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1 April 2006 Variable Response of Common Waterhemp (Amaranthus rudis) Populations and Individuals to Glyphosate
DAVID A. SMITH, STEVEN G. HALLETT
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Abstract

Putatively resistant (PR) and putatively susceptible (PS) common waterhemp populations were grown in the greenhouse and sprayed at the three- to four-leaf stage with glyphosate (0.63 kg ae/ha). Surviving plants from PR populations and randomly selected plants from PS populations were clonally propagated and the clones were sprayed with 0.1 to 10.0 kg/ha glyphosate. The glyphosate rates required to reduce growth by 50% (GR50) among the clones were relatively similar, but the concentration required to reduce growth by 90% (GR90) ranged from 1.5 to 16.3 kg/ha. The concentration of glyphosate required to kill 90% of plants (LD90) ranged from 2.3 kg/ha to over 10.0 kg/ ha. This range of responses to glyphosate in common waterhemp clones from different parts of the Midwestern United States indicates a risk of evolution of resistance in common waterhemp populations that are repeatedly selected by applications of glyphosate in the field.

Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer #3 AMATA.

Additional index words: Dose response, herbicide resistance, herbicide tolerance.

Abbreviations: GR50, the concentration of glyphosate required to reduce dry weights by 50%; GR90, the concentration of glyphosate required to reduce dry weights by 90%; LD90, the concentration of glyphosate required to kill 90% of plants; PR, putatively resistant; PS, putatively susceptible.

DAVID A. SMITH and STEVEN G. HALLETT "Variable Response of Common Waterhemp (Amaranthus rudis) Populations and Individuals to Glyphosate," Weed Technology 20(2), 466-471, (1 April 2006). https://doi.org/10.1614/WT-05-068R1.1
Published: 1 April 2006
JOURNAL ARTICLE
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