Agriculture: Small Grains Pest Management Guidelines

Loose Smut

  • Black loose smut of barley and oats: Ustilago nigra
  • Loose smut of barley: Ustilago nuda
  • Loose smut of wheat, triticale, and rye: Ustilago tritici
  • Symptoms and Signs

    Symptoms are usually not apparent until heading. Smutted heads usually emerge earlier than healthy heads. Diseased heads consist of olive-black masses of teliospores in the place of kernels. The smut spores are enclosed in a fragile, gray membrane that soon ruptures to release the airborne spores. By the time the grain matures, the spores are dispersed, leaving only a bare rachis.

    Comments on the Disease

    Most loose smut pathogens survive from one season to the next as dormant mycelium inside infected seed. The fungus that causes black loose smut survives as teliospores on the surface of contaminated seed. The black loose smut strains that attack oats are different from those that attack barley.

    Management

    Use certified smut-free seed. Hot water treatment can eliminate smut fungi from contaminated seed, but it must be used carefully to avoid reducing seed vitality. For information on hot water treatments, see UC ANR Publication 3333, Integrated Pest Management for Small Grains.

    Seed treatment with systemic fungicides is necessary because loose smuts are borne internally in seed.

    Common name Amount per cwt REI‡ PHI‡
    (Example trade name) (hours) (days)
    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, efficacy, application timing, honey bees, and environmental impact. Always read the label of the product being used.
     
    SEED TREATMENT
     
    A. CARBOXIN
      (Vitavax 34F) 2–3 oz 12 See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
      COMMENTS: For use on barley, oats, triticale, and wheat. Do not use treated seed for food, feed, or oil purposes. Do not graze or feed livestock on treated areas for six weeks after planting.
     
    B. TRIADIMENOL
      (Baytan 30) 0.75–1.5 fl oz NA See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: For use on barley, oats, rye, and wheat. Do not use treated seed for food, feed, or oil purposes. All seed treated with this product must be colored with an EPA-approved dye (e.g., 40 CFR 180.1001) that imparts an unnatural color to the seed to help prevent the inadvertent use of treated seed as food for people or feed for animals. Green forage may be grazed 40 days after seeding.
     
    C. DIFENOCONAZOLE/MEFENOXAM
      (Dividend XL RTA) 1.0 fl oz 48 See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Phenylamide (4)
      COMMENTS: For use on barley and wheat only. Do not use treated seed for feed or oil. Do not graze green forage for 55 days after planting. Do not plant any crop other than wheat within 30 days to fields in which treated seed was planted.
     
    D. TEBUCONAZOLE/THIRAM
      (Raxil-Thiram) 3.5–4.6 fl oz 24 See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Multi-site contact (M3)
      COMMENTS: For use on barley, oats, triticale, and wheat. Do not use treated seed for feed, food, or oil purposes. Barley, oats, triticale, and wheat green forage may be grazed or harvested for hay 31 days after seeding.

    Centum weight (cwt) is 100 pounds.
    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. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    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.
    NA Not applicable.
    Text Updated: 02/09
    Treatment Table Updated: 07/16