Spray Particle Size Distribution in Greenhouse ULV Applications to Poinsettia12

Abstract

Spray particle size distribution was studied in dense poinsettia foliage after mechanical aerosol (or ULV) applications of mineral oil resmethrin formulations for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), in a commercial greenhouse. A systematic arrangement of Teflon®-coated microscope slide sampling units was used to monitor both spray droplet distribution in horizontal and vertical directions in the foliage and particle size deposition on upper and lower leaf surfaces at each sampling position. Seven distinct application types, consisting of 2 avg particle size ranges (10–13 and 30–40 μ m mass median diam (MMD)) and 4 application techniques in different comhinations, were tested in a total of 19 spray tests. Microscope slide analysis provided MMD and avg deposition volume per unit of slide area data. Statistical analyses of these data indicated that 15–25 μ m MMD was the optimum spray particle size for greenhouse whitefly control and that application technique was an important factor. Spraying techniques that maximize the amount of air circulation within the foliage during application were most efficient.