Light infections are frequent in Kansas. Severe infections are rare but can occasionally result in smaller seed size, low test weight, and poor quality. The fungus can survive on infested leaf debris and on seeds. Spores are spread by wind or rain splashing. Symptoms appear as pale green to light yellow spots. On the lower surface, tufts of grayish mildew develop. Some leaves may yellow and drop. The seed and inner pod surface may be coated with whitish mold without exterior pod symptoms. The disease is favored by high humidity and cool temperatures. Young leaves are most susceptible and late plantings usually have more disease because spores are more abundant. Management is achieved by crop rotation and using resistant varieties.
Taken from Kansas State University Agricultural Experiment Station and Cooperative Extension Service Publication #C-449. Soybean Diseases, Dr. Douglas J. Jardine, Extension State Leader, Plant Pathology Program.