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Title: Herbicide-resistant weeds threaten soil conservation gains: finding a balance for soil and farm sustainability

Author
item SHAW, DAVID - Mississippi State University
item CULPEPPER, STANLEY - University Of Georgia
item OWEN, MICHAEL - Iowa State University
item Price, Andrew
item WILSON, ROBERT - University Of Nebraska

Submitted to: Council for Agricultural Science and Technology Issue Paper
Publication Type: Review Article
Publication Acceptance Date: 12/20/2012
Publication Date: 2/6/2012
Citation: Shaw, D.R., Culpepper, S., Owen, M., Price, A.J., Wilson, R. 2012. Herbicide-resistant weeds threaten soil conservation gains: finding a balance for soil and farm sustainability. Council for Agricultural Science and Technology Issue Paper. Paper No. 49. P. 1-16.

Interpretive Summary: With the advent of HR resistant crops and respective herbicides, tillage has become less important for weed management and, in fact, they have been the primary enabler for the success of USDA Natural Resource Conservation Service (NRCS) programs. As a result of efficacy and economics, GR crops are planted on the vast majority of corn, cotton, and soybean acres in the U.S. and many other nations. Palmer amaranth (Amaranthus palmeri) has become the dominant weed problem in southeastern U.S. cotton production because of evolved resistance to glyphosate. Inversion tillage has been clearly demonstrated to be an effective tool in managing this weed. Creative research programs have been developed which meet conservation compliance requirements and at the same time judiciously use tillage as an element for management of this species. Further research is critically needed in instances when few or no other options are available to ensure the economic viability of farming operations while addressing long-term soil quality concerns.

Technical Abstract: Tillage has been an integral part of agriculture since the dawn of civilization. Growers and scientists have long recognized both beneficial and detrimental aspects to tillage. There is no question that most tillage promotes soil loss, adversely affects surface water quality and negatively impacts soil productivity. Weed management is a primary reason for tillage, and until the development of highly effective herbicides, tillage was not optional. Furthermore, with the development of herbicide-resistant (HR) crops, particularly glyphosate-resistant (GR) crops, herbicides such as glyphosate replace the need for tillage either before or after crop planting. With the advent of HR resistant crops and respective herbicides, tillage has become less important for weed management and, in fact, they have been the primary enabler for the success of USDA Natural Resource Conservation Service (NRCS) programs. As a result of efficacy and economics, GR crops are planted on the vast majority of corn, cotton, and soybean acres in the U.S. and many other nations. However, when any single herbicide mechanism of action is used repeatedly without alternative management tactics, 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 GR weeds. A number of weed species have now exhibited resistance to glyphosate, and several are also cross-resistant to other herbicide mechanisms of action. There is now a large and growing threat to conservation gains because of the dire need to manage these resistant weeds through any means necessary, including tillage. NRCS currently has a number of herbicide resistance Best Management Practices (BMPs) that qualify for programs such as the Environmental Quality Incentive Program (EQIP). However, often these practices are not given priority status at the local level, 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 have not adequately brought these BMPs to growers, NRCS staff, and conservation district boards; without adequate and effective educational programs these practices cannot be implemented. In some instances, tillage is one of the few effective options to manage particular HR weeds. For example, Palmer amaranth (Amaranthus palmeri) has become the dominant weed problem in southeastern U.S. cotton production because of evolved resistance to glyphosate. Inversion tillage has been clearly demonstrated to be an effective tool in managing this weed. Creative research programs have been developed which meet conservation compliance requirements and at the same time judiciously use tillage as an element for management of this species. Similar programs are needed to help manage other HR species in other regions and cropping systems. Further research is critically needed in instances when few or no other options are available to ensure the economic viability of farming operations while addressing long-term soil quality concerns.