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Relationships Between Yield of Sweet Corn and Northern Leaf Blight Caused by Exserohilum turcicum. J. K. Pataky, Department of Plant Pathology, University of Illinois, Urbana 61801; Phytopathology 82:370-375. Accepted for publication 25 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-370.

Relationships between yield of six sweet corn hybrids that differed in resistance to northern leaf blight (NLB) and severity of NLB were examined in field experiments done in 1988, 1989, and 1990. Severity of NLB was assessed on an individual leaf basis and was weighted by the proportion of the total leaf area accounted for by each leaf. Three leaves (the primary ear leaf and the leaves immediately above and below the primary ear) accounted for about 3340% of the total leaf area. When a stepwise regression procedure was done, models with two independent variables were not significantly different from one variable models, and percentage of yield usually was explained by severity of NLB on the ear leaf or the leaves immediately above or below the ear. The effect of NLB on yield (based on weight of ears) was dependent on the resistance or susceptibility of the hybrid. Yields of susceptible hybrids were reduced in all three years. Yields of moderately resistant and resistant hybrids were not affected substantially. When severity in the upper 75% of the canopy was less than 8%, yield was not affected by NLB. Slope coefficients from regressions of percentage of yield on severity of NLB in the entire leaf canopy ranged from about 0.44 to 0.75. Lesions on husk leaves were detrimental to the appearance of ears of all hybrids.

Additional keywords: crop loss assessment, Helminthosporium turcicum, maize.