Liberty Link cotton herbicide getting in-depth reviews

Vargas, Madera County, Calif., Extension farm advisor, told producers and pest control advisers recently at the annual Cotton Field day at the West Side Research and Extension Center at Five Points, Calif., that the active ingredient in Bayer CropScience’s new herbicide, gluphosinate, is the same as in the tree and vine herbicide Rely.

It is a contact herbicide with a weed killing response somewhere in between rapid dieback paraquat and the slower Roundup.

FiberMax cotton varieties will be introduced next season in the Cotton Belt that are resistant to Liberty, but it will be several years before the same technology is available in Acala cottons. California Planting Cotton Seed Distributors is now evaluating Liberty Link cottons.

Bayer CropScience announced earlier it is seeking a California registration for Liberty herbicide, even though there are not California Acalas tolerant to it. It could be used on Liberty-tolerant FiberMax varieties being grown for seed in the valley. Most of the major seed companies use the San Joaquin Valley to produce planting seed. Vargas tested in the past as a post-directed weed control in cotton.

Vargas evaluated the Liberty Link system on tolerant varieties at the Five Points field station and said the "take home message" from his research is that treating seedling weeds with Liberty at the four-leaf stage or earlier is critical.

Vargas recorded control of almost 100 percent when weeds were sprayed early. "It is amazing how things really changed when weeds were treated at the five-leaf or greater stage. Control dropped to just about half of what it was at the four-leaf or earlier stage," he said.

Vargas added he has not seen that with Rely in trees and vines, but the weed spectrum is different there than in row crops.

10-leaf stage

Liberty controls pretty much the same weed as glyphosate, but can be applied up to the 10th leaf of the cotton plant without hurting the plant. The current generation of Roundup Ready cotton can tolerate the herbicide without damaging it only up to the four-leaf stage. That will change with the new Roundup Ready Flex technology expected to be available in 2006 allowing producers to apply Roundup over the top of the plant through the 12th to 14th node.

Tank mixing Liberty with Staple or MSMA can enhance control. "We have seen that a lot in our over-the-top work, especially with MSMA. You can really increase the effectiveness of Liberty with tank mixing," Vargas added.

Liberty’s active ingredient will offer another mode of action for controlling most of the same weeds as Roundup, thus providing a resistance management tool.

And so will another new cotton herbicide on the horizon, Envoke from Syngenta.

Its active ingredient is trifloxysulfuron sodium and controls a wide variety of weeds, but apparently not yellow and purple nutsedge in the San Joaquin Valley.

"We have sat in meetings at the Beltwide cotton conference and listened to our colleagues in the Southeast and Delta talk about how effective Envoke is on nutsedges, but we cannot get it to work here," lamented Vargas.

However, it is effective on many other weeds. "It is extremely effective on annual morningglory," said Vargas.

Envoke is safe to use over the top of conventional and transgenic cottons. It can be used post-directed as well. It is systemic and used at very low rates.

Arizona results

University of Arizona weed control specialist Bill McCloskey says in his state Envoke has "very good nutsedge suppression and does a good job on our broadleaf weeds, including morning-glories and pigweed."

Many of these new over-the-top herbicides and transgenic cottons prompted cash-strapped producers to abandon pre-plant herbicides like Treflan and Prowl.

However, Vargas that that trend is reversing, according to a call he received from the California Department of Pesticide Regulation asking why pre-plant herbicide use has been increasing of late.

"I think producers have seen problems in eliminating preplant herbicides and are going back to them to get overall, better weed control," he added.

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