Severity of gray leaf spot in perennial ryegrass as influenced by mowing height and nitrogen level

Gray leaf spot [Pyricularia grisea (Cooke) Sacc.] has become a great concer n for turf managers. Large losses of perennial ryegrass (Lolium perenne L.) turf caused by P. grisea epidemics have occurred in recent years. This fie ld study was conducted to investigate the effects of two maintenance practi ces on the severity of gray leaf spot in perennial ryegrass managed as golf course fairways and roughs. The study was initiated in 1998 and repeated i n 1999 at Lexington, KY. Treatments were two mowing heights (1.9 and 6.4 cm ) with a split-plot treatment of monthly applications of water-soluble nitr ogen (N) fertilizer between April and August at rates of 0, 36.6, and 73.2 kg N ha(-1). Disease severity was rated visually as the percent of plot are a blighted, and areas under disease progress curves (AUDPC) were compared s tatistically. There were no significant interactions (P greater than or equ al to 0.05) between mowing heights and N rates in either year. In both year s, AUDPC data showed no significant differences (P greater than or equal to 0.05) due to the effects of mowing heights. The effect of N fertility was significant (P less than or equal to 0.05) for both years. Plots treated wi th the highest N rate had significantly more gray leaf spot than those trea ted with the lowest N rate. Data indicated that turf managers may expect gr ay leaf spot to be equally severe between 1.9- and 6.4-cm mowing heights, a nd that applications of water-soluble N prior to or during environmental co nditions conducive for gray leaf spot development should be avoided.