Effect of surfactants and oils on the phytotoxicity of difenzoquat to Avena fatua, barley and wheat

Controlled drop (CDA) and conventional applications of difenzoquat to pot-grown Avena fatua were compared. With the recommended surfactant (0.5% v/v Agral), very low volume CDA was less effective than conventional spray application. However, addition of extra Agral or various blends of paraffinic oil with Agral and the surfactants Burtemul A2 or Burtemul P2 improved the effects of the CDA treatments. When difenzoquat was absent the additives were inactive against A. fatua. They had little direct effect on wheat and barley and did not substantially increase the phytotoxicity of difenzoquat to these crops. Oil/surfactant mixtures were less viscous than high concentrations of Agral, and so easier to spray. In a pot experiment, smaller (150 μm diameter) drops of difenzoquat solution were more active against A. fatua than larger (200 μm-300 μm) drops. Reduction of the spray volume within the range 40 litres/ha to 5 litres/ha also reduced phytotoxicity. An oil/surfactant additive improved the activity of all difenzoquat CDA treatments. There was slightly more effect at the lowest spray volume but interactions between additive and application treatments were not statistically significant. When simulated rain treatments were applied 2 h or 5 h after spraying, difenzoquat controlled drop application was much less phytotoxic than a conventional 150 litres/ha treatment. However, addition of an oil/surfactant mixture markedly improved the performance of CDA. When rain was withheld for 24 h the additive had relatively less effect. In the field an oil/surfactant mixture improved control of A. fatua by difenzoquat with both conventional and controlled drop treatments. The additive did not increase injury to the wheat crop. The oil/surfactant mixtures markedly improved the spreading and wetting properties of sprays. This reduced localised contact injury, which, it is suggested, improved uptake and translocation of difenzoquat.