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CONTROL OF THE MAJOR FOLIAGE DISEASES OF
TOMATOES GRON ON THE SANDY SOILS OF SOUTH FLORIDA
R, S. Cox and N. C. Hayslip
This report is a compilation of the latest
information on control of important
diseases of tomato. Spray programs for
staked and ground tomatoes are suggested.
INDIAN RIVER FIELD LABORATORY 1MI3EO REPORT 57-3
Fort Pierce, Florida
April 30, 1957
CONTROL OF THE MAJOR FOLIAGE DISEASES OF
TOMATOES RO"W ON THE SANDY SOILS OF SOUTH FLORIDA
R, S. Cox and N. C. Hayslipl/
Tomato crops grown in South Florida are threatened by several foliage
diseases, each of which causes severe losses to some plantings almost every years
Growers are thus faced with the necessity of adopting a spray program to protect
their crops from these diseases. Unfortunately, no one chemical or mixture of
chemicals has been found which will control adequately all of these diseases.
This complicates the control procedure to such an extent that a standard or set
spray program is impossible,
Late blight, gray leaf spot, Botrytis gray mold and bacterial spot have
caused widespread and severe damage to vast acreages of tomatoes during the past
ten years. The carbanate fungicides, nabam plus zinc sulfate, zineb, and maneb,
have effectively controlled late blight and gray leaf spot for several years.
Following widespread adoption of the dithiocarbamates, bacterial spot and
Botrytis gray mold have increased in importance.
Intensive research has been underway at the Indian River Field Laboratory
and other places in recent years to develop adequate controls for these diseases,
Definite progress has been made. It is now possible to single out any one of
these diseases and recommend a spray program which will control it. However,
there is little comfort in controlling one disease and having the crop destroyed
by another. Since it is not yet possible to recommend a single spray program
which will insure against all of these diseases simultaneously, a rather compli-
cated and flexible program for this complex problem is necessary.
The control measures differ according to the disease or diseases present.
Therefore, the grower must (1) know under what conditions to expect the disease
to develop; (2) be able to identify the disease, or have it identified by a
qualified specialist; (3) know the proper chemicals to use; and (4) use the
best method of spraying. This report is prepared to serve as an aid to tomato
LATE BLIGHT, Phytophthora infestans (Mont.) DBy,
The Disease-This fungus disease is well known to most tomato growers. The
severe epidemic which developed in South Florida in late February, 1957 was a
grim reminder that late blight is still capable of inflicting devastating losses
vhen conditions are ideal for its development, Late blight is most active from
November 15 to May 15, especially during prolonged rainy periods or when heavy
dews and fogs accompanied by cool nights prevail.
Latest Research-Spray trials underway during the February and March (1957)
late blight outbreak offered an excellent opportunity to evaluate the different
fungicides alone and in mixtures. In this test maneb, zineb and nabam plus zinc
1/ Associate Plant Pathologist, Everglades Stations Belle Glade, and Entomolo-
gist, Indian River Field Laboratory, Fort Pierce, respectively.
sulfate provided themost effective degree of control. Nabam plus zinc sulfate
caused considerable leaf yellowing and stunting of the plants. This material
is not recommended, Dichlone, though less effective, also provided an appre-
ciable degree of control. The mixtures, sineb plus dichlone and zineb plus
thiram, were equal in effectiveness to maneb and zineb used separately,
Suggestions on Control--Maneb (12 lbs/LOO) or zineb (2 lbs/100) is
recommended for the control of late blight if the grower does not need to aim
his control at Botrytis gray mold also. Zineb (1l lbs/O00) plus dichlone
(1/2 lb/100) is suggested for those growers who need to protect their crop from
both late blight and Botrytis, Under same conditions the combination of zineb
and dichlone may injure the plants, however, serious plant injury from this
mixture has been rare. It is suggested that ferbam (3 lbs/100) be substituted
for dichlone when the temperature is above 85 F in order to reduce the chance
GRAY LEAF SPOT, Stemphylium solani Weber
The Disease-The fungus causing gray lea# spot may attack tomatoes during
the fall, winter and spring. It is most active during warm humid weather.
While this disease does not normally kill the plants as rapidly as does late
blight, it can, under certain conditions, destroy a tomato planting at an
alarming rate. Gray leaf spot and bacterial spot are very similar in appear-
ance, but are controlled by different chemicals. Positive identification by
the plant pathologist in the area is desirable. The tomato varieties, Manalucie
and Manalee, are nearly immune to this disease.
Latest Research--Maneb and zineb are the standard materials for the control
of gray leaf spot, however recent research indicates that a new fungicide,
Dyrene, is superior to these chemicals. Dyrene did not give adequate late
Suggestions on Control-Maneb (1- lbs/100) or zineb (2 lbs/100) is recom-
mended for the control of gray leaf spot, Dyrene (2-3 lbs/100) has given
better control of this disease, however, it is not yet available to growers.
If Dyrene becomes available, growers should use it with the full knowledge that
it will not satisfactorily control late blight, For that reason it will be
necessary to use Dyrene either in mixtures with zineb or maneb, or in an
alternating spray schedule. Information on compatibility between Dyrene and
maneb or zineb is not available. Therefore, if these combinations are used'
they should be used on a trial basis. Growers producing vine-ripened tomatoes
should use the variety Manalucie which is near-immune to this disease*
GRAY MOLD, Botrytis cinerea Fr,
The Disease--Botrytis or gray mold became a severe problem on tomatoes
about eight years ago, and has caused heavy damage to both staked and ground
tomatoes in the Indian River, Devil's Garden--Immokalee, and Lower East Coast
areas ever since,
This disease is most active during periods of cool weather accompanied by
rains, fogs or heavy dews, 1inter and early spring crops suffer the greatest
amount of damage. The fungus attacks leaves, stems, blossoms and fruit. The
common name, gray mold, derives from the characteristic appearance of the spore
masses which occur on diseased 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, dichlone,
ferbam, thiram, Vancide 51 and Tennam gave good control under conditions of
moderate infection on ground tomatoes at the Indian River Field Laboratory; and
two chemicals, dichlone and ferbam, 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 combina-
tions of metal salts, including zinc sulfate, resulted in a sharp increase in
Botrytis--at least twice as much as in unsprayed check plots. Results of this
research have been published a-d may be obtained by requesting Florida
Agricultural Experiment Station Journal Series No. 501.
Field trials during the 1956-57 season indicated that Botrytis can be
controlled on a commercial basis using dichlone or a mixture of dichlone and
zineb. In experimental plots dichlone was effective when used in a mixture with
Dyrene or zineb. The thiram and ferbam plots were destroyed by late blight,
therefore no control data on Botrytis were obtained. These two materials in
mixture with zineb were effective against Botrytis, Nabam plus zinc sulfate,
maneb and zineb were ineffective vYhen used alone.
Suggestions on Control--Since a spray program must control all major
foliage diseases it is necessary to select a chemical treatment for Botrytis
which will also protect the plants from the other diseases. 1rith this in mind,
the following suggestions are made for the control of Botrytis:
A--For Manalucie (resistant to gray leaf spot)--Spray every 5 to 6 days
with 3/h lb. dichlone per 100 gallons of water. Do not use dichlone on hot
days (850 F or above) as in'ary may occur when temperature is high. Substitute
3 pounds of ferbam on hot days only. This schedule should control all major
foliage diseases except bacterial spot. However, if late blight appears, spray
with 1/2 pound dichlone plus l1 pounds zineb until that disease becomes inactive.
B-For Homestead, Grothen, Rutgers, etc. (not resistant to gray leaf spot)-
Spray every 5 to 6 days with 1/2 pound dichlone plus -l pounds zineb per 100
gallons of water, beginning when plants are 3 to 4 inches high. This mixture
should control all foliage diseases except bacterial spot. It is fairly effect-
ive in controlling Botrytis, but not equal to dichlone used without zineb.
Zineb must be added since dichlone will not control gray leaf spot,
BACTERIAL SPOT, Zanthomonas visicatoria (Doidge)
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 closely associated with warm periods of heavy and frequent rainfall.
Blowing rains provide the primary means by which the bacteria are spread around,
and it is under such conditions that growers suffer severe losses. Bacterial
spot was largely responsible for the heavy tomato losses during the fall of
1956 (estimated to be.50 to 75 percent in many areas).
Bacterial spot occurs on 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 leaf spot and certain other diseases.
It is of great 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 conditions 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 if seed
have not been treated when purchased. Dissolve the bichloride 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 a cool, dry place.
Treated seed should not be stored for more than two months. (Rote: The
importance of tomato 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 production of tomatoes as insurance
against possible seed transmission.)
B-Spray every 4 to 5 days during the rainy season, beginning when the
first true leaves appear. ]aix 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 and add streptomycin sulfate to give a concentration of 100 ppm.
During periods of fair weather the interval between applications may be
extended to 7 days. Good coverage is necessary. Continue these treatments
until the rainy season has passed. Separate treatments with zineb or maneb
must be made for the control of gray leaf spot and late blight.
SUGGESTED SPRAY SCHEDULE
Treat seed in prescribed manner with bichloride of mercury if they have not been
treated when purchased.
A. MANALUCTE (Resistant to gray leaf spot).
Through October 31: Neutral copper (2 lbs. metallic)!/ plus strepto-
mycin sulfate (100 ppm). If late blight conditions develop (cool
weather and heavy dews or fogs) add dichlone (1/2 lb.)
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 (850 F 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 Ibs.) may be added to
dichlone (1/2 lb,).
May 1: Discontinue dichlone (because this chemical may burn plants in
ho weather). Ferbam (3 lbs.) may be used if Botrytis is a problem and
_/ Figures in parenthesis indicate parts per million (ppm) or pounds per 100
gallons of spray.
blight is not active. Zineb (2 Ibs.) or maneb (1 Ibs.) may be used if
late blight is a problem and Botrytis is not active.
B. HOMESTEAD, GROTHERN, ETC. (Not resistant to gray leaf spot).
Through October 31: Neutral copper (2 Ibs. metallic) plus streptomycin
sulfate (100 ppm) for bacterial spot control. Maneb or zineb must also
be used at no greater than 7-day intervals for the control of gray leaf
spot, and possibly late blight. These treatments probably should be
applied separately until further research vith combinations is
November 1 through April 30: Dichlone (1/2 lb.) plus zineb (1-- Ibs.).
It acT erial s'ot is still a problem continue separate treatments of
copper (2 lbs, metallic) plus streptomycin (100 ppm) when needed, On
hot days (85o F or above) substitute ferbam (3 lbs.) in place of
dichlone plus zineb to prevent possible dichlone injury to the plants.
Then v.eather cools, return to the dichlone-zineb spray,
IMay 1: Discontinue dichlone (because this chemical may burn during hot
weather). Ferbam (3 lbs.) may be used if Botrytis is a problem and
late blight is not active. Zineb (2 lbs.) or maneb (1 lbs.) should
be used if Botrytis is not a problem.
GEMFRIC PND TRADE NAMES FOR TOMuATO FUNGICIDES
Streptomycin plus copper
Manzate, Dithane M-22
Dithane Z-78, Parzate
Agrimycin 100, Agri-