Rain, residual shortages add to weed woes

For cotton growers, frustration ruled in Arkansas and rains accelerated their problems in Tennessee.

Farmers took to heart the message to apply preemergence residual herbicides to cotton this year, but soon found frustration at the bottom of the jug.

“We’re glad cotton growers were receptive to our message,” says Ken Smith, University of Arkansas Division of Agriculture Extension weed specialist. “But sometimes, success can backfire, and the herbicide makers say they’re surprised by the demand and hadn’t anticipated it.”

Key Points

• Cotton growers take residual advice to heart this year.

• However, herbicide shortages frustrate growers with pigweed.

• Floods leave west Tennessee covered in pigweed.


Meanwhile in Tennessee, rains kept farmers out of the fields as preemergents waned and pigweeds flourished.

Smith and colleagues in surrounding Mid-South states spent the winter promoting the use of preemergent herbicides to prevent pigweed germination. A second application is needed to prevent pigweed coming up with cotton about three weeks later, however. But as growers came up on the application window, Cotoran, Direx and Caparol were in short supply. The demand for the residual herbicides was so great that some farmers had to wait until June.

The suggestion Smith gave for farmers who couldn’t get out the herbicides was “plow it up and start over.”

He adds, “That’s how critical it is to have a residual herbicide. They will lose the crop [to pigweed] if they don’t have it.” In Tennessee, Extension weed specialist Larry Steckel describes the situation as a perfect storm.

Wet weather and fading preemergence herbicides merged to create a perfect germination ground for glyphosate-resistant Palmer amaranth in west Tennessee.

In mid-May preemergence herbicides were fading fast, according to the University of Tennessee Extension weed specialist. “Moreover, it’s been too wet to spray postemergence as timely as we need.”

“This is shaping up into a perfect storm,” Steckel says. Experts stress getting a jump on glyphosate-resistant pigweed with residual herbicides before it gets larger than 3 inches. But with the wet weather this spring, pigweed has taken off. “It’s getting ahead of us in places, some sizable acres.”Consultants and farmers have been reporting heavy flushes of Palmer.

The No. 1 question is about spraying Ignite on cotyledon WideStrike cotton. Based on research in Georgia and Tennessee, you’ll see a 10% injury on cotyledon WideStrike cotton; typically 15% to 20% on more mature cotton, Steckel says. “The waxy cotyledons do not seem to show effects from Ignite like true cotton leaf will.”

Dual Magnum, mixed with Ignite on WideStrike cotton, has a benefit in dealing with glypohsate-resistant pigweed, Steckel says. Trials show this tankmix showed a zero to 5% injury rate compared to Ignite alone. “If Dual Magnum gets activated, this may save one or even two over-the-top Ignite applications on cotton,” he says.

Steckel also reports failure in plans to overlap herbicides in Roundup Ready Flex Cotton because of wet weather. “There are not any real good options for fields in this shape,” Steckel says.

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ALREADY TOO BIG: Waiting until glyphosate-resistant pigweed is 3 inches or more will lead to more pigweed, experts say.

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

All rights reserved. Copyright Farm Progress Cos. 2010.