Brown patch severity in perennial ryegrass as influenced by irrigation, fungicide, and fertilizers

Brown patch (Rhizoctonia solani Kühn) is a common and destructive disease of turfgrasses, but little information is available regarding its management by cultural practices. This 2-yr field study assessed the influence of irrigation, and N source alone or in combination with P and K on brown patch severity. Perennial ryegrass (Lolium perenne L. cv. 'Caravelle') was subjected to either morning or evening irrigation. Sodium nitrate, a quickly available non-soil reacting N source, was compared with sulfur-coated urea (SCU), a slowly available soil acidifying N source. Fertilizer treatments were applied three (May-September-October) and six (March-May-June-September-October-November) times annually, representing lower and higher N application rates, respectively. Forty-nine kilograms N per hectare were applied on each date for a total of 147 and 294 kg N ha^-1 yr^-1. Plots were split with one-half treated with iprodione [3-(3,5-dichlorophenyl)-IRN-(1-methylethyl)-2,4-dioxo-1-imidazolidine- carboxamide)] (3.1 kg ai ha^-1) on an extended 21-d interval. In non-fungicide-treated plots, brown patch severity was consistently reduced with morning irrigation when compared with evening-irrigation. Non-fungicide-treated plots fertilized with SCU generally had lower blight levels than NaNO₃-treated plots, regardless of N rate. In the second year, brown patch was more severe in plots treated with the high N rate, and P (72 kg ha^-1 yr^-1) and K (150 kg ha^-1 yr^-1) reduced blight for both N-sources in non-fungicide-treated plots. Sulfur-coated urea applied at the high N rate plus P and K resulted in blight levels equivalent to or less than low N. Fungicide-treated plots receiving the high rate of N from SCU plus P and K had the highest summer quality in both years. While low soil pH was weekly correlated (r = 0.352) with less blight, the slow N release characteristics of SCU were probably a more important factor in disease reduction than soil acidification. While brown patch severity was reduced by morning irrigation, SCU + P + K, and iprodione, an excellent level of summer turfgrass quality was not achieved using the extended fungicide application interval.