After mid-August, many soybean fields had patches of yellow plants. These plants exhibited yellowing of the top leaves, often followed by brown margins on the leaves. My colleagues and I received many questions on why soybean turns yellow prematurely and whether top dieback, a disease caused by the fungi Phomopsisand Diaporthe, is the cause. Visits to problematic fields and examination of samples submitted to Iowa State University Plant Disease Clinic revealed three factors that can stress soybean, consequently causing leaf yellowing.