Gaining Ground on Resistant Weeds

Palmer amaranth

This year was a mix of good news and bad news for Georgia growers in their fight to control and prevent the spread of glyphosate-resistant Palmer amaranth.

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  •  The Good: “I think our farmers were far more prepared for it, far more aggressive, and in some situations, did far better,” says Georgia Extension weed scientist Dr. Stanley Culpepper.
  •  The Bad: “There were situations where you did everything right, but if you’re in dryland production and you didn’t get timely rains, it didn’t matter how prepared or organized you were — sometimes you just can’t win,” he says. “If you don’t get timely rainfall to activate the residuals, sometimes it just doesn’t matter what you do.”

That’s why in Georgia and most other parts of the Cotton Belt, growers are encouraged to use an integrated approach to battle one of the most prolific and damaging weeds ever.

“We’re trying to develop integrated type programs, and by my definition that means we’re going to use multiple tactics for control,” Culpepper explains. “One of my objectives is to convince my growers that with herbicides alone, you will not survive. There’s no way.

“Herbicides are a critical component. Residuals and post-directed products are all essential, but they are just a part of the total program. In situations where you’re totally dependent on herbicides, and you’re not timely, or don’t get them activated by rainfall, you’re done. So we have to develop these integrated programs, whether it’s tillage or adopting cover crops, adding a mulching effect into our herbicide-based programs. These are good options.”

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In 2010, Georgia saw the adoption of more deep tillage, and so far, Culpepper says it did exactly what it was designed to do — reduce pigweed emergence by around 50%.

“Regardless, the addition of one of these practices, coupled with an aggressive herbicide program, is far more effective than the herbicide program alone,” says Culpepper. “Unfortunately, our growers likely hand weeded around 75% of our cotton crop during 2010, spending well over $15 million. But overall, the total hand-weeded cost-per-acre will be less than the average of $26 per acre noted in 2009, when we chopped pigweed out of half our crop.”

But even with the whole package, Culpepper says the economics of control will eventually make cotton unsustainable if glyphosate-resistant Palmer amaranth is not reigned in, or until better management practices and new traits evolve.

“This is very important — we’re not economically managing this pest,” he explains. “We cannot sustain the current input dollars when you consider herbicide costs, hand weeding and tillage. We’re pretty lucky with the value of cotton right now. If or when that leaves us, we have to have a more effective and economical program figured out to be more economically sustainable.”

Although some fields in Georgia were 100% weed-free in 2010, Culpepper says looks can often be deceiving.

“You can drive by a clean field in Georgia, and say it looks great. But if you get out the pocketbook, you very likely spent $55 or $60 for herbicides, another $20 to $25 hand weeding, or deep tillage,” he explains. “That’s $85 and maybe even $90 per acre in managing this one pest.”

Check Under the Hood
Hooded sprayers were a common sight back in the days prior to the introduction of the Roundup Ready trait, and Culpepper says they’re just another tool in the resistance-management toolbox now: “We’ve always had growers who have used hooded sprayers and layby rigs, and hooded sprayers do add one additional tool as long as they are used in a way that keeps the herbicide under the hood.”

But ultimately, the goal is to stay away from salvage situations. Start clean, stay clean.

“Will hooded sprayers help you control 8-inch pigweed in the row middle? Absolutely,” Culpepper says. “But the hooded sprayer is just one small component of a very complicated and complex system. With the hoods, you can use the most effective herbicide combination there is to control this pest. An application of Gramoxone plus diuron plus crop oil, instead of just diuron plus MSMA, is the best post-directed option to control emerged plants. We can get an 8-inch pigweed with Gramoxone, diuron and crop oil. But with diuron and MSMA, the pigweed needs to be 4 inches or less. It is very important to note – if growers don’t keep the Gramoxone off their cotton, they likely won’t be picking much cotton.”

Residual Thinking
In total, Bayer CropScience’s FiberMax and Stoneville brands, Monsanto’s Deltapine varieties and Dow’s PhytoGen varieties made up 88% of the seed sold in the U.S. in 2010. And with glyphosate resistance spreading west from Georgia, all three have integrated weed-management programs, or recommendations, in place to control or slow the pace of Palmer amaranth occurrences. For instance, Monsanto has launched the Roundup Ready PLUS program, and Bayer has introduced its Respect The Rotation initiative.

With Monsanto’s Roundup Ready PLUS, cotton farmers in the Southeast and Mid-South who follow the recommendations are eligible for a rebate of $20 per acre.

“Roundup Ready PLUS is a brand that we’ve launched that encompasses all of our weed-management solutions, regardless of crop. It represents our best management practices for how growers should go forward,” says Monsanto’s Steve Havera, cotton traits marketing lead.

“The goal is to reward growers for using residual herbicides, so it’s helping them to get multiple modes-of-action. It’s for preserving the technology on the market,” Havera continues. “We came up with regionalized recommendations. The incentive is to try to convince growers that they need the residual products. Everybody is onboard to be proactive with residuals in trying to control the weeds as best they can. It’s an industry approach, rather than having one farmer doing one thing and another not doing anything at all. It’s across all acres with Roundup Ready Flex, regardless of seed brand.”

Says Bayer’s Andy Hurst, Product Manager for Herbicide Tolerant Traits and Ignite: “In July we launched Respect the Rotation, which is an initiative based on recommendations from the Weed Science Society of America, the Herbicide Resistance Action Committee and others, that lends itself to good management practices for the purpose of avoiding weed resistance or managing weed resistance, if you have it. Respect the Rotation is specifically designed to elevate and heighten the grower adoption of some of the very key elements of resistance management.

“With LibertyLink we have an excellent technology that allows post-emerge applications with Ignite — the only non-selective alternative to glyphosate,” Hurst continues. “It’s a unique chemistry and it’s a phenomenal way to manage resistance. With LibertyLink, just like with Roundup Ready, the use of residual herbicides is a very important part of good integrated weed-resistance management. Particularly in the Southeast and Mid-South with resistant Palmer amaranth, one of the big advantages of LibertyLink is that it provides an opportunity to have two shots at that resistant weed.”

PhytoGen Cotton Development Specialist Steve Brown says that no matter what herbicide-tolerant trait a grower chooses, a program beginning with residual herbicides is essential.

“Whatever you do, you need a good foundation of residual chemistry,” says Brown. “Options include the dinitroanilines, Valor or Reflex, possibly diuron or Cotoran, and Staple. The preplant use of Valor or Reflex pre-emergence is very helpful for overall effectiveness in pigweed management. We strongly encourage a residual-based program.”

Prior to crop emergence, it’s critical to start clean.

“Some growers have used paraquat as an at-planting or after-planting burndown treatment before cotton peeks through. Monsanto is significantly upping the Roundup Rebate program, which is very good for growers,” he explains. “There is no one in Georgia, and probably south Alabama now, who doesn’t realize the need for residual tools. There is nobody out there who is going to be Roundup, Roundup, Roundup. You’ve got to have residual chemistry in the system. We won’t survive otherwise.”

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