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Weed Resistance Pushes North into Heart of the Midwest

Weed Resistance Pushes North into Heart of the Midwest

01 March 2012

ANALYSIS - Weed resistance was a key topic at today's 2012 Ag Issues Forum hosted by Bayer CropScience in Nashville, Tennessee, USA, writes Sarah Mikesell, TheCropSite senior editor.

Weed resistance may be thought of as past its prime as a hot topic, but based on experts' comments today, it's a hot problem that's not only not solved, but is pushing north into the heart of the Midwest.

Dr. Larry Steckel, associate professor of Plant Sciences at the University of Tennessee, said in 2008 Tennessee starting losing entire fields to palmer amaranth, which appears for now to be the worst out of a long list of resistant weeds documented in Tennessee.

Dr. Steckel said the implication of resistant palmer amaranth is a reduction in conservation tillage acres in cotton and soybeans plus overall increased grower costs, including additional herbicide costs, additional equipment and labor costs.

He also noted that field replanting is becoming more and more frequent due to palmer amaranth infestations. One solution is hiring a hand-weeding crew which can run $20 to $150 per acre.

In cotton, Dr. Steckel said he's seeing glyphosate-based systems replaced with the LibertyLink/Liberty herbicide based system.

Dr. Aaron Hager, associate professor Department of Crop Science at the University of Illinois, shared Dr. Steckel's concern noting that as resistant weed are clearly moving up the state of Illinois, he's struggling to help grower's manage their weed population.

The biggest trouble-maker in Illinois is waterhemp. And Dr. Steckel says herbicide resistance is stacking up, literally.

"Waterhemp has evolved resistance to six different herbicides families," Dr. Hager said. "But what is even more challenging is when we see stacked multiple resistance in waterhemp populations."

Andrew Wargo, business agent for Baxter Land Company in Watson, Arkansas, said that in the south US where they grow cotton, soybeans and corn, growers were rotating crops, but they weren't rotating their herbicide.

"Growing Roundup Ready corn, cotton and soybeans put too much pressure on the chemical to remain viable," Mr. Wargo said. "We probably performed 50 years of selection in about 15 years thanks to the Roundup Ready technology. What we must all guard against is making the same mistake again and put too much pressure on LibertyLink and Ignite (Liberty) herbicide."

Research in Arkansas has shown that proper use of cover crops like rye, following soybean or cotton harvest, is about 85 per cent effective in addressing palmer amaranth pressure.

He also noted that 80 per cent of cotton acres and 61 per cent of soybean acres are impacted by weed resistance in Arkansas. As a consequence, Mr. Wargo said that there is a marked difference in land rental value on acreage with a known weed resistance issue.

He said it's a very rapid process for weeds to take over a field. Often the first year a grower will see a few palmer amaranth weed escapes, the next year a significant patch will arise and the third year the field will not be harvestable.

Sarah Mikesell, Senior Editor

Sarah Mikesell, Senior Editor

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