Attack of the Superweed

Justin Cariker grabs a 7-foot-tall Palmer pigweed at his farm, bending the wrist-thick stem to reveal how it has overwhelmed the cotton plant beneath it. This is no ordinary weed: Over time it has developed resistance to Monsanto’s (MON) best-selling herbicide, Roundup. Hundreds of such “superweeds” are rising defiantly across this corner of the Mississippi Delta. “We’re not winning the battle,” Cariker, owner of Maud Farms in Dundee, Miss., says as he looks at weeds that tower over his infested cotton field like spindly green scarecrows.

Cariker’s superweeds represent a growing problem for Monsanto, whose $11 billion of annual sales are anchored in crops genetically engineered to tolerate Roundup, the world’s best-selling weedkiller. The use of Roundup Ready seeds has transformed farming in the 15 years since their debut, allowing growers to easily dispatch hundreds of types of weeds with a single herbicide while leaving crops unscathed. “When the Roundup system first came out, to a farmer this was the best thing that ever happened,” says Cariker, who used the labor-saving technology to double his planted acreage, to 5,000. “Farmers thought we had died and gone to heaven.”

Not exactly: It turns out the widespread use of Roundup has led to the evolution of far-tougher-to-eradicate strains of weeds. As a result, rivals such as Dow Chemical (DOW), DuPont (DD), Syngenta (SYT), and Bayer see an opportunity. They hope to revive sales of older herbicides still able to kill many Roundup-resistant weeds, allowing them to challenge Monsanto’s dominance in genetically modified crops. Still, the substitutes could eventually create weeds that survive multiple chemicals, just as increased use of antibiotics in pigs and chickens has led to the evolution of bacteria that resist multiple drugs, says Charles Benbrook, chief scientist at the Organic Center in Troy, Ore. “It’s akin to putting gasoline on a fire to put it out,” he says. “It’s a very high-risk gamble for the U.S. biotechnology and pesticide industry to go down this road.”

Crops created to survive Roundup or generic glyphosate (its active ingredient) now comprise 94 percent of soybeans, 73 percent of cotton, and 72 percent of corn grown in the U.S. Glyphosate is applied at seven times the rate of all other herbicides combined in U.S. soybean fields and 1.6 times the rate of all others in cotton fields, according to agriculture consultant Cropnosis.

Dow Chemical, DuPont, Syngenta, and Bayer are engineering crops to withstand alternative herbicides that can kill the weeds Roundup no longer can. Dow expects to begin collecting $1.5 billion in additional profit in 2013 by selling seeds for crops that tolerate a reformulated version of 2,4-D, a herbicide the U.S. first registered for sale in 1948 and one of the chemicals used in the Vietnam War-era defoliant Agent Orange.

Unrelenting Roundup use has caused 11 weed species to evolve glyphosate resistance in 26 U.S. states, with Palmer pigweed and horseweed the most widespread, according to the International Survey of Herbicide Resistant Weeds. They have invaded 14 million U.S. acres of cotton, soybean, and corn, and that will double by 2015, says Chuck Foresman, Syngenta’s head of corn crop protection. A Dow study this year found as many as 20 million acres of corn and soybeans may already be infested.

Monsanto Chief Executive Officer Hugh Grant says competitors’ efforts to develop their own herbicide-tolerant crops isn’t a threat to the company’s flagship business. Seed companies will cross-license each others’ genetics to create crops able to withstand multiple weedkillers, he says, and spraying fields with a mix of herbicides will kill the superweeds and give Roundup Ready crops new life. Monsanto itself is adding resistance to dicamba, an older weedkiller, to Roundup Ready crops for sale by 2015. “The cavalry is coming,” Grant says.

Until recently, Monsanto was adamant that continuous use of the chemical wouldn’t create resistant weeds. “Now that it has kind of blown up, it’s like, ‘We told you so,’” says William G. Johnson, a weed scientist at Purdue University. Creating crops that tolerate two, three, or four weedkillers, as seed companies plan, should help control the spread of Roundup-resistant weeds, Johnson says. Yet it may be only a matter of time before the alternatives face the same resistance. Says Johnson: “We could get these new technologies and be in wedded bliss for 10 or 15 years, but they do select for their own failure.” Indeed, ALS inhibitors, a class of herbicides that DuPont is engineering crops to tolerate, already has the biggest weed-resistance problem due to its popularity in the pre-Roundup era.

As the use of alternate herbicides rises, so does the risk of accidentally killing nearby crops, Purdue’s Johnson says. In the hot summer months, Dicamba and 2,4-D both tend to volatilize, turning the chemicals into vapor that can drift onto neighboring land. (Volatility isn’t a problem with glyphosate, which also is less of a threat to water than many herbicides because it binds to the soil, Johnson says.) That’s a big risk for row crops, grapes, vegetables, and flowers. To address that concern, Dow has formulated a less-volatile 2,4-D that buyers of its modified seeds will be required to use, says Tim Hassinger, vice-president of Dow’s global crops business. BASF also is developing a less-volatile dicamba product to work with Monsanto’s crop products, says Nevin McDougall, a senior vice-president.

In Tunica County, Miss., Cariker and his neighbors are returning to time-consuming and costly weed-control methods that had largely disappeared. Cariker this year plowed weed seedlings under the soil in the spring, sprayed a cocktail of costly chemicals before and during the growing season, and sent his crew out in the hot summer sun to hack down the surviving weeds with hoes and machetes. The goal is to keep the pigweeds from flowering; each plant can produce 500,000 seeds. Although the added fuel, labor, and chemicals plus lower yields will cut into Cariker’s income by more than $100,000 this year, he has little choice. Explains the farmer: “This can change the whole farming industry if we can’t get a handle on it.”

The bottom line: Weeds are developing resistance to Monsanto’s Roundup, the top-selling herbicide, giving rivals an opening to revive older products.