Integrated Pest Management

Summer Patch

Summer patch (Lee Miller, University of Missouri, Bugwood.org)

Summer patch (Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org)

main host is Kentucky bluegrass and fine-leaf fescue
very similar to necrotic ring spot; spots of summer patch are usually a little smaller than necrotic ring spot
during extended hot weather (daytime temp. 82-95 degrees F; nighttime temp. above 68 degrees F) infected plants die fast

occurs from late spring to early fall, but infected patches can still be seen next season
the fungus becomes active when the temperature at 3-inch depth reaches 60-70 degrees F on average

Control of summer patch is the same as for necrotic ring spot:

Avoid drought stress. During hot weather, light daily irrigation is necessary to reduce heat stress.
Maintain balanced and adequate fertility, especially nitrogen, potassium and phosphorus.
There are some cultivars that have shown some resistance in trials on the east coast. The National Turf Evaluation Program website lists the trials here.
Overseeding with perennial rye resolves the problem as perennial rye is resistant to the pathogen; other resistant cultivars are available in a variety of species.
Apply a fungicide (azoxystrobin; propiconazole; thiophanate-methyl) for control. Most products need to be applied by a commercial applicator.
Fungicide applications can be done in the spring but need to be started before the fungus enters the roots (when the average soil temperature at 3 inches depth is between 60-70 degrees F).