A technique to characterize spray deposit in orchard and tree canopies

This article evaluates drop deposition data from the sides of beverage can samplers wrapped with Kromekote(R) paper placed throughout a broadleaf (almond) canopy at three stages of foliage development. Some measure of 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 of insect mortality, and must be either assumed or determined in the field or laboratory by biological assessment. Data from two field studies conducted by the USDA Forest Service at Hennigan Orchard in Chico, California, in 1985 and 1994 are used to evaluate the amount and uniformity of spray droplet coverage on the can samplers. A quantitative representation of coverage (called the Relative Index) is developed to describe the drop deposition on the samplers and is then used to determine the spray deposition coverage produced by the various spray application systems tested. The overall performance of two types of spray systems is evaluated in terms of delivering spray on target at different canopy elevations, concluding: (1) The Relative Index formula developed herein for assessing drop recoveries on sides of beverage cans correlates data from all trials, (2.) The placement of beverage can samplers spatially across the orchard and at different elevations gives a good representation of the effects of spr-a,ting 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 fixed-wing aircraft system applications. (4.) Micronair atomizers spraying low rate produce less coverage on the sides of the can samplers at all elevations in the canopy than the other spray systems tested in these field studies.