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International Journal of Agronomy
Volume 2012 (2012), Article ID 168267, 7 pages
http://dx.doi.org/10.1155/2012/168267
Research Article

Interference of Selected Palmer Amaranth (Amaranthus palmeri) Biotypes in Soybean (Glycine max)

1Department of Crop Science, North Carolina State University, P.O. Box 7620, Raleigh, NC 27695-7620, USA
2Department of Horticulture Science, North Carolina State University, P.O. Box 7609, Raleigh, NC 27695, USA
3Department of Crop and Soil Sciences, University of Georgia, P.O. Box 478, Tifton, GA 31794, USA
4Department of Crop and Soil Sciences, University of Georgia-Southeast District, P.O. Box 8112, Statesboro, GA 30460, USA

Received 30 April 2012; Revised 16 July 2012; Accepted 20 July 2012

Academic Editor: Kassim Al-Khatib

Copyright © 2012 Aman Chandi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Palmer amaranth (Amaranthus palmeri S. Wats.) has become difficult to control in row crops due to selection for biotypes that are no longer controlled by acetolactate synthase inhibiting herbicides and/or glyphosate. Early season interference in soybean [Glycine max (L.) Merr.] for 40 days after emergence by three glyphosate-resistant (GR) and three glyphosate-susceptible (GS) Palmer amaranth biotypes from Georgia and North Carolina was compared in the greenhouse. A field experiment over 2 years compared season-long interference of these biotypes in soybean. The six Palmer amaranth biotypes reduced soybean height similarly in the greenhouse but did not affect soybean height in the field. Reduction in soybean fresh weight and dry weight in the greenhouse; and soybean yield in the field varied by Palmer amaranth biotypes. Soybean yield was reduced 21% by Palmer amaranth at the established field density of 0.37 plant m−2. When Palmer amaranth biotypes were grouped by response to glyphosate, the GS group reduced fresh weight, dry weight, and yield of soybean more than the GR group. The results indicate a possible small competitive disadvantage associated with glyphosate resistance, but observed differences among biotypes might also be associated with characteristics within and among biotypes other than glyphosate resistance.