How ACCase Resistance Shapes Weed Control

Worldwide, there are nearly 500 unique cases of herbicide-resistant weeds. Group 1 ACCase inhibitors have a long list of incidents in the U.S. and worldwide, yet are rarely discussed. 

 And even though ACCase-resistant grasses may not hurt yields as much as broadleaf weed species, they should still factor into a grower’s weed-control management decisions, says Reid Smeda, University of Missouri plant scientist. 

 “With farmers paying $200 to $300 per bag for seed corn with stacked traits – and getting into that price range for soybeans – it’s good to protect your investment,” he advises. “Don’t skimp on inputs such as weed control.”  

Grass weeds are quite competitive with corn early in the season, Smeda notes. 

“It’s risky to lose a solid stand establishment because grass weeds weren’t controlled early with the proper rates,” he says. “Grass weeds can also hold on to nitrogen, which can limit availability for young corn plants and compromise yield.” 

Smeda recommends three basic rules to follow to ensure the best possible control of tough-to-manage or resistant weeds. 

  1. Start with a pre-emergence residual herbicidethat targets the proper weeds in each field and consider adding overlapping residuals for additional control. 

“Using an overlapping residual puts less pressure on growers to choose only an ACCase inhibitor,” Smeda says. 

  1. Don’t walk away from using glyphosatejust because it is weak on certain broadleaf species. 

“In the majority of situations, it still works well on grasses,” Smeda says. “We need to rotate it with herbicides that have other modes of action to manage both grasses and broadleaves.” 

  1. Incorporate different modes of action when possible. 

“Don’t overuse the various chemistries for grass control, and include other modes of action and crop systems such as glufosinate,” Smeda says. 

Don’t mistake herbicide failure for weed resistance, Smeda adds. Herbicide failure can sometimes happen when weeds are too large to control, unfavorable weather impedes performance or the wrong type of herbicide is applied to target weeds. 


Photo Credit: ©2012 AgStock Images / Eric Crossan

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