Bilan des recherches menées par le groupe inter-organismes ACTA-INRA-SPV* sur la biologie d'Arvicola terrestris scherman en France (1979–1987)1

A l'issue de deux phases de forte densité des populations d'Arvicola terrestris scherman en France, un groupe de travail inter-organismes ACTA-INRA-SPV a été constitué pour entreprendre un programme de recherche sur ce rongeur, dans le but d'en contrôler les populations. C'est à l'INRA que revient le rôle de coordonner les travaux et notamment d'assurer les études sur la biologie de l'espéce. L'ACTA a mené des études en captivité, ainsi qu'une expérimentation de plein champ en Haute-Savoie. Enfin, le SPV a pris la responsabilité de l'évaluation au champ des rodenticides et du développement d'un systéme de prévision en Franche-Comté et en Auvergne-Limousin. L'article résume les 8 années de travaux et souligne les questions restées en suspens. II cherche à situer le problème d'A. terrestris dans la problématique plus vaste de l'étude des rongeurs ravageurs de cultures en France et débouche sur l'analyse des choix des thématiques scientifiques qu'il convient de développer dans le contexte agricole moderne.     

A pattern in the appearance of cucumber powdery mildew in Dutch glasshouses

An inquiry was held in 1982, 1983 and 1984 to collect information on the survival and dispersal of cucumber powdery mildew. Growers who planted a crop in December, January or February were asked when they observed mildew for the first time in their crop. A gradual increase in the number of infected crops was observed from planting until May. The earliest observations of infected crops were immediately after planting. The weeks of the first observation of mildew, the disease-free periods and the apparent rates of increase of infected crops are presented for various districts. In the districts with the highest crop density (Pijnacker), mildew was generally observed early in the growing season, while the apparent rate of increase of infected crops was higher than in other districts. In the district with the lowest crop density (Northern Netherlands), mildew was observed late in the growing season and the apparent rate of increase of infected crops was low. Possible means of survival and dispersal of inoculum are discussed. It is suggested that overwintering of inoculum is possible because cucumber plants are grown all year round. Dispersal of cucumber powdery mildew is suggested to take place by transportation of infected planting stock, visitors and wind.     

Note on the Control of Olive Fly (Dacus oleae [Gmel.]) by Means of Low and Ultra-low Volume Bait-spraying

In 1967, 1968 and 1969 the efficacy of aerial low volume and ultra-low volume bait-spraying against Dacus oleae (Gmel.) was compared in Greece. Results were mainly assessed by periodical trapping and by post-treatment countings of the percentage of attack in sampled olives. No difference between the effect of the two methods became apparent. It is deemed necessary, however, to repeat the experiments under conditions of heavier infestation.     

Radiochemical distribution and decline studies with bromoxynil octanoate in wheat

Bromoxynil octanoate labelled with ¹⁴C in the ring or in the cyano-group was applied to wheat seedlings at the two-leaf or fully-tillered stage and at rates equivalent to up to 16 oz a.i./acre. The plants were grown either in environmental chambers under controlled conditions for up to 28 days, or outdoors under field conditions for various periods up to harvest. Initially, elimination of radioactivity occurred more rapidly with bromoxynil-cyano-[¹⁴C]-octanoate than with bromoxynil-ring-[¹⁴C]-octanoate, indicating metabolic attack on the cyano group. Under outdoor conditions with ring-[¹⁴C]-herbicide applied at the two-leaf stage, only 12% of the radioactivity was retained after 28 days, principally in the treated leaves. When application was made at fully-tillered stage, about 33% of the ¹⁴C was retained after 56 days, almost entirely in the treated senescent leaves at the base of the plant. There was very little translocation of the herbicide or of any major metabolite. The level of radioactivity in harvested grain and in straw more than 7.5 cm above the ground was very low, even after very late application of ring-[¹⁴C]-labelled herbicide. The amount of bromoxynil octanoate, together with any metabolite retaining part of the aromatic ring, did not collectively exceed the equivalent of approx. 0.01 parts/million bromoxynil octanoate.     

The application of picloram-14C to bracken

Experimental systems were produced from fragments of bracken rhizome and picloram-¹⁴C was applied to frond laminae, rhizome apices, frond buds and roots and translocation assessed 7 days after treatment. The isotope was readily taken up by all organs and freely translocated to associated fractions of the rhizome except in the case of laminae from which distribution was very poor. Accumulation of activity in the roots was considerable following treatment of the frond buds but was limited in the frond buds. Poor translocation of herbicide from treated frond laminae is considered a possible explanation of poor control in the field when bracken is sprayed in July. Lapplication du picioram e¹⁴C à la fougère Des systèmes expérimentaux ont étéétablis en utilisant des fragments de rhizome de fougére et du piciorame ¹⁴C a été appliqué sur les limbes des frondes, les apex des rhizomes, les bourgeons des frondes et les racines. La migration fut évaluée sept jours aprés le traitement. L'isotope a été facilement absorbé par tous les organes et librement transporté aux fractions correspondantes du rhizome, sauf dans le cas des limbes è partir desquels la distribution a été très faible. L'accumulation de ractivité dans les racines a été considérable è la suite du traitement des bourgeons de frondes mais a été Iimitée dans les bourgeons de frondes. Une faible migration de I'herbicide depuis les limbes des frondes est considérée comme une explication possible du désherbage mediocre auchamp, lorsque la fougère est traitée en juillet. Die Anwendung von PicIoram-¹⁴C zu Adlerfarn Aus Rhizomstücken von Adlerfarn wurden Versuchsp-flanzen gezogen und auf die Wedelspreiten, Rhizomapices, Wedelknospen und Wurzein- Picloram-¹⁴C appliziert. Die Transiokation des Herbizids wurde eine Woche nach der Behandlung gemessen. Das lsotop wurde von alien Pflan-zenorganen schnell aufgenommen und in die dem Rhizom benachbarten Pflanzenteile transloziert; bei Behandlung der Wedelspreiten war jedoch nur eine geringe Verteilung fest-zustellen. Nach Behandlung der Wedelknospen war in den Wurzein eine beträchtliche, aber in den Wedelknospen nur eine geringe Aktivitätsanreicherung feststellbar. Für den schwachen Bekämpfungserfolg des Adierfarns im Freiland bei Spritzungen im Juli, wird die geringe Transiokation des Herbizids aus den Wedelspreiten als mögliche Erklärung angesehen.     

Timing of seedling emergence and reproduction in some tropical dicotyledonous weeds

The periodicities of seedling emergence of seventeen dicotyledonous weeds were determined and fourteen of these examined in detail. In addition, the periodicity of vegetative growth and reproductive development was recorded for all dicotyledonous species in the study area. Field emergence at monthly intervals during one year was compared with the emergence of seedlings from soil transferred to a shade house and kept moist. This comparison suggested that lack of water during the dry season was the dominant factor controlling germination, although several species failed to germinate when given adequate water under shade-house conditions indicating that innate or induced dormancy also occurred. Species were separated into two groups based on the liming and duration of their main phenological stages. The first group contained species which had individuals present throughout the year while plants in the second group died during the dry season and reappeared at the start of the wet season. Most species in the former had some individuals flowering or shedding seed all year round while the latter had a short period of vegetative growth followed by prolonged reproduction. The possibility of using emergence and phenological data for improving tropical weed control is discussed.     

Binucleate Rhizoctonia sp. AG G causing root rot in yacon (Smallanthus sonchifolius) in Brazil

A new rot caused by a binucleate Rhizoctonia sp. affecting the tuberous root cortex of the domesticated yacon ( Smallanthus sonchifolius ) has been observed in Brazil. Isolates of a binucleate Rhizoctonia sp. were collected from roots with rot symptoms and characterized by the number of nuclei per cell, hyphal anastomosis, RAPD molecular markers, ITS-5·8S rDNA sequence and pathogenicity tests. All isolates had a mean of 1·9–2·2 nuclei per cell and anastomosed with the binucleate Rhizoctonia sp. AG G-tester strain. RAPD analysis was carried out between 11 isolates recovered from yacon and 11 AG (A, Ba, Bb, Bo, C, D, F, G, O, P, Q) standard testers of binucleate Rhizoctonia sp. Genetic similarities of 94·8–100% were observed among isolates of the binucleate Rhizoctonia sp. from yacon and all isolates were genetically more closely related to the AG G tester than other strains according to upgma analysis using RAPD markers. Homologies of complete ITS nucleotide sequences were 100% between binucleate isolates of Rhizoctonia sp. from yacon and the AG G tester. According to pathogenicity tests, the isolates caused typical rot symptoms of yacon tubers 90 days after inoculation     

Efficacy of Different Control Methods Applied Separately and in Combination in Managing Root-knot Nematodes (Meloidogyne spp.) in Common Beans

Investigations on the efficacy of various methods of managing root-knot nematodes in microplots and under field conditions revealed that soil solarization, Furadan 5G and Tagetes erecta applied separately or in combination with other control methods, were the most effective in reducing the numbers of three root-knot nematodes, and root gall and egg mass indices. These management methods also resulted in significant increases (P0.05) in number of pods per plant, number of seeds per pod and 100-seed weight, and increased seed yield by up to 96.7 percent. Farmyard manure and Crotalaria ochroleuca were the least effective treatments. The use of T. erecta was the most economical root-knot nematode control method.