Application Equipment, Calibration, and Application Techniques
Domain 4 tests whether you can set up, calibrate, and operate sprayers and spreaders accurately and with minimal drift. The exam uses practical math: gallons per acre (GPA), gallons per 1,000 sq ft, nozzle output, speed, swath, and granular delivery. Accuracy protects the plant, the environment, and your license.
Liquid calibration
The key formula is GPA = (GPM × 5,946) ÷ (MPH × nozzle spacing in inches). One gallon per 1,000 sq ft equals 43.56 GPA. Calibrate by catching nozzle output for one minute, checking speed over a measured course, and measuring nozzle spacing. Replace nozzles that differ more than about 10% from the average. Pressure changes droplet size more than rate; speed and nozzle size set the rate.
Granular calibration
Set the spreader gate, collect output over a measured area such as 1,000 sq ft, weigh it, and adjust. Check the pattern with trays across the swath. Overlapping passes must match the swath width; half-rate passes at half-width are common for uniform coverage.
Application technique
Flat-fan nozzles suit boom spraying; flood nozzles deliver high volume; cone nozzles suit directed sprays. Keep the boom at the recommended height for overlap. Spray when wind is low and steady, avoid temperature inversions, and use buffers near water, storm drains, and sensitive plants. For ornamentals, direct spray to the target and avoid open blooms when pollinators are active.
Worked example
A boom has 20-inch nozzle spacing and runs at 3 mph. Each nozzle catches 16 oz in one minute. 16 oz ÷ 128 = 0.125 GPM. GPA = (0.125 × 5,946) ÷ (3 × 20) = 743.25 ÷ 60 = 12.4 GPA. If the label requires 2 gal per 1,000 sq ft (87 GPA), you must change nozzle size or slow down - not simply raise pressure.
Traps that cost marks
Do not calibrate once and assume it holds all season; nozzle wear and product changes matter. Do not use pressure to fix a rate error. Do not double-apply overlaps at row ends. Do not spray in wind or near water without buffers.