INTEGRATED WEED MANAGEMENT AND WEED SPECIES-DIVERSITY

Alternative practices for weed management, such as integrated weed man agement (IWM) may allow the persistence of weed populations below a gi ven economic threshold. Increased species diversity of weeds also may result. If diversity increases, and the number of ecological interacti ons also increases, weed species should be viewed as an interactive co mmunity, rather than an unrelated set of targets for control. In this review we summarize how diversity is evaluated in unmanaged systems, e xamine how IWM techniques may alter the diversity of weed species and suggest how strategies can be developed for managing weed diversity un der IWM. Methods used to evaluate diversity in natural systems may be used to evaluate weed diversity in alternative systems of weed managem ent. We made preliminary calculations of diversity for reduced tillage , modified herbicide use, crop rotation, critical period of weed contr ol, techniques to improve crop competitiveness, and alternative contro l methods. Many of these IWM techniques potentially may result in chan ges in weed species diversity. We examined potential effects of these changes in weed diversity within six primary elements of community eco logy: colonization, disturbance, the physical environment, interaction s with other communities, community interactions and community dynamic s. Opportunities to develop strategies of community management exist w ithin each of these elements. If diversity could be managed while main taining acceptable crop yields, some previously unrealized benefits of the presence of weeds could be seen, as predicted by relationships am ong plants of unmanaged communities. Moreover, the goal of producing a more sustainable system that incorporates the diversity of the weed c ommunity would be complemented by trends in policy towards encouraging biodiversity in agroecosystems.