While weeds generally are considered as the most important overarching production constraints in inland-valley cropping systems in West Africa, little is known about species' associations with environmental and crop management factors. Weed species' associations with seasonal and environmental factors, such as their position on the catena, soils and cropping systems, were studied during two seasons (dry and wet) in 45 arable fields of three inland valleys in south-western Benin, Africa. The three most dominant weed species were Dactyloctenium aegyptium, Commelina benghalensis and Digitaria horizontalis on the inland-valley crests (uplands), Ludwigia hyssopifolia, Corchorus aestuans and Ludwigia octovalvis on the sloping hydromorphic fringes and Leersia hexandra, Ipomoea aquatica and Fimbristylis ferruginea in the valley bottoms (lowlands). Echinochloa colona, Cleome viscosa and Talinum triangulare were the three most dominant species in the dry-season crops (maize or vegetables) and Leer.?hexandra, I.?aquatica and Sphenoclea zeylanica were the three most dominant species in the wet-season crop (rice). Ageratum conyzoides, Synedrella nodiflora and D.?horizontalis were observed throughout the catena. Problem weeds in inland-valley agro-ecosystems are those that combine a high frequency with a high submergence tolerance and ecological plasticity, C4 grasses, perennial C3 species with persistent root structures and broad-leaved species with high propagation rates. Weed management strategies that are aimed at increasing the resilience of rice-based cropping systems in the inland valleys of the southern Guinea Savanna of Africa should address the categories of problem species that were identified in this study. This can be done best by following an integrated approach, including the use of more weed-competitive cultivars and rotation crops. (Résumé d'auteur

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-We developed an interactive electronic weed identification tool, AFROweeds, and an online network, Weedsbook, for agricultural change agents to aid communication and offer assistance to rice farmers with specific weed problems. We collected quantitative and qualitative data to assess effectiveness and usefulness of these products with potential users. With the online version of AFROweeds, used on an electronic tablet, average weed identification time in the field was 7 min 6 s with 44% successful identifications. Poor mobile network coverage and slow internet were the main reasons for the relative long identification time and low success rate. A second trial was done with the offline version, preinstalled on a tablet. The average identification time was 6 min 34 s, with a success rate of 75%. The online network Weedsbook, established alongside AFROweeds, was assessed by the test users as a useful additional aid, enabling agricultural change agents and agronomists to exchange information or request assistance on all aspects of weeds and weed management. The potential improvements of both products are discussed.Keywords: rice / extension / lowland / sub-Saharan Africa / ICT / network Résumé -Des outils électroniques d'aide à l'identification et à la gestion des adventices du riz en Afrique pour des agents de vulgarisation agricole mieux informés. Afin que les agents de vulgarisation agricole puissent aider rapidement et efficacement les riziculteurs à améliorer leurs pratiques de désherbage, nous avons développé un outil électronique d'identification des adventices du riz, AFROweeds, et un espace collaboratif en ligne, Weedsbook. Nous avons collecté des donnéees qualitatives et quantitatives pour évaluer l'efficacité et l'utilité de ces produits avec des utilisateurs potentiels. Le premier test d'AFROweeds a été mis en oeuvre avec la version en ligne (par 3G), à partir d'une tablette électronique. Le temps d'identification moyen d'une espèce a été de 7 min 6 s avec un taux de réussite de 44 %. Une faible couverture du réseau mobile et la lenteur du réseau internet ont été les principales raisons de la longue durée d'identification et du faible taux de réussite. Le deuxième essai, hors-ligne, a été réalisé avec la version encapsulée, installée sur une tablette. Le temps d'identification moyen a été de 6 min 34 s, avec un taux de réussite de 75 %. Le réseau Weedsbook, établi en plus d'AFROweeds, a été évalué par des utilisateurs