Herbicide-resistant Weeds Threaten Soil Conservation Gains: Finding a Balance for Soil and Farm Sustainability

Tillage has been an integral part of crop production since crops were first cultivated. Growers and scientists have long recognized both beneficial and detrimental aspects of tillage. There is no question that most tillage operations promote soil loss, adversely affect (lower) surface water quality, and negatively impact soil productivity. Weed management is a primary reason for tillage, and until the development of highly effective herbicides, conservation tillage was not feasible. Furthermore, with the development of herbicide-resistant (HR) crops, particularly glyphosateresistant (GR) crops, herbicides such as glyphosate minimized the need for tillage as a weed control tactic; the resulting crop production systems have been primary enablers for the success of U.S. Department of Agriculture Natural Resource Soil Conservation programs. This material is based upon work supported by the U.S. Department of Agriculture’s (USDA) National Institute for Food and Agriculture (NIFA) Grants No. 201038902-20899, No. 2009-38902-20041, and No. 2008-38902-19327. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of USDA–NIFA. The balance between conservation tillage and herbicide-resistant weed management is the central issue addressed in this paper. (Left photo from ARS; middle photo from Howard F. Schwartz, Colorado State University, Bugwood.org; right photo from Shutterstock.) Herbicide-resistant Weeds Threaten Soil Conservation Gains: Finding a Balance for Soil and Farm Sustainability Glyphosate-resistant crops are planted on the majority of canola, corn, cotton, soybean, and sugarbeet acres in the United States and many other nations as a result of efficacy and economics. When any single herbicide mechanism of action is used repeatedly without alternative management tactics, however, selection pressure becomes intense for plants that are tolerant or resistant to that herbicide. The unintended consequence of the predominance of GR crops on the agricultural landscape has been intense selection pressure for the development of GR weeds. Several weed species now exhibit resistance to glyphosate, and most are also resistant to other herbicide mechanisms of action. There is now a large and growing threat to soil conservation gains because of the dire need in some situations to manage these resistant weeds through any means necessary, including tillage. Importantly, there are situations where the farmer does not need to modify or abandon his current conservation tillage practices in order to manage a resistant weed population. Best management practices (BMPs) that have been established for both proactive and reactive management of HR populations include recommendations on how to manage HR populations without the need for farmers to abandon conservation tillage systems. The Natural Resources Conservation Service (NRCS) currently has a number of herbicide resistance BMPs that qualify for programs such as the Environmental Quality Incentive Program. Often these practices, however, are not given priority status, and therefore they either are not listed as options at the local level or are not funded by soil conservation district boards. Additionally, educational programs are not adequately bringing these BMPs to growers, NRCS staff, and