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Olive-black masses of loose smut teliospores replace kernels of infected heads.

Small Grains

Loose Smut

Pathogens:
Loose smut of wheat, triticale, and rye: Ustilago tritici
Loose smut of barley: Ustilago nuda
Black loose smut of barley and oats: Ustilago nigra, but the strains
that attack oats are different from those that attack barley.

(Reviewed 2/07, updated 2/09)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms 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.

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/cwt R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  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
  (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) 0.5 fl oz 48 see comments
  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.
 
D. TEBUCONAZOLE/THIRAM
  (Raxil-Thiram) 3.5–4.6 fl oz/cwt 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.
 
+ 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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