Diversification and continuous cropping have largely been a consequence of soil moisture saved through the adoption of conservation tillage. Consequently, weed communities have changed and, in some cases, become resistant to commonly used herbicides, thus increasing the complexity of managing weeds. The main plots contain cutivars in two levels and sub-plots contain rye grass and wild oat with 0, 25 and 50 density. Utilizing the principle of varying selection pressure to keep rye grass and wild oat communities off balance has reduced weed densities, minimized crop yield losses, and inhibited adverse community changes towards difficult-to-control species. Varied selection pressure was best achieved with a diverse cropping system where crop seeding date, perennation, and species and herbicide mode of action and use pattern were inherently varied. Approaches to cropping systems, including balancing rotations between cereal and broadleaf crops, reducing herbicide inputs, organic production, and the use of cover crops and perennial forages, are discussed in light of potential systems-level benefits for weed management.
