3 years ago



At present, 2,4-D and

At present, 2,4-D and dicamba are minor corn and soybean herbicides (USDA NASS 2013, 2011), and where used they are applied early in the season at relatively low rates to avoid crop injury. However the high-level resistance conferred by genetic engineering to the new crops will facilitate application of several-fold higher rates of 2,4-D and dicamba than are used at present. Applications will also be made more frequently, and later in the season, similar to the use pattern of glyphosate with Roundup Ready crops (Center for Food Safety 2012b, Center for Food Safety 2012c). 2,4-D and dicamba will not displace glyphosate where these crops are grown, for several reasons. First, the new crops will come with additional resistance to glyphosate (and in some cases still other herbicides) (Table 1). Second, glyphosate will continue to be used because it kills certain weeds (e.g. grass family and perennial weeds) more effectively than either 2,4-D or dicamba. Third, the chemical companies will market dual products specifically for use with the resistant crops: Dow’s Enlist Duo (a combination of 2,4-D and glyphosate) and Monsanto’s Roundup Xtend (a dicamba/glyphosate mix). Thus, Roundup Ready farmers who switch over to these next-generation seeds will be applying high rates of 2,4-D or dicamba in addition to glyphosate at rates currently used (Center for Food Safety 2014b, Monsanto 2012). Herbicide efficacy trials show that application of high rates of either 2,4-D or dicamba alone cause considerable lasting damage to common milkweed, though not as much as glyphosate (Zollinger 1998). Ohio agronomists recommend either glyphosate or dicamba alone, or a mix of 2,4-D and glyphosate, to kill common milkweed (Loux et al. 2001). Thus, the application of the dual herbicide products (Enlist Duo or Roundup Xtend) to crops resistant to them will continue to eliminate what little common milkweed remains in corn and soybean fields at least as effectively as glyphosate has with Roundup Ready crops. The second major threat posed by these new multiple herbicide-resistant crops is a reduction in flowering plant communities that supply nectar to monarch adults. Loss of Habitat Due to Pesticide Drift Although monarch larvae can only thrive on milkweeds, adult butterflies feed on a wide variety of nectar-producing flowers (Tooker et al. 2002). They depend on flowers that are in bloom in their breeding habitat during the spring and summer, and then along migration routes to their winter roosts (Brower and Pyle 2004, Brower et al. in press). Monarchs that are breeding during spring and summer require energy derived from nectar for flying, laying eggs, mating, and other activities. In addition, the generation that migrates in the fall depends on nectar sugars (stored in the form of fat) to sustain themselves while overwintering, and perhaps also to fuel their northern migration the following spring (Brower et al. 2006). Herbicides, by definition, are toxic to plants, and they frequently drift beyond the boundaries of crop fields to affect wild plants growing nearby. Various models of herbicide spray drift suggest that from one percent (commonly) to 25 percent (occasionally) of the applied herbicide dose drifts beyond field boundaries to reach wild plants growing nearby (Holterman et al. 1997, Wang and Rautmann 2008, Boutin et al. 2014). Areas surrounding cropland provide most of the Monarch ESA Petition 60

iodiversity in agriculture-dominated landscapes (e.g. Boutin and Jobin 1998) such as the Midwest. Herbicide drift threatens the wild plants monarchs depend upon for nectar. The imminent introduction of next-generation herbicide-resistant crops, such as those resistant to 2,4- D and dicamba, discussed above, will lead to sharply increased herbicide use, drift, and associated damage to wild plants, reducing monarch nectaring habitat. Herbicide drift is greatly exacerbated by herbicide-resistant crops. This is demonstrated quite clearly by experience with Roundup Ready crops. Glyphosate has relatively low volatility and is not regarded as a drift-prone weed killer (Lee et al. 2005, p. 135). Nevertheless, it has become one of the top two herbicides (along with 2,4-D) implicated in herbicide drift complaints nationwide since the Roundup Ready era began (Association of American Pesticide Control Officials 1999, 2005). The high incidence of glyphosate drift injury is partly attributable to the expanded acreage and increased volume of use with Roundup Ready crops. The late application period—mid-season with Roundup Ready crops versus early season with conventional varieties —also increases the risk of drift injury. In a comprehensive study of the potential for herbicide drift to injure crops in Fresno, CA, scientists from the U.S. Environmental Protection Agency found that: Increased use of herbicide-resistant technology by producers creates the possibility of off-site movement onto adjacent conventional crops . . . Post-emergence application of herbicide to a genetically-modified (GM) crop often occurs when non-GM plants are in the early reproductive growth stage and are most susceptible to damage from herbicide drift (Ghosheh et al.,1994; Hurst, 1982; Snipes et al., 1991, 1992). Consequently, most drift complaints occur in spring and summer as the use of post-emergence herbicide applications increases (Lee et al. 2005, p. 15). Glyphosate drift from Roundup Ready crops has repeatedly caused extensive damage to wheat (Baldwin 2011) and rice (Scott 2009) in Arkansas, to rice (Wagner 2011) and corn (Dodds et al. 2007) in Mississippi, to rice in Louisiana (Bennett 2008), and to tomatoes in Indiana and adjacent states (Smith 2010), to cite just a few of many examples. A search of the online farm publication Delta Farm Press using the search term “glyphosate drift” yields 127 articles (search conducted June 5, 2014, see: Drift episodes sometimes give rise to lawsuits, as when farmers won compensation for onions damaged by glyphosate applied to Roundup Ready soybeans in Ontario, Canada (Lockery vs. Hayter 2006). Glyphosate drift injury can be extensive. In Mississippi, damage was reported on 30,000 to 50,000 acres of rice in 2006 (Wagner 2011). Glyphosate drift damage to wheat has prompted suggestions that it simply not be grown in Arkansas (Baldwin 2011). Tomato growers in Indiana, Michigan and Ohio suffered more than $1 million in glyphosate drift damage over four years (Smith 2010). Arkansas corn growers felt so threatened by drift that they switched to Roundup Ready varieties out of “self-defense” against glyphosate drifting from Roundup Ready soybean and cotton fields (Baldwin 2010). The frequency of crop injury from glyphosate drift demonstrates the threat that genetically engineered, herbicide-resistant crops pose to monarch habitat. Several studies suggest that glyphosate applied to crops engineered with resistance may have already reduced the abundance Monarch ESA Petition 61

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