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Arkansas weed control: Herbicide-resistant ryegrass in wheat

In my column in the Sept. 21 issue of Delta Farm Press, I discussed some of the cultural practices that can help you fight Hoelon-resistant ryegrass. These are a very important part of the battle plan.

Steve Powles of Australia, who is considered the world's foremost authority on the subject, told me Hoelon-resistant ryegrass was the first problem he encountered as a weed scientist that he couldn't solve by just changing herbicides. “Herbicide-resistant ryegrass has made a weed scientist out of me; before I was a herbicide scientist,” he said. They have had to use a whole array of cultural practices, along with herbicides, to continue to grow wheat in Australia.

To date we have been a little more effective with some alternative herbicides than they have been in Australia. However, this has only been to the tune of 50 to 70 percent control.

Perhaps our best labeled alternative herbicide has been Finesse applied as a pre-emergence treatment. Last year, quite a bit of Finesse was used. Unfortunately in many areas, we had a dry fall period and a lot of the herbicide did not receive activating rainfall.

We also get a few calls about crop injury with Finesse each year. It seems to be primarily where the seeds were either placed extremely shallow or on top of the ground. We have never seen injury in our research plots.

DuPont recommends Finesse be used only if the wheat is drill-seeded. In addition to providing 50 to 70 percent control of ryegrass in our plots, it will absolutely clean out the wild garlic and winter junk weed complex.

Finesse can only be used where soybeans will not be planted following the wheat crop or if STS soybeans are used. If you are going to doublecrop, make sure you have STS soybeans secured before using Finesse.

Another treatment that has looked decent in our plot work over the past three years has been two applications of Sencor. With wheat prices as they are, I doubt if many people are going to make two trips across the field. Perhaps it will depend on how bad the problem is.

When we used to just use the regular rates of Sencor after wheat was tillering, we essentially would get zero control of ryegrass. After we got the label to use the low rate of Sencor on two- to three-leaf wheat, we started looking at this treatment, followed by the higher rate, once the wheat was tillering. I really did not expect much out of the treatment. However, it has consistently been as good as about anything we have evaluated.

We are using a rate of 3 ounces per acre of Sencor on two- to three-leaf wheat and following with 5 to 10 ounces per acre, depending on soil type, on two- to three-tiller wheat. To attempt this treatment, you must plant a variety with good tolerance to Sencor. Good information on tolerance is available from county Extension agents.

We are looking at several experimental herbicides and also at Clearfield wheat in our program. Several of these are showing promise. Maybe we can stay ahead of the problem. However, I strongly recommend you also use good cultural practices, including the fallow till-and-smooth program.

Ford Baldwin is an Arkansas Extension weed scientist. e-mail:

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