What is in this article?:
- Trial looks at herbicide incorporation for controlling resistant pigweed
- Two herbicide treatments
- Good soil moisture
• A lot of growers become frustrated during planting time when they’re strip-tilling and trying to deal with larger Palmer amaranth with their herbicides.
• Many acres are going out of conservation-tillage and into conventional-tillage.
• Producers are looking at irrigated practices to activate residual herbicides, with residual herbicides being the cornerstone of management practices for resistant Palmer amaranth.
Two herbicide treatments
“We had two herbicide treatments at this site. One included Reflex plus Prowl H20, applying each product at 1 pint per acre, and we had a no-herbicide treatment. Reflex currently is registered as only a pre-emergence application on Georgia cotton.
“We had five application methods — the first a pre-emergence application of the herbicide right after we planted cotton. Then we looked at three different preplant incorporated methods of putting out a residual herbicide. One was using an L-tine roto-tiller before we planted cotton, and another was a field cultivator, incorporating at a depth of about 3 inches for both. We also used a disk harrow to preplant incorporate the Prowl and Reflex, at about a 6-inch depth, and we did that before planting. Then, we sprayed the residual herbicides and immediately came through with a strip-till rig.”
The site was irrigated one half inch before planting, says Kichler. “Then, the residual herbicides that were applied pre-emergence lay there for five days. So we applied another one half inch of water five days after we planted. We wanted to create a good environment for crop injury, as the cotton was emerging at that time.”
The pre-emergence applications of the residuals gave 99 percent control of Palmer amaranth, and the roto-tiller was just as effective at 95 percent. The disk harrow was least effective, giving 71 percent control.
“When we looked at the percent of Palmer amaranth control 38 days after planting, again the pre-emergence application of the Prowl and Reflex was the most effective, but the disk harrow gave us only 3 percent control, probably because the residual herbicides were buried deeper,” he says.
As a county Extension agent, dealing with resistance on a daily basis during the summer, Kilcher says cotton injury concerns are common among his growers.
“Cotton injury from Reflex can be severe if rainfall occurs during emergence. At 10 days after planting, the pre-emergence application of Prowl/Reflex gave us 20-percent injury. When we used tillage to incorporate the residuals, it gave us at least 50-percent less injury. In the pre-emergence treatments, there was more concentration of Reflex in the soil compared to the tillage applications where we diluted the residuals.”
The second experiment, he says, was conducted in Macon County in a dryland situation, with rainfall before the residuals were incorporated.