Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
On both potato and tomato early blight produces large brown areas on the leaf, usually with a concentric ring pattern. On potato early blight usually begins after flowering on susceptible varieties, especially once potatoes or tomatoes begin to senesce. The disease is favored by high humidity and periods of leaf wetness. Optimal temperatures for infection range from 75-80°F.
Control of early blight begins with crop rotation then protectant fungicides, such as chlorothalonil or mancozeb, should be applied every 7 to 10 days, depending on the weather. Once flowering occurs on potato a systemic fungicide is recommended for several sprays, especially if a susceptible variety is grown or early blight is found in the field. Systemic fungicides recommended for early blight control on potato include: Endura, Gem, Headline, Quadris, Reason, Revus Top, and Tanos. As always, follow pesticide labels for rates and usage. Revus Top and Tanos will also offer suppression of late blight. See the Potato Disease Advisory for P-day accumulations to predict early blight appearance. The same fungicide list applies for tomato, just substitute Cabrio for Headline. Alternate the protectant fungicide with the systemic fungicide combined with a protectant as per label instructions.
Early blight on potato
Early blight on tomato