Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2009
Publication Date: 10/1/2009
Citation: Burke, I.C., Reddy, K.N., Bryson, C.T. 2009. Pitted and Hybrid Morningglory Accessions Have Variable Tolerance to Glyphosate. Weed Technology. 23:592-598. Interpretive Summary: Morninglories are among the most troublesome weeds in agricultural and non-agricultural land throughout the U.S. Pitted morningglory is the most prevalent among morningglory complex that has become a difficult-to-control weed in the southern United States. Control of pitted morningglory in Roundup Ready crops with glyphosate is variable. Scientists at Southern Weed Science Research Unit, Stoneville, MS have conducted studies to investigate the variability in tolerance to glyphosate among 38 biotypes of pitted morningglory collected across southern United States. Pitted morningglory control with glyphosate ranged from 24 to 75% among the biotypes. This 51 percentage point range between the least and the most tolerant biotype indicated that the most tolerant biotype was 3-fold more tolerant than the least tolerant biotype. These results indicate the existence of variable tolerance to glyphosate at 0.5 lb/acre among the biotypes of pitted morningglory.
Technical Abstract: Greenhouse studies were conducted to investigate the variability in tolerance to glyphosate among 38 accessions of pitted morningglory collected from several southern United States. Glyphosate at 420 g ae/ha was applied postemergence to plants at 4- to 5-leaf stage and control was visually estimated 2 wk after treatment (WAT). Pitted morningglory control ranged from 24 to 75% among the accessions. This 51 percentage point range between the least and the most tolerant accession indicated that the most tolerant accession was 3-fold more tolerant than the least tolerant accession. No correlation was found between collection site (habitat) and the level of glyphosate tolerance. Control of two related species, cypressvine morningglory and red morningglory averaged 71 and 63%, respectively, and was similar to control of the most susceptible pitted morningglory accessions. Ivyleaf morningglory control with glyphosate was 50%. These results indicate the existence of variable tolerance to glyphosate at 420 g/ha among the accessions of pitted morningglory.