Wheat Streak Mosaic

Taxonomy

Domain	Viruses
Realm	Riboviria
Kingdom	Orthornavirae
Phylum	Pisuviricota
Class	Stelpaviricetes
Order	Patatavirales
Family	Potyviridae
Genus	Tritimovirus

Scientific Name

Tritimovirus Wheat Streak Mosaic Virus

Common Name

Wheat Streak Mosaic Virus (WSMV)

Wheat streak mosaic

Author: Mary Burrows, Jack Riesselman, Ned Tisserat, Jeff Stein

Cause

Wheat streak mosiac virus (WSMV), a potyvirus transmitted by the wheat curl mite.

Symptoms

Symptoms of WSMV include yellowing of the leaf in a streaked or stippled pattern next to the leaf veins. Plants can be stunted if infected early in the season. Symptoms often appear first at the edges of a field or near patches of volunteer wheat. Symptoms may not appear until after spring warm-up. The virus can also be transmitted mechanically, but this is not considered the primary mechanism of movement through the field.

Impact of Disease

Yield loss can range from insignificant to 100%. When the plant is infected early, heads may be sterile. Losses are generally more severe in years when the previous fall was abnormally warm or it was dry during the growing season.

Life Cycle of the Pathogen

WSMV is transmitted by the wheat curl mite. The mite is so small that it cannot be seen with the naked eye, but when present in high numbers can make the wheat leaf curl so that the upper surface is rolled inward. Look inside a curled leaf with a 10x magnifying lens and you will see small white, cigar-shaped insects if the mite is present. Mites are dispersed up to two miles if environmental conditions are cool and humid. During hot weather they desiccate rapidly and wind dispersal is minimal.

Both winter and spring wheat can be infected with WSMV. In winter wheat, infections that occur in the fall cause the most damage, even though symptoms may not be observed until the spring. Spring infections in winter wheat are less serious and are not as damaging. In spring wheat, infections are more devastating if they occur early in the growth cycle. Later spring infections cause much less damage.

Management Approaches

Available Models

A risk model is under development.

Biological Control

No biological control strategies have been developed for WSMV. Thrips are predators of wheat curl mites.

Cultural Management Practices

No varieties have shown consistent resistance to WSMV, however, some are considerably more tolerant than others.

Winter wheat seeded early in the fall is more likely to become infected with WSMV. For spring wheat, early seeding reduces the risk of WSMV infections.

The most important control measure is to destroy volunteer wheat and grassy weeds using herbicides or tillage. A three week period between volunteer control and crop emergence provides excellent control, since the mite cannot survive without green host tissue. Host destruction methods must be carefully considered in cases where neighboring plants are planted to a susceptible host.

Important: When volunteer wheat is sprayed with herbicide, mites sense their host is dying and will move to a new field, so avoid spraying next to spring wheat during cool, moist and windy weather. When the weather is hot and dry, it is less likely the mite will survive to find a new host. Wheat streak mosaic virus is transmitted at low levels in seed, but this is not considered an important source of inoculum in most years. Do not plant winter wheat next to late-maturing spring grassy hosts of WSMV such as spring wheat and corn.

Host Plant Resistance

Variety resistance is available in southern states such as Texas, Oklahoma, Nebraska, and Texas. Resistance deployed in the field is temperature sensitive and breaks down at temperatures above 27C. Resistance to WSMV does not necessarily confer resistance to other wheat curl mite transmitted viruses such as Triticum mosaic virus and Wheat mosaic virus (fmr. High Plains virus). Resistance to the wheat curl mite is also available in some areas but must be customized to the mite biotype prevalent in the area. Resistance to the virus and mite is not permanent and must be tested in the area where it is planted.

Chemical Management Program

Seed and foliar insecticide applications have not proven effective for control of WSMV. Insecticides may reduce populations of thrips and other insects that predate on wheat curl mites.

Consult pesticide 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 Wheat Diseases and Pests. 3rd Editions. 2010. American Phytopathological Society, St. Paul, Minn.

University of Nebraska extension publication EC1871 'Managing Wheat Streak Mosaic' Montana State University MontGuide MT200911AG 'Cereal viruses of importance in Montana'

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.