With the hot weather that we have experienced lately patch disease symptoms are/will beginning to appear on Kentucky bluegrass turf (tees, fairways, roughs). Two patch diseases, necrotic ring spot and summer patch can occur on Kentucky bluegrass from now through fall. In field diagnosis necrotic ring spot is normally the patch disease associated with Kentucky bluegrass. Often times if the summer is not too hot and dry necrotic ring spot commonly occurs. However, if the summer is hot, summer patch is a problem on high cut Kentucky bluegrass. Summer patch symptoms often as irregular patches, rings, or crescents. These symptoms often appear during hot (85 to 95 F) humid or wet weather. The disease is most prevalent on Kentucky bluegrass growing on compacted soils.
Cultural management practices that help reduce the severity of summer patch include relieving soil compaction, providing adequate fertility, and planting where applicable resistant Kentucky bluegrass cultivars. Promoting good drainage and reducing soil compaction are practices that are best accomplished in the autumn. Nitrogen applications during the summer should be moderate and if possible apply a slow release fertilizer instead of a quick release. Drought stress increases the severity of the patch diseases, thus proper watering is important.
Fungicide programs exist for summer patch. The most effective program is to apply the fungicide preventatively. Currently, there are no biological control products that work on summer patch.