There is a narrow margin of safety when using pesticides. For example, the difference between the amount of herbicide to kill the weeds and the amount that will damage the crop may be very small. If the chemical is applied too lightly, the weeds will not be controlled. If applied too heavily, the crop may be damaged.

Four common methods are described here which are similar to ASAE standards. They are easily adapted to all sprayers, such as small garden types, boomless and boom sprayers used for broadcast applications.

Note: wear approved safety equipment such as gloves, goggles, respirator and protective clothing. Avoid any contact with the spray. Avoid contamination of the area used for calibration.

Procedures for calibrating boom-type field sprayers are given under the following headings:

• Acre-Volume Method
• Area-Volume Method
• Time-Volume Method
• Calibration Chart (not covered in this sample)

Over the years the acre-volume method has been used which requires measuring and staking out one acre for the test. A desired speed and pressure should be obtained and test area sprayed. If you find this is not the desired amount of applied liquid, the rate of application can be changed by changing the operating pressure, ground speed or by changing nozzle sizes.

In order to determine the number of test runs required to cover the acre, select a convenient length of run. Multiply length of run times the width of your spray boom and divide into the number of square feet in an acre. For example, if you select a 415 ft. test run, and your boom width is 35 feet the formula would be:

43,560 ft.(2)/acre divided by 415 x 35 is approximately 3 runs per acre.

Put clean water in the tank. Be sure the tank is level during this filling. Put a sufficient amount to cover an acre according to tank gauge marks. If your tank does not have a guage, fill the tank.

Start the sprayer power unit and set the sprayer pressure. Use the desired reading as found under “Adjusting Operating Pressure.” NOTE: the rate of application varies with the pressure.

Select ground speed as recommended in the nozzle manufacturer’s data or as required by ground conditions. Establish desired speed before entering the test area. Set the throttle and select the gear. The rate of application also varies with ground speed.

Enter the test area and spray an acre. Observe the sprayer closely to make sure speed, pressure and nozzle output are maintained. Be sure sprayer is turned on and off at the exact starting and stopping points and on turns.

Add water to sprayer tank. Tank should be level. Carefully measure the amount of water required to bring water back to original level.

This is the amount of spray mix that the sprayer will apply per acre at that speed and pressure. If you find this is not the desired amount of pesticide recommended to be applied, change the rate of application and recheck. The rate of application can be changed by changing the operating pressure, ground speed, or by changing nozzle size(s).

Small adjustments in rate of application can be made by changing the pressure. Lower operating pressure reduces the volume of spray delivered. High pressure increases the volume of spray delivered.

A change in ground speed is the easiest way to obtain a small change in application rate. Faster ground speed decreases the volume applied per acre. Slower ground speed increases the volume. For a major change in the application rate, change the nozzle tip size. Larger tips increase the volume, smaller tips decrease the volume.

This method also requires measuring and staking a test area of approximately 1000 feet for broadcast and 2000 feet for band application.

To find broadcast area sprayed: area sprayed (broadcast) equals width of spray swath x length of run divided by 43,560 ft.(2)/acre.

By measuring the gallons of liquid used and dividing by area sprayed (broadcast) you come up with gallon to the acred applied.

For band application – find the acre sprayed in bands by: area sprayed (band) equals band width times number of bands in swath times length of run divided by 43,560 ft.(2)/acre.

Again, by measuring the gallons used in the test run and dividing by area sprayed (banded) gallons per acre is achieved.

Proceeded by putting water in the tank and note the level of the water. Put a sufficient amount to cover the test area. Tank should be level.

Start the sprayer power unit and set the sprayer presssure.

Establish the desired ground speed before entering test area.

Enter and spray the test area. Observe the sprayer closely to make sure a constant speed, pressure and nozzle output are maintained. Turn off sprayer on each turn.

Add water to the sprayer tank. Tank should be level.

Record the amount of water equal to bring water level back to original level.

Calculate the rate of application. Procedures vary for broadcast and band application.

For example, if your spray is 16 feet and the length of run is 1000 feet, 16 ft. x 1000 ft. divided by 43,560 ft.(2)/acre equals .37 acre sprayed.

If you used 8 gallons of water, 8 gallons divided by .37 acres equals 22 gallons per acre.

If you are checking band application, proceed as follows: NOTE: unless instructions indicate otherwise, calculate band sprayer coverage on actual band width. NOTE EXECEPTION – some recommendations for band spraying may be based on the total area of the land planted in a crop. In these cases, the width used in the calibration should be based on the row width even though only part of the row is sprayed. For example, rows 30″ apart sprayed with a six row sprayer applying 7″ band from one nozzle over each row. The calibration is based on 180″
and not 42″ actually sprayed.

If the band width is 12″, there are 6 bands and the length of run is 1200 feet, 1 ft. times 120 ft. divided by 43,560 ft.(2)/acre equals .16 acres sprayed.

Adjust application is needed. If this is not the desired amount of pesticide to be applied, rate of application can be changed by changing ground speed, pressure or nozzle size.

This method can be employed by staking out a test run of 100 ft. entering the test area and make the test run without spraying but measuring and recording the lapsed time. Then with a measuring device collect and record the amount from each nozzle in ounces.

Determine the average output per nozzle, in ounces. And the total output from all nozzles from which spray was collected and divide by the number of nozzles tested to obtain the average. Find rate of application. On 40″ rows, using 1 nozzle per row, the number of ounces per nozzle equals the number of gallons per spray mix that will be delivered per acre. For example, average output per nozzle is 17 ounces for the test run, the output per acre is 17 x 1, or 17 gallons.

For example, a 45 ft. boom at 6 mph with an 18 gpm reading from the meter would be:

Small rate changes of application can be made by changing spraying pressure or ground speed. For a major change in rate applied, change the tip of the nozzles.

If you are checking row and broadcast, proceed as follows:

For example, if the row width is 30″ and the average output per nozzle is 6 ounces for the test run, multiply the conversion factor 1.33 x 6 ounces.

Gallon/Acre = Ounces/Nozzle x Conversion Factor

Gallons/Acre = 6 x 1.33

Gallons/Acre = 8