Spray patterns of a low-volume air-blast orchard applicator

A low-volume, high-velocity air-blast applicator was modified and used to apply solutions containing a known volume of micron-sized fluorescent particles at four rates to groups of mature trees within an apple orchard.

Leaves were selected from designated areas on the sprayed trees and evaluated for surface coverage and quantity of material deposited, using a stereo microscope and ultraviolet light.

Application rate, leaf location, and leaf side were considered fixed effects, while trees, leaves within location, and sites within a leaf side were considered random.

Coverage analysis showed that as application rate increased, percentage of leaf surface covered increased, but even at the highest rate (70 gallons per acre), only about 50 percent of the leaf area received spray. Also, at the lowest rate (10 gallons per acre), virtually no material was deposited on leaves in the tree center.

Deposition density of fluorescent particles also increased as application rate increased, but at a lower rate than percentage of coverage. Deposition density and percent leaf coverage were both greater on top leaf surfaces than bottom leaf surfaces except for locations at the tops of trees.

Distance from the fan to the target area proved to be a more prominent factor in percentage spray coverage than foliage obstruction.

Therefore, use of higher rates and shorter distances with the low-volume applicator would seem necessary to attain the particle deposition and percentage of leaf coverage necessary for controlling fungal spores.