As growers move to modern, high-density planting systems to improve yield and orchard management, they need to match the sprayer output to the modern canopy. The closely planted trees and narrow rows require totally different operating parameters than the large, traditional tree canopies of older orchards.

Since coming to Cornell University in 1998, Dr. Andrew Landers has worked to provide growers with advice on how to spray these modern orchards and tested methods—some of them he developed—to modify their sprayer’s performance.

While growers know they need to change application volume, they often don’t change speed and volume of air—resulting in poor coverage, poor spray distribution, and a large plume of spray that drifts away, reducing cost efficiency, affecting off-target crops, and creating pollution, he said.

There are a half-dozen things that affect application rate: Forward speed, nozzle size, system pressure, airflow, liquid flow, and canopy structure. The work at Cornell has focused on matching airflow to the canopy, and changing airflow as the canopy develops.

“Ideally, air volume should match canopy volume,” he said. Ideally, that would change tree by tree, and deliver no spray where there is no tree.

Modern airblast sprayers are fitted with a gearbox, but usually the slowest fan speed is only about 20 ­percent slower than the fastest speed.

“Using a hydraulic motor to drive the sprayer fan allows the operator to regulate the air velocity leaving the sprayer,” Landers said. “At Cornell University, we retrofitted an axial fan airblast sprayer with a hydraulic motor and a hydraulic control valve, fitted in the tractor cab, to allow the operator to infinitely vary the fan speed from 0 rpm up to 540 rpm.

“The operator can reduce air speed during early to midseason applications and increase it for full canopy applications. Air speed and the subsequent spray plume can be adjusted when approaching the end of a block of trees, or near neighboring ­properties, drift-sensitive crops, roads, or water courses.”


Landers also developed the “Halsey doughnut,” an air restriction device made of two circular wooden plates with intake holes, the size of which can be adjusted simply by turning one plate. This restricts airflow at the fan intake.

“A number of modern sprayers are fitted with adjustable pitch propellers to provide a variable airflow,” he said. “Operators can manually adjust blade pitch either by turning a handle or altering individual blades.”

Cornell researchers also developed and patented an adjustable louvre system, electrically actuated, to adjust airflow from either tower sprayers or ­traditional airblast sprayers.

Current research projects include using a sensing system that detects canopy density and size to adjust airflow and liquid application rate in real time. “This allows small trees with sparse leaf growth to have less spray and less air and to increase airflow and liquid spray as the canopy develops,” Landers said.

The project is being evaluated in orchards and vineyards and is funded by the New York apple and grape industries