Pesticide Formulations, Mixing, and Application Equipment Calibration
Formulations and compatibility
Know the common formulations: emulsifiable concentrate (EC, solvent-based, can damage sensitive plants), wettable powder (WP, suspension, needs agitation), suspension concentrate (SC), soluble powder/liquid, granules (G), dusts, and fumigants. Adjuvants (surfactants, stickers, spreaders, drift retardants) modify performance; the label specifies which are allowed. Compatibility is critical-always jar-test tank mixes and add products in the label-recommended order (typically wettable powders first, then flowables, then emulsifiable concentrates).
Calibration fundamentals
Calibration matches output to the labeled rate. For broadcast sprayers, the core formula is: GPA = (GPM × 5940) ÷ (MPH × swath width in inches). Alternatively, use the 1/128-acre method: spray a measured area, catch output, and multiply. Nozzle selection, pressure, and speed all affect rate. Check nozzle wear-a worn nozzle can over-apply by 10% or more.
Traps to watch
- Mixing incompatible products without a jar test-can cause clogs or phytotoxicity.
- Using the wrong nozzle for the product (e.g., fine droplets for drift-prone areas).
- Forgetting to recalibrate after changing speed or pressure.
- Assuming more surfactant is better-excess can cause runoff or injury.
Worked example
A sprayer puts out 0.5 GPM per nozzle, travels 4 MPH, with a 20-inch nozzle spacing. GPA = (0.5 × 5940) ÷ (4 × 20) = 2970 ÷ 80 = 37.1 GPA. If the label calls for 20 GPA, increase speed or reduce pressure, then recalibrate. Rule of thumb: calibrate before every season and after any equipment change.