The situation is serious but “it’s not the end of the world,” says Wayne Keeling, Texas AgriLife professor, agronomy systems and weed science, in reference to discovery last summer of glyphosate resistant Palmer amaranth in several West Texas counties.

Keeling, speaking at a Bayer CropScience Southwest Cotton Technology and Innovation meeting in San Antonio, said Palmer amaranth, or pigweed, “has been the number one weed in Texas cropland for years, at least as far back as 1994, the beginning of the Roundup Ready era.

“In 1994, we still had a lot of acreage treated with products for pigweed,” he said. “Roundup was used on very little acreage. Also, 90 percent of acreage still had a pre-plant incorporated herbicide applied and 20 percent had a pre-emergence herbicide. Only 1 percent used post-emergence treatments but about 40 percent was spot treated.”

Keeling said farmers were still heavily reliant on cultivation. “Some 98 percent of the acreage was cultivated 3.1 times per season,” he said.

“We were using a lot of Atrazine but silver leaf nightshade was a problem. With Roundup, we cleaned that up.”

Keeling said discovery of resistant Palmer amaranth is particularly disturbing because it infests so many acres throughout Texas. “It’s in all cultivated cropland,” he said.

Keeling explained that widespread use of glyphosate has not created a super plant that’s resistant to the chemical. Resistant weeds, he said, are “naturally occurring plants with an inherited ability to tolerate herbicide.”

Widespread use of a particular herbicide will kill the susceptible weeds but leave the resistant ones to go to seed and spread. And Palmer amaranth can spread rapidly.