Response of selected horseweed (Conyza canadensis (L.) Cronq.) populations to glyphosate
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Protocols for Robust Herbicide Resistance Testing in Different Weed Species
Published on: July 2, 2015
Christopher L Main1, Thomas C Mueller, Robert M Hayes
1Department of Plant Sciences, The University of Tennessee, 2431 Joe Johnson Drive, 252 Ellington Plant Sciences Building, Knoxville, Tennessee, 37996, USA.
Abstract:
Horseweed (Conyza canadensis (L.) Cronq.) seed was collected in Illinois, Indiana, Kentucky, Mississippi, Missouri, and Ohio to determine susceptibility of different horseweed biotypes to glyphosate. Horseweed resistant to glyphosate was found in Mississippi, Ohio, and western Tennessee. In a separate experiment examining Tennessee biotypes, a dose response curve demonstrated that four times as much glyphosate was needed to achieve a 50% fresh weight reduction (GR(50)) in resistant biotypes when compared to a susceptible biotype. Resistant biotypes from Tennessee displayed a GR(50) of 1.6 kg/ha as compared to a GR(50) of 0.4 kg/ha in a susceptible horseweed population. Although growth was reduced, the resistant plants did not completely die and could potentially produce seed. Variation in glyphosate resistance was found among the populations tested.
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