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Corn+Soybean Digest

Exiling Atrazine? | Atrazine Still a Highly Effective Herbicide to Control Weeds in Corn

An old friend is still available to help control weeds. But despite the government's report that atrazine isn't contaminating municipal water systems or harming humans, there's concern the half-century-old, still highly effective herbicide could eventually get the ax.

If you grow corn, you probably count on some form of atrazine for weed control — growers have since 1958. “It's probably used on up to 80% of the corn acreage in the U.S.,” says Rod Snyder, National Corn Grower Association's (NCGA) director of public policy.

Snyder helped lobby for the “Big A's” survival during several years of studies by the Environmental Protection Agency (EPA) Office of Pesticide Programs (OPP). OPP determined that atrazine is safe when used according to approved label directions and precautions.

“In making this finding, the agency has ensured that children, women of child-bearing age and other sensitive subpopulations are protected,” says an EPA report.

“We absolutely think that atrazine is still a viable herbicide for corn growers,” says Snyder. “NCGA studies show that it provides about $28/acre through either yield gains or lower yield control costs.”

Brian Olson, Kansas State University Extension agronomist in Colby, points out that atrazine is part of tankmix herbicide programs that help growers maintain good weed control.

“A premix of atrazine is being applied on a lot of acres,” says Olson. “It's really needed early on. On Roundup Ready corn, we'll go with a premix of atrazine and any number of grass herbicides at half to two-thirds rate.”

Bob Hartzler, Iowa State University Extension agronomist, adds that atrazine remains one of the most versatile herbicides available, “in terms of the spectrum of weeds controlled, flexibility in application timing and crop safety.

“Its ability to improve the performance of other herbicides at relatively low rates is a key reason for its continued popularity,” he says.

Snyder says that with all of the no-till acres in corn production and likely more in the wake of proposed climate change cap-and-trade provisions, atrazine will remain a big part of weed-control programs.

He stressed the value of the herbicide in his testimony before EPA last May. “Atrazine is also a critical tool for conserving soil and mitigating climate change,” says Snyder.

“Data from USDA show that atrazine is the most widely used corn herbicide in conservation tillage systems, which can reduce soil erosion by as much as 90%, protecting water from sediment — the number one pollutant of U.S. waterways,” he says.

“With regards to climate change mitigation, using atrazine is an alternative to mechanical cultivation to control weeds, which reduces greenhouse gas emissions from plowing,” says Snyder. “Using atrazine in conservation tillage reduces erosion, the use of fossil fuels, carbon dioxide release and sedimentary pollution into streams and lakes.

“Atrazine is also an important tool in successfully managing weeds that are resistant to other herbicides,” he adds.

SNYDER SAYS THAT in NCGA's annual yield contest, featuring nine categories, atrazine bumped up yields across the board. In 2006, advantages ranged from an 11.5-bu./acre advantage in irrigated corn to a 46.9-bu. advantage in no-till/strip-till irrigated production.

In 2008 the yields of all the contest entries containing atrazine treatments showed an average 7-bu. increase when compared to the average yield of those entries without atrazine treatments.

Atrazine helps yields, is safe to use when applied correctly and “growers need all the tools they can get their hands on,” says Snyder.

Still, agriculture will likely continue to see challenges against the herbicide. “But we have the science that shows the safety of the product when it's used correctly,” he says.

In EPA testing of municipal water supplies in 2008, atrazine was not detected in excessive amounts. “There were 122 water systems tested in 10 states,” says Snyder. “None exceeded federal standards for water delivery systems.

“The bottom line is that no chemical has been studied as much as atrazine. Our goal is to make sure growers have as many tools available as possible and atrazine is one of them,” he says.

While the EPA was making its decision not to ban atrazine nationwide, there are counties in Wisconsin that have banned the herbicide. And the European Union also gives it a thumbs down.

“I think there is no doubt that there is a continued risk of atrazine being taken off the market,” says Hartzler. “I hope the people in charge of making these decisions base their conclusions on the science rather than pressure from parties on either side of the issue.”

The New York Times reported in August that some high-ranking EPA officials say new EPA administrator Lisa Jackson is likely to examine the atrazine question closer due to continued concerns over the safeness of the herbicide.

The newspaper took to task the EPA findings and reported that the new director has indicated the agency needs to take a close look at decisions made in the previous administration, and be certain about the science behind those judgments.

HARTZLER SAYS THERE are alternative herbicide treatments, but at a cost. “I believe we have enough alternatives that farmers will be able to continue to control weeds and produce corn economically,” says Hartzler. “However, for some growers there is no doubt that their weed-control costs would increase.

“The other concern is that it would increase the selection pressure for herbicide resistance to other classes of herbicides. The use of atrazine in combination with other products has helped delay the onset of herbicide resistance with the other chemicals.”

Snyder says that in countering the movement to remove atrazine from the list of herbicides, NCGA says “the 50 years of safe use, extensive monitoring data and the wealth of information supporting atrazine's safety to the environment reaffirms the overall safety of atrazine to aquatic ecosystems.”

Olson notes that there were several triazine herbicides that have been cancelled over time. “We don't have them any more,” he says. “If we lost atrazine, it would be difficult to replace. We need to keep it around.”

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