THE DISTRIBUTION OF AERIALLY-APPLIED SPRAY DEPOSITS IN SPRUCE TREES

Abstract

AbstractA plot of 6 m tall white spruce trees was treated with an aerial application of an oil-base spray containing a non-toxic compound, Tris (2 ethyl hexyl) phosphate (referred to as TOF), which was amenable to gas-liquid chromatographic analysis The spray was formulated and applied at a rate to approximate the eastern Canadian operational spruce budworm control sprays. Meteorological measurements were made in the airspace from mid-crown height to the height of spray emission for the period of spray application and deposition. Spray deposit collection units (kromekote cards and glass plates) were used to record spray deposit at ground level.Foliage samples and complete branches were taken from each of three trees at a series of heights and each of the four compass quadrants and returned to the laboratory for chemical analysis. Spray deposit was determined in terms of ppm TOF on the foliage. The kromekote cards provided information from which the drop size characteristics of the spray cloud and the deposit in terms of drops/cmK were determined; a colorimetric analysis of spray deposit on the glass plates indicated the volume of spray deposited.Analysis of the spray deposits on the foliage indicated gradients in deposits with most on the upper, outer, upwind portions of the trees and least on the lower, inner, downwind portions. These differences were significant. These gradients can be attributed to two weather factors (a) the prevailing wind drifting the pesticide cloud through the forest canopy resulting in a filtering to produce a decreasing gradient from upwind to downwind side of the tree, and (b) air eddies around the tree tops resulting in an increased deposit and slight penetration of the spray cloud on the outer downwind portions of the tree.This study demonstrates that a finely atomized spray applied to a white spruce forest under suitable weather conditions will give a deposit on the outer portions of the tree with a variation of only about 50% in spray deposit but with significantly less deposit on the inner, lower portions of the tree.