Integrated weed management and weed species diversity

Les méthodes alternatives de gestion des mauvaises herbes, telles que la gestion intégrée, peuvent permettre la persistance de populations de mauvaises herbes sous un seuil économique déterminé. Une diversité accrue des espèces de mauvaises herbes peut aussi en résulter. Si la diversité ainsi que le nombre d'interactions écologiques augmentent, les espèces de mauvaises herbes devraient être considérées comme une communauté interactive plutôt que comme un ensemble disparate de cibles contre lesquelles lutter. Cet article de synthèse résume les méthodes d'évaluation de la diversité dans des systèmes non gérés, examine comment les techniques de gestion intégrée peuvent modifier la diversité des espèces de mauvaises herbes, et finalement, suggère des façons de développer des stratégies pour gérer la diversité des mauvaises herbes par la gestion intégrée de celles-ci. Les méthodes utilisées pour évaluer la diversité dans les systèmes naturels peuvent servir à évaluer la diversité des mauvaises herbes dans des systèmes alternatifs de gestion intégrée. Nous avons effectué des calculs préliminaires de diversité pour le labour réduit, l'utilisation modifiée des herbicides, les rotations culturales, la période critique d'intervention contre les mauvaises herbes, les techniques d'amélioration de la compétitivité des cultures et les méthodes de lutte alternatives. Plusieurs de ces techniques de gestion intégrée peuvent éventuellement résulter en des modifications de la diversité des espèces de mauvaises herbes. Nous avons examiné les effets potentiels de ces changements sur la diversité des mauvaises herbes à l'intérieur de six principaux éléments de l'écologie des communautés: la colonisation, la perturbation, l'environnement physique, les interactions inter- et intra-communautés, et la dynamique de ces communautés. Des occasions de développer des stratégies de gestion des communautés de mauvaises herbes existent à l'intérieur de chacun de ces éléments. Si la diversité pouvait être gérée tout en maintenant des rendements acceptables, certains bénéfices découlant de la présence des mauvaises herbes et non encore considérés pourraient être observés, tel que le prédisent les relations existant entre les plantes de communautés non gérées. De plus, l'objectif d'obtenir un système de production plus durable, tenant compte de la diversité des communautés de mauvaises herbes, pourrait être accompagné d'orientations vers une politique encourageant la biodiversité des agro-écosystèmes.Alternative practices for weed management, such as integrated weed management (IWM) may allow the persistence of weed populations below a given economic threshold. Increased species diversity of weeds also may result. If diversity increases, and the number of ecological interactions also increases, weed species should be viewed as an interactive community, rather than an unrelated set of targets for control. In this review we summarize how diversity is evaluated in unmanaged Systems, examine how IWM techniques may alter the diversity of weed species and suggest how strategies can be developed for managing weed diversity under IWM. Methods used to evaluate diversity in natural Systems may be used to evaluate weed diversity in alternative Systems of weed management. We made preliminary calculations of diversity for reduced tillage, modified herbicide use, crop rotation, critical period of weed control, techniques to improve crop competitiveness, and alternative control methods. Many of these IWM techniques potentially may result in changes in weed species diversity. We examined potential effects of these changes in weed diversity within six primary elements of community ecology: colonization, disturbance, the physical environment, interactions with other communities, community interactions and community dynamics. Opportunities to develop strategies of community management exist within each of these elements. If diversity could be managed while maintaining acceptable crop yields, some previously unrealized benefits of the presence of weeds could be seen, as predicted by relationships among plants of unmanaged communities. Moreover, the goal of producing a more sustainable System that incorporates the diversity of the weed community would be complemented by trends in policy towards encouraging biodiversity in agroecosystems

A conceptual framework for research and technology transfer to support sustainable tree crop development

The participants at the Yaounde Roundtable in June 1999 concluded that research and technology transfer is a critical component of a regional Sustainable Tree Crops Program (STCP). Productivity enhancing and environmentally friendly technology will be critical to both the supply of tree crop products and farmer incomes. The primary tree crops targeted by STCP are cocoa, coffee and cashew. Additional tree crops may be considered within the context of diversification of cocoa, coffee or cashew production systems. A regional program is required to enhance the synergies to be gained by working across institutions and countries to successfully develop sustainable tree crop production. Furthermore, an integrated and holistic approach is necessary to link developments in research, technology transfer, market systems, information systems, grower and business support services, and policy change

EURISCO: The European search catalogue for plant genetic resources

The European Search Catalogue for Plant Genetic Resources, EURISCO, provides information about 1.8 million crop plant accessions preserved by almost 400 institutes in Europe and beyond. EURISCO is being maintained on behalf of the European Cooperative Programme for Plant Genetic Resources. It is based on a network of National Inventories of 43 member countries and represents an important effort for the preservation of world's agrobiological diversity by providing information about the large genetic diversity kept by the collaborating collections. Moreover, EURISCO also assists its member countries in fulfilling legal obligations and commitments, e.g. with respect to the International Treaty on Plant Genetic Resources, the Second Global Plan of Action for Plant Genetic Resources for Food and Agriculture of the United Nation's Food and Agriculture Organization, or the Convention on Biological Diversity. EURISCO is accessible at http://eurisco.ecpgr.org

Polymotu : A new concept of island-based germplasm bank based on an old Polynesian practice

The Polymotu concept (poly=many, motu=island) is to use the geographical isolation of special sites for conservation and reproduction of individual varieties of plants, trees and even animals. This concept is mainly derived from previous initiatives in conservation of coconut palms by ancient Polynesians and some contemporary Thais. A quite similar concept has also been used by New Zealanders for conservation of endangered bird species. For instance, when a small island is planted with only one variety of coconut palms, breeding occurs only within this variety and certified seednuts are naturally produced. Conservation is secured by both the geographical isolation of the islands and the availability of certified seednuts. In 2009, the Polymotu concept was included in the global coconut conservation strategy developed by the International Coconut Genetic Resources Network (COGENT) and the Global Crop Diversity Trust. It moves this global strategy towards the involvement of more countries, sites and stakeholders. The Polymotu concept was enriched in 2010 during a visit in Samoa, in order for farmers to diversify their genetic resources and increase their incomes. We are presently launching initiatives to develop Polymotu in various regions: the Kepulauan Seribu National Park at the north of Jakarta, Indonesia; the Fakarava biosphere reserve and the Tetiaroa atoll in French Polynesia, Fiji and Samoa. Factors influencing the acceptance of Polymotu by the various stakeholders are discussed, together with collaborative research to be conducted during implementation of the projects. This paper discusses the origins and precursors of the Polymotu concept; presents the firsts initiatives to launch research actions linked to the Polymotu project, and discusses the need for further research to fully implementation this concept

Impacts of type of fallow and invasion by Chromolaena odorata on weed communities in crop fields in Cameroon

In the humid forest regions of southern Cameroon in central Africa, sectoral and macroeconomic policy reforms introduced in the late 1980s have led to intensified land use, which in turn has resulted in, among other environmental consequences, shortened fallow systems dominated by the Asteraceae shrub, Chromolaena odorata (L.) King and Robinson, rather than by secondary forest species. A trial was established to determine the effect of shortened fallow duration and invasion by C. odorata on the weed flora in subsequent mixed food cropping systems. Plots were established in cleared 5- to 7-year-old fallow fields in which the vegetation was either dominated by C. odorata or not, and in which the dominant fallow vegetation in the previous crop–fallow rotation had been either C. odorata, forest, or herbaceous (not dominated by C. odorata). Cassava (Manihot esculenta Crantz), maize (Zea mays L.), and groundnuts (Arachis hypogaea L.) were intercropped and weed species were assessed 6, 14, and 30 weeks after crop planting. Soil analyses were conducted to assess the influence of edaphic traits on the distribution and abundance of dominant weed species. The results clearly indicated an enrichment of the weed flora with time after planting, but little difference between fallow histories. Two groups of weed species corresponded with soil characteristics: C. odorata, Cyathula prostrata, Mariscus alternifolius, Mikania cordata, Musanga cecropioides, and Trema orientalis were preponderant on soils with high clay, N, and C contents, and Ageratum conyzoides, Cyperus sp., Haumania danckelmaniana, Paspalum conjugatum, Pouzolzia guineensis, Richardia brasiliensis, Sida rhombifolia, Stachytarpheta cayennensis, Talinum triangulare, and Triumfetta cordifolia were preponderant on sandier soils with high pH, P, and Mg contents

Response of Chromolaena odorata to different tree densities in a tropical agrisilvicultural system. Aboveground biomass production, partitioning, decomposition and nutrient release

In low-input land-use systems combining timber trees with shade-tolerant understorey crops, it is essential to establish the effects of tree density upon weeds and the contribution of weeds to competition and nutrient cycling. Adjusting tree density may alter weed competition for light, water and nutrients, the storage of nutrients by weeds through growth and the release of nutrients via decomposition of slashed weed residues. The effects are reported of (1) two timber stand densities (TSDs) and, (2) retention versus burning of slashed vegetation at field preparation, upon Chromolaena odorata (kondengui), the dominant weed, in an agrisilvicultural system in southern Cameroon. The system comprised the timber species, Terminalia ivorensis, and plantain as an understorey crop. Total weed biomass was measured at the first weeding, 3 months after planting (MAP), and total weed biomass and aboveground biomass, partitioning and nutrient accumulation of C. odorata were measured at the second and third weedings, 7 and 12 MAP. Mass and nutrient loss were measured from stem and leaves placed separately in decomposition bags. Here, burning was not an appropriate weed management tool, as it resulted in greater weed biomass. A high TSD did reduce weed biomass. However, foliar nutrient concentrations were generally higher in high TSDs. Thus, retaining trees in the high TSD did not lead to any reduction in nutrient uptake by the C. odorata stand. Furthermore, in the high TSD, mass loss and nutrient release characteristics had higher coefficients, and a higher percentage of the total nutrients accumulated were released in the early stages of incubation, all increasing the risk of nutrients being lost from the topsoil. Thus, from a weed competition perspective, there were few benefits to retaining a high timber stand density