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Corn+Soybean Digest

Cotton Weeds Under Control

With strong yields and excellent weed control again in 1999, Roundup Ready (RR) cotton continues to grow in popularity among growers looking to keep their cultivators parked and cut hoeing costs.

In Texas, about half the state's 6 million cotton acres are transgenic varieties. And nearly all of those are from varieties with Monsanto's glyphosate herbicide resistant gene. In 1999, Monsanto estimated that about 5.6 million acres were planted in glyphosate-resistant cotton, a large portion of the nation's 13.9 million acres.

With this tolerance, glyphosate herbicides, such as Roundup Ultra, can be applied over-the-top through the four-leaf stage of growth. Post-direct applications, using a hooded sprayer to keep Roundup off stems and foliage, can be made later.

There are two key advantages for growers:

* Minimum tillage can be used to reduce wear and tear on equipment through less cultivation.

* Hand labor for hoeing can be virtually eliminated.

"The biggest advantage is that growers don't have to write checks to hoe hands every week," says John Gannaway, long-time cotton breeder for the Texas Ag Experiment Station in Lubbock.

"By and large, most people have been pleased with Roundup Ready cotton on the Texas High Plains," adds Randy Boman, Texas Ag Extension Service agronomist in Lubbock.

The trend doesn't stop in the Lone Star state. In Alabama, for instance, acreage has increased yearly since '97. "In the '99 season, our growers planted 70-80% of their crop in varieties containing the RR gene," says Mike Patterson, extension weed scientist at Auburn University.

In '99 Alabama trials, three early season RR varieties were in the top five among 42 varieties tested. Similar yield results came from Texas last year. Tests in several locations all placed RR cottons in the upper-yielding categories.

Mississippi trials had varied results. In tests where sprayed RR cotton was compared to unsprayed RR, yields were comparable, says Will McCarty, extension cotton specialist at Mississippi State University in Starkville. In other tests, however, sprayed and unsprayed RR cotton was outyielded by conventional varieties.

Wayne Keeling, systems agronomist for the Texas Ag Experiment Station in Lubbock, says the over-the-top herbicide program also provides long-term perennial weed control.

"A 1-qt application at the one- to two-leaf stage, one at the four-leaf stage and one post-direct application in mid-July provided 80-85% control in-season and a 50-60% reduction in perennial weeds in the next season," says Keeling.

RR cotton developed some early scars, but they've healed. In '97 and '98, some growers in Mississippi and other Southern states saw bolls prematurely fall from the then-new varieties. The problem was blamed on unseasonably cool weather and application problems. Settlements were made between Monsanto and producers.

"The RR label was changed for cotton after those problems," says McCarty. "The new label requires a 10-day to two-node of growth interval before directed spraying," he says. "The label changes, plus the availability of better RR varieties, have certainly improved this type cotton production. We had no complaints from Mississippi growers last year."

Several new RR varieties are available for 2000. "Many are varieties bred from recurrentparents that have been successful in our area," says Boman, adding that additional varieties have stacked Bollgard and RR genes.

Gannaway adds that more Buctril-resistant cotton varieties also are available. "We will probably see some Liberty Link cottons in the next few years," he says

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