RACHEL MARTIN, HOST:
Scientists have discovered some wild plants growing in a field in Kansas that have a kind of superpower. They can defy the most modern technologies designed to kill them off. It's the latest escalation in a long-running agricultural arms race - farmers versus weeds. NPR's Dan Charles has the story.
DAN CHARLES, BYLINE: There was a moment about 20 years ago when some farmers thought they'd defeated weeds forever. Biotech companies had given them a new weapon, genetically engineered crops, that could tolerate doses of the herbicide glyphosate, also known by its trade name Roundup. They could spray this chemical right over their crops, clear away the weeds even though the crops were fine. Stanley Culpepper, a weed scientist at the University of Georgia, says there was talk that maybe weeds would never defeat Roundup.
STANLEY CULPEPPER: So I was going to school during this time. And I was trained by some really, really amazing people. And I was even trained that there would never be a weed become resistant to Roundup because it was too complicated.
CHARLES: Too complicated because of the way Roundup kills plants. In 2005, though, Stanley Culpepper found some weeds in Georgia that Roundup could not kill. And not just any weed - it was a kind of monster weed called Palmer amaranth, or pigweed. And over the following years, the weeds spread like a plague across America's farmland. They're practically everywhere in the South now, spreading northward through the Midwest.
CULPEPPER: The impact is just unbelievable. We've invested over 1.2 billion - with a B - just in the cotton industry for controlling glyphosate-resistant Palmer amaranth since we first discovered it.
CHARLES: Biotech companies have rolled out a new answer - new genetically engineered crops that can tolerate two other weed killers, called dicamba and 2,4-D, so farmers can spray those chemicals on their fields to kill the weeds. There's a lot riding on these new products - billions of dollars. But now, even before they've been fully launched, they may be starting to fail.
The evidence for this is sitting in a greenhouse at Kansas State University, carefully tended by a graduate student here, Chandrima Shyam.
CHANDRIMA SHYAM: These are plants that were sprayed with 2,4-D. And this is the resistant plant. You can see that the resistant plants are pretty vigorous.
CHARLES: I see trays and trays of growing pigweed. These plants are the offspring of weeds that another Kansas State scientist, Dallas Peterson, noticed last summer in a field where he does research. They seemed to survive every chemical he threw at them.
DALLAS PETERSON: We were just not able to control or kill those weeds following those herbicide applications.
SHYAM: So we went to the field. We took - dug out the whole plant and brought them to the greenhouse and kept them in isolation.
CHARLES: Shyam and her colleagues collected the seeds, grew new generations of these plants to study them and found these plants can survive sprays of 2,4-D. Some also seem immune to dicamba. They're probably resistant to glyphosate. And if they showed up in one field, they're probably in other fields, too. Basically, they're a farmer's nightmare. Stanley Culpepper at the University of Georgia says he's not surprised; nobody should be surprised anymore by the superpowers of pigweed.
CULPEPPER: I'm telling you, as a weed scientist, it's just an absolute fascinating plant. It - you have to respect it. And the first thing to respect is, this plant will outsmart me if I do the same thing over and over again.
CHARLES: Culpepper tells farmers they still can control this weed, but they'll need to use a bunch of different tools - multiple chemicals, alternating crops, extra crops in the off-season to cover the soil. This can get expensive, though. Some farmers say they can't afford to do all of it. But Culpepper says they also can't afford to lose this battle with herbicide-resistant weeds.
Dan Charles, NPR News.
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