Linda Benedict, Williams, Billy James, Laird, Suzanne  |  3/1/2011 10:32:24 PM

A new herbicide for managing weeds in wheat

Bill Williams, Rakesh Godara and Suzanne Laird

Annual bluegrass and henbit are the most common and frequently targeted weeds in Louisiana wheat. Ryegrass is the most challenging weed to manage in Louisiana wheat and is increasing in abundance.

Finesse and metribuzin and are the most economical herbicides for managing annual bluegrass and henbit, but metribuzin is limited by wheat tolerance, and Finesse is limited by rotation. As a result, the herbicide Osprey is often the herbicide of choice for managing bluegrass and henbit. Osprey, however, often fails to control ryegrass beyond the four-leaf stage. Because of this the herbicide Axial has become the standard for controlling ryegrass, although it fails to control annual bluegrass or henbit.

The most effective herbicide programs for managing bluegrass, henbit and ryegrass in wheat consist of a late fall – November to early December – application of Sencor, Finesse or Osprey followed by a February application of Axial.

A new herbicide called PowerFlex has been evaluated in trials and demonstrations since 2007. The initial results were encouraging because PowerFlex controlled bluegrass and henbit as well as Osprey and controlled ryegrass as well as Axial. In 2008, however, Osprey, PowerFlex and Axial all failed to control ryegrass. PowerFlex also failed to control bluegrass in spring 2008.

It’s not well understood why ryegrass and bluegrass control were less in 2008 than in 2007. Planting in 2008 was delayed until December, resulting in later herbicide applications. Since 2008, PowerFlex has consistently controlled bluegrass, henbit, ryegrass, canary grass, cutleaf evening primrose, white clover, swinecress, buttercup and vetch. Power- Flex also suppresses wild garlic, which can be controlled by adding 0.33 ounce per acre of the herbicide Harmony Extra.

PowerFlex, a broad-spectrum herbicide, can be applied from the three-leaf to jointing stages but should be applied before grass weeds begin to produce additional stems and before broadleaf weeds are 2 inches tall. PowerFlex is best used in November or early December.

In areas with severe ryegrass infestations, a follow-up treatment with Axial in February may be needed. Ryegrass management in wheat requires two herbicide applications, one in late fall and one in February, to maximize wheat yield. If only one herbicide application can be made, it should be made in November to early December. In research trials, wheat consistently yields around 25 more bushels per acre when ryegrass is managed in November compared with February. Adding the herbicide Prowl at 1 pound active ingredient per acre to fall applications of PowerFlex improves ryegrass control at harvest from about 75 percent to 85 percent.

PowerFlex is applied at 3.5 ounces per acre regardless of soil type, wheat variety or weed growth stage. It must be applied with a nonionic surfactant or crop oil concentrate, although crop oil concentrate increases the risk of wheat injury. In most cases, nonionic surfactant is preferred. The addition of 32 percent urea ammonium nitrate at 2 quarts per acre improves the control of larger or stressed weeds. Like Osprey, Power- Flex will not control ryegrass resistant to ALS-inhibitor herbicides. The label does not include bluegrass as a controlled weed, and this limits PowerFlex’s usefulness in Louisiana.

Overall, PowerFlex is an excellent foundation herbicide. It does not have the tolerance issues associated with metribuzin or the rotation issues associated with Finesse. As with metribuzin and Finesse, PowerFlex takes care of most weeds in the fall and allows producers to focus on controlling ryegrass with Axial in spring.

Bill Williams, Associate Professor and Weed Management Specialist, Scott Research/ Extension Center, Winnsboro, La.; Rakesh Godara, Research Associate, Northeast Research Station, St. Joseph, La.; Suzanne Laird, Research Associate, Scott Research/Extension Center

(This article was published in the winter 2011 issue of Louisiana Agriculture magazine.)

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