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1 July 2006 Glyphosate-resistant Palmer amaranth (Amaranthus palmeri ) confirmed in Georgia
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A glyphosate-resistant Palmer amaranth biotype was confirmed in central Georgia. In the field, glyphosate applied to 5- to 13-cm-tall Palmer amaranth at three times the normal use rate of 0.84 kg ae ha−1 controlled this biotype only 17%. The biotype was controlled 82% by glyphosate at 12 times the normal use rate. In the greenhouse, I50 values (rate necessary for 50% inhibition) for visual control and shoot fresh weight, expressed as percentage of the nontreated, were 8 and 6.2 times greater, respectively, with the resistant biotype compared with a known glyphosate-susceptible biotype. Glyphosate absorption and translocation and the number of chromosomes did not differ between biotypes. Shikimate was detected in leaf tissue of the susceptible biotype treated with glyphosate but not in the resistant biotype.

Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats; AMAPA.

A. Stanley Culpepper, Timothy L. Grey, William K. Vencill, Jeremy M. Kichler, Theodore M. Webster, Steve M. Brown, Alan C. York, Jerry W. Davis, and Wayne W. Hanna "Glyphosate-resistant Palmer amaranth (Amaranthus palmeri ) confirmed in Georgia," Weed Science 54(4), 620-626, (1 July 2006).
Received: 3 January 2006; Accepted: 1 April 2006; Published: 1 July 2006

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