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Published on October 1, 2010 3:01AM

Last changed on October 29, 2010 9:19AM

Popularity of glyphosate gives rise to resistant weeds


Capital Press

Major crop developers are looking to forestall weed resistance to glyphosate, a popular herbicide, but critics claim the proposed solution will only escalate the problem.

Several agribusiness companies -- including BASF, Dow AgroSciences and Monsanto -- have asked the USDA to deregulate biotech traits that render crops impervious to several herbicides.

The idea is to "stack" these traits in corn, soybean and cotton lines that are already resistant to glyphosate, thereby enhancing farmers' weed-fighting arsenal.

Even if a weed can tolerate glyphosate, it would nonetheless be killed by dicamba, 2,4-D, glufosinate or another herbicide while the genetically engineered crop remains unharmed.

"You're forcing the weed to win the lottery twice," said Garry Hamlin, spokesman for Dow Agrosciences. The company is seeking to commercialize corn and soybeans that are resistant to 2,4-D and other herbicides.

Farmers inadvertently breed glyphosate-resistant weeds by regularly spraying the herbicide on their fields. Mutant weeds that can withstand the chemical are able to spread their genes while others die off, eventually causing widespread resistance.

Strains of ragweed, waterhemp, horseweed, Italian ryegrass and several other weeds have been confirmed to be glyphosate-resistant, according to the Weed Science Society of America.

Biotech critics blame this phenomenon on the expansive adoption of glyphosate-resistant "Roundup Ready" corn and soybeans since the mid-1990s, which led to increased usage of the herbicide.

"It just took off dramatically," said Bill Freese, science policy analyst for the Center for Food Safety, an anti-biotech activist group. "The same thing is going to happen with all these other herbicide-resistant crops."

Continually replacing chemicals that are losing their effectiveness is like being on a "pesticide treadmill" that's being sped up by the adoption of transgenic crops, he said.

Aside from leading to unstoppable weeds, the process results in more extensive applications of toxic chemicals, Freese said.

"That has impacts on the environment and human health," he said.

The federal agencies charged with regulating biotech crops and pesticides have failed to analyze the cumulative effects of rising herbicide use, Freese said.

"We need mandatory resistance management," he said.

Rotating corn and soybeans with cover crops can reduce the need for herbicides, Freese said. For example, alfalfa will crowd out weeds and farmers can mow the crop before undesirable plants go to seed.

For seed developers, though, it's preferable to promote a method that boosts revenues, he said. "They profit twice by selling these expensive biotech seeds and the associated herbicides."

Hamlin of Dow AgroSciences said it would be unrealistic to completely alter common agricultural practices on a large scale, particularly if farmers are opposed to the changes.

Introducing multiple modes of resistance to crops is a reasonable and immediate defense against the development of glyphosate-resistant weeds, he said.

"It's happening. If nothing is done, it's going to get worse," Hamlin said.

Seed developers say they're developing agricultural practices and training programs to help farmers prevent the further erosion of herbicide potency.

A "systems approach" of combining several pre-emergent and post-emergent chemicals is the most proficient way to reduce herbicide resistance in weeds, said Roy Fuchs, head of soybean research at Monsanto. The company wants to commercialize soybeans resistant to the herbicide dicamba.

"We don't want our farmers relying on a single class of chemistry," he said.

Farmers already have a great deal of experience with dicamba, which has been sprayed on grass crops like corn and wheat for decades, Fuchs said.

"The topics of volatility and off-site movement have been addressed with its current uses," he said.

As for the concerns about residual herbicide on the crop, Monsanto's new soybean trait contains a protein that contributes to the degradation of dicamba, Fuchs said. "The residue is extremely minimal."

Lee Van Wychen, science policy director for the Weed Science Society of America, said the overuse of any herbicide will eventually lead to resistance.

"I think producers are learning that lesson the hard way," he said.

With the growing prominence of glyphosate-resistant weeds, Van Wychen said he hopes farmers will be more open to using a multitude of control strategies.

As for the efficacy of new herbicide-resistant corn, soybean and cotton cultivars, it will ultimately depend on how they're employed in the field, he said.

"Every tool we can add to the toolbox is important," Van Wychen said. "How we use those tools is a different story."

Petitions reviewed

The USDA's Animal and Plant Health Inspection Service, which regulates genetically engineered crops, is currently reviewing petitions from several companies that want to commercialize new herbicide resistant traits in corn and soybeans.

* In 2008, Bayer requested deregulation of cotton that's resistant to glufosinate, a broad-spectrum herbicide that kills weeds by hindering the formation of a crucial plant enzyme. The biotech cultivar is also resistant to the cotton bollworm and related insect pests.

* In 2009, BASF proposed to deregulate soybeans resistant to imidazolinone, an herbicide that's primarily effective against broadleaf weeds by starving them of proteins required for growth.

* In 2009, Dow AgroSciences asked the agency to deregulate two new biotech crops. The company's new corn cultivar is resistant to ACCase inhibitors, a class of herbicides that kills grasses, and 2,4-D, which acts against broadleaf weeds. Though 2,4-D isn't as effective against grasses, it can damage corn plants once they reach a certain size. That same year, Dow proposed deregulating soybeans that are resistant to 2,4-D and glufosinate.

* In July 2010, Monsanto submitted a petition to deregulate soybeans resistant to dicamba, a broadleaf herbicide that kills weed by causing abnormal cell growth that disrupts the plant's nutrient intake.

-- Mateusz Perkowski


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