Byker, H. P., Soltani, N., Robinson, D. E., Tardif, F. J., Lawton, M. B. and Sikkema, P. H. 2013. Occurrence of glyphosate and cloransulam resistant Canada fleabane ( Conyza canadensis L. Cronq.) in Ontario. Can. J. Plant Sci. 93: 851–855. Canada fleabane is the second documented glyphosate-resistant (GR) weed species in Ontario, Canada. In 2010, the first eight GR Canada fleabane populations were identified in Essex County. In 2011 and 2012, an expanded survey was conducted to identify the occurrence of GR and cloransulam-resistant populations in Ontario. Seed was collected from field weed escapes in the early fall and sprayed in the greenhouse with 900 g a.e. ha−1 of glyphosate at the 10-cm rosette stage. Ninety-three and 54 additional sites were confirmed in 2011 and 2012, respectively. There are now 155 sites with confirmed GR Canada fleabane in Ontario in the counties of Elgin, Essex, Haldimand, Huron, Kent, Lambton, Middlesex, and Niagara region. Twelve and seven sites were identified with multiple resistant Canada fleabane (glyphosate and cloransulam) in 2011 and 2012, respectively in Elgin, Essex, Kent, Lambton, and Middlesex counties. This is the first survey documenting the occurrence of glyphosate-resistant and multiple resistant (glyphosate and cloransulam) Canada fleabane in Ontario and its distribution.

Vink, J. P., Soltani, N., Robinson, D. E., Tardif, F. J., Lawton, M. B. and Sikkema, P. H. 2012. Occurrence and distribution of glyphosate-resistant giant ragweed ( Ambrosia trifida L.) in southwestern Ontario. Can. J. Plant Sci. 92: 533–539. Giant ragweed is the first confirmed glyphosate-resistant (GR) weed in Canada. A survey was conducted to document the distribution of GR giant ragweed in southwestern Ontario. Giant ragweed seed was collected from 102 sites in Essex (70), Chatham-Kent (21), Lambton (10) and Waterloo counties (1) during the autumn of 2009 and 2010 prior to soybean harvest. Plants were grown in a growth room, sprayed with glyphosate at 1800 g a.e. ha−1 and classified as resistant or susceptible. GR giant ragweed has been confirmed at 47 new locations in three counties (Essex, Chatham-Kent and Lambton). The results from this survey indicate that GR giant ragweed biotypes occur across a greater area in southwestern Ontario than originally thought. This survey provides an important baseline for future surveys in the province.

Vink, J. P., Soltani, N., Robinson, D. E., Tardif, F. J., Lawton, M. B. and Sikkema, P. H. 2012. Glyphosate-resistant giant ragweed ( Ambrosia trifida L.) control with preplant herbicides in soybean [ Glycine max (L.) Merr.]. Can. J. Plant Sci. 92: 913–922. Giant ragweed populations in southwestern Ontario have evolved resistance to glyphosate. Glyphosate-resistant (GR) giant ragweed interference in field crops can lead to significant yield losses. Eleven field trials [five with preplant (PP) burndown only and six with PP burndown plus residual herbicides] were conducted in 2010 and 2011 on Ontario farms with GR giant ragweed to evaluate the efficacy of various PP herbicides applied prior to soybean planting. Glyphosate applied at the recommended field dose failed to adequately control GR giant ragweed. The PP herbicides 2,4-D ester, cloransulam-methyl and saflufenacil applied alone and with glyphosate provided 97–99, 68–100 and 71–94% control, respectively and resulted in soybean yields equivalent to the weed-free check. Combinations of glyphosate plus cloransulam-methyl or linuron controlled GR giant ragweed 8 wk after application (WAA), 75–95 and 95–98%, respectively. Residual control with glyphosate plus linuron resulted in soybean yield equivalent to the weed-free check. Based on these results, GR giant ragweed can be controlled prior to soybean planting in southwestern Ontario.

Byker, H. P., Soltani, N., Robinson, D. E., Tardif, F. J., Lawton, M. B. and Sikkema, P. H. 2013. Control of glyphosate-resistant Canada fleabane [ Conyza canadensis (L.) Cronq.] with preplant herbicide tankmixes in soybean [ Glycine max . (L). Merr.]. Can. J. Plant Sci. 93: 659–667. Glyphosate previously provided excellent control of Canada fleabane; however, with the evolution of glyphosate-resistant (GR) Canada fleabane in Ontario, alternative herbicides must be identified for control of this weed in soybean. The objective of this study was to identify preplant herbicide tankmixes that provide effective control of GR Canada fleabane. A total of 12 field trials were completed over a 2-yr period (2011, 2012) in fields previously confirmed with GR Canada fleabane. Preplant tankmixes of glyphosate (900 g a.e. ha−1) plus saflufenacil (25 g a.i. ha−1) or saflufenacil/dimethenamid-p (245 g a.i. ha−1) provided greater than 87% control 4 wk after application (WAA) across all sites. Glyphosate (900 g a.e. ha−1) tankmixed with metribuzin (1120 g a.i. ha−1), cloransulam-methyl (35 g a.i. ha−1) or flumetsulam (70 g a.i. ha−1) provided 78 to 99% control 8 WAA. Control of GR Canada fleabane prior to soybean emergence is essential as currently there are no herbicides that provide acceptable control in-crop. Because of the lack of in-crop options, spring residual herbicides may be required for season long control in regions where Canada fleabane emerges throughout the year to reduce Canada fleabane seed production and populations in subsequent years.

Ford, L., Soltani, N., Robinson, D. E., Nurse, R. E., McFadden, A. and Sikkema, P. H. 2014. Canada fleabane (Conyza canadensis) control with preplant applied residual herbicides followed by 2,4-D choline/glyphosate DMA applied postemergence in corn. Can. J. Plant Sci. 94: 1231–1237. Glyphosate resistant (GR) Canada fleabane (Conyza canadensis) is an extremely problematic weed in no-tillage farming operations. A total of five field trials were conducted over a 2-yr (2012 and 2013) period in Ontario to determine the level of GR Canada fleabane control with a two-pass weed control program of a pre plant (PP) residual herbicide followed by 2,4-D choline/glyphosate dimethylamine (DMA) applied POST. Among residual herbicide treatments evaluated, s-metolachlor (1600 g a.i. ha−1)+flumetsulam (50 g a.i. ha−1)+clopyralid (135 g a.e. ha−1) provided the most consistent (95–99%) control across all sites 8 wk after application (WAA). S-metolachlor/atrazine (1800 g a.i. ha–1) did not provide effective GR Canada fleabane control (21–86%) 8 WAA. The preplant residual herbicides followed by 2,4-D choline/glyphosate DMA (1720 g a.e. ha−1) POST provided 97–100% control. Glyphosate (900 g a.e. ha−1) applied PP followed by 2,4-D choline/glyphosate DMA POST provided 80–93% control 8 WAA. The application of 2,4-D choline/glyphosate DMA POST following any PP residual herbicide resulted in 97% or greater control of GR Canada fleabane. Results from this research demonstrate that residual herbicides applied PP followed by 2,4-D choline/glyphosate DMA POST provides excellent control of GR Canada fleabane, and also incorporates different modes of action thereby limiting the selection of resistant weeds.