Atrazine Alert

March 9, 2012 10:06 PM

EPA review begins anew for weed-control standard

p36 Atrazine Alert
Speak up and apply responsibly so atrazine isn’t banned by the EPA, says Kansas farmer Ken McCauley.

Ken McCauley will discuss the value of atrazine to agriculture and consumers with anyone who will listen. He hopes other farmers are equally passionate about discussing the merits of this more than 50-year-old, triazine-based herbicide, which remains the backbone of most weed-control programs in corn today. Without such conversations, McCauley fears, atrazine will not survive the relentless pressure from environmental groups who want to eliminate its use.

"Anytime I’ve had the opportunity to talk about it and how important it is, I’ve talked about it," says McCauley, who farms 4,600 acres of corn and soybeans with his son, Brad, near White Cloud in northeast Kansas.

In defense of atrazine, the former National Corn Growers Association (NCGA) president has written numerous letters, given speeches to civic groups and even testified before one of the Environmental Protection Agency (EPA) Scientific Advisory Panels.

The atrazine debate has been going on for decades. The most recent formal assessment of atrazine, initiated by EPA in the 1990s, will conclude sometime this summer. However, what few farmers realize is that atrazine is about to undergo another formal EPA review, scheduled to start in 2013.

"The process typically starts nine months ahead of time, so the old assessment and the new one will essentially overlap," says Jere White, chairman of the Triazine Network, a coalition of farmers and agricultural industry leaders who strive to keep triazine herbicides available in the U.S. and subject to review by sound science. White also serves as executive director of the Kansas Corn Growers Association and Kansas Grain Sorghum Producers Association.

White says not a week goes by that he doesn’t advocate on behalf of atrazine.

Farmers must speak up on issues that affect their livelihoods, echoes Reed Rubinstein, senior counsel for the U.S. Chamber of Commerce. EPA is moving away from place-based regulations supported by science to a holistic approach, he says, which includes social issues.

This transition does not bode well for atrazine, a valuable component in roughly 60 herbicides on the market today. Atrazine improves the weed control activity of these products, either in a tank-mix application or as a prepackaged product.

Herbicide use data shows that atrazine was applied to more than 53 million acres in the U.S. in 2009, according to Mike Owen, Iowa State University Extension weed scientist.

That year, atrazine was applied to about 60% of the corn acres, 60% of the sorghum acres and 80% of the sweet corn acres.

Owen contends that atrazine is a key component of both proactive and reactive management systems for herbicide weed resistance, especially those with resistance to glyphosate.

"The number of weeds with evolved glyphosate resistance continues to mount and, more importantly, the number of fields with glyphosate-resistant weed biotypes is escalating at an increasing rate," Owen reports.

Along with improved weed control, atrazine used in conjunction with other herbicides helps farmers reduce tillage passes and lessen the potential for soil erosion.

"Increased tillage has major economic, ecological and environmental implications to growers and to society in general," Owen says.

McCauley says atrazine is invaluable for its ability to kill weeds cost-effectively, and farmers simply can’t afford to lose it.

"If you put a dollar value on atrazine, I’d say it would cost me at least $20 per acre to replace
it; on 3,000 acres of corn, that’s $60,000," he says.

More information about the challenges that atrazine faces and how farmers can get involved in the process of keeping it available in the marketplace are available from the Triazine Network at

Promote Stewardship

If you believe a new herbicide chemistry is just around the corner, think again. Manufacturers have not introduced a herbicide with a novel mode of action to the marketplace for about 20 years, says Mike Owen, Iowa State University Extension weed scientist.

It’s important for farmers to be good stewards of atrazine by properly timing field applications and applying labeled rates to keep it viable in the years ahead.

Improper use of atrazine will only contribute to more resistance problems such as those found several years ago in Macon County, Ga., notes Eric Prostko, University of Georgia Extension weed scientist.

"We found instances of Palmer amaranth resistance to atrazine in a predominantly dairy area where they were using quite of bit of atrazine in their rotations," Prostko says. "We also found multiple cases of resistance there to glyphosate and ALS herbicides."

Triazine resistance is not new. The first report of it was in common groundsel in 1970.
Prostko says farmers must use multiple modes of action for weed control to stop resistance problems in corn, cotton and other crops.

Kansas farmer Ken McCauley agrees. He uses a fall application of 1.5 lb. per acre of atrazine in combination with 1 pint per acre of 2,4-D in his no-till corn to keep the fields clean through the following spring. In late May, he makes a post application of atrazine in combination with a residual herbicide. He says the post application allows corn plants to quickly grow and shade out any weeds that pop through the ground.

"That shade is free and natural, and there’s nothing we have to do then for the rest of the season," he notes.

Prostko encourages farmers to contact their county or state Extension weed specialist to confirm the modes of action they use in their fields.

In addition to triazine resistance, Prostko is concerned about resistance developing to Liberty herbicide.

"Cultural practices such as tillage, cover crops and row spacing can be used to help manage herbicide-resistant weeds," he says. "Reliance on herbicides alone is not enough in today’s world."

Confirmed Cases of Herbicide Resistance in Palmer Amaranth

For more than 10 years, Palmer amaranth has been developing resistance to one herbicide after another.

  • 1989: DNA herbicides (Treflan, Prowl) in Arkansas, South Carolina and Tennessee
  • 1994: ALS-inhibiting herbicide (Staple) in Arkansas, South Carolina and Tennessee
  • 2005: Glycine-inhibiting herbicide (Roundup) in Georgia and North Carolina
  • 2008: PS II–inhibiting herbicide (Atrazine) in Georgia
  • Possible future resistance: Ignite and PPO herbicides
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