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Wheat Streak Mosaic Virus


© Kansas State University, Department of Plant Pathology

Pathogen(s) causing disease:

Wheat Streak Mosaic Virus (WSMV)

Symptoms:

Initial spring symptoms of wheat streak mosaic virus usually show up in April on edges of fields near volunteer wheat. Look for yellow streaking or mosaic patterns on young leaves. Infected plants are stunted and tiller poorly. Tillers of infected plants are sometimes prostrate on the ground. As the weather warms, symptoms become more severe. Leaves on infected plants turn yellow from the tip down, but usually the leaf veins remain green longest. This gives the leaves a yellow and green striped appearance. Often, leaves fail to unfurl completely. You can look for curl mites with a 10X magnifying lens under the curled portion of the leaf. Curl mites look like tiny white rice grains.

Conditions:

 Symptoms of wheat streak mosaic often appear first at the edge of the field or in patches next to wheat volunteers. Under favorable conditions for development, the mite carrying the virus moves with the prevailing winds, and the symptoms of the disease soon may be observed throughout the field. Infection of winter wheat often occurs in the fall, but disease symptoms may not appear until spring, when temperatures increase.

The worst case scenario is when wheat gets hailed just before maturity. This leads to an early crop of volunteer, and mites move onto it very readily from the old crop. A cool, wet summer allows maximum survival of the volunteer wheat and the mites. Then a long, warm fall allows plenty of time for mites to move onto the newly seeded wheat and begin reproduction. A hot, dry spring is the final blow because infected plants have poor roots and are more susceptible to drought.

Mites depend on the wind to carry them to new plants. That is why infestations are worst northeast of volunteer fields (direction of prevailing wind is northeast). When they land on a plant, they move to the youngest unfurling leaf and begin feeding.

The next generation takes only 7 to 10 days to produce. They seem unaffected by cold winter temperatures and may even multiply during winter months. Their major weakness is their need for fresh plant material. In the absence of living leaves, they can only survive a few days.

Management:

The first and most important control is to break the bridge created by volunteer wheat. Volunteer should be killed at least 2 to 3 weeks prior to the emergence of the new crop. It may be killed by cultivation or by herbicides, but it must be a thorough job because just a few plants can harbor a lot of mites. Since mites travel in the wind, volunteer must be killed within 1/4 to 1/2 mile of the new field. The second control is to avoid early planting. Early planting allows the mites plenty of time to move into the field, reproduce, and spread. Waiting until after the "fly-free" date is recommended for wheat streak mosaic control. The third control is to plant a variety with resistance to the virus or the curl mite. Although many varieties have partial resistance, none are highly resistant to wheat streak mosaic.

Sources:

Kansas State University
North Dakota State University

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