Open access publications in the SLU publication database

Abstract

To provide necessary plant protection in orchards, spray drops are transported to and into
the apple tree canopy with an air jet from a fan sprayer. The interaction between the spray
air jet and the canopy is central to effective droplet transport, spray coverage and pest
control. Converging air jets were introduced as a way of improving the spray application.
In this study, a two unit cross-flow fan orchard sprayer, configured as converging or plane
(vertical fan units) air jets, were compared in several experiments. Inclining the top or
bottom fans towards the tree created different types of converging air jets. The influence
of these air jets on spray deposition, on air velocities and on forces acting on apple trees
was measured.
Deposition was measured throughout the season with fluorescent tracer on leaf sized
filterpaper targets inside canopies.
Different types of air velocity measurements were made with the fan sprayer passing the
tree. Peak velocities were recorded at positions throughout apple tree canopies, and indepth
measurements of several air velocity parameters were made inside, above and
beyond an apple tree canopy. Velocity pulse values were integrated over time. Air velocity
profiles were measured in stationary situations and compared to existing mathematical
models.
Forces and moments caused by the air jet striking the tree were measured with a new
method, utilizing a multicomponent force transducer, placed between the tree trunk and
the ground.
Compared to plane air jets, converging air jets resulted in significantly higher deposition
values, more uniformly distributed through the canopy. The converging air jets increased
the air velocity parameters in the denser parts of the canopy, and resulted in higher air
power and energy at those positions. Converging air jets transferred greater forces to the
canopy. This could be explained by the ability of the converging air jets to reduce the air
flow directed above the trees, thereby concentrate and increase the amount of spray liquid,
penetrating into the densest part of the canopy. Finally, an increased air velocity improved
deposition prerequisites. The new method for measuring forces and moments has a
potential to extend and complement other application technology measuring methods.
Keywords: air jets, air velocity measurements, anemometer, apple, application technology,
canopy, converging air jet, cross-flow fan, fan sprayer, fluorescent tracer, force
measurements, force transducer, orchard spraying, pest control, plant protection.
Author’s address: Sven Axel Svensson, Department of Agricultural Engineering, SLU,
Box 66, SE-230 53 ALNARP, Sweden. acke.svensson@bredband.net