Gray leaf spot has become more evident during the past 2 weeks, primarily in eastern Iowa. Lower leaves in some fields have numerous well-developed lesions. So far, ear leaves in most hybrid fields are free of disease or have a few small lesions. Current hybrids are generally less susceptible than they were a few years ago. During the past few years, few hybrid fields in Iowa have had gray leaf spot levels that would warrant a fungicide application. Criteria for fungicide applications in hybrids have relied on presilking disease levels. The corn crop is well past silking, but I have not seen any fields that I feel would have met these criteria.
Iowa State University
Munkvold, Gary P., "Gray leaf spot development" (2002). Integrated Crop Management News. 1762.
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