HPIPM:Covered Smut (barley)
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Covered Smut of Barley (Ustilago hordei)
'"`UNIQ--btaxobox-00000000-QINU`"' Compiled by Linnea Skoglund, Montana State University
Cause
Covered smut is caused by the fungus Ustilago hordei which attacks only barley, oats, rye, and a number of related grasses. It is one of the most common diseases of barley worldwide.
Symptoms
Infected plants appear normal until heading. Smutted heads emerge at the same time or slightly later than healthy ones. In some cases they may be "trapped" by the flag leaf sheath. Infected heads are readily visible in the field. Kernels are replaced by black smut sori, which are covered by a gray membrane. The membrane is the glume that usually remains intact until harvest or threshing. Awns and sometimes floral bracts also remain intact. Masses of teliospores may be visible in harvested grain if disease incidence is greater than a few percent. When this situation occurs the seed lot is designated "smutty" by federal grain inspectors and its economic value is reduced. Smut sori may also develop occasionally on leaf blades appearing as long streaks, and in nodal tissue.
Impact of Disease
Significant yield loss was fairly common prior to the advent of chemical seed treatment. Economic loss is still incurred in areas of the world where seed treatment is not implemented. Infected plants do not demonstrate symptoms until heading. Kernels of infected plants are replaced by masses of dark brown smut spores. Smutted heads are hard and compact. Infected plants may be stunted. Occasionally smut sori may also develop in leaf blades, where they appear as long streaks.
Life cycle of the Pathogen
Covered smut overwinters as teliospores on seed. Spores geminate when the soil temperature range is 67-77F (14-25oC) and soil moisture is low. It invades the coleoptile between germination and emergence. The degree of infection is determined by the amount of coleoptile tissue colonized. The greater the amount of infection on this tissue, the greater the number of tillers per plant infected. Once the coleoptile is penetrated, the fungus becomes established near the growing point and grows within its host. Mycelium eventually invades the flower primordia and fragments into thick walled teliospores. Millions of spores are produced in each smutted head. These spores replace the developing kernel tissue and sometimes the floral bract. Teliospores are grouped in structures called sori and commonly remain in association with infected spikes until harvest. Thin membranes that cover the sori are ruptured at this time and the spores are released and mix with healthy seed or fall to the ground. When the membrane ruptures prior to harvest, spores are wind blown to healthy seed. Teliospores contaminate the exterior portion of the seed, especially the crevice. Spores, which land between the kernel and the hull, germinate when adequate moisture is present. The mycelium arising from these spores goes dormant after it becomes established. Spores on the seed and dormant mycelium associated with hulls are responsible for most of the infection in the subsequent growing season. Infection from soil borne inoculum typically occurs in drier areas of barley production.
Management Approaches
Cultural Management Practices
Seed treatment is the most effective way to manage this disease.
Host Plant Resistance
Plant resistant cultivars.
Chemical Management Program
Always treat seed if there is a history of smut. Seed treatments also help protect against seed and seedling diseases.
Consult fungicide labels for additional rate, application, and safety information. Additional information and current labels can be found at http://www.greenbook.net or http://www.cdms.net.
References
Compendium of Barley Diseases. 2nd Edition. 1997. American Phytopathological Society. St. Paul, MN.
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.
