781 Research Article Received: 19 May 2010 Revised: 3 January 2011 Accepted: 23 February 2011 Published online in Wiley Online Library: 2 May 2011 (wileyonlinelibrary.com) DOI 10.1002/ps.2177 Benchmark study on glyphosate-resistant cropping systems in the United States. Part 5: Effects of glyphosate-based weed management programs on farm-level profitability † Jason W Weirich, a* David R Shaw, a Micheal DK Owen, b Philip M Dixon, b Stephen C Weller, c Bryan G Young, d Robert G Wilson e and David L Jordan f Abstract BACKGROUND: Glyphosate-resistant (GR) crops have changed the way growers manage weeds and implement control strategies. Since the introduction of GR crops, growers in many instances have relied on glyphosate almost exclusively to control a broad spectrum of weeds. This overreliance on glyphosate has resulted in the evolution of glyphosate resistance in some weed species. Growers and scientists are concerned about the sustainability of GR crops and glyphosate. When a grower is making decisions about weed control strategies, economic costs and benefits of the program are primary criteria for selection and implementation. Studies across six states were initiated in 2006 to compare the economics of using a weed resistance best management practice (BMP) system with a grower’s standard production system. RESULTS: Resistance BMP systems recommended by university scientists were more costly but provided similar yields and economic returns. Rotation of GR crops resulted in a higher net return (maize and soybean) compared with continuous GR crop (cotton or soybean) or rotating a GR crop with a non-GR crop (maize). CONCLUSION: Growers can implement weed resistance BMP systems with the confidence that their net returns will be equivalent in the short run, and, in the long term, resistance BMP systems will prevent or delay the evolution of GR weeds in their fields, resulting in substantial savings. c  2011 Society of Chemical Industry Keywords: resistance management; glyphosate; glyphosate resistance; glyphosate-resistant crops; economic benefit 1 INTRODUCTION Since the introduction of glyphosate-resistant maize (Zea mays L.), cotton (Gossypium hirsutum L.) and soybean [Glycine max L. (Merr.)] in 1998, 1997 and 1996, respectively, in the United States, the reliance on glyphosate as the primary or exclusive weed control tool has increased dramatically. Herbicide-resistant crops have the ability to increase weed control efficacy, simplify weed management and increase different herbicide sites of action used on a given crop to deal with resistant weed management strategies. 1–3 Glyphosate-resistant (GR) crops provide growers with the flexibility to control a wide range of weeds with little or no crop injury. 4–8 GR crops have increased confidence in weed control, which has increased the popularity of conservation tillage. 9 Other benefits that a grower may perceive when implementing a GR crop may include improved weed control, reduced management and labor inputs, less reliance on tillage for weed control and reduced herbicide cost. 9–12 Glyphosate has been an effective herbicide to control weeds that have evolved resistance to other herbicide modes of action. 13,14 Glyphosate inhibits the growth of plants by affecting aromatic amino acid biosynthesis through the inhibition of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS; 2.5.1.19) of the shikimate pathway. 15,16 With the introduction of GR crops, glyphosate can be applied directly to the crop with little concern for injury. However, since the introduction of GR crops, the use of tank mixtures and sequential applications of more than one family of herbicides has decreased, as many growers rely solely on glyphosate for weed control. Use of herbicide-resistant crops could increase ∗ Correspondence to: Jason W Weirich, Plant and Soil Sciences Department, Mississippi State University, 117 Dorman Hall, Mississippi State, MS 39762, USA. E-mail: weirichj@missouri.edu † This research was funded by Monsanto Company. a Mississippi State University, Mississippi State, MS, USA b Iowa State University, Ames, IA, USA c Purdue University, West Lafayette, IN, USA d Southern Illinois University, Carbondale, IL, USA e University of Nebraska-Lincoln, Scotts Bluff, NE, USA f North Carolina State University, Raleigh, NC, USA Pest Manag Sci 2011; 67: 781–784 www.soci.org c  2011 Society of Chemical Industry