To control yield-robbing weeds, farmers need a multipronged strategy. Experts recommend starting with a clean, weed-free field and keeping weeds at bay with timely applications of preemergence and postemergence herbicides. These herbicides should feature multiple modes of action — generally, the more the better.
With the Enlist weed control system, cotton farmers can adopt a program approach to weed control. The Enlist system features Enlist Duo herbicide, a combination of new 2,4-D choline and glyphosate. Growers who plant PhytoGen cottonseed with the Enlist trait can also apply glufosinate postemergence, providing more flexibility to broaden their weed control options.
Weed pressure costs cotton growers across the South by limiting yield. “It’s difficult to appreciate the total cost of weed pressure,” says Alan York, professor of crop science at North Carolina State University.
“We know how much herbicide costs and how much application costs,” York says. “We have programs that can estimate the weed-related yield loss we see at harvest. However, we can’t measure the future costs of allowing the weed seedbank to grow. Those weeds will require control — or will limit yield — in the coming years.”
Many growers have begun weed control efforts this spring with a burndown and, at planting, use of residual herbicide products. However, to start at the beginning, here’s a step-by-step rundown of a program approach.
6 Steps for Weed Management in Cotton
- Start clean with an effective burndown.
- Apply residual herbicides with varied modes of action.
- Scout fields to identify problem weeds and time postemergence applications.
- Apply postemergence herbicides with additional modes of action.
- Consider a lay-by application with an additional residual product to handle troublesome weeds.
- If necessary, manually remove weeds to reduce the weed seedbank.
Many growers have begun weed control efforts this spring with a burndown and, at planting, use of residual herbicide products. However, to start at the beginning, here’s a step-by-step rundown of the program approach.
The first step should be an effective burndown.
“Farmers can get in trouble if they can’t apply an effective burndown,” Lassiter says. Although this takes time and can be a challenge during a wet spring, a burndown provides a clean environment that allows farmers to plant without weeds competing for resources.
Another key to curbing weed growth is an efficient residual program. In North Carolina, York notes, marestail and Palmer amaranth are two difficult weed species that require diligent suppression. He recommends two herbicide modes of action at planting — something to keep in mind next year if seed is already in the ground.
“Residuals help control the weeds that are in the ground waiting to emerge,” York says. “Residuals offer an extended time period for a clean field after an effective burndown herbicide application. Every weed controlled preemergence is one we don’t have to worry about postemergence.”
In addition to multiple modes of action during burndown and preemergence, farmers need to watch for weeds that pop up as the crop emerges. This is the time of year when farmers need to be walking fields, identifying weeds and planning the first postemergence application.
Scott Wright, an Enlist field specialist who covers Midsouth states, says. “You have to know what weeds are in the field and adjust your application. The smaller the weed, the better your herbicide control.”
Lassiter points out Palmer amaranth grows fast: The window for effective control can be narrow. York says timing is critical. “We like to hit Palmer amaranth at a maximum of 3 inches,” he says.
When cotton growers see weeds appearing, it’s time to hit them with additional effective modes of action.
When farmers plant PhytoGen cottonseed with the Enlist trait, they can apply numerous modes of action to ensure season-long control. Three of those modes of action can come from Enlist Duo herbicide and glufosinate.
To help handle particularly troublesome weeds, cotton producers may consider including a lay-by application with an additional residual product in their weed management plan.
York says new technologies, including Enlist Duo herbicide, can be valuable in a successful weed control program. He cautions farmers to use low-drift formulations and follow product labels.
“We have to be extremely careful when making applications,” he says. “We have to control drift. We could lose these important technologies if we don’t.”
Wright also notes the importance of on-target application. “We’re confident Enlist Duo herbicide will stay on target when applied according to the label.”
“The key to controlling tough weeds, such as Palmer amaranth, is to reduce the seedbank,” York says. “We need to use the herbicides and technologies we have to limit weeds.”
Although herbicides are the first line of defense, York suggests pulling rogue weeds before they spread seeds. This reduces the seedbank and helps herbicides work better on the next crop.