Texas farmers have known it was coming for some time but they finally need to get serious about dealing with herbicide resistant weed species.

Herbicide-resistant weeds “are rapidly becoming a large concern for agriculture,” says Joshua McGinty, Texas A&M graduate student. “The need to accurately identify herbicide-resistant weeds, and the need for effective management strategies for specific resistance problems, has become increasingly important.”

Mcginty discussed herbicide resistance and management options at the recent Texas Plant Protection Association annual conference in Bryan, Texas.

Common waterhemp has emerged as a serious concern in south Texas, he says. In greenhouse tests in 2012, researchers evaluated 19 “waterhemp accessions … that exhibited signs of glyphosate resistance.” Varying rates of glyphosate were applied to identify resistance in the selected plants.

Of the 19 accessions, McGinty says, 17 showed greater than 50 percent survival 28 days after receiving a 1X rate of glyphosate. Eight exhibited greater than 50 percent survival following 4X the labeled rate.

He also evaluated various herbicide regimes to help manage herbicide resistance. “We confirmed the value of preplant and preemergence herbicide use,” he says. Products included fomesafen, pendimethalin, prometryn, pyrithiobac, s-metolachlor, and trifluralin. Those treatments were followed by “a variety of early-and mid-postemergence treatments. All treatments resulted in excellent control of Amaranthus species by mid- and late-season,” McGinty says. There were some differences among treatments early in the season.

“A key management component is to strive for 100 percent control. We have no silver bullet, but we recommend multiple control methods, including cultivation and multiple modes of action.”

Common waterhemp, he says, “is an extremely prolific weed that produces more than 1 million seed under ideal conditions. It has a high potential for mutation, and we select for resistance by using the same product over and over.”