Calibrating Your Field Sprayers

Did you know that by not calibrating your sprayer frequently enough, you could be risking fines and/or loss of your crop?

Calibrating your sprayer means accurately determining how much pesticide you are applying. If you apply more pesticide than the label allows, you are violating the law and could be fined and/or have your crop destroyed. Calibrating at least once per season, preferably several times, is absolutely necessary to ensure accurate application rates and effective pest control.

Sprayer calibration is equally important for planter box insecticide applicators. Follow the manufacturer's instructions for calibrating planters.

Tractor Spraying in a Field

Calibration Steps
There are different ways to calibrate a sprayer. These steps below are one method you can use.

Before calibrating, check your sprayer manufacturer's instructions; some require a special procedure for sprayer calibration. Here are the tools you will need: a watch, measuring tape, measuring container graduated in ounces, tip tester (determines flow rate for each spray nozzle in gallons per minute or liters per minute) and flags or stakes for marking. Also, a pocket calculator may help with the math. Always start with a clean sprayer.

  1. Fill your sprayer tank about half full with clean water.

  2. Measure the distance in inches between nozzles.

  3. In the field, mark out a test course that's the length corresponding to the distance between your nozzles. Use the chart on this page.

  4. Taking a running start, drive the entire test course from start to finish lines, driving at normal speed. Time the number of seconds required to complete the course.

  5. Keeping the engine RPM running at the same speed used on the course, park your rig and set the brakes.

  6. Set your sprayer pump pressure correctly for your spray tip type and desired gallons per minute (GPM).

  7. Using a tip tester or plastic container marked in ounces, collect water from a single nozzle for the same amount of time it took you to drive the test course. Repeat for each nozzle. If any one nozzle's output is 5% more or less than the others, replace it.

  8. Once all nozzles are outputting within 5% of each other, the average amount of water collected per nozzle equals your gallons per acre (GPA) output for your rig. For minor changes in output, adjust your sprayer pressure to achieve the GPA recommended by the pesticide label. For major changes, either change travel speed or nozzle tip size and recalibrate.

Sprayer Calibration Test Course Chart

Nozzle Spacing Unit

Test Course Length (ft.)

40

102

38

107

36

113

34

120

32

127

30

136

28

146

26

157

24

170

22

185

20

204

18

227

16

255

14

291

12

340

10

408