By STACY CAMPBELL
Cottonwood Extension District
Over the last several weeks, symptoms of wheat streak mosaic virus have been showing up in wheat fields across Kansas, including the Cottonwood District.
This disease complex can be caused by several viruses, including wheat streak mosaic virus, Triticum mosaic virus, and wheat mosaic virus (high plains). These viruses are vectored by the wheat curl mite, a near-microscopic mite that survives between seasons on volunteer wheat and other grassy hosts. These grassy hosts serve as a “green bridge” for mites to survive from one wheat crop to the next. Infections may occur in the fall or spring, but fall infections typically result in the highest levels of yield loss.
Although wheat streak mosaic infections can happen at any time, symptoms develop most rapidly at temperatures above 70°F. Symptoms have become more severe in Kansas over the last several weeks as temperatures have warmed.
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Will a fungicide help with my wheat streak infection?
No. There is no evidence that a fungicide application will do anything to stop the progression of wheat streak mosaic complex or preserve yield in infected fields. Fungicides are specifically formulated to kill diseases caused by fungi (leaf & stripe rust, leaf spots, head scab, etc.) but have no activity against viral diseases like wheat streak mosaic.
In addition, fields that have moderate to severe wheat streak mosaic infections will often have reduced yield potential that will diminish the economic return from a fungicide applied to control one of those other diseases (rust, leaf spots, or head scab).
Why is the wheat streak complex so severe and widely distributed this season?
Although we are still trying to understand the extent of the damage across the state, says Kelsey Anderson Onofre, Extension Wheat Pathologist, there are a few factors that came together this season that may have contributed to the outbreak.
Wheat streak complex can be more severe in years where summer moisture that favors volunteer wheat establishment is followed by a warm fall that favors mite reproduction. In 2024, although August was relatively dry, precipitation in July and September would have supported late volunteer wheat emergence. Wheat curl mite populations prefer warm, dry weather and reproduce at high rates between 75-85°F. These mites only survive short periods (8-10 days) when conditions are warm, but during that time, they can lay up to 20 eggs. This rapid population growth can lead to a 25% increase in population size over the course of just two weeks.
In 2024, Kansas experienced a very warm fall with higher-than-normal temperatures from September through November. These conditions may have sustained periods of time that were highly favorable for mite reproduction and movement across fields.
Is there anything I can do this season to help slow down the progression of the disease?
No. Efforts to control wheat curl mites with foliar miticides and/or insecticidal seed treatments have never proven effective and have not been shown to reduce the spread or severity of the viruses.
What can we do to prepare for the 2025 planting season?
The most critical way to prevent wheat streak complex infection is to control volunteer wheat after harvest and continue to control any secondary flushes of volunteer prior to planting.
We also need to watch for hidden volunteer wheat in summer crops and cover crops. Although curl mites prefer wheat, they can also survive the summer on other grass species. Avoid planting wheat early to reduce the length of time mites have to increase their numbers and transmit disease.
Information provided by Kelsey Andersen Onofre, Extension Wheat Pathologist.
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or by calling 785-628-9430.