Lower formulation pH does not enhance bentazone uptake into plant foliage

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 faba) 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 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