Improved herbicide technology continues to arm cotton producers with new weed control tools.

Roundup Ready, Buctril and Touchdown systems are proved in the field. But one of the newest herbicide systems — LibertyLink — should arm growers with expanded weed control made available through postemergent applications all season long.

Weed scientists with Auburn, Mississippi State, Texas A&M and Texas Tech universities have recorded excellent weed control from LibertyLink lines in both dryland and irrigated tests.

“This year (2002) was our second year of testing the LibertyLink system in Alabama,” says Michael Patterson, extension weed scientist at Auburn. “It's demonstrated good technology that is comparable to Roundup Ready or other glyphosate products in many aspects.”

Peter Dotray, weed scientist for both Texas A&M and Texas Tech in Lubbock, has had similar experiences. “In head-to-head comparison, LibertyLink has performed as well as other herbicides labeled in cotton,” he says.

Patterson says that at least 80% of Alabama cotton producers have adopted Roundup Ready varieties. From 60% to 80% of all U.S. cotton production is in the Roundup Ready family. And while LibertyLink has been available in some corn lines for several years, 2003 is projected to be its first year labeled for cotton.

For growers concerned about the possible development of herbicide resistance due to consistent use, Patterson says LibertyLink cotton offers an alternative.

Dan Reynolds, Mississippi State weed scientist, agrees. He thinks the system is going to offer new opportunities. “It's a change in mode of action to help in resistance management,” he says. “It's another tool to be able to lessen any impact of resistance, which is being seen in some parts of the South.”

LibertyLink is part of Bayer CropScience, which recently acquired Aventis CropSciences. Pending expected government approval, commercial cotton varieties that contain the LibertyLink gene are expected to be available on a limited basis in several FiberMax cotton varieties, including picker and stripper varieties.

FiberMax, also a Bayer product, has become a popular name among many growers because of its quality lint yields. Bayer CropScience says LibertyLink cotton varieties should be available on a large scale for 2004.

Liberty herbicide is technically known as glufosinate-ammonium. It inhibits the enzyme glutamine synthetase in plants, leading to a rapid disruption of photosynthesis. It's highly biodegradable and has very low toxicity. It is labeled to control numerous broadleaf and grassy weeds.

Broadleaf weeds controlled by Liberty herbicide include: pigweed species, morningglory species, sicklepod, sunflowers, cocklebur, hemp sesbania, prickly sida, black nightshade, Florida beggarweed, cutleaf evening primrose, and Roundup Ready soybeans. Grassy weeds controlled by Liberty include Texas panicum, barnyardgrass, crabgrass, watergrass and johnsongrass.

One apparent advantage of Liberty is its ability to control morningglories.

“All products have strengths and weaknesses,” says Dotray. “Roundup technology is good, but there is a weakness in controlling morningglory. Liberty may have a role in providing added morningglory control for growers.”

Patterson says glyphosate herbicides can provide sound postemergent weed control until the fifth leaf growth stage. “We've found that Liberty kills weeds effectively and this cotton should be tolerant until first bloom (up to 70 days pre-harvest),” he says.

Brent Burns, a Texas Tech research associate, monitored LibertyLink studies in 2002. “We've worked with both experimental lines and Aventis (Bayer) lines,” he says, noting that the herbicide was applied at 28 oz/acre and higher amounts. “From the tolerance standpoint, we've seen no visual injury to cotton plants sprayed with Liberty.”

The herbicide system provided “excellent burndown control” when used following initial applications of Treflan and Caparol herbicides, says Burns.

Three LibertyLink picker varieties and one stripper variety are expected to be available on a limited basis for 2003, says Russ Perkins, a Bayer CropScience tech service representative in Lubbock. “There should be a large supply of commercial varieties for use by growers in 2004,” he adds.

Another new herbicide, Envoke, from Syngenta, is effective on a wide variety of common weeds, including sicklepod and morningglory, Patterson points out. “Like glyphosate, it can be applied after the weeds emerge,” he says. “However, its biggest advantage is that applications can be made to all cotton varieties — conventional and genetically modified alike.”

The weed scientists agree that this system should also fit well in production trends toward reduced tillage, fewer applications of pre-emergent herbicides and increased use of broad-spectrum postemergent herbicides in cotton and other crops.

Reynolds says it's important that, if possible, LibertyLink lines be coupled with the Bt gene. “We will eventually need a stacked gene product,” he says.

The cost of FiberMax LibertyLink varieties is still under consideration, but is expected to be comparable to that of Roundup Ready lines. Bayer representatives say it will “be priced to value and be cost-effective.”

Whether or not growers use the product will come down to the bottom line, says Reynolds. “Whether it's the same or less money will determine if it is a ‘go’ product.”