The Optimum Size for Insecticide Spray Droplets

The optimum size for insecticide spray droplets is that size which gives maximum control of the target insect with minimum insecticide and minimum ecosystem contamination. Spray droplets found to be efficient in delivery of insecticide to the target insect are those with size range allowing them to be airborne and to be transported to the target by atmospheric transport and diffusion. Therefore, optimum-size droplets are those sizes small enough to be produced in maximum numbers for maximum coverage and large enough to have an optimum critical impingement velocity for optimum impingement on the target insect. Field research data which trace the point of deposition of spray droplets by size in insect ecosystems have been obtained from the fluorescent particle spray droplet tracer method. Data obtained indicate that the optimum size for insecticide spray droplets is in the range of 20µ diameter. No data were found that spray droplets larger than 100µ diameter have any substantial probability of efficient delivery of insecticide to the target insect or to its proximate foliage (where spray residues could act by secondary foliage contact). Spray droplets of 50-100µ diameter were marginal in efficiency.