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Corn+Soybean Digest

Stay on Top of Weedshifts

Depending on where you are in the Cotton Belt, last year you either had too much water or not enough. And that probably didn't make your herbicide program look very good.

Georgia extension cotton specialist Steve Brown says, "It was a dry year and Roundup Ready just didn't do it in some areas." He saw a few problems with morningglory and erratic control of nutsedge. Thirty percent of Georgia's cotton was Roundup Ready.

"Our farmers went faster than I wanted to go with it," says Brown. "We just seriously underestimated the desire for convenience. We still don't know all that much about how these new varieties will perform."

This cotton specialist says the post-direct combination of Bladex and MSMA in conventional cotton looked as good as anything. The combination of Staple and Cottoran was an effective tool for pigweed.

"If it was up to me, I'd be putting out Treflan preplant and back off the rates. I think we need to use weed management tools other than Roundup if we're facing heavy nutsedge or morningglory pressure," he adds.

In North Carolina, extension cotton specialist Keith Edmisten says the Roundup Ready cotton looked fine.

"We haven't seen any major shifts in weeds yet, but we expect them," says Edmisten. "Anytime you change a herbicide or a cultural practice, that will happen."

Edmisten is predicting that morningglory, Florida pusley and day flower are weeds to keep an eye on. "But it could be something else we never even suspected," he says.

In the Delta flatlands, Missouri extension weed specialist Andy Kendig says, "Last year was a challenge for weed control in all crops. Wet conditions early in the year weakened pre-emergence herbicides, stimulated weed germination and kept farmers from making postemergence treatments. We had a general problem with additional weed germination. We also had more weeds than usual because we had so much moisture.

"One of our bigger problems in Roundup Ready cotton has been Palmer amaranth, which can grow extremely fast after cotton reaches the four-leaf stage (and past the time Roundup can be applied over the top). When Palmer is taller than the cotton, post-directed Roundup does little."

The weed specialist also says that economics is pushing more and more cotton into conservation tillage. He estimates that about 10% of Missouri cotton is now planted in either no-till or minimum-till.

"We're definitely seeing a shift in the weed spectrum with reduced tillage," says Kendig. "The cocklebur goes away, but we get an increase in woody vines such as trumpet creeper."

Kendig echoes Brown's observation about conventional herbicides. "There's a lot of room for them in cotton production," he says.

"I'm not overly concerned about weed shifts in Roundup Ready cotton because Roundup may not become a stand-alone in cotton," Kendig says. "Cotton is much less competitive than soybeans, and with a lack of residual activity, Roundup Ready cotton may require additional residual herbicides that soybeans do not."

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