Cotton weed control options increasing

Cotton producers who have asked for more choices in weed control are in luck this year. Several new products will be available for use this season, says Mike Patterson, Auburn University Extension weed scientist.

The new products include Envoke from Syngenta; Sequence — a mixture of Dual Magnum and Touchdown for spraying over-the-top of Roundup Ready cotton, also from Syngenta; Suprend — Caparol mixed with Envoke, also from Syngenta; Ignite, to be used on Liberty Link cotton, from Bayer; and Valor, a directed spray herbicide from Valent.

“Envoke is a traditional herbicide developed by traditional means,” says Patterson. “It is designed to be used on all varieties, including conventional cotton. It is used at a very low rate, about one tenth ounce per acre.”

Envoke, he adds, is a postemergence, over-the-top broadleaf herbicide. “It doesn't have grass activity at the rates we're using, so you'll have to pick up grass with another herbicide. Purple and yellow nutsedge, Florida beggarweed and bristly starbur are some of the weeds this herbicide will help control,” he says.

The low rate of one tenth ounce per acre is equivalent, says Patterson, to 1 teaspoon of material per acre. “Envoke also has activity on peanuts, corn and soybeans. So, whenever you spray it on a cotton field that is adjacent to one of these other crops, be mindful that drift can injure the other crops,” he says.

Envoke also can help when growers are rotating Roundup Ready crops, he says.

“Some producers plant Roundup Ready soybeans and then follow that with Roundup Ready cotton. Eventually, we'll probably be getting into Roundup Ready corn. If you had a Roundup Ready soybean crop that was followed by cotton, this herbicide probably could help you take those volunteer soybeans out of the cotton,” he explains.

Envoke does have weaknesses, including grasses, says Patterson. A major weakness, he adds, is smallflower morningglory, but there are weed control programs that can help growers overcome this weakness.

Ninety percent of the cotton grown in Alabama is Roundup Ready, so Envoke has to be marketed as a material that can be used on a Roundup Ready crop, he says.

“So we need to talk about how Envoke will fit into a Roundup Ready weed control program. Envoke does not have appreciable grass activity, so we probably need to use a yellow herbicide in a Roundup Ready crop. These could include trifluralin or Prowl. In reduced-tillage situations, you could put Prowl in with the burndown and hopefully get the rainfall needed to get activation prior to planting.”

Next, he says, growers can apply glyphosate at the two-leaf cotton stage. “If you have smallflower morningglory in the field, you probably need to add a little Staple. This also will give you some residual benefits.”

Envoke, says Patterson, cannot be applied until cotton has at least six true leaves, and preferably more. “If you put it on any earlier, you risk crop injury such as stunting and yellowing. If cotton is under stress when you apply Envoke — such as cool, wet conditions — then you also could incur injury.”

Following glyphosate, Envoke at the eight-leaf stage will pick up broadleaf weeds, including morningglory, beggarweed and bristly starbur, he says. Growers then can go to a layby application and complete their weed control program.

The second scenario, says Patterson, would be no yellow herbicide but a glyphosate/Dual combination at the two-leaf stage. “That is, if you don't have any Texas panicum in the field. Dual will not control Texas panicum from a residual standpoint. Glyphosate will kill it, but Dual will not help by preventing further germination of the weed. You'll need to use a yellow herbicide prior to planting if you have Texas panicum.”

Assuming no Texas panicum, a grower then can go to an Envoke application at the eight-leaf stage, if there is no smallflower morningglory in the field. If you do have smallflower morningglory, you'll need to put on Staple at the four-leaf stage and follow that with Envoke at eight leaves. You then can finish with a layby treatment, says Patterson.

For growers who want to plant a conventional cotton variety, they would need to incorporate a yellow herbicide in conventional-tillage or Prowl with the burndown at pre-emergence, he says‥

“Then, you would want to use a residual behind the planter, something like Cotoran, Karmex or Caparol. You can follow that with Staple at the two-leaf stage, apply Envoke at the eight-leaf stage and then put on your late directed or layby application.”

There are several choices for directed and layby sprays, says Patterson.

“When using these products, you should mix them either with MSMA or Roundup for complete weed control. Whether you mix with MSMA or glyphosate, in my opinion, depends on the size of the annual grasses you're trying to kill in the middles. If you have large grasses, in addition to broadleaf weeds, you need to be using glyphosate.

“If you don't have large grasses, then MSMA would be a good choice if for no other reason than you're changing chemistry and getting away from using glyphosate.”

There are several “do nots” associated with Envoke, says Patterson. Cotton should be at least at the six true-leaf stage, maybe even at eight leaves, he says. Cotton shouldn't be stressed by cool, wet conditions when the application is made, and growers shouldn't mix anything with Envoke but a non-ionic surfactant.

Ignite herbicide from Bayer can be used over-the-top on Liberty Link cotton, says Patterson. “This is very similar to Roundup Ready herbicide technology. Ignite is glufosinate while Roundup is glyphosate. These two herbicides kill weeds differently. Ignite will kill weeds quicker, but you need more spray volume, about 15 gallons per acre.”

As for managing the crop, it'll be very similar to what growers now are doing with the Roundup Ready system, he says, but Ignite has much more tolerance than the current generation of Roundup Ready.

“We can spray Ignite on up into the bloom stage on Liberty Link cotton. But there is no cross-over between Roundup Ready and Liberty Link. If you spray Roundup on Liberty Link, you'll injure or kill it, and the same thing will happen if you spray Ignite on Roundup Ready.”

Ignite provides foliar activity only, with no residual effects, says Patterson. Ignite is broad spectrum, with about 80 weed species and grasses on its label, he says.

“Ignite probably won't control as large a pigweed or as large a grass as glyphosate. However, it will be better on most morningglory species than glyphosate. It also picks up large beggarweed, bristly starbur and tropic croton. It will burn peanuts pretty good, so it might be useful to control volunteer peanuts in cotton.”

Ignite will not be as strong as glyphosate on perennial grasses and the nutsedge species, notes Patterson.

Peanut producers will be familiar with Valor herbicide, he says. It is registered for pre-emergence activity on peanuts behind the planter.

“In cotton, Valor has a preplant burndown label, with a 30-day restriction. Mixed with glyphosate, it'll help control primrose and provide soil residual activity on marestail. I see its value in cotton as a directed spray. This product, mixed with MSMA or Roundup, will be valuable as a layby treatment in cotton.

“As a late directed or layby treatment, mixed with MSMA or glyphosate, Valor will kill most of the broadleaf weeds and grasses growing in a cotton field. After that, it'll provide a short residual so it won't interfere with a fall cover crop.”

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