Interaction of nitrogen source, application timing, and fungicide on Rhizoctonia blight in ryegrass

Rhizoctonia blight (RB), incited by Rhizoctonia solani Kiihn, is a common disease of cool-season turfgrasses. This 2-year field study was conducted to determine the influence of N source, N application timing, and fungicide treatment on RB severity in 'Caravelle' perennial ryegrass (Lolium perenne L.). Ringer Lawn Restore (Ringer), a slow-release N source, was compared to water-soluble urea. Nitrogen was applied according to either a spring (March, May, June, and September) or fall (September, October, November, and May) schedule. Plots received either N only or N plus the fungicide iprodione (3.1 kg a.i./ha applied at 21-day intervals). RB was reduced with fall-applied Ringer compared to spring-applied urea in both years in fungicide-free plots. Nitrogen generally enhanced foliar mycelium growth and RB during the initial infection periods (i.e., late June to late July). By mid- to late August there were extremely high levels of blighting among all fungicide-free treatments. Nitrogen source and N application time had no effect on the level of blighting in iprodione-treated plots. During early disease outbreaks, iprodione did not always prevent foliar mycelium from appearing, but it did protect turf from severe RB. Iprodione reduced blighting, but the level of disease suppression and resulting turfgrass quality provided on the extended spray interval was not acceptable for high- quality golf course fairways. Chemical name used: 3-(3,5- dichlorophenyl)-N- (1-methylethyl)-2,4-dioxo-1-imidazolidine carboxamide (iprodione).