Weeds in agricultural landscapes*. A review

There is currently an increasing societal and political shift towards more sustainable agricultural systems to provide both food production and ecological biodiversity levels. This shift has recently modified scientific questioning and brought up new research challenges for agro-ecological research. This is the case in particular for weed management, where issues have so far largely focused on the conflict between weeds and crop productivity. Here, we review recent findings that have led to a changing perception on weeds in agro-ecosystems and upcoming areas in terms of weed management options. Our main findings are that weeds have numerous interactions with other organisms and, in turn, some of these interactions can have direct, either negative or positive, effects on the functioning of the agro-ecosystem. Many interactions are species-specific, and therefore assessing the role of weed communities in the agro-ecosystem would benefit from further development in the functional grouping of weed species. In terms of weed management our review shows that alternative cropping systems can deliver both good levels of crop productivity and of weed management at the field level. Weeds respond to landscape attributes and there is a need to fully assess the scope for utilizing the spatio-temporal organization of cropping systems and uncultivated habitats as a tool for minimizing weed infestations. Weeds are also submitted to biological regulation through the predation of their seeds and further research is required to assess the effect of cropping systems and landscape on levels of weed natural enemies, and therefore on the potential contribution of biological regulation in the management of weeds