How to Manage Pests
UC Pest Management Guidelines
Sclerotium Blight (Southern Blight)
Pathogen: Sclerotium rolfsii
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Sclerotium blight affects circular areas of turf, enlarging up to 9 feet in diameter; some plants may remain alive in the centers of these areas. Sometimes only partial circles or crescent-shaped areas of affected turf are seen. The turfgrass turns reddish brown as it dies. Infected plants appear completely necrotic. As the fungus advances, abundant white mycelia appear on the turfgrass. Light to dark brown sclerotia, which are tiny, hard, resting bodies that resemble mustard seeds, develop at the base of the stems and may help identify this disease.
Bentgrasses, bluegrass, fescues, ryegrasses, dichondra are susceptible to southern blight.
CONDITIONS FAVORING DISEASE
The fungus survives in thatch as sclerotia. Spread is by sclerotia and infected plant parts. The disease is favored by warm or hot weather, high moisture, and heavy thatch. Initial infections commonly occur in late spring, when air temperatures rise above 75°F; several days of drought followed by high soil moisture appears to be conducive to high levels of sclerotia germination. Optimal conditions for disease development are air temperatures of 85° to 95°F coupled with high moisture in the thatch layer from precipitation, high humidity, or over irrigation.
Prevent the development of Sclerotium blight by following good cultural practices. Fungicides may be necessary in areas where this disease is chronic.
The disease appears to be less destructive on well fertilized, vigorously growing grass. Control thatch and use good sanitation practices around equipment, because both aerifying and verticutting can spread the fungus sclerotia. Avoid overirrigation.
In areas where southern blight is chronic, fungicide applications can be made in late spring before the development of symptoms; otherwise, apply fungicides soon after symptoms are seen.
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