Upland rice-based cropping systems in the Mid-West of Madagascar suffer from low soil fertility, and weed pressure further reduces the already low yields of 1.5 - 2 t/ha. About twelve years ago, an agroecological practice based on a no-till system with Stylosanthes guianensis, a cover crop used as a live mulch, was introduced. This system has been proved to enhance soil fertility but its effect on weed community was not yet studied. Thus this research focuses on the effect of stylosanthes on weed infestation. In the administrative units of Ankazomiriotra and Vinany, interviews and focus groups were performed with 40 farmers. The aim was to map farmers' knowledge of and opinion about weeds and stylosanthes. According to farmers, most dangerous species were Striga asiatica, Richardia scabra, Eleusine indica, Digitaria spp., Cleome hirta and Cyperus spp., due to their capacity to reduce crop yield and the difficulty to eliminate them from the field. The general perception is that weed abundances decreased in the system with stylosanthes. Furthermore farmers feel that S. asiatica problems are less pronounced in this system, which is in line with the general knowledge that this hemi-parasitic weed decreases in more fertile soils.