Interactions occurring during the surfactant‐enhanced foliar uptake of seven model organic compounds were examined using two homogeneous surfactants, hexaethylene glycol monotridecyl ether (C13E6) and hexadecaethylene glycol monododecyl ether (C12E16). Surfactant–compound and compound–surfactant interactions were detected by measurement of their relative uptake rates following application of c. 0·2 μl droplets of the corresponding radiolabelled formulations. The magnitude of surfactant–compound interaction was found to vary according to the physicochemical properties of both the compound and the surfactant, and was influenced by surfactant concentration and target plant species. Interactive and non‐interactive mechanisms, both leading to substantial enhancement of compound uptake, could be identified, but their precise nature could not be elucidated. Although penetration of C13E6 into the site of application appeared to be essential in order to activate the uptake of a compound, substantial absorption of C12E16 was not always required to produce the same effect. The results are discussed in the light of possible sites and modes of action for activator polyoxyethylene surfactant adjuvants.

Summary: Résumé: Zusammenfassung The effect of different adjuvants on the foliar uptake of difenzoquat methyl sulfate and sodium 2,4‐D was studied in wild oat and field bean plants growing under controlled environmental conditions. The 14C‐herbicides were applied to leaves as c. 0–2‐μl droplets, usually containing 0.5 g 1−1 active ingredient, plus adjuvants in the range 0.05–5 g 1−1. The addition of non‐ionic polyoxyethylene surfactants to solutions of both herbicides could induce considerable foliar uptake. Aliphatic C13C13 alcohol surfactants generally improved uptake more than nonylphenol surfactants when used at equivalent concentrations and ethylene oxide (EO) contents. The surfactant threshold for enhancement of difenzoquat uptake in wild oat was very low (0.05 g 1−1), whilst that in field bean was much higher (>0.5 g 1−1). For 2,4‐D, surfactants at >0–5 g 1−1 were needed to produce substantial increases in its uptake into both species. Although surfactants of low EO content (5–6) were less efficient at promoting difenzoquat uptake than those of higher EO content (10–20), particularly in wild oat, there was little dependence on surfactant EO content for enhancement of 2,4‐D uptake. Adjuvants with humectant properties also promoted penetration of difenzoquat, but less so than alcohol or nonylphenol surfactants. For formulations of both 14C‐herbicides translocation was directly related to the quantity of radiolabel that had penetrated the leaf tissue. Effets de la formulation avec différents adjuvants sur l'absorption foliaire du difenzoquat et du 2,4‐D: modeles experimentaux sur la folle avoine et le haricot L'influence de differents adjuvants sur l'absorption foliaire du difenzoquat methyl sulfate et du 2,4 D sodium a eétéétudiée chez la folle avoine et le haricot, cultivés sous des conditions environnementales contrôlées. Les herbicides marquees au 14C ont ete appliquées aux feuilles sous forme de gouttelettes de 0,2 μl contenant 0,5 g 1−1 de matière active, avec en plus des adjuvants de 0,05 à 5 g −1. L'adjonction de surfactants polyoxyethylénes non ioniques aux solutions des deux herbicides pourrait induire un absorption foliaire importante. Les surfactants d'alcools aliphatiques C13/C15 ont généralement augmenté la pénétration mieux que les surfactants de type nonylphénol utilises à une concentration équivalente et que les oxydes d'éthylènes (EO). Le seuil de surfactant pour l'amélioration de l'absorption de difenzoquat sur folle avoine était très bas (0,05 g 1−1) tandis que sur haricot, il était beaucoup plus éievé (> 0,5 g 1−1). Pour le 2,4 D, des surfactants à une dose de >0,5 g 1−1 sont nécessaires pour produire une amelioration de son absorption chez les deux espéces. Bien que les surfactants à faible teneur en EO (5–6) fussent moins efficace pour favoriser l'absorption du difenzoquat que ceux a forte teneur (10–20), spécialement pour la folle avoine, il y avait une petite dépendance sur la teneur en EO pour l'amélioration de l'absorption du 2,4 D. Les adjuvants avec des propriétés d'humectation ...