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Late Blight - Phytophthora infestans
 HOSTS: Potato, tomato, occasionally eggplant. DESCRIPTION:
Watersoaked spots enlarge into brown blotches on older leaves first.
Leaf undersides may be covered with a gray to white moldy growth.
Infected leaves, petioles, and stems shrivel and die. Tomato fruit
develops dark, greasy-looking spots that enlarge until the fruit rots.
Potato tubers show irregular, slightly depressed areas of brown to
purplish skin. LIFE
CYCLE: The
fungus overwinters on crop debris. At 91 – 100% humidity and optimum
temperatures of 65 – 72° F. (cool days plus warm nights), inoculum
carried by wind and water infect young plants. When weather is
favorable, infection moves so fast that plants appear to have been
damaged by frost. CONTROLS:
Temperatures above 86° F. decrease infection. Plant resistant
varieties when possible. Use Blight-free seed and destroy volunteer
plants. Spray copper when weather is humid / wet and temperatures are between 60 and 75° F. For potatoes, keep tubers covered by hilling with soil throughout the growing season. |
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