Nitrogen Form and Rate of Nitrogen and Chloride Application for the Control of Summer Patch in Kentucky Bluegrass. D. C. THOMPSON, Faculty Research Associate, Department of Plant Science, Cook College, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903. B. B. CLARKE, Associate Professor, Department of Plant Pathology, and J. R. HECK MAN, Assistant Professor, Department of Plant Science, Cook College, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903. Plant Dis. 79:51-56. ccepted for publication 16 September 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0051.

The influence of nitrogen form and rate of nitrogen and chloride application on turf quality and summer patch severity was assessed in Kentucky bluegrass cv. Fylking at one site for 2 yr. Plots were artificially inoculated with a five-isolate mixture of Magnaporthe poae in 1990. Every 3 wk, varying rates of ammonium sulfate or calcium nitrate (to supply 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 In 1990, patch diameter, patch severity, and rhizosphere pH were slightly reduced by the application of ammonium sulfate. In 1991, onset of summer patch symptoms was delayed, and patch development and pH of the rhizosphere and bulk soil were greatly reduced where ammonium sulfate was applied. The high (196 kg N ha-1 yr-1) rate of ammonium sulfate reduced summer patch severity up to 75% compared with the same rate of calcium nitrate. Chloride application did not influence disease severity, turf quality, or soil pH. In general, urf quality was not significantly influenced by the form of nitrogen or the rate of nitrogen application.

Keyword(s): cultural management, fertility.