Nitrogen Form and Rate of Nitrogen and Chloride Application for the Control of Summer Patch in Kentucky Bluegrass.

Abstract

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 1991. 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, turf quality was not significantly influenced by the form of nitrogen or the rate of nitrogen application