Re-Registration for Herbicide Demonstrates Challenges

Atrazine, an effective and widely used broadleaf herbicide, will be due for registration review by the EPA in 2018, per federal pesticide law.

Last summer, the EPA’s initial ecological review examined the effects of trace concentrations of atrazine in streams on amphibians and fish, as well as on other plants and animals.

The agency’s review of human health impacts was scheduled for the third quarter of this year; however, the timing of the registration review is now unclear, given the transition of a new administration in the U.S. Executive Branch.

A request for comment by Iowa Farmer Today was not returned by the EPA.

Losing a tool

For Iowa farmers, the issues of atrazine use echo many of the larger challenges faced by U.S. ag today — defending the importance and legitimacy of farming practices to a non-farming public, fighting the selective pressures of biology against tougher weeds each year and growing crops profitably as the costs of farming rise and revenues fall.

Bob Hemesath, a Winneshiek County, Iowa, farmer and chairman of the Iowa Corn Growers Association, summarized the comments submitted by many Iowa farmers to the EPA regarding the ecological review of atrazine.

“It’s safe, effective, and it’s an economical herbicide,” Hemesath said. “It’s the most tested herbicide out there. It’s been used for probably 50 years.”

Hemesath, like many farmers, is a licensed private pesticide applicator.

He sprays his own fields with a herbicide mix that includes a reduced rate of atrazine in complement with other active ingredients as part of his weed-control program.

In its preliminary ecological risk assessment, EPA scientists decided average atrazine concentrations in water at or above 5 µg/L (about 5 parts per billion) for several weeks may lead to reproductive effects in fish.

This conclusion has been refuted by other groups.

No timeline on a final decision on ecological risks from the EPA has been set.

Nonetheless, if the EPA were to limit atrazine concentrations to this level in streams, Hemesath said “farmers will probably stay away.”

“We won’t be able to meet the levels they are talking about. It will change a lot of my program,” Hemesath said, describing how he would respond to what would effectively be an atrazine ban.

He said atrazine is one of many tools needed to control weeds. By alternating herbicide chemistries, farmers are able to keep the chemicals they have effective in controlling weeds, he explained.

“It would be a big hit to farmers to not be able to use atrazine — economically and from an agronomic standpoint,” Hemesath said.

He said the costs of banning atrazine have been estimate in the range of $30 to $50 per acre.

Agronomic perspective

Mike Owen, an Iowa State University Extension weed specialist and professor, said atrazine is “very important” in the control of many of the annual broadleaf weeds in corn.

It is effective in both pre-plant

and post-planting applications against Iowa’s toughest weeds like waterhemp.

“If you look at the amount used, certainly the area treated, no other herbicide has been used as much or as often in corn,” Owen said.

All new herbicide products for corn registered in the last 25 to 30 years have included atrazine as a tank mixture recommendation, he explained.

Triazine resistance (atrazine is a triazine class herbicide, Herbicide Group 5) in waterhemp has been detected in approximately 50 percent of the fields in Iowa, but the number of plants with this characteristic per field are “still pretty small,” Owen said.

As a result, farmers perceive that it is working “very well,” he explained.

Given rate restrictions and environmental considerations, it’s probably best to use atrazine in a post-planting application, Owen said. Soil applied premixes may not have the same residual control.

In the late ’60s and ’70s, the average use rate of atrazine was around 3 pounds per acre, Owen said.

Today, farmers use much less for practical reasons. As soybeans became more popular, rates were reduced to limit carryover injury to soybeans, Owen explained.

Furthermore, as more became known about ground water and surface water contamination, setbacks from tile intakes and limits on the size of corn during application were put in place to minimize risks.

“We still use it as a very important tool in weed management, but I think we just use it more judiciously — and dare I say more effectively — than when we used it as a soil applied material,” Owen said.

In terms of replacements or alternatives to atrazine, there aren’t any so far.

In the past, new products may have implied they would be an effective replacement for atrazine, Owen said.

“First thing they do is add atrazine as a tank mix option to the label. There has not been a replacement for atrazine,” he said.

The time is now for farmers to put practices in place which limit environmental impacts and resistance issues, Owen said.

“All management practices, if you focus on a single tactic, then the target of that tactic — weed, bug, disease, nematode — the target of that tactic is going to evolve to overcome that tactic,” Owen said.

Farmers finding solutions

The idea of limiting runoff to manage nutrients has many of the same concepts as pesticide control, he said. When practices like buffer areas along streams are put in place, many benefits are accrued indirectly by the public, he said.

“The consequences of not doing so is going to be increased regulatory authority,” Owen said, pointing to new herbicide labels as an example.

Owen said Iowa farmers have successfully employed strategies that limit runoff to manage atrazine concentrations in sensitive watersheds and soil types around the state.

Iowa law specifies lower application rates in certain Iowa counties, including the Karst topography region in northeast Iowa.

“If science proves these levels are a potential problem, management can address these issue and overcome these concerns,” Owen said. “I’m very confident farmers will respond and change practices (if needed).”

Hemesath’s farm operation in Winneshiek is already subject to specific state regulations, including setbacks for tile intakes.

“It’s just a matter of understanding what the limits are,” Hemesath said. “Very few people use the full rates of atrazine.

“We as farmers, we’re all about safety and environmental responsibility. If we’re using something that isn’t safe, we want to know about it and be able to deal with it.”

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