Below is the email sent out to growers from our 5-county Extension Agent Gene McAvoy.
"Early today I received a report of late blight on tomato in the Immokalee area. At present it is confined to one farm with one hot spot and scattered infections.
Growers would be well advised to scout susceptible crops carefully as the forecast for the coming weekend and into next week calls for foggy conditions and a good a chance of rain early next week which will be conducive to disease development.
Looking back at past occurrences in the Immokalee area, we have seen the disease start up around this time several times over the last 15 years perhaps aided by attenuated spray schedules and reduced vigilance around the Holidays.
Late blight is caused by the fungus Phytophthora infestans, which is a pathogen of potato and tomato. This disease can spread quickly and devastate a tomato or potato field within a few weeks if not properly controlled.
The disease thrives under cool and wet conditions. Temperatures between 50 and 80 F combined with moist conditions such as rain, fog, heavy dews, or relative humidity above 90 percent are conducive for disease development. Night temperatures in the mid-fifties with daytime temperatures from the mid-fifties to mid-seventies are ideal for this disease.
Since the disease can spread so rapidly, growers should scout their fields thoroughly each day, especially when cool and wet conditions conducive to disease development prevails.
Late blight symptoms on leaves appear as irregularly shaped brown to purplish lesions with indefinite border lesions that can span veins. The lesions may be seen any time of day, on any stage of plant growth and on leaves of any age. Velvety, white fungal growth may appear on the lower surface of affected leaflets early in the morning before leaves dry and/or in the lower canopy.
On stems, purplish lesions may be found any where on the stem. Cottony, white growth of fungus on stems with lesions can often be seen early in the morning and/or in the lower canopy. Stems with lesions are brittle and break easily. Lesions are confined to epidermis and cortex. Leaf rolling and wilting is often associated with stem lesions and purpling of leaflets may occur in some varieties.
Begin a spray program with fungicides if late blight is in your area or weather conditions are suitable for late blight development. After harvest, kill infected foliage to minimize tuber infection.
[Chemicals listed were for growers and removed from this post.]"
Home gardeners:
http://edis.ifas.ufl.edu/pp121
"To control late blight, begin with disease-free transplants. Next, space plants far enough apart in the garden so that plants will dry off quickly during the day. If late blight is a yearly problem in your garden, you may have to resort to periodic use of fungicide sprays."
Mr. Gene McAvoy recommends copper fungicide for organic growers and chlorothalonil for those of you that are not organic.
Copper fungicide (organic) can be found at most big box stores.
Here are some chlorothalonil products available (not organic):
Bonide 880 Fungonil Fungicide, 16-Ounce
GARDENTECH -2115 DACONIL FUNGI CONC 16OZ
Daconil Liquid Ornamental & Vegetable Fungicide 32oz Quart
