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Wheat growers battle resistant weed

LITTLE ROCK, Ark. -- For the second year in a row Arkansas and several other states have applied with the EPA for a Section 18 for the herbicide mesosulfuron-methyl (manufactured by Bayer CropScience) for the control of Hoelon-resistant ryegrass in winter wheat. This herbicide was formerly known as Falcon, but the name has been changed to Osprey.

Whatever the name, it is by far the best option I have evaluated in my program to replace Hoelon as the herbicide of choice for ryegrass control. Osprey has performed well in my trials regardless of timing, formulation and tank-mix partner. We have controlled ryegrass from three leaves all the way up to five to six tillers. However, I believe the label will go after three-leaf to one- to two-tiller ryegrass, if granted.

Italian and other biotypes of ryegrass continue to be the top weed problems faced by Arkansas wheat growers. I know this weed is a problem in several other states as well.

Even though wheat acres were down last year in Arkansas, reports of new fields where Hoelon failed came in at an alarming rate.

Around the world, ryegrass is known to contain much genetic diversity. There are biotypes of ryegrass that are currently resistant to numerous families of herbicides.

I hope that the EPA will grant us the Section 18 for Osprey this year. Osprey has been moved to the "reduced risk" status, which indicates that it is relatively safe to the environment and poses little threat to human health. Theoretically this also means a speedy approval process for a full registration.

Other options should the Section 18 fail are limited. Probably the most feasible is to use a full rate of Finesse herbicide applied pre. You must get good, timely activating rainfall for this herbicide to perform well on ryegrass.

Also, crop rotation is a limiting factor for many. This option is the best in wheat, followed by fallow rotations. If you are following wheat with soybeans, you must use an STS soybean following the use of Finesse herbicide. There are a few STS/Roundup Ready stacked varieties now, which may help out some if you use this program.

You may have also heard of the new Clearfield wheat system. Like in rice, you have to use a variety of wheat specifically developed to be tolerant to the herbicide. Beyond is the product that was registered for use on Clearfield Wheat.

I have been working with a graduate student who just finished the second year of his masters degree program evaluating several rates, timings and tank-mixes of Beyond for Clearfield wheat. It performs fairly well on ryegrass. I will probably rate it an 8 in recommendations for 2004. However, at this time there are no varieties available for the soft red winter wheat market that we have here in the South. Clearfield wheat and Beyond herbicide are currently fully registered for use.

Once I find out whether or not we are granted a section 18 for Osprey herbicide, I will write a follow-up article with rates and timings that have worked well for us.

Bob Scott is the University of Arkansas Extension weed specialist.

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