Researchers have idea why atrazine effectiveness declines

Despite modern technologies and the age of instant information, groupthink, or the faulty decision-making of the whole, can emerge in almost any circumstance.

In farming, such collective error may have impeded researchers for years from realizing the valid reason why the effectiveness of a popularly used herbicide, atrazine, has been significantly compromised.

Jason Krutz, USDA-ARS soil scientist in Stoneville, Miss., says an adapted microbrial population is the culprit, not weed resistance. “Our field studies indicate that if you are applying atrazine every year or every other year, you're reducing your residual weed control by about half,” Krutz said.

Research studies have begun on sentinel plots at Elizabeth, Miss., to determine exactly how many years are needed to skip applications of atrazine before its effectiveness resumes.

“For years scientists looked for this evidence and it wasn't there. Then all of the sudden it's in our backyard,” Krutz said.

“The mindset was so much ingrained. We (researchers) all assumed that atrazine was very stable. But Mother Nature adapted. She has a strange way of doing these things.”

There is ample, sound proof, according to Krutz. “A study has evidenced that at nine days, 60 percent of atrazine is gone in an adapted field, and in another field that has never had atrazine, less than 14 percent of it is gone.”

The herbicide was first manufactured by Syngenta and introduced into agriculture in the early 1970s. Atrazine was labeled generic several years ago and because its retail cost is relatively inexpensive — between $3 and $4 an acre — it's used widespread on farms across the country, including on sugarcane crops throughout Louisiana and on corn grown in the Delta.

Krutz said that although atrazine remains one of the most inexpensive applications a farmer can apply to a crop, “if you put out something ineffective it is potentially one of the most expensive treatments made because it is a waste. I'm not saying it's spraying water, but …”

Trey Koger, USDA-ARS agronomist, said there are a lot of corn/cotton and corn/soybean rotation systems in the Delta, and of those rotations, the most popular practice is using Roundup Ready corn complemented with atrazine.

He said considering the new evidence coming to light about atrazine, farmers' options consist of not applying atrazine for at least two years before reapplying, or continuing to use atrazine without much residual benefit, or to complement Roundup Ready with an expensive alternative to atrazine. Costs of alternatives range from $6 an acre to $20 an acre, depending on rate and formulation utilized.

“The economics still drives the industry,” Koger said. “We can tell a lot of farmers this, and they may not listen. But if atrazine was $10 (an acre), believe me, they would listen to every word.”

Koger cautioned though that there could be industrywide consequences, depending on the course of action farmers choose: “If the option taken is to only use Roundup Ready, then this would only increase the chances of developing resistance in glyphosate — only that much more selection pressure on the Roundup technology.”

In Houma, La., Ed Richard, research leader at the USDA-ARS Sugarcane Research Laboratory, says historically atrazine has been applied on all of that state's sugarcane crops. Today, he estimated, half of the crops are sprayed with atrazine to control morning-glories.

He is uncertain that adapted microbes explain atrazine's inconsistent results, however. “We are exploring that reason as a possibility,” he said.

“It's in the early stages of testing, but there are other factors to consider, such as the soil conditions, and the timing of the application.

“We don't yet have a good handle on why our control is off, but there are a lot of possibilities to consider.”

Krutz first looked at the cause of atrazine's diminishing effectiveness while completing doctoral studies at Texas A&M in 2003. He said two peers, one in Colorado and one in Tennessee, have basically come to the same conclusions in recent months.

He said that when he and a colleague first revealed their suspicion about atrazine to peers, overall reaction was skeptical. “He's had some people tell him, ‘Forget it, you're wrong,’” Koger said. “There have been a lot of obstacles in front of him he's had to overcome, but this is important information.”

Related studies at the Stoneville station have already been initiated to determine an alternative weed management strategy.

The possibility that farmers might considerably decrease their application of atrazine could have prudent ramifications in another area: the environment.

Atrazine remains one of the most heavily monitored chemicals by the EPA, included on at least three different regulatory lists; European countries banned use of the chemical several years ago.

“From an environmental standpoint, decreased persistence of atrazine in soil may drastically reduce the movement of this herbicide to lakes and streams,” Krutz said.

e-mail: [email protected]

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