Agriculture: Turfgrass Pest Management Guidelines

Necrotic Ring Spot

  • Necrotic ring spot: Ophiospharella korrae (=Leptosphaeria korrae), Ophiospharella namari (=Leptosphaeria namari)
  • Description of the Disease

    Necrotic ring spot appears as large, ring-shaped patches that often cause depressions in the turf. Rings may vary from a few inches to several feet in diameter. Individual plants appear to have drought stress and can be stunted or discolored red, yellow, or tan. Lower stems and roots are often covered with black runner hyphae, and in advanced stages, the affected tissue (roots, rhizomes, and crowns) may turn necrotic and black or brown. Dark fungal structures (hyphae and pseudosclerotia) may sometimes be visible on affected plant parts. The fungus survives as mycelia in plant debris and in the thatch layer. The disease can also be spread by mechanical equipment and infested sod.

    Susceptible Turfgrasses

    Fine fescues and bentgrasses. On bermudagrass, the pathogen causes a disease known as spring dead spot.

    Conditions Favoring Disease

    Necrotic ring spot development is favored by cool, wet conditions in spring and early fall. Drought stress and high compaction can intensify symptoms later in the season.

    Management

    Follow good management practices; systemic fungicides have proven effective when applied on a preventive basis.

    Cultural Control

    Maintain the highest mowing height possible to help prevent the development of this disease. Follow recommended irrigation practices to avoid drought stress. Avoid excessive nitrogen fertilization. Resistant varieties of Kentucky bluegrass are available. Replant with other species such as perennial ryegrass or tall fescue.

    Treatment Decisions

    In areas where necrotic ring spot occurs frequently, begin treatment of spring infections when soil temperatures reach 60°F and continue until environmental conditions are no longer favorable for the disease in summer. Apply fungicides in an adequate volume of water, or apply enough water after application, to allow the fungicide to penetrate into the root zone.

    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) 0.4 oz/1000 sq ft 4 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    B. IPRODIONE
    (Chipco 26019) 8 fl oz/1000 sq ft See label Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
    C. MYCLOBUTANIL
    (Eagle 20EW) 1.2–2.4 fl oz/1000 sq ft 24 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
    D. PROPICONAZOLE
    (Banner Maxx) 4 fl oz/1000 sq ft 12 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
    E. THIOPHANATE-METHYL
    (Fungo Flo) Label rates 12 Until dry
    MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
    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