Below normal temperatures and wet conditions, such as Iowa is experiencing this spring, provide ideal conditions for the occurrence of major alfalfa foliar diseases. While producers are waiting for temperatures to warm up and the soil to dry, they should not forget to check their alfalfa fields as the season progresses into May. High levels of foliar diseases in May can cause early defoliation for the first cutting. In a cool, wet spring, spring black stem, Leptosphaerulina leaf spot, and downy mildew are most common in first-year alfalfa crops in Iowa.
Iowa State University
Yang, Xiao-Bing, "Cool, wet spring favors alfalfa foliar diseases" (2007). Integrated Crop Management News. 1088.
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