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 concern for turf managers. Large losses of perennial ryegrass (Lolium perenne L.) turf caused by P. grisea epidemics have occurred in recent years. This field study was conducted to investigate the effects of two maintenance practices 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 in 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 nitrogen (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 area blighted, and areas under disease progress curves (AUDPC) were compared statistically. There were no significant interactions (P ≥ 0.05) between mowing heights and N rates in either year. In both years, AUDPC data showed no significant differences (P ≥ 0.05) due to the effects of mowing heights. The effect of N fertility was significant (P ≤ 0.05) for both years. Plots treated with the highest N rate had significantly more gray leaf spot than those treated with the lowest N rate. Data indicated that turf managers may expect gray leaf spot to be equally severe between 1.9- and 6.4-cm mowing heights, and that applications of water-soluble N prior to or during environmental conditions conducive for gray leaf spot development should be avoided.