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BOTRYTIS BLIGHT AND BACTERIAL SPOT ON TOMATOES
R. S. Cox and N. C. Hayslip
This report is a compilation of the latest in-
formation on control of important diseases of
tomato in south Florida, Spray programs for
staked and ground tomatoes are suggested,
INDIAN RIVER FIELD LABORATORY MIMEO REPORT 57-2
Fort Pierce, Florida
December 12, 1956
BOTRYTIS BLIGHT AND BACTERIAL SPOT ON TOMATOES
R. S. Cox and N. C. Hayslip a/
The Disease---Botrytis, or gray mold became a severe problem on tomatoes about eig:4
y';s ago, and has caused heavy damage to both staked and ground tomatoes in the
"'idian River, Devil's Garden-Immokalee, and Lower East Coast areas ever since. For
s',ec unknown reason Botrytis has not been a serious problem in the Homestead and
This disease is most active during periods of cool or cold weather when the
humidity is high--especially during cool nights with heavy dews or fogs. Winter sndi
eArly spring crops suffer the greatest amount of damage. The fungus attacks leaven,
stems, blossoms and fruit. It is known as Botrytis cinerea Fr. The name, gray mi'!I
drives from the characteristic appearance of the spore masses which occur on dieas-
ed fruit, stems and leaves.
Latest Research---An intensive study of this disease was made during the 1955-56
tomato season on staked and ground tomatoes. Five chemicals gave good control unier
conditions of moderate infection on ground tomatoes at the Indian River Field Laborq
tory, and two chemicals held the disease in check under severe infection on staked
tomatoes in a test in Palm Beach County. An interesting observation was made during
these studies; use of nabam plus various combinations of metal salts, including zinc
sulfate, resulted in a sharp increase in Botrytis--at least twice as much as in un-
sprayed check plots.
Suggestions on Control--Since a spray program must control all major foliage di-
seases it is necessary to select a chemical treatment for Botrytis which will also
protect the plants from the other diseases. With this in mind, the following sug-
gestions are made for the control of Botrytis:
A--For Manalucie (resistant to gray leafspot).- Spray every 5 to 6 days with
3/4 lb. dichlone (Phygon XL) per 100 gallons of water, beginning at thinning time or
sooner if late blight is present in the area Do not use dichlone on hot days (850F
or above) as injury may occur when temperature is high. Substitute four pounds of
ferbam on hot days only. This schedule should control all major foliage diseases ex-
cept bacterial spot. However, if late blight appears, spray with 1/2 pound dichlone
plus 1-1/2 pounds zineb until that disease becomes inactive.
B--For Homestead, Grothen, Rutgers, etc. (not resistant to gray leafspot)- Spray
every 5 to 6 days with1/2 pouL-nd dicone plus 1-1/2 pounds sineb per 100 gallons of
water, beginning when plants are 3 to 4 inches high. This mixture should control a,1
foliage diseases except bacterial spot. It is fairly effective in controlling Botry-
n, but not equal to dichlone uned without zineb, Since dichlone will not con'tr~ o
giay leafspot, zineb must be added.
The Disease---This disease has caused widespread and severe damage to south Florida
tomatoes every fall, and sometimes during the winter and spring seasons. It is close-
I' Associate Plant P:.th.-logia-t, Everglades Staticn, Belle Glade, and Entomologist,
Indian River Field LabcratLry, Ft; Pierce, respect lively,
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ly associated with warm periods of heavy and frequent rainfall. Blowing rains pro-
vide the primary means by which the disease is spread around, and it is under suc'
conditions that growers suffer severe losses. Bacterial spot was largely responsibi
for the heavy tomato losses during the fall of 1956 (estimated to be 50 to 75 per-
cent in many areas)4
The organism which causes bacterial spot, Xanthomonas visicatoria (Doidge)
(Dows.), attacks the leaves, stems, blossoms and fruit, causing defoliation, blossom
drop and often spotting of the fruit. The small dead spots on the leaves are easily
confused with gray leafspot and certain other diseases. It is of major importance
for the grower to know which disease is present because the control is radically
different for the different ones,
Latest Research---Several experiments were conducted in the fall of 1956, Since con-
ditions were ideal for the development of this disease, some important control data
were obtained. Neutral copper plus streptomycin sulfate gave the best control, and
copper alone was superior to streptomycin alone,
Suggestions on Control---A.-Treat seed with bichloride of mercury. Dissolve the bi-
chloride of mercury in water so as to have a 1-2000 solution (29.2 grains in one
gallon of water). Place seed in a cheesecloth bag (do not fill bag over 1/3 full)
and immerse in the solution for five minutes. Gentle agitation during this period
is desirable, Next, rinse the seed in running water for 15 minutes then dry them
quickly by spreading in a thin layer in the sun, Store in cool, dry place. Treated
seed should not be stored for more than two months. (Notet The importance of to-
mato seed transmission of bacterial spot is not clearly established. However, it is
a matter of record that this disease can be transmitted by tomato seed. Since seed
treatment costs so little it seems advisable to include this operation in the pro-
duction of tomatoes as insurance against possible seed-borne infections.)
B--Spray every 4 to 5 days during the rainy season, beginning when the first
true leaves appear. Mix a fixed copper compound (such as Tri-basic-copper sulfate
or copper A) at the rate of about 2 pounds metallic Cu per 100 gallons water plus
100 p.p.m, streptomycin sulfate, During periods of fair weather the interval be-
tween applications may be extended to 7 days. Good coverage is necessary. Continue
these treatments until the rainy season has passed, or until the plants become so
large that the cost of the copper-streptomycin spray is prohibitive. Separate treat-
ments with zineb or maneb must be made for the control of gray leafspot and late
The importance of recognizing the difference between bacterial spot and gray
leafspot cannot be over-emphasized. Gray leafspot often develops when growers are
treating for the control of bacterial spot, Since the copper and streptomycin treat-
ment is not effective against this disease. It is never advisable to leave zineb or
maneb out of the spray program for more than one week unless Manulucie (resistant to
gray leafspot) is used, The use of dichlone on Manalucie and dichlone plus zineb on
other tomato varieties is discussed under Botrytis blight.
Studies with spray mixtures are in progress in an attempt to develop a combi-
nation treatment which will control gray leafspot as well as bacterial spot.
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SUGGESTED SPRAY SCHEDULE
Treat all seed in prescribed manner with bichloride of mercury.
A. MANALUCIE. (Resistant to gray leaf spot).
Through October 31: Neutral copper (2 lbs. metallic) plus streptomycin
sulfate (100 p.p.m.). If late blight conditions develop (cool weather
and heavy dews or fogs) add dichlone (3/4 lb.)4
November 1 through April 30: Dichlone (3/4 lb.). Add neutral copper
and streptomycin if needed (during rainy periods) for bacterial spot
control. On hot days (85oF or above) use ferbam (3 lbs.) in place of
dichlone to prevent possible injury to the plants. If late blight
develops under this schedule, zineb (1-1/2 lbs.) may be added to
May 1: Discontinue dichlone (because this chemical may burn plants
in hot weather). Ferbam (3 Ibs.) may be used if Botrytis is a problem
and late blight is not active. Zineb (2 lbs.) or maneb (1-2/2 lbs.)
may be used if late blight is a problem and Botrytis is not active.
B1 HOMESTEAD, GROTHEN, ETC. (Not resistant to gray leafspot).
Through October 31: Neutral copper (2 Ibs. metallic) plus strepto-
mycin sulfate (10O p.p.m.) for bacterial spot control. Maneb or
zineb must also be used at no greater than 7 day intervals for the
control of gray leafspot, and possibly late blight. These treat-
ments probably should be applied separately until further research
with combinations is completed. Some growers may wish to use a mix-
ture of the copper and streptomycin with zineb (1-1/2 lbs.) or maneb
(1 lb.) on a trial basis.
November 1 through April 30: Dichlone (1/2 lb.) plus zineb (1/1/2 Ibs.).
If bacterial spot is still a problem continue separate treatments of
copper (2 lbs. metallic) plus streptomycin (100 p.p.m.) when needed.
On hot days (850F. or above) substitute ferbam (3 lbs.) in place of
dichlone plus zineb to prevent possible dichlone injury to the plants.
When weather cools, return to the dichlone-zineb spray.
May 1: Discontinue dichlone (because this chemical may burn during
hot weather). Ferbam (3 Ibs.) may be used if Botrytis is a problem and
late blight is not active. Zineb (2 Ibs.) ori-anei~Tl-3/2 lbse) should
be used if Botrytis is not a problem.