Occurrence of Gaeumannomyces Patch Disease in Maryland and Growth and Pathogenicity of the Causal Agent. P. H. Dernoeden, Assistant Professor, Department of Agronomy, University of Maryland, College Park 20742. N. R. O'Neill, Research Plant Pathologist, USDA, ARS, Beltsville, MD 20705. Plant Dis. 67:528-532. Accepted for publication 10 October 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-528.

Gaeumannomyces patch disease of turf caused by Gaeumannomyces graminis var. avenae (GGA) was observed on Penncross creeping bentgrass turf (Agrostis palustris) at four locations in Maryland in 1979 and 1980. Affected turf appeared as bronzed, reddish brown, or light yellow patches 15–60 cm in diameter. Dead or thinning turf was observed in the centers of these patches. Dark brown runner hyphae and simple hyphopodia were present on roots, crowns, and basal sheaths of diseased plants. Mean ascospore lengths for three GGA isolates ranged from 84.5 to 113.2 μm, within the range previously reported for GGA. Most perithecia were borne between leaf sheaths, but some isolates produced perithecia on roots in sandy soil. Pathogenicity tests showed that seedlings of all bentgrass species used as turf are very susceptible to the disease. Exeter colonial bentgrass (A. tenuis) seedlings, however, showed a significantly higher level of resistance to the disease than Astoria colonial and Penneagle creeping bentgrasses. The most rapid daily growth rate of four GGA isolates on potato-dextrose agar occurred at 25 C. No growth occurred at 35 C and growth declined significantly (P = 0.05) from the optimum temperature. The described symptomatology of the disease and supportive data provide the first documented record of Gaeumannomyces patch of bentgrass turf in the mid-Atlantic region of the United States.

Keyword(s): Agrostis canina, Kingstown, Ophiobolus patch.