Agronomy Talk

Agronomy Talk: SPRAYER SETUP

Published on Wednesday, December 2, 2020

All sprayers have common elements, regardless of make or type. Every sprayer includes a tank, pump, boom, and nozzles. Things like flow rate, boom width, and pressure all impact your gallons per acre (GPA) when making applications. This document will help you work through all the formulas so you can make necessary applications at the rate you desire.


  • Pre-Emergent Herbicides (clean field/no emerged weeds) = 10 GPA
  • Post-Emergent Herbicides (emerged weeds) = 15 to 20 GPA
  • Fungicides/Insecticides/Foliar Nutrition = 15 to 20 GPA
  • Higher application rates often result in increased coverage, which is a driving factor in efficacy.
    • Always follow rate guidelines on the label for the chemical(s) you are applying. 


GPA = (GPM x 5,940) / (MPH x W)

  • GPA = Gallons Per Acre
  • GPM = Gallons Per Minute
  • 5,940 = Constant for this Formula
  • MPH = Speed You Will Be Traveling
  • W = Nozzle Spacing in Inches

GPM = (GPA x MPH x W) / (5,940)

  • This equation is more useful to the end-user because it will guide you to the right nozzle size.


  • You should only use approved nozzles as indicated on the chemical label.
  • Nozzle selection is a key factor in selecting application speed (MPH) and application rate (GPA).
  • As a rule of thumb, your nozzle type (combined with pressure) will dictate droplet size.
    • Large (Coarse) Droplets = Low drift and decreased coverage. This is best for systemic herbicides.
    • Small (Fine) Droplets = Higher drift potential and increased coverage. This is best for contact herbicides, insecticides, fungicides, and foliar nutrition products. 

Once you have decided on the type and size of nozzle that will work best for you, you need to calibrate your sprayer. Sprayer calibration should take place at the beginning of every season after any mechanical changes are made. Sprayer calibration also provides a good opportunity for you to confirm that your sprayer is performing as expected and that there are no clogged or damaged nozzles.


  1. Fill your sprayer with clean water
  2. Turn on the sprayer and pressurize the system to the application level
  3. Using a measuring cup or similar, catch the water from one nozzle for 30 seconds
  4. Calculate the equivalent amount in gallons per minute 

Example: One nozzle had an output of 4 cups of water in 30 seconds

  • 4 cups = 32 fluid ounces
  • 32 ounces = 0.25 gallons
  • 0.25 gallons per 0.5 minutes = 0.5 gallons per minute

It’s important to remember that changes in pressure greatly affect nozzle output. With certain nozzles, if you quadruple the pressure, nozzle output doubles. If nozzles are operated outside of the manufacturer recommended range, both pattern and droplet size will be affected.


Your sprayer should be thoroughly rinsed when switching between crops and even crop-specific herbicide trait technologies. Some herbicides are more prone to contaminate future applications. Products such as atrazine, dry products, and many growth regulators will remain in the system unless a proper cleanout procedure is followed. Some products will specify the required cleanout procedures so as always, refer to the appropriate label for that process. Generally, a triple-rinse procedure will provide a sufficiently clean sprayer system. 


  1. Empty the sprayer completely
  2. Fill the tank half-full with clean water and rinse the inside of the tank
  3. Pressurize the system and agitate for 30 minutes
  4. Turn on the boom and let it run for 10 minutes
  5. Remove any end caps, nozzles, and screens and let them soak in either an acetone/water or ammonia/water solution
  6. Pump the remaining water through the boom with the nozzles and end caps removed
  7. Rinse nozzles, end caps, and screens with clean water and reinstall
  8. Fill the tank half full again and add a tank cleaner of your choice
  9. Agitate the solution for 30 minutes
  10. Charge the boom with that solution and then turn off the sprayer and let it sit for at least one hour, overnight would be best
  11. Follow steps 3 to 7, but do not the soak nozzles, end caps, and screens again
  12. Repeat steps 2 to 6 one final time

Proper cleanout measures are important for tendering equipment and transfer pumps in addition to the sprayer itself. These processes can seem confusing and time consuming, but proper preparation can help you avoid any issues that may cost you time and money in the future. 

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Author: Alex Long

Categories: Agronomy, Agronomy Talk


Alex Long

Alex Long

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