Loose smut of oats and false loose smut of barley are caused by the fungus Ustilago nigra (Syn. U. avenae). The fungus is widespread in most barley growing regions of North America and probably the world. Strains pathogenic to barley or oat are not known to cause disease in the other host. The pathogen is seedborne in both barley and oat, and infects plants between germination and seedling emergence. The fungus grows internally within the plant throughout the season, but plants are generally asymptomatic through the heading. During the boot stage, the fungus invades floral tissues and converts them into masses of dark brown teliospores. The teliospores are dispersed by wind to healthy plants, where they infect the seed and start the process over again. The pathogen survives between barley or oat crops in contaminated seed.
Disease symptoms of loose smut and false loose smut are similar and are obvious after heading as dark brown heads with masses of teliospores. Affected heads tend to be taller and emerge slightly earlier than healthy heads. Awns may or may not be present on diseased heads. As the teliospores are dispersed, a bare or nearly bare rachis appears. Plant damage is generally low from this disease (1% or less incidence), but can approach 10% if untreated.
Biological control strategies have not been developed for false loose smut of barley or loose smut of oat.
Plant only high quality seed free of the pathogen. Varieties are available that are resistant to most races of the fungus and provide excellent control. Hot water treatments may reduce or eliminate the pathogen from seed, but can also reduce germination and seed quality.
Seed treatment with surface-active or systemic fungicides gives excellent disease control and should be used routinely.
Product List for Loose Smut False Loose Smut:
Pesticide |
Product per 100 lbs seed |
Remarks |
|
Difenoconazole |
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|
Dividend Extreme |
1-4 fl oz |
Seed treatment; 55 day PHI |
|
Dividend |
0.5-1 fl oz |
Seed treatment; 55 day PHI |
|
PCNB |
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|
PCNB 2-E Liquid |
4.2-12.3 fl oz |
Seed treatment |
|
Tebuconazole: various formulations and mixtures available |
||
|
Raxil-Thiram |
3.5-4.6 fl oz |
Seed treatment |
|
Raxil MD |
5-6.5 fl oz |
Seed treatment |
|
Raxil MD-W |
5 fl oz |
Seed treatment |
|
Raxil MD Extra |
5 fl oz |
Seed treatment |
|
Raxil Xt |
0.16-0.20 oz |
Seed treatment |
|
Triadimenol |
||
|
Baytan 30 |
0.75-1.5 fl oz |
Seed treatment; poor control |
|
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Small Grains, Disease, Loose Smut, False Loose Smut, Oat, Barley
Date: 3/9/2005