Changes from the U.S. Environmental Protection Agency (EPA) to atrazine registration could affect as much as 45 million acres of corn and would be "detrimental" to conservation tillage practices, according to a Syngenta scientist.

The EPA is considering lowering the Level of Concern (LOC) from 15 parts per billion (ppb) down to 3.4 ppb. It would impose the following restrictions for watersheds that might meet or exceed a 3.4 micrograms/liter threshold:

  • banning atrazine use when soils are saturated or above field capacity
  • banning atrazine use during storms and 48 hours before any severe weather is forecast
  • banning aerial application of atrazine
  • limiting the application of atrazine to 2 pounds of active ingredient per acre per year.

In addition, the EPA is seeking to require record keeping for applications of atrazine, including the name and certification of the applicator, product name and registration number, crop, location, size and area of application, and other data.

Farmers would have to select from among various options in the watershed where atrazine has been identified as an area of concern. If more atrazine than certain thresholds was applied, growers would have to choose from these proposed mitigation efforts:

  • No pre-emergence applications on crops
  • Vegetative filter strips at least 30 feet wide on A and B hydrologic group soils
  • Vegetative filter strips at least 100 feet wide on C and D hydrologic group soils
  • Grassed waterway
  • Field border
  • Irrigation water management
  • Cover crops
  • Contour buffer strips
  • Contour farming
  • Terrace farming
  • Strip cropping
  • Soil incorporation up to 1 inch
  • No-tillage or reduced tillage

Richard Brain, an ecotoxicologist with Syngenta, challenges the mitigation efforts, saying they're predicated on inflated modeled exposure estimates at the county level. He takes issue with the EPA's criteria for analysis, too.

"The LOC itself is tenuous and based on scientifically indefensible analyses," he tells No-Till Farmer. "These mitigations potentially affect 20-45 million acres of corn, primarily in the Midwestern U.S. and are likely to be detrimental to no-till practices."

Daniel Perkins, scientist and owner of The Ag Insight, says one of his spray drift publications intentionally uses atrazine as the test compound.

"When defending use of any given product, especially one as important as atrazine to no-till practices, it is important to address ecotoxicology (e.g. the LOC) and the exposure (e.g. spray drift) in two different ‘work streams’ of scientific data/information to provide data for a more representative risk assessment that includes defensible science and best-available information rather than overly-conservative, or even precautionary, assumptions," Perkins writes.

Trade groups, like the National Corn Growers Association, have also been critical of the consideration.

The EPA is accepting public comments about atrazine until Sept. 6. Since the public comment docket was reopened for the reconsideration on June 30, 3 comments have been submitted to the EPA. 

"We need atrazine available for farmers to use without unwarranted restrictions," writes commenter Bob Pogatchnik. "Weed control will be important in the future as some weed species are resistant. Loss of yield due to weed pressure may cause worldwide shortages."

Anyone who wishes to comment may do so online here. More information about the court case leading up to the review is available here. After considering comments on the proposed revisions, the EPA will determine if any changes are warranted to the proposed revisions and then release its decision on the re-evaluation. 

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