September 21, 2015
Weed control in wheat has become more of a struggle in recent years. This is due to more wheat following corn where volunteer Roundup Ready corn can be an issue, Poa becoming more of a weed problem in wheat and herbicide resistance development in ryegrass.
Volunteer Roundup Ready corn management.
There have been several calls about burning down volunteer Roundup Ready corn before wheat planting. In our research there have only been two herbicides that controlled the volunteer corn. One was 40- 48 oz/A of Gramoxone Inteon applied with 0.25 percent NIS at 15 gal/A. Coverage and rate are critical to make this work.
The other option was to use 0.5 oz/A of Finesse which also did a good job plus it provides residual control of ryegrass and many broadleaf weeds. Of course, like all PREs, it works best when it receives a rain within seven to 10 days after application to activate. However, if it does not get an activating rain, the weed control can be inconsistent. One thing to remember is if Finesse is used, only STS or Bolt soybeans can be planted for double crop in the summer.
Bluegrass control in wheat.
Bluegrass (aka Poa) can be a serious issue in some wheat fields especially if it becomes established before or with the wheat. If Poa becomes established with the wheat it can deter tillering and readily compete for nitrogen. Typically one of the best ways to manage bluegrass is to start clean. Using either tillage or Gramoxone Inteon at 40 oz/A will be a good way to manage this pest.
Still another option is to apply metribuzin at 2 oz/A POST emergence over the wheat that is at 2 to 4 lf. This timing of a metribuzin application has been a very inexpensive way to manage bluegrass and very small broadleaf weeds like henbit.
When it comes to ryegrass control, some type of two pass approach works best. It can either be a PRE followed by a POST or two POST applications. One reason for this is that wheat is more susceptible to yield loss from ryegrass that emerges with it in the fall than ryegrass that emerges in the spring. Therefore a PRE followed by an early POST application can remove that potential yield loss.
Though it is not used much in Tennessee, Axiom is a good herbicide for bringing residual ryegrass control PRE.
Zidua recently was labeled delayed PRE in wheat. This timing can be hard to hit but in our research has been very effective on ryegrass and Poa.
Over the last several years we have had a fairly extensive flush of ryegrass in the spring. A POST application is often required to clean this up. ALS-inhibiting herbicides (Osprey, PowerFlex and Finesse Grass and Broadleaf) have been used extensively to control ryegrass in wheat.
ALS-resistant ryegrass is present in West Tennessee. Therefore Axial has increasingly been used for ryegrass POST. Unfortunately, Axial-resistant ryegrass was confirmed in Arkansas this year. A two-pass program that utilizes two different modes of action will be the most sustainable method to manage ryegrass long term.
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