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Many options Wheat crop begins with weed control

Although the spring freeze this year devastated wheat yields on many farms, there is a lot of interest in planting wheat this fall. In Arkansas three weeds typically required herbicide applications: (1) ryegrass, (2) ryegrass and (3) wild onion/garlic.

There are a number of options for ryegrass control, beginning at pre-emergence.

Finesse herbicide provides excellent control of ryegrass and most other wheat weeds and it is cheap. If that sounds to good to be true, there are some catches.

Like any other pre-emergence treatment it requires rain for activation. If weeds germinate prior to it being activated, Finesse will not work. It has little ryegrass activity when applied postemergence.

Finesse herbicide can injure regular soybeans planted in a field the year after it is used, so you must grow an STS-tolerant soybean. A few good STS/RR stacked-trait beans are available. Ask the folks who sell you soybean seed for a list or call your county agent.

If Finesse is not an option for you, ryegrass control becomes mostly a postemergence endeavor. Prowl herbicide received a federal label for wheat last year, but it is labeled for use only after the wheat has emerged. Unfortunately, that often is after the ryegrass has emerged too. This timing does a good job on later-emerging winter annual broadleaf weeds such as henbit, chickweed and buttercup.

Prowl is a good tank-mix partner with postemergence grass herbicides for wheat such as Hoelon, Osprey and Axial.

Prowl has had excellent crop safety in our trials, including pre-emerge and delayed pre-emerge timings, but these uses are not labeled.

Due to a heavy reliance on Hoelon herbicide over the years, many wheat farms in Arkansas have developed significant populations of Hoelon-resistant ryegrass. On farms that do not have a history of Hoelon use, it is still an excellent option for ryegrass control in both fall and spring timings.

The new herbicide Axial from Syngenta has a slightly different structure than Hoelon, but it is in the same family of chemicals with the same mode of action. At our Hoelon-resistant site near Willow Beach, Ark., Axial seemed to control Hoelon-resistant ryegrass. Results have not been consistent, however.

I am concerned that with all the different populations and biotypes of ryegrass, it may not always be a good option where Hoelon-resistant ryegrass is the target.

Osprey herbicide has performed well in our trials for ryegrass control. It controls annual bluegrass and has activity on many broadleaf weeds, except mayweed and wild onion/garlic.

Application timing is a matter of debate with Osprey. It has no residual activity. While the fall is the best time to control ryegrass from a weed control and yield standpoint (less time for ryegrass to compete with wheat), ryegrass often emerges late in the fall or early in the spring after an application of Osprey.

Adding Prowl to a fall application of Osprey will sometimes provide the added residual needed for season-long ryegrass control.

Many growers elect to apply Osprey in early spring to avoid this problem, Often it is tank-mixed with Harmony Extra for wild garlic control. This timing allows months of weed competition, but may limit weed control trips across the field to one.

For the most severe infestations of ryegrass, a two- or three-step approach may be needed. This could include fallowing a field for a year, or allowing the ryegrass in a field to emerge before applying a tillage or burn-down treatment prior to planting. A program approach of two different ryegrass herbicide treatments such as Finesse followed by Osprey, or Hoelon or Axial in the fall followed by Osprey in the spring might also be needed.

One new issue that has emerged in wheat is controlling horseweed. Typically horseweed is not a tremendous yield-robber in wheat. Finesse and even Prowl applied pre-emergence to horseweed will provide pretty good control. In the spring, however, you should not pass up an opportunity to control horseweed in wheat if you find it in the field, especially if the field is to be planted to soybeans later in the summer.

Most of horseweed in Arkansas is resistant to glyphosate. We also recently found a population that we strongly believe to be resistant to ALS herbicides such as Harmony Extra, Firstrate and Envoke. There are not many good options to control glyphosate-resistant horseweed after wheat is harvested or after soybeans are planted.

For spring horseweed control in wheat, I suggest using a full rate of Harmony Extra plus 1 to 1.5 pints of 2,4-D. For severe infestations, adding 2 ounces to 4 ounces of Clarity can improve efficacy of this treatment even more.

Even light infestations of ryegrass can significantly impact wheat yields. Although it takes fairly substantial infestations of most broadleaf weeds to impact yield, harvest difficulties and the quality of harvested grain are often affected by broadleaf weeds.

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