Agronomic and environmental factors influence weed composition and canola competitiveness in southern Manitoba

Canola yield in Manitoba has reached a plateau in recent years. The causes for this, as related to agronomic, environmental, weed interference and canola competitiveness factors, were identified using observational data from 31 canola fields in southern Manitoba in a 2-yr on-farm research study. Agronomic and environmental factors contributing to weed density and composition were determined with multivariate canonical correspondence analysis. Agronomic and environmental factors most influential on absolute and relative canola biomass were determined with multiple regression analysis. Most weeds were adaptable across a broad range of crop environments; however, some functional groups of weeds were either positively or negatively favored by specific environmental or agronomic conditions. Absolute canola biomass prior to bolting was greater as soil growing degree days (GDD) increased and canola was dense and seeded early. Lower weed density, increased soil GDD, and reduced surface soil moisture were significant factors contributing to higher relative canola biomass. Results from this study indicate that seeding canola early and at a rate sufficient. to achieve a dense crop stand can increase canola competitiveness and reduce weed interference.