EPA: Final guidance on pesticide resistance coming by year's end

By Stephen Davies

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WASHINGTON, Nov. 3, 2016 - EPA plans to release final guidance by the end of the year to help growers and applicators deal with weed and pest resistance, agency officials said Thursday at a meeting of the Pesticide Program Dialogue Committee (PPDC). They also provided updates on dicamba “over the top” registration, endangered species risk assessments, and the use of epidemiology in assessing pesticide risks.

PPDC members represent large segments of American agriculture: chemical manufacturers, applicators, conservation and public health groups, farmworkers, retailers, and state and federal agencies. They get together twice a year to hear from - and provide feedback to - officials in EPA's Office of Pesticide Programs (OPP).

“We hope to finish these this calendar year,” Bill Chism, a senior biologist in OPP's economic analysis division, said, referring to draft guidance documents published in June.

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The guidance divides 28 herbicide “modes of action” into three categories of concern (low, moderate, high), “based on the risk of developing herbicide-resistant weeds.” MOAs associated with glyphosate, 2,4-D, atrazine and glufosinate are classified as being of “high” concern.

The guidance includes 11 elements to be included in herbicide resistance management and stewardship plans. Only the MOAs of high concern would require all 11.

One element common to all plans, however, is scouting fields before and after application. Marc Lame, of the National Environmental Health Association in Bloomington, Indiana, asked whether EPA had any plans to measure compliance.

“That's one of the things we're trying to piece together at this point,” Chism said. “It's something we're concerned about but we really don't have an answer yet.”

Jack Housenger, director of OPP, said the agency doesn't have the resources to ensure that farmers are scouting fields. And besides, “We don't want to go out and bust users for not scouting before and after (application).” Fields are scouted to assess herbicide effectiveness and the possibility of resistance.

Scouting is also an aspect of the proposed registration of dicamba for “over the top” applications in cotton and soybeans genetically engineered to tolerate the herbicide. EPA is currently reviewing comments on its March 31 proposal, and expects to make a final decision by the 2017 growing season.

Allen McLaurin, a cotton grower from North Carolina who represents the National Cotton Council on the PPDC, said that weed resistance to long-relied-upon products containing glyphosate and glufosinate, for example, makes dicamba “one of our last resorts.”

“It's going to be imperative for us as growers to get out and do proper scouting,” he said. “We cannot afford to get resistance to this new product, which is all we've got left in the pipeline that we know of.”

Other subjects that came up at the PPDC:

Synergy: Housenger said that since EPA found out that Dow AgroSciences had included claims of potential synergy in a patent application for Enlist Duo, a combination of 2,4-D and glyphosate that the agency recently re-approved, “synergistic potential has become a very, very important issue with OPP. Historically, we considered synergy uncommon.” Now, however, OPP plans on examining potential synergy for every new active ingredient proposed, he said.

Endangered species: EPA plans to issue final biological evaluations for chlorpyrifos, diazinon and malathion in January; the draft BE's found that the Fish and Wildlife Service or National Marine Fisheries Service would have to prepare Biological Opinions to evaluate the effects of chlorpyrifos and malathion on 1,725 species, and on 1,416 species for diazinon. The agency also is working on draft BE's on carbaryl and methomyl for release in the spring. Anita Pease, associate director of OPP's Environmental Fate and Effects Division, said EPA is working to refine its range maps for listed species and using 24-hour averages to measure exposures. “We got some estimated exposures (in the evaluations) that were exceedingly high,” Pease said, pledging “to make those numbers a little more realistic.”

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Epidemiological framework: In the next few months, OPP plans to issue a final “framework” for using epidemiology studies in human health risk assessments, said Dana Vogel, director of OPP's Health Effects Division. CropLife America recently asked the agency to accept public comments on the framework, and the group's PPDC rep, senior director for regulatory policy Ray McAllister, reiterated that request at the meeting. But Vogel said OPP received adequate feedback on the document from a Scientific Advisory Panel that was held in 2010. The draft framework has been used in evaluations of atrazine, chlorpyrifos and, perhaps most prominently, in a recent issue paper that found glyphosate was not likely to be a human carcinogen. McAllister asked whether OPP would revisit those evaluations if the final framework turns out to be different from the draft, but Housenger said that was unlikely - and only “if there's a great departure” between the draft and final frameworks. “The science can be changed at any time and we'll revisit it if needed,” Housenger said.

Glyphosate: Vogel said there is still no firm date for a Scientific Advisory Panel on the carcinogenic potential of glyphosate, and offered no further details on why the SAP was postponed. EPA initially said it needed more expertise on epidemiology on the panel, then said one of the panelists had voluntarily withdrawn. Vogel would say only that she hopes the meeting will take “over the next couple of months or so.”

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