First Report of Gray Leaf Spot on Perennial Ryegrass in Indiana.

Pyricularia grisea, the causal agent of gray leaf spot on turfgrass, was isolated from symptomatic perennial ryegrass (Lolium perenne) leaves collected from a golf course in north-central Indiana in August 1999. Gray leaf spot is an emerging threat to stands of perennial ryegrass in the mid-Atlantic and Midwestern United States (1). Symptoms were first evident in taller (6 cm) mown, rough areas surrounding golf course fairways. Field symptoms included diffuse patches (1 to 4 m in diameter) of thin, yellow-tan turf. Within larger affected areas, some of the turf was dead and matted. Close inspection revealed the presence of typical tan-gray lesions with brown margins and fish hook-like distortion of infected leaf blade tips. Incubation of affected turf in a saturated environment at 23°C for 16 h resulted in production of numerous three-celled, pear-shaped conidia characteristic of those produced by P. grisea. A pure culture of the isolate was grown on V8-juice agar in darkness at 29°C. After 10 days, the culture was exposed to continuous light for 4 days at 23°C to induce sporulation. Conidia were washed from the colony surface with sterile distilled water. Two-week-old perennial ryegrass plants in 8-cm-diameter pots were inoculated with the conidial suspension. Typical gray leaf spot symptoms resulted after incubation of inoculated plants at 27°C for 72 h in a saturated atmosphere. Uninoculated control plants exposed to the same environmental conditions remained healthy. This is the first report of gray leaf spot on perennial ryegrass in Indiana. Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.