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Weeds are a major threat in tropical regions where climate conditions favor their growth and development. This is particularly true in low-input rice-based cropping systems in the Malagasy highlands, where weed management is mainly done by manual removal. Crop rotation is often promoted as an efficient way to control weed infestations, while the role of fertilization is more controversial. In this study, we compared rice monoculture to three rainfed rice-based two-year rotations: rice followed by groundnut, rice followed by sorghum-cowpea mixture, and rice followed by a velvet-bean crotalaria mixture. Each rotation was tested with two levels of fertilization (5 t DM ha−1 organic manure, sole or in combination with mineral fertilizer - 400 kg ha−1 NPK + 200 kg ha−1 urea). We assessed the effect of rotation and fertilization on weed composition, diversity, biomass and rice yield. Additionally, the farmers' perception of weed harmfulness and the relation between their assessment of weed harmfulness and rice production was tested. Our results showed that weed biomass significantly decreased rice yield but only under the low fertilization level. The rotation of rice with the velvet bean-crotalaria mixture was efficient in reducing weed biomass, modified weed community composition and allowed to achieve the highest rice yield. A significant negative relationship was found between weed community harmfulness index and weed species richness. Yet, the lowest rice yield was observed under rice monoculture despite a higher species richness over years and under high fertilization level. The lack of significant correlation between the harmfulness index and the actual rice yield is probably because our index is partly based on farmer's perception, and only on major weeds. More studies on tropical weed harmfulness are needed to support the design of ecologically intensified cropping systems.

Access to AdvenAlg is via the URL address: www.wikwio.org/alg/ which currently allows the identification of 125 important species of algerian weeds in field crops. They are divided according to their noxiousness into 15 agronomically major species, 20 secondary species, and 90 minor species. This modern computer-assisted identification (CAI) method allows simple and precise identification of plant species based on illustrated characters (and not described by botanical jargon as is the case with classic dichotomous keys), therefore in a graphic manner, by creating a composite portrait of the plant. Emphasis is placed on vegetative characters to enable recognition of incomplete samples. A composite portrait of the plant is created using a process allowing the free choice of characters, error management, the absence of technical terminology and self-correction. At any time, it is possible to access macro photographs and descriptive texts and print them. The AdvenAlg database, available in French or English, will be gradually updated with other species of crop weeds from the same phytogeographic region. All AdvenAlg species sheets can also be consulted on the Wiktrop collaborative portal dedicated to the sharing and dissemination of knowledge on weeds in tropical and Mediterranean crops: http://portal.wiktrop.org.

Intercropping, i.e., growing several species in the same field for a major part of their growing periods, often improves yield and weed control, but their performance greatly varies across situations. The aim of this study was to evaluate the effects of bi-species legume–cereal intercrops on weed dynamics and their impact on crop production, in the absence of nitrogen or water stress, via simulations with FlorSys. This individual-based 3D model simulates daily crop–weed seed and plant dynamics over the years, from cropping system and pedoclimate, focusing on competition for light. The study tested seven species proportions in two species mixtures (wheat–faba bean and barley–pea) and nine spatial sowing patterns in three species mixtures (triticale–faba bean, wheat–faba bean, wheat–pea), in both cases comparing the intercrops with the corresponding sole crops (controls). Intercrops and controls were inserted into rotations and simulated over 30 years and repeated with 10 climate scenarios from South-Western France, either with or without weeds. The simulations showed that: (1) the intercrops that best controlled weeds were barley–pea and triticale–faba bean, (2) the spatial pattern alternating one cereal row with one legume row as well as the 67 %-cereal–33 %-legume and 100 %-cereal–50 %-legume species proportions were those that maximised yields and minimised losses due to weeds, (3) the weed biomass in intercrop was greater than or equal to that of the sole cereal, and less than that of the sole legume, and (4) legumes benefitted more from intercropping than cereals because cereals are more competitive against weeds. Intercrop yield was best when combining species with contrasting shading responses (etiolated with stockier plants, leafy with stemmier plants) but early and good plant emergence was essential, particularly for weed suppression.

Les prairies et pâturages représentent 25 % des terres émergées. Une exploitation efficiente et durable de ces ressources fourragères nécessite notamment une gestion adaptée des plantes envahissantes très souvent responsables de leur dégradation. Cette gestion nécessite de disposer de connaissances sur leur comportement et pour cela une bonne identification. Le portail collaboratif Wiktrop aide à identifier les adventices et facilite le partage et la diffusion des connaissances sur les adventices tropicales et leur gestion entre acteurs de terrain et scientifiques. Ces connaissances permettent d'améliorer les pratiques de contrôle des adventices dans l'ensemble des régions tropicales et méditerranéennes. La contribution des utilisateurs est un facteur important de la qualité et de l'étendue des informations mises à disposition. Ce portail évoluera prochainement avec l'intégration des plantes fourragères et des plantes de services tropicales.

CONTEXT: In Guadeloupe, the use of a persistent pesticide (chlordecone) contaminated one third of the island's agricultural soils, causing a major environmental crisis. In the aftermath, banana farmers significantly changed their management practices to decrease their pesticide use. With the support of research, farmers have tested and adopted various agroecological practices, such as planting cover crops and using vitroplants and fallow. However, the use of animals to decrease pesticide use on banana plantations has not yet been explored. OBJECTIVE: This study aimed to co-design agroecological cropping systems that integrate animals as an alternative means to manage weeds. METHODS: The study was based on co-design workshops involving farmers, advisors and scientists, a survey of local practices of integrating animals within cropping systems, on-farm experiments with four farmers during which a total of 20 four-month-old male lambs were introduced within their cropping systems, and reflexive monitoring two and six months after the end of the experiments. RESULTS AND CONCLUSIONS: The introduction of sheep into cropping systems was the option deemed the most promising after three co-design workshops. Animals already were integrated into some banana-based farming systems in the study area, but this integration mainly consisted of cattle grazing on fallow land. The on-farm experiments highlighted that sheep made it possible to reduce the herbaceous cover on banana plantations by almost 60%. The growth performance of the lambs allowed by the herbaceous cover was within the range observed for this breed when reared on pastures (50–139 g/day). In this experiment, the lambs were not reared for meat, since the animals were, unsurprisingly, contaminated by chlordecone. The farmers appreciated that the practice enabled them to eliminate a labor-intensive activity (removing by hand the vines around the banana pseudo-stem) and radically reduce brush cutting. Piloted by a technic

Agroecological studies on sugarcane intercropping commonly generate complex datasets. A generic database (AEGIS – Agro-Ecological Global Information System) has been developed to facilitate the use of these datasets. The data described in this paper includes data from 8 experiments carried out on Reunion Island from 2012 to 2021 under three soil and climatic conditions to assess the capacity of cover crops in the sugarcane inter-row to control weed growth. Each experiment consisted of the comparison of three treatments in the inter-row: i) sugarcane with chemical weeding, ii) sugarcane with a cover crop sowed in the inter-row, and iii) sugarcane with spontaneous weed flora in the inter-row. The datasets contain data for sugarcane and cover crop observations (e.g., yield), weed flora, including 104 weed species (e.g., ground cover), crop management (including manual and chemical weedings), soil analyses, and daily weather. This dataset provides an adequate experimental dataset to calibrate or validate crop model simulations under intercropping.

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.

Oil palm is the most productive oil crop, but its high productivity is associated with conventional management (that is, high fertilization rates and herbicide application), causing deleterious environmental impacts. Using a 22 factorial experiment, we assessed the effects of conventional vs reduced (equal to nutrients removed by fruit harvest) fertilization rates and herbicide vs mechanical weeding on ecosystem functions, biodiversity and profitability. Analysing across multiple ecosystem functions, mechanical weeding exhibited higher multifunctionality than herbicide treatment, although this effect was concealed when evaluating only for individual functions. Biodiversity was also enhanced, driven by 33% more plant species under mechanical weeding. Compared with conventional management, reduced fertilization and mechanical weeding increased profit by 12% and relative gross margin by 11% due to reductions in material costs, while attaining similar yields. Mechanical weeding with reduced, compensatory fertilization in mature oil palm plantations is a tenable management option for enhancing ecosystem multifunctionality and biodiversity and increasing profit, providing win–win situations.

Ce texte de 20 pages fut le support d'une singulière conférence donnée en 1999 à l'invitation de l'Association européenne des étudiants en paysagisme qui se réunissait une fin de semaine à Versailles sur un thème encore très actuel : du paysage à l'assiette. Texte saisissant à notre époque où les approches territorialisées et le concept de santé globale sont à l'honneur. Maître-mot : diversité, incluant celle des pratiques agricoles et la chimio-diversité des herbicides, en faveur du pré-requis essentiel de la santé des sols alliée à la biodiversité générale dans la biosphère. A certains détails, on pourrait dater le texte si on n'en connaissait pas la date, mais son propos général reste 25 ans après d'une poignante pertinence ; support d'une conférence informelle prononcée à des étudiants hyper-motivés par un professeur passionné déjà à la retraite, sa publication aurait certes mérité l'affinage d'une relecture du vivant de l'auteur ; mais à peu de chose près, son contenu pourrait encore faire l'objet d'une leçon inaugurale sinon au Collège de France du moins à Sup-Agro Montpellier ou à l'Université d'agriculture de Wageningen. L'avant-propos (valant préface) de 8 pages est lui-même assez consistant, il présente la genèse de cette aventure éditoriale écrite à plusieurs mains, et l'enrichit par d'intéressantes remarques mycologiques du premier auteur - à tout seigneur tout honneur - à qui on doit la publication hybride (sur papier et en ligne) de ce texte dans les Annales de la SHHNH. Références bibliographiques, publications consultées et une rubrique de remerciements font office de post-face (2 pages). Que nos agro-malherbologues en herbe en prennent de la graine et de la vivacité, ainsi que de l'inoculum bactério- et myco- symbiotique pour, ici et ailleurs sous d'autres cieux, rallier - une gageure ? - agriculteurs et autres citoyens, également heureux autour de leurs terroirs soigneusement façonnés, aux airs, eaux et sols sains ou assainis, porteurs de belles cu

The epidemiology of yam viruses remains largely unexplored. We present a large-scale epidemiological study of yam viruses in Guadeloupe based on the analysis of 1124 leaf samples collected from yams and weeds. We addressed the prevalence of cucumber mosaic virus (CMV), Cordyline virus 1 (CoV1), Dioscorea mosaic associated virus (DMaV), yam asymptomatic virus 1 (YaV1), yam mosaic virus (YMV), yam mild mosaic virus (YMMV), badnaviruses, macluraviruses and potexviruses, and the key epidemiological drivers of these viruses. We provide evidence that several weeds are reservoirs of YMMV and that YMMV isolates infecting weeds cluster together with those infecting yams, pointing to the role of weeds in the epidemiology of YMMV. We report the occurrence of yam chlorotic necrosis virus (YCNV) in Guadeloupe, the introduction of YMMV isolates through the importation of yam tubers, and the absence of vertical transmission of YaV1. We identified specific effects on some cropping practices, such as weed management and the use of chemical pesticides, on the occurrence of a few viruses, but no crop-related factor had a strong or general effect on the overall epidemiology of the targeted viruses. Overall, our work provides insights into the epidemiology of yam viruses that will help design more efficient control strategies.

Grassland represents more than half of the agricultural land. Numerous metrics (biomass, functional trait, species composition) can be used to describe grassland vegetation and its multiple functions. The measures of these metrics are generally destructive and laborious. Indirect measurements using optical tools are a possible alternative. Some tools have high spatial resolutions (digital camera), and others have high spectral resolutions (Near Infrared Spectrometry NIRS). A plenoptic camera is a multifocal camera that produces clear images at different depths in an image. The objective of this study was to test the interest of combining plenoptic images and NIRS data to characterize different descriptors of two Mediterranean legumes mixtures. On these mixtures, we measured biomass, species biomass, and functional trait diversity. NIRS and plenoptic images were acquired just before the field measurements. The plenoptic images were analyzed using Trainable Weka Segmentation ImageJ to evaluate the percentage of each species in the image. We calculated the average and standard deviation of the different colors (red, green, blue reflectance) in the image. We assessed the percentage of explanation of outputs of the images and NIRS analyses using variance partition and partial least squares. The biomass Trifolium michelianum and Vicia sativa were predicted with more than 50% variability explained. For the other descriptors, the variability explained was lower but nevertheless significant. The percentage variance explained was nevertheless quite low, and further work is required to produce a useable tool, but this work already demonstrates the interest in combining image analysis and NIRS.

For situations and crops as diverse as sugarcane in Réunion (a French overseas department), grown in systems close to monoculture, and cotton in Cameroon, grown in rotation with food crops, the gruelling manual weed control operations using hoes (the daba in Cameroon and the mattock in Réunion), traditionally inherent to family farming, have been considerably alleviated by the emergence then widespread implementation of chemical weed control, manual in Cameroon and partially motorised in Réunion. Based on these two examples taken from his experience as a tropical agronomist in Northern Cameroon and in Réunion, the author concludes that in just a few decades, family farming and chemical weed control have forged very strong links, which are now difficult to undo.

Infestations by the parasitic weed genus Striga result in significant losses to cereal crop yields across sub-Saharan Africa. The problem disproportionately affects subsistence farmers who frequently lack access to novel technologies. Effective Striga management therefore requires the development of strategies utilizing existing cultural management practices. We report a multiyear, landscape-scale monitoring project for Striga asiatica in the mid-west of Madagascar, undertaken over 2019–2020 with the aims of examining cultural, climatic, and edaphic factors currently driving abundance and distribution. Long-distance transects were established across the middle-west region of Madagascar, over which S. asiatica abundance in fields was estimated. Analysis of the data highlights the importance of crop variety and legumes in driving Striga density. Moreover, the dataset revealed significant effect of precipitation seasonality, mean temperature, and altitude in determining abundance. A composite management index indicated the effect of a range of cultural practices on changes in Striga abundance. The findings support the assertion that single measures are not sufficient for the effective, long-term management of Striga. Furthermore, the composite score has potential as a significant guide of integrated Striga management beyond the geographic range of this study.

Premise: Weed removal in agriculture is typically achieved using herbicides. The use of autonomous robots to reduce weeds is a promising alternative solution, although their implementation requires the precise detection and identification of crops and weeds to allow an efficient action. Methods: We trained and evaluated an instance segmentation convolutional neural network aimed at segmenting and identifying each plant specimen visible in images produced by agricultural robots. The resulting data set comprised field images on which the outlines of 2489 specimens from two crop species and four weed species were manually drawn. We adjusted the hyperparameters of a mask region‐based convolutional neural network (R‐CNN) to this specific task and evaluated the resulting trained model. Results: The probability of detection using the model was quite good but varied significantly depending on the species and size of the plants. In practice, between 10% and 60% of weeds could be removed without too high of a risk of confusion with crop plants. Furthermore, we show that the segmentation of each plant enabled the determination of precise action points such as the barycenter of the plant surface. Discussion: Instance segmentation opens many possibilities for optimized weed removal actions. Weed electrification, for instance, could benefit from the targeted adjustment of the voltage, frequency, and location of the electrode to the plant. The results of this work will enable the evaluation of this type of weeding approach in the coming months.

The parasitic weed genus Striga causes huge losses to crop production in sub-Saharan Africa, estimated to be in excess of $7 billion per year. There is a paucity of reliable distribution data for Striga; however, such data are urgently needed to understand current drivers, better target control efforts, as well as to predict future risks. To address this, we developed a methodology to enable rapid, large-scale monitoring of Striga populations. We used this approach to uncover the factors that currently drive the abundance and distribution of Striga asiatica in Madagascar. Two long-distance transects were established across the middle-west region of Madagascar in which S. asiatica abundance in fields adjacent to the road was estimated. Management, crop structure and soil data were also collected. Analysis of the data suggests that crop variety, companion crop and previous crop were correlated with Striga density. A positive relationship between within-field Striga density and the density of the nearest neighbouring fields indicates that spatial configuration and connectivity of suitable habitats is also important in determining Striga spread. Our results demonstrate that we are able to capture distribution and management data for Striga density at a landscape scale and use this to understand the ecological and agronomic drivers of abundance. The importance of crop varieties and cropping patterns is significant, as these are key socio-economic elements of Malagasy cropping practices. Therefore, they have the potential to be promoted as readily available control options, rather than novel technologies requiring introduction.

Con base en las recientes aplicaciones exitosas de técnicas de Aprendizaje Profundo en la clasificación, detección y segmentación de plantas, proponemos un enfoque de segmentación de instancias utilizando un modelo Mask R-CNN para la detección de malezas y cultivos en tierras de cultivo. Evaluamos el rendimiento de nuestro modelo con la métrica de precisión promedio de MSCOCO, contrastando el uso de técnicas de aumento de datos. Los resultados obtenidos muestran cómo el modelo se adapta muy bien en este contexto, abriendo nuevas oportunidades para soluciones automatizadas de control de malezas a gran escala.

Herbicides used in agriculture pollute water worldwide. However, several weed management alternatives can reduce herbicide applications. The understanding of interactions between agronomics and the learning and social processes that favor changes in practices on a territorial scale is still far from complete. Despite the call for systemic change approaches, most studies are still based on technology transfer. Research and extension services provide references on alternative weed management practices and promote their use among farmers. We surveyed 33 farmers in a 45 km2 tropical catchment plus five institutional extension services. We analyzed changes in weed management practices on the 33 farms belonging to three different agricultural chains: local diversified horticulture, sugarcane, and export banana. For each change, we analyzed the learning processes and the networks involved in information exchanges. First, we show that the complexity of the practices promoted by extension services limits their adoption. Second, we show that simple practices adopted by farmers are part of a slow trajectory of change involving the gradual acquisition of knowledge. A redesign of cropping systems can emerge as the result of a gradual adding of complexity in practices and/or a specific systemic change on a cropping system scale. Sharing knowledge and resources in a non-competitive way speeds up changes among farmers sharing resources and promotes the redesigning of cropping systems. Third, we show that the structure and functioning of relational networks limit changes in practices on a watershed scale. We thus recommend that innovation design should incorporate co-designing of the pathway of change, by designing a succession of simple changes rather than a complex final system only. We recommend including non-competitive resource pooling among farmers in the co-designing of innovation.

Common ragweed (Ambrosia artemisiifolia L.) is widespread in soybean (Glycine max L.) fields in southern Québec. Biotypes resistant to ALS (group 2) herbicides are commonly reported in conventional crops where these herbicides are used. Reported cases are voluntary and potentially underestimate the occurrence of resistance. A survey was therefore undertaken in 2014 and 2015 in soybean fields treated with a Group 2 herbicide. Common ragweed seeds were collected from 123 fields. Seedlings were grown and tested for resistance using the recommended rate of imazethapyr (100.8 g a.e. ha-1). Weed populations were classified as susceptible, developing resistance (less than one third of plants classified as resistant) or resistant (at least one third of plants were resistant). Twenty populations were then selected based on these resistance levels and treated with four doses of the herbicide (0, 100.8, 201.6, and 403.2 g a.e. ha-1). Resistance to imazethapyr was detected in 81% of samples (21.1% were classified as developing resistance and 59.4% were classified as resistant). Populations classified as developing resistance had a resistance factor of 1.04, while populations classified as resistant had a resistance factor greater than 5. These results confirm the presence of multiple populations of imazethapyr-resistant common ragweed in Quebec., La petite herbe à poux (Ambrosia artemisiifolia L.) est très fréquente dans les champs de soya (Glycine max L.) du Québec méridional. Des biotypes résistants aux herbicides qui inhibent l’acétolactate synthase (ALS) (Groupe 2) sont fréquemment signalés dans les champs où ces herbicides sont utilisés. Les cas rapportés se font sur une base volontaire et sous-estiment potentiellement la fréquence réelle de la résistance. Une enquête a donc été réalisée en 2014 et en 2015 dans des champs de soya traités avec un herbicide du groupe 2. Des graines ont été récoltées dans 123 champs. Des plantules ont été testées pour leur résistance avec une dose recommandée d’imazéthapyr (100,8 g e.a. ha-1). Les populations ont été classifiées sensibles, résistantes (au moins un tiers des plants étaient résistants) ou présentant une résistance en développement (moins du tiers des plants étaient résistants). Vingt populations ont ensuite été sélectionnées selon leur degré de résistance et traitées avec quatre doses d’herbicide (0; 100,8; 201,6 et 403,2 g e.a. ha-1). De la résistance à l’imazéthapyr a été détectée dans 81 % des échantillons (21,1 % classifiés avec une résistance en développement et 59,4 % classifiés résistants). Le facteur de résistance des populations avec de la résistance en développement était de 1,04 et celui des populations résistantes était supérieur à 5. Ces résultats confirment la présence de multiples populations de petite herbe à poux résistantes à l’imazéthapyr au Québec.

Since the early 2000s conservation agriculture (CA) has been promoted in the Lake Alaotra region of Madagascar for a more sustainable and profitable agriculture. There is, however, little known about its performance in low-input rainfed rice-based cropping systems. We conducted a study during two growing seasons (2013/14 and 2014/15) on an experiment that was established in 2009 at the agricultural research station of the National Center for Applied Research and Rural Development (FOFIFA) in the Lake Alaotra region of Madagascar. The experimental setup was a randomized block design with four replications. Two soil/residue management treatments were studied, conventional tillage without residue retention (CT) and no-tillage with residue retention (NT). These two treatments were tested for a 2-year rotation of maize + Dolichos lablab followed by rice (MD//R) and a 3-year rotation of maize + Stylosanthes guianensis, followed by S. guianensis in the second year, and rice in the third year (MS//S//R). During the 2013/14 and 2014/15 seasons, two levels of weed pressure: 'high' and 'low' were introduced as a split-plot design on the rice plots. The main determining factors of rice yield in the study region were studied: radiation interception, weed infestation, soil moisture and soil mineral nitrogen (N). Our results showed that five to six years of continuous practice of NT with retention of high amounts of crop residues (more than 5 Mg DM ha−1) on the soil surface had a significant (p = 0.02) positive effect on rice yield, irrespective of the level of weed pressure and type of crop rotation. CA systems significantly (p < 0.05) reduced weed density and biomass as compared to CT particularly during the vegetative stage of the rice crop in the two growing seasons, which to a certain extent explained the yield gains under CA. In contrast, treatment effects on soil moisture and mineral N contents were marginal. The positive effects of CA on reduced weed pressure may constitut