Agriculture: Turfgrass Pest Management Guidelines

Sclerotium Blight (Southern Blight)

  • Sclerotium rolfsii
  • 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.

    Susceptible Turfgrasses

    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.

    Management

    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 Amount to use Ag Use
    REI‡
    NonAg Use
    REI‡
    (Example trade name) (hours) (hours)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
    A. AZOXYSTROBIN
    (Heritage) 0.2–0.4 oz/1000 sq ft 4 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    B. FLUTOLANIL
    (Prostar WG) Label rates 12 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
    C. TRIADIMEFON
    (Bayleton 50 Turf and Ornamental) Label rates 12 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
    1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. 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 a fungicide with a different mode-of-action group number.
    Restricted entry interval (REI) 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.
    Text Updated: 09/09
    Treatment Table Updated: 12/16