This common fungal disease of tomatoes and potatoes first appears as dark brown spots on leaves. On close examination, the spots show a pattern of concentric brown rings. Spots may enlarge and merge, and the leaves will turn yellow and die. Infected plants slowly lose leaves from the bottom up as the disease progresses. Tomato plant stems may also be infected, and eventually tomato fruit will display leathery black lesions. If the disease progresses relatively slowly, gardeners can usually expect to harvest usable fruit, but the quality and yield will be reduced. When potatoes suffer from early blight, their leaves display similar black spots and the tubers become covered with brown, corky spots.
The early blight fungus overwinters in plant residues in the soil; the disease spreads rapidly in warm, humid conditions.
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