Phyllosticta leaf spot is an occasional, minor disease of soybeans. It rarely affects yield. Plants are susceptible to infection at all stages. 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 may be visible. These are pycnidia, the fruiting structures of fungus. Disease also may progress to the petioles, stems and pods. The fungus likely survives in infested crop residue. Cool, moist conditions favor disease development.
Management is usually not needed. Crop rotation and tillage will reduce survival of Phyllosticta sojicola.
Photo by Adam Sisson