"There's really been a lot of misleading PR in this area and kind of a systematic denial of this troubling trend," he said in an interview.
Experts from Iowa, where much of the nation's corn and soybeans are grown, do not dispute the general findings, although they do say they may be overblown.
Roundup is considered safer to human health than a lot of the older herbicides on the market, said Mike Owen, professor of agronomy at Iowa State University,
Still, he agrees with Benbrook that there may be trouble ahead.
Corn, soybean and cotton farmers are on an "herbicide treadmill," Benbrook said. As they have continued to use glyphosate, it hasn't worked as well as it used to. So they spray more. Some weed strains have developed a resistance. They just won't die.
If you're not a farmer, this may seem like an annoyance; if you are a farmer, battling millions of weeds, it can increase costs substantially. But the biggest problem for consumers is that farmers have to use other, older chemicals to kill the glyphosate-resistant weeds.
Benbrook is worried about one in particular, 2,4-D that has been linked with birth defects, reproductive problems and certain cancers.
"The more farmers try to spray their way out of this corner they've backed themselves into, the worse it's going to get," Benbrook said.
Batra points out that resistance has been a problem with other herbicides, too. But Benbrook and others say resistance develops faster with glyphosate because of the way it's applied — to some 90 percent of the corn, cotton and soy in the country, several times a year.
"It's going at a pace that was unimaginable and could not have happened in the absence of Roundup Ready technology," he said.
Bob Hartzler, a professor of weed science at Iowa State University, said we're not at a crisis point — yet.
"The chemical companies have been very good at coming up with new technology to stay ahead of the resistance, but whether in the future they'll be able to is up in the air," he said. "Now, you look to the future, there's nothing there."