First Report of Field Resistance of Colletotrichum graminicola on Turf to Benzimidazole Fungicides in the United States. W. W. Shane, Department of Plant Pathology, Ohio State University, Columbus 43210. T. K. Danneberger, Department of Agronomy, Ohio State University, Columbus 43210. Plant Dis. 73:775. Accepted for publication 5 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0775C.
Anthracnose, caused by Colletotrichum graminicola (Ces.) Wils., was a problem on a bentgrass/ annual bluegrass putting green at a country club in Cincinnati, Ohio, during the summer of 1987. Isolates of C. graminicola collected from the site were tolerant to benomyl in vitro. After 3 days at 27 C, radial growths of tolerant isolates (average of three isolates) on potato-dextrose agar amended with 0, I, 10, 100, 500, and 1,000 mg. a.i. of benomyl (Tersan 1991 50WP) per liter were 18.4, 19.7, 17.8, 13.1, 9.4, and 3.8 mm, respectively; those of sensitive isolates (average of two isolates) were 16.2, 2.9, 2.8, 2.0, 0.5, and 0.0 mm, respectively. Benzimidazole fungicides had been used routinely for at least 5 yr at the site where the tolerant isolates were found. Benzimidazole fungicides have been recommended, labeled, and, in many states, routinely used for control of anthracnose on turfgrass. This report serves as a warning that tolerance of C. graminicola to benzimidazole fungicides can be a significant problem facing turfgrass managers.