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.

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.

. 2013. Glyphosate-resistant Canada fleabane [Conyza canadensis (L). Cronq.]: Dose response to glyphosate and control with postemergence herbicides in soybean in Ontario. Can. J. Plant Sci. 93: 1187Á1193. Glyphosate-resistant (GR) Canada fleabane was first reported in Ontario in 2010. Twelve field studies were conducted over a 2-yr period (2011, 2012) to determine the biologically effective dose of glyphosate in the field and to determine the efficacy of postemergence herbicides for control of GR Canada fleabane. A dose between 1271 and 5652 g a.e. ha(1 was required for a 50% reduction in Canada fleabane biomass depending on site and year. To achieve acceptable (95%) control with glyphosate, 18 840 to 43 200 g a.e. ha(1 of glyphosate was required across all sites. Therefore application of glyphosate at these doses for acceptable ( 95%) control is not economical. None of the postemergence herbicides labeled for use in soybean provided acceptable (95%) control, with cloransulam providing the greatest control (67%) 4 wk after application. Therefore, GR Canada fleabane must be controlled prior to soybean emergence as current herbicides registered in soybean for postemergence use do not provide sufficient control to prevent soybean yield loss. (2011, 2012), les auteurs ont proce´de´a`douze e´tudes sur le terrain en vue d'e´tablir la dose de glyphosate biologiquement efficace au champ et de de´terminer l'efficacite´des herbicides post-leve´e contre la vergerette du Canada RG. Il faut entre 1 271 et 5 652 g de matie`re active par hectare pour re´duire la biomasse de la vergerette de moitie´, selon le site et l'anne´e. Pour parvenir a`un degre´de lutte acceptable ( 95 %) avec le glyphosate, il a fallu appliquer 18 840 a`43 200 g de matie`re active par hectare at ous les sites. Pareille quantite´de glyphosate pour arriver a`combattre la vergerette de manie`re acceptable ( 95 %) ne s'ave`re pas e´conomique. Aucun des herbicides post-leve´e susceptibles d'eˆtre utilise´s avec le soya, selon l'e´tiquette, n'autorise une lutte acceptable (95 %) contre la vergerette du Canada, le cloransulam donnant les meilleurs re´sultats (67 %), quatre semaines apre`s application. En conclusion, la vergerette du Canada RG doit eˆtre de´truite avant la leve´e du soya, car les herbicides actuellement homologue´s pour une application post-leve´e dans la culture ne permettent pas une lutte ade´quate pour e´viter les pertes de rendement.