June 6, 2008
With our wheat crop is basically made for the year, now may seem like a strange time to write about wheat weed control. However, if you look at wheat weed control plots, especially ryegrass control, you know that now is the best time to see what worked and what did not.
For a very long time, Arkansas producers basically relied on Hoelon herbicide for ryegrass control. That led to a serious problem for us in Arkansas with almost every county in Arkansas reporting Hoelon-resistant ryegrass.
We now use Finesse and Osprey herbicides, and to a lesser degree, Axial XL and Prowl H2O herbicides, to battle ryegrass. Both Finesse and Osprey are ALS herbicides, and to date at least one population of ryegrass that is resistant to ALS chemistry has turned up in Arkansas.
However, resistance to Hoelon is by far our biggest problem.
Axiom, a new product from Bayer CropSciences, is a premix containing the products metribuzin (Sencor) and flufenacet. It product has performed well as a pre or early-post at our Hoelon-resistant ryegrass location near Scott, Ark.
It actually looks best under this severe ryegrass pressure in a program as either a tank-mix with Osprey or followed by Osprey.
One appealing thing about this approach is resistance management, because it provides three modes of action against ryegrass (although the metribuzin part is somewhat weak on this specific pest).
Finesse herbicide (Glean + Ally) for some time has been the best pre-emergence product that I have looked at for ryegrass control in wheat. If you can get a rain to activate it, Finesse alone often provides season-long, acceptable ryegrass control.
A common mistake that many have made is to apply Finesse post-emergence on already emerged ryegrass and hope for the same results. Control failures also often occur when no rainfall is received for activation.
A new formulation called Finesse Grass and Broadleaf (Glean + Everest (flucarbazone-sodium)) is now available and will work better on emerged ryegrass in this early postemergence timing.
The product looked very good timed to three-leaf to four-leaf ryegrass in our plots this year.
Finesse Grass and Broadleaf will control emerged ryegrass and provide the long residual that growers expect from Finesse.
With these Glean-containing products you must rotate to STS soybeans the following year or unacceptable crop damage will occur. From a resistance management standpoint both Finesse products contain ALS herbicides.
The new product from Dow AgroSciences called PowerFlex (pyroxsulam) looks very good in our program so far. Similar in spectrum to Osprey herbicide and also in the ALS group of chemistry, it has performed very well on ryegrass this year as well as several other broadleaf weeds.
We have only evaluated it for one year. It has been researched more extensively in the Southwest.
We put at least one treatment of pyroxsulam at every location this year in preparation for a fall of 2009 launch in Arkansas. We observed excellent control of both ryegrass and Hoelon-resistant ryegrass, as well as control of henbit, curly dock, buttercup and red sorrel in our plots.
PowerFlex did not control wild garlic, primrose, cudweed or horseweed.
Currently there is a nine-month rotation to soybeans on the PowerFlex label; Dow is working to shorten this. There are currently no fertilizer timing restrictions.
One of the most exciting things about this product to me is that it may be priced very competitively.
Ryegrass has once again proven to be a difficult weed to control in Arkansas. More and more, I feel like we have not only Hoelon-resistant ryegrass, but also ryegrass that has the ability to germinate in both the fall and spring, making one-shot programs difficult to time.
The best plots in my program again this year were the two-shot programs of a pre (such as Finesse or Axiom) followed by a post (Osprey, Axial XL or PowerFlex).
The second-best plots combine a post herbicide with a residual herbicide (such as Osprey + Prowl, or others) applied late in the fall.
I know most of you do not want to use a two-shot approach in wheat due to cost, but the hard fact is most one-shot programs will just not provide 100 percent control of heavy ryegrass infestations.
I do not know if you noticed or not, but we have gone from a heavy reliance on acc-ase chemistry (Hoelon and Axial XL) to heavy reliance on ALS chemistry (Finesse, Finesse G&B, Osprey, PowerFlex) for ryegrass control. It is only a matter of time.
Currently, Axiom and Prowl H2O are the only options that are neither ALS nor acc-ase inhibitors. Incorporation of these two products into a program approach will help curb the development of ALS-resistant ryegrass.
For years, growers have use either tillage or Roundup (glyphosate) prior to wheat emergence to control the first early flush of ryegrass, which is often a very effective control method.
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