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UC Pest Management Guidelines

Sclerotium blight damaged areas on mixed species turf; photo shows characteristic ring shape of infested areas.


Sclerotium Blight (Southern Blight)

Pathogen: Sclerotium rolfsii

(Reviewed 9/09, updated 9/09)

In this Guideline:


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.


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.

Cultural Control
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.

Treatment Decisions
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.

Common name Example trade names Ag Use
NonAg Use
(trade name)   (hours) (hours)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a fungicide, consider general properties as well as information relating to environmental impact.
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) 4 until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Carboxamide (7) 12 until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T
F. Wong, Plant Pathology, UC Riverside
M. A. Harivandi, UC Cooperative Extension, Alameda County
Acknowledgment for contributions to Diseases:
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside

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