Lower formulation pH does not enhance bentazone uptake into plant foliage

摘要

Lower pH generally favours the diffusion of weak acid compounds in vitro into plant cells. Such a rule may not be applicable to the uptake of formulated weak acid herbicides applied to plant foliage in vivo. In this study, the effect of spray formulation pH (5, 7 and 9) on the foliar uptake of a weak acid herbicide, bentazone which is used as a formulated salt, was investigated using three plant species, mustard (Sinapis alba), wheat (Triticum aestivum) and bean (Vicia faha). Greater uptake of the herbicide occurred at pH 9 and pH 7 than at pH 5 on mustard and wheat leaves. Uptake of bentazone into bean was slow (<20 percent after 24 h) regardless of carrier pH. However, in the presence of a surfactant, faster uptake was achieved with higher pH. The results are discussed in relation to the lipophilicity and the solubility of weak acid chemicals as influenced by pH.