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New Zealand Plant Protection 55 (2002): 163-167

Lower formulation pH does not enhance bentazone uptake into plant foliage

Z.Q. Liu

ABSTRACT

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.

Keywords: uptake, bentazone, weak acid herbicides, pH.

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