The cause of later-maturing symptoms is unknown. Be aware that male sterilized plants also stay green late into the season and can be misidentified as virus-infected plants. These plants have very few pods. Cercospora leaf blight, caused by Cercospora kikuchii , was prevalent this growing season. Although this disease is not yield limiting in Iowa, severely infected plants have purple seed stain .
Infected seeds have a pink to purple discoloration on the seed coats.
The pathogen is seedborne and also survives in crop residues. Damage from bean leaf beetle also causes seed discoloration. This summer, large populations of bean leaf beetles caused damage in some soybean fields. Insect wounds on pods are recognized by the bite marks and are often associated with discolored seeds, which can be mistaken as a disease problem. Some fungi can infect beetle-damaged seeds by entering through the wounds and thereby reduce the germination rate.