A Washington State University researcher says genetically-modified crops have led to an increase in herbicide use, contrary to claims by proponents of the crops.

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For years, proponents have argued that genetically-modified crops help reduce the use of herbicides. The claim, in fact, is on the chemical-giant Monsanto’s website.

That never sat well with Charles Benbrook, a researcher at Washington State University. So he decided to check the facts.

“I got into this originally to try to keep the biotech industry honest,” he said. According to his peer-reviewed paper published recently in the journal Environmental Sciences Europe, it’s quite clear: Genetically-modified crops have led to a significant increase in the use of herbicides.

At a time when as much as 90 percent of the U.S. corn, soybeans and cotton in production are genetically engineered, the use of herbicides will continue to increase, leading to the introduction of more herbicide-resistant weeds, he said. This can lead to all sorts of troubles down the road for farmers.

Karen Batra, a spokeswoman for the Biotechnology Industry Organization, which represents Monsanto, said other studies have come to different conclusions. Moreover, she said, genetically-modified crops have done more environmental good than harm.

New way to kill pests

For years, large-scale farmers have relied on chemicals to control pests, including herbicides that kill weeds and insecticides that kill bugs. But in the 1990s, companies like Monsanto introduced seeds that were genetically engineered to deal with pests in new ways.

Some crops were spliced with a gene that was resistant to the Monsanto weedkiller Roundup, generically called glyphosate. Farmers could spray their “Roundup Ready” crops with glyphosate knowing the chemical would kill the weeds but not the crops. They also altered crops to resist bugs.

Some consumers are uncomfortable with genetically-engineered food, concerned it may have unforeseen effects on human health. Benbrook was more interested in the weeds.

Examining data from regular U.S. Department of Agriculture (USDA) surveys of corn, cotton and soy production, Benbrook said he learned Monsanto was right — initially.

Herbicide and insecticide use decreased for the first few years after these crops were introduced, in 1996. Insecticide use is still lower than it was, although it is creeping upward.

Herbicide application, however, then began to steadily increase. Benbrook calculates 527 million additional pounds of herbicides were used on these genetically-engineered crops between 1996 and 2011. The increase far outstrips the much smaller decrease in insecticide usage. All told, an additional 404 million pounds of the chemicals were used, a 7 percent increase, he said.

Now in 2012, many farmers are spraying about 25 percent more herbicide on each acre of their genetically-modified crops than they would if they were planting conventional varieties, according to Benbrook.

“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.

Trouble ahead?

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.”

Maureen O’Hagan: 206-464-2562

or mohagan@seattletimes.com