The influence of form of deposit on the phytotoxicity of difenzoquat applied as individual drops to Avena fatua

SUMMARY Difenzoquat was applied as individual drops (200–400 μm diameter) to Avena fatua, using concentrations in the range 25–200 g/litre, this being appropriate to very low volume, controlled drop application. Increases in the concentration of difenzoquat within this range, or the use of larger drops, reduced the inhibition of growth of A. fatua. Increasing or decreasing the surfactant concentration from that recommended for field use also decreased performance of difenzoquat. The herbicide was more active when applied to the base of leaves and to younger leaves than to leaf tips and older leaves. In most cases reduced activity of difenzoquat was related to increased localised scorch and reduced movement of 14C-labelled herbicide from the treated region.