Spray atomization and deposition patterns of one newtonian and two pseudoplastic formulations after aerial application over a mature conifer forest in Newfoundland

Abstract

Spray atomization and deposition patterns of three formulations were investigated in five aerial spray trials in Newfoundland, to understand the inter‐relationships between physical properties, drop size spectra and recovery of the spray volume at ground level. Diflubenzuron (DFB) was sprayed at 30 g active ingredient in 2.0 L/ha. Futura XLV (Fu‐XLV) and Thuricide® 48LV (Thu‐48LV), spray formulations of Bacillus thuringiensis (B.t.), were both applied undiluted at 30 BIU/ha, but in volume rates of 2.1 L/ha and 2.36 L/ha respectively. Each of the three formulations was applied over a 15 ha plot using a Piper Pawnee aircraft fitted with six Micronair® AU5000 atomizers. Spray drops were sampled with Kromekote® cards and deposits were collected on glass plates. Physical properties measured were: viscosity at variable shear rates, volatility and surface tension. The viscosities increased progressively from low (for DFB), moderate (for Thu‐48LV) to high (for Fu‐XLV) values, showing a gradual increase in pseudoplastic behaviour of the three formulations. The volatility data indicated an inverse relationship to the viscosities, but the surface tensions were similar for all the formulations.

The highly pseudoplastic Fu‐XLV atomized into the least wide drop size spectrum. The Newtonian formulation of DFB, on the other hand, atomized into the widest drop spectrum; and the moderately pseudoplastic Thu‐48LV, into an intermediate drop spectrum. Thus viscosity and volatility were more important factors in liquid atomization and drop deposition, than surface tension. Among the three meteorological factors measured, relative humidity appeared more important in drop deposition than did wind speed and temperature, within the range measured.