The Frequency and Persistence of Volunteer Canola (Brassica napus) in Québec Cropping Systems^*

Abstract

The presence of volunteer canola is becoming a significant agro-ecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer canola in Québec cropping systems by surveying fields that included a single canola crop since 1995. A survey was conducted in 131 fields in the main canola-growing areas of Québec: in the Saguenay-Lac Saint-Jean region and the Québec City–La Pocatière area. Volunteer canola plants were counted in 0.25-m2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer canola plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, corn, and soybean. Average densities of 4.9 and 3.9 plants/m2 were found 1 yr after canola production in fields and field margins, respectively. Volunteer canola densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 yr after production. Dense stands of volunteer canola were found before postemergence herbicide application in no-till fields (9.8 ± 4.1 plants/m2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer canola plants observed in no-till fields near Québec City and Ottawa included plants that had overwintered, either originating from fall-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer canola may not have been a cause of concern until now. However, producers should be made more aware of the potential short-and long-term problems associated with potential gene flow between different herbicide-tolerant canola (HT canola) varieties and also between HT canola and related weed species.

The Biology of Canadian Weeds. 137. Brassica napus L. and B. rapa L.

“…In Quebec, rootstocks of B. napus may remain alive after harvest, overwinter, and regrow as volunteers the following year (Simard et al 2002). Similar observations have not been reported in B. rapa.…”

“…(b) Seed Production and Dispersal * In eastern Canada, domesticated B. napus that overwintered as a rootstock after harvest produced more than 3000 seeds plant (1 as a volunteer during the following season (Simard et al 2002). No information on seed production in volunteer B. napus in western Canada was found in the literature.…”

“…In fields, the seed bank and population density of volunteer B. napus and B. rapa decreases rapidly with increasing time since the last canola crop in Canada (Simard et al 2002;Gulden et al 2003b;Gulden et al 2004b) and Europe Lutman et al 2003). In Saskatchewan, the seed bank population was 23 to 40%, B2%, and negligible in the first, second, and third spring after seed bank establishment, in a study where seed bank replenishment was not allowed (Gulden et al 2003b).…”

Long-term persistence of GM oilseed rape in the seedbank

“…Available studies demonstrate that OSR persists for 5-6 or up to 8 years in agricultural fields (Simard et al 2002; …”

“…In general, studies suggest that the majority of seeds disappear from the seedbank within 2 years (Crawley et al 1993(Crawley et al , 2001Simard et al 2002). Recent models predict over 10-year OSR seed persistence in cultivated soil (Lutman et al 2005;Begg et al 2006), but empirical studies confirming this have not been available (but see Messean et al 2007).…”