Life cycle management of volunteer canola (Brassica napus L.) in western Canada
Geddes, Charles M.
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Volunteer canola (Brassica napus) is among the top five most abundant weed species in western Canada. Yet, several knowledge gaps in volunteer canola management remain, particularly in crops with herbicide-resistance traits similar to canola [i.e., soybean (Glycine max)]. Large seed losses at harvest, seedbank persistence, phenotypic plasticity, rapid growth and development, efficient resource uptake and prolific plant fecundity all contribute to volunteerism in this crop species. This thesis research consisted of five field studies conducted in Manitoba, Canada, from 2013 to 2016 and aimed to discover effective tools for management of volunteer canola with particular focus on effective management for soybean production. Soil disturbance in early autumn, shortly after canola harvest, halved the persistence of volunteer canola over winter compared with zero tillage. Early autumn soil disturbance doubled autumn seedling recruitment, regardless of tillage implement, and winterkill effectively terminated the volunteer canola seedlings. Soil texture contributed to opposing seasonal dynamics of the volunteer canola seedbank. Soils with fine texture (clays) were associated with greater survival of volunteer canola seed over winter, but reduced seed survival over summer compared with coarse textured soils (loamy sands). Volunteer canola was a competitive weed in soybean due to rapid growth and development during soybean establishment. Individual cultural or physical weed management tools in soybean had minimal effect on volunteer canola seed production or biomass accumulation when implemented alone. Spring-seeded inter-row living cereal mulches in soybean, however, interfered with volunteer canola early during the growing-season and reduced volunteer canola seed production by about one-third (by up to 9,000 seeds m^-2). In another study, volunteer canola interference with soybean increased as soil mineral N increased. This research showed that volunteer canola is a competitive weed that is difficult to manage in soybean production. Using timely post-harvest soil disturbance for volunteer canola seedbank depletion, planting soybean on fields with limited soil mineral N and growing inter-row living cereal mulches with soybean for early-season interference with volunteer canola should be effective components of an integrated program for management of volunteer canola in western Canada.