Below-normal temperatures and wet conditions, like those Iowa is experiencing this spring, provide ideal conditions for alfalfa foliar diseases. High levels of foliar diseases in May can cause early defoliation for the first cutting, says X.B. Yang, Iowa State University plant pathologist. In a cool, wet spring, spring black stem, Leptosphaerulina leaf spot and downy mildew are most common in first-year alfalfa crops in Iowa. Spring black stem causes plant defoliation and leads to reduced yield and quality. Leptosphaerulina leaf spot attacks young and old leaves. Downy mildew causes chlorotic blotches on upper leaf surfaces and a white to gray mold on lower leaf surfaces. Learn more about these diseases and treatment suggestions at