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How to Forestall Herbicide-Resistant Weeds

Applying a mix of herbicide sites of action with cultural practices like narrow rows can help keep weeds at bay.

Glyphosate-resistant weeds garner lots of the headlines when it comes to resistance.

It’s important to remember, though, that herbicide resistance isn’t just limited to glyphosate, says Dane Bowers, herbicide technical product lead for Syngenta. “Herbicide resistance is a biological process,” he says. Steps like repeated use of any single herbicide site of action can eventually lead to resistant weeds.

At last week’s Commodity Classic in San Antonio, Texas, Bowers noted that weeds topping the resistant list include Palmer amaranth and waterhemp. “Ragweeds are also quite problematic across the country,” he adds.

With no new herbicide sites of action coming down the pike, it’s important that farmers use existing strategies to forestall herbicide resistance, say weed-control specialists.

“The best weed control doesn’t allow weeds to get out of the ground,” says Dawn Refsell, Valent USA field market development specialist. Overlapping residual herbicide strategies can help farmers achieve this.

An overlapping residual plan is one in which a preemergence residual herbicide is applied. This is followed by an in-crop application of another residual herbicide usually made at the same time as another nonselective herbicide in herbicide-tolerant systems like Roundup Ready or Liberty Link. Extending residual control is one way to help keep weeds at bay.

A mix of tactics is also important, adds Bowers. “It’s not just about using different herbicides,” he says. “It’s also about using tillage when appropriate, maybe using cover crops, or planting narrow rows. It’s about anything you can do to make the crop more competitive against weeds.”


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