ALBERT

Notes: Third harmonic generation near the focal point of a tightly focused beam is used to probe microscopical structures of transparent samples. It is shown that this method can resolve interfaces and inhomogeneities with axial resolution comparable to the confocal length of the beam. Using 120 fs pulses at 1.5 μm, we were able to resolve interfaces with a resolution of 1.2 μm. Two-dimensional cross-sectional images have also been produced. © 1997 American Institute of Physics.

Notes: Summary. Experiments with granular dichlobenil have been carried out under glasshouse conditions, in order to estimate the area of contamination near the surface and the leaching beneath by the toxicant from individual granules. Special techniques using a restricted range of granule size and ryegrass as indicator plant have been developed.The area of contamination produced by grouping several granules together or by granules containing different concentrations of toxicant, increased generally with, but not in proportion to, the amount of toxicant applied. The area of contamination and the depth of leaching were smaller in moist soil than in drier soil, due possibly to the transport and action of dichlobenil in the vapour state. When granules were placed on sub-irrigated soil, the maximum area of contamination was reached after 6 days for 7.5% granules, and after 12 days for 15% and 25% granules; after 19 days, the area decreased markedly, especially in the case of 7.5% granules. Soil composition, especially organic matter content, affected strongly the area of contamination near the surface and the leaching beneath.The importance of uniform distribution of granules in field practice is stressed in conclusion.Migration dans le sol du dichlobénil appliqué sous forme de granules

Notes: Résumé. Une série d'essais de laboratoire et en plein champ ont été effectués pour étudier le comportement du PEBG (S-propyl N-butyl-N-éthylthiolcarbamate), et les possibilités de son utilisation pour le désherbage des betteraves, en comparaison d'autres herbicides.Les pertes par volatilisation du PEBC ne paraissent pas constituer un facteur important de disparition lorsque l'herbicide est appliqué sur un sol sec, sans incorporation mécanique; l'activité herbicide est même accrue après une exposition de plusieurs jours à la sèche du sol. La teneur du sol en argile et en matière organique modifient l'activité du PEBC.Dans les essais en plein champ sur betteraves sucrières, fourragères et potagères, le PEBC était pulvérisé, en pré-semis ou en pré-émergence, sur un sol sec, et l'herbicide était activé, après un intervalle allant de 12 h à 48 h, par une irrigation par aspersion ou par une pluie. En pré-semis, on a comparé au Iraitement non incorporé, l'incorporation super-ficielle par roulage et l'incorporation profonde par disquage; l'activité herbicide du PEBC était significativement inférieure quand on incorporait profondément. Dans deux essais de pré-émergence, l'incorporation par roulage a été comparée à un traitement non incorporé; l'efficacité sur les mauvaises herbes sensibles au PEBC était un peu ineilleure quand la pulvérisation était suivie d'un roulage.L'action du PEBC était très bonne contre les graminées annuelles et assez bonne contre Amaranthus spp. et Portulaca oleracea, qui constituent la majorité des advent ices infestant les champs de betteraves en Israël. Les crucifères étaient assez tolérantes et les adventices pérennes étaient résistantes. Les betteraves sucrières, fourragères et potagères ont toléré des doses de PEBC capables de réaliser un désherbage satisfaisant. L'activité du traitement a persisté durant 1 à 2 mois.Dans les conditions sptéifiques de la culture betteravière en Israël, l'application du PEBC avant la levée, suivie éventuellement par un roulage, constitue done un traitement herbicide intéressant.Studies on the behaviour of PEBC (S-propyl N-butyl-N-ethylthiolcarbamate) and its use for weed control in beet

Notes: Ten herbicides, bromacil, chlorthal-dimethyl, diphenamid, diuron, fluometuron, neburon, prometryne, pyrazon, simazine and trifluralin at two doses were repeatedly sprayed, in autumn and in spring, for 4 consecutive years on non-cultivated, sprinkler-irrigated field plots. Herbicidal effect was assessed at 1–2 month intervals on the natural weed population and after each observation a paraquat + diquat spray destroyed emerged weeds. The response of various weed species to herbicides varied markedly but a herbicide-induced shift in the composition of weed population did not occur, presumably because of the paraquat treatment.The overall phytotoxicity to weeds present was, in decreasing order: diuron, bromacil, simazine, trifluralin, prometryne, neburon, fluometuron, pyrazon, diphenamid, chlorthal-dimethyl. Persistence of herbicides was in decreasing order: diuron = bromacil, simazine, neburon (at higher rate), fluometuron, trifluralin, prometryne. Control produced by pyrazon improved with the number of applications, but that of diphenamid and chlorthal-dimethyl remained weak and short. After repeated applications, the activity of these herbicides increased or remained at similar level, but in no case decreased.Soil samples were taken 5 months after each application and bioassayed. Phytotoxic residues were detected beneath the disturbed top-soil from bromacil, diuron, fluometuron and simazine after the first application, and from neburon after the second application; residues from trifluralin were found in the top soil only after the fifth application. After the seventh spraying, residues of bromacil were found in the 45–60-cm soil layer.Ammonia content in soil samples taken from treated plots after the fourth, sixth and seventh application was generally similar to the untreated control. In these samples, nitrate content appeared to be correlated negatively with remaining weed number; the control thus contained less nitrate than efficient herbicidal treatments. Soil samples taken after the seventh application of bromacil, diuron, fluometuron, neburon and simazine, which contained appreciable residual concentrations, did not show significant differences from control, in an in vitro nitrification test.