Frogeye leaf spot, caused by the fungus Cercospora sojina, was first reported on soybean in Japan in 1915. The first report of the disease on soybean in the United States was in 1924. Frogeye leaf spot is now considered to occur worldwide. However, the disease is most serious in warm regions or during periods of warm, humid weather. Symptoms of frogeye leaf spot occur primarily on leaves although the causal fungus may also infect stems, pods and seeds.
Lesions are small, circular to somewhat irregular spots that develop on the upper leaf surfaces.
Initially the spots are dark and water soaked in appearance. As the lesions age, the center of the lesion becomes light brown to light gray in color. Older lesions have a light center with a darker red to purple-brown border. Lesions may merge to kill larger areas of the leaf surface. Heavily spotted leaves may wither and drop prematurely.