North Carolina research targets glyphosate-resistant horseweed

For a soybean or corn farmer, a crop of horseweed is as bad as the plague. An ordinary-looking green-leafy plant, horseweed grows among soybean, corn, cotton and small grain crops, usurping nutrients and water and weakening nearby crops.

The flat, rosette-shaped plant can ultimately grow to heights up to 10 feet. And in some cases, glyphosate, the active ingredient in Roundup, won't kill it.

Farmers increasingly are planting Roundup Ready crops, crops such as cotton and soybeans that are resistant to Roundup herbicide. This resistance allows farmers to spray a crop with Roundup, which kills weeds but leaves the crop unscathed. Weed control in a Roundup Ready crop is generally less time-consuming and less expensive.

However, in some cases, weeds are developing resistance to glyphosate. An economical nuisance for years, glyphosate-resistant horseweed has been among the top of the list for weed complaints in North Carolina.

Working with an $80,000 grant from the U.S. Department of Agriculture's Cooperative State Research, Education, and Extension Service (CSREES), Robert Richardson, assistant professor of crop science and North Carolina Cooperative Extension specialist, will study the effectiveness of cover crops on horseweed control.

The grant was provided through the Southern Regional Integrated Pest Management Grants competition.

Because horseweed tends to prevail more in fields in which tilling has been reduced, Richardson will explore how cover crops, particularly rye, affect its growth. Field studies have noted higher populations of horseweed and cutleaf evening primrose in cornfields that have little tilling and no cover crop.

According to Richardson, studies have indicated that rye cover crops often deter weeds that prefer undisturbed areas. His research will include examining how horseweed and cutleaf evening primrose are established and how various cover crops affect their populations. He anticipates reducing herbicide usage by 25 percent.

As a result of the study, Richardson's team will create Extension publications detailing cover crop planting and will update current Extension crop production and pest management guides.

The Regional Integrated Pest Management Grants competition for the southern region is managed by the Southern Region Integrated Pest Management Center, which is located in the College of Agriculture and Life Sciences at North Carolina State University.

For a copy of Richardson's grant proposal, or for other funded proposals, see

Those interested can also contact Rosemary Hallberg at 919-513-8182 or e-mail [email protected]

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