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Corn+Soybean Digest

Weed Resistance Depends on Grower Management Plan

Paul Baumann, speaking at the annual Ag Tech Conference in Commerce, TX, says recent technology, specifically herbicide-resistant crops, may increase the likelihood of herbicide-resistant weeds.

In some cases, “field-crop economics support use of only Roundup Ready crops,” Baumann says. “It's an economical, highly effective weed control strategy, but presents pressure to select for resistance.”

He says thousands of acres in the Southeastern U.S. already have problems with glyphosate-resistant Palmer Amaranth (pigweed), the most commonly occurring weed pest for cotton growers in many parts of Texas.

The case for increased weed resistance includes the way we use glyphosate, he says. “It's highly effective and used several times in a season. We also have slow development of new alternative chemistry from industry.”

But Baumann makes a good case against widespread resistance. “Roundup has no residual soil activity,” he said. “Also, a good rotation program to non-Roundup Ready crops — wheat, for instance — discourages weed resistance. Our best weapon is to alternate chemistries with different sites of action or add them to our program.”

Baumann says farmers should develop production programs to prevent or at least delay weed resistance. That program should start with chemistry rotation. “We also need to consider adding soil-applied herbicides in Roundup Ready crops.

“Consider tillage, especially before or after planting. It may pay to do some tillage if resistant weeds are present. Also consider switching to conventional varieties in fields with resistant weed populations.

“Eliminate suspected resistant weeds immediately,” Bauman says. “One surviving weed in 10 acres produces a lot of seed. Kill it. Stop additional applications of a susceptible herbicide if you suspect resistance.”

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