Role of Formulation Ingredients and Physical Properties on Droplet Size Spectra, Deposition, and Persistence of Aerially Sprayed Aminocarb and Mexacarbate in Forest Litter and Soil Samples

Abstract

Experimental observations made in five aerial spray trials on the inter-relationships between formulation ingredients, physical properties, droplet size spectra, deposit concentration, litter and soil residues, and persistence characteristics of aminocarb and mexacarbate are described. Spray was applied over conifer forests in New Brunswick, using a Cessna 188 aircraft and Micronair® atomizers. Droplets were sampled at ground level using Kromekote® cards. Deposits of the active ingredients (AI) were collected on glass plates. The physical properties measured were relative viscosity, surface tension, volatility, and viscosity-shear rate relationship; of these, relative viscosity and volatility played significant roles on droplet size spectra and deposition patterns of the sprays. The aqueous formulations of the two insecticides were the least viscous and most volatile. They provided the smallest droplets and lowest droplets/cm2, AI deposits on glass plates, and litter and soil residues; they also had shorter persistence than the oil-based formulations. As the relative viscosity of the formulations increased, their volatility decreased gradually, and there was a progressive increase in droplet sizes, droplets/cm2, deposits of AI, and litter and soil residues. The heavy-oil-based, non-volatile formulation of aminocarb showed slight deviation from this trend with respect to droplet sizes, but the AI deposits and litter and soil residues were still the highest for this formulation, which persisted for a relatively longer period of time than all other formulations. However, none of the formulations caused any undue persistence of the residues in soil, since the levels reached below the detection limit (4 ppb) within five days after treatment.