Glyphosate-resistant Palmer amaranth pigweed confounds growers and researchers alike with its persistence and vigor, but progress is being made in finding ways to economically suppress this yield-robbing pest in cotton.

One potential method is controlling Palmer amaranth by using a heavy rye cover crop, as described by University of Georgia Extension economist Don Shurley at this year’s Beltwide Cotton Conferences held in New Orleans.

“If you let Palmer amaranth get away from you, it can be a hopeless situation, sometimes making fields not harvestable,” says Shurley, who has been working with other researchers for the past two years in looking at the possibility of using a heavy rye cover as a possible solution to the pigweed problem.

“We’re looking at growing a tall rye cover crop – about 7 to 8 feet tall – and we’re going through it with a roller, laying it down. You can also spray and burn it down as you’re rolling it down, so you’re doing a burndown treatment as well. You’ll plant in the same direction that you’re doing the rolling,” says Shurley

Then they go in, open up a strip, and plant into the heavy cover, he explains, subsoiling in the same operation. “Then, we plant directly into that heavy cover, in the same direction in which the rye was laid down.”

Another alternative, he says, is that while the rye is still small, you could go through it with a hooded sprayer and kill off a 12-inch strip where you want to plant.

“In the tests in which I’ve been involved, we had 12-inch areas in the drill plugged up so that we didn’t put any rye in there. In the rows where you’re going to plant your cotton, you’ll create a rye-free zone. You’ll still roll it, but you’ll have rye-free zones in the field,” he says.

The treatments

In this particular study, there were seven locations over a two-year period. These are large, on-farm plots, with four replications of each, planted in Roundup Ready Flex varieties.

“We had the solid rye, the 12-inch strip, and with the herbicides still being broadcast in the latter situation. In the third option, we had the rye-free zone but the preplant incorporated and the preemergence herbicides were banded, putting them down only over the row in the rye-free zone. The fourth and final treatment was conventional strip-till cotton.”

Each of the three rye treatments received roughly the same herbicide treatments, he says.

Specific treatments included Gramoxone plus Valor at burndown (plus 2,4-D in the no-rye treatment), Direx plus Reflex plus Gramoxone in the preplant incorporated treatment (no Gramoxone in the banded treatment), Warrant plus Roundup Ready Max in the first postemergence treatment, Dual plus Roundup Max in the second postemergence treatment, and Direx plus MSMA in the layby direct treatment.

Twenty pounds of nitrogen were applied on the rye, with an extra 20 pounds of nitrogen applied on the cotton.