Summary. The phytotoxicities in a number of soils of lenacil, linuron, prometryne and simazine to two indicator plants were determined in field and glasshouse experiments. The results were compared with estimates of the adsorption capacity of the soils obtained by two methods using dimethylaminobenzaldehyde as a model adsorbate. The possible influence of other soil properties was also considered.
One of the adsorption measurements had some predictive value for glasshouse behaviour but was not markedly superior to soil organic carbon content for this purpose. None of the factors studied was usefully correlated with field performance. Results from field experiments in spring were poorly correlated with those from similar experiments in autumn. Neither set of field results related closely to those obtained in the glasshouse. It is concluded that the influence of climate was more important than that of soil type.
La phytotoxiciti de quelquts herbicides dans des experiences en pots et en plein champ, en relation avec les propriétés du sol
The uptake of herbicides such as atrazine by emerged plants is closely associated with the ingress of water required for transpiration and development (Davis, Gramlich & Funderburk, 1965). The results reported here were obtained in the course of experiments with turnip seeds during the process of germination. They show that at this earlier stage of development the initial accumulation of atrazine can be independent of water uptake, and takes place onto the seed coat. Under field conditions many weed seeds can be expected to make initial contact with soil-applied herbicides at a similar stage of development.Glass-fibre discs 9 cm in diameter were placed in petri dishes and moistened with 6 ml of aqueous suspensions of commercially-formulated atrazine wettable powder containing 50% w/w a.i. Samples of turnip seeds (cv. Green Globe), weighing 2'10 g and consisting of approximately 1000 seeds were exposed to atrazine by placing them on the treated discs for times ranging from 0-58 to 36-0 hr. The seeds were either dry at the start of exposure, in which case they rapidly imbibed water from the discs, or they were 'pre-imbibed', in which case there was negligible water uptake except at the longest exposure. Seed samples were pre-imbibed by immersion in distilled water at 4° C for 15 hr followed by careful blotting; these samples had taken up on average 0-53 g water/g dry seeds before being placed on the atrazine-treated discs.There were three replicates of each treatment. At the end of the exposure period the seeds from two replicates were removed from their dishes and rinsed several times in distilled water. Four groups of ten seeds were separated from each rinsed sample, planted into separate pots of relatively non-sorptive soil, and grown in the glasshouse to indicate the phytotoxicity of the quantities of atrazine which had been accumulated. The fresh weights of the above-ground parts of the seedlings were recorded when the controls had grown to the early 2-leaf stage, and expressed as a percentage of the appropriate distilled-water controls. The quantity of atrazine which each of these samples had accumulated was deduced from chemical estimation of the amount which remained in each dish and its washings, using hydrolysis and ultra-violet spectrophotometry
Agrochemical Division, Ciba-Geigy (UK) L td., IJ/hittlesford, Cambridge CB2 4QT.Summary. As a powder seed treatment on wheat, barley and oats a mixture of quinacetal-sulphate + maneb + y -BHC gives a disease control spectrum similar to that of organo-mercury standards, except against oat leaf spot '(pyrenophora avenae) on which quinacetal-sulphate + maneb i s more effective. In small-plot trials under poor seed-bed conditions the quinacetal-sulphate mixture gave improved crop establishment compared with organo-mercury standards possibly due to improved activity against soil-borne pathogens. Overdose rates were better tolerated than overdoses of organo-mercury + y -BHC. Of 63 farmers in the UK supplied with seed treated in commercial equipment, 60 obtained improved plant stands with quinacetal-sulphate + maneb t y -BHC in comparison with organo-mercury standards. The farm results wereachieved in favourable as well as unfavourable seed-bed conditions and appear to be due t o the better tolerance by individual cereal seeds of overdoses of the quinacetal-sulphate mixture. PANS 20: 127-128, 1974.
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