U.S. Farmers Widen the Pesticide Arsenal to Combat Weeds

U.S. farmers are dousing their fields with a wider array of herbicides, helping some turn a corner in the war on super weeds but adding new costs and environmental concerns.

Farmers for a decade have fought weeds that developed resistance to the nation's dominant weed killer, glyphosate, which is widely sold by Monsanto as Roundup. Now they're finding success deploying larger quantities of other, sometimes older herbicides.

About 42 million acres of soybeans planted in 2012 were treated with non-glyphosate herbicides, double the 2006 total and equivalent to 57% of all soybean acres, according to a U.S. Department of Agriculture(USDA) report this year.

Farmers increasingly have turned to some herbicides considered harsher than glyphosate. In 2012, they used more than six million pounds of 2,4-D, nearly four times the 2005 level, according to USDA data. Use of dicamba more than doubled to 87,000 pounds over the same period.

Farmers are having to brush up on their chemistry. Travis Starnes, 36 years old, who grows corn, wheat and soybeans near Monroe, N.C., said he's again relying on a notebook of chemical recipes his family compiled in the early 1990s, before Roundup became dominant, to plan his herbicide use.

"Basically, it's like history repeats itself," Mr. Starnes said.

The trend has been a boon to companies that sell herbicides, including Dow Chemical , BASF , Bayer , DuPont , Syngenta and Monsanto, which offers products other than Roundup. They are concocting and seeking regulatory approval for new formulations of old chemicals that are designed to be friendlier to the environment, and for corresponding herbicide-resistant seeds.

Thanks to the bigger arsenal, some farmers now say they are gaining ground in their war against the super weeds. In the South—where a longer growing season and warm climate have made it the battle's front line—fewer cotton and soybean acres were lost last year to invaders such as pigweed, marestail and ryegrass, according to farmers, academics and industry officials.

"Most farmers feel like they are either winning or fighting to a draw," said Bob Scott, a weed science professor at the University of Arkansas. "They're not losing fields anymore."

But success is costly. Some farmers' herbicide expenses have doubled or tripled since resistant weeds set in, cutting deeper into budgets at a time when corn prices are down 38% from their 2012 peak and soybean prices are off by 16%.

U.S. soybean growers spent on average $25.10 per acre on crop-protecting chemicals in 2012, up 51% from 2006 after adjusting for inflation, according to the USDA. Chemicals represented about 12% of soybean farmers' operating costs in 2012. U.S. farmers spent $13.7 billion that year on all agricultural chemicals, the most on record and nearly two-thirds higher than in 2002.

"It's an expensive battle," said Bo Stone, who grows 2,300 acres of corn, wheat and soybeans near Rowland, N.C.

Mr. Stone estimates that he has boosted spending $15 to $20 per acre over the past five years on herbicides to control palmer amaranth, known as pigweed, which can grow 3 inches a day. Average soybean revenue in his region is $328 an acre, according to federal data.

St. Louis-based Monsanto revolutionized the pesticide business when it began selling genetically modified seeds in the mid-1990s. Some seeds were altered to withstand sprays of glyphosate, which kills plants by halting their internal protein production.

Farmers embraced Monsanto's Roundup, which could destroy many weeds while leaving crops unscathed. Among U.S. soybean growers, glyphosate rose from 15% of herbicide use in 1996 to 89% in 2006. At that time, about two-thirds of domestic soybean fields relied solely on glyphosate to control weeds. In 2012, glyphosate dropped to 83% of herbicide use in soybeans, according to the USDA, with about 42% of U.S. soybean acres being treated solely with glyphosate.

The USDA's data on herbicide use is no longer collected annually due to budget constraints, an agency spokeswoman said.

Monsanto sells $4.5 billion a year of pesticides—mostly Roundup, analysts say—and billions of dollars' worth of corn and soybean seeds genetically engineered to survive them.

Scientists for decades have observed weeds capable of withstanding herbicides, but applying Roundup to the same fields every year speeded up the development of immunity in some weeds, researchers say.

Broader use of herbicides is reviving concerns over their effects. Two major Roundup alternatives, both developed decades ago, are dicamba, which kills by spurring uncontrollable growth that outpaces a weed's nutrient supply, and 2,4-D, which disrupts plant cells that carry water and nutrients.

Environmental groups and some farm activists fear that increased use of the harsher chemicals will make more people sick and destroy more delicate crops, like grapes, that may be located nearby. Monsanto and Dow say the products are safe if used properly, and that new formulations will be less likely to affect other fields than older versions. Inhaling the products poses little health risk to humans. However, drinking some forms of 2,4-D has been found to harm kidneys and skeletal muscles in humans, while dicamba is moderately toxic to eyes and can cause diarrhea and abdominal pain if swallowed in large amounts, according to the National Pesticide Information Center.

Glyphosate, which studies have shown strongly adheres to soil and poses lower health risks for humans, is considered milder.

Monsanto is seeking federal approval for a new version of dicamba, and for soybean and cotton seeds capable of withstanding it. Dow aims to introduce a new version of 2,4-D, along with related corn and soybean seeds. The companies say the products are safe.
Meanwhile, some farmers have returned to an expensive, but proven, method of weed control: the hoe.

Hand-weeding, which can cost farmers up to $150 an acre, has again become common in some parts of the country.