Researchers writing in the latest issue of the journal Weed Science provide important insights on the control of herbicide-resistant giant ragweed – a plant shown to produce significant yield losses in Midwest corn and soybean crops.

Since giant ragweed is resistant to multiple herbicide sites of action, researchers at the University of Minnesota set out to determine the impact of alternative control strategies on both the emergence of giant ragweed and the number of giant ragweed seeds in the weed seedbank. They evaluated six, three-year crop rotation systems, including continuous corn, soybean-corn-corn, corn-soybean-corn, soybean-wheat-corn, soybean-alfalfa-corn and alfalfa-alfalfa-corn.

Researchers found that corn and soybean rotations were more conducive to giant ragweed emergence. Thirty-eight percent fewer giant ragweed plants emerged when the crop rotation system included wheat or alfalfa.

They also found that adopting a zero-weed threshold can be a viable approach to depleting the weed seedbank, regardless of the crop rotation system used. When a zero-weed threshold was maintained, 96 percent of the giant ragweed seedbank was depleted within just two years.

“Since the ragweed seedbank is short-lived, our research shows it is possible to manage fields infested with giant ragweed by simply eliminating weeds that emerge before they go to seed,” says Jared Goplen, a member of the research team.

Herbicide-resistant giant ragweed is rapidly becoming a major threat to corn and soybean production in the Midwest and elsewhere. This research will help growers utilize crop rotation as a much-needed additional strategy for managing this weed.

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Seedbank Depletion and Emergence Patterns of Giant Ragweed (Ambrosia trifida) in Minnesota Cropping Systems
Authors: Jared J. Goplen, Craig C. Sheaffer, Roger L. Becker, Jeffrey A. Coulter, Fritz R. Breitenbach, Lisa M. Behnken, Gregg A. Johnson, Jeffrey L. Gunsolus

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