Why is soybean yellowing prematurely?

Abstract

<p>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 <em>Phomopsis</em>and <em>Diaporthe</em>, 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.</p>