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This article in CM

  1. Vol. 5 No. 1
    Accepted: Mar 07, 2006

    * Corresponding author(s): mjv@udel.edu
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Paraquat-Resistant Horseweed Identified in the Mid-Atlantic States

  1. Mark J. VanGessel *,
  2. Barbara A. Scott and
  3. Quintin R. Johnsona
  1. a Department of Plant and Soil Science, University of Delaware, Georgetown 19947


In 2003, a small percentage of horseweed (Conyza canadensis) plants survived sequential paraquat applications in a research trial conducted in a commercial field. This research project focused on determining if this horseweed population was resistant to paraquat. The susceptible biotype required a paraquat application of 0.03 lb ai/acre to reduce biomass by 50%, while the suspected-resistant biotype required 0.7 lb ai/acre. This consists of a 22-fold difference in response between the two biotypes. This is the first documented case of paraquat-resistant horseweed in the Mid-Atlantic states and the second reported case in the United States for this species.

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