Disease Note

Distribution of Race 3 of Cochliobolus carbonus on Corn in North Carolina. S. Leath, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695. K. J. Leonard, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 70:800. Accepted for publication 16 April 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-800e.

In general, Cochliobolus carbonus Nelson causes a minor leaf spot of corn (Zea mays L.), but race 3 can cause significant leaf damage. Race 3 has predominated in the mountains of North Carolina since at least 1970 (1,2). From 1971 to 1976, 22% of isolates from the western Piedmont, but only 9% of those from eastern North Carolina, were race 3 (1). During 1976–1977, 64% of isolates from the western Piedmont and 17% of those from eastern North Carolina were race 3 (2). A continued increase of race 3 in eastern North Carolina would threaten the state’s primary corn production area. In 1985, we tested 202 isolates from five fields—three in the western Piedmont and two in eastern North Carolina. Lesion type was determined on Pioneer Brand 3369A seedlings inoculated in the greenhouse. We found that 20, 19, and 17% of the isolates from the three western fields and 28 and 4% of those from the two eastern fields were race 3. Prevalence of race 3 has not increased in North Carolina since 1977.