Spring and Summer Black Stem and Leaf Spot Diseases of Alfalfa

Both spring black stem and leaf spot, and summer black stem and leaf spot, in alfalfa are caused by two different fungi. In Nebraska, spring black stem and leaf spot becomes severe after cool, wet weather. It usually is a problem on the first cutting, and can reduce hay yield and quality. Summer black stem and leaf spot can develop rapidly the final week before harvest; by itself the disease usually isn't severe enough to cause economic loss, though in the presence of other leaf diseases, severe leaf loss can occur.