If you're growing cotton in the Southeast, you're probably using one of three systems — conventional-tillage with non-Roundup Ready varieties, conservation-tillage with a Roundup Ready crop or conservation-tillage with non-Roundup Ready hybrids.
“It's important that we understand the tillage/herbicide interactions in each of these systems,” says Mike Patterson, Auburn University Extension weed scientist. “If you're using conventional-tillage with non-Roundup Ready, you're probably using the old herbicide technology. Conservation-tillage with a Roundup Ready crop probably is the easiest system.”
A grower planting conventional-tillage cotton with non-Roundup Ready varieties must do everything possible to keep his fields clean of a broad spectrum of broadleaf weeds and annual grasses, says Patterson.
“Make sure your tillage kills all of the weeds and incorporate a yellow herbicide such as Treflan or Prowl. For grasses and pigweeds, you need to use a pre-emergence herbicide.
“Ten years ago, about 80 percent of our cotton crop was receiving an application of Cotoran or fluometuron. Now, we probably couldn't find 5 percent of our acreage where Cotoran is put behind the planter. You need to mix it with other compounds, such as Zorial or Command. Some growers are using Staple with Cotoran behind the planter. You also can lightly incorporate fluometuron and Zorial before putting seed into the ground,” he says.
If you apply Cotoran behind the planter, and you don't receive rain for two to three weeks, you've probably wasted your money, he adds. “If you lightly incorporate, you stand a better chance of picking up some sicklepod and morning-glory,” he says.
It's difficult, says Patterson, to find a farmer these days who's putting a cultivator in his fields. “Most growers use either a directed broadcast spray or a hooded sprayer. If you're planting conventional with non-Roundup Ready varieties, make at least two post-directed sprays, starting when cotton is 6 inches tall, using a herbicide that's not too hot.
“If the Cotoran isn't activated, be prepared to use Staple and MSMA over-the-top when cotton is young. A layby treatment will be required to take cotton through to the end of the season.”
If you're using a conservation-tillage system with Roundup Ready varieties, you've hopefully killed all existing weeds prior to planting, notes Patterson.
“It's much like using primary tillage, but you're substituting a chemical herbicide for tillage. It's important in this system that you make sure the weeds are dead before putting seed into the ground.
“If you don't want to put a residual material behind the planter, be ready to spray cotton with glyphosate at the one-leaf stage to kill that first flush of weeds. This assumes that you receive regular rainfall and have a pretty good population of weeds.”
Growers then should come back at the four-leaf stage with another shot of glyphosate, he says. This should take the cotton up to about 10 to 12 inches tall, when a post-directed spray will be needed, he adds.
“If you can get your cotton up to that height, even if small weeds come in, you can use one of several products underneath the plant to carry it further. And then, of course, you use a layby treatment. Many growers who are using Roundup at layby, but some also are using a residual material to carry them on through until the canopy closes.”
Planting cotton in a conservation-tillage system with non-Roundup Ready varieties is difficult for any grower, says Patterson. “You need to start off with a good burndown treatment, and then you need a good pre-emergence program, with fluometuron or Cotoran as the backbone. You'll want to add another product to that treatment — something like Prowl.
“In the past couple of years, I haven't been too happy with Prowl on the surface behind the planter. If you have residue, the Prowl doesn't seem to be getting down into the grass and weed germination zone. With this system, be prepared to use Staple and MSMA early in the season. Staple is relatively expensive. But if you have young cotton with weeds growing in it, it's one product that'll help you out.”
Growers then should make at least two post-directed sprays followed by a layby, he says. “One treatment that has looked pretty good when we didn't use Prowl is a Touchdown/Dual application sprayed over-the-top of three-leaf cotton. This is a registered treatment.”
Several new weed control products are on the horizon for cotton producers, says Patterson. One of these products, from Syngenta, is a very low-rate herbicide.
“Trifloxysulfuron kills primarily broadleaf weeds over-the-top in cotton. This product should be available for use next year. We're not sure what the trade name will be. It's used at a rate that's about one-tenth the rate of Staple, at .0063 pound per acre. That's no more than a tablespoon per acre. It has activity on morningglory, sicklepod and pigweed.”
The Liberty Link cotton production system should be ready next year on a limited basis, says Patterson. “It kills weeds about equal to glyphosate, with some minor differences. It's quicker than glyphosate, in my opinion, and it has a much wider window of application. We've sprayed Liberty over-the-top of blooming cotton with no adverse effects.”
Aim, he says, is an FMC product with a burndown, directed spray and harvest aid label. “I've had limited experience with this material. I'm not sure you want to use it as a burndown because it doesn't control grasses or cutleaf evening primrose. It's extremely hot as a directed spray. Cotton should be at least 16 inches tall with bark down on the bottom, and the spray should be kept down on the bark.
“You may be replanting if you spray young cotton with Aim. It has no residual activity. By itself, it will not control sicklepod, and it doesn't have activity on grass. The best fit for this material in cotton may be as a harvest aid.”
The herbicide Valor could have a label for use on cotton this year, says Patterson. “We've looked at Valor for about three years. It's another low-rate material, and the closest replacement for Bladex we'll see for a directed spray. It already has a label for peanuts as a pre-emergence treatment. They're anticipating a post-directed label for cotton in 2003. It's a very active material that gives you some residual following a post-directed spray.”