ASSESSING THE PRACTICAL IMPORTANCE OF WEED EVOLUTION - A RESEARCH AGENDA

If food production is to become more sustainable, weed management syst ems will become subject to many internal and external constraints; the se may sharply limit the available range of weed control methods. If s o, it will be imperative to preserve efficacy of acceptable weed contr ol methods by defending these against weed adaptation. Moreover, rapid and ongoing weed adaptation may explain the persistent nature of yiel d losses to weeds despite technological advances. Research is needed t o assess the practical importance of ongoing weed evolution. The first step is to determine the risk of rapid weed adaptation to diverse con trol measures. Experimentally, this risk can be evaluated by determini ng heritabilities of traits conferring resistance to control measures, and then using ecological genetic methods to measure the actual magni tude of selection for such traits. Models of multivariate trait evolut ion can be used to determine the net effect of evolutionary forces bea ring on weed adaptation to an integrated weed management system (IWMS) . It may also be possible to take a preventive approach by designing a gricultural systems so that their large-scale structure impedes weed a daptation to IWMS.