Effects of formulation with different adjuvants on foliar uptake of difenzoquat and 2,4-D: model experiments with wild oat and field bean

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 C-14-herbicides were applied to leaves as c. 0.2-mu-l droplets, usually containing 0.5 g l-1 active ingredient, plus adjuvants in the range 0.05-5 g l.1. The addition of non-ionic polyoxyethylene surfactants to solutions of both herbicides could induce considerable foliar uptake. Aliphatic C-13/C-15 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 l-1), whilst that in field bean was much higher (>0.5 g l-1). For 2,4-D, surfactants at >0.5 g l-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 C-14-herbicides translocation was directly related to the quantity of radiolabel that had penetrated the leaf tissue.