Disease Review: Brown Patch

It seems as if summer has finally caught up with us. An unusually mild July has left us and August has brought with it more typical Iowa summer weather. With increasing temperatures and humidity, coupled with the rain we received this past weekend, conditions have once again become favorable for disease development. Out at the ISU Horticulture Research Station we started our week off by discovering an outbreak of brown patch on some of our creeping bentgrass greens.

The turfgrass disease known as brown patch is caused by the fungal pathogen Rhizoctonia solani and can affect all of the cool-season turfgrass species. Brown patch is a summer disease whose development is triggered by hot, humid weather, night time temperatures above 65°F and long periods of dew. During these conditions brown patch may appear overnight. Brown patch is also considered a high nitrogen disease and excessive amounts of nitrogen in your fertility program during the summer can contribute to a brown patch problem.

Brown patch usually produces a circular brown to olive green patch with a grey perimeter giving a ‘smoke ring’ appearance. Often, more than one patch will be evident in an affected area with the appearance of the unique ‘smoke ring’ pattern more clearly defined on low mown turf. Individual leaf blades of the affected turfgrass will show lesions with a chocolaty brown margin. The brown patch lesions are most visible when observed on tall fescue, although they are present on all turfgrass species infected with brown patch.

One of the easiest ways to decrease disease pressure from brown patch is to implement a proper fertility program to avoid excess nitrogen during the summer months. Also, trying to promote shorter dew periods by avoiding late evening irrigation can help reduce the possibility of a brown patch. There are also a number of fungicides that provide brown patch control such as Heritage, Daconil, Medallion, Clearys 3336, and many others.

Nick Dunlap
GCSAA Campus Representative
Turfgrass Management
Iowa State University
njdunlap@iastate.edu