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Effect of Levels of Corn Residue on the Epidemiology of Gray Leaf Spot of Corn in Ohio. N. R. X. de Nazareno, Former Graduate Student, Department of Plant Pathology, Ohio Agricultural Research and Development Center (OARDC), The Ohio State University, Wooster 44691. P. E. Lipps, and L. V. Madden. Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center (OARDC), The Ohio State University, Wooster 44691. Plant Dis. 77:67-70. Accepted for publication 3 August 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0067.

The effect of soil-surface residue level (0, 10, 35, and 85% soil coverage) on the progress of gray leaf spot of corn, caused by Cercospora zeae-maydis, over time was studied in Ohio during two environmentally different growing seasons. Area under the disease progress curve (AUDPC) was calculated and analyzed with analysis of variance followed by orthogonal polynomials. In the first year, under favorable environmental conditions for disease development, the relationship between disease severity and amount of residue on the soil surface was positive, significant at P < 0.01, whereas in the second year, under dry conditions less favorable for disease development, the relationship was significant at P = 0.07. However, the linear orthogonal polynomial of residue level was significant for AUDPC in both years (P <0.001 and <0.04 for 1990 and 1991, respectively). Final severity, as measured by lesions per leaf, for the favorable and unfavorable years was 12.6118.3 and 0.43.2, respectively. AUDPC for the 85% residue level was clearly higher than the other levels for the favorable weather year. Under unfavorable conditions, there was a tendency for disease severity to be similar between 0 and 10% residue levels and lower than the 35 and 85% residue levels. Our study shows that any tillage method leaving residue on the soil surface favors gray leaf spot development and that disease increases with amount of residue. Tillage systems leaving greater than 35% residue cover may result in high disease levels, especially under environmental conditions favorable for disease development.