Sounding the Alarm

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Since its discovery in 2004, glyphosate resistant Palmer amaranth has kept extension specialists and weed scientists with their hands full. When the resistant strain began popping up elsewhere – first in other counties, then other states, and finally in other regions of the Cotton Belt – those same industry experts were the first to sound the alarms. Four years later, they’ve got a better grasp on managing the problem.

But sounding the alarm is an every day challenge. That’s why Cotton Incorporated dedicated an entire session to the growing problem at their Cotton Management Seminar held in Tunica, MS, in November. The location of the seminar wasn’t just happenstance. Resistant pigweed is beginning to show up in alarming numbers in the Mid-South.

“We see glyphosate resistance as a national issue,” said Dr. Robert Nichols of Cotton Incorporated, while citing the problem’s westward movement from Georgia since 2004. “I would call it an emerging weed in the Mid-South, except our friends in Arkansas might disagree, seeing as how they already have this problem.” He went on to say that all Mississippi counties north of Highway 82 will be increasingly vulnerable to the problem in the near future.

Monsanto Program has Palmer in its Crosshairs

When Monsanto rolled out their Roundup Ready Cotton Performance Plus pilot program last year, the idea was simple enough. The company wanted to educate more growers on the importance of diversifying chemistries when managing glyphosate resistant Palmer amaranth. Monsanto also wanted to promote good management practices in those areas that may not be directly affected by resistant weeds yet.

In retrospect, it’s clear that both those missions were accomplished, according to Paul Callaghan, Cotton Traits Marketing Manager for Monsanto. Last season’s pilot program targeted growers who were familiar with the resistance problem in Georgia and the Carolinas, but was also available to growers in South Alabama who hadn’t yet been affected by glyphosate resistance.

“We wanted to see if growers had a reaction to using more residuals in that area as a preventative, and the answer to that question was ‘yes’ as well,” says Callaghan. Growers across the belt are generally hip to the looming threat that resistance poses, according to Callaghan, but they may not be financially able or willing to take preventative measures where the problem has yet to arise.

As those South Alabama growers found out last year, the Roundup Ready Cotton Performance Plus program is capable of solving that problem. Mid-South and Southeast growers who plant Roundup Ready or Roundup Ready Flex are eligible to participate in the program, which offers rebates to those who use any of the six qualifying herbicides. The program promotes the use of Valor, Reflex or Cotoran pre-plant, PARRLAY or Dual Magnum during early post, and Direx during layby. Any of the products can be used individually for its specific rebate, or a combination of three of the herbicides can be implemented for a total of up to $12 back per acre. Rebates are to be distributed through retail outlets.

Of the six products Monsanto is offering rebates for, only PARRLAY belongs to the company. The step of promoting competitors’ products is unprecedented according to Monsanto spokesperson Janice Person, who hopes growers will recognize the reasoning behind that business move.

“We’re proactively going out there and saying that we want them to consider changing their programs, and so we’re willing to put money on other people’s products to do that,” says Person. Callaghan thinks that decision is not lost on growers.

“We found out that the program was very well received. Growers appreciated the help from a financial standpoint, and they appreciated the help in managing against resistance,” says Callaghan of last year’s 1,400 participants in the pilot program.”

Dr. Alan York of North Carolina State University further illustrated the movement of the weed epidemic. “2004 was the first sighting. We call that the epicenter, in Macon County, Georgia.”

To an expert like York, the weed’s success in such a wide variety of places is academic.

Designer Weed

“If you were going to design a weed, you’d use the blueprint for this one,” York says.

“(It has a) very efficient carbon fixation. It is water use efficient, and has very high temperature tolerance – optimum for photosynthesis at 180 degrees. So when it’s hot and dry, and the crop is struggling to hang on, this thing is happy. It grows very fast – an inch or two a day – and gets very big. Obviously it’s very competitive with the crops.”

In short, the resistant pigweed travels fast, appears quickly, and perhaps most problematically, grows to an unmanageable size almost overnight. At 2 inches tall, the weed can be easily managed. The problem of course, is that it cannot be easily spotted at 2 inches, and often by the time you see it, it has grown too large to kill with conventional chemistry.

“The difference between where it’s manageable and the size where it’s too big to control in a good growing environment might be 72 hours,” says Dr. Larry Steckel with the University of Tennessee. “We’re talking hours to be able to get out there. And as big as a lot of our growers have gotten, that’s going to be a challenge to get across that many acres, over the top, in that time period.”

A Greater Challenge

The general consensus among weed experts is that while Roundup Ready technology made life easier for growers, it also lulled them into a false sense of security. Because of the proliferation of the resistant gene, they say, cotton producers must unlearn some of the habits that came about with Roundup Ready practices.

“We all know that Roundup Ready technology was a good thing. It was idiot proof. But what it did was make our growers into weed sprayers. This resistance is going to make us go back and be weed managers,” says York.

Because of the plant’s ability to get out of hand so quickly, Steckel and other leading weed scientists are advising growers from the Southeast to the Mid-South to take pre-emptive steps against resistant pigweed.

“Even without the glyphosate resistance, we’re making a recommendation for something residual either pre-emergence, or maybe its Valor pre-plant and in that case we’d probably still want to follow it with something pre. We are trying to limit our PPO inhibitors to one application per year. And we are trying to not depend on ALS materials any more than we have to,” says Steckel.

Barnes is the senior editor for Cotton Grower magazine. In addition to writing for the magazine, he assists in online content production and in event production. He joined the Cotton Grower staff in May 2008.

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