With the increase in wheat acreage, I have been asked about wheat weed control. The primary weed to be concerned about this time of year is ryegrass. I have always considered mid-December to be the best time to control ryegrass.
When I was with the University of Arkansas, we had a rather aggressive applied research program for ryegrass control — especially Hoelon-resistant ryegrass.
Bob Scott has continued that program and has put together some good information on some of the newer herbicides. That information is available through Arkansas county Extension agents.
There are three choices for postemergence control of ryegrass and two choices if the ryegrass is Hoelon-resistant. Where there is no history of Hoelon resistance, Hoelon is the standard the others must be compared to.
It can be used at rates as low as 1.33 pints per acre this time of the year if the ryegrass is small and no residual control is desired. You can push the rates as high as 2.67 pints per acre and get both postemergence and residual activity. My favorite rate this time of year is 2 pints per acre.
We did a lot of surfactant and crop oil concentrate work with Hoelon and never found a consistent advantage to adding either. Hoelon has activity only on ryegrass. Scott rates it a 9 on susceptible ryegrass and a 3 on resistant ryegrass.
If Hoelon resistance is suspected or if the field has a history of frequent Hoelon use, another herbicide would be a better choice.
Axial is the newest of the ryegrass herbicides and one I have not personally worked with. The application rate is 8.2 ounces per acre with 9.6 ounces of Adigor adjuvant. The application timing is two-leaf and larger wheat and one-leaf to two-tiller ryegrass. Now should be the ideal application time in most situations.
Axial is a postemergence grass herbicide closely related to herbicides such as Hoelon, Select and Poast. Scott has rated Axial a 9 on non-resistant ryegrass and a 7 on Hoelon-resistant ryegrass. He reported that it has actually been better than a 7 at his Willow Beach research location, but since there are so many biotypes of ryegrass and resistant ryegrass, he is being conservative with the rating until more information is available with the herbicide.
Axial has no residual activity and mostly just has activity on ryegrass.
The third herbicide is Osprey. It has been in the research program for years and has consistently provided excellent control of both susceptible and resistant ryegrass species. Scott rates it a 9 on both.
It also has activity on annual bluegrass and some of the broadleaf species such as vetch and buttercups. The application timing is from four-leaf to two-tiller ryegrass. The rate is 4.75 ounces per acre with 1.33 to 1.5 pints of a methylated seed oil adjuvant or 0.5 percent nonionic surfactant plus an ammonium source.
Where the objective is herbicide rotation for resistance, Osprey would be the herbicide of choice since it has a different mode of action than Hoelon and Axial.
I get a lot of questions about re-infestation behind a fall herbicide application. I have enough folks say it has happened to believe it. In general however, most of the ryegrass will emerge in the fall.
My philosophy is kill what is up now and worry about re-infestation later. If you do not, you could well find yourself in a salvage situation come spring.
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