How to Manage Pests
UC Pest Management Guidelines
Pathogen: Magnaporthe poae
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Summer patch appears as circular yellow or tan areas up to 1 foot in diameter, consisting of dead and dying plants. Roots, crowns, and stolons are affected by a dark brown rot. Young roots may appear healthy, although dark brown hyphae may be present on these tissues. Vascular discoloration and cortical rot occur in later stages of the disease. On occasion, patches may retain centers of green, apparently unaffected grass. The fungus can survive as mycelia in plant debris or in host tissue.
This disease has been reported on red fescue, Chewing's fescue, hard fescue, perennial ryegrass, and creeping bentgrass, but appears to be most destructive to annual bluegrass and Kentucky bluegrass.
CONDITIONS FAVORING DISEASE
Infections occur when soil temperatures are consistently at 65° to 70°F, and symptoms tend to appear when air temperatures are 83°to 95°F or higher. The disease is most severe on closely mowed turf (e.g. golf greens) with heavy irrigation or high soil moisture.
Follow good cultural practices to prevent the development of summer patch. Fungicides may be required for control if summer patch has been a problem in previous years.
Promote root growth by soil aeration and slow-release nitrogen. Improve drainage, reduce compaction and mechanical damage or traffic, control thatch, and avoid drought stress. Irrigate based on evapotranspiration needs of turfgrass. Do not set mowing height lower than necessary. Lightly water (syringe) turf during periods of hot weather to reduce heat stress.
In areas where summer patch is frequent, begin fungicide applications when soil temperatures begin to be consistently in the 65° to 70°F range. This may be 3 to 4 weeks before symptoms are typically seen. Apply fungicides in a water volume equivalent to about 2 to 4 gal/1000 sq. ft. of water in fungicides to ensure materials reach the root zone. Fungicide applications made after strong symptom expression are generally ineffective.
Repeated applications of fungicides from the same chemical class for summer patch control may contribute to the development of fungicide resistance in anthracnose for the benzimidazole, DMI, and QoI (strobilurins) fungicides because the diseases tend to occur during the same period.
UC IPM Pest Management Guidelines: Turfgrass
A. Downer, UC Cooperative Extension, Ventura County
Acknowledgment for contributions to Diseases:F. Wong, Plant Pathology, UC Riverside
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside