Old friends killing old foes again

Old school herbicides Avadex and Edge are teaching new lessons to resistant wild oats

Two “old friends” might be enlisted in the chemical fight against herbicide resistant weeds.

One of them is Avadex, said Mike Grenier of Gowan Canada, which acquired Avadex from Monsanto in 2004.

Avadex, with the active ingredient of triallate, is a Group 8 herbicide that has been shown in trials to control wild oats that are resistant to Group 1 and 2 herbicides.

Grenier told those at the Jan. 21 Agronomy Update in Lethbridge that the rise of herbicide resistant weeds is driving renewed interest in the product, although there is some known resistance to Group 8 herbicides.

Avadex is approved for cereals, oilseeds and specialty crops such as peas, mustard, flax and sugar beets. Granules applied to the soil surface are activated once moistened. Wild oats are controlled when the plants grow through the treated layer of soil, so about one-half inch of incorporation is recommended.

Grenier said zero-till stubble is the perfect target for the herbicide granules because the advent of minimum and zero tillage has ended up distributing weed seeds near the surface. In thick stubble, residue would have to be managed before application.

The label allows fall as well as spring application.

A liquid option is suitable when there is less than 30 percent surface stubble. In that form, the herbicide must be incorporated within 24 hours of application.

Another old friend is Edge, a Group 3 pre-emergent herbicide. Once commonly used on oilseeds, it fell out of use with the advent of herbicide tolerant canola and integrated use of glyphosate in pre-seeding.

Brian Wintonyk of Dow AgroScience said Edge, with its active ingredients of ethalfluralin and trifluralin, used to be incorporated three to four inches deep in conventional tillage.

However, that doesn’t work with minimum tillage systems. Weed seeds must be in contact with the treated soil layer to be affected, and Edge is not water mobile so it does not move to get in contact with weed seeds.

Wintonyk said it will not be active early in the season to control initial weed flushes, so some other form of weed control will be needed.

Fields must be direct seeding for at least two years with less than 30 percent disturbance for Edge to be effective. The product is safe for use on oilseeds and legumes against foxtail, pigweed and kochia, but it only suppresses wild oats.

Focus, a Group 15 herbicide, might be a new friend in the herbicide resistance battle, said Mitch Long of FMC Canada, which bought Cheminova last year.

The herbicide’s active ingredient is pyroxasulfone, and it is registered for corn and soybeans. FMC has applied for registration on spring wheat, winter wheat and lentils, and will potentially add field peas, chickpeas, potatoes, carrots, fababeans and sunflowers.

It controls a wide spectrum of grassy weeds.

Long said Focus shows 80 percent control of wild oats on the surface and 65 percent control at a two-inch depth.

The label is narrow for broadleafs, and the company has applied for wider listings including cleaver, stinkweed, lamb’s quarters, kochia and wild buckwheat.

Focus forms a barrier on the surface, so it is applied before planting or just afterward. Rainfall incorporates and activates it, and it is then taken up by roots and shoots.

It is not recommended on soil with more than seven percent organic matter.


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