Crop competition for weed management in Conservation Cropping Systems

Conservation cropping with stubble retention and no-till is very important for improving soil condition and water use, and for increasing soil carbon in the temperate cropping zone of south-eastern Australia. However, tillage and stubble burning are replaced by herbicides for weed control, leading to increased selection pressure for herbicide resistance (especially glyphosate). In addition, retained stubble can reduce crop competitiveness due to poor crop establishment, reduced early crop vigour, and use of wider crop row widths to avoid blockages and facilitate sowing. The opportunities to increase crop competition by choice of crop, cultivar and elevated seeding rates for improved weed management and herbicide performance are reviewed. Crop competition is a simple and cost-effective way for farmers to improve weed control, increase herbicide efficacy and prolong the life of useful chemicals by reducing the rate of development of herbicide resistance. The future performance of herbicides is expected to decline with the spread of resistance and with climate change to hotter and drier conditions. The roles of infrequent strategic burning and tillage, as well as other cultural control tactics for effective weed management in these systems are also discussed.