The effect of different spray liquids on the foliar retention of agricultural sprays by wheat plants in a canopy.

The aim of this work was to examine the effect of liquid properties on spray retention in a range of situations representative of practical pesticide application. Liquids with different physical properties were sprayed with conventional flat-fan and air-induction nozzles onto outdoor-grown wheat plants (Triticum aestivum L cv Axona) at growth stages between GS 22 and GS 35. Since total retention is affected by leaf surface as well as plant growth stage and canopy density, the experiments included spraying both single leaves and groups of plants with different canopy densities. Retention on whole plants was strongly influenced by plant growth and canopy properties. Individual leaf surfaces were not as water-repellent as was found previously for younger indoor-grown plants, reducing the effect of dynamic surface tension on retention. This, combined with the increased probability of droplets hitting foliage in a denser canopy, gave reduced differences in retention between liquids when compared with similar measurements made previously on younger plants. With a leaf area index greater than 7, retention on whole plants was almost independent of liquid. Air-induction nozzles gave lower levels of retention than flat-fan nozzles, with this difference greatest when spraying high dynamic surface tension liquids and at low crop densities.