Management in Soybean and Investigating mechanisms of glyphosate resistance in an Ontario common ragweed (Ambrosia artemisiifolia L.) biotype
Glyphosate-resistant (GR) common ragweed was first reported near Windsor, Ontario from seed collected in 2011. Common ragweed was previously reported to be resistant to glyphosate in the United States in 2004; however, the mechanism(s) conferring glyphosate resistance in these biotypes has (have) not been identified. Therefore, the purpose of this research was to identify alternative herbicides to control glyphosate-resistant common ragweed in soybean and investigate known mechanisms of resistance to determine the mechanism of glyphosate resistance in the Ontario GR common ragweed biotype. Field experiments established close to Windsor, Ontario concluded that sequential applications of saflufenacil/dimethenamid-P, linuron, or metribuzin preplant (PP) followed by (fb) fomesafen postemergence (POST) provided more consistent control of GR common ragweed than a single application of any of these herbicides in soybean. The “metribuzin biologically effective rate” study concludes that a minimum of 786 g a.i. ha-1 is required for 95% control of GR common ragweed in soybean. This study concludes that GR common ragweed can be controlled with a PP followed by POST herbicide program and that metribuzin has a role in the control of GR common ragweed in soybean. In addition, in dicamba-resistant (DR) soybean, control of GR common ragweed was most consistent with sequential applications of dicamba. At 28 days after the post-emergence application (DAB), dicamba applied PP (fb) POST at 300 fb 300 g a.e. ha-1, 300 fb 600 g a.e. ha-1, or 600 fb 300 g a.e. ha-1 provided up to 98, 99 and 99% GR common ragweed control, respectively. Glyphosate resistance in the GR Ontario common ragweed biotype was not due to mutations at positions 102 and 106 in the EPSPS gene, or due to reduced absorption and translocation of glyphosate compared to the susceptible biotype. Further research is required to determine the mechanism of resistance in this biotype.
Holly P. Byker, Annemarie C. Van Wely, Nadar Soltani, Mark B. Lawton, Darren E. Robinson, and Peter H. Sikkema. Single and sequential applications of dicamba for the control of glyphosate-resistant common ragweed in glyphosate- and dicamba-resistant soybean. Canadian Journal of Plant Science. 98(3): 552-556. https://doi.org/10.1139/cjps-2017-0118