Integrated approaches to managing weeds in spring-sown crops in western Canada

In western Canada, the move to integrated weed management (IWM) with reduced dependence on herbicides is being driven by low crop prices, weed resistance to herbicides, and environmental concerns. A rational step when implementing IWM is to determine if herbicide application is required in the first place. Crop yield loss models have been developed to assist with this decision. However, the weed economic threshold will be influenced considerably by management practices. Field studies showed that enhancing crop competitiveness through planting competitive varieties at relatively high seeding rates and through strategic fertilizer placement including sub-surface banded or point-injected nitrogen can reduce the impact of weeds on crop yield and the amount of weed seed entering the soil seed bank. Enhancing crop competitiveness also improved herbicide performance, especially when herbicides were applied at reduced doses. The inclusion of an early-cut silage crop in a rotation dramatically reduced wild oat (Avena fatua L.) populations in barley (Hordeum vulgare L.) while growing sweet clover (Melilotus officinalis ( L.) Lam) as a green manure in rotation with cereal and oilseed crops showed tremendous potential to suppress weeds. Other studies demonstrated that weed management should not be considered in isolation since it can influence the severity of alternative pests, for example, damage due to Delia spp. in canola (Brassica napus L.). Further studies are required to examine the cumulative long-term effects of integrating the various weed management practices on all components of the crop ecosystem including weeds, diseases and insects.