The impact of seed treatment, cultivar and crop density on canola (Brassica napus) competitiveness against volunteer barley (Hordeum vulgare)
Canola is an important crop in western Canada that has become intensively managed with purchased inputs. By knowing the relative contribution of seed treatment, seeding rate, and cultivar to canola competitiveness against weeds and yield producers can adjust input decisions and maintain yield goals but increase net gain. Field experiments took place during 1999 and 2000 in the Brandon region of western Manitoba. Treatments included; two canola cultivars (Invigor 2273 &, Exceed), the presence/absence of volunteer barley, four target canola densities (37.5, 75, 150 & 300 plant/m2) and four seed treatments (non-treated, mixture of thiamethoxam, difenoconazole, fludioxonil and metalaxyl-M (Helix), and a mixture of lindane, carbathiin and thiram (Vitavax RS) with and without furrow placed terbufos (Counter). Using greenhouse experiments we examined the effect of seed treatment on canola's competitiveness in the absence of pests using a target neighbour design. In general, cultivar and seeding rate influenced canola growth, yield and competitiveness greater than seed treatment. Crop stand was only affected by seeding rate. Seed treatment offered excellent protection from flea beetles, but protection did not always translate into improved canola growth, weed suppression or yield gain. In the absence of pests Vitavax RS hindered canola competitiveness, while Helix was similar to bare seed. The hybrid variety Invigor was more competitive with weeds and higher yielding than Exceed canola. Early, vigorous seedling growth resulting from using a seed treatment may not be as important for canola competitiveness as vigor from heterosis and crop density. Thiamethoxam was a good replacement for the environmentally problematic lindane for flea beetle management; however, producers with moderate to low flea beetle infestation or those interested in integrated pest management may be better off increasing seeding rate or using a hybrid variety to help control weeds and better optimize yield.