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Bulletin 235 July, 1931
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director
CRIMP--A NEMATODE
DISEASE OF STRAWBERRY
By A. N. BROOKS
TABLE OF CONTENTS
INTRODUCTION ..... ........... ............
SYMPTOMS ............
ETIOLOGY ....... .....
Inoculation Experiments
Diseased plant material ..........
Nemas occurring on crimped plants...
Relation of Nematode to Host ....
Thermal Death-point of Nematodes Infesting
Hot Water Treatment of Crimped Plants.
Seasonal Development .......... ..............
Dissemination of Nematode .................................
From one locality to another .................
Plant to plant ......... ... ....... ..........
CONTROL MEASURES --..... .......... ..
Disease-free plants set on disease-free soil.....
Roguing out of crimped plants........................
Crop rotation -....- .................
PAGE
3
4
6
13
... .... .. .. .. ... ..... -........ 3
... . .. ..... ............ 4
.. .. -...... .... .............. ... 1 3
the Buds of Crimped Plants........... 16
18
...... .... ............ i21
.... ...... ....... .. .. ... ....... ....... 2 1
....................... .................... ... .................... 2 1
SUMMARY ....................................... ................................... ............ ....................... 25
LITERATURE CITED .............................. ........................... --- 27
TECHNICAL BULLETIN
Bulletins will be sent free upon application to the
Agricultural Experiment Station,
GAINESVILLE, FLORIDA.
Bulletin 235 July, 1931
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director
CRIMP--A NEMATODE
DISEASE OF STRAWBERRY
By A. N. BROOKS
TABLE OF CONTENTS
INTRODUCTION ..... ........... ............
SYMPTOMS ............
ETIOLOGY ....... .....
Inoculation Experiments
Diseased plant material ..........
Nemas occurring on crimped plants...
Relation of Nematode to Host ....
Thermal Death-point of Nematodes Infesting
Hot Water Treatment of Crimped Plants.
Seasonal Development .......... ..............
Dissemination of Nematode .................................
From one locality to another .................
Plant to plant ......... ... ....... ..........
CONTROL MEASURES --..... .......... ..
Disease-free plants set on disease-free soil.....
Roguing out of crimped plants........................
Crop rotation -....- .................
PAGE
3
4
6
13
... .... .. .. .. ... ..... -........ 3
... . .. ..... ............ 4
.. .. -...... .... .............. ... 1 3
the Buds of Crimped Plants........... 16
18
...... .... ............ i21
.... ...... ....... .. .. ... ....... ....... 2 1
....................... .................... ... .................... 2 1
SUMMARY ....................................... ................................... ............ ....................... 25
LITERATURE CITED .............................. ........................... --- 27
TECHNICAL BULLETIN
Bulletins will be sent free upon application to the
Agricultural Experiment Station,
GAINESVILLE, FLORIDA.
BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola RAYMER F. MAGUIRE, Orlando
A. H. BLENDING, Bartow FRANK J. WIDEMAN, West Palm Beach
W. B. DAVIS, Perry J. T. DIAMOND, Secretary, Tallahassee
STATION EXECUTIVE STAFF
JOHN J. TIGERT, M.A., LL.D., President R. M. FULGHUM, B.S.A., Asst. Editor
WILMON NEWELL, D.Sc., Director IDA KEELING CRESAP, Librarian
H. HAROLD HUME, M.S., Asst. Dir., Re- RUBY NEWHALL, Secretary
search K. H. GRAHAM, Business Manager
S. T. FLEMING, A.B., Asst. Dir., Admin. RACHEL McQUARRIE, Accountant
J. FRANCIS COOPER, M.S.A., Editor
MAIN STATION-DEPARTMENTS AND INVESTIGATORS
AGRONOMY
W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S., Assistant
J. D. WARNER, M.S., Assistant
JOHN P. CAMP, M.S.A., Assistant
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian in
Charge
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
Husbandry
W. M. NEAL, Ph.D., Assistant in Animal
Nutrition
C. R. DAWSON, B.S.A., Assistant Dairy
Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C. E. BELL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
H. W. WINSOR, B.S.A., Assistant
H. W. JONES, B.S., Assistant
COTTON INVESTIGATIONS
E. F. GROSSMAN, M.A., Assistant
P. W. CALHOUN, B.S., Assistant
ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, Ph.D., Assistant
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph.D., Head
L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist
ENTOMOLOGY
J. R. WATSON, A.M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant
L. W. ZIEGLER, B.S., Assistant
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist
HAROLD MOWRY, B.S.A., Associate
M. R. ENSIGN, M.S., Assistant
A. L. STAHL, Ph.D., Assistant
G. H. BLACKMON. M.S.A., Pecan Culturist
C. B. VAN CLEEF, M.S.A., Greenhouse
Foreman
PLANT PATHOLOGY
W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, M.S., Mycologist
BRANCH STATIONS AND FIELD WORKERS
L. O. GRATZ, Ph.D., Asso. Plant Pathologist in charge, Tobacco Exp. Sta. (Quincy)
R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
W. A. CARVER, Ph.D., Assistant Cotton Investigations (Quincy)
RAYMOND M. CROWN, B.S.A., Field Asst., Cotton Investi-ations (Quincy)
JESSE REEVES, Farm Superintendent, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
GEO. D. RUERLE, Ph.D., Assistant Plant Pathologist (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
W. L. THOMPSON, B.S., Assistant Entomologist (Lake Alfred)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Sta. (Belle Glade)
R. W. KIDDER, B.S., Foreman, Everglades Experiment Station (Belle Glade)
R. N. LOBDELL, M.S., Assistant Entomologist (Belle Glade)
F. D. STEVENS, B.S., Sugarcane Agronomist (Belle Glade)
H. H. WEDGEWORTH, M.S., Associate Plant Pathologist (Belle Glade)
B. A. BOURNE, M.S., Associate Plant Physiologist (Belle Glade)
J. R. NELLER, Ph.D., Associate Biochemist (Belle Glade)
A. DAANE, Ph.D., Associate Agronomist (Belle Glade)
FRED YOUNT, Office Assistant (Belle Glade)
M. R. BEDSOLE, M.S.A., Assistant Chemist (Belle Glade)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
C. M. TUCKER, Ph.D., Associate Plant Pathologist (Hastings)
H. S. WOLFE, Ph.D., Asso. Horticulturist in charge, Sub-Trop. Exp. Sta. (Homestead)
L. R. TOY, B.S.A., Assistant Horticulturist (Homestead)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
FRED W. WALKER, Assistant Entomologist (Monticello)
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
W. B. SHIPPY, Ph.D., Assistant Plant Pathologist (Leesburg)
C. C. GOFF, M.S. Assisant Entomologist (Leesburg)
J. W. WILSON, Ph.D., Assistant Entomologist (Pierson)
*In cooperation with U. S. Department of Agriculture.
CRIMP-A NEMATODE DISEASE
OF STRAWBERRY
By A. N. BROOKS
INTRODUCTION
Crimp is the most widespread of any of the major diseases
of strawberry in Florida, being found in all of the areas where
strawberries are grown commercially. It has been recognized
by Florida growers for many years and has been designated by
them as French bud, white bud, red bud, brier bud, and crimp.
The first two of these terms are misnomers, because the affected
buds are not chlorotic or white, but usually of a reddish cast and
crinkled. Hence, the last three terms are more descriptive of
the disease. Since the initiation of the work in Florida upon
this disease, the writer has chosen to use the term "crimps" or
"crimp" as the common name (4)', because these terms are most
descriptive, and "crimps" was first used by Darrow in describing
the disease. (5)
Crimp is identical with the "dwarf" disease, as described by
Plakidas (9, 10) for Louisiana and by Stevens (12) for other
southern states. Crimp may be the same as the "red plant" dis-
ease as described by various workers in Great Britain (1, 2, 3,
7, 11), but is distinct from their so-called "cauliflower disease".
Outside of Florida the writer has observed crimp upon plants
at Chadbourn, North Carolina, and the disease has also been
found upon a small percentage of plants shipped into Florida
from Arkansas during 1929 and 1931. The disease is probably
widespread throughout the southern states, as has been sug-
gested by the survey made by Mook (8).
However, losses due to crimp are evidently not of as great
economic importance in the other strawberry-growing areas of
the United States as they are in central Florida, due to the warm-
er, moister weather which prevails at the latter place. The
losses incurred are twofold, (1) through a reduction in the num-
ber of plants propagated for fall setting and (2), through a re-
duction in the yield and quality of fruit produced by crimped
plants. Losses in individual fields have ranged from 0 to 75 per-
'Reference is made by number (italic) to Literature Cited, in the back
of this bulletin.
Florida Agricultural Experiment Station
cent, with an estimated loss of 2 percent for central Florida in
which area the following studies were made.
For a better understanding of the relationship of the various
factors involved in this disease, it is necessary to give a brief
outline of the cultural practices employed in the raising of straw-
berries in central Florida, since they differ somewhat from those
employed elsewhere. Strawberry plantations are usually re-
newed each year. Plants, mainly of the Missionary variety,
secured chiefly from Arkansas and Maryland during February
and March, are set out on wide beds and allowed to make run-
ner plants until June, at which time the runner plants are trans-
planted to other beds, where they in turn produce runner plants
for setting from September through October for fruit production.
From each 1,000 plants the grower secures from the north dur-
ing February and March he can, under favorable conditions pro-
duce 15,000 to 50,000 plants for fall setting. Furthermore, he
is dependent upon locally grown plants for fall setting and can-
not use successfully plants shipped in from the north at that
time. Hence, any disease which reduces the number of plants
propagated during the summer is of vital importance to the
grower. After plants are set in the fall, they are kept free
of runners, so they produce large crowns and bear fruit from
the latter part of November until May, when they are usually
plowed under.
Crimp may appear at any time of the year when the tempera-
ture is sufficiently high and the plants are putting on new
growth. The disease is most prominent during the rainy sea-
son, July through September. Cold weather checks the progress
of the disease and affected plants then put on normal growth,
but with the advent of warm weather the disease symptoms re-
appear. The diseased plants which are not fatally affected are
worthless as fruit producers because of the lateness and in-
ferior quality of their fruit. Investigations of crimp in Florida
have extended over a period of several years and the results ob-
tained are set forth in this bulletin.
SYMPTOMS
Crimp is a bud disease, affecting the young leaves as they de-
velop. Affected plants, with one bud to the crown, have a spread-
out, spider-like appearance, due to a few normal leaves having
developed before conditions became favorable for rapid develop-
Bulletin 235, Crimp-A Nematode Disease of Strawberry 5
ment of the disease (Fig. 1). Under conditions less favorable
for development of the disease, as lighter infestation or lower
temperature, there is less contrast between the healthy and af-
fected leaves (Fig. 2). The development of affected leaves is
materially inhibited and the leaves are deformed, ranging in size
from mere rudiments to almost normal. The leaflets are crimped
and crinkled, cupped, narrow in proportion to their length, with
a reddish cast which is most conspicuous on the serrations, veins,
and petioles. The tips of young leaves and stipules of severely
diseased plants show a dry and brown condition. The green
color of both young and old leaves is darker than normal (Fig.
3) and they are more brittle. Petioles are usually less pubescent
than normal, in fact, almost glabrous.
A
ftb--
Fig. 1.-Crimped strawberry plant, showing spread-out, spider-like growth
due to the development of a few normal leaves during the warm autumn
season before the disease developed.
In severe cases the disease may kill the main bud, with the
subsequent death of the plant, unless lateral buds chance to de-
Florida Agricultural Experiment Station
velop. In most cases, these lateral buds produce small, normal-
shaped leaves on long spindly petioles. Plants with multiple
bud crowns may have both healthy and diseased buds, and also
produce both healthy and diseased runner plants (Fig. 4), the
reason for which will be explained subsequently. The usual
thing, however,
is for all runner
plants from a dis-
eased mother
i plant to show
Scrimp.
ETIOLOGY
At the initia-
tion of the work
upon crimp sev-
Seral factors were
.A suggested; soil
conditions, fu n-
f gus or bacterium,
or virus. The first
~ .. -suggestion was
discarded after a
survey of the
Fig. 2.-Strawberry plant showing less contrast s
between length of petioles of healthy outer leaves strawberry-grow-
and crimped bud leaves than Figure 1 as a re- ing area showed
sult of slower development of plant and disease
during cool weather. that crimp ap-
peared on various
soil types. However, it was found to a greater extent in wetter
than in drier soil, the reason for which will be given later. Since
no fungus or bacterium could be observed by microscopic exam-
ination of diseased plants nor isolated from them, the second
suggestion was rejected. It was then thought that the trouble
might be of a virus nature, as suggested by Plakidas (9).
INOCULATION EXPERIMENTS
Diseased plant material: A preliminary experiment was
started in December, 1927, to ascertain if crimp were a trans-
missible disease. The crowns and roots of 60 crimped plants
were crushed in a mortar, mixed with distilled water, and the
mixture placed in the buds of 90 healthy plants, injuries being
made by passing a fine needle through the mixture into the buds.
Bulletin 235, Crimp-A Nematode Disease of Strawberry 7
The inoculated plants were then covered with bell jars for 48
hours. These 90 plants were in the field at the center of a two-
row bed containing 270 plants, thus leaving the 90 healthy plants
at each end of the bed to serve as checks.
Fig. 3.-Healthy strawberry plant, showing contrast with
crimped plants in Figs. 1 and 2.
Observations were made at frequent intervals but no symp-
toms of crimp appeared while these plants were fruiting, i.e. up
to the first of May. However, soon after the plants started to
put on active vegetative growth during the latter part of May,
the disease appeared among the inoculated plants, but not among
the check plants. By the middle of July all of the inoculated
plants were crimped, whereas the check plants remained healthy
with the exception of the two immediately adjacent to each end
of the plot of inoculated plants. The disease had spread to these
four plants. The healthy plants had completely filled their por-
tions of the bed with runner plants, whereas the diseased plants
had produced but two or three runners per plant. The results
of this preliminary experiment showed that crimp was a trans-
missible disease, possibly of a virus type capable of mechanical
inoculation.
Florida Agricultural Experiment Station
On the strength of these results a series of inoculation ex-
periments were performed, using as inoculum diseased plants
which had been finely ground by being passed three times
through a food chopper, using successively the three finest
plates. This material was diluted one-half with sterile distilled
water and either used in this condition or filtered through cotton,
filter paper, or a Berkefeld filter, grade "N". The inoculum was
introduced into the growing points of the buds of healthy plants
by means of a 26-gauge hypodermic needle, except in the case of
the unfiltered mixture. The latter was placed in the bud by
means of a blunt-tipped pipette, and pricked in with a fine steel
needle. The inoculated plants were covered with bell jars for
48 hours after inoculation.
v4
0
4i
p
/c
iC
Fig. 4.-Crimped strawberry plant, A, developing two crimped runners,
B and C, and one healthy runner, D.
Sixty-eight of the inoculations were made upon healthy plants
which had been set in 8 inch pots, kept in a cheesecloth house,
~~3~.
Bulletin 235, Crimp-A Nematode Disease of Strawberry 9
and 1,632 were made upon healthy plants set in the field. The
later lot of pants were set 12x12 inches upon two wide flat
beds in checked rows. One bed contained 1,080 plants, the other
contained 2,244 plants. Half the number of plants on each bed
were inoculated, half served as checks. The bed of 2,244 plants
was divided into 51 square plots of 36 plants each and 17 rect-
angular plots of 24 plants each. Inoculated plots were alternated
with uninoculated plots in checkerboard fashion. On the bed of
1,080 plants alternate plants were inoculated. Results of these
experiments are summarized in Table I.
TABLE I.-RESULTS OBTAINED BY INOCULATING HEALTHY STRAWBERRY
PLANTS WITH FINELY GROUND CRIMPED BUDS AND WITH FILTERED EX-
TRACT OF SUCH MATERIAL.
Sinoculum No. of plants
Treatment of inoculum Date of inoculations Inoculated Diseased
Berkefeld filtered ......I Oct. 15-16-17, 1928 923 0
SNov. 13-14-17-25, 1928
Cotton filtered ............ Nov. 19, 1928 168 0
Paper filtered .............. Sept. 21-Nov. 15-17, 1928 177 0
Jan. 25, 1929 1
Unfiltered ...................... Oct. 17-30, 1928 432 0
1 Jan. 25, 1929 I
Since the coarsely crushed inoculum in the preliminary ex-
periment was highly successful in producing crimp, and the finely
ground, and filtered inoculum in the above experiments did not
produce the disease, it was evident that the grinding and filtering
had removed the causal agent. These results pointed strongly
toward some causal agent other than a virus.
Nemas Occurring on Crimped Plants: During December, 1928,
nematodes were found in abundance in the buds and axils of the
leaves of crimped plants, while healthy plants had but few nemas
present in them. Actual counts were made during 1929-30 of the
nemas present in 207 crimped buds and in 249 healthy buds and
the buds were grouped into classes according to the number of
nemas present. The results obtained from the crimped buds are
given in Table II. The 207 crimped buds examined contained a
total of 48,764 nemas, an average of 235 nemas per bud, where-
as the 249 healthy buds examined contained but 46 nemas, an
average of 0.18 nemas per bud. No nemas were found in 235
Florida Agricultural Experiment Station
of the healthy buds, while the other 14 contained from 1 to 8
nemas each.'
TABLE II.-CLASSIFICATION OF 207 CRIMPED STRAWBERRY BUDS ACCORDING
TO NUMBER OF NEMAS PRESENT.
No. of nemas per No. buds Total nemas Av. nemas per
plant (class range) per class per class Ibud per class
1-100 .................................. 63 4,071 66
101-200 ............................. 43 5,610 131
201-300 .............................. 35 8,732 249
301-400 .............................. 35 11,557 330
401-500 ............................... 15 6,713 447
501-600 ............................ 3 1,781 593
601-700 ........................... 9 6,011 667
701-1000 ............................ 0 0 0
1001-1100 .......................... 4 4,289 1,072
Through the kindness of Dr. B. T. Galloway crimped plants
were sent to the Office of Nematology of the United States De-
partment of Agriculture for identification of nemas present.
A letter dated January 18, 1929, from Dr. N. A. Cobb stated
that the following species were found in the crowns of the crimp-
ed plants: Aphelenchus olesistus Ritzema-Bos., Tylenchus pseu-
dorobustus Steiner, and T. pratensis de Man. During March,
1929, Dr. G. Steiner came to Florida to make further identifica-
tions and observations upon the nematodes which had been found
in crimped plants. For several weeks during the following sum-
mer the writer spent some time with Dr. Steiner at the Office of
Nematology. These studies revealed that Aphelenchus fragariae
Ritzema-Bos. was the species occurring most abundantly in the
crimped buds, but not in healthy ones. The nemas in the axil-
lary spaces of the outer leaves were mainly free-living forms.
In January, 1929, a water suspension of nemas was obtained
from crimped buds and introduced into the buds of five healthy
plants in pots kept in a cheesecloth house. The suspension con-
tained approximately 15 nemas per drop. One drop was intro-
duced into each bud and the bud tissues injured by pricking
with a fine needle. After seven weeks these plants showed slight
symptoms of the disease. By March, one bud of one plant had
2A letter from Dr. Ernst A. Bessey, Nov. 4, 1929, states I studied
this disease incidentally while I was working on the root-knot nematode
and found it to be quite widely prevalent throughout the South, from Vir-
ginia south to Florida. This work was carried on mainly in the years
1905 to 1908. I first became familiar with the disease in 1901. the
cause was a species of Aphelenchus."
Bulletin 235, Crimp-A Nematode Disease of Strawberry 11
gone "blind". Microscopic examination of this plant showed
that nemas were abundant in the blind bud. By May, three of
the remaining four plants showed definite crimp symptoms. To
determine if the nematodes might be the cause of crimp more
extensive inoculation experiments were performed.
Early in February, 1929, Missionary strawberry plants were
secured from Maryland and planted 12 by 18 inches on a wide
flat bed in check rows. There were 20 rows of 130 plants each,
making a total of 2,600 plants. The bed was divided into 26
square plots containing 100 plants each. The inoculated and
uninoculated plots were alternated in checkerboard fashion.
The plants of eight plots were inoculated with water suspen-
sions of nematodes obtained by teasing apart crimped buds in
distilled water. The suspensions of nemas were introduced into
the buds of the healthy plants by means of a pipette, without
making any injuries, as this had been thought to be unnecessary.
The inoculated plants were then covered with bell jars for 48
hours.
The plants of five plots were inoculated with the filtered juice
expressed from the buds of crimped plants. In the preparation
of this inoculum the crimped buds were finely ground in a fine
food chopper and then mixed with an equal volume of distilled
water. The liquid was filtered through paper and passed
through a Berkefeld filter, grade "N". The filtrate was intro-
duced into the buds of the healthy plants by means of a hypo-
dermic needle. The plants were covered with bell jars for 48
hours after inoculation.
The results of the experiment are given in Table III.
Since all attempts to transmit crimp by means of hypodermic
needle inoculations with the filtered juice from crimped buds had
failed, an attempt was made to transmit it by aphids, as was
suggested by Plakidas (9). At the same time inoculations with
nematodes were made to serve as checks. During the period
from March 5 to May 19, 1930, aphids of the species Myzus frag-
aefolii Cockerell and Aphis forbesii Weed, were transferred
from crimped plants in the field to 50 healthy plants in 6" pots
which were kept in a cheesecloth house and protected from in-
festation by other insects. From 20 to 40 aphids were placed on
each plant, and the plants were then covered with fine mesh
wire cages until the aphids had become established and were
colonizing.
During the same period the buds of 73 healthy plants in 6"
Florida Agricultural Experiment Station
TABLE III.-RESULTS OF INOCULATING HEALTHY STRAWBERRY PLANTS
WITH WATER SUSPENSIONS OF NEMATODES FROM CRIMPED STRAWBERRY
BUDS AND WITH FILTERED JUICE FROM SIMILAR BUDS.
Total number
Total number of plants
Dates of al developing
Kind of inoculum used inoculation inoculated crimp up to
inoculated crimp up to
June 12,
1929
3/29/29 100 51
3/29/29 100 23
Nematode 4/12/29 100 60
5/ 7/29 100 33
Suspension 5/ 8/29 100 15
5/11/29 100 35
5/11/29 100 55
5/22/29 100 29
S 3/29/29 100 0
Filtered 4/12/29 100 0
5/ 9/29 100 0
Extract 5/11/29 100 0
5/11/29 100 0
Check plants ................ Uninoculated 1300 0
pots were protected from insects as described above and inocu-
lated with water suspensions of nemas from crimped plants.
In most cases the nemas were obtained from the same plants
from which the aphids had been transferred. Ten healthy
plants, uninoculated, served as checks for each of the two kinds
of inoculation. The results of these inoculation experiments are
summarized in Table IV.
TABLE IV.-A COMPARISON OF THE ABILITY OF NEMAS AND THE APHIDS,
Myzus fragaefolii AND Aphis forbesii, TO TRANSMIT STRAWBERRY CRIMP.
Number
of Percent-
t Number crimped Percen-
Kind of inoculation Date of plants plants age of
inoculation plants plants crimped
inoculated up to plants
June 17, plants
1930
3/19/30 8 8 100
5/ 9/30 20 16 80
Nematode 5/ 9/30 10 6 60
5/16/30 20 16 80
_5/19/30 15 10 67
Aphis forbesii, 3/ 5/30 10 0 0
and 3/31/30 10 0 0
Myzus 4/ 5/30 10 0 0
fragaefolii 4/30/30 10 0 0
(mixed population) 5/ 9/30 10 0 0
Check plants ............................ Uninoculated 20 0 0
Bulletin 235, Crimp-A Nematode Disease of Strawberry 13
It will be observed from the table that none of the 50 plants
to which aphids had been transferred developed crimp, although
the aphids colonized and multiplied readily upon them. Also
none of the uninoculated plants crimped. On the other hand,
56 of the 73 plants inoculated with nemas developed crimp.
From the results given in Table IV it will be seen that in no
case was crimp transmitted by aphids, whereas inoculation of
healthy plants with nematodes from crimped buds produced a
high percentage of infection. All of the uninoculated plants
remained normal. These results are not in agreement with those
reported by Plakidas (9) in which he secured transmission of
dwarf by means of aphids in a test in which he used six plants
for inoculation and four for controls. However, as he has stated,
"In this lot (of Klondike plants obtained from North Carolina)
a relatively high percentage of the plants was subsequently
found to be infected with dwarf."
Since the buds of crimped plants contain nematodes in great
numbers, whereas the buds of healthy plants contain practically
none, and since crimp has been successfully transmitted by trans-
ferring nematodes from crimped buds to healthy ones and it has
not been transmitted by transferring aphids from crimped to
healthy buds, nor by hypodermic inoculations of healthy buds
with filtered juice of crimped buds, it is concluded that crimp is
not a virus disease but is caused by infestations of the buds by
nematodes. The nematode causing the disease is probably Aphe-
lenchus fragariae as this species is most abundant in the diseased
buds. Of course these experiments have not eliminated the pos-
sibility that crimp is caused by a virus which is transmitted only
by nematodes. However this is a problem which would be rather
difficult to solve.
It appears probable that the extreme malformed growth of
crimped plants is due to toxic as well as mechanical injury by
the nematodes.
RELATION OF NEMATODE TO HOST
A study of the relationship of nematodes to the crowns of
crimped strawberry plants proceeded along two lines: (1) the
determination of the plant part most heavily infested, (2) the
relationship of the nemas to the plant tissue, i.e. whether endo-
or ectoparasitic.
A microscopic survey of the various parts of crimped plants
shows that the nemas occurred only at the bases of the leaves
Florida Agricultural Experiment Station
and in the buds. The relative numbers of nemas present in
these positions were determined by removing carefully the leaf
bases and attached stipules one by one and teasing them apart
in drops of water on micro slides. Buds were treated in like
manner. Then a count was made of the nemas found in each
drop. In case the drop contained too many nemas to be easily
counted it was diluted and divided among several slides. Healthy
plants were treated similarly for comparisons. The results of
these counts are summarized in Table V. It was found that the
nemas were more numerous at the bases of the inner leaves of
crimped plants than at the bases of the outer leaves. The re-
verse was true of healthy plants. The buds of crimped plants
contained nemas in large numbers, while those of healthy plants
contained practically none. In both cases the nemas at the
bases of the outer leaves were mainly free-living forms, whereas
those at the bases of the inner leaves and in the buds were chiefly
of the species Aphelenchus fragariae.
TABLE V.- COMPARISON OF THE AVERAGE NUMBER OF NEMATODES AND
THEIR LOCATION IN 38 CRIMPED STRAWBERRY AND 33 HEALTHY STRAW-
BERRY PLANTS.
Average number of nematodes
Per leaf base
Condition pr
of plant o M Per bud Plnt
o p 6 Plant
od d O d 1 d o o o
S z2 :z z a z
Crimped .... 5.7 6.1 4.0 5.5 5.8 7.9 8.5 10.9 14.3 16.6 199.9 280.9
Healthy ... 5.09 3.06 1.252.65 1.66 2.00 0.69 0.66 0.42 0.36 0.06 11.0
'Numbers designate position of leaf relative to bud.
The second point to determine was whether the nematodes
causing crimp are endo- or ectoparasitic. It had been found that
nemas could be obtained easily by washing leaf bases and stip-
ules, and buds which had been pried open in water. This sug-
gested that many of the nemas were outside the tissue. Con-
sequently, an experiment was performed in which the leaf bases
and attached stipules of crimped plants were removed carefully
and each washed rapidly in a drop of water on a micro slide.
The plant part was then removed to a drop of water on another
slide and teased apart. Buds were opened and similarly treated.
A count was made of the nemas thus obtained and the results
Bulletin 235, Crimp-A Nematode Disease of Strawberry 15
are shown in Table VI. Since 75 percent of the total number of
nemas present in the diseased plants were readily washed off
the plant tissue into the first drops of water, it is apparent that
they were outside the tissue. The mere fact that 25 percent of
the nemas appeared in the drops of water in which the tissue
was teased apart does not prove that they were inside the tissue
because, due to the compact arrangement of the leaf hairs, the
nemas might not be removed readily in the first drop of water.
TABLE VI.-COMPARISON OF THE NUMBER OF NEMAS OBTAINED BY RAPIDLY
WASHING IN WATER LEAF-BASES AND BUDS OF CRIMPED STRAWBERRY
PLANTS WITH THE NUMBER OBTAINED BY TEASING APART THE WASHED
MATERIAL IN OTHER WATER.
Number of nemas obtained
By washing By teasing
tissue apart tissue '
Number and kind :, Q
of plant parts .
) 5 C )
BZB 0 o' a
45 buds of mother plants .......-.. 8,417 80.5 2,040 19.5 10,457 232
136 leaf-bases of mother plants' 1,069 74.5 367 25.5 1,436 11
301 buds of Runner plants ............ 10,067 70.8 4,160 29.2 14,227 47
'Only the three innermost leaf-bases were used.
To determine definitely whether the nemas were inside or out-
side the plant tissue, diseased buds were fixed in warm Flem-
ming's strong fixative and embedded in paraffin according to the
usual procedure. Both transverse and longitudinal sections
were cut. After the sections had been mounted on micro slides
and the paraffin dissolved they were run down through the al-
cohols to water and then bleached in hydrogen peroxide until
the osmic acid staining of the nemas was sufficiently light to
make them easily recognized. Most of the plant tissue was much
lighter in color than the nemas. The slides were washed, run
up through the alcohols to xylol and mounted in balsam. Micro-
scopic examination of these slides showed that none of the nemas
were in the plant tissue, but were located in the bud only in those
protected air spaces to which they could migrate from the out-
side without penetrating the plant tissue (Fig. 5). Hence, the
nematodes causing crimp are ectoparasitic and not endoparasitic.
Florida Agricultural Experiment Station
This finding is in accord with the description given by Goodey
(6) as to the relation of Aphelenchus fragariae to its host plant,
in the red plant disease of strawberry in Great Britain.
Fig. 5.-Longitudinal section of crimped strawberry bud, showing the head
and anterior portion of nema (indicated by arrows).
The Aphelenchi possess spears or sucking tubes which would
enable them to secure their food from their host plant under
ectoparasitic conditions.
THERMAL DEATH-POINT OF NEMATODES INFESTING THE BUDS
OF CRIMPED PLANTS
Three series of tests were made in an attempt to determine the
thermal death-point of the bud-infesting nemas. In the prelim-
inary tests, a water suspension of nemas from the buds of crimp-
ed plants was made containing approximately 600 nemas per cc.
Five cc. of this suspension were placed in each of 24 culture
Bulletin 235, Crimp-A Nematode Disease of Strawberry 17
tubes. Three tubes were used for each temperature-time trial
and 3 untreated served as checks. The tubes were immersed
half their length in a constant temperature water bath for a
given time, then removed and quickly cooled to room tempera-
ture. The contents of the tubes were immediately examined for
active nemas. The temperatures and durations of treatments,
together with the results obtained, are given in Table VII.
TABLE VII.-RESULTS OF TESTS TO DETERMINE THE THERMAL DEATH-POINT
OF NEMAS REMOVED FROM THE BUDS OF CRIMPED STRAWBERRY PLANTS.
H Condir on of nemas after treatment'
Hot Water Treatment Tube 1 Tube 2 Tube 3
48'C. 30 min. ............................ -
47'C. 30 min. ............................ + +
46C. 30 min. ............................ + + +
45C. 30 min. ............................ + + +
48'C. 20 min. ............................ -
48C. 10 min ........................... + -
48C. 5 min. ..................... + + +
Check (untreated) ................. + + +
'+ = active nemas present; = active nemas absent.
The methods of procedure employed in the second series of
tests were similar to those of the preliminary tests but with one
exception. Instead of examining the contents of all tubes of
each test for active nemas immediately after the heat treatment,
one tube was examined at that time, a second 24 hours later and
the third 72 hours after treatment. This was done to give the
surviving nemas which had been temporarily stunned a chance
to resume activity. Results of this experiment are given in
Table VIII.
In this experiment it was found that 72 hours was too long
an interval after treatment for observation of active nemas, as
those in the check tube were inactive, at the end of that period.
In the two foregoing experiments the temperature given is
that of the water in the bath, and the time is the interval that
the tube was immersed in the water. The temperature of the
5cc. of suspension inside the tube was not taken. Hence the re-
sults are merely comparative and are somewhat comparable to
those which might be obtained by so treating the buds of crimped
plants.
In the third series of tests the counts of active Aphelenchi were
kept separate from the other forms of nemas associated with
18 Florida Agricultural Experiment Station
TABLE VIII. RESULTS OF TESTS TO DETERMINE THE THERMAL DEATH-
POINT OF NEMAS REMOVED FROM THE BUDS OF CRIMPED STRAWBERRY
PLANTS.
Condition of nemas at the intervals
Hot Water Treatment indicated after treatment
Hot Water Treatment
0 hours 24 hours 72 hours
48C. 30 min. .................... -
20 .......................... --
15 .......................... +
10 ....................... +
20 ..-............... -
15"------------ --------- +
15 ......................-
46C. 30 min ....-...-...---..-.. + + 4 -
20 ................ ..- + + -
15 .................... ....... + + -
10 ................... I + +
Check (Untreated) ..................... .. + + -
'+ = active nemas present; = active nemas absent.
them. A suspension of nemas containing approximately 30
Aphelenchi per cc., together with the other forms associated
with them, was obtained from crimped buds. One cubic centi-
meter of this suspension was placed into each of 88 culture
tubes. There were 22 different temperature-time treatments
with four tubes in each. After treatment, the contents of two
tubes of each set were examined immediately and the other two
tubes were placed in a refrigerator and their contents examined
20 hours later. Results of the various treatments are given in
Table IX.
From the results of the first and second series of tests it ap-
pears that nemas from the buds of crimped plants can be inacti-
vated by keeping them in water suspensions at 48C. for 30 min-
utes. In the third series where each tube contained 1 cc. of
suspension instead of 5 cc. and where the counts of active
Aphelenchi were kept separate from the other nemas, the therm-
al death-point of the Aphelenchi was found to be 480C. for 10
minutes, 470C. for 20 minutes, and 460C. for 30 minutes.
HOT WATER TREATMENT OF CRIMPED PLANTS
If nematodes were the cause of crimp and it were possible to
free a crimped plant of nemas by some treatment which would
not seriously affect the plant itself, all subsequent growth should
be normal. Even before the thermal death-point of the nema-
Bulletin 235, Crimp-A Nematode Disease of Strawberry 19
TABLE IX.-RESULTS OF TESTS TO DETERMINE THE THERMAL DEATH-POINT
OF Aphelenchi AND OTHER NEMAS REMOVED FROM THE BUDS OF CRIMPED
ST-AWBERRY PLANTS.
Number of a
0 hou
Hot Water Tube 1
Treatment
r64
s.
480C. 20 min. ........
15 ........
10 .......
5 ......
47"C. 30 Min.........
20 ........
15 ........
10 .......
46C. 40 min ........
30 ........
20 ........
20
15 ........
10 .
45C. 30 min. ........
20 ........
15 ........
10 ........
44 C. 40 min. .......
30 ........
20 ........
Check
(Untreated) ......
0
0
0
1
0
0
0
0
1
0
0
10
4
0
0
0
0
0
20
0
0
O
0
0
0
O L
4
0
O _
0
0
0
0
0
0
0
2
2
0
0
1
1
0
0
0
1
0
7
2
2
13
t
20
ve nemas observed immediately and
hours after treatment
rs
Tube 2
0 00
0 0
0_0
0 1
0 0
0 0
0 1
0 0
0 0
0 1
0 0
2 2
0 0
0 0
0 1
1 0
1 2
0 6
32 21
20 hours
Tube 3
0 0
0 0
0 0
2 2
0 0
0 0
0 3
1 2
5 5
0 1
0 3
1 4
1 2
2 5
0 0
2 1
5 4
0 0
0 5
0 1
3 2
14 8
Tube 4
42
)1 1
0 0
0 0
0 0
0 0
1
0 0
1 3
1 2
2 3
0 2
0 1
0 6
2 2
1j 7
2 1
1 2
4 5
0 0
0 7
0 2
3 1
19 7
todes had been determined,
it was decided to
expose crimped
plants to hot water treatment in an effort to free the plants of
nematodes, using temperatures suggested by G. M. Darrow dur-
ing a conversation upon control of cyclamen mite on strawberry.
During May and June, 1929, 400 crimped plants were removed
from the field, treated with hot water at 48C. for 30 min. and
then set out in land free of crimp. At the same time 200 un-
treated crimped plants were transplanted to the same plot to
serve as checks. Neither treated nor untreated plants survived
the transplanting. Similar attempts were made during the fall
of 1929 with like results.
Florida Agricultural Experiment Station
It was then decided to use potted crimped plants for treat-
ment so that they could be placed in shade for a week after
treatment before being exposed to direct sunlight.'
Crimped plants in 4" or 6" pots were immersed in a constant
temperature water bath for various time-temperature treat-
ments. Since nemas had been found only in leaf bases and buds,
the blades of the older leaves were held out of the water, to give
the plant a better chance to recover after treatment. The buds
and leaf bases were covered by water during treatment. The
plants were immediately cooled by water spray after the treat-
ment, placed in shade for a week, and then in direct sunlight.
Untreated crimped plants in pots served as checks.
The results of the various treatments are given in Table X.
TABLE X.-RESULTS OBTAINED BY TREATING CRIMPED STRAWBERRY PLANTS
WITH HOT WATER TO FREE THEM OF NEMAS.
Date Hot water
treatment
5/15/30 48'C. 20 min.
5/24/30 48'C. 20 min.
6/17/30 49'C. 20 min.
6/17/30 47'C. 20 min.
6/18/30 49C. 20 min.
6/18/30 47C. 20 min.
6/30/30 48C. 10 min.
6/30/30 46"C. 30 min.
I Untreated
No. of plants Results as per final obser-
treated I vation July 22, 1930
4 in 4" pots I All plants developed
Normally
3 in 4" pots One plant died.
3 in 6" pots Five plants developed
I normally.
7 in 6" pots All plants developed
Normally
7 in 6" pots Four plants developed
normally.
Three plants showed crimp
to a less degree than be-
fore treatment.
5 in 6" pots One plant died.
I Four plants developed
Normally.
1
5 in 6" pots I All plants showed less
crimping but were not
Normal.
3 in 6" pots I All plants showed crimping.
Experi-
ment
No.
1
2
3
4
5
6
7
8e
Check i
I All plants showed crimping.
A 1 nlants were crimped.
13 in 6" pots
I 20
"The writer is indebted to Mr. W. D. Wood, Quarantine Station, Dis-
trict of Columbia, for this suggestion as to a successful procedure in
handling plants subsequent to the hot water treatment.
Bulletin 235, Crimp-A Nematode Disease of Strawberry 21
The results of the foregoing experiments tend to show that
crimp is not a virus disease but is caused directly by nemas.
Treating the buds of crimped plants at 48C. for 20 minutes
was sufficient to kill the nemas in the buds and restore the plant
to normal growth.
SEASONAL DEVELOPMENT
Crimp has been found at all seasons of the year in central
Florida, although it is most noticeable during the rainy season,
July to October. In the spring, the disease may be found as
early as March, upon infested nursery stock shipped in during
February from nurseries farther north. On the other hand, the
fruiting plants set out the previous fall usually do not show
symptoms of crimp until the latter part of May, due to the lack
of vegetative growth of the plants until that time.
In the fall the plants continue to show crimp symptoms until
the advent of cool weather. The plants may apparently recover
from the disease during December when the air temperature is
too low for nema development and yet high enough for plant
growth to take place. However, with the advent of warm
weather and the renewal of leaf growth, these plants will again
display crimp symptoms due to the renewed activity of the
nemas. To determine this point, crimped plants were marked
in the field during the fall and observed through their stages of
apparent recovery during December and reappearance of the
disease in April or May, as were likewise crimped plants which
had been removed from the field and set in pots, kept in a cheese-
cloth house.
DISSEMINATION OF NEMATODE
From One Locality to Another:-During the past few years
it has been shown that nurseries, most probably unknowingly,
have shipped crimped plants from state to state. The disease
was discovered on Missionary plants shipped to Plant City,
Florida, during February, 1929, and on Blakemore plants shipped
during March, 1931. These shipments originated in Arkansas.
The disease has also been found in plants originating in North
Caro ina. In this way crimp is being spread over a wide area.
This is due to the fact that recent y infested plants ordinarily
do not show crimp symptoms and hence escape detection at time
of shipping, or to the fact that the plants are shipped at a time
of year when crimped plants have apparently recovered and do
not show the symptoms.
Florida Agricultural Experiment Station
Locally, in the central Florida area, infested plants are used
unknowingly for fall setting with the result that the fields are
irregularly spotted with diseased plants three to four weeks
after setting time. In this way, the disease is often carried to
fields not previously infested.
Plant to Plant:-During periods of heavy rainfall the dissem-
ination of crimp in the nursery or field is rapid, especially if the
water washes over or ponds over the plants. In central Florida
this spread is most rapid from July to October. The spread is
from higher to lower ground, often causing 100 percent disease
among the plants in the lowest portions of an infested field, while
the percentage disease among the plants on the higher ground is
considerably less, often only 1 to 2 percent. Stevens and Mook
(13) have shown this to be true in their study upon dwarf in
North Carolina.
To a limited extent, it may be possible for the nemas to mi-
grate from plant to plant in films of moisture as might occur
during heavy dews, but no work has been done to establish this
fact.
Diseased plants usually produce diseased runner plants, al-
though occasionally both healthy and diseased runners may de-
velop from a diseased plant. The method by which this takes
place was demonstrated as follows: The tips of runners at
various stages of development were removed from crimped
plants and their nemic content determined. Eighty-eight runner
tips were examined and 76 were found to contain a total of 2,301
nemas while 12 of the tips contained none. Even when the run-
ner was but 1/ to 1 inch long the number of nemas in the tip was
sometimes more than 200. At the same time a similar examina-
tion was made of the tips of runners from healthy plants. Two
of 132 tips examined contained a total of 6 nemas, the other 130
tips contained none. Thus, one way in which crimp is spread
from plant to plant is by the runner tip becoming infested with
nemas as it pushes through the axillary space of the leaf of the
mother plant. This also explains why a crimped plant may pro-
duce both healthy and diseased runners. If the axillary space is
infested with nemas during the time the runner tip is passing
through it, a crimped runner plant is the result, but if the space
is not infested at this time, a healthy runner plant is produced.
Healthy plants may become infested from the soil, by rain
washing the nemas or eggs into the buds. In September, 1927,
800 plants were secured from a local grower and set out on land
Bulletin 235, Crimp-A Nematode Disease of Strawberry 23
which had had crimped plants the previous two seasons. That
the source of plants was clean was determined by a careful pre-
vious inspection of the nursery beds from which they came,
and inspection of fields later set to plants from the same nursery
beds. The plants were set on beds six inches high, Due to the
extreme dry weather, surface or flood irrigation had to be used.
The middles between beds were filled with water which was
then splashed over the plants by means of boards fastened to
garden rakes. During October crimp appeared and by the first
part of December, 75 % of the plants displayed the disease symp-
toms. This showed that the nema causing crimp can live over
from year to year in the soil and that water washing over or
ponding over healthy plants may transfer nemas from soil to the
buds and cause the disease. This accounts for much of the in-
fection which takes place during the rainy season. However, if
land is well drained, infection from the soil is slight.
Furthermore, during periods of lower temperatures and less
rainfall, infection from the soil is practically nil. During the last
week in September and first part of October, 1929, 20 healthy
plants were set in 8" pots containing soil which had been taken
from around crimped plants in the fields. At the same time,
100 healthy plants were set in the field in areas from which
crimped plants had just been removed. These plants were ob-
served from time to time throughout the fruiting season-De-
cember to March-but none developed crimp. An explanation
for this apparent failure of infection from the soil at that time
involves several factors. (1) There is less likelihood of washing
or ponding of water over plants at that time, as the rainfall is
light during that season. (2) At that time plants are main-
tained under the hill system instead of the matted row, conse-
quently the individual plants have free circulation of air about
them, resulting in a drier environment. (3) The temperatures
are lower, thus slowing down nema activity. The mean monthly
temperatures and rainfall for the period are shown in Table XI.
TABLE XI.-MEAN MONTHLY TEMPERATURES AND RAINFALL AT TAMPA,
FLORIDA, DURING THE SUMMER AND AUTUMN MONTHS.
Month Temperature Rainfall inches
Degrees F.
July ....................-- ...... ... 81.3 7.93
August ................................. I 81.7 8.01
September ............................ 80.2 6.76
October -------....----.. ...-........ 74.3 2.98
N ovember .............................. 67.1 1.73
December ... .......... ..-......I. 61.6 1.98
Florida Agricultural Experiment Station
Thus, it is possible to use infested fields for October setting
of plants provided the plants themselves are free of the disease
at setting time. This simplifies control measures which have
been worked out upon the basis of producing clean plants for fall
setting. The acreage involved in nursery beds is much less
than that in fields set for fruit production. Hence, there is a
greater chance of securing disease-free land for the purpose.
CONTROL MEASURES
DISEASE-FREE PLANTS SET ON DISEASE-FREE SOIL
As has just been mentioned, the nursery beds have been con-
sidered the logical place to apply control measures so as to pro-
duce clean plants for fall setting.
In central Florida the grower must be assured of a source of
clean plants from the north for his February setting. Up to
this time the greatest difficulty lies in the fact that plants are
inspected shortly before shipping. Due to the cold weather of
the late fall and winter very few of the infested plants display
crimp symptoms at shipping time, but will soon develop symp-
toms under the influence of the higher temperatures prevailing
in central Florida. The only safe way is to inspect the northern
nurseries during the summer months when the disease is ap-
parent and certify only those nurseries which are free of the
disease for shipment of plants to central Florida.
With a source of clean plants and well drained land which is
free of crimp the Florida grower can produce clean plants for fall
setting, at which time he can use infested fields without much
danger of the plants becoming infested from the soil. The area
of land involved in plant propagation is comparatively small,
hence it is a fairly easy matter for the grower to follow this
method of preventing the development of crimp.
ROGUING OUT OF CRIMPED PLANTS
During the spring of 1929 roguing experiments were carried
on with the cooperation of three growers. Nursery beds which
had been set in February with plants from northern nurseries
were inspected once a week, and all crimped plants were pulled
up and removed from the beds. This work was continued until
the middle of June, by which time the beds were so matted with
plants as to make further roguing impracticable. Another grow-
er had nursery plants which had been set in February and among
Bulletin 235, Crimp-A Nematode Disease of Strawberry 25
which crimp was developing in three parts of the nursery. How-
ever, he could not be induced to rogue out the crimped plants
and hence his patch served excellently as a check for the experi-
ment.
In the three patches where roguing was practiced the disease
was controlled on the better drained land but could not be con-
trolled on the land which stood under water after heavy rains.
However, these three growers used for fall setting only the
plants from the better drained land with the result that there
was only 1 to 5 percent crimps appearing in the fields set in the
fall, whereas the grower who did not rogue out the crimped
plants on his nursery beds had 75 percent crimp appearing in the
fields set during the fall.
Roguing. pays only where nursery plants are grown on well
drained land and is valueless if the land is extremely wet. It
should be used only where the first method of control cannot be
followed. Thus, adequate drainage is another aid in preventing
the spread of crimp.
CROP ROTATION
If the nemas causing crimp are specific for strawberries there
is a chance then to decrease the number of these nemas in the
soil by crop rotation.
In central Florida, crimp is more abundant in fields in which
strawberry plants are carried over from year to year. The gen-
eral practice of securing plants from the north each year and
destroying the old plants after they have fruited has a tendency
to keep crimp down to the minimum.
SUMMARY
Crimp, also known as French bud, brier bud, etc., has been
present in Florida for many years. It is identical with "dwarf"
of Louisiana and may be the same as "red plant" of Great
Britain. Apparently crimp is more destructive in Florida than
elsewhere, as it reduces the number of plants propagated and
causes fruit production to be late and of inferior quality.
Crimp is a bud disease affecting the development of young
leaves. Affected leaves range in size from mere rudiments to
almost normal, are crinkled, cupped, darker green and more
brittle than normal, less pubescent, and usually of a reddish cast.
Nematodes, mostly Aphelenchus fragariae, were found in
Florida Agricultural Experiment Station
abundance in diseased buds but not in healthy ones. The nemas
are located in the axillary spaces of the leaves and folds of the
buds, which shows that they are ectoparasitic and not endopara-
sitic.
Uniformly successful inoculations were made by introducing
suspensions of the nemas into buds of healthy plants. Hypo-
dermic needle inoculations with the filtered extract of diseased
plants did not produce the disease in healthy plants, nor did
strawberry aphids, Myzus fragaefolii or Aphis forbesii, trans-
mit the disease from crimped to healthy plants.
The thermal death-point of the nemas involved was found to
be 480C. for 20 minutes or 470C. for 30 minutes.
Potted crimped plants which were immersed in warm water,
480C. for 20 minutes, were restored to normal growth. The hot
water treatment, however, is too tedious to be recommended as
a means of commercial control.
Crimp is most noticeable during warm, moist weather, July to
October in central Florida. During cool weather diseased plants
apparently recover and put on normal growth but when warm
weather again prevails the crimp symptoms reappear.
Infestation of strawberry buds by nemas from the soil is ac-
complished chiefly by heavy rains, and water washing or pond-
ing over plants. Tips of runners become infested as they push
through infested axillary spaces of leaves. Crimp is introduced
into new territory by the use of diseased nursery plants.
In central Florida control has been accomplished by securing
disease-free plants in February or March and setting them on
disease-free land to propagate plants for fall setting. Healthy
plants can be set in infested fields as soon as the summer rainy
season ends without much danger of their buds becoming in-
fested from the soil.
Roguing out crimped plants in the nursery beds during the
early spring has met with some success on well drained land,
but is valueless on wet land.
Renewing of strawberry plantations each year decreases the
nema population, and crop rotation may also be of further value
in this respect.
Bulletin 235, Crimp-A Nematode Disease of Strawberry 27
LITERATURE CITED
1. BALL, E. Some observations on "red plant" of strawberries. Ann.
Rpt. Agr. & Hort. Res. Station, Long Ashton:73-77. 1926.
2. BALL, E., C. E. T. MANN and L. N. STANILAND. Strawberry investi-
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