Bentazone uptake into plant foliage as influenced by surfactants and carrier pH

The influence of surfactants and carrier pH on the foliar uptake of bentazone, a representative weak acid herbicide, was studied using bean ( Vicia faba) and mustard ( Sinapis alba) plants. The promoting effect of surfactants on bentazone uptake varied with surfactant hydrophobe structure, ethylene oxide ( EO) content, and surfactant and bentazone concentrations. Among the 5 hydrophobe moieties tested, the efficiency order was C-13/C-15 linear alcohols > C-10 linear alcohol > C-16/C-18 linear alcohols > nonylphenol > octylphenol. For C-13/C-15 linear alcohol surfactants of differing EO content, the enhancing effect on bentazone uptake was 5 EO > 10 EO > 14 EO. All surfactants improved uptake more when bentazone was applied at low concentration. The effect of carrier pH ( 5, 7, and 9) on the uptake of bentazone, applied both as unformulated acid and as a sodium salt, was also investigated in this work. Lower carrier pH did not provide greater uptake for bentazone sodium salt and was only beneficial for the uptake of bentazone acid applied at very low concentration. The results are discussed in relation to the current knowledge on pesticide uptake as influenced by surfactants and the change in lipophilicity and solubility of weak acid chemicals at different pH.