Adoption of Best Management Practices to Control Weed Resistance by Corn , Cotton , and Soybean Growers

In 2008, agricultural producers planted more than 80% of US cotton and corn acreage and more than 90% of soybean acreage to transgenic glyphosate-tolerant, Roundup Ready® (RR) seed varieties (US Department of Agriculture Agricultural Marketing Service [USDA AMS], 2008; USDA National Agricultural Statistics Service [NASS], 2008). Many studies report significant pecuniary and non-pecuniary benefits to growers from using glyphosate-resistant varieties (Gianessi, 2008; Marra, Pardey, & Alston, 2002; Marra & Piggott, 2006; Mensah, 2007; Piggott & Marra, 2008). The evolution of glyphosate-resistant weeds threatens the sustainability of these benefits, however. The number and range of glyphosate-resistant weeds has been increasing in the United States since commercialization of RR crops (Heap, 2009). The evolution of weed resistance to herbicides also poses problems for other herbicide-resistant crops, such as LibertyLink® or Clearfield® crops. The potential for pests or weeds to develop resistance in response to frequent applications of a narrow set of chemicals with the same mode of action is well established in the literature (Carlson & Wetzstein, 1993; Holt & Lebaron, 1990; Powles & Shaner, 2001; Shaner, 1995). Beckie (2006, pp. 793) identifies, “recurrent application of highly efficacious herbicides with the same site of action” and “annual weed species that occur in high population densities” as key risk factors for the evolution of herbicide resistance in weeds. However, strategies for reducing the risk of pest resistance are also well-documented (Burgos et al., 2006; Culpepper, York, & Kichler, 2008; Gressel & Segel, 1990; Monsanto, 2009a, 2009b; Mueller, Mitchell, Young, & Culpepper, 2005; Nalewaja, 1999; Prather, DiTomaso, & Holt, 2000; Steckel, Hayes, & Rhodes, 2004; Stewart, 2008). Commodity groups, extension specialists, and Monsanto have recommended that growers adopt various best management practices (BMPs) to prevent or delay the spread of glyphosateresistant weeds (Burgos et al., 2006; Culpepper et al., 2008; Monsanto, 2009a, 2009b; Steckel et al., 2004; Stewart, 2008). These strategies fall under the more general rubric of integrated weed management (IWM), components of which include weed scouting; avoidance on over-reliance on a compound or compounds with a single mode of action against weeds; preventing herbicide-resistant gene spread, non-chemical control such as tillage, and crop rotations. A key element of this strategy is diversifying herbicides used, relying on multiple compounds with different modes of action. This study examines the frequency of grower adoption of 10 different BMPs to prevent or delay weed resistance. Primary survey data on more than a thousand US corn, cotton, and soybean growers was used to characterize the nature of BMP adoption. Count-data models were estimated to explain the total number of BMPs frequently practiced. Ordered-probit regressions were used to explain the frequency of individual BMP adoption. George B. Frisvold University of Arizona