While glyphosate-resistant Palmer amaranth pigweed has gotten a lot of attention lately in farming circles, other herbicide resistance issues have been confirmed in growers’ fields and could present challenges in the future.

“When we talk about herbicide resistance, we’re talking about weeds that you could at one time kill with a given herbicide, but now you can’t. These are weeds that you could control before some type of mutation occurred,” says Scott McElroy, associate professor-weed science, at Auburn University.

McElroy discussed resistance issues during the recent Alabama Sprayer Clinic, held in Shorter.

He and other researchers are testing thousands of plants from throughout the state for signs of resistance, he says, focusing on glyphosate and/or dicamba resistance to horseweed, common ragweed, annual ryegrass and annual bluegrass.

“Every state surrounding Alabama is getting hammered with herbicide-resistant weeds,” says McElroy. “Do we have problems we’re not aware of, is there something unique about Alabama agriculture, or are we just that good that we’re not having problems?”

It has been confirmed, he says, that herbicide-resistant horseweed is an issue in Alabama fields.

“Ten to 15 years ago, we typically would not have thought of horseweed as a summer, row-crop weed. It was a weed that occurred during the winter, and we burned it down. But with the popularity of no-till production and glyphosate-resistant crops, we’re getting a weed that wasn’t a problem several years ago, but it’s now a major issue,” he says.

After glyphosate-resistant horseweed was confirmed, says McElroy, growers began moving towards glyphosate/dicamba mixtures for controlling the weed.