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Description of the subject. Weed pressure is a main biotic constraint in tropical agriculture. Cover crop mixtures have increased in popularity to limit weed growth through competition for resources, but the relationship between cover crop diversity and weed suppression is still under debate. Objectives. This study aimed to assess the impact of increasing cover crop diversity (one to four species) on weed control during two growing seasons (tropical summer and winter) in Reunion Island. Method. Weed control was expressed regarding ground cover by weeds and weed aboveground dry mass in the mixtures during four months of growth and its response to cover crop traits was tested using structural equation models. Results. While cover crops reduced weed ground cover and dry mass by 60% and 68% on average in summer and winter, respectively, a higher number of cover crop species within a mixture did not increase mean weed control. Nonetheless, weed control was influenced by the mixture composition and improved when including Guizotia abyssinica. Additionally, cover crop traits explaining weed control differed between growing seasons. In summer, weed control was mainly explained by the final cover crop aboveground biomass and leaf area (depletion strategy). In contrast, weed control was mainly explained by the cover crop rate of increase in ground cover (obstruction strategy) in winter. Conclusions. Using traits to characterize cover crop mixture enables us to identify mixtures of species and traits adapted to different growing conditions. Our study suggests that particular attention on species identity rather than diversity should be paid in mixture to improve weed control in tropical conditions.

Introduction La gestion des connaissances, ou Knowledge Management, est une démarche managériale pluridisciplinaire, dont l’aboutissement est le développement de méthodes pour constituer un capital cognitif au service d’une organisation selon un objectif initialement défini. Une centaine de définitions sont toutefois mentionnées par Girard et Girard (2015), en lien avec la perception polysémique du terme « connaissance », telle que située sur la pyramide DIKW (Data, Information, Knowledge and...

Dans un monde confronté aux changements climatiques et à des pandémies en lien avec la destruction des milieux naturels, les enjeux liés à la préservation de la biodiversité sont dorénavant bien connus et ont donné lieu à des accords internationaux majeurs, comme le protocole de Nagoya. Dans ce contexte mondial, les recherches menées au Sud sont primordiales. Les contributions rédigées ici par des chercheurs dʼAfrique, de lʼocéan Indien, dʼAsie du Sud-Est et dʼEurope traduisent la vigueur de la recherche sur la biodiversité dans les pays intertropicaux francophones. Documenter la diversité des écosystèmes végétaux locaux, mieux connaître les savoirs traditionnels et les utilisations populaires des plantes ou des champignons, valoriser le rôle des collections botaniques, identifier des chaînes de valorisation économique responsables, gérer durablement les écosystèmes et leurs ressources, élaborer des outils stratégiques pour une gouvernance environnementale basée sur la science et, enfin, montrer la nécessité de lʼimplication citoyenne et de lʼensemble des acteurs concernés, tels sont les grands thèmes déclinés ici. Cet ouvrage collectif intéressera tous ceux qui travaillent sur la biodiversité des écosystèmes intertropicaux. Il souligne la nécessité dʼune science de lʼaction au service du développement durable.

Reducing the use of synthetic pesticides in crop protection, and antibiotics in livestock farming, is a challenge. A project funded in 2017-2018 by the INRA-CIRAD Glofoods meta-programme explored plant biodiversity with a view to conserving it more effectively and putting it to optimum use, by compiling its uses in the Knomana knowledge base. The project was developed in light of the expertise acquired in East Africa by the University of Greenwich and Kew Royal Botanic Gardens (ADAPPT and OPTIONS projects). The organic farming supply chains keenly subscribe to the approach adopted. In addition to managing already established pests, some invasive alien species (e.g. the insects Spodoptera frugiperda and Tuta absoluta) are already being considered. The inventory of plant extract uses, either under experimental conditions or in current practice, was based on publications provided by researchers affiliated to the PPAf (Plantes Pesticides d'Afrique) informal network, launched in Cameroon and Burkina Faso. After extending the search to other geographical areas (Africa, then Asia), Knomana holds 46,300 descriptions as of April 2022, each representing a use for plant health, public health (insect vectors of diseases), animal health (including fish farming) and human health (pathogens only). The descriptions are based on 71 items of information, including the plants used, target organisms, and the protected crops and animals. In all, 2,540 plant species are listed, covering 717 species of target organisms. The base is described using an ontology and analysed by constructing conceptual classifications to highlight new knowledge (e.g. the repellent effect of a species that can be used in a push-pull strategy), and to identify gaps that need to be filled, such as effects on non-target organisms. An extension of Knomana is planned to include the plurality of services offered by these species.

International audience

The objective of this study was to investigate the effect of general factors such as crop, regional climate or country on the weed flora and weed abundance in rainfed crops in tropical regions. For this purpose, we used 24 weed survey datasets from 4 climates, 11 crops and 11 countries in the tropics. These datasets are available in public access on the CIRAD Amatrop dataverse. This represents a set of 6 069 weed surveys, covering a total of 1 388 taxa. The data were analysed using different complementary approaches, including infestation diagrams, species correlation and co-occurrence matrices, corrected ecological profiles, and PCAIV. The results show that in the tropics there is a background of fairly common and ubiquitous species that are found in varying abundance in almost all situations. Ageratum conyzoides is the only Major general species, while Rottboellia cochinchinensis, Digitaria horizontalis, Bidens pilosa, Cyperus rotundus, Commelina benghalensis, Euphorbia heterophylla, Eleusine indica, Euphorbia hirta and Tridax procumbens are General species, present in more than 15% of the records. The climate factor, depending on rainfall and altitude, which influences temperature, selects certain indicator species for different situations. The crop factor does not have a particular selective effect and the country highlights local flora. Crops are themselves dependent on climate. It is nevertheless possible to know which species are most likely to be found in a plot of a crop, under a given climate and in a given country. However, it seems that it is the combination of the edaphic and climatic nature of the plot that most accurately determines the floristic composition of the weed flora, although we were unable to analyse this due to the lack of complete information on these factors for all the datasets used. Finally, out of the 1 388 taxa taken into account, only about 300 species constitute the core of the weeds of tropical rainfed crops, because of their frequency, their abundance or their character as indicators of particular agro-ecological conditions.

International audience; The EPPO code used for plants is a five-letter code more or less based on the species name. It is short, simple, unambiguous and does not change even when botanical nomenclature evolves. In tropical weed research work, EPPO codes are used in several ways: For weed community studies, EPPO codes are used for species records in the field, for data storage, aggregation and management, and for statistical analysis, mainly for tables and graphs to facilitate understanding of the results. For botanical specimens stored in the reference herbarium, the EPPO code is mentioned on the label, while for botanical photos it is associated with the date and time as combe-20210312-983421.jpg to name the photo file and facilitate its storage without risk of duplication. Finally, all species pages of the Wiktrop collaborative portal (http://wiktrop.portal.org), which is dedicated to tropical and Mediterranean weed species, have a "Brief" chapter mentioning the EPPO code of the species, which facilitates the search for a species by this code. This EPPO code is very useful for our scientific work

The objective of this study was to investigate the effect of general factors such as crop, regional climate or country on the weed flora and weed abundance in rainfed crops in tropical regions. For this purpose, we used 24 weed survey datasets from 4 climates, 11 crops and 11 countries in the tropics. These datasets are available in public access on the CIRAD Amatrop dataverse. This represents a set of 6 069 weed surveys, covering a total of 1 388 taxa. The data were analysed using different complementary approaches, including infestation diagrams, species correlation and co-occurrence matrices, corrected ecological profiles, and PCAIV. The results show that in the tropics there is a background of fairly common and ubiquitous species that are found in varying abundance in almost all situations. Ageratum conyzoides is the only Major general species, while Rottboellia cochinchinensis, Digitaria horizontalis, Bidens pilosa, Cyperus rotundus, Commelina benghalensis, Euphorbia heterophylla, Eleusine indica, Euphorbia hirta and Tridax procumbens are General species, present in more than 15% of the records. The climate factor, depending on rainfall and altitude, which influences temperature, selects certain indicator species for different situations. The crop factor does not have a particular selective effect and the country highlights local flora. Crops are themselves dependent on climate. It is nevertheless possible to know which species are most likely to be found in a plot of a crop, under a given climate and in a given country. However, it seems that it is the combination of the edaphic and climatic nature of the plot that most accurately determines the floristic composition of the weed flora, although we were unable to analyse this due to the lack of complete information on these factors for all the datasets used. Finally, out of the 1 388 taxa taken into account, only about 300 species constitute the core of the weeds of tropical rainfed crops, because of their frequency, their abundance or their character as indicators of particular agro-ecological conditions.

International audience; Le contexte tropical Objectif : Utiliser des approches relatives à la science des données pour analyser les contraintes d'enherbement dans les cultures tropicales à une échelle globale. Une masse de données hétérogènes complexes à assembler, stocker, partager et analyser

Cover plants have a high potential to manage weeds through competition for shared resources in tropical agrosystems. Assessing the abilities of a large number of different plant species to compete with weeds requires long-term experiments in different pedoclimatic environments. Our study was based on a set of 10 trials including 46 species of cover plants and performed from 2016 to 2018 in three sites in Reunion. Our aim was to identify and measure plant traits that optimize plant coverage and weed control by cover plants under tropical climate. We characterized two traits of interest (a soil coverage efficiency index and a coverage growth rate) using a hierarchical clustering analysis and compared them between plant area of origin, life cycle or growth habit. The ability for cover plant to cover efficiently and rapidly the soil increased with growth rate in height and leaf appearance rate while tends to decrease with thermal time for emergence. Accordingly, weed control efficiency (low weed coverage and dry mass) was strongly correlated and increasing with cover plant growth rate in coverage, height and biomass. The characterization of plant species using functional traits enabled to identify cover plants which could be used in tropical agrosystems as an alternative to herbicides. Assuming that the spatial and temporal combinations with the main crop will determine the performances of the system, we discussed a trait-based methodology to identify the cover plants adapted to sugarcane agrosystems in Reunion.

Description of the subject. Cover plants have a high potential to deliver ecosystem services such as weed, pest or erosion control, as well as nitrogen fixation. Due to the large diversity of cover plants available, the choice of a plant to deliver these services is crucial because the spatial and temporal combinations with the main crop will determine the performances of the cropping system. Objectives. In this study, we aim to assess the growth and trait response of 16 cover plant species depending on four sowing dates in Reunion island. Method. Comparison of species was based on various traits such as aboveground biomass, ground coverage, height or radiation use efficiency. Results. Some species were performing well in both warm and cool season (e.g. Penisetum glaucum, Guizotia abyssinica), while others were more specific to warm (e.g. Crotalaria juncea, Canavalia ensiformis) or cool (e.g. Avena sativa, Pisum sativum) season. Among species and sowing dates, ground coverage and plant height were positively correlated with the ratio between leaf and aerial biomass. Conclusions. Considering the species maximum height and radiation use efficiency, we discussed a trait-based selection of species adapted to crop mixture or fallow with sugarcane in Reunion island. Even based on few traits, this approach allowed us to identify cover crop to test in sugarcane based cropping systems.; Description du sujet. Les plantes de couverture ont un fort potentiel pour fournir des services écosystémiques tels que le contrôle des mauvaises herbes, des parasites ou de l'érosion, ainsi que la fixation de l'azote. En raison de la grande diversité des plantes de couverture disponibles, le choix d'une plante pour fournir ces services est crucial car les combinaisons spatiales et temporelles avec la culture principale détermineront les performances du système de culture. Objectifs. Dans cette étude, nous avons évalué la croissance et la réponse des traits de 16 espèces de plantes de couverture en fonction de quatre dates de semis à la Réunion. Méthode. La comparaison des espèces s’est fondée sur divers traits tels que la biomasse aérienne, la couverture du sol, la hauteur ou l'efficacité d'utilisation de la lumière.Résultats. Certaines espèces ont été performantes à la fois en saison chaude et en saison fraîche (e.g. Penisetum glaucum, Guizotia abyssinica), tandis que d'autres étaient plus spécifiques à la saison chaude (e.g. Crotalaria juncea, Canavalia ensiformis) ou à la saison fraîche (e.g. Avena sativa, Pisum sativum). Au sein des espèces et des dates de semis, la couverture du sol et la hauteur des plantes furent positivement corrélées avec le rapport entre la biomasse foliaire et aérienne.Conclusions. En tenant compte de la hauteur maximale des espèces et de leur efficacité d'utilisation de la lumière, nous avons discuté d'une sélection basée sur les traits des espèces adaptées au mélange des cultures ou à la jachère avec la canne à sucre à la Réunion. Cette approche, même si fondée sur quelques traits, nous a permis d'identifier des plantes de couverture à tester dans les systèmes de culture de la canne à sucre.

Cover plants have a high potential to manage weeds through competition for shared resources in tropical agrosystems. Assessing the abilities of a large number of different plant species to compete with weeds requires long-term experiments in different pedoclimatic environments. Our study was based on a set of 10 trials including 46 species of cover plants and performed from 2016 to 2018 in three sites in Reunion. Our aim was to identify and measure plant traits that optimize plant coverage and weed control by cover plants under tropical climate. We characterized two traits of interest (a soil coverage efficiency index and a coverage growth rate) using a hierarchical clustering analysis and compared them between plant area of origin, life cycle or growth habit. The ability for cover plant to cover efficiently and rapidly the soil increased with growth rate in height and leaf appearance rate while tends to decrease with thermal time for emergence. Accordingly, weed control efficiency (low weed coverage and dry mass) was strongly correlated and increasing with cover plant growth rate in coverage, height and biomass. The characterization of plant species using functional traits enabled to identify cover plants which could be used in tropical agrosystems as an alternative to herbicides. Assuming that the spatial and temporal combinations with the main crop will determine the performances of the system, we discussed a trait-based methodology to identify the cover plants adapted to sugarcane agrosystems in Reunion.

Among other challenges, the already increasing incidence and intensity of extreme climate events are a major threat to global crop production. Sugarcane represents the main source of sugar and important part of ethanol and material for electric energy productions in tropics and sub-tropics and grown in climatic areas subjected to extreme events. Reunion Island presented extremely contrasting climates and is regularly subjected to tropical cyclones. In this study, we used the crop model MOSICAS, combined with spatial databases (sugarcane field boundaries, soil type, meteorological data and irrigation management practices) to predict the potential and water-limited cane yield over the entire island from 1998 to 2018. Therefore, we compared them to actual cane yield from sugar producers in five agro-climatic zones. The average total yield gap (YGT, i.e. difference between potential cane yield and actual yield) over Reunion Island was 96 t ha-1 , of which 66% was due to water deficit. YGT increased to 120 t ha-1 with increasing temperature, radiations and precipitations, highlighting the influence of others biotic and abiotic limiting factors. Extreme climate indices were calculated for heavy rain, extreme winds, high temperature and drought at the agro-climatic zone scale and their influence on yield gap was assessed using a Principal Component Analysis (PCA). Yield gap was strongly correlated with the first axis of this PCA (ρ=0.56), highlighting how extreme precipitation induced increase in YGT. Based on a clustering analysis on extreme precipitation and wind, 4 agro-climatic clusters were defined. Actual yield loss (difference between yield and the yield of the best year in the same zone) was in average 10 t ha-1 higher in the cluster with the highest precipitation and wind than the cluster with low extreme events, and sugarcane losses could reach 28 t ha-1. The objective of this study was to assess the impact of extreme climate variability on cane yield gap in Reunion Island. It highlights how sugarcane yield is constrained by both abiotic factors and extreme events occurrence in Reunion Island. The implication for sugarcane management under extreme events is discussed.

La gamme réduite de produits herbicides disponibles en culture de canne à sucre et les restrictions d'usage en cours conduisent à promouvoir des pratiques alternatives. Le positionnement de ces opérations doit prendre en compte la dynamique des infestations de mauvaises herbes afin d'améliorer leur efficacité. Des suivis phénologiques ont été effectués à La Réunion en 2017 et 2018. Sur un site donné, chaque mois, le sol d'une nouvelle placette est travaillé pour faire démarrer les germinations à différentes époques de l'année. Deux fois par semaine, le stade phénologique (levée, apparition des feuilles, floraison, fructification) de plusieurs individus sont notés après leur levée. Pour 17 espèces, les traits de vie (époque de levée, délais de floraison et de fructification) ont pu être déterminés. Ces valeurs varient selon la saison et les espèces de saison chaude (Trianthema portulacastrum, Boerhavia sp) se différencient nettement de celles de saison froide (Sonchus oleraceus, Argemone mexicana). Connaître ces traits de vie fournit des informations pour caler les méthodes de lutte afin d'augmenter leur efficacité et éviter la production des graines de mauvaises herbes.

Les adventices sont les principaux bioagresseurs de la canne à sucre à La Réunion. En conditions tropicales, la lutte contre l'enherbement représente un enjeu majeur de la filière pour améliorer ses performances techniques. A ce jour, la canne à sucre par son emprise sur la SAU de l'île (54 %), est une production végétale très consommatrice d'herbicides, seul pesticide autorisé en canne, malgré un IFT relativement bas (3,4) par rapport à celui d'autres cultures. Le projet CanécoH a pour objectif d'identifier, tester, comparer et évaluer différentes pratiques de désherbage alternatif au tout chimique dans différentes situations de production. Le projet s'appuie sur divers outils inhérents à la culture de la canne, comme les variétés, la gestion de la paille de canne après récolte, mais mobilise aussi des techniques autres comme le désherbage mécanique, l'utilisation de plantes de services, autant de pratiques visant à réduire de 50 % l'IFT tout en maintenant voire améliorant la productivité agricole. Les travaux sont conduits en station expérimentale ou chez l'agriculteur. Des résultats encourageants ont montré une réduction possible de plus de 50 % de l'IFT mais entrainent une augmentation du temps de travail et des investissements en matériels parfois importants. Ces résultats doivent être confortés dans le temps tout en adaptant, combinant et améliorant les techniques et les outils afin de conduire les agriculteurs dans un changement plus durable et économiquement rentable.

Dans les parcelles de riz pluvial du Moyen Ouest malgache, région du Vakinankaratra, la plante semi-parasite Striga asiatica compte parmi les adventices les plus dangereuses pour le riz selon les agriculteurs. Dans les cas les plus extrêmes, la récolte de riz peut être totalement perdue. L'effet du 2,4-D appliqué avant l'émergence du parasite, a déjà été démontré dans le cas d'une autre espèce, Striga hermonthica, affectant le sorgho. Afin de savoir si un effet similaire serait observable dans le cas de Striga asiatica, ce produit a été appliqué à 4 dates sur des parcelles semées avec une variété de riz pluvial sensible au striga. Un traitement T1 de pré-mergence du striga à 30 jours après semis (JAS) et 3 traitements de post-émergence à 45 (T2), 60 (T3) et 75 JAS (T4), ont été mis en place et comparés à des témoins adjacents non traités dans un dispositif à 4 répétitions. Des comptages de striga ont été effectués tous les 7 jours jusqu'à récolte, et le rendement a été mesuré à récolte. Le traitement T1 permet de diminuer de 80% l'infestation de striga en moyenne jusqu'à 75 JAS en comparaison des témoins non traités tandis que T2 diminue de 50% l'infestation ce qui se traduit par des rendements en riz supérieurs. Ces résultats prometteurs méritent d'être confirmés lors d'une prochaine campagne.

Le retrait de l'asulame pour le désherbage en postlevée de la canne à sucre rend difficile la gestion des populations de graminées. Les applications en traitement dirigé de rattrapage avec des herbicides non sélectifs sont également compromises par le retrait du glufosinate et celui programmé du glyphosate. A la suite d'essais conduits précédemment, un herbicide non sélectif de la canne à sucre à base de mésotrione + nicosulfuron 75+ 30 g/l a été homologué pour des applications de postlevée en dirigé dans l'interrang de la canne à 0 ,75 l/ha répétable une fois. L'emploi de deux adjuvants a été testé en 2014 et en 2018 dans trois essais sur des flores composées de graminées et de dicotylédones. Cette adjonction améliore sensiblement le niveau d'efficacité du traitement. En outre ces essais confirment l'importance du respect du stade de développement des graminées lors de l'application de cet herbicide.

Le projet Knomana (Knowledge management on pesticide plants in Africa for a safer food and a better environmental health) a été construit en réponse à l'appel à projet du métaprogramme INRA-Cirad Glofoods. Ce projet, qui s'est déroulé de juin 2017 à fin décembre 2018, visait à recenser les connaissances publiées sur les plantes à effets pesticide, antimicrobien, antiparasitaire et antibiotique en Afrique pour une meilleure sûreté alimentaire et une meilleure santé de l'environnement. Le recensement a conduit à la création d'une base de connaissances intitulée "Knomana", conçue à partir de la structure de la Base PPAf qui avait été présentée lors d'un congrès tenu en 2016 à Perpignan. 585 documents de natures diverses ont été collectés par les moyens usuels de recherche bibliographique, 250 d'entre eux ont été analysés. Les résultats ont été intégrés dans la Base Knomana après un travail important de révision et actualisation de tous les noms botaniques. La saisie manuelle des informations a permis de remplir 28 870 lignes, chaque ligne représentant une " connaissance ". Le nombre total d'espèces végétales à effet pesticide/antibiotique présentes dans la base est de 966 (122 familles botaniques). 253 espèces d'organismes cibles des extraits de plantes ont été recensés dont 194 présents en Afrique, dans les domaines de la santé humaine (dont santé publique), santé animale et végétale. En dehors de l'espèce humaine, quatre espèces animales sont actuellement mentionnées dans la base et le nombre d'espèces végétales à protéger est de trente-quatre.Un autre objectif du projet Knomana était d'exploiter la base ainsi créée de manière informatique, par navigation ou exploration. Cette exploitation se poursuit après le projet, notamment par l'encadrement de doctorants avec le LIRMM tout comme le travail de vérification des saisies.

La production agricole tropicale est en pleine mutation et la gestion des enherbements est un élément majeur de la stratégie de l'agriculteur. L'élaboration d'itinéraires de gestion des adventices requiert de plus en plus de connaissances, sur la biologie des espèces, leur comportement dans les milieux cultivés et l'efficacité des pratiques de désherbage. L'accès à l'information est maintenant facilité par les infrastructures numériques en constante évolution, mais nécessite que la connaissance soit partagée, mise à jour et diffusée de façon continue. Une part de connaissance est présente chez chacun des acteurs (producteurs, vulgarisateurs, chercheurs, enseignants), mais sa compilation et sa diffusion présentent différentes contraintes d'ordre réglementaire, humain et technologique. Le portail collaboratif WIKTROP permet à tous les acteurs du monde agricole tropical de partager et diffuser leurs connaissances et leurs questionnements sur les adventices tropicales et leur gestion. Il est associé à des applications mobiles facilitant son utilisation au bureau, sur le terrain ou pour des formations.

Le Bourgeois Thomas,Rodriguez Alain,Véla Errol,Marnotte Pascal,Fried Guillaume. Focus Une plante, Une espèce : Ibicella lutea (Lindl.) Vand Eselt - Nouvelle observation d’une curieuse plante dans la Haute Garonne. In: Le Journal de botanique, n°79, 2017. Septembre. pp. 53-55.

Organic Farming excludes the use of synthetic chemicals to protect plants in the field or during grain storage and questions the use of antibiotics for livestock and breeding or aquaculture. One way to limit major constraints of chemicals pests and diseases) is to use active plants parts or plants-based products, as it has been described in the literature for plant and animal health. Our current work consists in building a knowledge database from existing literature and implementing exploration methods to support the extraction of knowledge by the potential users (smallholders, advisors, extensionists, researchers, producers, etc.). In early May 2018, the knowledge base gathered data from 227 documents, dated from 1957 to 2017. Ninety-four percent of the 33,400 uses recorded concerned sub-Saharan African countries.

Efficient control of weeds is only achievable through a clear and sound knowledge of their biology and ecology. The Weed Identification and Knowledge in the Western Indian Ocean (WIKWIO) portal (http://portal.wikwio.org/) has been developed to meet this objective. It aims at building and leveraging a science and technology network to consolidate existing scientific and technical knowledge, and facilitating the sharing of new information. Although the portal currently covers the Indian Ocean region, most of the tropical weeds that are documented are also present in many other sugarcane-producing countries. This paper highlights the benefits that this resource can have to growers for managing weeds in their fields. The WIKWIO portal is the outcome of a three-year collaboration among weed scientists of CIRAD (France), CNDRS (Comoros), FOFIFA (Madagascar), IFP (India) and MSIRI (Mauritius). A community of stakeholders involved in weed knowledge and management, also collaborated in the action. Experts from the six research institutions worked on a list of nearly 470 species of tropical weeds. They compiled and validated information on the biology, ecology, distribution, agronomic importance and management of each weed species in datasheets in both English and French. Each weed has been fully illustrated with high- resolution pictures and scanned herbarium sheets to provide additional details. Botanists and computer engineers set up an information system to host these data, in addition to other tools that facilitate rapid weed recognition and documentation. The portal became operational in early 2014 and was improved with various options at the completion of the project in February 2017. More than 750 users have registered on the WIKWIO network, contributing over 10,000 observations of weeds, many of them encountered in sugarcane fields in various parts of the world. All the observations posted on the website are geo-referenced, thus providing useful data on their ecological distribution. Identified species are linked to the appropriate datasheets, giving insights into their management and control. Weed identification is possible via a computer-aided tool (IDAO) available on the portal. This resource and the possibility of uploading observations onto the network are accessible through applications (apps) on mobile devices enabling easy use in the field for rapid weed control decision and intervention. The WIKWIO portal enhances a collaborative and participative approach by sharing knowledge and providing practical information. It can serve as a platform for establishing and reinforcing a community of sugarcane growers seeking help or exchanging experience on weed management issues. Nowadays, with the easy and rapid access to internet connectivity, timely assistance may be obtained through the portal. The latter takes place in a 'numerical agriculture' approach that is expected to evolve into a website for tropical weeds.

Cover crops are increasingly being used for weed management in tropical regions as an alternative to herbicides. However, selecting the most suitable cover crop to be associated with a main crop requires long-term investigation. Here we present details of a set of trials conducted over two years to assess the ability of various cover crops to limit weed growth in sugarcane agrosystems. Firstly, 55 species/varieties were assessed in terms of their growth cycle and viability at three different locations in tropical conditions on Reunion Island. This trial allowed selection of cover crop species that would be suitable for either rotational cropping or intercropping with sugarcane. Secondly, 10 species were selected and grown in large plots in four different trials. This allowed for assessment of their ability to limit weed growth in monospecific plots and where mixtures of cover crops were grown. After two months of growth, the most productive cover crops showed the ability to limit weed growth to fewer than 30% of the plot (e.g. crotalaria, oat and millet). The less productive cover crops were unsuccessful in limiting weeds. In comparison, all combinations of two cover crops tested in this experiment were able to limit weed growth to fewer than 30% of the plot area. These trials highlight some key cover crops that are suitable for intercropping and rotations in sugarcane agrosystems as alternative to herbicides.

In lowland rice, weeds are generally well controlled by submergence, line transplanting and mechanical weeding. In upland rain-fed rice, weed control is highly challenging especially due to a peak workload at the beginning of the rainy season and weeding is done manually. This study aimed at determining the critical period of weed interference in a low-input upland rice cropping system, in order to optimize the timing of weeding. During the rainy season 2016-2017, a field experiment was conducted in Madagascar, Ivory station (19°33.29'S, 46° 24.913'E). Eight different weeding regimes were tested: a group of early weed interference (weedy until 20 DAS [days after sowing], 40 DAS and 60 DAS); a group of late weed interference (weedy from 20 DAS, 40 DAS and 60 DAS); two controls (weed-free and weedy). The experimental layout was a randomized complete block design with four replications. Data collected were weed cover at 20, 40 and 60 DAS, rice grain yield and weed biomass at harvest. The average rice yield in the weed-free control was 2.020 kg.ha-1, and in the weedy control it dropped down to 10 kg.ha-1 indicating more than 99% of yield loss. Early weed interference until 20, 40, and 60 DAS caused respectively yield losses of 6%, 60% and 87%; and late weed interference from 20, 40 and 60 DAS caused respectively yield losses of 63%, 39% and 9%. It indicated that weed presence before 20 DAS and after 60 DAS induced minor yield losses, while in-between these dates rice should be kept free from weed competition to avoid substantial losses. This information should advise farmers to better plan the timing of weeding, avoiding to invest labour in weeding when only a small increase in yield can be expected. This experiment will be repeated in the coming rainy season to confirm these results.

Organic Farming excludes the use of synthetic chemicals to protect plants in the field or during grain storage and questions the use of antibiotics for livestock breeding or aquaculture. One way to limit major constraints of chemicals (pests and diseases) is to use active plants parts or plants-based products, as it has been described in the literature for plant and animal health. Our current work consists in building a knowledge database from existing literature and implementing exploration methods to support the extraction of knowledge by the potential users (smallholders, advisors, extensionists, researchers, producers, etc.). In early May 2018, the knowledge base gathered data from 227 published documents, dated from 1957 to 2017. Ninety-four percent of the 33,400 uses recorded concerned sub-Saharan African countries.