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Here They Come Again

Posted by Drew Lyon | September 16, 2020

Wild oats were not a problem I experienced in my 22 years in western Nebraska. When I accepted my current position at WSU in 2012, I did some reading to familiarize myself with the weed issues I might be faced with. There were numerous scientific papers from the region on wild oats, so I thought it would be one of the weed species I would need to address. However, as I drove around eastern Washington talking to farmers and county Extension faculty, I saw very few fields with wild oats in them and nobody mentioned wild oats as a major concern. I could see wild oats growing along roadsides and field edges, but only occasionally in fields. Consequently, I took wild oats off my list of concerns and began work on other grass weed issues in wheat such as downy brome, Italian ryegrass, and rattail fescue.

Over the past couple of years, however, I have observed wild oats moving out of the roadsides and field edges into fields. On a recent drive between Starbuck and Waitsburg, I was surprised to see how many wheat fields had significant infestations of wild oats. It seems that the herbicides that we have relied on for wild oat control for the past decade or more are no longer as effective as they used to be. Just as we have done with downy brome and Italian ryegrass, we have selected wild oat biotypes resistant to the ALS-inhibiting (Group2) and ACCase-inhibiting (Group 1) herbicides that have served as the main, and often the only, management strategy for annual grass control in wheat.

The Herbicide Resistant Weeds Map indicates that wild oat biotypes resistant to several herbicides have been confirmed in eastern Washington. Dr. Ian Burke’s lab has confirmed the presence of herbicide-resistant wild oat biotypes in Columbia, Lincoln, Whitman, and Walla Walla Counties. Biotypes resistant to the ACCase-inhibiting herbicides clodinafop (Discover NG), pinoxaden (Axial XL, Axial Bold, Axial Star), and quizalofop (Assure II, Aggressor) have been confirmed, as have biotypes resistant to the ALS-inhibiting herbicides imazamox (Beyond, Raptor), mesosulfuron (Osprey, Osprey Xtra), propoxycarbazone (Olympus), pyroxsulam (PowerFlex HL, TeamMate, GoldSky, OpenSky, PerfectMatch), and sulfosulfuron (Outrider).

In a 2019 field study conducted near Pullman, we found that while Axial Bold (pinoxaden + fenoxaprop) improved wild oat control in spring wheat compared to Axial XL, Tacoma 1EC (fenoxaprop), Discover NG, Everest 3.0 (flucarbazone), Olympus, and OpenSky, no herbicide provided commercially acceptable control of wild oats in that field.

As if we didn’t have enough to worry about with widespread herbicide resistance in downy brome and Italian ryegrass, it now appears that we will have herbicide-resistant wild oats to deal with. To learn more about herbicide resistance in eastern Washington, visit the Herbicide Resistance Resources page on the Wheat and Small Grains website.

Dry wild oats.
Photo courtesy of Mark Thorne.
Wild Oats.
Photo courtesy of Henry Wetzel.
Wild oat field.
Photo courtesy of Mark Thorne.

3 thoughts on "Here They Come Again"

  1. Aaron Esser says:

    As I look at the herbicide resistant weeds map, I see wild oat in Lincoln County that is resistant to clodinafop (Discover), pinoxaden (Axial XL), quizalofop (Assure II & Aggressor), and imazamox (Beyond). My question is…Is this one wild oat plant coming from the same farm resistant to these 4 herbicides or is it potentially 4 wild oat plants resistant to a single herbicide and potentially each wild oat coming from different farms?

    1. Drew Lyon says:

      Aaron, in Lincoln County, one wild oat biotype was cross-resistant to all four herbicides you have listed. Early in Dr. Burke’s herbicide resistance screening program, which is partially supported by the Washington Grain Commission, biotypes were often resistant to a single herbicide, but in recent years, many of the samples submitted have been cross-resistant to several herbicides. The development of cross-resistance in many weed biotypes makes weed management more difficult as it reduces the effectiveness of herbicide rotation as a management option. It is sometimes said that herbicides are not the solution to herbicide resistance. The development of cross-resistance supports that statement. -Drew

      1. Anonymous says:

        Thanks Drew.

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