3 years ago



and diversity of nectar

and diversity of nectar plants in and around agricultural fields, from direct applications as well as spray drift (e.g. Blackburn and Boutin 2003, Gove et al. 2007). Next-generation, genetically engineered, herbicide-resistant crops will greatly exacerbate these impacts. 2,4-D and dicamba are volatile herbicides prone not only to spray drift (like glyphosate), but also vapor drift, which is much more unpredictable and difficult to control (Behrens and Lueschen 1979, Sciumbato et al. 2004). While spray drift happens only while the herbicide is being applied, vapor drift occurs when an herbicide previously deposited on plant surfaces and the ground volatilizes and moves off-site, and is favored by hot conditions and temperature inversions (Johnson and VanGressel 2012, United States Geological Survey 2003). Vapor drift helps explain why 2,4-D and dicamba, though much less heavily used than glyphosate, have been leading culprits in drift-related crop injury, with 2,4-D ranking first or second along with glyphosate (Association of American Pesticide Control Officials 1999, 2005). Crops damaged by 2,4-D and dicamba drift, often at quite low levels, include grapes, cotton, soybeans, sunflowers, and many fruits and vegetables (Hebert 2004, Egan et al. 2014a, Doohan et al. 2014). Despite numerous restrictions on formulation types and application methods intended to mitigate drift, 2,4-D continues to cause widespread crop injury (Hebert 2004). Though damage often occurs to crops in adjacent fields, area-wide impacts are not uncommon. For instance, in 2006 volatilization of 2,4-D damaged cotton on upwards of 200,000 to 250,000 acres in five counties in Arkansas, likely due to multiple applications in the area and weather conditions that promoted vapor drift (Bennett 2006). In 2012, a single 2,4-D application damaged 15,000 acres of California cotton as well as a pomegranate orchard, with cotton damage verified as far as 100 miles from the application site (Cline 2012). In the Canadian Prairies, 2,4-D, dicamba and other herbicides are frequently found in the air and in rain (Tuduri et al. 2006). At the high end of concentrations detected in rainfall in Alberta, Canada, a mixture of four herbicides (2,4-D, dicamba, MCPA and bromoxynil) was found to negatively impact test plants, leading the researchers to conclude that “occasional high levels of herbicides detected in rainfall in southern Alberta could harm beans and tomatoes grown in the area” (Hill et al. 2002). Extensive monitoring in Washington State has shown that 2,4-D injury to grapes occurs “from regional nonpoint sources estimated to be as far as 10 to 50 miles away, and correlates with airborne 2,4-D concentrations rather than local pesticide use” (Hebert 2004). The frequency of such area-wide impacts, including those from regional off-target movement and “toxic rainfall,” will increase dramatically with the surge in use anticipated with the planting of resistant crops. USDA has projected that 2,4-D-resistant corn and soybeans would increase annual agricultural use of 2,4-D by three- to seven-fold: from 25.6 million pounds at present to anywhere from 77.8 to 176 million lbs./year by 2020, depending on how widely they are grown (Figure 24). Pennsylvania State University weed scientists have projected a similarly large increase in 2,4-D and dicamba applications if soybeans resistant to them are approved (Mortensen et al. 2012). Increased drift injury will not be limited to sensitive crops, but will affect wild plants as well. 2,4-D and dicamba selectively kill broadleaf plants, and are less effective on grasses (Rasmussen 2001, US EPA 2006, Center for Food Safety 2012a). This will make them particularly injurious Monarch ESA Petition 62

to butterflies, especially with frequent application over a broad area, as would occur with 2,4-D and dicamba-resistant crops. A study of pesticide effects on butterflies in agricultural areas of England showed that restricting the use of “persistent broadleaf herbicides” near field edges would result in more butterflies in the landscape. In one experiment, researchers sprayed the bulk of the field with the usual complement of pesticides, but modified the spraying apparatus such that only selective grass-killing herbicides were applied to the field edges. They found that there were indeed more butterflies after implementing this measure, and also that there were more flowering plants, “thereby increasing the availability of nectar resources for butterfly species,” as well as more biodiversity in general (Longley and Sotherton 1997, pp. 8-9). Several new field studies in the United States—undertaken to assess the potential effects of dicamba use with dicamba-resistant crops—support the English findings. Bohnenblust (2014) found that drift-level doses of dicamba delayed flowering of alfalfa, and both delayed and reduced flowering of common boneset (Eupatorium perfoliatum), a wildflower that provides resources to many insect species. In addition, common boneset flowers were less visited by all pollinators when treated with dicamba at rates simulating drift. Monarch ESA Petition 63

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