Weed expert shares story of glyphosate resistance

Published online: Dec 17, 2013
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Having witnessed the pains glyphosate herbicide-resistant weeds have caused his state's growers, University of Tennessee weed scientist Tom Mueller advises Idaho sugarbeet growers to avoid rotations with Roundup Ready corn.

Glyphosate is the active ingredient in Roundup, a herbicide manufactured by Monsanto. Monsanto has engineered several crops, including corn, soybeans and alfalfa, with genetic resistance to Roundup for easy weed control. In Idaho, all sugarbeet acres are Roundup Ready.

Though no glyphosate-resistant weeds have been detected in Idaho-where growers have diverse crop rotations and utilize different chemicals to break up the glyphosate cycle-Mueller nonetheless advises using pre-emergence herbicides and a weed control program with multiple modes of action. He emphasizes other cheap chemistries are available for corn, and beet growers should at least mix another product in the tank if they plant Roundup Ready corn seed.

Mueller, who spoke to growers in Burley Dec. 12 at the Snake River Sugar Beet Conference, said Tennessee soy beans and cotton have all been Roundup Ready since 2000. Resistant horse weed surfaced as a Tennessee nuisance in 2002. In 2007, resistant Palmer pigweed emerged, forcing many of the worst-hit farmers out of business.

It's become common now for Tennessee growers to send crews of workers into fields to hand-pick Palmer pigweed.

"I can assure you 10 years ago, nobody was ever thinking about sending a whole crew out in the field," Mueller said.

In the nation's Corn Belt, where farmers often rotate Roundup Ready corn with Roundup Ready soy beans, three-quarters of growers who participated in a recent survey by BASF Crop Protection suspect glyphosate resistance has made weeds on their farms more difficult to control. More than two-thirds of growers surveyed plan to apply pre-emergence herbicide this season, and more than half intend to add another herbicide to their programs to prevent resistance. Half of growers also say they'll use herbicides that attack weeds with multiple sites of action, and 47 percent will use overlapping residual herbicides.

Monsanto spokesman Trent Clark said best practices for Roundup have been on the product's label since it was released in the late 1970s, but he believes there's a "growing recognition that (growers) need to take that recommendation of best management practices very seriously."

Greg Dean, an agronomist with Amalgamated Sugar, said many of his growers take the threat of Roundup resistance extremely seriously, and others don't take it seriously enough.

"When we give grower presentations, we're trying to make them aware that Roundup resistance is out there. It's very real, and if we don't do anything to alter it, it will probably be at our doorstep sooner rather than later," Dean said.

Don Morishita, a University of Idaho Extension weed scientist, also has concerns about Idaho rotations with Roundup Ready corn and sugarbeets and advises growers to mix a chemical with a different mode of action in with Roundup.

"I still do hear some farmers saying, `But it's a whole lot cheaper to just use Roundup and not use other herbicides.' That's pretty scary," Morishita said.

Source: www.capitalpress.com