Application Equipment, Calibration, and Techniques
Equipment types and components
Know the major application methods: sprayers (boom, airblast, backpack), granular spreaders, seed treaters, baits, foggers, and soil injection/fumigation. For sprayers, understand nozzles (flat fan, hollow cone, full cone, even fan), pumps, regulators, agitation, and filters. Trap: nozzle wear increases flow and changes pattern; replace worn nozzles rather than compensating with pressure.
Calibration math
Calibration determines the actual application rate. Common formulas:
- GPA = (GPM × 5940) / (MPH × W) where W is nozzle spacing in inches.
- GPA = (ounces collected × 5940) / (seconds × MPH × W) for a single nozzle.
- Amount of product = (rate per acre × treated acres) / product concentration.
Calibrate with water before adding pesticide, check output from multiple nozzles, and recalibrate after changing nozzles, speed, pressure, or formulation.
Worked example
A boom sprayer has 20-inch nozzle spacing and travels 5 MPH. Collecting from one nozzle for 30 seconds yields 10 ounces. GPA = (10 × 5940) / (30 × 5 × 20) = 59,400 / 3,000 = 19.8 GPA. If the label calls for 20 GPA, the setup is essentially on target. If a 100-gallon tank is used at 20 GPA, it covers 5 acres; at a 1 qt/acre product rate, add 5 quarts.
Techniques and drift management
Use the largest droplet size consistent with coverage, lower boom height, use drift-reduction nozzles, spray when wind is low and away from sensitive areas, and respect buffers. Match pressure to nozzle design; too high pressure creates fines and drift. Clean equipment between products to prevent crop injury, and triple rinse.
Common traps
Mixing units (ounces vs. gallons, feet vs. inches); forgetting that speed changes GPA inversely; calibrating with product in the tank; and assuming a nozzle's rated output is accurate after wear.