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Indian River Field Laboratory Mimeo Report IRL 4=6 September 10, 1964
FACTORS AFFECTING SPRAY MATERIAL RECOMMENDATIONS FOR CONTROL OF TOMATO FOLIAGE
DISEASES IN THE INDIAN RIVEi AREA
Robert E. Stalll/
The choice of materials for control of foliage diseases of tomato seems to
always be perplexing to farmers. In spite of continued research to simplify the
problem, more complicated ramifications seem to evolve.
Bacterial spot (caused by Xanthomonas vesicatoria (Doidge) Dows), gray leaf
spot (caused by Stemphylium solani Weber), late blight (caused by Phytophthora
infestans (Mont) DBy), and botrytis gray mold (caused by Botrytis cinerea Fr)
cause the most economic damage to tomato foliage in the Indian River area.
These four foliage diseases must be prevented to obtain a profitable crop.
Since control measures are based on a preventative principle, the right material
or materials should be on the plants at optimum distribution and concentration
before conditions become favorable for disease development.
To arrive at the best spray schedule certain factors must be considered.
These factors are important enough to make alterations of the spray schedule
desirable and without their knowledge intelligent programs for disease control
can not be used. These factors are discussed in this mimeo report along with
spray schedule recommendations.
Seasonal occurrence of the diseases.--Combinations of temperature, moisture,
and tomato vine maturity are important in determining the incidence of the diseases
on susceptible varieties. All four diseases can probably be found in all months
of the year, but usually the diseases are most severe during the periods indicated
in table 1. Bacterial spot is the most prevalent disease during the late summer
and early fall months. As this disease subsides with decreasing rains, gray leaf
spot, late blight and gray mold become more prevalent. The probability of these
diseases occurring remains high during the period of cool weather and mature vines
during the late fall and winter months. Gray mold and late blight then decrease
and gray leaf soot becomes the most abundant disease in the spring months.
Varietal susceptibility.--All varieties of tomato planted in Florida are
susceptible to bacterial soot, late blight, and botrytis gray mold. However, a
very high degree of resistance to gray leaf soot is present in certain varieties.
Manalucie, Indian River, Eanapal, and Marion are resistant and the strains of
Homestead and Grothen's Globe are susceptible.
Interestingly, the main effect of the varietal differences in susceptibility
to gray leaf spot is in changing the number of materials that can be used in
preventing gray mold. Thus, the cheaper materials, thiram and ferbam, can be used
on resistant varieties instead of the more costly Dyrene. The former materials
should not be used on gray leaf soot susceptible varieties, because of their
ineffectiveness against that disease.
1/ Associate Plant Pathologist, Indian River Field Laboratory, Ft. Pierce, Florida.
Nature of soil.--Botrytis gray mold does not develop on plants growing on
soils that are calcareous in nature, and because of this, a preventative spray
program for this disease is not needed. Liming practices can also decrease
development of the disease. To anticipate the effect of the lining practices,
knowledge of the amount of P20O that is expected to be applied is necessary.
For example, a preventative spray program is not needed on plants that are
growing on sandy soils that have been treated with 3-4 tons of hi-calcic lime
per acre, if not more than 200-250 lbs. of P20O per acre will be applied during
the crop. If applications of 750-1000 lbs. of P20g per acre is anticipated, a
preventative spray program will probably be beneficial.
The effectiveness of the spray materials.--A spray program can only be
developed after the knowledge of the best material, or materials to prevent a
certain disease has been obtained. In addition, the effect of the materials against
other diseases and the relative merits of combinations of materials should be known.
Often use of one material for control of a disease may sacrifice control of another
disease. Also, combinations of materials may be different than the addition of the
effects of the materials used separately.
Relative ratings of recommended materials and combinations of materials are
presented in table 2. This is information gained during numerous tests at the
Indian River Field Laboratory.
Recommendations for foliage disease control of tomato.--With the above
information in mind a spray program can be chosen to fit most tomato culture
situations in the Indian River area. These situations and corresponding suggested
spray programs are presented in table 3. Alterations of these programs are even
possible to fit changing disease prevalence due to changes in seasons or soil
Table 1. Expected prevalence of h foliage diseases of tomato by the month,
Bacterial Late Gray leaf Botrytis
Month spot blight spotaf gray mold
August ++++b/ +
September ++++ +
October ++++ ++
November ++ + ++++
December + +++ ++++ ++
January + ++++ + ++++
February + ++++ ++++
March + ++++ ++ +++
April + ++++ ++++ ++
May ++ ++ ++++ +
June ++ ++++
a/ Vine maturity seems to be a major influencing factor and prevalence listed
corresponds to the yearly two crop system in the Indian River area. The
prevalence may be different in other areas of Florida.
b/ In rating system, ++++ means maximum probability of disease and means
very little disease expected.
Table 2. Relative control of m.jcr foliage diseases of tomato in the Indian River
area by recommended fungicides, bactericides, or combinations.
Fungicide ...T. omato Foliage Disesee ..
or % Lbs / Botrytis Late Gray Baotedial
bactericide active 100 gals. gtay mold blight leaf spot spot
Manebi/ 80% 1i,5 ++++ +++
byrene 50 2.0 4+++ ++ ++++
thiran 65 15 4+++ + +
Ferbam 76% 3.0 ++4 + ++
Copoer 5$3. o ++ ++
Maneb + Dyrehe 1.0+1.0 ++ ++++ + ++
Maneb + thiram 1.0+1.0 +4 ++++ +++
Maneb + ferbam 1.0+3.0 4+ ++++ +++
M1heb + copper 1.5+4.0 +++ ++ ++4
g/ Same rating could be applied for zineb, except zineb id slightly less effective
Under epidemic bonditionst
b/ In rating system ++++ mheahs maximum control and means no control.
Table 3. Recommended spray programs for control of tomato foliage diseases under
certain tomato culture conditions.
Tomato culture conditions
Routine conditions with all diseases expected, i.e.,
gray leaf spot susceptible variety and soils
Routine conditions, tith gray leaf spot resistant
variety and soils non-calcareous.
Routine conditions with gray leaf soot susceptible
variety and soils calcareous.
Routine conditions with gray leaf spot resistant
variety and soils calcareous.