WASHINGTON, June 8, 2016 - EPA is taking a “holistic” approach to managing herbicide-resistant weeds, releasing new guidance last week that the agency says is “intended to provide herbicide users and registrants useful strategies that, when implemented, will slow herbicide resistance and prolong the useful life of herbicides.”

“The number of herbicide-resistant weeds and the affected acreage infested is rapidly increasing,” EPA says in its “Guidance for Herbicide-Resistance Management, Labeling, Education, Training, and Stewardship.” And it warns that growers “are facing severe economic impacts… with up to 100 percent crop loss in some cases” from the weeds.

Although EPA released a similar draft guidance document addressing pesticides in general, it said it is “primarily focusing on herbicides” because they are the most widely used agricultural chemicals, with over 285 million acres treated on nearly 800,000 farm operations in 2012. 

Also, “unlike fungicides and insecticides, there have been no new herbicide (modes of action, or MOAs) developed in the last 30 years,” the guidance said. “Therefore, users do not have a new MOA to control herbicide-resistant weeds and it’s important to protect the long term efficacy of these chemistries.” 

Glyphosate-resistant weeds are a particular problem. In 1988, glyphosate was applied to about 80 million acres, but by 2014, the total acreage treated had increased to nearly 300 million acres. From 2010 to 2012, the area of glyphosate-resistant weeds almost doubled, from 33 million acres to over 61 million acres. 

Glyphosate-resistant weeds can lighten farmers’ wallets. USDA reported that in 2010, “growers with glyphosate-resistant weed problems received over $67 per acre less for corn and over $23 per acre less for soybeans due to increased costs to control weeds.” And in 2010 and 2011, growers in Georgia spent over $100 million to control glyphosate-resistant Palmer amaranth in cotton fields.

The guidance divides 28 MOAs 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 elements.

EPA said in the guidance that it plans to implement herbicide-resistance measures “for new herbicide active ingredients and new uses of herbicides proposed for use on herbicide-resistant crops.” 

EPA initially issued the draft herbicide resistance management measures in its proposal to register new uses for dicamba-tolerant cotton and soybeans, prompting the Weed Science Society of America (WSSA) and affiliated groups, which commented on the guidance as part of that proposal, to ask for a separate notice and comment period. EPA did so, and has asked for comments on the two draft guidance documents by Aug. 2.

In its May 31 comments, WSSA said EPA should, “for simplicity and to preserve the utility of all herbicides,” group all MOAs together in one category of “resistance concern.”

One of the elements of a management plan (for moderate or high-concern MOAs) would require herbicide registrants “to report new cases of likely and confirmed resistance to EPA and users yearly.”

WSSA suggested EPA require reporting of two different categories: suspected and confirmed cases. The association said that for suspected cases, “It is vital to limit these reports to those evaluated by trained experts and that they not include resistance reports from outside this group.” 

The “confirmed” category “would allow academics and industry to provide scientific data confirming that a certain weed is resistant to a specific herbicide,” WSSA said. “We feel that reports of new resistant species for a given MOA should be confirmed by appropriate lab or greenhouse testing.” 

“The National and Regional Weed Science Societies believe that early reporting of suspected newly evolved resistance cases will be a critical part of a plan to alert the agricultural community in time to increase vigilance and institute mitigation measures before newly identified resistant weed populations become widespread,” WSSA said. 

WSSA was joined in its comments by the Aquatic Plant Management Society, the Northeastern Weed Science Society, the North Central Weed Science Society, the Southern Weed Science Society, and the Western Society of Weed Science.


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