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Reminders for Spring Postemergence Herbicide Applications in Wheat for Grass Weed Control

Posted by Andrew Hulting, Oregon State University | December 22, 2021

With flooding rains occurring and snow falling in some areas of our region this week, it may be difficult to envision making spring postemergence herbicide applications in wheat. But before you know it, we will be through the holiday season and our thoughts will be turning to late winter/early spring wheat growing conditions. As we transition into spring over the next several months, depending on your location around the PNW, here are some reminders about maximizing the efficacy of your spring postemergence wheat herbicides.

A competitive wheat crop with an adequate stand is the key cultural weed management strategy to limit impacts of grass weeds.  But there are some additional considerations to maximize postemergence control of grass weeds with herbicides as we transition into the spring.

In general, it is important not to apply most postemergence herbicides when cold, wet weather is expected within one week following application (or several days before the application for that matter).  Reduced weed control efficacy and crop injury may occur when maximum daytime temperatures are less than 40°F after herbicide application, and severe crop injury may occur if freezing environmental conditions occur. If possible, growers need to time late winter and spring applications of herbicides including Outrider®, Osprey® or Osprey Xtra®, PowerFlex HL®, Axial XL® or Axial Bold®, Everest® and Beyond® to avoid these types of environmental conditions to maximize grass weed control efficacy.  In addition, each of these products has its own unique adjuvant system (additions of NIS, AMS, COC, and MSO, for example) that must be utilized to achieve grass weed control and limit potential for wheat injury. Always refer to the product label and our current recommendations for your growing region for each product and for product updates in the PNW Weed Management Handbook.

A herbicide efficacy trial in winter wheat in western Oregon.

With the increase in adoption of pyroxasulfone herbicides in wheat, a question that I am often asked this time of year by wheat growers is to give my recommendation on the best postemergence grass herbicides to tankmix with pyroxasulfone-containing products when making delayed preemergence, early postemergence or sequential applications of Zidua® or Anthem Flex® to control already germinated and emerged grass weeds in wheat. What I can say is that we have good success tank mixing pyroxasulfone products with Osprey and PowerFlex HL. We have conducted a number of studies since 2015 that have explored many of the application timings and tank mix possibilities of Zidua and Anthem Flex (with PowerFlex HL and Osprey) compared to standard flufenacet + metribuzin (Axiom DF®) treatments for the control of both susceptible and multiple herbicide resistant Italian ryegrass. We have quantified slight injury to the wheat from the Axiom DF treatments but there has been no wheat injury from the Zidua or Anthem Flex treatments or when either of these two products were tank mixed with PowerFlex HL or Osprey. Only the preemergence application timings to the multiple resistant Italian ryegrass resulted in satisfactory control of that biotype, underscoring the importance of application timing to maximize the preemergence control potential of the pyroxasulfone products when managing Group 2 ALS-resistant biotypes of grass weeds in winter and spring wheat.

Keep these key ideas in the back of your mind as we transition through winter so that when the time comes this spring you are prepared to make timely and effective herbicide applications to your wheat crop.

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