Be aware that a mottled seed coat is not always the result of SMV infection. Some physiological stresses also can cause seed coat discoloration, which complicates diagnosis. Another viral disease is bean pod mottle virus. This disease is spread by the bean leaf beetle. The virus also can be seedborne and thus become established in your field by planting infected soybean seed.
Infected seed has a dark gray discoloration for soybean seeds with a black hilum.
Infected plants stay green late in the fall. Last year, bean leaf beetle was abundant, which explains the prevalence of bean pod mottle virus . The damage in soybean caused by this insect also can result in seed discoloration. Furthermore, insect damage often enhances infections by some fungal diseases, including Phomopsis seed decay. Because of the mild winter this year, insect vectors of these soybean diseases may have a higher survival rate, which means a higher risk of viral diseases if infected soybean seeds are planted.