A biological framework for developing a weed management support system for weed control in winter wheat: Weed competition and time of weed control

There is a need to target weed control practices more precisely, both for economic and environmental reasons. The development of a Weed Management Support System for winter wheat provides a tool for the effective transfer of optimum advice on herbicides and weed control to farmers and their advisors. The proposed system defines the need for weed control and then selects the treatments to meet that need. Tn order to define the need for control, potential effects of the weeds on wheat yield and profitability have to be integrated with population dynamics data on the longer-term consequences of leaving weeds untreated. This paper concentrates on the competitive effects of weeds and on the effects of herbicide timing, using data for Stellaria media and Alopecurus myosuroides as examples. It describes key elements of a predictive approach to weed management, including; how to predict yield losses, how to incorporate risk into these estimates, reasons for allocating weeds to a limited number of competition classes and the effects of timing of control on yield loss.