INFLUENCE OF MOWING HEIGHT, NITROGEN-SOURCE, AND IPRODIONE ON BROWN PATCH SEVERITY IN PERENNIAL RYEGRASS

Brown patch (Rhizoctonia solani Kuhn) is a destructive disease of turf grasses, but more is known regarding its management with fungicides th an by cultural practices. This held study was conducted to determine t he influence of mowing height and nitrogen (N) source on brown patch s everity. 'Caravelle' perennial ryegrass (Lolium perenne L.) was subjec ted to two mowing heights (1.7 versus 4.5 cm) and fertilized with one of eight N sources at Fates of 196 kg N ha(-1) yr(-1) from 1991 to 199 3. Plots were split with one-half receiving iprodione thylethyl)-2,4-d ioxo-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 tri al the N sources alone were assessed on a perennial ryegrass fairway i n 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 b lighting was more severe in plots mowed to a height of 4.5 cm. Blighti ng was reduced by iprodione at both mowing heights, and summer turfgra ss quality was improved in all plots receiving N plus iprodione. Ammon ium sulfate in 1991 and Sustane and Ringer Lawn Restore-treated turf i n 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 levers equivalent to most fungicide-treated plots in 1992, but the quality of non-fungicide-treated plots was infe rior. No N source had any significant effect on brown patch at Pikesvi lle in any year. No single N source combined with iprodione was consis tently associated with improved disease suppression or turf quality. T here was no apparent relationship between brown patch severity and soi l pH or crown tissue carbohydrates. Plant parasitic nematode populatio n densities were not influenced by any N source.