Agriculture: Turfgrass Pest Management Guidelines

Leaf Spot

  • Bipolaris sorokiniana
  • Description of the Disease

    Leaf spot occurs on leaf blades, sheaths, and stems as circular to elongated purplish or brown spots with brown colored centers and purplish to dark brown borders. Spots may be found on turfgrass leaves throughout the site, indicating spread by windborne spores. Crown and roots are frequently affected with a dark brown rot. Plants with crown infections are weakened and may die in hot, windy weather, resulting in a thinning out of the turf in scattered areas.

    Susceptible Turfgrasses

    Bentgrasses, bluegrasses, fescues, and ryegrasses are susceptible to leaf spot. The fungus survives in infected grass plants or grass debris and may be seedborne. Spores are airborne.

    Conditions Favoring Disease

    The disease is favored by warm temperatures (70° to 90°F), high humidity, extended leaf wetness, and closely cropped turfgrass. It is more severe under high nitrogen fertilization.

    Management

    Follow good management practices to prevent the development of leaf spot. Fungicides are usually not warranted.

    Cultural Control

    Reduce shade and improve soil aeration and water drainage. Avoid dry spots, overfertilizing with nitrogen, and maintain as high a cutting height as possible. Avoid prolonged leaf wetness by irrigating in pre-dawn, or early morning hours. If possible, increase air movement.

    Treatment Decisions

    Leaf spot usually is not serious enough in California to warrant the use of fungicides, although they may be used in areas where leaf spot is severe.

    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. CAPTAN
      (Captan 4L or 50 WP) Label rates See label Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
     
    C. CHLOROTHALONIL
      (Daconil Action) Label rates 12 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
     
    D. FLUDIOXONIL
      (Medallion) 0.25–0.5 oz/1000 sq ft 12 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12)
     
    E. IPRODIONE
      (Chipco 26019) 3–4 fl oz/1000 sq ft See label Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
     
    F. MANCOZEB
      (Fore 80 WP, Dithane M-45) 4–8 oz/1000 sq ft 24 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
      COMMENTS: Dithane M-45 registered for use on sod farms only.
     
    G. MYCLOBUTANIL
      (Eagle 20EW) 1.2 fl oz/1000 sq ft 24 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
     
    H. PROPICONAZOLE
      (Banner Maxx) 1–2 fl oz/1000 sq ft 12 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
     
    I. THIOPHANATE-METHYL
      (Fungo Flo) Label rates 12 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
     
    J. TRIFLOXYSTROBIN
      (Compass) Label rates 12 Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
     
    K. VINCLOZOLIN
      (Curalan EG, Touche EG) 2.7 lb/acre (1 oz/1000 sq ft) 120 (5 days) Until dry
      MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
    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