Factors influencing the survivorship of the burrowing nematode,Radopholus similis (Cobb.) Thorne in two types of soil from banana plantations in Martinique

The burrowing nematode, Radopholus similis (Cobb.) Thorne, causes the most damage to bananas. To minimize nematicide applications, cropping systems that use fallow, crop rotation and clean planting material have been developed in the French West Indies. In order to optimize the benefit of the intercropping period, we studied the survivorship of R. similis in different soil types and conditions. We monitored the survivorship of calibrated populations of R. similis in the laboratory on a Nitisol and on an Andosol, two soils derived from volcanic ashes and pumices. We studied water potentials ranging from 0 to ?700 kPa on undisturbed soil and on soil previously frozen to get rid of living nematodes. Mortality of adult R. similis decreased regularly, and was fairly well described by Teissier's model. In the previously frozen soils, R. similis survived longer in wet soils (half-life of 21–46 days at 0 to ?5 kPa) than in dry soils (half-life of less than 10 days between ?80 and ?250 kPa). In contrast, in undisturbed soils, R. similis survived longer in dry soils: half-lives ranged from 57 days at ?273 kPa to 17 days at water saturation in the Andosol, and 36 days at ?660 kPa to 14 days at water saturation in the Nitisol. These results are consistent with the absence of anhydrobiosis in R. similis, unlike Pratylenchus coffeae. P. coffeae survivorship curves over time do not follow a model derived from exponential decrease like Teissier's model. These results also show that the recommended one year host-free period required to sanitize soils cannot be shortened without risk, even if flooding the soil could improve it.     

Biological effects and metabolism of fenoxycarb after treatment of the fourth and the fifth instars of the tobacco budworm,Heliothis virescens F.

Treatment of 4th and 5th instar larvae of Heliothis virescens with different amounts of fenoxycarb induced an increase in weight of the 5th larval instar, prolongation of the 5th larval instar period, or the formation of dauer larvae. No effects were observed during the 4th instar and the moult to the 5th larval instar. To check whether these effects were due to persistence of fenoxycarb in treated larvae, metabolism of this chemical was analysed. Larvae were fed with radio-labelled fenoxycarb at the first day of the 4th or at the first day of the 5th larval instar. Behaviour of the radio-labelled compounds was followed during each instar. At the time of gut purge, the whole of the radio-labelled material was excreted. The effects observed during the 5th instar of 4th-instar-treated larvae do not appear to be due to the persistence of fenoxycarb. The main metabolites of fenoxycarb were identified using coupled gas chromatography and mass spectrometry.     

Field effectiveness and biodegradation of cyclic imides in lettuce field soils

When 42 field trials, carried out from 1975 to 1989 in the Perpignan region (France) for control of lettuce drop caused by Sclerotinia minor, were compared, a decrease in the field effectiveness of cyclic imides was perceptible, beginning approximately in 1985. Moreover, in 15 out of 46 commercial lettuce fields surveyed in 1988 and 1989, the effectiveness of iprodione was less than 80%, the level of acceptability for the growers. In these fields, fungicide degradation, estimated by 3,5-dichloroaniline formation, was faster than in soils in which S. minor was adequately controlled. Statistical analyses showed that the iprodione degradation index was strongly linked to the history of fungicide treatment and was weakly correlated to soil pH or clay content. All the fields characterized by low iprodione effectiveness were associated with high levels of fungicide treatment and high degradation index. Moreover, we observed that soil from a field which had received iprodione for more than ten years did not degrade vinclozolin quickly, while soil from another part of the same field which had been treated with vinclozolin for eight years degraded vinclozolin faster than iprodione.     

Interaction of benzimidazole-N-sulfonamides with the cytochrome b/c1 complex of Pythium aphanidermatum

Experiments with intact cells and submitochondrial fractions of Pythium aphanidermatum (Edson) Fitz. indicated an interference of benzimidazole-N-sulfonamides with the NADH- or succinate-driven electron transport system between cytochromes b and c. Comparison with Ustilago maydis (DC) Corda and Botrytis cinerea Pers. ex Fr. revealed that this effect is Oomycetes specific. The molecular interaction between benzimidazole-N-sulfonamides and the mitochondrial cytochrome b/c₁ complex from P. aphanidermatum has been investigated. Binding assays with [¹⁴C]52232 RP (dimefluazole) indicated a time- and dose-dependent labelling of two proteins. The molecular mass of one labelled protein and the competition of the binding with antimycin A suggest that benzimidazole-N-sulfonamides interact with the Q₁-centre of cytochrome b. Furthermore, experiments with doubly labelled [³H][¹⁴C]CGA 323103 revealed a possible irreversible inactivation of the b/c₁ complex leading to covalent linkage of the dimethylsulfonamoyl moiety to the target site.     

Oils for weed control: Uses and mode of action

The role of oils in herbicide treatments is reviewed, both in terms of their own intrinsic activity and of their enhancement of the performance of other herbicides. The phytotoxicity of oils can be related to their physical properties. Their efficacy as adjuvants can vary with the plant/pesticide combination involved, and differences may also be observed between oils of mineral and vegetable origin. The possible mechanisms involved in the enhancement of activity by oils are discussed and areas of work that might elucidate these fun her are indicated.     

Versuche mit einem Prostaglandinanalog zur Zyklussynchronisation beim Rind unter hormonanalytischer und klinischer Kontrolle

1. Durch intramuskulare Injektion von 0,5 mg des Prostaglandinanalogs ICI 80 996 beim Rind während der Gelbkörperphase des Zyklus kann nach 15–24 Stunden ein Abfall der Progesteronwerte unter 1 ng/ml Blutplasma und damit eine nachhaltige Luteolyse erreicht werden. Die sich anschließende Brunst ist ovulatorisch und feral. Das Präparat wird ohne Nebenwirkungen vertragen. 2. Durch zweimalige Injektion (d. h. je 1 mal 0,5 mg i. m.) im Abstand von 11 Tagen kann dieser Luteolyseeffekt zu Brunstsynchronisationen herangezogen werden; dabei ist eine Zykluskontrolle oder Brunstbeobachtung nicht erforderlich. 3. in 8 Feldversuchen konnte bei 213 Tieren ein Synchronisationserfolg von 90,6 % und, nach KB in der 1. induzierten Brunst, ein Konzeptionsergebnis von 54,7 % (bzw. von 60,1 %, wenn man die Auswertung auf die erfolgreich synchronisierten Tiere beschränkt) erzielt werden. Die KB bei 119 nicht behandelten Kontrolltieren, die in 5 dieser 8 Versuche zur Verfugung standen, war zu 60,3 % erfolgreich. 4. In einem Problembestand konnte die Fertilitätslage durch das biotechnische Vorgehen der Prostaglandinanwendung unmittelbar nicht verbessert werden 5. Die palpatorischen Ovarbefunde zum Zeitpunkt der KB ergaben, daß Tiere mit aprungbereiten Follikeln'zu 65 %, mit kleinen, nicht reifen Follikeln zu 50,8 % und mit bereitsgesprungenen Follikeln zu 15,8 % konzipierten. 6. Die bei einem Teil der Versuche eingesetzte zusdtzliche Behandlung mit 1,0 bzw. 1,5 mg des Gonadotropin-Releasinghormons (LRH-Hoechst 471) i. m. zum Zeitpunkt der Besamung zeigte bezüglich des Konzeptionsergebnisses eine positive Tendenz.