Agriculture: Small Grains Pest Management Guidelines

Covered Smut

  • Covered smut of barley and oats: different races of Ustilago hordei
  • Covered smut of wheat, also called common bunt and stinking smut: Tilletia caries, Tilletia foetida
  • Symptoms and Signs

    Plants are stunted and heads emerge later than normal. Kernels are replaced by dark gray spore masses that are enclosed in a gray membrane that persists until maturity and is partially covered by floral bracts. If the spore masses are crushed to release spores, they have a distinctive odor, similar to that of decaying fish.

    Comments on the Disease

    Covered smut spore masses burst during harvest, spreading spores to healthy grain and to the soil. The fungi survive from one season to the next on the surface of infested seed or in the soil.

    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. Treatment of seed with contact-type fungicides will control covered smut because the fungus is on the outside of the 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 34% F
      (Vitavax 34) 2–3 oz 12 NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
      COMMENTS: For use on barley, oats, triticale, wheat. Do not use treated seed for food, feed, or oil purposes.
     
    B. CARBOXIN 17%
      MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
      . . .PLUS. . .
      THIRAM 17% F
      (Vitavax 200) Barley, wheat, oats: 3–4 fl oz 24 NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
      COMMENTS: Do not use treated seed for food, feed, or oil purposes.
     
    C. CARBOXIN 17%
      MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
      . . .PLUS. . .
      PCNB 17% F
      (Vitavax PCNB) Barley, wheat, oats: 3–4 fl oz NA NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
      COMMENTS: This product is not labeled for use in California, but seed treated in and obtained from another state can be legally used in California even for a chemical not registered on small grains in California. Contact your retail seed dealer for information and availability. Do not use treated seed for feed or oil. 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. Follow label requirements for labeling treated seed.
     
    D. PCNB 24% EC Label rates See label NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
      COMMENTS: This product is not labeled for use in California, but seed treated in and obtained from another state can be legally used in California even for a chemical not registered on small grains in California. Contact your retail seed dealer for information and availability. For use on barley, oats, and wheat only. Do not use treated seed for food, feed, or oil purposes.
     
    E. MANCOZEB 80% DF
      (Dithane M45) Barley: 2.7–4.2 oz
    Wheat: 2.2–3.3 oz
    Oats: 4–6.3 oz
    24 NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
      COMMENTS: Do not use treated seed for feed or oil. 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. Follow label requirements for labeling treated seed.
     
    F. TRIADIMENOL
      (Baytan 30) 0.75–1.5 fl oz NA NA
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: For use on barley, oats, rye, and wheat. Do not use treated seed for feed or oil. 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. Follow label requirements for labeling treated seed. Green forage may be grazed 40 days after seeding.
     
    G. 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.
     
    H. TEBUCONAZOLE/THIRAM
      (Raxil-Thiram) 3.5–4.6 fl oz 24 NA
      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, oat, 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