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Summary: Résumé: Zusammenfassung In 1986, the Working Group on Biological Control within the European Weed Research Society planned a weed survey in 10 major crop systems throughout Europe. They were: (1) winter and (2) spring cereals, (3) maize and sorghum, (4) potatoes, (5) sunflower and soya, (6) colza (winter rapeseed), (9) sugar beet and (10) temperate orchards and irrigated Mediterranean orchards. Questionnaires were sent out to prominent weed scientists in all 26 European countries to rate the abundance and frequency of important weeds according to three classes for all crop systems in their respective countries. The results of the survey are presented. Based on the per cent of maximum score attained by individual weed species the 15 most important weeds were determined for each crop, and the 20 top scoring weeds for all crop systems combined. The prospects for biological control of weeds in Europe are discussed. Etude européenne des mauvaises herbes de dix cultures majeure.s en vue d'identifier les possi‐bilités de lutte biologique En 1986, le Groupe de travail sur la lutte biologique au sein de la Société Europeenne de Mal‐herbologie (European Weed Research Society) a organisé une enquete sur les mauvaises herbes présentes dans dix cultures majeures d'Europe: (1) céréales d'hiver et (2) d'été, (3) maïs et sorgho, (4) pomme de terre, (5) tournesol et soja, (6) colza, (7) cultures légumières, (8) vignes et verges méditerranéens non irrigués, (9) bet‐terave à sucre et (10) vergers de la zone tem‐pérées et méditerranéens irrigués. Des questionnaires ont été envoyés à des mal‐herbologues reconnus des 26 pays européens pour, au moyen d'une classification à trois niveaux, évaluer dans leur pays 1'abondance et la fréquence des mauvaises herbes importantes dans ces systèmes de culture. Les résultats de 1'enquête sont présentés. Les 15 mauvaises herbes les plus importantes ont été déterminées pourchaque culture en fonc‐tion du pourcentage du score maximum atteint par les différentes espèces, ainsi que les 20 mauvaises herbes obtenant les plus haul scores pour toutes les cultures combinées. Les possibilités de lutte biologique centre les mauvaises herbes en Europe sont discutees. Erhebung über die Verbreitung europäischer Unkrautarten als mögliche Zielefiir eine biologis‐che Bekämpfung in zehn Hattptkultiiren Die Arbeitsgruppe ‘Biologische Bekämpfung’ der Europäischen Gesellschaft für Herbologie plante 1986 eine Unkrautaufnahme in 10 großen Kulturen in ganz Europa: (1) Wintergetreide. (2) Sommergetreide, (3) Mais und Sorghum, (4) Kartoffel, (5) Sonnenblume und Soja, (6) Winterraps, (7) Gemüse, (8) Wein und nichtbewässerte mediterrane Obstkulturen, (9) Zuckerrübe und (10) mitteleuropäische und bewässerte mediterrane Obstkulturen. Das Ergebnis einer Umfrage in allen 26 europäischen Ländern über die Abundanz und Frequenz wichtiger Unkräuter wird dargestellt. Die 15 für jede Kultur wichtigsten Arten und die 20 allgemein häufigsten Arten wurden bestimmt. Die Möglichkeiten der biologischen Unkrautbekämpfung in Europa...
Spoiled and diffuse knapweed, Centaurea maculosa Lam. and C. diffusa Lam., both of European origin, are two of the most important rangeland weeds in North America. Surveys for potential biological control agents started in 1961, and agents were first introduced in 1970. So far, 11 phytophagous insect species of European origin have been released in North America. Despite legislation (restricted transport), large‐scale application of herbicides and reductions in seed production of up to 95% by the existing seed‐feeding biocontrol agents established, knapweed infestation has further increased during the last decade, covering nearly 2‐8 and 13 million ha for spotted and diffuse knapweed, respectively. In this paper, the biocontrol programme is reviewed critically and the present status analysed. To reach a break‐through in knapweed control, a cumulative stress approach is now envisaged, by extending the stress imposed by the biocontrol agents to increasing competition by the other vegetation through grazing regimes and reseeding programmes. Four steps to optimize the biocontrol effect and which lead to the integration of biocontrol into range management are described and suggestions, both scientific and political, are presented to render biological control more efficient and predictive.
Many prime wetlands in North America have been degraded following encroachment by the exotic plant purple loosestrife. Conventional methods are unsuccessful in providing long-term control. Host specificity studies demonstrated the suitability of two leaf beetles, Galerucella calmariensis and G. pusilla, as biological weed control agents. Adults oviposited only on plants within the genus Lythrum. The only species other than purple loosestrife where adult feeding and oviposition occurred and that supported successful larval development was winged lythrum. Swamp loosestrife and winged lythrum may be vulnerable to limited attack by newly emerged teneral adults. Evaluation of the potential environmental impact of the two leaf beetles showed that benefits of an introduction outweigh potential risks to winged lythrum or swamp loosestrife. Their field release was approved in 1992.
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