Symptoms and Signs
Initial symptoms of Stemphylium leaf spot on leaves consist of small (0.13 to 0.25 inch diameter), circular to oval, gray‑green leaf spots. As the disease progresses, leaf spots enlarge, remain circular to oval in shape, and turn tan in color. Older spots coalesce, dry up, and become papery in texture. Visual signs of fungal growth are generally absent from the spots; hence this problem is readily differentiated from foliar diseases in which purple growth (downy mildew), green spores (Cladosporium leaf spot), or acervuli (anthracnose) develop within circular lesions. Overall, symptoms resemble the tan, circular spots caused by pesticide or fertilizer damage. Weeds or other reservoir hosts have not been identified. This pathogen is seedborne.
This disease appears to be of minor importance and no spray controls are recommended.