Growers, York said, “are making progress. It’s not nearly as bad as it used to be. We were having problems with Palmer amaranth before Roundup Ready, and we did a good job of control. But growers selected for resistance by using only Roundup.”

Resistance complicates production. “We’re dealing with it but we’re having to throw the kitchen sink at it.” Control efforts include changing chemistry and management systems. “We’ve gone back to using residual herbicides and direct sprayers,” among other things, York said.

Grower surveys in Georgia, South Carolina and Tennessee also show severe problems with resistant Palmer amaranth. “Farmers in South Carolina are going back to hand weeding. Before resistance showed up only 5 percent were weeding by hand. After resistance, that increased to 50 percent at its peak.”

York said farmers in the Southeast had moved increasingly to no-till production. “To deal with resistant Palmer amaranth, many have moved back to conventional tillage. They are incorporating herbicides, using more residuals and some are using a bottom plow. We see more hooded sprayers and direct spray applications. All those changes have increased production costs. Before resistance, weed control cost about $25 per acre. After resistance, weed control expense is $60 per acre, almost three times as much.”