Key Issues Perspective

Key Issues Perspective: Rotate Herbicides in Corn on Corn

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The potential profit from corn production has encouraged more continuous corn acres during the past five years, and to a degree, the crop that grows waist-high quite early in the growing season can hide some herbicide-resistant weeds.

“I think people need to walk their corn fields at the end of the year to see if they are having issues with resistant weeds and be willing to change their herbicide program right away because if they wait, the problem is going to just magnify,” said Doug George, vice president and agronomy manager for George Brothers Propane & Fertilizer at Sutton, Neb.

Herbicide-resistant marestail can overgrow a field without rotation of herbicide modes of action. “My herbicide recommendations have changed quite a bit the last couple years looking at what is going on, especially with our resistant marestail issue,” George said. “I don’t want to see that weed after the crop is up. Eliminating it before the crop is out of the ground is what we are trying to do.”

Marestail is the main herbicide-resistant weed of concern in George’s retail service area, but George is concerned with keeping other weeds from developing resistance in customers’ fields, too. “The main thing is to get multiple modes of actions of herbicides in the field. Bayer has Corvus that has the multiple modes of action, and you can follow with Laudis and Roundup postemerge, but then there also is the whole LibertyLink trait option and Liberty herbicide.

This is just one company’s herbicide solution, although George incorporates other company’s herbicide options, too, just as long as they allow a good burndown as a first shot preemergence with multiple modes of action—three or four. The follow-up postemerge needs to also be at least two modes of action, George explained.

Dave Byrum, Bayer technical service consultant (TSC) in Iowa, says that having farmers use best management practices is the most important aspect in controlling herbicide-resistant weeds. He said, “With all the growers that I work with in west central Iowa, many of which are corn-on-corn growers, they are all unique to themselves and their weed control needs.

But Byrum said the potential for herbicide-resistant weeds means that best management for every grower is using a few different herbicides to provide multiple modes of action, just like George recommends. The complexity of knowing the modes of action of each herbicide and their strengths in grass and broadleaf weed control points toward a practice of putting together a three-year to five-year plan for herbicide use that will assure not using the same five or six modes of action continuously and in the same sequence. “Capreno is one of our best options for weed control in corn, but we are also at risk for HPPD-resistant weeds. Knowing what’s going on in an individual field is the first step toward long-term success,” Byrum said.

Growers should rotate different herbicide traits and not be afraid to include various companies’ products while continuing with a two-trip program in most cases. “Farmers should plan for a two-pass program with a foundation herbicide down followed by a postemergence application where you are continually using multiple modes of action,” Byrum said. “Recognizing the places where we do have true resistance and not being afraid to recommend a competitive product is the best management practice,” Byrum said.

Glyphosate resistance is the most recognized problem, but Byrum said good planning can stop the spread of weed resistance to triazine and HPPD herbicides, too. All of this is part of Bayer’s Respect the Rotation education program that educates ag retailers, crop consultants and farmers about the need for herbicide mode of action rotation, as well as rotation of crops and traits.

For more information, contact Byrum at

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