The last Roundup? Superweeds resistant to widely used herbicide may lead to less environmentally safe farming

Friday, July 9, 2010 02:53 AM

By David Mercer

ASSOCIATED PRESS

Jerry McCulley sprays the weed killer glyphosate, or Roundup, on his corn crop in Auburn, Ill. Farmers in that state and elsewhere are finding that some weeds have developed an immunity to the herbicide. Scientists say substitute herbicides are more toxic.

SETH PERLMAN | ASSOCIATED PRESS
Jerry McCulley sprays the weed killer glyphosate, or Roundup, on his corn crop in Auburn, Ill. Farmers in that state and elsewhere are finding that some weeds have developed an immunity to the herbicide. Scientists say substitute herbicides are more toxic.

Palmer amaranth is among the weeds becoming resistant to Roundup, farmers say.

UNIVERSITY OF ARKANSAS |
Palmer amaranth is among the weeds becoming resistant to Roundup, farmers say.

CHAMPAIGN, Ill. – When the weed killer Roundup was introduced in the 1970s, it proved it could kill nearly any plant while still being safer than many other herbicides, allowing farmers to give up harsher chemicals and reduce tilling that can contribute to erosion.

But 24 years later, a few sturdy species of weed resistant to Roundup have evolved, forcing farmers to return to some of the less environmentally safe practices they abandoned decades ago.

The situation is worst in the South, where some farmers now walk fields with hoes, killing weeds in a way their great-grandfathers were happy to leave behind. And the problem is spreading quickly across the Corn Belt and beyond, with Roundup now proving unreliable in killing at least 10 weed species in at least 22 states. Some species, such as Palmer amaranth in Arkansas and water hemp and marestail in Illinois, grow fast and produce tens of thousands of seeds.

“It’s getting to be a big deal,” said Mike Plumer, a 61-year-old farmer and University of Illinois agronomist who grows soybeans and cotton near the southern Illinois community of Creal Springs. “If you’ve got it, it’s a real big deal.”

When Monsanto introduced Roundup in 1976, “it was like the best thing since sliced bread,” said Garry Niemeyer, who grows corn and soybeans near Auburn in central Illinois.

The weed killer, known generically as glyphosate, is absorbed through plants’ leaves and kills them by blocking the production of proteins they need to grow. The U.S. Environmental Protection Agency considers it to have little toxicity to people and animals, and it’s less of a threat to the environment because it quickly binds to soil and becomes inactive.

Monsanto’s introduction of seeds designed to survive Roundup made things even better for farmers because they could spray it on emerging crops to wipe out the weeds. Seeds containing Monsanto’s Roundup Ready traits are now used to grow about 90 percent of the nation’s soybeans and 70percent of its corn and cotton.

With increased reliance on Roundup, herbicide use on corn decreased from 2.76pounds an acre in 1994 to 2.06 in 2005, the most recent year for which the U.S. Department of Agriculture has data. Spread that out over the 81.8 million acres planted in 2005, and it’s a decrease of more than 57 million pounds of herbicides annually.

Farmers also found they could cut back or, in some cases, eliminate tilling, reducing erosion and fuel use.

But with any herbicide, the more it’s used, the more likely it’ll run into individual plants within a species that have just enough genetic variation to survive what kills most of their relatives. With each generation, the survivors represent a larger percentage of the species.

St. Louis-based Monsanto maintains the resistance is often overstated.

“We believe that glyphosate will remain an important tool in the farmers’ arsenal,” Monsanto spokesman John Combest said.

That said, the company has started paying cotton farmers $12 an acre to cover the cost of other herbicides used alongside Roundup to boost its effectiveness.

The trend has confirmed some food-safety groups’ belief that biotechnology won’t reduce the use of chemicals in the long run.

“That’s being reversed,” said Bill Freese, a chemist with the Washington, D.C.-based Center For Food Safety, which promotes organic agriculture. “They’re going to dramatically increase use of those chemicals, and that’s bad news.”

The first weeds in the U.S. that survived Roundup were found about 10 years ago in Delaware.

Monsanto and other companies are developing new seeds designed to resist older herbicides such as dicamba and 2,4-D, a weed killer developed during World War II and an ingredient in Agent Orange, which was used to destroy jungle foliage during the Vietnam War and is blamed for health problems among veterans.

Penn State University weed scientist David Mortensen estimates that in three or four years, farmers’ use of dicamba and 2,4-D will increase by 55.1 million pounds a year because of resistance to Roundup.

Dicamba and 2,4-D both easily drift beyond the areas where they’re sprayed, making them a threat to neighboring crops and wild plants, Mortensen said. They could also threaten wildlife.

This article appeared in the Columbus Dispatch: http://www.oeffa.org/news/wp-admin/post-new.php