Influence of mowing height, nitrogen source, and iprodione on brown patch severity in perennial ryegrass

Brown patch (Rhizoctonia solani Kühn) is a destructive disease of turfgrasses, but more is known regarding its management with fungicides than by cultural practices. This field study was conducted to determine the influence of mowing height and nitrogen (N) source on brown patch severity. 'Caravelle' perennial ryegrass (Lolium perenne L.) was subjected to two mowing heights (1.7 versus 4.5 cm) and fertilized with one of eight N sources at rates of 196 kg N ha^-1 yr^-1 from 1991 to 1993. Plots were split with one-half receiving iprodione [3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1-imidazolidine-carboxamide) ] (3.1 kg ai ha^-1 applied on a 21-d interval) and the other half receiving none. The complete combination of treatments were assessed at Silver Spring, MD, and in a second trial the N sources alone were assessed on a perennial ryegrass fairway in Pikesville, MD. In non-fungicide-treated plots, turf maintained at 1.7 cm was blighted more by brown patch in 1991, but in 1992 and 1993 blighting was more severe in plots mowed to a height of 4.5 cm. Blighting was reduced by iprodione at both mowing heights, and summer turfgrass quality was improved in all plots receiving N plus iprodione. Ammonium sulfate in 1991 and Sustane and Ringer Lawn Restore-treated turf in 1992 were associated with less blighting among non-fungicide-treated plots at Silver Spring. Non-fungicide-treated Sustane and Ringer Lawn Restore plots had blight levels equivalent to most fungicide-treated plots in 1992, but the quality of non-fungicide-treated plots was inferior. No N source had any significant effect on brown patch at Pikesville in any year. No single N source combined with iprodione was consistently associated with improved disease suppression or turf quality. There was no apparent relationship between brown patch severity and soil pH or crown tissue carbohydrates. Plant parasitic nematode population densities were not influenced by any N source.