Application Equipment, Calibration, and Techniques
Equipment families
Compressed-air and backpack sprayers suit crack-and-crevice, spot, and baseboard work; boom sprayers cover turf and rights-of-way; granular spreaders handle dry formulations; ULV and fogging equipment produce very fine droplets for specialized uses; bait guns and dusters place material precisely with minimal off-target deposition.
The variables that control output
Output is set by nozzle orifice size, pressure, and travel speed. Flow through a nozzle increases with the square root of pressure - quadrupling pressure only doubles flow, which is why turning up pressure is a poor way to change rate and a good way to create drift. Smaller droplets drift farther; larger droplets deposit closer to the target. Nozzle wear enlarges the orifice and raises output, so nozzles are wear items with a replacement schedule.
Calibration, step by step
- Clean and inspect the equipment, especially nozzles and screens.
- Fill with water only (never pesticide) and mark a known area - 1,000 square feet is convenient for hand sprayers.
- Spray the area at your normal walking pace and normal pressure.
- Measure the volume used and convert to a per-area rate.
- Recheck after any change of nozzle, pressure, speed, or product.
Worked example
A backpack sprayer uses 2 gallons of water over 1,000 square feet. Per acre: 43,560 ÷ 1,000 = 43.56, and 2 × 43.56 ≈ 87 gallons per acre. If the label calls for 1 gallon of product per 100 gallons of spray, that mix delivers about 0.87 gallons of product per acre - check that against the labeled rate per acre before mixing.
Traps in questions
Calibrating with the actual pesticide, failing to recalibrate after a nozzle change, assuming doubling pressure doubles output, and forgetting that walking faster reduces the applied rate.