Emergence timing of volunteer canola (Brassica napus L.) in spring wheat (Triticum aestivum L.) fields in Manitoba
Lawson, Arvel Nicole
Volunteer canola is commonly observed in western Canadian cropping systems but characterization of the emergence timing of this species to date has been largely qualitative. The commercialization of genetically engineered (GE) herbicide tolerant B. napus varieties, in combination with a rise in the annual acreage of seeded canola over the past two decades, provides a partial explanation for the increased occurrence of volunteer canola in western Canada. The presence of GE herbicide tolerant volunteer canola, even at low densities, introduces several complications for crop production including the limitation of certain crops and herbicides in the years following a canola crop, the existence of a potential pollen source for the dispersal of transgenes to neighboring canola crops, weedy relatives, and subsequent canola crops, and the contamination of canola seedlots. The emergence period of volunteer canola was tracked in situ in commercial spring wheat (T. aestivum) fields located within the Aspen Parkland ecoregion of Manitoba, Canada. Monitoring of volunteer canola emergence commenced prior to wheat crop seeding and ended four weeks after in-crop herbicide application. There has been no published record of overwintering volunteer canola plants in western Canada. Thus, the volunteer canola plants observed in this study were assumed to have originated from seed germination in the spring. The production fields examined represented three common tillage regimes: conventional tillage (fall tillage and spring tillage), low disturbance direct seeding (narrow openers), and high disturbance direct seeding (wide sweeps). The emergence period of volunteer canola was seasonal in nature, with the majority of emergence occurring prior to seeding or in-crop herbicide application... Based on the observed emergence period of this species, current management practices in spring wheat appear to be well timed for the control of volunteer canola. Nevertheless, sprayer misses do allow volunteer canola plants to become part of the species metapopulation and these plants also have the potential to contribute seed to the seedbank. Growing a competitive crop such as spring wheat, which has a wide range of herbicide options available to control volunteer canola, appears to decrease the overall negative impact of volunteer canola in the year immediately following a canola crop.