Catching output from a boomless sprayer.
Catching output from a boomless sprayer.

Each year, we get many calls from people wanting to know how much pesticide to put into their spray tank. Regardless of the size of the tank or the chemical, we cannot answer that until we know the volume being put out by the sprayer. Without that information, it is impossible to calculate the right mix, get the desired results and comply with label requirements. The only exception is when the mix is on a percentage volume basis, usually for individual plant treatments. The only way to determine sprayer output is to calibrate your sprayer.

There are several methods to calibrate a sprayer and any mathematically correct one is fine. Following are the methods I recommend for calibrating boom, boomless and air blast sprayers.

Boom sprayer. The first method is the 1/128 of an acre or ounce method. The steps are outlined here. This method catches the output from each nozzle for the time it takes that nozzle to cover 1/128 of an acre. The output is measured in ounces; since there are 128 ounces in 1 gallon, the number of ounces collected equals gallons per acre. A YouTube video demonstrating this method is here. The second method uses an online calculator  here. This method measures the nozzle output for 30 seconds and uses the sprayer speed and nozzle spacing to calculate gallons per acre. It also has a feature to print the calibration information for future use.

Boomless sprayer. The first method is the 1/8 of an acre or pint method. The steps are outlined here. This method catches the output for the time it takes to cover 1/8 of an acre. The output is measured in pints; since there are 8 pints in 1 gallon, the number of pints collected equals gallons per acre. A YouTube video demonstrating this method is here. The second method uses an online calculator at bit.ly/boomless-calibration. This method measures the output for 30 seconds and uses the sprayer speed and effective spray width to calculate gallons per acre. It also has a feature to print the calibration information for future use.

Orchard/Air blast sprayer. The first method is in a publication available at bit.ly/orchard-sprayer. The basics of this method are to fill the sprayer to a known volume, spray at the intended operating speed and pressure over a known distance, and measure the amount of water required to refill the sprayer to the original volume. The amount required to refill the sprayer is then used with the tree spacing or size to calculate gallons per acre. The second method uses an online calculator here. This fills the sprayer to a known volume, operates the sprayer for 60 seconds and measures the amount required to refill the sprayer to the original volume. The time for the sprayer to travel a known distance in the orchard is then measured and, with the tree spacing or size, used to calculate gallons per acre. It also has a feature to print the calibration information for future use.

Verify the calibration accuracy by measuring the actual volume required to spray a field of known acreage. If the application volume is off by more than 10 percent, adjust your mix calculations accordingly or recalibrate.

While sprayer calibration seems intimidating and not worth the effort to some people, it is critical to safe, accurate and cost-effective pesticide use.