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Resistant weeds jeopardize soil conservation

Selection pressure has resulted in weed species that have made adaptations for survival in conjunction with tillage.

Herbicides were developed during the twentieth century to be used with conventional tillage for weed control. Conservation (or minimum) tillage subsequently evolved, which enabled less soil damage when used with herbicides. Selection pressure, however, has resulted in weed species that have made adaptations for survival in conjunction with tillage. A new Issue Paper from CAST, Herbicide-resistant Weeds Threaten Soil Conservation Gains: Finding a Balance for Soil and Farm Sustainability, examines the impact of certain weed management practices on soil conservation objectives and addresses ways to mitigate negative effects.   

The U.S. government has put several federal policies and programs in place that help determine the selection and implementation of crops and conservation programs in relation to herbicides and tillage. The authors of this paper discuss those programs with regard to:

  • The disagreement among organizations, there being no simple solutions;
  • The need for collaboration among all parties; and
  • A case study of Palmer amaranth, "one of the most high-profile problems," in Georgia cotton.

The balance between conservation tillage and herbicide-resistant (HR) weed management is the central issue addressed in the paper. As the authors state, "The fundamental conflict facing many producers with HR weed management issues today is the choice between using tillage or land stewardship practices that protect soil and water resources."

A few of the paper's conclusions include the following:  

  • Soil conservation is threatened by HR weeds
  • Growers are including and/or intensifying tillage practices because of HR weeds
  • Education programs are needed to show how HR weeds can be managed without losing recent gains
  • More research is necessary regarding HR weed management and soil conservation goals

Task Force Authors:

  • David Shaw, Chair, Mississippi State University
  • Stanley Culpepper, University of Georgia
  • Micheal Owen, Iowa State University
  • Andrew Price, National Soil Dynamics Laboratory
  • Robert Wilson, University of Nebraska

The full text of Issue Paper 49 may be accessed free of charge on the CAST website at, along with many of CAST's other scientific publications. The paper also is available in hard copy for a shipping/handling fee. CAST is an international consortium of scientific and professional societies, companies, and nonprofit organizations. It assembles, interprets, and communicates credible science-based information regionally, nationally, and internationally to legislators, regulators, policymakers, the media, the private sector, and the public.

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