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A SINGLE uncontrolled common waterhemp plant resistant is surrounded by controlled plant carcasses
<p> A SINGLE uncontrolled common waterhemp plant (resistant) is surrounded by controlled plant carcasses.</p>

Traditional methods, new products could help weed resistance management

In&nbsp;the last two years Texas has come into&nbsp; the real world of weed control issues. Glyphosate resistant common waterhemp has been identified in Southeast and Central Texas. Gglyphosate resistant Palmer amaranth (pigweed) has been identified on the Texas High Plains,

Paul Baumann may have never claimed kinship with John the Baptist, but at times over the past decade he may have felt something “like a voice crying in the wilderness,” as he tried to warn folks that injudicious use of one specific herbicide would result in selecting for weeds resistant to it.

And lo, it has come to pass. Baumann, Texas A&M AgriLife Extension weed specialist in College Station, says in the last two years Texas has come into  the real world of weed control issues with two developments. (1) Glyphosate resistant common waterhemp has been identified in Southeast and Central Texas. And (2) glyphosate resistant Palmer amaranth (pigweed) has been identified on the Texas High Plains, especially in cotton production areas. So far, Palmer amaranth resistance has not shown up in Central and Southeast Texas to his knowledge

Baumann will present some of his findings, observations and recommended control programs at the 2013 Beltwide Cotton Conferences in San Antonio, Jan. 7 through 10.

He’s been cautioning Texas growers about the potential for resistance for 10 years or more. A slide he used back in 2001 still shows the reasons why resistance is likely to develop. “Not many wanted to hear that back then,” he says.

The common waterhemp issue has been on his radar since 2005, when the first cases of resistance began to show up. “It was pretty quiet for awhile,” he says, “and the drought of 2011 kind of kept it under wraps. But, in 2012, farmers verified resistance and realized it wasn’t just missed application.”

Palmer amaranth resistance (to glyphosate) was identified for the first time in the High Plains in 2011.

Late season scouting

Baumann recommends farmers pay attention to their fields late in the season, looking for weeds that escaped all attempts at control. “It might be too late in some parts of Texas,” Baumann says, “but farmers can check for patches of weeds that were not killed with glyphosate applications.” Fields with consistent infestations across the field could indicate application errors, but those patches that were not controlled at all could result from one or two resistant weeds going to seed last year.

“I’m seeing more of this than I want to,” Baumann said.

He’s looking at program approaches to control and prevent resistance. “We’re considering the whole ball of wax,” he says. “That includes a soil-applied herbicide followed by a postemergence herbicide, with or without Roundup (glyphosate).”

Dicamba, and 2, 4-D also may play roles in resistant weed management. “We may use all the traditional methods and then incorporate new technology that could be available in the next couple of years, including dicamba and 2, 4-D tolerant cotton varieties.

“We will not throw Roundup under the bus,” he says. “It’s too good and too economical. But we have to be more aware of other modes of action.”

Roundup resistance should provide a lesson. “As we get new technology, including, dicamba and 2, 4-D tolerance, we must make certain we don’t ruin it by neglecting to use herbicides with alternate sites of action,” Baumann says.

A back to the future approach also may be necessary. “We might see some growers go back to more conventional cotton varieties, back to ground zero, the approach we used 15 years ago to control weeds before we had Roundup-resistant varieties.”

Growers had other serious issues back then, including things like silver leaf nightshade in the High Plains and morningglory in Central Texas. “We have really reduced the impact of those weeds,” Baumann says. “Thanks to technology, we cleaned those problems out of the fields.”

That could give farmers a window of opportunity to go back to “the cadre of herbicides we were using 15 years ago. We may see those (old) problems develop, but we will have new products in the pipeline.

“We still have a good selection of chemicals available. We still have holes, but those will be filled, and we will keep working around these issues.”

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