A Fluorescent Pigment to Measure Spray Coverage

Abstract

Spray coverage was determined by measuring emission of visible light from 5/8-inch-diameter areas of fluorescent pigment-sprayed leaves when they were exposed to ultraviolet light in a Turner Huorometer. Plum trees and grapevines were sprayed with air-carrier sprayers traveling at constant speed, air volume, and air velocity. Gallons per acre were varied by changing nozzles, and the amount of pigment and insecticide used was adjusted in an attempt to apply equal amounts per acre at each rate of liquid spray used. On plum trees, deposits of pigment on the upper leaf surface were smaller than on the lower surfaces regardless of where the leaf samples were taken on the tree. These differences increased as the volume of spray per acre decreased. On grapevines, the highest deposits were found on the upper surface of the outside leaves and the lowest deposits on the upper surface of the leaves in the centers of the vines. Differences in mean deposits from applications of 392, 212, and 106 gallons per acre were very small. It is suggested that spray-coverage data may best be presented in deposit-frequency tables that permit estimation of relative areas that are overdosed or underdosed. On both plum and grape leaves there was a tendency for the number of leaf samples in the lowest deposit categories to increase as the gallons per acre decreased.