New herbicides help producers mix up modes of action to fight resistance

Farmers can fend off herbicide-resistant weeds and make money by changing up their weed control program

How can thinking about resistance help us economically in the short and long term?” This was a question posed by Brad Ewankiw, a project manager for FMC Canada, during a presentation on FMC’s new herbicides at North Star Genetics’ annual soybean grower information day in Morris March 27.

Ewankiw pointed to pre-emergent residual herbicides as a key option for diversifying producers’ modes of action and diminishing the risk of resistance.

“Residual herbicides help by reducing emergence and therefore reducing the selection pressure on post-emergent application, and by adding different modes of action to the mix,” said Ewankiw. “Most resistance is about selection, and if you’re using one mode of action over and over again you’ll eventually have a problem.”

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Ewankiw emphasized that pre-emergent weed control is as important as post-emergent weed control for soybeans, and allows producers to maximize yield by keeping the crop clean early and reduce selection pressure by reducing weed emergence.

Among the herbicide-resistant weeds on growers’ radar is glyphosate-resistant kochia, now confirmed in all three Prairie provinces, and glyphosate-resistant Palmer amaranth (Palmer pigweed), which was spotted in South Dakota last year and is moving north. “Experts are saying that the next three weeds that could be a concern are wild oat, cleavers and green foxtail,” said Ewankiw. “We need to be looking south and thinking about how we can change our grower practices up here.”

Ewankiw pointed to several studies illustrating the effectiveness of early weed control, including recent North Dakota State University soybean trials that looked at the impact of weed removal timing on yield potential. According to Ewankiw, researchers saw an average of 20 bushels per acre yield potential lost when herbicide application was delayed to the V4 stage.

FMC offers new pre-emergent residual herbicides that are “quite a bit different” than older herbicides, according to Ewankiw. They do not get tied up with crop residues or volatilize into the air. Also, they do not require soil incorporation, and can be tank mixed with any glyphosate at any rate.

One product is Authority, a pre-seed/pre-emergent liquid flowable herbicide with extended residual activity that is effective against broadleaf weeds such as cleavers and kochia. The active ingredient is sulfentrazone, a Group 14 PPO Inhibitor.

Producers have two options when deciding to use this product — Authority or Authority Charge, which also contain the Group 14 herbicide carfentrazone. Authority Charge “heats up glyphosate on broadleaf weeds,” Ewankiw said, and provides additional activity on emerging weeds such as dandelion and narrow-leafed hawk’s beard.

Another product Ewankiw highlighted is Focus, a new Group 15 herbicide with a flexible-use pattern that provides burn-off for emerging weeds and residual impacts on early-season weed pressure. “It’s the same application timing as Authority, and has lower water solubility, low soil adsorption, low crop residue affinity, and low volatility,” he said. Focus, which also contains carfentrazone, is active on both grassy and broadleaf weeds.

Residual weed control herbicides should be applied prior to planting, especially if producers are using a drill that isn’t moving a lot of soil laterally, or pre-emergence. Ewankiw said the products work by creating a barrier on the soil surface. They are then taken up by the roots and shoots of germinating weeds.

“We can’t be sustainable if we’re not thinking about resistance management, but we also can’t be sustainable if we’re not making money in the short term. It’s about both,” he said.

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