Cuticular penetration of foliar-applied diflufenican in Galium aparine L

The herbicide diflufenican is an effective pre-emergence compound used for the control of 'difficult' dicotyledonous weeds in winter cereals. It is less efficient when applied post-emergence, activity being found to depend on the dose reaching the apical meristems. Contact with diflufenican had no significant effect on other parts of the plant and translocation was negligible. In the absence of surfactants, the uptake of diflufenican was minimal and complete approximately 2h after treatment. Surfactant incorporation increased the time over which uptake occurred, efficiency depending on surfactant type and lipophilicity. 'Silwet L- 77' (1.0 g litre-1) was the only surfactant tested which caused sufficient damage to the apex to prevent subsequent recovery of the plant. The effect of nonylphenol ethoxylate surfactants at concentrations above the critical micelle concentration (< 1.0 g litre-1) appeared to be partly attributable to leaf damage caused by the surfactant, possibly facilitating uptake. Increasing leaf coverage by surfactants did not necessarily improve uptake and activity.