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Dark gray spore masses replace the kernels of barley spikes infected with covered smut.

Small Grains

Covered Smut

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

(Reviewed 2/07, updated 2/09)

In this Guideline:


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/cwt R.E.I.+
(trade name)   (hours)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM Program, taking into account efficacy. Also consider the general properties of the fungicide as well as information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
SEED TREATMENT
A. CARBOXIN 34% F
  (Vitavax 34) 2–3 oz 12
  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
  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
  MODE OF ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
  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.
 
D. PCNB 24% EC Label rates See label
  MODE OF ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
  COMMENTS: For use on barley, oats, and wheat only. A minimum of one part product and one part water is recommended. Do not use treated seed for food, feed, or oil purposes.
 
E. MANCOZEB 80% DF
  (Dithane M-45) Barley: 2.7–4.2 oz Until dry
    Wheat: 2.2–3.3 oz  
    Oats: 4–6.3 oz  
  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
  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) 0.5 fl oz 48
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Phenylamide (4)
  COMMENTS: For use on 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/cwt 24
  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.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 actions (for more information, see http://www.frac.info/). 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 fungicide with a different mode of action Group number.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Small Grains
UC ANR Publication 3466
Diseases
R. M. Davis, Plant Pathology, UC Davis
L. F. Jackson, Agronomy, UC Davis

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