Yield Loss Potential of Phaeosphaeria Leaf Spot of Maize Caused by Phaeosphaeria maydis in the United States

The ability of Phaeosphaeria leaf spot (PLS) to reduce yields of maize was evaluated over two winter growing seasons in southern Florida. Nine commercial maize hybrids, varying in reaction to PLS, were planted in a split-plot design with hybrids as whole plots and inoculated versus uninoculated treatments as subplots. The most susceptible hybrid, Pioneer brand 3489, sustained a significant reduction in grain yield (11 to 13%) and 400-kernel weight (5 to 10%) in the trials. Regression analyses indicated that grain yields and 400-kernel weights were reduced 0.23 and 0.16%, respectively, for each percent increase in PLS severity at the mid-dent stage. Because most U.S. maize hybrids are resistant, and PLS develops late in the grain-filling period, its potential to cause substantial losses in the United States appears limited at this time.