Response of Selected Horseweed (Conyza canadensis (L.) Cronq.) Populations to Glyphosate

• Published in: Journal of agricultural and food chemistry Vol. 52; no. 4; pp. 879 - 883
• Main Authors: Main, Christopher L, Mueller, Thomas C, Hayes, Robert M, Wilkerson, John B
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 25.02.2004
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; biotypes; Chemical constitution; Chemical control; Conyza - drug effects; Conyza canadensis; Dose-Response Relationship, Drug; Drug Resistance; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Glycine - analogs & derivatives; Glycine - pharmacology; Glyphosate; herbicidal properties; herbicide resistance; herbicide-resistant weeds; Herbicides - pharmacology; Midwestern United States; Parasitic plants. Weeds; Phytopathology. Animal pests. Plant and forest protection; plant growth; plant response; Southeastern United States; Tennessee; Weeds; Midwestern United States; Southeastern United States; Tennessee; Agricultural chemical product; Conyza canadensis; Weed; Pesticides; Geographical origin; Compositae; Glyphosate; Herbicide; horseweed; Sensitivity resistance; horseweed distribution; Dicotyledones; Angiospermae; Distribution; Spermatophyta; glyphosate resistance
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf0351927

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 (GR50) in resistant biotypes when compared to a susceptible biotype. Resistant biotypes from Tennessee displayed a GR50 of 1.6 kg/ha as compared to a GR50 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. Keywords: Glyphosate; glyphosate resistance; horseweed; Conyza canadensis; horseweed distribution