Tomato Diseases: Black Leaf Mold (Pseudocercospora fuligena)
Major symptoms occur on the foliage but they may also occur on petioles, stems, and fruit peduncles (but not on the fruit itself).
All stages of growth are attacked.The initial symptoms appear as small, pale yellow lesions with no definite margins on either the upper or lower leaf surface. The lesions on the lower leaf surface have a white fungal growth that turns to gray to black as the fungus sporulates. Later, black sooty fungal growth will occur on both the upper and lower leaf surfaces. This distinguishes it from leaf mold (Fulvia fulva = Cladosporium fulvum) where the fungus sporulates on the lower leaf surface only and where the fungal growth is generally of a lighter brown to purple color.
As the disease develops, the affected areas on each leaf will coalesce to form large patches. The affected leaves wilt, dry with age, and usually remain hanging on the plant with a dark soot-covered appearance.
Disease development is slow and severe symptoms are usually present only late in the season; however, major yield losses are possible if infection occurs early. Seed-borne infection has not been reported.