Purple seed stain is caused by C. kikuchii . This disease is a minor production problem in Iowa. This fungus causes Cercospora leaf blight during a growing season. Frogeye leaf spot has been found causing damage in a few fields. This disease is caused by C. sojina and also is seedborne.
Infected seeds have areas of dark gray to brown.
Seed coats sometimes have cracks and flakes. Cerecospora fungi survive in crop residues after introduction from seeds. The disease may build up when conditions are favorable for disease development next season. The seed coat will have discoloration starting from the hilum. Discoloration may be eggshell or dark gray, depending on the hilum.