A simple nozzle design/modification is presented which takes advantage of the known effect of the increasing biological efficacy of a pesticide with decreasing drop size for insecticides and perhaps fungicides. However, applying active ingredient (AI) in unassisted fine sprays leads to poor canopy penetration and increased drift hazard. Therefore, the air entrained by medium-coarse nozzles spraying water is utilised to impart kinetic energy to a finer spray containing AI. A fine nozzle is sprayed into a medium-coarse spray at an angle of approximately 15 degrees from vertical approximately 10 cm below the medium-coarse nozzle, spraying into the direction of travel of the sprayer. The subsequent spray cloud consists of: small drops, typically < 200 mu m, containing AI; small to large (< 700 mu m) drops containing no AI; and drops of all sizes (20-700 mu m) containing various concentrations of AI, caused by drops containing AI coalescing in-flight with drops without AI. Consequently, a substantial proportion of the large drops in the spray cloud that would normally contain excessive quantities of AI carry none, allowing for the possibility of a reduction in AI requirements for pest control. The atomisation characteristics and potential drift problems of such a nozzle system were investigated. The results show that the velocity characteristics of the carrier (medium) spray were imparted to the fine spray, removing the problem of low spray cloud kinetic energy. Coalescence of drops in-flight was approximately 50%. Drift measurements in a large wind tunnel showed that drift increased four-fold at 4 m/s windspeed and approximately two-fold at 2 m/s. Taking into account the expected reduction in AI requirements, at 2 m/s, drift was quantitatively approximately the same as that of the medium nozzle. (C) 1997 Elsevier Science Ltd .
