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Pigweed: Be afraid, very afraid

Like prophets crying in the wilderness, Larry Steckel and fellow weed scientists in the Mid-South have been sounding off about the coming woes of glyphosate-resistant Palmer amaranth, or pigweed.

Well, it’s here.

Arkansas growers faced glyphosate-resistant pigweed in a big, ugly way last year. Steckel, the University of Tennessee Extension weed scientist, believes 2010 may be a pivotal year for pigweed in Tennessee.

Three years ago, Steckel brought University of Georgia Extension weed scientist Stanley Culpepper, the man who discovered the first incidence of glyphosate-resistance pigweed in Macon County, Ga., to the Mid-South with his warning. Today, Georgia growers are in a “desperate situation,” says Eric Protsko, University of Georgia Extension weed scientist, who spoke at the Tennessee Grain and Soybean Conference. To combat the problem, one grower had to spend $50,000 on hand-hoeing. Some 54% of the cotton acres in Georgia are hand-hoed due to the spread of glyphosate-resistant pigweed. A single female pigweed can produce upward of a half a million seeds. The seed can be spread by pollen.

“I want to scare you,” Protsko said. “For those of you sitting on the fence thinking that this is not your problem, I hope to scare the crap out of you.”

Steckel said pigweed resistance “is on our doorstep.” Virtually every field in the Tennessee counties along the Mississippi River has glyphosate-resistant pigweed, Steckel said. The pest also showed up across the Tennessee River in Giles County.

The trouble is “folks are spending $40 per acre and spraying for pigweed when it’s 8-10 inches tall and not getting control. That’s way too tall. You shouldn’t let pigweed get over 4 inches before you spray,” he said.

Key Points

• Glyphosate-resistant pigweed has arrived in the Mid-South.

• Growers should be afraid not to take action, experts say.

• Bottom-line advice: Manage weeds, don’t just spray them.

Options to consider

In both cotton and soybeans, there are options. In dryland cotton, Steckel recommends a variety that can tolerate Ignite herbicide. In soybeans, the choices are Roundup Ready, Liberty Link or conventional varieties. The LL soybean system didn’t catch on in its first year of release in 2009, but Steckel said more growers may try it in 2010 because of pigweed.

He’s also recommending a preplant and/or preemergence in soybeans and cotton. An postemergence application as soon as possible becomes critical if the preemergence application doesn’t work, Steckel said.

“The other big change that glyphosate-resistant pigweed is bringing? We’ve got to scout these fields and get on pigweed timely,” Steckel said. In a bulletin for soybean growers, he and Angela McClure wrote: “In order to manage glyphosate-resistant pigweed, you have to know, not assume, that the preemergent application has worked. If the pre was activated, then the field will still need to be scouted to determine if the pre is beginning to work.” If the pre doesn’t work in cotton, he recommends two shots of Ignite over the top.

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SCARY FELLOWS? Not really, but glyphosate-resistant pigweed should scare “the crap out of you,” say Ut Extension weed specialist Larry Steckel, (right) and Eric Protsko of The University of Georgia.

This article published in the April, 2010 edition of MID-SOUTH FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.