Aerially Released Spray Penetration in a Tall Coniferous Forest Canopy

Abstract

An aerial spray deposition project was designed to evaluate aerial application to an eastern hemlock (Tsuga canadensis) canopy to combat hemlock woolly adelgid (Adelges tsugae). This adelgid, residing in the forest canopy at the nodes of branchlets, offers a difficult target. The study collected 1840 deposition samples on live and artificial collectors (not including auxiliary studies) positioned to evaluate canopy penetration of spray applied from above the canopy by helicopter. The results of the study show that canopy penetration is achieved with 3% to 8% of applied material (corrected for foliar area) deposited on the lowest samplers and 6% to 12% deposited on samplers positioned in hard-to-reach locations in the mid-canopy. The study also suggests that it might not be necessary to apply as fine a droplet distribution (release DV0.5 values of 87 and 108?m are used in most of the trials described here) as originally thought to achieve coverage in this deep canopy. A second article will compare these data to existing models.