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Control of resistant pigweed comes at a price

Control of resistant pigweed comes at a price
“Our growers are getting good control from the $150 million they’re spending, and we haven’t gotten that in many years,” says Stanley Culpepper, University of Georgia Extension weed scientist.

Georgia cotton producers are spending approximately $150 million per year to control glyphosate-resistant Palmer amaranth pigweed.

The good news this year is they may be getting their money’s worth.

“Our growers are getting good control from the $150 million they’re spending, and we haven’t gotten that in many years,” says Stanley Culpepper, University of Georgia Extension weed scientist.

“We’re having a great year as far as management, but we’re having a challenging year as far as sustainability.”

Poll: Pigweed: did you make progress this year?

Culpepper was one the featured presenters during this year’s Sunbelt Agricultural Expo Field Day held in Moultrie, Ga. About 400 farmers, agribusiness professionals and others made 42 stops during the half-day tour to hear researchers and company representatives discuss cutting-edge technology along with long-standing production and variety work.

The field day is an opportunity to preview a portion of what can be seen during the 35th Sunbelt Ag Expo, set for Oct. 16-18.

Three or four things will occur over the next few years that’ll help farmers in their continuing battle to control resistant pigweed, says Culpepper.

“If you’re a cotton producer, you’re well aware of a herbicide called Warrant — you’re using it postemergence in your cotton crop. But when we come to talk with you this winter, we’ll tell you to use it pre-emergence. In fact, I think it’s the safest pre-emergence material we can use in cotton.

“We won’t use Warrant by itself. We’ll still need to tank-mix it with another chemistry to help protect it. But it will reduce our input costs a little bit, and it also will reduce our herbicide injury slightly,” he says.

Researchers also are examining the role of a rye cover crop in the battle against herbicide-resistant pigweed.

Using large rye

“I think this will be a significant factor to growers in the next three to four years,” says Culpepper. “We’re looking at using very large rye — 6 to 8 feet tall. We roll the rye, and then we plant cotton into it. There are different systems, but what we can do with the rye is to block the sunlight from getting to the ground.

“Pigweed will not emerge without sunlight, so we can basically use a rye cover crop to manipulate the amount of emergence, thereby improving overall weed control. And we can do it with less herbicide inputs to help offset the cost of the rye and the other challenges of that system,” he says.

A final change that will occur for producers in 2015 or 2016 is that they will have cotton that can safely be sprayed over-the-top with 2,4-D, says Culpepper.

“We’ll also have cotton that can be sprayed with dicamba — you may be more familiar with the products Clarity or Banvil, which contain dicamba as an active ingredient. The weed management programs in those technologies will be much more simplistic and much more effective. In fact, as far as the weed management program itself, we’re ready to go today. That’s not so much a concern. The concern is how to manage off-target movement from those plants.”

For example, says Culpepper, very low rate of 2,4-D will damage sensitive cotton. “So if you’re growing 2,4-D-resistant cotton but your neighbor is not, then we have a concern. We have to study and understand off-target movement as we adopt these new technologies.”

Off-target movement usually comes in one of two ways, he explains.  “If we spray when the wind is blowing and it moves in the wind, then you’re in trouble.

“The other way is even more challenging, and that’s volatility. You basically spray the herbicide, it sits on the ground, and then an environmental condition helps to lift the herbicide from the soil so that it can move around.

“So volatility has to be addressed. We can’t have a good farmer going out and putting out everything as it needs to be done only to have the herbicide lift and move to sensitive crops.

We’re working on new formulations with all of these products, and we’re testing them to see how likely they are to lift from the soil. In one of our experiments, we put the different formulations of herbicide under a plastic dome with sensitive crops, and we can see which formulations are more volatile than others. That way, when the technology does become available, we can help our growers avoid the negativity of off-target movement.”

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