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Weeds Becoming Immune To Roundup

June 22, 2010

A few sturdy species of weed are proving to be a fair fight for Roundup weed killer.

At least 10 weed species are withstanding the blow of Roundup in at least 22 states.  Some of the species, such as Palmer amaranth in Arkansas and water hemp and marestail in Illinois, grow fast and big, producing tens of thousands of seeds.

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

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

Glyphosate, the weed killer, 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 aside from the plants it is sprayed on; it is less of a threat to the environment because it quickly binds to soil and become 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 growing alongside them.  Seeds containing these traits are now used to grow about 90 percent of the nation’s soybeans and 70 percent of its corn and cotton.

With the increased use of Roundup, herbicide use on corn decreased from 2.76 pounds an acre in 1994 to 2.06 in 2005, the most recent year for which the U.S. Department of Agriculture has data.

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

The more herbicide that is used, the more likely it will run into individual plants within a species that have just enough genetic variation to survive what kills most of their relatives.  The survivors represent a larger percentage of the species with each generation.
 
Monsanto maintains the resistance is often overstated, noting that most weeds show no sign of immunity.

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

The company started paying cotton farmers $12 an acre to cover the cost of other herbicides to use alongside Roundup to boost its effectiveness.

The trend has confirmed some food safety groups’ belief that biotechnology will not 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,” he told AP.

The first weeds that became immune to Roundup were discovered about 10 years ago in Delaware.

Agriculture experts said the use of other chemicals is already creeping up.  Monsanto and other companies are developing new seeds designed to resist older herbicides like 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.

Mortensen said that dicamba and 2, 4-D both easily drift beyond the areas where they are sprayed, making them a threat to neighboring crops and wild plants.  That could also threaten wildlife.

“We’re finding that the (wild) plants that grow on the field edges actually support beneficial insects, like bees,” he said.

Australian weed scientists Stephen Powles has been vocal about saving Roundup, calling it a near-miraculous farming tool.

Powers told AP that Australia has been dealing with Roundup-resistant weeds since the mid 1990s, but changes in farming practices have helped keep it effective.  That has included using a broader array of herbicides to kill off Roundup resistant weeds and employing other methods of weed control.

Freese, the Center for Food Safety chemist, said that those alternative methods, such as planting so-called cover crops like rye to hold back weeds during the winter and other times when field are not planted with corn, soybeans or cotton, are the key.

Otherwise, he said, “We’re talking a pesticide treadmill here. It’s just coming back to kick us in the butt now with resistant weeds.”

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