"In north Alabama’s Tennessee Valley, it was estimated that more than 95 percent of the acreage was planted in Roundup Ready last year," says Mike Patterson, Auburn University Extension weed scientist. "We don’t expect Roundup Ready acreage to decrease this year. A few farmers in Alabama still grow non-transgenic cotton, but it’s probably only about 25,000 to 30,000 acres. We still have good conventional varieties producing good yields and quality, but growers aren’t planting them."
The Roundup Ready technology has done much to simplify weed control in cotton, he says, but it’s not without drawbacks. Glyphosate-resistant horseweed has been confirmed in Tennessee, and Patterson doesn’t expect it to respect state lines.
"If it’s in Tennessee, it’s only a matter of time before it’s found in Alabama. Also, morningglories and pigweed are becoming more troublesome since we stopped using some of our soil residual materials.
"We haven’t seen any significant problems yet because it takes a while for weed resistance to build. But I don’t doubt that it’ll be only a matter of time. It’s inevitable whenever you put so much pressure on one technology," he says.
Patterson advises growers who are planting Roundup Ready cotton this year to insure that their herbicide applications are made in a timely manner.
"Some growers are trying to crowd the four-leaf stage with their first application. If they haven’t put down a residual like Prowl, Treflan or Cotoran to slow those weeds, and they wait until the four-leaf stage either to save money or time, early weed competition could cause problems."
Early competition, especially if it’s a grass problem, can stunt cotton growth, he adds. Patterson advises Roundup Ready growers who don’t put down a residual to consider making two reduced-rate applications of Roundup.
"You probably could make one reduced-rate application at the two-leaf stage and another at the four-leaf stage, rather than crowding the four-leaf stage. You probably could cut your rate in half on those two applications, from 1 pound active ingredient to one half pound."
Minimum-tillage producers of Roundup Ready cotton might need to go in sooner, he says. "We have a lot of reduced-tillage cotton in Alabama, and some growers are seeing good-sized winter weeds like primrose that escape the burndown spray. You don’t have to do a perfect job with your burndown spray in Roundup Ready cotton because you can come back and hit it with a little Roundup at the one-leaf stage."
Growers will see several changes in cotton herbicides this year, says Patterson. Monsanto’s latest glyphosate formulation is Roundup Weathermax., and Bayer is introducing Liberty Link cotton. In addition, the price is being reduced for Dupont’s Staple, he says.
Roundup Weathermax is a 5.5 pound-per-gallon glyphosate formulated as a potassium salt. This version of Roundup is more concentrated, has a lower viscosity, and contains its own surfactant system. The standard maximum rate per application in Roundup Ready cotton is 22 fluid ounces per acre.
Monsanto says the addition of ammonium sulfate in mixture with Weathermax and flowables (diuron, prometryn, etc.) helps to re-suspend the mixture if you have to let the sprayer sit overnight. They also recommend either using a drift reducing agent or drift reduction nozzles when spraying Weathermax but not both together.
Liberty Link cotton hopefully is in the process of getting a full federal label, says Patterson. However, the company representatives say seed is so limited that only a few acres will be available for Alabama, and this probably will be rationed out through their sales staff.
"If you do get the opportunity to try some on your farm, it can be managed very similar to Roundup Ready technology. I would suggest you put down a dinitroaniline herbicide like trifluralin (preplant incorporated) or Prowl (incorporated or pre-emergence) to help with grass and pigweed control.
The price of Staple reportedly is down by about 15 percent, which is good news, says Patterson.
"Staple has been a valuable addition to our cotton weed management program in the past couple of years because it has good activity on pigweed and morningglory in a tank-mix with glyphosate early, or for postemergence control of broadleaf weeds in conventional cotton varieties.
"Staple applied behind the planter either alone or with some fluometuron (Cotoran, etc.), prometryn (Caparol, etc.), or diuron (Direx, etc.) will provide good residual control of several broadleaf weeds including morningglory, sicklepod and pigweed."
Envoke is Syngenta’s "new kid on the block." says Patterson.
The chemistry and mode of action is similar to Staple, but this product works at about one-tenth the rate of Staple and will control sicklepod postemergence up to 4 inches to 6 inches tall, he adds.
It also has good nutsedge, morningglory, pigweed and redweed activity.
A section 18 request for the use of Envoke on conventional cotton was not approved for 2003. However, Patterson says the product should receive a full Section 3 label allowing growers to use it in 2004.