Phyllosticta leaf spot of soybean
Phyllosticta leaf spot is caused by the fungus Phyllosticta sojicola. Lesions most often occur on leaves and are circular, oval, and irregular or V-shaped. Lesions appear gray or tan and have a narrow, dark margin. In older lesions, numerous small, black specks (i.e., pycnidia) may be visible.
The fungus likely survives in infested crop residue and can be seed transmitted. Cool, moist conditions favor disease development.
Crop rotation and tillage will reduce survival of the fungus. Phyllosticta leaf spot lesions. Image: D. Mueller
Small, black pycnidia may be observed in older lesions. Image: A. Sisson