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Pesticide Mixing and Sprayer Calibration Equations

Young farmer analyzing data on a tablet computer beside a crop sprayer.
(U.S. Department of Agriculture photo)

Written collaboratively by Eric Jones, Philip Rozeboom, Adam Varenhorst, Madalyn Shires, Stephen Robertson, Jill Alms, and David Vos.

Pesticides need to be applied at proper rates to ensure effective control of the pest. If too little product is applied, the pest will not be controlled. If too much product is applied, the pest will be controlled but other undesirable and unintended consequences may occur. Pesticides need to be added to the spray tank at the correct amount as well as the correct spray output for efficacy and safety.

Pesticide Mixing Equation

Pesticides should be measured out with clean containers. Liquid-formulated pesticides should be measured with a container with graduations (marks showing the amount poured in) to ensure that the correct amount is being added to the spray tank. Dry-formulated pesticides should be weighed using a quality scale to ensure the correct amount is being added to the spray tank.

The following equation is used for general pesticide mixing.

The pesticide rate divided by the spray output multiplied by the mix size equals the amount of pesticide to add to a spray tank. For additional help with this equation, please call SDSU Extension at 605-688-6729.

Below is a detailed illustration of how the units are cancelled out and the amounts are derived.

When pesticide rate over acres is multiplied by acres over gallons, then multiplied by gallons over spray tank, acres and gallons are cancelled out. For additional help with this equation, please call SDSU Extension at 605-688-6729.

A detailed example of calculating the correct amount of pesticide is provided below.

In this example, 32 fluid ounces over an acre times an acre over 15 gallons, times 500 gallons over a spray tank equals 1,067 fluid ounces of pesticide added to the spray tank. For additional help with this equation, please call SDSU Extension at 605-688-6729.

The amount of pesticide to add can be converted to other units if the measurement is more convenient or intuitive.

The equation is the same when mixing a dry formulation of a pesticide. Be sure to use the correct units. A detailed example is provided below.

: In this example, 1 ounces over an acre times an acre over 15 gallons, times 500 gallons over a spray tank equals 33.3 ounces of pesticide added to the spray tank. For additional help with this equation, please call SDSU Extension at 605-688-6729.

Sprayer Calibration Equation

Before calibrating your sprayer, be sure the sprayer is in working order without leaking fittings and/or nozzles and that your tank/lines are clean. When catching water from the nozzle, wear proper protective equipment, and only use clean water when calibrating the sprayer.

Sprayer output in gallons per acre, multiplied by speed in miles per hour, multiplied by nozzle spacing in inches, divided by 5,940 equals the amount of water to catch after 1 minute in gallons per minute. For additional help with this equation, please call SDSU Extension at 605-688-6729.

Below is a detailed illustration of how much water is to be collected if the desired output is 15 gallons per acre applied at 10 miles per hour with a nozzle spacing of 20 inches. The “5940” of the equation is a constant value taking into consideration all the variables rather than having to do extensive math and cancel out units.

EQ-04: Sprayer output in gallons per acre, multiplied by speed in miles per hour, multiplied by nozzle spacing in inches, divided by 5,940 equals the amount of water to catch after 1 minute. For additional help with this equation, please call SDSU Extension at 605-688-6729.

The amount of water to be caught can be divided by four to determine the amount of water to be caught in 15 seconds. The amount of water to catch can be converted to other units if the measurement is more convenient or intuitive. Collect water from each nozzle for the appropriate time period to ensure that all nozzles are working properly. A nozzle should be replaced if the output is ±10% of the desired output.

If the desired output is unknown, one can use the output (gallons per minute) collected to determine the current output (gallons per acre) of the sprayer. The equation described above can be rearranged, and a detailed illustration is below.

Gallons per minute multiplied by 5940 divided by miles per hour times nozzle spacing in inches, equals gallons per acre. For additional help with this equation, please call SDSU Extension at 605-688-6729.

Sprayers should be calibrated after long periods of storage, changes in nozzle types/pesticides, drastic weather changes, and periodically to ensure the correct about of product is being applied.