, and Lore Mathers is Graduate
Research Assistant, Food and Resource Economics Department, University of Florida,
Gainesville, Florida.
ASSESSMENT OF THE LONG TERM ECONOMIC IMPACTS OF THE LOSS OF
METHYL BROMIDE ON FLORIDA
TABLE OF CONTENTS ............................... .......
ABSTRACT .......... ....................................
ACKNOWLEDGEMENTS ......................................
EXECUTIVE SUMMARY ......................................
SECTION 1. INTRODUCTION ...................................
Organization of this Report ..................................
SECTION 2. THE EVOLUTION AND USE OF METHYL BROMIDE IN THE
VEGETABLE AND CITRUS INDUSTRIES ..................
H historical Overview ......................................
Development and Use of the Chemical .....................
M ethyl Bromide in the Soil .............................
Methyl Bromide as a Potential Contributor to Ozone
D epletion . . . . . . . . .
Legal Development Surrounding Methyl Bromide ................
Methyl Bromide and Safety-Health Concerns ...................
Application of Methyl Bromide as a Soil Fumigant ...............
SECTION 3. CHEMICAL AND NON-CHEMICAL ALTERNATIVES TO
METHYL BROMIDE USE .............................
Chemical Alternatives to Methyl Bromide ..........................
Basamid Granular ...................................
V orlex . . . . . . . . . . .
Vapam ...........................................
Telone II and Telone C-17 ..............................
C holorpicrin . . . . . . . . . .
Non-Chemical Alternatives ..................................
Reduced Use of Methyl Bromide ................. ........
Constructed Barriers .................................
Crop Rotation ........... ................ .... ......
i
. . . . . . . . 29
Solarization ................... .................... 30
M microwave ........................................ 31
Soil Flooding ...................................... 31
Soil Amendments .................... ............. 31
Host Plant Resistance ................................. 32
Fallow Land ...................................... 33
Cover Crops ..................................... 33
SECTION 4. COMMODITY PRODUCTION AND PEST CONTROL PRACTICES 34
W atermelons ........................................... 34
Cultural Practices ................................... 34
D diseases ......................................... 36
Nematodes ........................................ 38
W eeds .......................................... 39
Insects .... ... ... .... ....... .... ... .. .... ..... 40
Trends .......................................... 40
Tom atoes ............................................. 40
Cultural Practices ................................... 41
Planting Techniques ................................. 44
Staking ............... ............................ 45
D diseases ............... ....................... 45
Nematodes .................................... ... 50
W eeds .................................. ..... 50
Insects .. .. .... ... .... ..... ..... .... ... ... .. .. 51
Strawberries ........................................... 51
Cultural Practices ................................... 52
D diseases ......................................... 54
Nematodes ..................................... 56
W eeds .......................................... 57
Insects .... ..... .... ........ .... .. ... .. .. .... .... 58
Peppers .............................................. 58
Cultural Practices .................................. 59
Diseases ................................... ....... 61
Nematodes ......... .............................. 63
W eeds .......................................... 63
Hot Water or Steam .
Insects . .
Eggplant ...........
Cultural Practices
Diseases . .
Nematodes ....
Weeds ... ..
Insects .......
Cucumbers .........
Cultural Practices
Diseases ......
Nematodes ....
Weeds .......
Insects .......
Squash ..............
Cultural Practices
Diseases ......
Nematodes ....
Weeds .......
Insects .......
...... 78
. . 80
......80
. .. 81
. ..... 81
...... 82
Fresh Citrus .............
SECTION 5. ECONOMIC IMPACT OF A METHYL BROMIDE BAN .......... 87
Objectives ............................................. 87
The Impact on Production of Vegetables from a Methyl Bromide Ban ........ 88
M ethodology ...................................... 88
Empirical Results ...................................90
The Impact of a Methyl Bromide Ban on the Florida Citrus Industry ........ 98
Solution of the Model ................................ 100
Oranges, Tangelos and Tangerines ........................ 102
Total Impact ...................................... 104
The Overall Economic Impact on the State of Florida ................. 105
iii
.64
.. 65
.... 67
... 69
.... 70
.... 71
.... 71
.... 72
.. 74
.... 76
. 76
....76
.... 77
.... 78
III II II
II II II
SECTION 6. SUMMARY AND CONCLUSIONS ........................
Sum m ary ............................................
109
109
Conclusions .......................................... 111
Limitations of the Study and Suggestions for Further Research ... .... .. 112
REFERENCES
APPENDIX A.
APPENDIX B.
APPENDIX C.
APPENDIX D.
APPENDIX E.
APPENDIX F.
APPENDIX G.
LIST OF COMMON METHYL BROMIDE FORMULATIONS ....
COMMERCIAL APPLICATION OF METHYL BROMIDE ......
114
124
129
ALTERNATIVES TO METHYL BROMIDE AND THEIR USE IN
FLORIDA ...... ....... ........................ 132
THE MARKET FOR FLORIDA FRUIT AND VEGETABLES .... 147
A MATHEMATICAL MODEL OF THE NORTH AMERICAN WINTER
VEGETABLE MARKET .. ........................ .. 157
A MATHEMATICAL MODEL OF THE WORLD MARKET FOR FLORIDA
GRAPEFRUIT .................................. 197
NEXT BEST ALTERNATIVES TO METHYL BROMIDE FOR FLORIDA
FRUIT AND VEGETABLES .......................... 201
ABSTRACT
Methyl bromide is a critical pesticide that is used in producing many fruit and vegetable
crops grown in Florida and the nation. It is a broad spectrum pesticide serving as an insecticide,
nematicide, herbicide and fungicide. The environment which prevails in Florida makes the use
of methyl bromide critical to the competitiveness of these crops in the U.S. and international
markets. The Environmental Protection Agency (EPA) declared in November 1993 that methyl
bromide was a Class I ozone depletor, and as such must be phased out of use by the year 2001.
Commodities analyzed in this bulletin included tomatoes, bell peppers, cucumbers, squash,
strawberries, watermelons and fresh citrus. Alternative chemical and non-chemical production
and marketing practices are discussed. Because no known alternatives exist that will effectively
substitute for methyl bromide, Florida is estimated to lose over $620 million in shipping point
value of fresh fruit, vegetables, and fresh citrus, worth over $1 billion in total sales in Florida,
and more than 13,000 jobs. Florida will reduce acreage by more than 43 percent if methyl
bromide is banned and no suitable alternatives are developed. Production of these crops will
cease in Palm Beach County and tomato production in Florida will decline by more than 60
percent. The primary beneficiary of this policy will be Mexico who, as a developing country,
will have 10 additional years to use methyl bromide in producing and marketing their crops.
Production will increase significantly in Mexico for all tomatoes (80 percent), bell peppers (54
percent), cucumbers (7 percent), and eggplant (143 percent).
ACKNOWLEDGENIENTS
We would like to acknowledge the support and assistance of several individuals who
contributed to the completion of this project. This project could not have been completed as
well or as thoroughly without their assistance.
We would first like to acknowledge the assistance of Drs. Joe Noling, Nematologist at
the University of Florida Citrus REC-Lake Alfred; George Hochmuth, Nutrition Vegetable
Specialist at the University of Florida Horticultural Sciences Department; Donald Maynard,
Vegetable Specialist at the University of Florida Gulf Coast REC-Bradenton; and Bill Stall,
Weed Control Specialist at the University of Florida Horticultural Sciences Department. These
gentlemen, along with Lorne Mathers, gave support that allowed this project to produce the
horticultural details of how methyl bromide worked and to identify the alternatives to and the
consequences of its removal. They helped in identifying alternative production practices and
choosing the alternatives that would be used if methyl bromide is banned. Their horticultural
knowledge contributed greatly to the success and results of this research.
We would also like to acknowledge the support of Scott Smith, Economic Analyst, Food
and Resource Economics Department, University of Florida, for his assistance in budgeting
crops and the alternatives to methyl bromide. Mr. Samual Scott, graduate research assistant in
the Food and Resource Economics Department, extended his M.S. thesis research and provided
estimates of demand flexibilities for eggplant, squash, watermelon, and strawberries.
Our thanks to Richard Kilmer and Richard Weldon, Food and Resource Economics
Department, University of Florida, who reviewed an earlier draft of this manuscript and made
several helpful suggestions.
Finally, we acknowledge that any errors in this document are the responsibilities of the
authors and not those who assisted in or funded the project.
vi
EXECUTIVE SUMMARY
Methyl bromide is an important chemical which is used in the production and marketing
of a wide range of agricultural products throughout the world. In Florida, it is used both as a
pre-plant soil fumigant and as a post harvest fumigant for many of the fruits and vegetable crops
produced in the state to control a wide array of pests. Methyl bromide has been identified as
a Class I ozone depleting chemical, and its production and use will be banned in United States
in 2001.
Methyl bromide is used as pre-plant fumigant for many of the fruit and vegetable crops
produced in central and south Florida. It is used in conjunction with plastic mulch and provides
an effective control for weeds, nematodes, and other soilborne pests in the production of
tomatoes, peppers, eggplant, cucumber, squash, strawberries, and watermelons. Methyl bromide
is also utilized as a post harvest fumigant to control fruit fly on fresh citrus shipped to other
citrus producing states. As Florida is a major supply region for many of the crops which benefit
from the use of methyl bromide, the proposed ban will affect both Florida producers and U.S.
consumers of fresh fruits and vegetables marketed in the November through May period.
In this study, a comprehensive review of previous work related to methyl bromide was
conducted. A survey of extension specialists in the production areas was utilized in conjunction
with the literature review to identify existing production systems and possible alternatives to
methyl bromide. After crop production systems had been delineated, further consultation with
horticultural scientists at the University of Florida provided detail on possible alternatives to
methyl bromide and the impact of alternative production practices on crop yields and production
costs.
It was recognized that the use of plastic mulch in conjunction with methyl bromide is the
primary production system employed by Florida farmers who produce tomatoes, peppers,
eggplant, and strawberries destined for the winter market in the United States. Cucumber,
squash, and watermelon may be produced as second crops which utilize the same plastic mulch.
It was also determined that methyl bromide provides effective control for nematodes, weeds, and
soilborne pests. It may also be applied with chloropicrin, which is an effective fungicide.
Alternative fumigants to methyl bromide include Vorlex, Vapam, and Telone. Each of these
alternative fumigants have disadvantages relative to methyl bromide which explains, in part, why
the use of methyl bromide dominates in the Florida fresh winter produce industry. A main
result from this component of the study is that production systems based upon plastic mulch will
survive in the absence of methyl bromide. Non-chemical alternatives such as steam or
solarization are experimental at this time. The use of crop rotations offers one plausible
alternative but is impractical in the east coast production area because of high land costs.
The use of methyl bromide as a post harvest fumigant was also analyzed. Fresh citrus
is the major crop on which post harvest fumigation is widely practiced. This is done to control
the possible presence of fruit flies in fresh fruit to be shipped to other citrus producing states.
Currently, all fresh citrus destined for the export market is not fumigated. No viable alternatives
could be identified for use in post harvest fumigation.
To conduct economic analyses of the impact of a ban of methyl bromide, two
mathematical models were developed. The first models the North American winter fresh
vegetable market. The second is a modification of an existing model of the world market for
Florida grapefruit.
The North American winter fresh vegetable market model included supply and demand
relationships for tomatoes, peppers,-eggplant, cucumbers, squash, watermelon, and strawberries.
The months included in the model are those months in which Florida is an important supply
region to the market. For tomatoes, peppers, eggplant, cucumbers, and squash, the model
spans the November through May period. Mexico is included as the alternative supply area for
tomatoes, peppers, eggplant, cucumbers, and squash for the November through May period.
Texas is a competing supplier of peppers in November and December. California is the
competing supplier of strawberries. Florida is active in the strawberry market from December
through March. No other region is a major supplier of watermelon in May. The North
American market is divided into four major demand regions whose central points were assumed
to be New York City, Chicago, Atlanta, and Los Angeles.
Analysis of a methyl bromide ban on Florida citrus growers was conducted in two parts.
First, a model of the Florida grapefruit market was modified to account for the methyl bromide
ban. It was assumed that a ban on post harvest fumigation of citrus would result in a loss of
the markets in other citrus producing states. This scenario was analyzed in the grapefruit model.
It was determined that fresh grapefruit would be reallocated to non-citrus producing states; there
would be no impact on processed grapefruit utilization. The analysis conducted for fresh
oranges, tangelos, and tangerines considered only the fresh market.
The results of the economic analysis are:
the loss of methyl bromide would have a devastating effect on Florida winter fresh
vegetable producers;
Florida production of tomatoes for the winter market will decline by 60 percent;
Florida will lose market share in both peppers (63%) and cucumbers (46%);
Eggplant will no longer be produced in Florida for the winter market;
All vegetable production in eastern Palm Beach county will cease; Dade county will no
longer produce tomatoes;
Lesser effects are projected for squash, which is not a major user of methyl bromide;
The Florida strawberry industry will suffer a major contraction of production (69%);
There will be a 40% decline in the production of double crop watermelons in Florida;
Both Mexico and Texas will expand production of vegetables; Mexican tomato
production will expand by 80%; its pepper production by 54%; its eggplant production
by 123%;
The economic loss to Florida is substantial. The FOB value of lost fruit and vegetable
production is $620 million;
The projected loss of FOB revenue to the Florida citrus industry is $13 million;
The total economic impact of a methyl bromide ban to the state of Florida is estimated
at approximately $1 billion and 13,000 jobs.
The economic analysis is based upon the best information currently available regarding
crop yields and production costs associated with alternative production systems. Further
research is needed to validate the assumptions made in the economic analysis.
The conclusion of the study is that the Florida winter fresh vegetable industry will face
dire consequences if new alternatives to methyl bromide are not identified before the ban of
methyl bromide is scheduled to take effect.
SECTION 1
INTRODUCTION
Methyl bromide is a broad spectrum pesticide used on a number of agricultural crops.
As a soil fumigant it serves as an insecticide, nematicide, herbicide and fungicide. It also serves
as a fumigant for stored commodities for protection against pests such as fruit fly and rodents.
Parties to the Montreal Protocol on Substances that Deplete the Ozone Layer (commonly referred
to as the Montreal Protocol) declared at their November 1992 meeting that methyl bromide had
an ozone depletion potential (ODP) of 0.7. This level is well above the 0.2 ODP required to
classify it as a Class I ozone depleter. The United States enacted the Clean Air Act in 1992.
The Clean Air Act requires that all Class I ozone depleting compounds be banned. The EPA
has informed the producers and users of methyl bromide that its production and importation will
be banned beginning January 1, 2001.
In Florida, methyl bromide has been important to the production of several fruit and
vegetables. 'Old land disease' became a problem for many farmers in the 1950's and 1960's
because of the buildup of pests in soils when individual fields were cultivated intensively for
several years. Farmers initially solved this problem by moving to virgin land. They would then
farm the land until old land disease set in, and then repeat the process by renting different land
to farm which had not been farmed recently. Land pressures from urban encroachment and
protection of the environment made this type of farming more difficult and new farming
practices had to be developed to take advantage of the declining agricultural land base.
McMillion (1972) and Volin and McMillion (1973) first demonstrated that the old land disease
complex could be controlled effectively by increasing the percent of chloropicrin injected with
methyl bromide. Tomato producers began using plastic mulch in combination with soil
fumigates in 1973. Other vegetable crops rapidly adopted this practice soon thereafter. As a
result, it was now possible to farm intensively without having to rotate into less intensive, lower
profit cropping systems for several seasons. In a subtropical environment which is conducive to
the rapid build-up of a wide array of economically important soilborne pests, methyl bromide
has proven to be a consistent, effective means of control for these pests.
The importance of methyl bromide as a fumigant and the environmental problems
associated with its use have led to a current critical situation in the Florida agricultural industry.
Because of the success farmers realized in using methyl bromide since the 1960's, little research
has been conducted with regard to the identification and evaluation of alternatives which could
now be used as effective substitutes to methyl bromide. The alternative identified as having the
most potential for succeeding methyl bromide, Vorlex, (USDA, NAPIAP, 1993) has been
voluntarily removed from the market by its manufacturer (NOR-AM Chemical Company)
because of the expense required to register the compound with the U.S. Environmental
Protection Agency (EPA)., This action makes Vorlex unavailable to farmers and others. Other
chemical and non-chemical alternatives have been identified, but those alternatives are not as
economically effective as methyl bromide in controlling the broad spectrum of pests that can
affect Florida growers.
Recently a USDA NAPIAP (1993) report estimated the impact of removing of methyl
bromide from agricultural use. That study suggested that removal of methyl bromide would
result in an economic loss of approximately $850 million to $1 billion to U.S. agriculture,
depending on whether Vorlex was available as a substitute. Another $500 million loss would
be imposed on imported items that could not use methyl bromide for quarantine treatment. Food
products produced in the U.S. that would be impacted the most included fresh market tomatoes
($160 million with Vorlex/ $340 million without), peppers ($130 million), strawberries ($110
million), cucumbers ($72 million), melons ($29 million), fresh citrus ($25 million), and eggplant
($12 million). The only other food item impacted by more than $1 million dollars was grapes
($3 million).
The products identified in this report are some of the leading agricultural products grown
in Florida. Florida grew 134,550 acres of these items (excluding citrus) which sold for a total
shipping point value of more than $1 billion in the 1992/93 season (Table 1.1). Fresh citrus
sales amounted to an another approximately $600 million.
Table 1.1. Acreage and value of selected fruits and vegetables grown in Florida, 1992/93.
Commodity Acres Value ($1,000)
Cucumber 15,800 65,699
Eggplant 2,150 13,568
Peppers 21,100 179,383
Tomatoes 48,400 626,048
Strawberries 5,100 102,724
Watermelons 42,000 66,600
Total 134,550 1,054,022
Source: FASS, Florida Vegetable Summary 1992-1993.
Because the food crops showing the potential for the most impact from the removal of
methyl bromide are also some of the same crops which are important to Florida, the issue of
removing methyl bromide is especially important to Florida. The primary objective of this
report is the estimation of the economic impact of the removal of methyl bromide on the Florida
agricultural sector and consequently on the economy of the State of Florida.
Organization of this Report
This report is organized to first (Section 2) provide a historical background on the
development and use of methyl bromide in the Florida fresh produce industry. Alternative
chemical and non-chemical production systems that do not use methyl bromide are presented in
Section 3. A discussion of the crops that are important to Florida that use methyl bromide
follows (Section 4) with a presentation of production practices used for each crop. Finally, the
economic consequences of a methyl bromide ban are estimated and presented (Section 5) and
conclusions are drawn from the analysis (Section 6). References and appendices that support
the analyses follow.
SECTION 2
THE EVOLUTION AND USE OF METHYL BROMIDE IN THE
VEGETABLE AND CITRUS INDUSTRIES
Methyl bromide is marketed as a broad spectrum pesticide that acts as an insecticide,
nematicide, herbicide, and fungicide when used in the fumigation of soils (Noling and Overman,
1988). The chemical plays an important role when used as a preplant fumigant which reduces
soilborne pest populations and enables continued cropping of the same land year after year. It
is also used as a fumigant in greenhouses, transplant beds, and potting soils. Methyl bromide
is also used as an acaricide and rodenticide in the treatment of nondwelling space and packaged
materials. The intended purpose for the chemical dictates which formulation of the compound
is used (refer to appendix A for examples of various formulations of methyl bromide, their
restricted uses, and their listed items of control). Methyl bromide is injected into soil as a
liquid, however, once in the soil the chemical converts to a gas moving through open soil pore
spaces (Noling, 1993b). This chemical is registered as a restricted use pesticide due to its acute
toxicity (refer to Table 2.1 for properties of methyl bromide).
Methyl bromide is produced by both natural and man-made processes (IFAS-Chemically
Speaking, April, 1992). The ocean is reported to be the primary source of naturally-made
methyl bromide (Sze and Ko, 1991). Man-made methyl bromide is a product derived from the
treatment of brine, which is pumped from underground sources, such as natural brine or oil field
brines. Processing methods require that the brine be treated with chemicals or undergo heat
reaction to obtain bromine. Bromine is then used to produce methyl bromide (Kent, 1974).
Table 2.1 Physical and chemical properties of methyl bromide
COMMON SYNONYMS:
Bromomethane
M-B-C Fumigant
Embafume
Monobromomethane
FORMULA: CH3Br
MOLECULAR WEIGHT: 94.95
BOILING POINT AT 1 atm: 38.5F = 3.60C = 276.8K
FREEZING POINT: -135F = -93*C = 180k
CRITICAL TEMPERATURES: 376*F = 191 C = 464k
SPECIFIC GRAVITY: 1.68 at 20*C (liquid)
LIQUID SURFACE TENSION: 24.5 dynes/cm = 0.0245 N/m at 15C
VAPOR (GAS) SPECIFIC GRAVITY: 3.3
RATIO OF SPECIFIC HEATS OF VAPOR (GAS): 1.247
LATENT HEAT OF VAPORIZATION: 108 Btu/lb = 59.7 cal/g =
2.50 x 105 J/kg
HEAT OF COMBUSTION: -3188 Btu/lb = -1771cal/g = 74.5 x 105 J/kg
Source: Weiss (1986)
The chemical is manufactured and distributed in the United States, Israel, United Kingdom,
Ireland, Germany, Greece, Yugoslavia, The Netherlands, Spain, Italy, Japan and France.
Methyl bromide is sold in various formulations. These can range from 100% methyl
bromide to a mixed formulations with various proportions of chloropicrin. Due to the odorless
characteristic of methyl bromide, low concentrations of chloropicrin (2 percent) are used as a
marker for detection of escaping methyl bromide fumes (Noling, 1993b). Combined with methyl
bromide, chloropicrin at higher concentrations (such as 33%) serves to enhance fungicidal
activity to aide in the control of soilborne diseases.
When used for treatment of grain storage structures, buildings, ships, cargos, and other
listed structures, methyl bromide is effective as an acaricide and rodenticide. Some of the pests
controlled include granary weevils, cockroaches, and beetles. When the chemical is used in crop
production, it is considered a nematicide, fungicide, insecticide and herbicide. Important
nematodes controlled by methyl bromide include root knot and stubby root nematode (Overman
and Jones, 1980). Examples of diseases that methyl bromide controls are Fusarium,
Verticillium, Rhizoctonia and Pythium. Insects controlled include wireworm and grubs. As a
herbicide, methyl bromide is important in the control of many different weeds such as nutsedge,
pigweed and nightshade.
Historical Overview
Development and Use of the Chemical
"Old land disease", a well documented phenomenon in tomato production, is caused by
the increase in pests such as weeds, nematodes, and plant pathogens due to continuous mono-
cropping of the same land year after year. The population of pests unique to these crops builds
up in the soil over a period of time. When additional land is available, farmers can rotate to
7
other fields that have not been used for two or three years, thus reducing the incidence of those
pests that negatively affect the crop (Bewick, 1989).
Due to increased competition in Florida for agricultural land by urban development and
environmental pressures, increased land prices and decreased land availability have resulted in
farmers searching for alternative methods of pests control (Bewick, 1989). According to
Johnson and Feldmesser (1987), the first use of a fumigant may have been as early as 1872
where experiments proved the efficacy of carbon disulfide as a nematicide. Carbon disulfide
was used in grape production in France, however, it was discontinued due to the development
of pest resistant rootstocks. Chloropicrin was first tested as a soil fumigant in 1919. Research
was then initiated in California and Hawaii. Later it was used as a soil fumigant in pineapple
production in Hawaii. Large quantities of chloropicrin were made available by the United States
government and were targeted for use in seed beds, greenhouses, and specialty crops. When
supplies diminished, commercial use of this chemical decreased.
A marked increase in research on the use and efficacy of soil sterilants was conducted
during the 1950's. During this time, it was found that methyl bromide and chloropicrin gave
the most effective, consistent control of soilborne pathogens (Williamson et. al. 1955).
Research on application methods during the 1960's found that the use of vinyl or
polyethylene films, applied after soil injection of methyl bromide, increased pest control
efficacy. In 1965, Geraldson et al. (1965) introduced the raised bed, methyl bromide, plastic
mulch culture to Florida tomato producers (Bewick, 1989). The use of plastic mulch also
proved to reduce leaching of fertilizers, to retain soil moisture and to increase weed control over
a longer period of time (Martinkovic and Nesheim, 1993). However, system complexity and
the time and expense involved in field removal of plastic mulch resulted in slow adoption of this
technique during the early 1960's.
The 1970's saw a dramatic increase in the use of the whole systems approach (plastic
mulch and fumigation). A majority of the tomato producers in Florida began using either plastic
mulch or a combination of plastics and fumigation (Bewick, 1989).
"The systems approach was developed for tomato production in south Florida, but
by 1978 it had become an integral part of tomato production in every part of the
state. By 1978, 81% of tomato fields were mulched and 64% of tomato fields
were fumigated. Of those fields that were fumigated, 94% were mulched. Six
soil fumigants most frequently used were: methyl bromide (67% methyl bromide
+ 33% chloropicrin), Vorlex, Vapam, Telone, EDB and DBCP. Of these, the
first three are broad spectrum, and the last three are more specifically
nematicides" (Bewick, 1989 p. 66).
Of the six soil fumigants listed, methyl bromide, Vapam and Telone are the only remaining
chemicals currently available.
Methyl Bromide in the Soil
The chemical reactions of methyl bromide (MB) occurring in the soil are important to
understanding the effectiveness of methyl bromide. As a soil fumigate methyl bromide is
applied as a liquid via tractor drawn chisels or shanks six to eight inches deep in the soil. Due
to its high vapor pressure, it volatilizes rapidly and moves through the soil by mass flow and
then by diffusion (Munnecke and Gundy, 1979). Soil movement of gaseous phase methyl
bromide is specifically affected by soil moisture content. Methyl bromide follows a path of least
resistance. If soil moisture is too low, unobstructed air passages will allow methyl bromide to
rapidly diffuse out of the soil and be lost to the atmosphere. If the soil is too wet, movement
of the fumigant through the soil pores will be blocked and result in reduced effectiveness, due
to lack of movement and dilution of the chemical by the presence of water (Munnecke and Van
Grundy, 1979).
Soil type has also been found to influence the effectiveness of soil fumigation uses of
methyl bromide. Munnecke and Gundy (1979) stated that the more coarse and less compact the
soil, the more effective the fumigant is. Goring (1967) found that clays can absorb fumigants,
however, organic matter was implicated as the major source of absorption in the soil. Thus,
without an increase in application rate, high levels of organic matter can negatively influence
the effects of fumigation (Munnecke and Gundy, 1979).
Soil moisture, as it affects organisms in the soil, is an important factor that influences
a fumigant's effectiveness. Munnecke, et al. (1959) found that at higher levels of relative
humidity, there was increased uptake of methyl bromide into the spores of Alternaria solan
resulting in enhanced efficacy. In other studies, temperature was demonstrated influence to the
effectiveness of fumigants. Munnecke and Bricker (1978) and Kenaga (1961) found that when
methyl bromide is applied under warmer temperatures, there was an observed increase in
effectiveness.
Overall, plants have been observed to grow better in soils that have been fumigated.
Improved plant growth is due to the reduction in soilborne pest populations and/or disease
pressures, such as fungal pathogens, insects, nematodes and weeds. Exceptions, however, do
occur where plants do not produce or grow well in fumigated soils (Munnecke and Gundy,
1979). In some cases, poor growth responses occur due to reduced mycorrhizal propagule levels
in soil. Mycorrhizae are important in the uptake of some elements such as phosphorous. This
problem was especially prominent in citrus seed beds, where plants appeared chlorotic and
stunted (Tucker and Anderson, 1972). Another reason for unfavorable growth response in some
plants to methyl bromide fumigation is the accumulation of bromide ions in soil (Gentle et al.,
1989). Accumulation of these ions can often be corrected by leaching via irrigation.
Methyl Bromide as a Potential Contributor to Ozone Depletion
The ozone is a layer of atmosphere located approximately 9-21 miles from the surface
of the earth. This layer is important in reflecting ultraviolet rays and reducing the loss of heat
from the earth (Villee et al., 1989). There are several chemicals that have been implicated in
the possible destruction of ozone, one of which is methyl bromide.
There is considerable uncertainty and controversy associated with the identification of
sources of atmospheric bromine compounds. There are several reasons for uncertainty
associated with estimates derived from the calculations of atmospheric bromine compounds,
including the calibration of measurements, identification of sources and sinks, and the inter-
relationship between removal of atmospheric methyl bromide and contributions from known and
unknown sources (Watson and Albritton, 1991a).
Both natural and anthropogenic sources have been implicated as significant contributors
of methyl bromide in the atmosphere. The contributions of various sources of methyl bromide
to total atmospheric concentrations have not been clearly characterized, however, anthropogenic
sources have been implicated (Watson and Albritton, 1991a). Based on recent estimates,
approximately half of the total methyl bromide used for soil fumigation is thought to find its way
into the upper atmosphere. This equates to an estimated 30,000 metric tons per year
(Chemically Speaking, 1992b). Methyl bromide is also produced by natural means, and there
is evidence implicating the oceans as a major contributor to stratospheric concentrations of
methyl bromide (Sze and Ko, 1991).
Ozone depletion potential (ODP) is a factor which determines how much a chemical
contributes to the depletion of the ozone. As a result of the U.S. Clean Air Act of 1990, a
chemical with an ODP of 0.2 or higher must be phased out of production and use by the year
2000 (Chemically Speaking, 1992b). Based on knowledge about removal of methyl bromide
from the atmosphere, the atmospheric life expectancy of methyl bromide has been calculated to
be 1.6 years, with an uncertainty factor of about 4 (Sze and Ko, 1991).
"Methyl bromide emissions from fumigation application may have accounted for
1/10 to 1/20 of the current global ozone loss, according to the modeling
calculations discussed at an international science workshop in Washington, D.C.
convened at UNEP's request" (Chemically Speaking, 1992b).
Legal Developments Surrounding Methyl Bromide
The Clean Air Act of 1990 (CAA) is a U.S. federal law, whose primary objective is to
maintain and to enhance the quality of the earth's atmosphere. Title VI of the CAA, called the
"Stratospheric Ozone Protection", lists ozone-depleting substances in either Class I or Class II.
If the substance is classified as Class I, then its ozone depletion factor is greater than 0.2, and
the substance will be required to be phased out by the year 2000. However, if the substance
falls under Class II, then it has a ozone depletion factor less than 0.2 and will be required to be
phased out by the year 2015 or 2030 depending on the situation.
The Clean Air Act allows anyone to petition the Environmental Protection Agency (EPA)
in order to list a substance to be classified as a ozone depletor (EPA, 1993). After being
petitioned, the EPA is required to respond to the petition within 180 days. There are certain
exemptions for special cases of known ozone depletors, however the specifications under which
methyl bromide would qualify are unclear.
On December 3, 1991 the Natural Resource Defense Council (NRDC), the Environmental
Defense Fund (EDF) and the Friends of the Earth (FOE) petitioned the EPA requesting that EPA
add methyl bromide to the list of class I ozone depletor substances, reduce production of methyl
bromide by fifty percent by 1992 and accelerate phaseout of methyl bromide by January 1, 1993.
"The petition also requested that EPA order this accelerated phaseout of
methyl bromide based on the (EPA) Administrator's emergency powers
under section 303 of the (Clean Air) Act to protect public health or
welfare or the environment" (EPA, 1993 p. 15030).
The Methyl Bromide Working Group is an industry group comprised of the three major
methyl bromide manufacturers. The Methyl Bromide Working Group responded to this petition
by submitting two letters to the EPA Administrator regarding the addition of methyl bromide
to the list of ozone-depleting substances. The first letter emphasized the lack of evidence
implicating anthropogenic sources of methyl bromide in the destruction of the ozone and
maintained that this lack of evidence does not warrant emergency action by the Agency under
section 303. The second letter called for the denial of the petition again citing the scientific
uncertainty of the impact of anthropogenic sources of methyl bromide on the atmosphere (EPA,
1993).
At the fourth meeting of the Montreal Protocol, an international agreement between
member nations to oversee the manufacturing and trade of ozone depleting substances, members
agreed to: (1) amend the Protocol to add methyl bromide to the list of potential ozone depletors
as a controlled substance, (2) adopt an Ozone Depletion Potential (ODP) of 0.7 for methyl
bromide, and (3) freeze its production (with exemptions for quarantine and pre-shipment use)
at 1991 levels beginning in 1995.
"The Parties adopted the recent scientific assessment of 0.7 for the ODP,
acknowledging this as the best estimate despite the uncertainties related to this
estimate" (EPA, 1993 p. 15030).
This amendment was to become effective January 1, 1994, if twenty parties (countries)
ratified the amendments. However, if twenty parties had not ratified the amendments by the
deadline, the amendments were to enter into force ninety days after the twentieth party ratified
the amendments (EPA, 1993).
In response to the aforementioned petition filed by the Methyl Bromide Working Group,
the EPA rejected the phaseout schedule proposed by NRDC, FOE, and EDF. The EPA
indicated that, because of limited information regarding possible substitutes for the chemical
methyl bromide, the most stringent schedule it can propose includes a production and
consumptive freeze at 1991 baseline levels beginning January 1, 1994, along with a total
phaseout by January 1, 2001.
The EPA announced on the 19th of January, 1993, a proposal to phase out or limit
production and use of chemicals believed to be involved in stratospheric ozone depletion. This
proposal would apply to chemicals produced domestically and imported. Companies may
continue use through available supplies or recycling after the deadline, however, U.S. companies
may produce above levels set by the EPA in order to supply the essential domestic requirements
of developing countries. Developing countries may continue use of chemicals until the year
2010 (Chemically Speaking, 1993).
Methyl Bromide and Safety/Health Concerns
Methyl bromide is listed as a restricted use pesticide due to acute toxicity. According
to the specimen label for methyl bromide, it is for retail sale to, and use only by, Certified
Applicators, or persons under their direct supervision, and only for those uses covered by the
Certified Applicator's certification. The chemical is a gas which is colorless, tasteless, and
odorless unless in high concentrations. The chemical can be applied as a liquid, however at
room temperature, the chemical converts into a gas which can be inhaled and result in
respiratory problems, which is considered to be the most common and serious injury associated
with methyl bromide. Symptoms associated with methyl bromide may not occur for several
hours or days because the chemical is not found to be irritating to the eyes or the upper
respiratory tract, unless substantial amounts are inhaled into the lungs. Inhaling substantial
amounts can lead to irritation of the cells lining the lungs which can result in pulmonary edema
(fluid in the lungs), sometimes leading to death (Noling, 1993b). Methyl bromide is not as
effectively absorbed through the skin, however it can cause skin blisters and enter the circulatory
system through absorption of the skin. A range of 8,600 to 60,000 parts per million (ppm) have
been found to be fatal in humans (Noling 1993b). Therefore, threshold concentrations have been
established as a safety guideline prior to entering into a treated area. According to the specimen
label, if there are amounts of 5 ppm or greater present in the air, then entry into the treated
region should be delayed for 48 hours.
Chloropicrin can be used at low concentrations as an odorant in conjunction with methyl
bromide for detection of escaping fumes of methyl bromide. Chloropicrin is an irritant to the
eyes and respiratory tract and allows detection prior to inhalation of substantial quantities of the
chemical. It has been recommended that chloropicrin (not less than 2%) be used in conjunction
with methyl bromide for detection of atmospheric methyl bromide (Noling, 1993b).
Application of Methyl Bromide as a Soil Fumigant
In preparing a field for subsequent use of methyl bromide, plowing and disking should
be performed to turn under old crop residue in order to reduce detrimental soil organisms and
to allow for decomposition of crop residue. Disking ensures that large clods of soil are broken
down and aids in leveling the field for ease of future activities such as bed formation. Bed
formation can be done using a disc hiller or bedding disc. The soil should be analyzed for pH
adjustment and fertilizer requirements (Hochmuth, 1989a). Bed widths generally range from 24
to 36 inches depending on the crop and irrigation type. The height of the bed is approximately
8 inches. The number of beds between irrigation-drainage furrows varies from one to four,
depending on the soil type and drainage capabilities of the land.
Methyl bromide for preplant fumigation is sold in pressurized gas cylinders, in various
formulations with chloropicrin. The chemical is delivered via a positive pressure system using
nitrogen gas for pressure. Methyl bromide is injected into the soil as a liquid to a depth of 8
to 12 inches using tractor drawn chisels or shanks spaced no more than 12 inches apart. The
liquid then vaporizes and diffuses through the soil from the point of injection. One or more
shanks per bed may be required depending on the width of the bed. Rates of application can
range from 100 pounds to over 400 pounds of active ingredient per acre depending on the
purpose and field conditions (for rates of application for methyl bromide, refer to appendix B
for formulation and application rates for a desired crop).
Methyl bromide is used with chloropicrin in various formulations as a preplant soil
fumigant. At low concentrations (up to 2%), chloropicrin is used as a marker for detection of
escaping fumes of methyl bromide. At higher concentrations, such as 33%, chloropicrin is used
as a fungicide (Noling and Overman, 1988). In Florida, two formulations are primarily used:
Brom-O-Gas (98% methyl bromide and 2% chloropicrin) and Terr-O-Gas (67% methyl bromide
and 33% chloropicrin).
Immediately following bed formation, a polyethylene tarp (plastic mulch) must be
applied. This mulch serves to reduce the loss of methyl bromide to the atmosphere as it
vaporizes in addition to other horticultural benefits. In situations where plastic mulch is a
component of the whole-systems approach, the plastic mulch is installed and remains throughout
the life of the crop. There are several types of plastic mulch, depending on the use or purpose
and time of the year installed. Growers may use plastic mulch that is gray, clear, white, black,
or white laminated on black. For example, in the spring, the use of black plastic can raise soil
temperatures to levels which are conducive to young plant growth. However, during the fall,
the soil temperatures are already warm and the use of white plastic is preferred, because white
plastic reflects light, resulting in cooler soil temperatures, as compared to black (Decoteau et
al., 1989).
The thickness of plastic can vary from .25 to 1.5 millimeter or thicker. Thicker plastic
mulches correspond to greater decreases in atmospheric loss of methyl bromide. Other
advantages of plastic mulch include increased weed control, increased moisture retention, and
decreased fertilizer leaching (Hochmuth, 1988a). The width of the plastic mulch can range from
48 inches to up to 72 inches, depending on the equipment used and type of crop planted. In
regions where plastic mulch is used, a grower may plant a second crop on the same field
following the first crop (generally called doubled cropping), thereby using resources that remain
from the first crop. These resources can include residual chemicals including fertilizer,
insecticide, etc., and plastic mulch.
"If properly managed, double cropping can allow a grower to produce a second
crop, with a short turn-around time, with minimum inputs compared to the first
crop" (Hochmuth, 1992, p. 1).
When choosing a second crop, a grower may consider a crop that (1) has a short growing
season, (2) requires low input of fertilizers, and (3) is known to do well on plastic (Hochmuth,
1992). However, the choice is often dictated by market demands and price. Recommendations
for a second crop include vine crops such as watermelon, cucumber, pumpkins, and squash
following primary crops such as strawberry, peppers, or tomatoes.
Cultural practices used in a double cropping system are important. Removal of the first
crop debris, following final harvest of the first crop, is important for reduction of insects and
disease organisms that may be associated with the primary crop. This may be accomplished by
spraying a herbicide chemical to kill the upper portion of the plant or mowing prior to spraying
to enable the chemical to more effectively kill the plant. Some contact herbicides such as
paraquat do not translocate through the plant and kill the root system. In this situation, some
fumigant chemicals can be used to effectively kill the primary crop, including the root system.
Application of fumigant chemicals (labeled for injection) can be done using a drip irrigation
system if this system is already present.
A second crop can be planted by either direct seeding or transplants. Seeding can be
accomplished by hand, however there are several machines available that can cut a hole in the
plastic and install the seed or plug-mix seed combination. Transplants can be installed via hand
or machine (Hochmuth, 1992).
The use of a double-cropping system often requires the application of additional fertilizers
for the second crop. There are several methods that can provide supplemental fertilizers such
as cutting holes in the plastic to apply either liquid or dry fertilizers, applying fertilizers via
irrigation (e.g., drip system) or using a liquid injection wheel (Hochmuth, 1992).
A double cropping system of pepper and cucumber production in Palm Beach County,
Florida is common. The pepper crop is considered the primary crop and is generally produced
using full-bed plastic mulch with seepage irrigation. This system generally requires that all soil
additives such as fumigants and fertilizers be added prior to application of plastic mulch. If the
plastic mulch from the first crop is in satisfactory condition, it is often re-used for a second crop
of cucumbers. It should be recognized that methyl bromide is not reapplied to the second crop.
The advantages of planting a second crop are that it (a) helps provide additional returns to fixed
costs beyond the variable cost of producing the second crop (e.g., land rent) and (b) re-uses
plastic mulch and other inputs (i.e., fumigant fertilizers, chemicals, and irrigation systems) that
would otherwise need to be applied if not present from the first crop.
SECTION 3
CHEMICAL AND NON-CHEMICAL ALTERNATIVES TO METHYL BROMIDE USE
In this section possible alternatives to methyl bromide are discussed. It is important to
remember that some of these alternatives should not be considered viable alternatives to methyl
bromide at the present time, but rather construed as researchable alternatives. It is also
important to remember that some of these methods may take several years to reduce pest
populations to levels that enable the grower to produce crops that may be comparable to yields
experienced when methyl bromide is used.
There are numerous fumigant and non-fumigant alternatives that include the use of
chemicals, cultural practices, biological controls, heat, and the concept of integrated pest
management. Currently, some of these techniques are being evaluated and hold promise of
being viable alternatives. However, none of the alternatives identified currently provides the
efficacy exhibited by methyl bromide.
The first category of alternatives includes fumigant chemicals Basamid, Vorlex, Vapam,
Telone, Chloropicrin, and reduced amounts of methyl bromide. The second category includes
non-chemical alternatives including crop rotation, cover crops, heat treatment, flooding,
biological controls, host plant resistance, and fallow land.
Chemical Alternatives to Methyl Bromide
Basamid-Granular
Basamid-Granular is classified as a soil sterilant containing the active ingredient
dazomet. In some studies, it has been shown to be effective in the control of fungus, weeds,
nematodes, and soil insects. Basamid has been used in Europe for over 20 years, however this
chemical has only limited EPA registered uses in the United States. According to McElroy
(1985), it is used for preplant control of most weeds, nematodes, and soil fungi in tobacco
seedbeds, forest tree seedbeds, and ornamental propagating beds (for a brief review of
information derived from the specimen label for Basamid-Granular, refer to Appendix C-l).
Upon application to the soil, dazomet reacts with water and chemical components in the
soil to produce a sterilizing agent called methylisothiocyanate (MITC) (Neumann et al., 1983).
When dazomet contacts water in the soil, the chemical breaks down to MITC, resulting in the
formation of a gas which then diffuses throughout soil. Most recommended uses suggest that
application be done several months prior to planting to ensure the chemical is not present at time
of planting. Otherwise, some of the chemical may still be residual in soil, resulting in crop
damage. This is often considered a limiting factor due to time constraints for planting crops.
To be effective, Basamid-Granular must be soil incorporated to ensure uniform soil distribution.
The advantages of dazomet include its ease of application which can be done in one step
and its low environmental impact with no substantial volatile compounds being released into the
atmosphere. Also, application of the granular form is considered low risk to applicators due to
the nature of the chemical being inert until activated by water in soil. Another advantage is that
the control exhibited by this chemical is considered broad in spectrum (O'Brian and
VanBruggen, 1990).
Some of the disadvantages are that the chemical is less predictable, and it can result in
spotty effectiveness if it is not incorporated well and distributed evenly throughout the soil.
Planting before the soil is properly aerated can result in crop phytoxicity.
Vorlex
Vorlex is a restricted use pesticide that can be applied as a preplant soil fumigant, for
both the field and greenhouse, for control of soilborne diseases, nematodes, weeds and insects.
Vorlex is comprised of two active ingredients, 1,3-dichloropropene and methylisothiocyanate or
MITC (Vorlex specimen label). When applied properly, Vorlex vaporizes and moves through
the soil by diffusion. The Vorlex specimen label states that it is cleared for use in all vegetables
and strawberry production (for a brief review of information derived from the specimen label
for Vorlex, refer to Appendix C-2).
Tarping the soil (plastic mulch) is not required but it can be considered an advantage
when using Vorlex as a fumigant. Increased efficacy is exhibited when plastic mulch is used.
Vorlex. was indicated as being the next best alternative to methyl bromide due to increased
control of diseases, weeds, nematodes, and insects as compared to other alternatives (USDA,
NAPIAP 1993). However, Vorlex still does not exhibit the kind of control demonstrated by
methyl bromide. Another disadvantage of Vorlex is that it requires a longer waiting period prior
to entering the field, and therefore may interfere with crop planting dates.
The manufacturer of Vorlex (NOR-AM Chemical Company) requested a voluntary
removal of Vorlex from registration with the EPA in November, 1991. The EPA responded in
August, 1992, with approval of cancellation for registration of Vorlex. Vorlex was classified
by the EPA as a List B re-registration product which includes products that are used in the
production of food. This type of classification requires numerous, costly studies for EPA
registration. The research studies for Vorlex were considered old enough for the EPA to require
new studies. The manufacturer examined the market share of Vorlex and the cost of new studies
in order to conform to EPA standards, and concluded that it was not economically in their best
interest to continue sale and distribution in the United States. Another factor that played a role
in their decision to withdraw registration of Vorlex is that the chemical comprises only a small
portion of their business. At the time of the announcement of removal of Vorlex, several
companies approached the manufacturer to take over the division for Vorlex sale and
distribution, however, after evaluation of the situation regarding the economics and the cost of
new studies, these companies chose not to pursue the opportunity.
The manufacturer requested that EPA consider (a) registration of Vorlex as a minor use
chemical and (b) possible flexibility regarding the studies required for re-registration. EPA
responded by recommending that Vorlex be viewed as a new product (since it had been
voluntarily removed from registration) requiring approval by the registration division of EPA
instead of consideration by the re-registration division. If the EPA were agreeable to flexibility
in registration requirements and the economic situation favored the production of Vorlex (i.e.,
removal of methyl bromide from the market), the manufacturer might consider the possibility
of appropriate testing required for registration of Vorlex as a minor use product.
Vapam
Metham sodium, also known as Vapam, can be applied to the soil as a preplant, soil
fumigant for control of soilborne pathogens such as nematodes, weeds, fungi and insects.
Metham sodium is considered a water soluble, alkaline chemical. When combined with water,
which is acidic in comparison with metham sodium, the chemical becomes unstable and
decomposes to its active form of methylisothiocyanate (MITC). Once the chemical is placed in
the soil, MITC will volatilize from a liquid to a gaseous phase which enables it to flow
throughout the pores of the soil. However, MITC has a high affinity for the liquid phase;
therefore, the chemical does not move as readily through the soil as does methyl bromide
(Noling, 1991).
There are several factors that influence the efficacy of Vapam when applied to the soil.
Soil temperature and moisture play an important role in the conversion of metham sodium to
MITC. If the soil temperatures are too high and soil moisture is low, conversion is increased,
and the chemical may diffuse out of the soil too quickly, not allowing for an accumulation of
the chemical in the soil and effective control. If the soils are too wet and temperatures are cool,
the rate of decomposition to MITC is decreased. Under this condition the chemical cannot
accumulate in the soil to levels that are needed for effective control. If temperatures are low
or excessive water is applied after application of the chemical, the MITC may remain in the soils
longer than desired and result in delayed planting (Gerstl et al., 1977).
Several studies have also shown that soil type influences available MITC. Gerstl et al.
(1977) found that soils high in organic matter or clay incurred a delay in the amount of MITC
available to diffuse throughout the soil. Thus, for effective results, clay soils or soils high in
organic matter can require higher initial concentrations of Vapam.
For field application, Vapam can be applied using a chisel or an irrigation system. For
application via chisel, it is recommended that soil temperatures at 3 inches in depth are in the
range of 60 to 90 degrees Fahrenheit. Soil moisture should be approximately 50 to 80% of field
capacity. Rates of application need to be adjusted depending on environmental and field
conditions (Noling, 1993d). Vapam has been commonly applied via chisel injection, placed
approximately 6 inches apart. For effective results, one must treat 50% of the bed, which would
require two chisels per bed.
Due to the water solubility of Vapam, it is also labelled for application through overhead
irrigation. A study conducted by Sumner (1988) found increased efficacy against Rhizoctonia
soani and Pythium sp. when metham sodium was applied via overhead irrigation, as compared
to chisel application for a fall crop of turnip, kale, mustard and collard. However, reduced
control of root diseases and decreased plant stand in the spring crops of snap bean, okra,
cucumber, tomato, and pepper were also observed. Increasing application rates resulted in
improved control of soilborne diseases such as Pythium WS., Fusarium Wp. and saprophytic
fungi.
Chemical application of Vapam via drip irrigation is a form of chemigation (Haman et.
al., 1990). This method requires that the metham sodium be premixed prior to injection and
continuously supplied at specific locations for a period of time. There are several factors that
influence chemigation for pest control, including emitter spacing, type and length of irrigation
tubing, openings in the plastic which can allow diffusion into the atmosphere, and
soil/environmental conditions (Noling, 1993d). Overman et al., (1987) compared methyl
bromide (67%) plus chloropicrin (33%) injected via shanks 30 cm apart prior to plastic
application, to metham sodium injected via one drip line per bed. This study was conducted for
three seasons and found that yields for 'Sunny' tomato variety increased for both treatments,
however, by the third season yields were collected only from the methyl bromide-chloropicrin
plot. The area treated with metham sodium was desiccated with Fusarium wilt and root knot
nematode.
One advantage of Vapam is that it can be applied through an irrigation system.
However, soil temperature and moisture can dramatically influence the effectiveness of this
chemical. In addition, another major disadvantage of Vapam is the waiting period prior to
entering the treated area, which is dependent on environmental conditions. Planted crops will
incur damage, or be killed, if the chemical is still in the soil at the time of planting (Noling,
1991). Finally, Vapam is not as effective in control of diseases and nematodes when compared
to methyl bromide (Overman et al., 1987). Erratic or reduced control by Vapam is a common
occurrence, and more material may be required to approach desirable levels of control. As a
result of increased amounts of Vapam applied for effective control, the question arises as to how
much leaches through the soil and enters the water table (for a brief review of information
derived from the specimen label for Vapam, refer to Appendix C-3).
Telone II and Telone C-17
Telone II is a restricted use pesticide, which contains the active ingredient 1,3-
dichloropropene. This chemical can be used in crop production of eggplant, tomato, pepper,
strawberry, melon, cucumber, and citrus, as well as other crops. Telone C-17 is a multi-
purpose, preplant soil fumigant containing 77.9% 1,3 dichloropropene and 16.5% chloropicrin.
This chemical can be used for control of nematodes, soilborne fungi, and weeds, for some high
value field and vegetable crops (Dunn and Noling, 1993). The chloropicrin (16.5%) controls
some soilborne fungi, but not Sclerotonia or Rhizoctonia species.
Information regarding water contamination remains unclear. The manufacturer suspended
sale of Telone in south Florida prior to fall 1993, although it could legally still be used in south
Florida. Telone is currently sold and distributed in south Florida on a limited basis, and it is
simultaneously undergoing research for information regarding questions about safety and
contamination.
Environmental conditions are important for effective control with Telone. Youngson
(1982) found that Telone II was more readily leached from sandy soils than loam soils. Turner
(1970) discussed the influence of air space in the soil upon the effectiveness of Telone II. As
water is added to the soil, the amount of air space is decreased. This resulted in an observed
decrease in efficacy for nematode control, due to the decreased movement of the fumigant
through the pore space. It is advisable to apply the chemical during the fall, when drier
conditions exist, which allows the chemical to diffuse through the soil for increased efficacy.
This can be a limiting factor when considering planting dates and delayed use of the field (for
a brief review of information derived from the specimen labels for Telone II and Telone C-17,
refer to Appendices C-4 and C-5).
Chloropicrin
Chloropicrin is mixed in varying formulations with methyl bromide. At low
concentrations this chemical is primarily used as a marker for escaping fumes of methyl
bromide. Use of this chemical by itself, as a soil fumigant, is cost prohibitive. However, due
to its fungicidal properties, chloropicrin when mixed with methyl bromide at higher
concentrations is effective in the control of soilborne diseases. This chemical is not considered
to be as effective as a herbicide, nematicide, or insecticide as compared to methyl bromide
(Noling and Overman, 1988) (for a brief tabular review of information derived from the
specimen label for Chloropicrin, refer to Appendix Table D).
Non-Chemical Alternatives
Reduced Use of Methyl Bromide
In order to reduce emissions of methyl bromide into the atmosphere several alternatives
are being studied. One possible alternative could be reduction of the crop bed size: from 32 to
36 inches in width to 24 inches in width. The result is less chemical required to treat the bed
area. Preliminary studies have shown a 33% reduction in use of methyl bromide using this
method. Another alternative is to increase the amount of chloropicrin as a percent of the total
formulation so that less methyl bromide is used. Finally, the use of thicker or impermeable
plastics for bed covers can reduce the loss of methyl bromide by as much as 75%.
Constructed Barriers
Studies are currently in progress to evaluate the use of a barrier-type construction to
protect plants from nematodes. A sleeve inserted into the ground surrounding the plant can
provide a barrier against nematodes migrating into the root zone. However, a study examining
this method found that nematodes moved vertically into the rootzone from below, casting doubt
on its viability for controlling nematodes. Further research is being done using a V shaped
barrier to examine movement of nematodes into the root zone.
Crop Rotation
Crop rotation can be defined as "diversifying crops over time" and can be useful in
reducing the incidence of pests such as nematodes, pathogens and weeds. This method is
considered a viable alternative, depending on the pests and situation at the time of consideration.
For example, biological requirements of the pests and agronomic and economic implications may
dictate whether this is a feasible alternative (Flint and Roberts, 1988). The advantages of crop
rotation include improvement of soil texture, conservation of water, and improved weed control.
These advantages result because of rotation into crops with different cultural practices than those
practiced for the prior crop (Flint and Roberts, 1988).
In the state of Florida however, rotation to a selected crop in order to reduce populations
of certain pests may result in an increase in numbers of other pests such as nematodes and/or
fungi (Rhoades et al., 1966). Another disadvantage of this method is that it may take several
years of rotation to reduce populations to acceptable levels.
Hot Water or Steam
Byars and Gilbert (1920) found that heat treatment of potting soils or greenhouse soils
killed root knot nematodes and fungi such as Rhizoctonia and Pythium. A researchable
alternative to methyl bromide is an extension of that treatment whereby hot water treatment of
the field or injecting hot water into the soil via shanks is done to control some soilborne pests
such as nematodes. A machine has been developed that kills weeds and other potentially
dangerous pests by scalding. However, the machine is prohibitively expensive at the present
time (Ulrich, 1993).
Steam sterilization of potting or greenhouse soils has also been found to be effective and
is used extensively to treat medium used to grow transplants for vegetable production. The use
of steam sterilization for field application is considered cost prohibitive and dangerous for
workers involved. Cost of application can exceed $2500 per acre. This method is not
considered as effective against weeds and nematodes as methyl bromide.
Solarization
Solarization requires the trapping of heat under a transparent polyethylene tarp, to raise
soil temperatures high enough to prove lethal to plant pathogens and pests in the soil (Devay,
1991b). Soil solarization has been found to be effective in the control of nematodes (Lamberti
and Greco, 1991) and (Satour et al., 1991) weeds (Abu-Imailech, 1991), and fungi and bacteria
(Devay, 1991a). However, for effective control, this method is dependent on several factors,
such as temperature and moisture.
This method is most effective when practiced during the warmest part of the year, with
bright sunny days for 4 to 8 weeks raising soil temperatures to lethal levels for control of
nematodes (Heald, 1987). Soil moisture is important in this treatment for maximum heat
transfer to soilbore organisms and reduction of evaporative heat loss, providing a greenhouse
effect (Noling, 1992). Other factors that influence the effectiveness of solarization include air
temperature, length of day, sunlight intensity, and thickness and light transmittance of the plastic
being used (Devay, 1991b).
In Florida however, the hottest part of the year experiences cloud cover with heavy
rainfall. Thus, water collects on the surface of the plastic, resulting in heating the water instead
of the soil. Another problem with solarization as a non-chemical alternative to methyl bromide
use is that much of the soil is of the sandy type in vegetable producing regions of Florida.
These soils drain well and do not retain moisture, which is required for effective transfer of heat
to soilborne organisms (Noling, 1992). Soil solarization is ineffective in the control of nutsedge,
which is a major weed problem in certain regions of Florida. Other considerations when using
plastic for solarization are the longevity and disposal of the plastic. The integrity of the plastic
is broken down over time by ultraviolet radiation, and the cost to remove and dispose of plastic
can exceed $235 per acre (Noling, 1992). Soil solarization using clear plastic in conjunction
with a biological antagonist (such as an increased population of beneficial microorganisms to
reduce nematode populations) or a registered nematicide, may be an alternative for control of
soilborne pests such as nematodes.
Microwave
Research has been conducted to examine use of microwaves to sterilize the soil. At
10,000 watts it took 280 hours to treat 7,200 linear feet of 8 inches of soil. Soil has a
tremendous buffering capacity and soil moisture becomes a limiting factor when using this
method.
Soil Flooding
Flooding has been found to reduce populations of root knot nematode. Greenhouse tests
showed that one month of flooding, followed by one month of dry period, and finally one more
month of flooding, reduced numbers of root knot nematode (Rhoades et al., 1966). In Florida
however, current permitting requirements and limited water resources impede the use of this
practice.
Soil Amendments
The use of soil amendments is a means of biological control. For example, Rodriguez-
Kabana and Morgan-Jones (1987) examined the use of organic and inorganic materials that
release ammoniacal nitrogen that enables beneficial microorganisms to suppress populations of
nematodes. The release of nitrogen has been found to increase microorganisms that are
considered agnostic to nematodes. However, raising soil populations to desired levels often
resulted in phytotoxic symptoms in plants. Large amounts of nitrogen were required for
effective use of this treatment, and it proved to be cost prohibitive.
Kloepper et al. (1992) looked at the use of rhizobacteria to treat seeds. This study found
that rhizobacteria derived from the roots of antagonistic plants may be beneficial in reducing
populations of phytopathogenic nematodes. The use of soil amendments will require further
research before commercial application of this method could be considered.
Host Plant Resistance
Host plant resistance (HPR) is an alternative that enables the plant to grow and produce,
despite populations of pests. This method identifies genes that confer resistance to a given plant,
and once identified, is introduced into the desired plant. For example, the gene Mi was
identified for resistance to root knot nematode in the wild species of tomato. This gene was then
introduced into varieties of desirable cultivars of tomato (Fassuliotis, 1987). However, the
identified Mi gene is considered heat instable, therefore, in regions of warm temperatures the
resistance to root knot nematode is lost (Roberts, 1992). Genes for resistance have also been
identified for other crops such as sugar beet and beans (Fassuliotis, 1987). Once the gene has
been identified and introduced into the desired cultivar, however, another problem has been that
new virulent races or pathotypes occur, which can overcome the new resistant cultivar
(Fassuliotis, 1987). As these experiments suggest, host plant resistance for use in commercial
operations is limited due to problems associated with identification and transfer of genes to
desired cultivars (Roberts, 1992).
Fallow Land
Many soilborne pests can be controlled by depriving them of suitable plants upon which
to feed (Christie, 1959). However, allowing a parcel of land to remain fallow for a period of
time has several limitations. First, cost to growers may inhibit the option for land to remain
fallow. In addition, when allowing a field to be fallow, introduction of weedy species can
harbor pests and actually negatively affect the reduction of nematodes. Minton and Parker
(1987) found that nematodes were higher in the fallow plots, versus plots that were planted in
rye during the fallow period. It was suggested that weeds that took over the fallow plot may
have been a better host to the nematode than the plot in rye. It has also been found that clean
fallow, such as treatment of a field with herbicides to control weeds, can reduce root knot
nematode. However, this method is not recommended for Florida due to the loss of organic
matter, which may dry and erode (Rhoades et al., 1966). Use of chemicals to control weeds
is much slower in reducing populations of nematodes because the nematodes move deeper into
the soil, and are not subjected to adverse weather conditions (Noling, 1992).
Cover Crops
The use of cover crops has been found to reduce populations of soilbore pests, however
it is dependant on the type of cover crop used. For example, the use of clover was found to be
ineffective as a cover crop due to the inability of the plant to cover the field and inhibit the
growth of other species of weeds that may present a more suitable host.
SECTION 4
COMMODITY PRODUCTION AND PEST CONTROL PRACTICES
Watermelons
Approximately 45,000-60,000 acres of watermelon are planted annually in Florida,
making Florida the leading state in the production of watermelons. During the 1991-92 season,
approximately 53,000 acres were planted of which 45,000 acres were harvested (FASS, 1993).
Varieties grown in Florida include Charleston Gray, Charlee, Crimson Sweet, Jubilee,
Jubilee II, Mirage L.S., Prince Charles, Royal Jubilee and Sangria (Maynard, 1992).
Watermelon harvests begin in April or May progressing north and west and end in July. Some
watermelons are grown in the fall in south and central Florida (Stall and Showalter, No Date).
When practicing double cropping, watermelon is a good crop to follow crops such as
tomato or pepper. Watermelon is only grown on plastic as a second crop in South Florida,
otherwise it is grown on an open bed system with no plastic or methyl bromide. In North
Florida an estimated 3,000 acres of watermelon are grown on plastic as a first crop in order to
hit the early market window. Plastic mulch enables the grower to plant earlier in the season due
to the warming effect upon the soil when using mulch.
Cultural Practices
Watermelon production can occur on a variety of soil types, however, it is not
recommended to plant watermelon on muck soils. In order to improve the effectiveness of
herbicides and fumigants, it is suggested to plow under old crop residue for decomposition of
organic matter. The soil pH should be checked and adjusted as required (Maynard, 1992).
Disking the field can ease future activities, such as bed formation. In areas where standing
water is a problem, it is important to form beds, approximately 3 to 8 inches in height for
drainage. Several machines can shape the beds, such as disc hillers or a bedding disc. A bed
press can be used where plastic is installed. For watermelon production using plastic mulch,
chemicals and fertilizers applied to the soil should be applied prior to the application of the
mulch. The top of the beds should be approximately 20 to 24 inches across and covered with
plastic 48 inches wide (Maynard, 1992).
Watermelons can be planted by direct seed or by using transplants, however, bare root
transplants are not recommended. When using the direct seed method, it is important to place
several seeds together to ensure a good stand. Thinning of seedlings can be performed later.
If plastic mulch is used, direct seeding can be done using the plug-mix method using a plug-mix
planter. If transplants are used, containers or peat pellets should be used in order to maintain
an intact root system for successful transplant of watermelon. There are several machines that
are designed to install transplants (Maynard, 1992). Use of seeds is common, however, some
growers who grow hybrid watermelons on mulch are using transplants. Growers using hybrids
may be more inclined to grow watermelon on mulch.
Application of fertilizer becomes important depending on the method of production
system used including (1) non-mulched with overhead irrigation, (2) full-bed mulch with
overhead irrigation, (3) non-mulched with drip irrigation, and (4) open bed production with drip
irrigation. Fertilizer application methods vary according to the production system.
For non-mulched production with overhead irrigation, it is suggested that all phosphorous
(P), micronutrients, and 25 to 50 percent of required nitrogen (N) and potassium (K) be
incorporated into the bed prior to planting. The remaining N and K can be applied in two
sidedress applications approximately four to six weeks after emergence of seedlings. Any
additional requirements can be applied as needed. Full-bed mulch production with overhead
irrigation requires that all fertilizers are incorporated into the bed prior to application of mulch.
Any additional requirements of nitrogen (N) and potassium (K) can be added by the use of a
liquid fertilizer injection wheel. For watermelons grown as a non-mulched production system
with seepage irrigation, it is recommended to incorporate all of the phosphorus (P) and
micronutrients, and approximately 15 to 20 percent of the nitrogen (N) and potassium (K) into
the bed prior to planting. The application of the remaining N and K should be applied as a
sidedress band along the shoulders of the bed outside of the tips of the vines (Maynard, 1992).
For watermelons grown using drip irrigation, it is recommended to incorporate 20 to 40 percent
of nitrogen (N) and potassium (K) with all phosphorus (P) and micronutrients prior to planting.
Any additional requirements can be applied via the drip irrigation as needed. Insects are used
for pollination in the production of watermelon.
Diseases
Methyl bromide is used as a method of control for several diseases found in watermelon
production, such as damping-off and fusarium wilt.
Damping-off can be caused by Pythium, Fusarium and Rhizoctonia spp. This disease
affects watermelon seedlings, causing necrosis and death of the plant. The soilborne fungi can
invade the plant at or below the soil level.
Cultural practices recommended for control of damping-off include ensuring crop residue
is well turned under or decomposed, avoiding planting in soils that are cool, and using healthy
transplants. Use of treated seeds is also suggested.
Table 4.1 lists non-fumigant chemicals that can be used to control damping-off in
watermelon. Fumigant chemicals such as Vapam or Telone C-17 may also be effective in
control of this soilborne disease.
Table 4.1. Chemicals for the control of damping-off.
Common Name Trade Name
Metalaxyl 2 Subdue G
Metalaxyl 25 Subdue II
Metalaxyl 25.1 Ridomil 2E
NOTE: For rate, use, and application to seed bed and field, refer to pp. 468-469 of the Florida
Plant Disease Control Guide, 1993.
Fusarium wilt, caused by the fungus Fusarium oxysporum f.sp.niveum, infects the root
and stem of a watermelon plant. An overall wilting may result or individual runners may be
affected. Roots may become brown and a soft rot can sometimes develop near the crown
(Maynard, 1992).
Cultural practices used to control fusarium wilt include use of disease free transplants,
removal of or plowing in plant debris after harvest, rotation with a non-susceptible crop,
fumigation, delayed thinning and use of plant resistant varieties such as Charleston Gray,
Crimson Sweet, Dixielee, Jubilee, Sugarlee, and Sweet Princess. Even in resistant varieties,
infestation of the disease can still occur. It is also suggested to avoid old land that has been
planted with watermelon or to have known infestation of fusarium.
There are no chemicals listed for management of fusarium wilt. However, fumigant
chemicals such as Vapam or Telone C-17 may aid in the control of the soilborne disease.
Nematodes
Methyl bromide is used to control several nematodes that pose a threat to watermelon
production, including sting and root knot nematode. However, losses as a result of root knot
are not that common. This may be because plantings usually occur on acreages that have a long
rotation into pasture.
Cultural practices used to control nematodes include crop rotation which can.be used to
decrease populations of root knot nematodes in a given location. For example, corn, sorghum,
bahia grass, bermuda grass and pangola digit grass have been identified in reducing populations
of nematodes. It is also important to ensure complete removal or breakdown of the infested
crop. Cultivation can remove plants that harbor nematodes. Use of plants that are nematode
free and healthy is important in the battle with nematodes.
There are several non-fumigant and fumigant chemicals that are used for control of
nematodes including Vydate L, a non-fumigant, and Telone I or Telone C-17, a fumigant
chemical (for rate and application method, refer to pp. 96-97 of the Florida Nematode Control
Guide, 1993).
Weeds
Several methods have been identified to reduce weed populations including crop
competition, mechanical control, mulching, and use of chemicals. It is recommended to use
several of these methods in combination to obtain effective weed control. Disking, hoeing,
mowing, or cultivation can also be an effective method of weed control. Crop competition can
be a method of control by not only increasing the number of crop plants to effectively compete
against weeds for water and nutrients, but also ensuring a healthy crop population by using good
water and nutrient management practices. The use of plastic mulch in conjunction with fumigant
chemicals can be effective in the control of many weeds. The mulch itself acts as a barrier to
many weeds, with the exception of nutsedge which can grow through the plastic.
Methyl bromide is used as a method of control for weeds found in watermelon
production, such as crab grass, panicum, goosed grass, and lambsquarter. The following is a
list of other chemicals that can be used to control weeds. Bensulide (Prefar) is preplant
incorporated and used for control of germinating grasses. Bensulide + naptalam is applied
preplant or pre-emergence for a wide range of weed control. Diquat (Diquat) can be applied
post-emergence, for burdown of vines after final harvest. Sethoxydim (Poast) is used for post-
emergence control of grass weeds. Paraquat (Gramoxone) is used as a post-emergence contact
for control of all emerged weeds, and it is used in row middles between beds or as a pre-
emergence application. Ethalfluralin (Curbit) is applied pre-emergence & post-emergence, for
control of grasses such as goose grass, crabgrass, fall and Texas panicum, and broadleaf signal
grass. Glyphosate (Roundup) can be used prior to planting for removal of weeds for planting.
Naptalam (Alanap) is applied as a pre-emergence for control of germinating annuals such as
lambsquarter, pigweed, and carpet weed. For post transplant, it is recommended to apply this
chemical immediately after transplant for control of annual weeds. DCPA (Dacthal W-75) is
applied as an early post-emergence (for application rates and comments, refer to pp. 312-316
of the Florida Weed Control Guide, 1993).
Insects
Insects, such as wireworm, may increase in population with the removal of methyl
bromide in watermelon production. Methods of control of wireworm include Diazinon, a non-
fumigant, and Telone II or Telone C-17, a fumigant chemical (Florida Insect Control Guide,
1993).
Trends
Currently, central Florida watermelon growers do not use methyl bromide to any great
extent, due to the ability of growers to rent pasture land that has not been used for watermelon
production for several years. As the use of hybrids increases and availability of land becomes
limited, the practice of using methyl bromide could increase over the next few years.
Tomatoes
The primary areas of tomato production in Florida include Dade County, the East coast,
Palmetto/Ruskin area, Southwest Florida, and West, North and North-Central Florida. Acreage
in production in Florida has varied between 41,000 and 62,000 acres over the last decade.
During the 1991-92 season total state production was estimated at 51,300 acres. Acres planted
by production area are shown in table 4.2. There are many varieties of tomatoes grown in
Florida. Sunny is the leading variety with 51.7% of acreage for the 1991-92 season, followed
40
by Solarset (10.5%), Agriset (9.8%), and Bonita (7.8%). BHN 90, Olympia, Heatwave and
Colonial are used on most of the remaining acreage in production (FASS, 1993).
Table 4.2. Acres of tomatoes planted in Florida by production area for the 1991-92 season.
Production Area Acres
Dade County 5,100
East Coast 6,000
Palmetto/Ruskin 15,400
Southwest Florida 21,200
West, North and North-Central 3,600
Source: FASS, 1993.
Cultural Practices
A field should be plowed and disked to turn under old crop residue in order to reduce
detrimental soil organisms. The soil should be analyzed for any additional additives required,
such as lime for pH adjustment. Then the bed is shaped, fumigated, and fertilized using a bed
disk. If plastic is to be applied, then a bed press is used to apply plastic following the bed disk.
Black plastic is normally used, however, during the early fall when temperatures can still be
relatively warm, growers may use black with a white band over the middle region, gray, or
white to reduce the temperature of the surface of the bed. Some advantages of plastic
include increased weed control, moisture retention, and reduced loss to leaching of fertilizer
(Hochmuth, 1988a).
There are several types of bedding production systems in Florida including (1) non-
mulched tomato, (2) strip mulched tomato, (3) full-bed mulch with seep irrigation, (4) full-bed
mulch with overhead irrigation, or (5) full-bed mulch with drip irrigation.
In non-mulched tomato production, fertilizer is incorporated into the soil and then a band
or strip four to five inches wide of nitrogen (N) and potassium (K) are incorporated along the
edge of the bed. Subsurface or overhead irrigation can be used for application of water.
In strip mulched tomato production, all micronutrients are incorporated into the soil along
with 20% of nitrogen (N) and potassium (K). A band of fertilizer is placed two to three inches
below the surface of the plastic. The strip of plastic is ten to twelve inches wide and is placed
in the center of the bed with tomatoes growing through the hole in the plastic. Overhead or
subsurface irrigation can be used for application of water.
In full-bed mulch systems with seep irrigation, all soil requirements such as fumigants
and fertilizers are added prior to the application of plastics. Any additional application of
fertilizers can be done using an injection wheel. The following is a sequence of operations that
may be used in a full-bed mulch system with seep irrigation. First, land preparation includes
installation of irrigation, drainage system, and pH adjustment. Second, application of fertilizers
includes total micronutrients with phosphorus (P) incorporated along with 10-15% of nitrogen
(N) and potassium (K) added to the soil. Third, formation of bed includes application of mole
cricket bait and herbicides for weed control. Fourth, the remaining fertilizer is applied in a nine
to ten inch band on either side at one to two inches in depth. This step also includes fumigation,
pressing of beds, and application of plastic mulch. To prevent escaping fumes of fumigant, the
edges of the plastic are covered with soil to seal the edges (Hochmuth, 1988a). Fifth, water is
maintained approximately fifteen to eighteen inches below the soil surface to ensure seepage into
the root zone and to maintain moisture. By maintaining a moist environment, a nutritional
concentration gradient exists. This allows the banded nitrogen (N) and potassium (K) to diffuse
into the soil and replace those nutrients already incorporated into the soil. Plastic is extremely
important in maintaining soil moisture, otherwise the nutrients can be lost to leaching by natural
rain, or the soil may dry out and result in evaporative loss of soil moisture (Geraldson, No
Date).
Mulched tomato production with overhead irrigation is similar to a full-bed mulch system
with seep irrigation with the following exceptions. In sandy soils all fertilizers are incorporated
into the soil. In areas with a soluble salt problem, a percentage of fertilizer is incorporated into
the soil and any remaining fertilizer is added as required. Perforated plastic is not required,
since the water that is applied, soaks in at the hole in the plastic and is sufficient to supply plant
needs. Some methods of overhead irrigation include the use of travelling guns, solid set
sprinklers, or center pivot systems. One disadvantage of overhead irrigation is the threat of the
spread of foliar diseases due to increased moisture on the leaves. In rockdale soils perforated
plastics are required due to minimal lateral water movement in the soil. Placement of
superphosphate close to the transplant is also required for uptake because phosphate is considered
immobile in the soil.
A mulched tomato production system with drip irrigation is similar to a full-bed mulch
system with seep irrigation with the exception of the following. Drip irrigation is accomplished
either by tubes or drip tape which is placed approximately four to five inches below the soil
surface prior to the application of plastic. Placement below the soil surface protects the tape
against mice and cricket damage. Drip irrigation enables the grower to apply fertilizer via
irrigation. Total phosphorus (P) and micronutrients, and 20-40% of total nitrogen (N) and
potassium (K) are applied prior to mulch application and planting. The remaining N, K, and
other nutrients required during the life cycle of the plant can be injected using the irrigation
system (Hochmuth, 1988a).
Planting Techniques. There are three techniques that are normally used in planting
tomatoes: direct planting of the seed, bare root transplants or containerized transplants. The
primary method practiced on rockdale soils in Dade County is direct planting of the seed through
the plastic mulch using a plug mix method. This method requires tomato seed, fertilizer, and
water to be mixed with vermiculite and peat. This mixture is allowed to sit for 12 to 48 hours
and enables the seed to imbibe (absorb or to take up) water, thus beginning the germination
process. This mixture is then placed in the field by a plug mix planter machine. When placed
in the field, a machine either burs or cuts a hole in the plastic, then inserts the plug mixture
in the soil. There are usually several seeds per plug, requiring labor to weed out the undesirable
plants after they have grown a few inches. In a bare root transplant method, plants are grown
in fumigated soils with a pH range of 6.0 to 6.5. Once the seedlings have reached a height of
five inches, they are ready to transplant. The transplant soil must be moist when transplanting
for ease of removal, however the soil must not be soaked due to enhanced environment for
detrimental organisms to enter the transplants. Containerized transplants are grown in a multi-
cell or tray pack system. Trays can be styrofoam or plastic, and they must be sterilized prior
to installation of seeds. Transplants are usually raised in a greenhouse to optimize growing
conditions (Hochmuth, 1988a). A large percentage of tomato growers purchase their transplants
for installation.
Staking. Stakes are approximately forty-eight inches in length and are placed in the
ground within the row when plants are approximately two to three weeks old. Plastic twine is
used to tie the plant to the stake and is usually done three to four times during the growth of the
plant. Plastic twine is used due to the ease of removal by burning. Once the final harvest is
complete, plants are killed with herbicides (usually Paraquat which is a quick reacting contact
spray), and then the plastic is slit down the middle and lifted out of the soil (unless a second
crop is planted to re-use the plastic). Stakes can be removed by a stake puller and sterilized by
either steam or methyl bromide (Hochmuth, 1988a). When sterilizing stakes with methyl
bromide, the stakes must first be moistened, then a tarp is placed over the entire stack and
fumigated. This method is usually only done in areas of high fungal disease activity,
however this is not a common practice. Another method used to sterilize stakes is placing
stakes in a barrel containing a solution of clorox and water (Stall, 1993).
Diseases
Methyl bromide is used as a method of control for several diseases found in tomato
production including fusarium crown and root rot, bacterial wilt, southern blight, and
verticillium wilt.
Fusarium crown and root rot (Fusarium oxysporum f. sp. radius lycopersici (FORL))
is a fungus which is severe in southern production regions of Florida. FORL invades the plant
through wounds and natural openings such as new root shoots. Symptoms occur as brown
lesions which can girdle the hypocotyl at the root/shoot juncture. In tomato seedlings the fungus
can cause yellowing, stunting, and loss of cotyledons (source of food). Field symptoms are
exhibited by wilting of the plant during the warmest part of the day but the plant may recover
during the evening hours. As the plant begins to bear fruit the increased stress may cause
symptoms to become more prominent. Some plants may produce irregular fruit and in some
situations may lead to death (McGovern and Datnoff, 1992).
Cultural practices used to control FORL include using disease free transplants, avoiding
over-watering, and using mixed tray types such as plastic or styrofoam due to different watering
requirements. Trays should be disinfected prior to reuse. Avoid injury to transplants or later
stages of plant development because wounds provide an entry point for a pathogen. Maintain
optimum soil pH between 6-7 and do not drag trays along the ground because the trays can pick-
up spores and spread disease. Remove or plow in plant debris after harvest to reduce
populations of soil pathogens and sterilize stakes prior to re-use. Rotate with a non-susceptible
crop, such as a monocot type of plant like corn (McGovern and Datnoff, 1992).
The use of a biological control which increases the populations of microorganisms such
as Trichoderma harzianum, Aspergillus ochraceus Glomus intraradix, orPenicillium funiculosum
can effectively decrease the populations of FORL in the soil (McGovern and Datnoff, 1992).
Heating the soil by the use of transparent plastics in conjunction with biological control
may be a viable alternative in the control Fusarium crown rot (McGovern and Datnoff, 1992).
Chemical controls are another method of management of Fusarium Crown and root rot. Soil
fumigants such as methyl bromide mixed in varying concentrations with chloropicrin, have been
found to be effective in the control of FORL (McGovern and Datnoff, 1992). Other chemicals
include formulations containing methylisothiocyanate.
Bacterial wilt is caused by Pseudomonas solanacearum and expresses symptoms such as
dark discoloration near ground level. The plant appears to be stunted before signs of wilting and
yellowing appear. Cultural practices for control of bacterial wilt include fumigation of land
prior to installation of seedbeds or field planting. In order to reduce the spread of disease, it
is recommended to avoid flooded conditions and avoid movement of tractors from infested fields
to non-infested fields. It is also recommended not to plant in fields that have a history of disease
problems.
Table 4.3 contains a list of chemicals that can be used to control bacterial wilt. The
principal chemicals are chloropicrin, methyl bromide, and Vapam.
Table 4.3. Chemicals for the control of bacterial wilt.
Common Name Trade Name
Chloropicrin 96.5 Chlor-O-pic/Picfume
Methyl Bromide 68 Brom-O-Sol/Brozone
Methyl Bromide + Chloropicrin 67:32 MC-33/Terr-O-Gas 67
Metam Sodium 32.7 Vapam/Fume V
NOTE: For rate, use, and application to seed bed and field, refer to pp. 440-461 of the Florida
Plant Disease Control Guide, 1993.
Southern blight is caused by Sclerotium rolfsii and attacks the plant at or below ground
level by completely girdling the plant. This prevents movement of water or nutrients through
the plant thereby limiting support to the upper portion of the plant. As a result the plant wilts
and eventually dies. Young plants such as seedlings are especially susceptible, but as the plant
becomes more woody, it becomes more resistant to attack (Florida Plant Disease Control Guide,
1993).
If a field inspection reveals plants infected with southern blight, the plants should be
removed and disposed of by burying or burning. It is recommended to avoid excess water in
the field by following proper irrigation and drainage practices. Flooding can lead to spreading
of the disease by dissemination of sclerotia, however they are too heavy to spread by
atmospheric means such as wind. It is also recommended to plow under crop residue at least
6 inches in depth to reduce increases in populations of soil pathogens (Florida Plant Disease
Control Guide, 1993).
In Table 4.4 a list of chemicals that can be used to control southern blight is presented.
Table 4.4. Chemicals for the control of southern blight.
Common Name Trade Name
Chloropicrin 96.5 Chlor-O-pic/Picfume
Methyl Bromide 68 Brom-O-Sol/Brozone
Methyl Bromide + Chloropicrin 67:32 MC-33/Terr-O-Gas 67
Metam Sodium 32.7 Vapam/Fume V
PCNB 75 Terraclor 75WP
NOTE: For rate, use, and application to seed bed and field, refer to pp. 440-461 of the Florida
Plant Disease Control Guide, 1993.
Verticillium wilt, caused by Verticillium albo-atrum, does not kill the plant, however,
it does disable the plant where it can no longer effectively take up nutrients. Symptoms do not
become apparent until fruit set. Symptoms consist of diurnal wilting, where the plant regains
turgor during the evening hours, and marginal yellowing.of the leaves (Florida Plant Disease
Control Guide, 1993).
Cultural practices for management of verticillium wilt include use of resistant or tolerant
varieties. It is recommended to rotate the crop with a non-susceptible crop and avoid
overwatering. It is also recommended to not plant on land with a known history of Verticillium
wilt and to practice sanitation methods, including removal or plowing under of plant debris after
harvest and disinfecting stakes used during crop production. (Florida Plant Disease Control
Guide, 1993).
Table 4.5 contains a list of chemicals that can be used to control Verticillium wilt. The
principal chemicals are chloropicrin, methyl bromide, and Vapam.
Table 4.5. Chemicals for the control of verticillium wilt.
Common Name Trade Name
Chloropicrin 96.5 Chlor-O-pic/Picfume
Methyl Bromide 68 Brom-O-Sol/Brozone
Methyl Bromide + Chloropicrin 67:32 MC-33/Terr-O-Gas 67
Metam Sodium 32.7 Vapam/Fume V
NOTE: For rate, use, and application to seed bed and field, refer to pp 440-461 of the Florida
Plant Disease Control Guide, 1993.
Nematodes
There are several nematodes that pose a constant threat to Florida tomato production.
The most common are: root knot nematode, which is found in sand, muck, and rock base soils;
stubby-root nematode, which is found in sand and muck soils and; sting nematode, which is
found in sand soils.
There are several fumigant and non-fumigant chemicals that are used for control of
nematodes. Nemacur and Vydate are two non-fumigant nematicides which are not as effective
against root knot nematode as are fumigant type chemicals. Fumigant nematicides include
methyl bromide plus chloropicrin (varied ratios), Vapam, Busan 1020, and Telone II and Telone
C-17. (Florida Nematode Control Guide, 1993).
Weeds
Some common weeds found in tomato production in Florida are nightshade, eclipta alba,
goosegrass, southern crabgrass, bermudagrass, yellow nutsedge, pigweed, morning glory,
carolina geranium, ragweed, and parthenium. Methods of weed control include mechanical
weed control, crop competition, crop rotation, biological weed control, and chemical use. To
obtain effective weed control it is suggested to use two or more of these methods in
combination.
Mechanical weed control includes turning weeds under by cultivation, however several
studies have shown that this process germinates more weeds by disturbing the seeds that lie
below the surface. Crop competition increases the number of crop plants to effectively compete
against weeds for water and nutrients. Crop rotation helps control weeds because monocropping
year after year results in build up of weeds that are tolerant to monocropping cultivation
practices. Biological weed control includes introduction of an organism to reduce the population
of undesirable pests.
Chemical weed control includes use of herbicides and fumigants to control weeds. Non-
fumigant chemicals include: DCPA (Dacthal) which controls germinating annuals; Diquat which,
via contact, burs down vines after final harvest; MCDS (Enquik) which is a post-emergence
control of broadleaf weeds; Metribuzin (Sencor) which controls post-emergence of small weeds;
Napropamid (Devrinol) which is a preplant incorporated-control for germinating annuals (applied
before plastic application); Paraquat (Gramoxone) for post-emergence contact-control for all
emerged weeds (used in row middles between beds); Sethoxydim (Poast) for post-emergence
control of grass weeds; and Trifluralin (Treflan) applied preplant for control of germinating
annual weeds (for application rate and comments, refer to pp. 339-342 of the Florida Weed
Control Guide, 1993). Fumigant chemicals used to control weeds include methyl bromide and
Vapam.
Insects
Insects, such as wireworm, may increase in population with removal of methyl bromide
in tomato production. Methods of control for wireworm include Diazinon, a non-fumigant
chemical, and Telone and methyl bromide which are fumigants (for application rates and
comments refer to the Florida Insect Control Guide, 1993, p. 542).
Strawberries
Approximately 3,000 to 5,500 acres of strawberries are planted annually in Florida. For
the 1991-92 season, 4,700 acres of strawberries were harvested in Florida. Hillsborough and
Manatee counties produce the majority of the strawberries, harvesting approximately 4,200 acres
in 1991-92. The value of this crop in Florida was estimated at more than $94 million for the
1991-92 season (FASS, 1993). Some of the varieties grown include Oso Grandy, the most
popular, followed by Selva, Sweet Charlie (a Florida variety), and Seascape. Transplants are
set in October and harvest generally begins in December, peaking in March and early April with
some late harvest into May (Albregts and Howard, 1984). Some double cropping does occur
using vegetables such as pepper, eggplant, or squash, however this is not considered a common
practice. Some growers use cover crops to build up organic matter and return some of the
nutrients to the soil and to reduce infestation of weeds during the fallow period.
Cultural Practices
The primary production method in strawberry farming is a full-bed mulch system using
overhead irrigation in conjunction with seepage or drip irrigation. Farmers sometimes use
recycled water collected in pits for irrigation.
The field should be plowed prior to planting and disked to turn under old crop residue
in order to reduce detrimental soil organisms. The field should then be leveled for proper
drainage to prevent areas of flooding. The soil should be analyzed for any additional additives
required, such as lime or sulfur for pH adjustment (Kostewicz, 1976).
Strawberries are grown on beds to reduce flood damage to the crop. The height of the
bed ranges from 7 to 9 inches depending on the amount of drainage that is required (Hochmuth,
1988c). Beds are fumigated using a soil fumigant chemical such as methyl bromide.
Application of fertilizer requires that total micronutrients and phosphorous (P) are
incorporated into the bed with a percentage of nitrogen (N) and potassium (K) also added. The
remaining N and K can be banded along the outside edge of the row. The application of black
ethylene plastic is commonly used and is important for cultural reasons, such as weed control,
reducing erosion, and leaching of nutrients (Hochmuth, 1988c).
Field preparations such as bed shaping, fertilizing, and fumigation are gradually done in
one step, followed by the application of plastic in a separate operation. Generally, row bedding
ranges from two to four rows of strawberries per bed. When using two rows per bed, spacing
between plants is approximately 12 inches, however, as growers increase the number of rows
per bed, they will increase the spacing between plants to compensate for decreased row spacing
(Albregts and Howard, 1984).
The use of overhead sprinklers is common practice and is required to establish
transplants. Overhead irrigation is used for several days after setting transplants to reduce heat
stress damage to the plants. Overhead irrigation is also important for cold protection. This
method allows the grower to apply water over the plant. The actual phase change from liquid
to ice releases heat that is absorbed by the plant for protection against cold temperatures
(Albregts and Howard, 1984).
Strawberry plants can be classified as either dormant or non-dormant. Those plants that
have not been exposed to temperatures below 45F are non-dormant, meaning there has been
little accumulation of starch in the roots for vegetative development. Strawberry plants classified
as dormant have received a number of hours below 45F and have accumulated a sufficient
amount of starch in the roots to supply food for vegetative growth. Most growers purchase their
transplants from nurseries located in the northern regions of the U.S. or Canada. These plants
can accumulate the required amount of hours below 45*F in order to sustain itself once
transplanted to the field. The plants received from nurseries in the north are partially dormant
because it is important to have a plant with enough starch in the roots to establish itself in the
field, and then begin flowering. If the plants receive too many hours below 45*F, resulting in
total dormancy, vegetative growth would be enhanced for several months and little flowering
would occur (Albregts and Howard, 1984).
Diseases
Methyl bromide is used as a method of control for several diseases found in strawberry
production including black root, Rhizoctonia bud rot, Rhizoctonia hard brown rot and
Verticillium wilt.
Black root is a complex of organisms which causes stunting of plants, blackening, and
decay of roots as a result of lack of oxygen in the soil (Hochmuth, 1988c). Cultural practices
recommended for control of black root include digging around the plants in the nursery which
provides soil aeration and aids in new root development. In Table 4.6, the chemicals that can
be used to control black root are listed. The principal chemicals are chloropicrin, methyl
bromide, and Vapam.
Table 4.6. Chemicals for the control of black root, rhizoctonia, and verticillium wilt.
Common Name Trade Name
Chlor-O-Picrin 96.5 Chlor-O-Pic, Picfume
Methyl bromide 98-100 Brom-O-Gas, MC-2R,
Terr-O-Gas 98 or 100
Methyl bromide 68 Brom-O-Sol, Brozone
Methyl bromide + MC-33, Terr-O-Gas 67
Chloropicrin 67:32
Metam sodium (SMDC) Vapam
Source: Florida Plant Disease Control Guide, 1993, pp. 426-427.
Rhizoctonia bud rot, caused by Rhizoctonia solani, attacks the bud portion of the plant
and can lead to death of lateral buds and sometimes the entire plant. Appropriate planting depth
is an important cultural management technique because the chances for infection increase if the
plant is planted too deep. In addition, avoid planting in areas where known species exists, and
allow the cover crop to dry prior to turning it under by cultivation. Cool weather and humid
weather are conducive environmental conditions for plant infection. Chemical controls include
the use of Benomyl or Thiram which can be used to aid control of foliar diseases caused by
Rhizoctonia species. In Table 4.6, the additional chemicals that can be used for preventive
control of Rhizoctonia caused diseases are listed.
Rhizoctonia hard brown rot, caused by Rhizoctonia solani, can affect the fruit, however
affected areas can be removed, and the fruit is still edible. Cultural practices for control of
Rhizoctonia hard brown rot include the use of mulch which reduces contact of the plant with the
soil. Chemical management of the disease includes the use of Benomyl or Thiram, which can
be used to aid in the control of diseases caused by Rhizoctonia species. Table 4.6 lists
chemicals that can be used for preventive control of Rhizoctonia caused diseases.
Verticillium wilt, caused by Verticillium albo-atrum, exhibits symptoms such as mature
leaves with inter-veinal browning which can cause eventual death of the tissue. This disease is
prevalent in calcareous soils in south Florida, however, it is not as common in central Florida
(Hochmuth, 1988c). Cultural practices to control verticillium wilt include the use of resistant
or tolerant varieties, however, these varieties are not currently available in Florida. It is
important to avoid injury to transplants and avoid installation of infected plants (Florida Plant
Disease Control Guide, 1993). It also is recommended to remove or plow in plant debris after
harvest of previous crops (Albregts and Howard, 1984). Table 4.6 lists chemicals that can be
used to control verticillium wilt. The principal chemicals are chloropicrin, methyl bromide, and
Vapam.
Nematodes
There are several nematodes that pose a constant threat to Florida strawberry production,
with the most common being sting and root knot nematode followed by bud and leaf nematode
(Hochmuth, 1988c).
Cultural practices for control of nematodes include the use of non-host cover crops. It
is also recommended to allow crop debris to completely decay prior to installation of new
strawberry plants (Hochmuth, 1988c). Telone II is a nematicide that is registered for use in
strawberry production (for rate and application method, refer the Florida Nematode Control
Guide, 1993, p. 110).
Weeds
Some common weeds found in strawberry production include nutsedge, indigo, carolina
geranium, and cutleaf evening primrose. Several cultural practices have been identified to
reduce weed populations including crop competition, mechanical control, crop rotation, cover
crops, and use of chemicals. To obtain effective weed control, it is suggested to use two or
more of these methods in combination.
Mechanical control of weeds includes turning the weeds under by cultivation using a disk
or by hoeing. Mechanical control of weeds also includes mowing. Crop competition increases
the number of plants to effectively compete against weeds for water and nutrients. Mono-
cropping year after year can result in the build up of weeds that are tolerant to cultivation
practices. Crop rotation can reduce the population of weed species specific to strawberry
production practices. The use of a cover crop during the off season can reduce populations of
undesirable weeds. Herbicides and fumigants can also be beneficial in controlling weeds.
The following chemicals can be used to control weeds in strawberry production. DCPA
(Dacthal) controls germinating annuals. MCDS (Enquik) is applied post-emergence to row
middles for control of broadleaf weeds. Napropamid (Devrinol), a preplant incorporate, can be
used to control germinating annuals. It is also applied before plastic application or as a surface
application. Sethoxydim (Poast) is applied post-emergence for control of grass weeds. Paraquat
(Gramoxone) is a post-emergence contact used for control of all emerged weeds. It can be used
in row middles between beds or as a pre-emergence application (for application rate and
comments, refer to the Florida Weed Control Guide, 1993). Methyl bromide plus varying
concentrations of chloropicrin can be used for preplant treatment of beds. The formulation of
98 percent methyl bromide and 2 percent chloropicrin is primarily used due to effective control
of nutsedge.
Insects
Insects such as wireworm may increase in populations with removal of methyl bromide
in strawberry production. Alternative methods of control for wireworm include non-fumigant
chemicals such as Lorsban, Dyfonate and Diazinon. Telone is a fumigant chemical used to
control wireworm (Florida Insect Control Guide, 1993).
Peppers
Peppers are considered a warm season crop with approximately 33% of United States
production occurring in the state of Florida (Gull, No Date). Approximately 20,000 to 23,000
acres of peppers are planted annually in Florida. For the 1991-92 season 20,600 acres of
pepper, valued at $170.8 million, were harvested. The leading counties for harvested acreage
included Collier (with 4,500 acres in 1991-92) and Palm Beach (with 5,500 acres in 1991-92)
(FASS, 1993). Florida produces peppers for the early and late-season, while Georgia and South
Carolina produce peppers for mid-season demand. Due to its physical characteristics, California
Wonder is the primary variety grown in Florida. Commercial users, such as restaurants, prefer
this blocky, four-lobed pepper because sliced in half, it remains stable when placed on a plate,
as compared to the three lobed pepper. Other varieties include Early Calwonder, Gator Bell,
Jupiter and Shamrock (Hochmuth, 1988b).
Cultural Practices
Double cropping is practiced in pepper production in order to use plastics or residual
fertilizers and chemicals. In west Palm Beach County double cropping may include an onion
or bean crop. When double cropping with beans, planters seed beans into the bed between the
pepper holes. When double cropping with onions, onion transplants are installed by hand. In
the Immokalee area, squash and cucumber have been used as a double crop with pepper.
The cultural practices for pepper production are very similar to tomato production. The
primary production method for pepper in the Palm Beach area is a full-bed mulch system with
seepage irrigation. Full-bed mulch production with seep irrigation requires that all soil
additives, such as fumigants and fertilizers, be added prior to the application of plastics. The
following is a sequence of operations that may be used in full-bed mulch production with seep
irrigation. First, the field should be plowed and disked to turn under old crop residue in order
to reduce detrimental soil organisms. Second, leveling of the field is required for proper
drainage and irrigation. Third, the soil should be analyzed for any additional additives required,
such as lime or sulfur for pH adjustment. Fourth, initial fertilizer application should be
completed, including all micronutrient and phosphorous (P) requirements and 10 to 15 percent
of total nitrogen (N) and potassium (K) requirements. Additional amounts can be applied
through an injection wheel as needed (Hochmuth, 1988b). Fifth, bedding (shape the bed),
fumigation, and application of fertilizer are done prior to the application of plastic. Advantages
of plastic include increased weed control, moisture retention, and reduced loss to leaching of
fertilizer. Black plastic with a painted white strip down the middle may be used during early
fall plantings. The white reflects the sun, creating cooler surface temperatures and reducing the
incidence of plant burning when portions of the plant come in contact with the plastic.
It is important to maintain water approximately 15 to 18 inches below the soil surface
to ensure seepage into the root zone and sustain moisture. By maintaining a moist environment,
a nutritional concentration gradient exists. This allows the banded nitrogen (N) and potassium
(K) to diffuse into the soil and replace those nutrients already incorporated into the soil. Plastic
is extremely important in sustaining the moisture, otherwise the nutrients can be lost to leaching
by natural rain or the soil may dry out and result in evaporative loss of soil moisture (Geraldson,
et al., 1965). Seepage irrigation can be an effective tool to limit root growth to the treated soil
in the bed area. By raising the water table, the growth of the root is restricted to the bed region.
Mulched production of peppers using the drip system is similar to full-bed mulch with
seep irrigation with the exception that water requirements are met by the use of drip irrigation.
Drip irrigation can be supplied either by tubes or drip tape which should be placed
approximately two to three inches below the soil surface prior to the application of plastic to
protect against damage incurred from mice and insects. Initial fertilizer application should be
comprised of all micronutrients and phosphorous (P) with 20 to 40 percent of total nitrogen (N)
and potassium (K) requirements. Additional N and K can be injected into the system during the
growth of the plant.
Pepper plants can be established either by transplants or direct seeding. Transplants can
be grown in a greenhouse nursery or in the field using fungicide treated seeds planted in
fumigated areas. The transplants then may be placed in the field by machine (Hochmuth,
1988b). Direct seeding using the "plug mix" method is considered most effective. The "plug
mix" is a mixture of seed, water, and soil placed in the ground by a planter machine. The
planter can be used for both mulched and nonmulched bed type production systems (Rose,
1974).
The bed shapes are similar in size and contour as is found in eggplant and tomato
production, however two or three rows of peppers may be grown on one bed. Stakes are usually
placed every two or three plants and are one-half the length of those used for tomato production.
Baling twine is used to wrap stake-to-stake to provide a support for pepper plants between the
stakes. Clorox and water can be used to sterilize stakes when required, however usually after
use and prior to storage, removal of dirt from stakes has been found to be adequate for control
of harboring pests that may remain on the stakes. Once the final harvest is complete, plants are
killed with herbicides, such as Paraquat or Roundup. Mowing may be used to remove excess
plant debris. A machine may then be used to pull up plastics and roll it into bales for disposal.
Diseases
Methyl bromide is used as a method of control for several diseases found in pepper
production such as damping-off and southern blight.
Damping-offcan be caused by Pythium sp. and Rhizoctonia sp. Symptoms are exhibited
by rotting at or below the ground level leading to the death of the seedling. Cultural practices
used to control damping-off include planting in well drained soils and planting in areas
containing reduced amount of decomposed plant debris. The use of fungicide treated seed can
also be an effective method of control. Table 4.7 lists chemicals that can be used to control
damping-off.
Table 4.7. Chemicals for the control of damping-off.
Common Name Trade Name
Chloropicrin 96.5 Chlor-O-Pic\Picfume
Methyl bromide 98\100 Brom-O-Gas\MC-2R
Methyl bromide 68 Brom-O-Gas\Brozone
Methyl bromide 67:32 MC-33, Terr-o-gas 67
Metam sodium Vapam
Metalaxyl 25 Subdue II
Metalaxyl 25.1 Ridomil 2E
NOTE: For rate, use, and application to seed bed and field, refer to pp. 390-393 of the Florida
Plant Disease Control Guide, 1993.
Southern blight, caused by Sclerotium rolfsi, attacks the plant at or below ground level
by completely girdling the plant, preventing water and nutrient movement to support the upper
portion of the plant. As a result, the plant wilts and eventually dies (Florida Plant Disease
Control Guide, 1993, p. 395). Cultural practices used to control southern blight include plowing
under all crop debris and ceasing to plant in areas with a known history of disease. Another
alternative is to rotate with a grass crop in fields with high populations of the disease (Florida
Plant Disease Control Guide, 1993, p. 395). Treatment of soil with multipurpose fumigants
such as Vapam or methyl bromide containing varying concentrations of chloropicrin also aids
in the control of the disease, if disease is present at the time of treatment.
62
Nematodes
There are several nematodes that pose a constant threat to Florida pepper production.
The most common are: (a) root knot nematode which is found in sand, muck, and rock base
soils; (b) stubby-root nematode found in sand and muck soils, and; (c) sting nematode found in
sand soils.
There are several fumigant and non-fumigant chemicals that are used for control of
nematodes. Vydate and Nemacur are two non-fumigant nematicides which are not as effective
against root knot nematode as fumigant type chemicals. Fumigant nematicides include methyl
bromide plus chloropicrin (varied ratios), Vapam, Busan 1020, and Telon II and Telon C-17
(Florida Nematode Control Guide, 1993, p. 11-115).
Weeds
The most common weeds found in pepper production are similar to those found in tomato
or eggplant production in Florida. These include nightshade, eclipta alba, goosegrass, southern
crabgrass, bermuda grass, yellow nutsedge, pigweed, dodder and morning glory. To reduce
weed populations, several methods have been identified including cover crops, mechanical
controls and use of chemicals. To obtain effective weed control, it is suggested to use two or
more of these methods in combination (Florida Weed Control Guide, 1993, p. 325).
Mechanical control can include turning the weeds under by disking. Cover crops can
help control problem weeds during the off season, however, the type of cover crop chosen
should not harbor pests or diseases that are detrimental to the pepper plant (Florida Weed
Control Guide, 1993, p. 325).
The use of herbicides and fumigants can also help in weed control. The following is a
list of non-fumigant chemicals that can be used to control weeds. DCPA (Dacthal) is used to
control germinating annuals. MCDS (Enquik) can be used for post-emergence control of
broadleaf weeds in row middles. Napropamid (Devrinol) is used preplant for control of
germinating annuals and should be applied before plastic application, or as a surface application.
Paraquat (Gramoxone) is applied post-emergence, as a contact chemical for control of all
emerged weeds, and can be used in row-middles (between beds), or as a pre-emergence
application. Sethoxydim (Poast) is used for post-emergence control of grass weeds. Trifluralin
(Treflan) is incorporated pretransplant and controls annual weeds. Diquat (Diquat) can be used
for burn down of crop after final harvest. Clomozone (Command) is applied preplant for control
of annual grasses and certain broadleaf weeds (Florida Weed Control Guide, 1993). The use
of fumigant chemicals such as methyl bromide or Vapam also reduces populations of certain
weeds.
Insects
Insects such as wireworm may increase in population with the removal of methyl bromide
in pepper production. Methods of control for wireworm include non-fumigant chemicals such
as Diazinon and Fonofos. Telone can work as a fumigant type of control (Florida Insect Control
Guide, 1993, p. 491).
Eggplant
Florida represents 51% of the commercially grown eggplant produced in the United
States (Gull, no date). Approximately 2,000 to 3,000 acres of eggplant are planted annually.
For the 1991-92 season, 2,550 acres of eggplant were harvested in Florida, with a cash value
of $16.9 million. Palm Beach County (East) harvested the most eggplant with 1,050 acres. The
remaining acres of eggplant for the 1991-92 season were harvested from various other counties
(FASS, 1993). The major type of eggplant grown in the Palm Beach area is the Classic variety
(Shuler, 1993). Other varieties include Florida Market and Florida Beauty (Hart, no date).
Eggplant production can generally occur year round. The vegetable crop that follows
eggplant in a double cropping production system depends upon prevailing environmental and
economic factors. Pepper or cucumber are the preferred vegetables when double cropping with
eggplant. Double cropping eggplant is not considered a common practice in Palm Beach
County.
Cultural Practice
The cultural practices for eggplant production are very similar to tomato production. The
primary production method for eggplant in the Palm Beach area is the full-bed mulch system
with seepage irrigation. This system requires that all soil additives, such as fumigants and
fertilizers, be added prior to application of plastics. The field should be plowed and disked to
turn under old crop residue in order to reduce detrimental soil organisms. The soil should be
analyzed for any additional additives required, such as lime or sulfur for pH adjustment
(Kostewicz, 1976). Then bedding (shaping the bed), fumigating, and fertilizing are done prior
to the application of plastic. Advantages of plastic include increased weed control, moisture
retention, and reduced leaching of fertilizer (Hochmuth, 1988a).
It is important to maintain water approximately 15 to 18 inches below soil surface to
ensure seepage into the root zone and sustain moisture. By maintaining a moist environment,
a nutritional concentration gradient exists. This allows the banded nitrogen (N) and potassium
(K) to diffuse into the soil and replace those nutrients already incorporated into the soil. Plastic
is extremely important in sustaining the moisture, otherwise the nutrients can be lost to leaching
by natural rain, or the soil may dry out and result in evaporative loss of soil moisture
(Geraldson, et al., 1965).
Methyl bromide plays an important role in the full-bed mulch process. The chemical
formulation primarily used in the Palm Beach area is 98% methyl bromide and 2% chloropicrin.
Some growers are using 67% methyl bromide and 33% chloropicrin in areas where fungal
diseases are prominent. This is due to the effective control exhibited by chloropicrin as a
fungicide.
Eggplant can be established by direct field seeding or as transplants (Hart, no date).
Transplants are usually purchased by the grower and installed in the field by machine (Shuler,
1993).
Stakes are usually placed in the rows when plants are two to three weeks old. Plastic
twine is used to tie the plant to the stake and is usually done three to four times during the
growth of the plant. Plastic twine is used due to the ease of removal by burning. Once the final
harvest is complete, plants may be killed with a herbicide such as Paraquat or Roundup. Some
growers remove old vegetation by mowing, without the aid of herbicides. Plastics are then
removed, unless a second crop is planted to re-use the plastic. Approximately 60 to 70 percent
of eggplant grown in the Palm Beach area use stakes which are either placed by every plant, or
every other plant within the row. Stakes can be removed by a stake puller and can be sterilized
by either steam or methyl bromide. However, growers in the Palm Beach area usually re-insert
the opposite end of the stake in the ground for the second crop without sterilization.
Diseases
Methyl bromide is used as a method of control for several diseases found in the
production of eggplant including damping-off, bacterial wilt, southern blight and verticillium
wilt.
Damping-off is exhibited by rotting at or below the ground level leading to the death of
the seedling. Damping-off can be caused by Fusarium, Pythium, and Rhizoctonia species.
Recommended cultural practices to control damping-off include planting in well drained soils
and not planting in areas containing large amounts of decomposed plant debris. Chemicals are
another method of disease control. The use of fungicide-treated seed can also be an effective
method of control. Table 4.8 lists chemicals used to control damping-off.
Table 4.8. Chemicals for control of damping-off.
Common Name
Chloropicrin 96.5
Methyl Bromide 98-100
Methyl Bromide 68
Methyl Bromide + Chloropicrin 67:32
Metam Sodium 32.7
Metalaxyl 25.1
Metalaxyl 25.
Trade Name
Chlor-O-Pic/Picfume
Brom-O-Gas/MC-2R
Terr-O-Gas 98 or 100
Brom-O-Sol/Brozone
MC-33/Terr-O-Gas 67
Vapam/Fume V
Ridomil
Subdue II
NOTE: For rate, use, and application to seed bed and field, refer to pp. 368-371 of the Florida
Plant Disease Control Guide, 1993.
Bacterial wilt, caused by Pseudomonas solanacearum, can express symptoms such as dark
discoloration near ground level. The plant will appear healthy with little or no signs of
yellowing prior to death. Cultural practices for control of bacterial wilt include avoiding crop
land with known disease infestation, fumigating land where seedbeds or fields are placed, and
rotating with crops that are not considered susceptible to bacterial wilt such as grass, legumes,
or cucurbits (Florida Plant Disease Control Guide, 1993). Pre-plant fumigation with methyl
bromide using various formulations containing chloropicrin is also effective for control when the
disease is present in the soil at the time of treatment.
68
Southern blight, caused by Sclerotium rolfsii, attacks the plant at or below ground level
by completely girdling the plant, thereby ceasing movement of water or nutrient to support the
upper portion of the plant. As a result, the plant wilts and eventually dies (Florida Plant Disease
Control Guide, 1993). Cultural practices for the control of southern blight include avoiding
planting in areas of known infestation and rotating with crops such as grasses, legumes, or
cucurbits (Florida Plant Disease Control Guide, 1993). Chemicals that are considered
multipurpose pre-plant fumigants include Vapam and methyl bromide. Methyl bromide
formulations containing higher concentrations of chloropicrin have been found to provide control
of southern blight if it is present at time of treatment.
Verticillium wilt, caused by Verticillium albo-atrum, affects the vigor of the plant.
Symptoms consist of diurnal wilting (where the plant regains turgor during the evening hours)
and marginal yellowing of the lower leaves of the plant. Cultural practices for the control of
Verticillium wilt include rotating with a non-susceptible crop such as grasses, legumes, or
cucurbits and avoiding planting in fields with a known history of disease (Florida Plant Disease
Control Guide, 1993). Chemicals that are considered multi-purpose pre-plant fumigants include
Vapam and methyl bromide. Methyl bromide formulations containing higher concentrations of
chloropicrin have been found to provide control of Verticillium wilt if it is present at time of
treatment.
Nematodes
There are several nematodes that have been identified in eggplant production. The most
common are: (a) root knot nematode, found in sand, muck, and rock base soils; (b) stubby-root
nematode found in sand and muck soils; and (c) sting nematode found in sand soils.
There are several fumigant and non-fumigant chemicals that are used for control of
nematodes. Two non-fumigant chemicals include Nemacur and Vydate, however these chemicals
are not considered as effective against root knot nematode as fumigant type chemicals. Fumigant
nematicides include methyl bromide plus chloropicrin (varying ratios), Vapam, Busan 1020, and
Telone II and Telone C-17 (Florida Nematode Control Guide, 1993).
Weeds
The most common weeds found in eggplant production in Florida are nightshade, eclipta
alba, goosegrass, southern crabgrass, bermuda grass, yellow nutsedge, pigweed, and morning
glory (Shuler, 1993). To reduce weed populations, several methods have been identified
including cultural control, mechanical control, and use of chemicals. To obtain effective weed
control, it is suggested to use two or more of these methods in combination.
Methods of cultural control include using plastics, planting grass in row middles, or
planting cover crops during the off season. Cover crops can be used to control populations of
undesirable plants.
Mechanical weed control includes turning the weeds under by cultivation using a disk
or plow to reduce weed infestation during the off-season or while the crop is growing. Chemical
weed control includes the use of herbicides and fumigants.
The following chemicals can be used to control weeds. DCPA (Dacthal) is used to
control germinating annuals. MCDS (Enquik) is used post-emergence for control of broadleaf
weeds in row middles. Napropamid (Devrinol) is a pre-plant incorporated for control of
germinating annuals. It must be applied prior to plastic application. Paraquat (Gramoxone) is
a contact-control for all emerged weeds. It is used in row middles between beds. Sethoxydim
(Poast) is a post-emergence spray for control of grass weeds (for application rate and comments
concerning these chemicals, refer to p. 317 of the Florida Weed Control Guide, 1993).
Fumigant type chemicals such as methyl bromide mixed with varying concentrations of
chloropicrin can be used for control of weeds prior to planting a crop. Vapam can also be used
to treat soil prior to planting a crop.
Insects
Insects such as wireworm may increase in population with the removal of methyl bromide
in eggplant production. Methods of control for wireworm include Telone and methyl bromide
(for application rates and comments regarding Telone, refer to pp. 111-112 of the Florida Insect
Control Guide). Methyl bromide is also used as a pre-plant fumigant for control of soilborne
insects.
Cucumbers
Approximately 16,000 to 23,000 acres of cucumbers are planted annually in Florida. For
the 1991-92 season 16,500 acres of fresh market cucumbers and 2,500 acres of processed
cucumbers were harvested in Florida, primarily in Collier, Manatee, Hardee, Palm Beach (East),
Hendry and Lee counties. In Florida, 2,500 acres of pickling cucumbers were harvested in the
1991-92 season (FASS, 1993). There are numerous varieties of (slicing) cucumbers such as
Dasher II, Floracuke, Early Triumph, Poinsett 76-S, Sprinter 440, and Raider. Pickling
varieties can include Addis, Calypso, or Carolina (Hochmuth, 1988d).
Cultural Practices
In cucumber production, the field should be plowed and disked to turn under old crop
residue in order to improve the efficacy of herbicides and fumigants. The soil should be
analyzed for any additional additives required, such as lime or sulfur for pH adjustment.
Disking can be used to incorporate the lime and to improve the condition of the field for bedding
(shaping the bed). The height of the bed may range from 3 to 8 inches depending on the
drainage requirements of the field. Bed formation can be accomplished using machines such as
disc hillers or bedding discs. Fertilizer and fumigation practices should be done prior to the
application of plastic mulch. If plastic is to be applied, a bed press should follow the plastic to
ensure close contact between the surface of the soil and the plastic. Advantages of plastic
include increased weed control and moisture retention, reduced leaching of fertilizer and faster
crop development. Another benefit derived from the use of mulch is reduction of belly rot
(Hochmuth, 1988d).
Application of fertilizer depends on the production system used. There are several types
of bedding production systems used in Florida including (1) non-mulched production of
cucumbers, (2) mulched production with overhead irrigation, (3) mulch production with seep
irrigation, and (4) mulch production with drip irrigation.
Non-mulched production of cucumbers requires the following for fertilizer application.
If phosphate is lacking in the soil, a band of phosphate should be applied close to the roots, due
to the immobility of the element. It may also be necessary to band micronutrients on calcareous
soils. Some micronutrients can also be applied to foliage. Under normal conditions both
phosphate and micronutrients can be incorporated into the soil. Apply 50% of nitrogen (N) and
potassium (K) at the time of planting with the remaining amount applied in a split application
during the early part of the growing season. Any additional requirements can be added as
necessary (Hochmuth, 1988d). Plastic and methyl bromide are not used in this situation.
Mulched production with overhead irrigation is similar except that it requires that total
fertilizer requirements be applied prior to the application of plastic. Mulched production using
seepage irrigation requires that total micronutrients and phosphorous (P) be incorporated into the
bed. From 10 to 15 percent of the nitrogen (N) and potassium (K) are applied prior to the
application of the mulch with the remaining amount banded in a narrow strip or groove along
the surface of the bed preceding the application of the mulch (Hochmuth, 1988d).
It is important to maintain water approximately 15 to 18 inches below, soil surface to
ensure seepage into the root zone and sustain moisture. By maintaining a moist environment,
a nutritional concentration gradient exists. This allows the banded nitrogen (N) and potassium
(K) to diffuse into the soil and replace those nutrients already incorporated into the soil. Plastic
is extremely important in sustaining the moisture, otherwise the nutrients can be lost to leaching
by natural rain, or the soil may dry out and result in evaporative loss of soil moisture
(Geraldson, et al., 1965).
Seepage irrigation can be an effective tool to limit root growth to the treated soil in the
bed area. By raising the water table, the growth of the root is restricted to the bed region.
A mulched system using drip irrigation incorporates 20 to 40 percent of the required
nitrogen (N) and potassium (K), all phosphorus (P), and micronutrients prior to planting. Any
additional requirements can be applied via the drip irrigation as needed.
Cucumbers planted using mulch with overhead, seepage or drip irrigation are usually
planted as a second crop following pepper, tomato, or eggplant. Cucumbers can benefit from
any residual effects of methyl bromide and any remaining fertilizers. It is important to
remember that there is no residual methyl bromide in the soil, however if properly applied,
population of weeds and soilborne pathogens may be reduced to the extent that the second crop
can derive benefits from the application for the first crop.
Large growers use vacuum seeders which cut a hole in the plastic and places the seed in
the hole. Smaller growers use a barrel which rolls along and punches a hole in the plastic, and
laborers riding behind the barrel manually place seeds in the hole. In non-mulched cucumber
production, a standard seeder can be used. Plantings are arranged with one row per bed, three
to four seeds per location, and approximately four feet between plants. Plug mix can also be
used, however, using plug mix is not considered a common practice.
At the end of the season of a full-bed mulch system, a machine can be used to remove
the plastic, while a cutter bar simultaneously eliminates any remaining cucumber vines.
Diseases
A cucumber crop may be grown as a second crop following a tomato, eggplant or pepper
crop. In this way, cucumbers are grown in a double cropping system using the full-bed mulch
system. Residual benefits of methyl bromide can be derived from the application for the first
crop. As a result of the initial application of methyl bromide, residual benefits can include a
decrease in populations of soilborne diseases, for the period of time in which the cucumber crop
can be successfully grown. An increase in disease activity such as damping-off and fusarium
wilt may result in the event that methyl bromide is no longer available.
Damping-off can be caused by Pythium, Rhizoctonia spp. Seeds can become infected
and fail to germinate. This disease affects cucumber seedlings, causing necrosis and death of
the plant. The soilborne fungi can invade the plant at or below the soil level (Florida Plant
Disease Control Guide, 1993).
Cultural practices recommended for control of damping-off include avoiding planting in
soils that are not conducive to favorable emergence of seedlings, using fungicide treated seeds
and planting as shallow as possible (Hochmuth, 1988d).
Table 4.9 lists chemicals that can be used for the control of damping-off. It is also
recommended that treated seed be used. Fumigant chemicals such as Telone or Vapam may also
aid in the control of soilborne diseases.
Table 4.9. Chemicals for control of damping-off.
Common Name Trade Name
Metalaxyl 2 Subdue G
Metalaxyl 25 Subdue II
Metalaxyl 25.1 Ridomil 2E
NOTE: For rate, use, and application to seed bed and field, refer to pp. 356-367 of the Florida
Plant Disease Control Guide, 1993.
Fusarium wilt is caused by Fusarium oxysporum f. sp. cucumerinum which infects the
plant at any stage of development. An overall wilting may result or individual runners may be
affected (Florida Plant Disease Control Guide, 1993).
75
Cultural practices used to control Fusarium wilt include rotation with a non-susceptible
crop on a five year rotation schedule, using crops such as crucifers, legumes, or solanaceous
plants. Chemical controls include metam sodium (for rate, use, and application to seed bed and
field, refer to the Florida Plant Disease Control Guide, 1993, pp. 356-67).
Nematodes
Methyl bromide is used to control several nematodes that pose a threat to cucumber
production, including sting and root knot nematode. Methods of control of nematodes include
avoiding planting in known infested fields and treating fields with chemicals. There are several
non-fumigant and fumigant chemicals that are used for control of nematodes. Non-fumigant
chemicals include Vydate, Mocap 10G and Mocap 10. Fumigant chemicals include Telone II
(for rate and application method refer to the Florida Nematode Control Guide, 1993, pp. 96-7).
Weeds
Several methods have been identified for controlling weed populations including crop
competition, mechanical control, mulching, and use of chemicals. To obtain effective weed
control, it is suggested to use several of these methods in combination (Hochmuth, 1988d).
Mowing, disking, hoeing, or cultivation can be effective methods of weed control. Crop
competition can be a method of control by not only increasing the number of crop plants to
effectively compete against weeds for water and nutrients, but also ensuring a healthy crop
population by using good water and nutrient management practices. The use of plastic mulch
in conjunction with fumigant chemicals can be effective in the control of many weeds. Methyl
bromide is used to control weeds such as crabgrass, panicum, goosegrass, lambsquarter, and
nutsedge. The mulch itself acts as a barrier to many weeds with the exception of nutsedge
which can grow through the plastic. The use of chemicals such as herbicides can also be used
to control weeds.
The Florida Weed Control Guide (1993) lists chemicals that can be used for weed
control. Bensulide (Prefar) is preplant incorporated for control of germinating grasses.
Bensulide+naptalam can be applied preplant or pre-emergence, for a wider range of weed
control. Diquat (Diquat) is applied post-emergence, for burdown of vines after final harvest.
Sethoxydim (Poast) is used for post-emergence control of grass weeds. Paraquat (Gramoxone)
is applied as post-emergence contact for control of all emerged weeds. It can be used in row
middles between beds, or it can also be applied as a pre-emergence application. Ethalfluralin
(Curbit) is applied either pre-emergence or post-emergence for control of grasses such as goose
grass, panicum, or lambsquarter. Glyphosate (Roundup) is used prior to planting for removal
of weeds. Naptalam (Alanap) is applied pre-emergence for control of germinating annuals such
as lambsquarter, pigweed and carpet weed. This chemical can also be applied post-emergence
immediately after transplant for control of annual weeds. Other herbicides include Clomoxone
(Command 4EC) applied preplant and DCPA (Dacthal W-75) applied as an early post-emergent
(for application rate and comments, regarding these chemicals refer to the Florida Weed Control
Guide, 1993, pp. 312-6).
Insects
In cucumber production, insects such as wireworm may increase in populations with the
removal of methyl bromide. Methods of control for wireworm include Diazinon, a non-fumigant
chemical which controls wireworm and Telone which is a fumigant (for application rates and
comments, refer to pp. 441-446 of the 1992-1993 Florida Insect Control Guide, 1993).
Squash
Squash is grown throughout the state of Florida with the exception of the Everglades
region. The primary squash production area is located in southeast Florida. Squash is harvested
from early September to July. Summer varieties that are harvested immature include: Cracker,
Sundance, and Lemondrop. Winter varieties that are harvested mature include: Royal Acorn,
Tay Belle, and Ponca. There are numerous other varieties that are also grown in Florida (Olson
and Sherman, No Date). In the 1991-92 season, approximately 12,500 acres of squash were
harvested in the state of Florida (FASS, 1993).
Cultural Practices
Squash can be planted as a single crop without mulch and as a second, and sometimes
third crop, in a multiple cropping system, using the full-bed mulch system.
In Florida, squash grown as a single crop uses the open bed system which does not
require plastic or the use of methyl bromide. The field is plowed and checked for leveling,
especially in areas where seepage irrigation is to be used. Soil requirements are tested, and soil
amendments are applied, such as lime for adjustment of pH. Disking may be required to
prepare the field for planting (Kostewicz, 1976). The development of slightly raised beds may
be required in areas where flooding may occur. This can be accomplished using a disc hiller
or a bed disc. The initial application of fertilizer is applied as a band or strip 2 to 3 inches to
the side of and below the seed. Supplemental fertilizer should be applied as needed during the
growing season (Olson and Sherman, No Date). Irrigation can be supplied via overhead or
seepage system.
Squash is also planted as a second crop in a double cropping system following either a
tomato or pepper crop. The double cropping system may use the full-bed mulch system
requiring the use of plastic in conjunction with methyl bromide (Hochmuth, 1993). Methyl
bromide is not registered for use in squash production, however, when squash is planted as a
second crop following tomato or pepper, it can benefit from the residual effects of methyl
bromide from the initial application for the first crop.
The following is a description of a sequence of operations that may occur during the
installation of the full-bed mulch system. The field should be plowed and checked for leveling,
especially in areas where seepage irrigation is to be used. Soil requirements are tested, and soil
amendments are applied, such as lime for adjustment of pH. Disking may be required to
prepare the field for planting. A bed disc or disc hiller can then be used to shape the beds. A
bed press may follow to ensure good contact between the surface of the bed and the plastic. All
chemical and fertilizer requirements are applied prior to installation of the plastic. After
completed harvest of first crop (such as tomato or pepper), an application of a herbicide, such
as paraquat, can be used to kill any remaining vines. A cutter bar or mower may then be used
to remove any remaining debris. Squash may then be direct seeded into the same bed.
Additional application of fertilizer, such as nitrogen (N) and potassium (K), may be required and
can be injected via an injection wheel or drip system if the drip system is already in place.
Irrigation requirements can be met by the use of seepage, drip, or overhead irrigation.
Diseases
Methyl bromide is used as a method of control for several diseases found in squash
production. One of the more prevalent diseases found in squash is damping-off.
Damping-off can be caused by Phythium spp. and Rhizoctonia solani. This disease can
affect young plants causing the plant to collapse at the soil line, and it can cause seeds not to
germinate (Florida Plant Disease Control Guide, 1993). A cultural method of control for
damping-off includes avoiding planting in soils that have unfavorable moisture and temperature
regimes. The chemical control methods for damping-off are listed in Table 4.10.
Table 4.10. Chemicals for the control of damping-off.
Common Name Trade Name
metalaxyl 2 Subdue G
metalaxyl 25 Subdue II
metalaxyl 25.1 Ridomil 2E
metalaxyl Ridomil 2E
NOTE: For rate, use, and application ethods, refer to the Florida
Plant Disease Control Guide, 1993, pp. 410-6.
Nematodes
Methyl bromide is used to control several nematodes that may pose a threat to squash,
including sting and root knot nematode. Symptoms occurring with sting or root knot nematodes
include stunting, chlorotic appearance, wilting of the plant and galling or a stubby root system.
Cultural control methods for nematodes include allowing land to remain fallow, rotating
to a different crop, and flooding. However, it is recommended not to plant in fields heavily
infested with nematodes (Olson and Sherman, no date).
Chemical control methods for nematodes include Vydate L, a non-fumigant, and Telone
II and Telone C-17, a fumigant chemical (for additional information refer to the Florida
Nematode Control Guide, 1993).
Weeds
To reduce weed populations, several weed control methods have been identified,
including crop competition, mechanical control, mulch, and herbicides. In order to increase
effectiveness, it is recommended to use at least two of these methods together. Establishment
of a good crop stand can shade the ground and reduce germination of weeds. Mechanical
control, such as light disking, can control weeds, however, additional weeds may result because
some weeds require disturbance of the soil in order to germinate. Use of mulch in conjunction
with fumigants can be effective for weed control. Plastic mulch can aid in the control of weeds
by acting as a barrier. However, nutsedge will still grow through plastic (Florida Weed Control
Guide, 1993). Table 4.11 contains a list of chemicals that are used in the production of squash.
Table 4.11. Chemicals for the control of weeds in squash production.
Herbicide Time of application Rate (lbs. AI./Acre) Mineral
6
DCPA Early post-emergence 8-10
(Dacthal W-75)
Diquat Burndown of vines 0.25
(Diquat H/A after harvest
Glyphosate Prior to planting 0.5-1.0
(Roundup)
Paraquat Pre-plant or pre- 0.63-0.94
(Gramoxone Extra) emergence
Sethoxydim Post-emergence 0.188-0.28
(Poast)
Source: Florida Weed Control Guide, 1993.
Insects
In squash production, insects such as wireworm may increase in population with the
removal of methyl bromide. Methods of control for wireworm include Diazinon, a non-
fumigant, and Telone I and Telone C-17, a fumigant chemical (Florida Insect Control Guide,
1993).
Fresh Citrus
An important use of methyl bromide is as a post-harvest fumigant for agricultural
products. In Florida, citrus is the most important user of methyl bromide on a post-harvest
basis.
Although the majority of Florida citrus is processed into juice, fresh marketing still
represent an important source of revenue to Florida citrus producers. In Table 4.12, the
production and utilization of oranges, grapefruit, and tangerines is presented. Note that while
over 90 percent of Florida-produced oranges are typically processed, approximately 50 percent
of the grapefruit grown in Florida and over 60 percent of the tangerines produced in Florida are
marketed in fresh form.
Fumigation is used in Florida citrus mainly to kill fruit flies which are found sporadically
in the state. While fruit flies may be found throughout the citrus producing region in the state,
only fresh citrus fruit destined for domestic markets in other citrus producing states (California,
Arizona, Texas, and Hawaii) is routinely fumigated. The number of cartons of fresh citrus
fumigated in Florida over the 1984 to 1993 period is shown in Table 4.13.
There are two major types of grapefruit produced in Florida: white seedless and red
seedless1. In Table 4.14, production and utilization of white seedless grapefruit is presented.
Inspection of this table suggests that while a large proportion of white seedless grapefruit is
processed, exports of fresh white seedless grapefruit has expanded over the past decade. In
'Both pink seedless and red seedless varieties are grown in Florida. While the USDA uses
the term "colored" to categorize both pink and red seedless fruit, the terminology most widely
used in the industry is to simply refer to all varieties which are not white as "red seedless
grapefruit". This convention is adopted in this study.
83
Florida citrus: utilization of production (1000 boxes).
Oranges Grapefruit Tangerines
Season Fresh Processed Fresh Processed Fresh Processed
1983-84 7,640 109,060 16,661 24,239 1,858 1,117
1984-85 6,652 97,248 14,988 29,012 945 895
1985-86 8,960 110,240 19,620 27,130 1,189 761
1986-87 8,870 110,830 20,938 28,862 1,462 878
1987-88 9,520 128,480 23,110 30,740 1,614 836
1988-89 8,488 138,112 23,902 30,848 1,639 1,261
1989-90 5,922 104,278 13,344 22,356 999 701
1990-91 12,451 139,149 23,923 21,177 1,227 723
1991-92 11,552 128,248 22,841 19,559 1,965 635
1992-93 10,693 175,807 23,156 31,994 2,065 735
Source: Citrus Summary, various issues.
Table 4.13. Florida citrus fumigated with methyl bromide.
Number of Cartons
Season
1984-85
1985-86
1986-87
1987-88
1988-89
1989-90
1990-91
1991-92
1992-93
67,100
92,400
67,200
459,900
242,452
520,275
4,190,050
3,281,843
1,340,345
Source: Florida Department of Agriculture.
Table 4.12.
Utilization of certified Florida white grapefruit, 1980-81 through 1992-93.
Year Fresh Export Processed Total
-------------- 00boxes--- -----------
1980-81 4,671 2,984 20,205 27,860
1981-82 4,638 3,231 18,968 26,837
1982-83 5,420 3,112 12,750 21,282
1983-84 4,121 3,036 15,347 22,504
1984-85 4,061 1,196 19,445 24,702
1985-86 3,752 2,890 18,863 25,505
1986-87 2,928 4,040 19,812 26,780
1987-88 2,430 5,378 21,179 28,987
1988-89 2,088 5,635 19,666 27,389
1989-90' 1,178 2,637 13,946 17,761
1990-91' 1,988 5,901 13,506 21,395
1991-92' 1,144 5,257 12,339 18,740
1992-93* 1,155 4,516 19,615 25,286
'Includes Canada in Export.
Source: Division of Fruit and Vegetable Inspection, Florida Department of Agriculture.
Table 4.15. Utilization of certified Florida red grapefruit, 1980-81 through 1992-93.
Year Fresh Export Processed Total
-----------------------1000boxes---------------------
1980-81 6,284 2,136 5,698 14,118
1981-82 6,240 1,736 6,405 14,381
1982-83 7,121 1,650 3,531 12,302
1983-84 6,726 1,940 4,371 13,037
1984-85 7,874 1,636 6,653 16,163
1985-86 10,041 2,649 5,111 17,801
1986-87 9,915 3,698 6,143 19,756
1987-88 9,831 4,959 6,807 21,597
1988-89 9,309 6,149 7,830 23,288
1989-90' 5,967 3,072 7,010 16,049
1990-91' 9,746 5,584 6,067 21,397
1991-92' 9,975 5,554 6,002 21,531
1992-93' 10,297 6,130 10,631 27,058
'Includes Canada in Export.
Source: Division of Fruit and Vegetable Inspection, Florida Department of Agriculture.
Table 4.14.
In particular, the opening of the Japanese fresh citrus market has resulted in large increases
of shipments of fresh white seedless grapefruit to Japan. In Table 4.15, production and
utilization of pink seedless grapefruit production is shown. The primary market outlet for pink
seedless grapefruit has always been the fresh market. Production of pink seedless grapefruit in
Florida has expanded rapidly over the past decade. By the 1991-92 season, pink seedless
grapefruit has overtaken white seedless grapefruit as the most important grapefruit variety
produced in Florida.
While the percentage of fresh citrus marketing from Florida that has been fumigated has
historically been small, the major impact of a methyl bromide ban on the Florida citrus industry
is that no viable alternative exists as a post harvest control for fruit fly. Thus, a ban on methyl
bromide is likely to result in the loss of markets in other citrus producing states, namely
California, Hawaii, Arizona, and Texas.
It is important to note that the export market for fresh Florida citrus will not be affected
by a methyl bromide ban. Both European and Asian markets have refused to accept fruit which
has been fumigated with methyl bromide. Therefore no methyl bromide treated product has
been shipped to those markets in recent years.
As methyl bromide is used only in the post harvest fumigation of citrus destined for the
fresh market, a ban of methly bromide would have no direct effect on the processed citrus
industry. It is possible, however, that with no alternative available to fumigate fruit destined
for other citrus producing states, a ban of methyl bromide might result in an increase of
processed utilization at the expense of fresh market utilization.
SECTION 5
THE ECONOMIC IMPACT OF A METHYL BROMIDE BAN
Objectives
The objective of the economic analysis is to quantify the effect a ban on methyl bromide
use is expected to have on the state of Florida. Methyl bromide has been identified as a critical
chemical for the efficient production of several vegetable crops and in the marketing of fresh
citrus. It is used as a soil fumigant in several vegetables and fruit and as a fumigant for fresh
citrus packaging prior to shipping to other areas susceptible to crop or product damaging pests
common to the shipping area.
The vegetable and fruit crops analyzed in this research are those crops which are likely
to be most impacted if methyl bromide is no longer available as a soil fumigant. Those crops
identified included tomatoes, bell peppers, cucumbers, squash, eggplant, strawberries and
watermelons. Not all of these crops require methyl bromide to be used as a soil fumigant in all
circumstances, however, methyl bromide may impact the economic outcome of all production
systems because of production losses in crop production systems where methyl bromide is used.
Citrus is impacted because methyl bromide is used on fresh citrus as a post harvest
fumigant prior to shipping. No fresh citrus from Florida is allowed to be shipped to California,
Texas, Arizona, and Hawaii without fumigation of the packed fruit because of the danger of
carrying fruit fly from Florida into one of these producing areas. A ban on the use of methyl
bromide would currently eliminate these states as markets for Florida fresh citrus because no
effective alternative exists for methyl bromide for post harvest use.
The Impact on the Production of Vegetables from a Ban on Methyl Bromide
Methodology
Methyl bromide has been identified as a critical soil fumigant used in the production of
several vegetable and fruit crops, those being tomatoes, bell peppers, cucumbers, eggplant,
squash, strawberries and watermelons. While methyl bromide may not be critical to all crops
in all production systems, it is currently used in each of these crops in some production systems
within some production areas in Florida.
Production of these crops are economic enterprises that growers produce in expectation
of a positive return to their investments. These crops compete with each other and other crops
and enterprises for resources used in their production. Growers of these crops also compete
with other producers who can produce and ship these same products during the season that
Florida growers have them available.
A partial equilibrium model can be used to evaluate the effects a change in the industry
may have on the production and marketing of various crops from various regions. In the model
used here (see Appendix E for a more detailed discussion of the model), these crops were
modeled in a monthly model considering production from each of the major producing regions
in Florida and from other regions in the U.S. and Mexico which grow and sell during Florida's
season. See Appendix D for further discussion of the crops, months, and competing regions
included in the economic analysis.2
2As noted in Appendix D, two separate analyses are conducted. One analysis encompasses
those fruit and vegetable crops which are annuals, e.g. tomatoes, peppers, etc.; the other
analysis deals with the perennial crops, namely citrus.
88
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