Those benefits are the reason the vast majority of U.S. soybean, corn, and cotton crops are glyphosate tolerant. Unfortunately, this practice doesn’t work as well as it once did. Glyphosate-resistant weeds, like horseweed, are popping up in Hartman’s fields. And his aren’t alone. The first ones were found in 2000 in a Delaware soybean field; by 2009, 5.4 million acres were affected. As of June 2010 the 19 immune weed species had infested 11.4 million acres.
As with any herbicide, the more it’s used, the more likely resistance will emerge. “This isn’t particular to genetic engineering,” says Matt Liebman, Iowa State University agronomy professor. “It’s happened throughout the history of pesticides. Resistance develops to one and it becomes less effective, so you create the next one, and so on.” The problem, says Gurian-Sherman, is that “no one has developed any new effective herbicides since Roundup.”
Monsanto’s solution is to engineer a trait for resistance to an older herbicide called dicamba. By stacking dicamba resistance on top of glyphosate resistance, one crop can tolerate both herbicides. “Roundup has been revolutionary in helping farmers control weeds and is still effective on more than 300 weed species,” says Roy Fuchs, Monsanto’s global oilseed technology lead. “If we can give farmers a more dynamic weed-control system, it will ensure the longevity of Roundup.” Only five weeds are resistant to dicamba, he adds. Other companies are developing dual-herbicide products, such as a soybean from Dow Agrosciences that’s resistant to glyphosate and the herbicide 2,4-D.
Critics say the problem isn’t the soybeans themselves but rather the chemicals applied to them. Though glyphosate is only slightly toxic to birds and practically nontoxic to fish and honeybees, the EPA concludes, it is deadly to amphibians. Most pesticides don’t have to be tested on amphibians, and few people looked into the effect, until University of Pittsburgh biologist Rick Relyea.
In 2005 Relyea found that in tanks designed to mimic ponds, recommended Roundup doses caused an 86 percent drop in total tadpole mass. Even at one-third the concentration, it killed up to 71 percent of tadpoles. The culprit is a surfactant added to make Roundup penetrate leaves, not the herbicide’s active ingredient, says Relyea. Because so little is known about how pesticides affect amphibians—and the resulting domino effect through the food chain—it’s difficult to predict what might happen as farmers adopt dicamba or 2,4-D on top of glyphosate, says Relyea. “But there’s often concern when you put more pesticides in the environment.”
Penn State weed ecologist Dave Mortensen estimates that if 2,4-D and dicamba-resistant soybeans are widely adopted, herbicide use on that crop will increase by 70 percent in a few years. That’s what Monsanto is counting on. “Dicamba is older, farmers know how to use it, and it’s off-patent, so it won’t be expensive,” says Fuchs. He notes that there are concerns about volatilization—the herbicide readily converts to a gas and drifts onto nearby plants. To reduce that risk, Monsanto, with chemical company BASF, is developing a less volatile formulation. Of course, it would be patented and would thus cost more. Mortensen has found that dicamba moves 60 to 180 feet from where it’s sprayed. He’s also looked at one of the new formulations, which “are less likely to move as gas, but they’re still moving outside the field.”
“Dicamba is a lot nastier than glyphosate, because of volatilization and its toxicity,” says the Center for Food Safety’s Freese. It’s slightly toxic to bobwhite quail and mallards, and may cause developmental or reproductive problems in mammals that feed on plants exposed to it. Any nearby broadleaf plants, including tomatoes, peppers, and cabbage, are susceptible. Steve Smith, director of agriculture for Red Gold, America’s largest private canned-tomato processor, told Congress last September that “the widespread use of dicamba herbicide possesses the single most serious threat to the future of the specialty crop industry in the Midwest.”
While frustrated by the weeds, Hartman says dicamba isn’t an option for him at this point. “Dicamba will kill the weeds, but it could also kill my neighbor’s grapes. He’s a friend,” he says, adding with a smile, “and I drink his wine.”
It could also hurt habitat just now being recognized for its ecological importance. “We’re realizing that the weedy field edge, the non-crop elements like hedgerows and forest, are really important to habitat provision,” says Mortensen. “It’s important for pollinators like wild bees and other insects.” Colony collapse disorder, which has devastated some commercial honeybee colonies, is spurring research into wild bees as important backup pollinators. Most plants on the fringes are broadleafed, and thus vulnerable to dicamba. “Herbicide drift will clearly restructure plant communities on the field edges and in these fragmented pieces,” says Mortensen. “We certainly expect that the insect populations built on these edges will be affected. And anything eating those insects or nesting in those plants would potentially be at risk, too.”