How to Manage Pests
UC Pest Management Guidelines
Microdochium Patch (Fusarium Patch, Pink Snow Mold)
Pathogen: Microdochium nivale
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Microdochium patch is also called Fusarium patch as well as pink snow mold in areas that receive snowfall; the fungus can attack turf underneath the snow cover, causing considerable damage if fungicides are not applied before snowfall. This disease also occurs during periods of cool, wet weather in areas of northern California that receive no snow.
The disease appears as small, circular dead spots (up to several inches in diameter) that have a pinkish color. Often white to pink mycelia are evident in affected areas in the early morning. Small white to pink spore masses (sporodochia) can develop on infected and dead plants. The fungus survives in plants and plant debris as dormant mycelia.
Annual bluegrass and creeping bentgrass are very susceptible to this disease.
CONDITIONS FAVORING DISEASE
The pathogen can be active across a broad range of cooler temperatures (32° to 65°F), but air temperatures above 70°F inhibits the growth of the fungus and can shut down the progression of the disease.
Providing good soil aeration and water drainage and reducing shade can discourage the incidence of Microdochium patch. Monitor the evapotranspiration needs of turfgrass to schedule irrigations. Avoid excess nitrogen fertilization, especially in fall and maintain the soil pH between 6.5 and 6.7. High levels of potassium tend to suppress the disease. If Microdochium patch has been a problem in previous years, apply a fungicide in fall before symptoms develop.
High levels of nitrogen in fall or winter months may increase susceptibility to the fungus, although a nitrogen application in spring after environmental conditions no longer favor Microdochium patch development may aid the recovery of affected areas. High potassium levels may help suppress the disease. Maintain soil pH around 6.5 to 6.7.
In areas where Microdochium patch is chronic, apply fungicides before the advent of cool, wet weather (late fall to early spring), and continue applications until the environmental conditions no longer favor pathogen development. Resistance to dicarboximide and benzimidazole fungicides has occurred in parts of the United States but has not yet been reported in California.
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