Each year from 1991 to 1999, a disease matching the description of gray leaf spot (1) was observed in the central and north central regions of Illinois. Disease severity was low (<10% blight) from 1991 to 1994 and 1999 and was severe (>50% blight in some areas) from 1995 to 1998. The disease was observed on Lolium perenne (perennial ryegrass) golf course fairways and sports fields. Isolations of Pyricularia grisea were made from L. perenne collected from golf courses in Bloomington, Decatur, Kankakee, Pekin, Urbana, and Moline, IL. All isolates were collected from surface-sterilized, symptomatic leaves. Cultures were maintained on one-fifth strength potato-dextrose agar (PDA) and induced to sporulate on full-strength oatmeal agar. All isolates in culture displayed vegetative and conidial characteristics similar to those previously described for P. grisea (1). Twenty-five different L. perenne germ plasms were inoculated with isolate WF9826 (Kankakee) using a suspension of 1 × 105 conidia per milliliter. The 4-week-old lawns (100 plants per 3-cm-diameter cone-tainer) of each ryegrass germ plasm were inoculated by spraying foliage with the conidial suspension until runoff. Inoculated and uninoculated lawns were enclosed in plastic bags and placed in an incubator (16 h light; 28°C) for 7 days. Disease severity was rated using a scale of 0 to 10 (10 = 100% blight). Each treatment was replicated three times, and all experiments were repeated four times. Small blue-gray, water-soaked lesions with dark brown borders were observed on leaves of all inoculated ryegrass germ plasms. Advanced symptoms included blighting of much of the leaves. The mean disease severity rating was 3.8 (range 2 to 7) for all experimental units and all 25 germ plasms. P. grisea was isolated from leaves that were inoculated with WF9826. This is the first report of gray leaf spot of perennial ryegrass caused by P. grisea in Illinois.
Reference: (1) P. J. Landschoot et al. Plant Dis. 76:1280, 1992.
