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Corn+Soybean Digest

Flex-ing Muscles Against Weeds

Some growers can hardly remember farming without it. In fact, some cultivators are parked and covered in cobwebs. Hoes are rusty. Yes, Roundup Ready cotton has spoiled many a producer. And about the only major burden in growing glyphosate-resistant cotton has been weeded out.

Roundup Ready, available on a small scale in 2005 and more plentiful in '06, is enabling producers to make full-season over-the-top herbicide applications. No more restrictions on spraying past the fourth leaf stage — something Arkansas grower Bob Bevis says could convince him to plant more acres in the new varieties if they can yield.

“We have from 5%-10% of our acres in Flex this year (2006),” he says. “I want to make sure the Flex varieties can yield like our other varieties before I plant a large amount of it.”

Monsanto, makers of Roundup herbicide, received U.S. regulatory clearance for Roundup Ready Flex cotton in March 2005. There was anticipation that as much as 25% of the 2006 domestic cotton crop would be in the Flex category, says Randy Boman, Texas A&M University Extension cotton agronomist in Lubbock.

Flex has been available as a single trait product and stacked in combination with other traits such as Bollgard II.

Sandy Stewart, Louisiana State University (LSU) cotton specialist, notes that the Flex system allows growers to apply higher rates of glyphosate over-the-top — until “at least through the first bloom” — which helps control even more difficult weeds.

“Herbicide applications should be timed by weed size and not the size of cotton,” he says. “Roundup Ready Flex technology allows farmers to control weeds when they need controlling.”

Bevis was ready for Flex. He's been planting glyphosate-resistant seed since it was first made available for cotton in 1997. His cotton is rotated with grain sorghum on his Scott, AR, farm. He and his son Robby also grow soybeans rotated with milo and rice.

“Roundup Ready cotton has really been one of the greatest things I've seen in my farming career,” says Bevis. “It has allowed us to expand our cotton production to a size that makes it economically viable in hard times. Without Roundup Ready technology, we couldn't farm on the scale we do right now.”

Pigweed and morningglory are two of his biggest weed problems. Timing is essential in keeping them under control. In his typical herbicide program, Bevis normally applies his first shot of glyphosate when a stand is established.

“About 10 days later we come back with a second shot,” he says.

With the old glyphosate system, wet weather sometimes makes it difficult to get all treatments down before the fifth leaf stage.

“That has been the weak link in this system,” Bevis says. “If there are later weed problems, we have to come back with hooded sprayers.”

With Roundup Ready Flex, he hopes to eliminate most of the hoods “and hopefully allow us to do a much better job of controlling pigweed.”

Bevis' crop consultant, Merritt Holman, helps him map out his cotton program. Holman has been involved in variety development in Flex research plots in the central Arkansas region.

With the glyphosate technology, Holman says growers are able “to get over more acres more quickly and have less labor invested in the crop.” There's also a better level of safety, since there is less concern with herbicide drift and crop injury.

Despite these advantages, the restrictions on applications before the fifth leaf caused problems.

“Monsanto listened to its customers here and in other areas,” says Holman. “They realized that one of the primary weaknesses was the early cutoff. Flex, just as the name implies, gives us much more flexibility and relieves much of the risk associated with the early cutoff.”

Texas A&M's Boman says Roundup Ready Flex “is some outstanding technology” because of its full-season capabilities for weed control. He and Holman say that about the only negative aspect of the new glyphosate-resistant lines may be the cost factor.

Tech fees differ from region to region. Holman says that in his area, a typical Bollgard/Roundup stacked cotton variety costs about $32/acre for the Bt technology and another $7-8/acre for the glyphosate, putting the total cost at $40-42/acre for seed. He thinks a Bollgard II/Roundup Flex stacked variety will cost an additional $20/acre more than a Bollgard/Roundup variety.

“I think growers will rapidly adapt to that technology if the price is right, the varieties yield and glyphosate resistance is delayed,” says Holman.

Many Delta area producers are concerned about glyphosate-resistant weeds that are emerging in some areas. The marestail problem and a resistant ragweed that popped up in 2004 are keeping field scouts on their toes.

“Resistance could force a major change in our herbicide use pattern in all our crops,” says Holman.

LSU's Stewart says the Flex technology should help farmers reduce labor, eliminate some trips with the cultivator across the field, avoid purchasing additional specialized application equipment and reduce the loss of soil from the field.

LSU studies show that cotton yields are maximized with eight weeks of weed-free growth following germination. The increased plant resistance of the Flex cotton to glyphosate should allow farmers to use higher rates of the herbicide to control difficult weeds, says Stewart.

Bevis knows the value of using glyphosate and Bt cotton varieties. “We got away from it (Bt-stacked) for one year to try and save some on tech fees,” he says. “We had a bad tobacco budworm outbreak, so I'm now a firm believer in stacked varieties.”

Boman says that even with new technologies like Flex, growers should select cotton varieties that are proven in their areas.

“Keep it simple and be a smart shopper,” says Boman. “Compare several characteristics among many varieties and then key the most valuable of those characteristics to typical growing conditions on your farm.

“Growers can't control the growing environment or climate from year to year, but they can select and plant varieties that fit their farms. Two of the most important characteristics are genetic potential for yield and lint quality.”

Advanced genetic traits such as herbicide tolerance and insect and disease resistance are also valuable, but they, too, should be evaluated based on performance in local field trials, he says.

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