Application Equipment, Calibration, and Environmental Protection
Application Equipment
Nozzles control the spray
Nozzle type sets droplet size and pattern. Flat-fan nozzles are standard for broadcast herbicide and require overlap from adjacent nozzles; hollow cones give smaller droplets for foliar insecticide and fungicide; air-induction and flood nozzles produce coarser droplets that reduce drift. Flow through an orifice rises with the square root of pressure, so doubling pressure increases output by only about 41 percent while making far more drift-prone fines. Change pressure to change droplet size, change nozzles to change rate.
System components and maintenance
Pumps must resist the formulation's solvents and abrasives; diaphragms and roller pumps handle most wettable powders well. Agitation keeps suspensions uniform, and screens protect nozzles, but a screen finer than the nozzle orifices will plug and starve the pattern. Check nozzle output against its rated flow at the rated pressure: replace any nozzle more than 10 percent above rating or showing a distorted pattern. Clean tanks between products, especially between herbicide groups that damage sensitive crops.
Traps
- Raising pressure to increase rate instead of changing nozzles.
- Using brass nozzles with abrasive wettable powders.
- Ignoring worn nozzles that over-apply and streak.
- Leaving an unprotected fill connection that allows backflow into a water supply.
Worked example
A nozzle rated 0.40 gallons per minute at 40 psi is run at 20 psi. New flow equals old flow times the square root of the pressure ratio: 0.40 times the square root of 0.5, or 0.40 times 0.707, which is about 0.28 gallons per minute. Output dropped 30 percent, so the sprayer must be recalibrated before use.
Calibration and Environmental Protection
Calibrate with numbers, not guesses
Calibration determines the spray volume actually delivered per acre. The standard relationship is gallons per acre equals gallons per minute per nozzle times 5940, divided by miles per hour times nozzle spacing in inches. Measure speed over a known distance with a full tank, measure nozzle output with a measuring cup, and confirm swath or nozzle spacing. Then compute how many acres the tank will cover and how much product to add. Granular applicators are calibrated the same way by catching and weighing output over a measured distance.
Environmental fate
Whether a pesticide leaches to groundwater depends on its water solubility, soil adsorption, and persistence, plus site conditions: sandy low-organic soils, shallow water tables, and heavy irrigation or rain soon after application all raise risk. Runoff moves product across the surface on sloping ground and compacted soils; buffer strips and incorporation reduce it. Volatility and drift are separate problems: volatility depends on the product and temperature, drift on droplet size and wind. Spray when wind is roughly 3 to 10 mph and avoid inversions, when fine droplets hang and move unpredictably.
Traps
- Mixing units, such as acres with 1000 square feet.
- Forgetting to recheck speed with a different gear or load.
- Treating near water or sensitive habitat without checking the label and endangered species restrictions.
- Spraying during an inversion because the air feels calm.
Worked example
A sprayer with 0.40 gallons per minute nozzles, 20 inch spacing, at 5 mph: acres per minute equals 5 times 20 divided by 5940; gallons per acre equals 0.40 times 5940 divided by 5 times 20, or 2376 divided by 100, giving 23.8 gallons per acre. A 100 gallon tank therefore covers about 4.2 acres.