Developing a Plan for Resistance in the Southwest
January 31, 2013 The good news for Texas cotton producers, at least according to Texas A&M Extension Weed Scientist Dr. Wayne Keeling, is that they’re not strangers to Palmer amaranth – or careless weed, as it’s known throughout much of the state.
The bad news, however, is that the glyphosate-resistant version of the troublesome weed pest was officially confirmed within the state’s borders for the first time recently.
“(Palmer amaranth) has always been the number one weed here,” Keeling says. “But until last year there was no identified resistance. Well, that’s changed. We documented a little bit last year, and a whole lot this year.”
Keeling says he helped document around a dozen confirmed cases of glyphosate resistance in 2011, often at the request of cotton farmers in his area. Keeling and his Texas A&M Extension counterparts tested the weeds against up to eight times the recommended label rates of glyphosate products, often with little to no response from the weeds.
“This year we’re telling people – those who can’t or don’t want to bring them in to us – to just go out there and hose the weeds down with Roundup and see if that will kill them,” Keeling says. “People have done that. In instances where the plant is withstanding 88 ounces, in some cases, that’s a pretty good confirmation you’re dealing with a resistant plant.”
For years, Texas had been one of the last holdouts for glyphosate-resistant pigweed. Growers in the rest of the Cotton Belt have grappled with this weed pest stretching as far back as 2005, in some areas.
Many felt it was only a matter of time before resistance crept into Texas cotton fields. And in a state where water is already at a premium, any moisture-robbing weed pests could cause serious headaches.
Growers in Texas do have a few factors in their favor, however. Researchers at Monsanto and Dow both plan on releasing new herbicide-tolerant trait packages within the next three to four years that will help growers diversify their plans of attack against glyphosate resistance. For its part, Bayer has already brought forth its Liberty packages to counteract herbicide resistance.
But in the near term, Keeling and his Extension counterparts in Texas are well-schooled in how best to handle the problem. And in the Southeast and Mid-South, weed scientists are more than willing to share their own experiences of what to do when glyphosate-resistance emerges in your own back yard.
Learning from Experience
Mid-South Extension experts like the University of Tennessee’s Dr. Larry Steckel say they can empathize with Texas growers. It was only six growing seasons ago when Steckel first documented glyphosate resistance in his own state, after all. His first bit of advice for Texans dealing with the resistance problem for the first time is to avoid getting lulled into a false sense of security.
“It was 2006, when we first documented it in two counties near the Mississippi River,” Steckel says. “It kind of surprised us, because we had seen it in 2005, and confirmed it in 2006. In 2007, we looked around and thought ‘Well this isn’t so bad, because it hasn’t really blown up.’
“Well, then 2008 happened, and it was like we got a critical mass of it. It seemed like it snuck up on a lot of fields. It shocked a lot of growers, and it shocked me, really.”
Today, Steckel says many of his growers are spending up to $120 an acre on resistance management, and that doesn’t include labor costs for chopping crews in some instances. No one understimates the problem now.
“Don’t get lulled to sleep by this stuff,” says Steckel. “Proactive resistance management is by far more economical than reactive management.”
Keeling and other Extension weed scientists echo Steckel’s sentiments here. Although it may seem counterintuitive, a proactive herbicide program could ultimately save growers a fortune.
“For us in Texas, Treflan or Prowl is the basis of where we want to start,” Keeling says. “If you get that out, you’ve solved about 80% of your pigweed problems. My focus is on how to figure out programs where you hardly ever see a pigweed come up. Control them with residual herbicides, then take out the occasional escape with Roundup and the other methods.”
Keeling’s thoughts on taking out every pigweed escape should sound very familiar to Mid-South cotton producers. Extension experts there have been advocating a no-nonsense approach to glyphosate-resistant pigweed in recent years.
Arkansas Extension weed scientist Dr. Ken Smith has been promoting a weed control program he’s named “Zero Tolerance” in recent years. As the name suggests, this plan calls for action on every single pigweed that pops up. Smith says this mindset is a necessity, based on the number of seeds a single Palmer amaranth plant can produce.
Smith says he had his staff count the number of seeds on a mature pigweed plucked from an Arkansas field, and they didn’t stop until they reached the grand total of 1.8 million seeds. That number prompts Smith to ask a pointed question to his growers.
“How good is your weed control program? Does it take out 99% of the pigweeds on your farm? Can it get 99.9%?” he asks. “At 1.8 million seeds, anything less than 100% control might not be enough.”
Because of these overwhelming numbers, Smith says he shifted the focus of his weed control program to reducing the pigweed seed bank.
“We’ve gone into soil seed bank management. If you do that, it makes everything else – the spraying and chopping – much easier.
Smith explains the genesis of his Zero Tolerance program proudly.
“We went into a 60 acre field and we did not allow a single pigweed to go to seed,” he says. “That took us 110 hours of hand labor. You can do the math. That’s an expense, but that expense is not near the end of the problem.
“How many of you would give $17 an acre, on top of your herbicide program, to not have a pigweed go to seed? It paid off in that field, and it will continue paying off,” Smith says.
Keeling agrees with Smith’s mindset, insisting that a hard stance against pigweed escapes was commonplace in Texas in the not-so-distant past.
“I remember as a youth, that used to be a good farmer’s mentality before herbicides,” Keeling says. “If they saw a pigweed out there, they’d go get it manually. They knew if it went to seed, there’s a whole bunch of weeds they’ve got to deal with next year. So we’re kind of going back to that mindset.
“If you don’t have any resistant weeds yet, or if it’s just emerging, if you can stop it there before you have any widespread problems, you’re going to pay yourself back many times as a result,” he adds.
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