Agriculture Reference
In-Depth Information
Refuge requirements are reduced for multiple-toxin Bt cotton varieties
in some areas.
EPA has eliminated the minimum refuge requirement for
certain Bt cotton varieties that express multiple toxins in areas that appear to
have sufficient unstructured refuge, but not for Bt corn varieties that express
multiple toxins. The latter are less toxic to an important target pest known as
the western corn rootworm, which might inherit Bt resistance as a partially
dominant trait. Recently, western corn rootworm larvae were collected from
Iowa Bt cornfields that showed evidence of root damage, and laboratory
assays later confirmed that their progeny were less susceptible to Bt toxins
(Gassmann et al., 2011). This has raised concerns about regulatory compliance
and a continued need for minimum refuge requirements for Bt corn growers.
Evolution of Glyphosate Resistance in Weeds
The herbicide glyphosate is more environmentally benign than the
herbicides that it replaces. Glyphosate controls a wide array of weeds and is
used on most of the HT corn, soybeans, and cotton grown in the United States.
Glyphosate has been the most heavily used pesticide in the United States since
2001 (Grube et al., 2011), due in part to the popularity of HT crops and the
steady decline in its price following the expiration of glyphosate's patent in
2000 (Duke and Powles, 2008).
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Because the pollen and seeds of many
different weed species can disperse between farms in the atmosphere and in
conjunction with the movement of animals and farm equipment, economic
incentives for adopting best management practices (BMPs) that maintain the
effectiveness of glyphosate over time are reduced (Miranowski and Carlson,
1986).
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The economic and biological impacts associated with any farmer's
pesticide-use decisions will accrue not only to that farmer, but to other nearby
farmers as well. Unless resistance management is coordinated across farms,
economic incentives for farmers to account for the effects of their decisions on
resistance are reduced, even on their own farms. This is because the
effectiveness and longrun economic benefits of using BMPs to manage
resistance depend on the level of adoption by nearby farmers, while the short-
run costs of BMP adoption are borne solely by the adopters.
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In this setting,
resistance can evolve at an economically inefficient rate because market-based
economic incentives are insufficient to promote an efficient level of BMP
adoption (Hueth and Regev, 1974; Feder and Regev, 1975).
This reduction in economic incentives to adopt BMPs and the economic
and environmental benefits associated with the HT crop-glyphosate
