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Farmers may need a little something extra in herbicide-resistant systems

You almost hesitate to use the word, but could it be that farmers have become spoiled by the changes in cotton weed control that have occurred with the advent of glyphosate-resistant technology?

“How many people set fenders for their post-directed rigs this year?” asks Charles Ed Snipes, weed scientist, professor and assistant head of the Delta Research and Extension Center in Stoneville, Miss. “I’d be willing to bet not nearly as many as three or four or five years ago.”

Snipes, a speaker at Cotton Incorporated’s Crop Management Seminar in Robinsonville, Miss., on Nov. 10, was referring to the new era of weed control vs. the old that forced growers to post-direct herbicides to control broadleaf weeds in cotton.

He talked about change as a lead-in to a discussion of one of the latest developments in weed control technology – Ignite on Liberty Link cotton.

“We’ve gotten a little lazy in our weed control,” he said. “It’s fun to go out and pretty much zero out things a lot easier than we could before. It’s gotten so that if we can’t go across the field with a 60-foot boom, people don’t get excited about it.”

Reporting on the results of his and his other weed scientists’ work with Ignite, Snipes says farmers may need to rely on a “program approach” for applying Ignite on Liberty Link cotton. But the same could be said for glyphosate-resistant cotton, as well, he notes.

“I think we’re rediscovering the need for residual herbicides even in the glyphosate system,” he said. “I think you can see that by the time we get to lay-by with no residual herbicide in the system – this year especially – annual grass was very predominant in the middles.

“Given the problems we had, I think you’ll see people putting down residual herbicides even in the glyphosate programs.”

Most of the weed scientists Snipes contacted in preparation for his speech used a common approach – two applications of Ignite with or without a pre-emergence herbicide or other residual material.

In general, researchers applied 32 ounces of Ignite per acre postemergence on 3-inch cotton (typically two to three leaves) followed by 32 ounces on 6-inch cotton (typically six to eight leaves) in 10 to 20 gallons of water per acre.

“Timeliness of the first application is important for annual grass and pigweed,” Snipes quoted John Wilcut, weed scientist with North Carolina State University, as saying. “You can play catch up, but it will be ugly and probably expensive.”

“It is easier to control 3-inch palmer amaranth with Ignite than it is 6-inch,” says Snipes, speaking about research in Georgia. “That’s nothing that we probably didn’t know already. But farmers need to jump on these weeds early and don’t figure they have it licked with just one shot of Ignite.”

Being late on the 3-inch application can cause problems, especially on larger weeds, according to Stanley Culpepper, weed scientist with the University of Georgia.

“It appears 100 percent of the growers (using the technology) are very happy,” Snipes quoted Culpepper as saying. “They did learn that if you were late and weeds were large, the initial burn/desiccation was misleading as larger weeds ‘suckered’ back out.”

Besides Wilcut and Culpepper, Snipes also quoted from research by Alan York, Extension weed scientist with North Carolina State University; Larry Steckel, Extension specialist with the University of Tennessee; and Mike Patterson, Extension specialist with Auburn University.

In his research, Snipes said the addition of Cotoran and Prowl pre-emergence or Dual Magnum with the first Ignite application followed by Ignite appeared to boost control of pigweed and barnyardgrass over Ignite followed by Ignite alone in 2003.

In 2004, all the treatments appeared to provide good control of morningglory, pigweed, velvetleaf and hemp sesbania whether Cotoran and Prowl or Dual were added or not. But the inclusion of the latter improved the control of barnyardgrass considerably, according to Snipes.

Similar results were reported for pigweed and morningglory control in Tennessee and for palmer amaranth control in Georgia.

The addition of Staple appeared to improve palmer amaranth control in tests in Georgia and Staple plus Prowl or Dual provided increased control of velvetleaf, morningglory and annual grasses in studies at the Belle Mina Research Farm in Alabama.

“I think Staple is a good addition to any one of these programs, and I’m not keying primarily on the pigweed issue,” says Snipes. “I feel like Staple will help with morningglory and hemp sesbania in a glyphosate program, and I think it will help with pigweed in the Ignite system. I think it’s still a player that I’m glad to have around when we need it.”

Alan York’s research at North Carolina State indicated that applying grass herbicides such as Fusilade and Select can improve the control of annual grasses such as crabgrass and goosegrass in the Liberty Link system.

“Ignite is not as good on annual grasses as the grass herbicides,” says Snipes, “Dr. York’s work also indicates some antagonism may occur if you attempt to tank mix Ignite with the grass herbicides.”

Other North Carolina research by NC State’s John Wilcut showed that glyphosate and glufosinate provided equivalent control of all weeds except goosegrass.

“With a systems approach including an early postemergence treatment followed by layby, sicklepod, the three predominant morningglory species, large crabgrass and goosegrass were controlled at least 95 percent, regardless of the herbicide-resistant system,” Wilcut said.

“What he’s saying is that the problems with Roundup and Ignite are similar,” said Snipes. “If you’re going to have problems with Ignite under these conditions, you’re going to have the same kind of problems with Roundup.”

Comparisons of the Roundup Ready and Liberty Link systems are inevitable, says Snipes.

“Each technology has strengths and weaknesses. Roundup Ready needs timely applications to achieve adequate morningglory and hemp sesbania control,” he said. “Liberty Link needs timely applications to achieve adequate pigweed and annual grass control, especially goosegrass.

“We think growers need to look at the system that best fits their conditions and can help them make the most money,” he noted.

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