A TECHNIQUE TO CHARACTERIZE SPRAY DEPOSIT IN ORCHARD AND TREE CANOPIES

Abstract

This article evaluates drop deposition data from the sides of beverage can samplers wrapped withKromekote paper placed throughout a broadleaf (almond) canopy at three stages of foliage development. Some measureof foliage coverage uniformity is necessary to evaluate application quality and to improve methods of aerial application.Uniformity of coverage is found from drop data on target elements, while potential biological effectiveness is a measure ofinsect mortality, and must be either assumed or determined in the field or laboratory by biological assessment. Data fromtwo field studies conducted by the USDA Forest Service at Hennigan Orchard in Chico, California, in 1985 and 1994 areused to evaluate the amount and uniformity of spray droplet coverage on the can samplers. A quantitative representationof coverage (called the Relative Index) is developed to describe the drop deposition on the samplers and is then used todetermine the spray deposition coverage produced by the various spray application systems tested. The overallperformance of two types of spray systems is evaluated in terms of delivering spray on target at different canopyelevations, concluding: (1) The Relative Index formula developed herein for assessing drop recoveries on sides ofbeverage cans correlates data from all trials. (2.) The placement of beverage can samplers spatially across the orchardand at different elevations gives a good representation of the effects of spraying the canopy in both field studies. (3.)Helicopter spray system applications show greater uniformity of deposit on the sides of the beverage cans than the fixedwingaircraft system applications. (4.) Micronair atomizers spraying low rate produce less coverage on the sides of thecan samplers at all elevations in the canopy than the other spray systems tested in these field studies.