NITROGEN FORM AND RATE OF NITROGEN AND CHLORIDE APPLICATION FOR THE CONTROL OF SUMMER PATCH IN KENTUCKY BLUEGRASS

The influence of nitrogen form and rate of nitrogen and chloride appli cation on turf quality and summer patch severity was assessed in Kentu cky bluegrass cv. Fylking at one site for 2 yr. Plots were artificiall y inoculated with a five-isolate mixture of Magnaporthe poae in 1990. Every 3 wk, varying rates of ammonium sulfate or calcium nitrate (to s upply 0, 98, or 196 kg N ha(-1) yr(-1)) and combinations of potassium sulfate and potassium chloride (to provide 0, 122, or 244 kg Cl ha(-1) yr-1) were applied from May to October during 1990 and 1991. In 1990, patch diameter, patch severity, and rhizosphere pH were slightly redu ced by the application of ammonium sulfate. In 1991, onset of summer p atch symptoms was delayed, and patch development and pH of the rhizosp here and bulk soil were greatly reduced where ammonium sulfate was app lied. The high (196 kg N ha(-1) yr(-1)) rate of ammonium sulfate reduc ed summer patch severity up to 75% compared with the same rate of calc ium nitrate. Chloride application did not influence disease severity, turf quality, or soil pH. In general, turf quality was not significant ly influenced by the form of nitrogen or the rate of nitrogen applicat ion.