Summer Patch

Utah Pest Fact Sheet

USU Extension/Plant Pest Diagnostic Lab

Utah Plant Disease Control No. 40

 Revised March 1998


Summer Patch

Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician

Thick hyphae
Annual bluegrass crown with characteristic dark colored, thick hyphae (as indicated by arrow) produced by the summer patch fungus Magnaporthe graminicola.
Dark hyphae

Another view of dark hyphae typically produced by the summer patch fungus.

Summer Patch

Summer patch and necrotic ringspot of turf are common fungal diseases in the lawns of Utah. Summer patch is cause by Phialophora graminicola and necrotic ringspot by Leptosphaeria korrae.


Summer patch is a warm weather disease. Symptoms are present during the months of May through September. The symptoms are similar to those of necrotic ringspot, consisting of the dead circles and arches that range in size from several inches to several feet in diameter. The summer patch fungus also produces the microscopic, dark hyphae on the surface of the grass crowns and the leaf sheaths. These hyphae tend to be larger than those found with necrotic ringspot but are much less common on the plant tissue.


Cultural techniques that prevent the lawn from becoming stressed will help prevent this disease. In early spring or fall, the lawn should be aerated. Aeration improves water penetration and reduces thatch, thus alleviating conditions that cause stress. Nitrogen fertilizer should be applied frequently at low rates or in slow release forms such as sulfur coated urea or IBDU. This avoids undesirable flushes of growth which are more susceptible to disease. Mow the lawn at a height of 2-3 inches often enough so that only 30-40% of the leaf length is removed per mowing. In most soils, the lawn should be watered infrequently and deeply. Sandy soils will require more frequent, light irrigation. Wet the entire rot zone when irrigating.


Cultural techniques provide the most reliable control of summer patch, but in difficult situations fungicides may be necessary. It can be controlled with Tersan 1991, Fungo 50, Rubigan, and Cleary's 3336. The turf area to be treated should be irrigated the night before. The next day the fungicides should be applied and irrigated in before they dry on the foliage. These fungicides are best used as a preventative. Bayleton can also control summer patch, but it must be applied before the fungus becomes active in early summer.



Precautionary Statement: All pesticides have benefits and risks, however following the label will maximize the benefits and reduce risks. Pay attention to the directions for use and follow precautionary statements. Pesticide labels are considered legal documents containing instructions and limitations. Inconsistent use of the product or disregarding the label is a violation of both federal and state laws. The pesticide applicator is legally responsible for proper use. This publication is issued in furtherance of Cooperative Extension work. Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Vice President for Extension and Agriculture, Utah State University.