Angiosperm Flora of India

Frequency, Distribution, and Characterization of Horseweed ( Conyza canadensis ) Biotypes with Resistance to Glyphosate and ALS-Inhibiting Herbicides

Publication Type:Journal Article
Year of Publication:2009
Authors:Kruger, GR, Davis, VM, Weller, SC, Stachler, JM, Loux, MM, Johnson, WG
Journal:Weed Science
Date Published:2009
ISBN Number:00431745

Greenhouse studies were conducted to determine the prevalence of resistance to acetolactate synthase (ALS)-inhibiting herbicides in 266 Indiana horseweed populations, both glyphosate-susceptible and glyphosate-resistant, and to characterize the response of selected biotypes to combinations of glyphosate and doransulam. Populations with individuals resistant to ALS inhibitors were more frequent in the northern half (38% of the populations in the NW and 50% of the populations in the NE) of Indiana than in the southern half (26% of the populations in the SW and 5% of the populations in the SE).Only 2% of the populations appeared to be resistant to both glyphosate and ALS inhibitors in an initial greenhouse study.Horseweed populations with resistance to ALS inhibitors exhibited herbicide doses required for 50% reduction in plant growth (GR50) values ranging from 14 to 255 g ai ha of cloransulam. The resistant : susceptible (R: S) ratio for four horseweed populations with suspected resistance to glyphosate and ALS inhibitors ranged from 0.3 to 50 and from 2.5 to 8.1 for cloransulam and glyphosate, respectively. The tank mixtures exhibited an antagonistic response to 3 of the 16 combinations of cloransulam and glyphosate on the susceptible population. The tank mixtures exhibited primarily an additive response to those same combinations in the multiple-resistant populations, but the response was occasionally synergistic for two of the four populations. The additive response between glyphosate and cloransulam indicates that, where the level of resistance is fairly low, combinations of these herbicides should be more effective for control of multipleresistant populations compared with application of a single herbicide.

Short Title:Weed Science
Taxonomic name: 
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