Application, Distribution and Efficacy of Electrostatically Charged Sprays on Chrysanthemums

Abstract

A hand-held sprayer, producing an electrostatically charged air-atomized spray, was used apply small droplets Dv0.5: 25um), in low volumes (∼ 30 1/ha) of aqueous sprays, to bench grown, potted chrysanthemums. Spray distribution was assessed using water-sensitive paper clipped to leaves, and microscopic examination of fluorescent tracer deposits. The biological efficacy of the deposits was determined from bioassays in which bifenthrin was applied against aphids (Aphis gossypii). These data were compared with results obtained in the laboratory using a uniform droplet generator. Particular emphasis was placed on the proportion of the spray deposits on leaf undersides, since this is where most pests occur, and upon behavioural responses of A. gossypii to sub-lethal residues of this pyrethroid. Positioning a hot-wire probe within the plant canopy showed how changes in droplet size, number of droplets available and air velocity may have influenced spray distribution at specific localities. Spray penetration of the canopy, and upper : lower leaf surface deposition on the plants had its greatest biological efficiency when the nozzle was aimed into the row, horizontally, with an air pressure of 138KPa. Comparing numbers of droplets per second, measured by the probe at different locations, with the corresponding deposits, showed that deposition and distribution were most uniform towards the center of the row, and this is attributed to still air allowing electrostatic forces to influence deposition.