EFFECTS OF MONODISPERSE ALCOHOL ETHOXYLATES ON MOBILITY OF 2,4-D IN ISOLATED PLANT CUTICLES

Effects of monodisperse ethoxylated n-alcohols on the mobility of 2,4-dichlorophenoxyacetic acid (2,4-D) in cuticular membranes isolated from pear (Pyrus communis L.) and bitter orange (Citrus aurantium L.) leaves, and from green pepper (Capsicum annuum L.) and tomato (Lycopersicon esculentum L.) fruits were measured. The surfactants were of the type C(i)E(j), where i is the number of carbon atoms of the alcohol, j is the number of ethylene oxide groups and i = 2j. Surfactant effects on mobility increased with time and were inversely proportional to the mobility of 2,4-D in cuticles prior to surfactant treatment. C4E2 was barely effective. C6E3, C8E4 and C10E5 were the most effective surfactants, as they increased the mobility of 2,4-D by 15- to 20-fold and the effects were established very rapidly. As the molecular weights of the surfactants increased, their effects decreased and the time-dependence of effects became more pronounced. Response (susceptibility) of cuticles to surfactant treatment varied among plant species and increased in the order bitter orange < tomato < pear < pepper. Surfactant effects did not correlate with HLB or with cuticle-water partition coefficients of surfactants tested. It is argued that penetration of surfactants into cuticles is a prerequisite for increasing 2,4-D mobility and that effects should be proportional to the surfactant concentration in the cuticles. Since rates of foliar penetration are proportional to solute mobilities in cuticles it is expected that the surfactants that were most effective in this study would be suitable accelerator adjuvants for systemic pesticides.