Some growers use a mancozeb based fungicide early in the season and then switch to chlorothalonil as harvest time approaches. These fungicides will also protect against infection by anthacnose, a disease of the fruit. High soil fertility levels also can help reduce the severity of early blight. We have not seen any yet this season, but growers should be scouting tomato and potato plantings for symptoms of late blight, as it is also more likely to develop during periods of wet weather. Symptoms of late blight can appear on leaves stems and fruit.
Lesions start as small, dark, water-soaked areas.
These areas rapidly expand into large brown lesions that affect large areas of the leaves. Infected leaves eventually turn completely brown, shrivel, and die. These advanced symptoms may look similar to a severe early blight infection. During periods of moist weather a white fuzz or mold may be observed on the undersides of affected leaves in or surrounding the brown lesions. Symptoms on the fruit look similar to those of buckeye rot, which is caused by another species of Phytophthora .