Sprayer Calibration Basics: Tips for Getting the Correct Amount of Coverage and Measuring Safely

Authors: Natalie Hoidal and Ken Rost (Frost Inc.). Calibrating your sprayer before you spray is an important step to ensure you are applying the correct amount of product to your crop. This article gives step-by-step instructions on calibrating a small-scale sprayer for fruit and vegetable farms. This includes calculating how much product to use on small plantings, a question we receive frequently.

Calibration of a manual sprayer – gallons per acre

Image: Ken Rost

1. Always calibrate with water
2. Spray a set area (340 sq feet), and count the number of seconds it takes
3. Make sure to keep a consistent walking speed and pumping speed if you're using a sprayer with a mechanical pump
4. Spray into  separate a container for the same amount of time and collect the water
5. Measure the amount of water in your container; Ounces collected will equal your output in gallons / acre
6. Use label instruction for amount of product included in each gallon of total volume

Calibration example:
It takes you 50 seconds to spray 340 sq feet. Then, you spray water into a collection container for 50 seconds and collect 25 oz. So, your output is 25 gallons per acre (GPA). (This is because 340 sq. feet is 1/128 of an acre, and a fluid ounce is 1/128 of a gallon, so by calibrating with an area of 340 sq. feet, you eliminate some conversion steps in your math equation.)

The label you plan to use tells you to use 32 oz (2 pints) per acre of concentrate. You’ve just calculated that at your speed, you will be spraying 25 gallons of water per acre. However, you have a small sprayer that holds only 4 gallons. 

32 ounces / 25 GPA = 1.28 ounces per gallon

*Multiply the ounces per gallon by the size of your sprayer. If your sprayer holds 4 gallons in this case, multiply 1.28 ounces * 4 gallons; you'll get 5.12 ounces. This is the quantity of concentrated product you will add to your 4 gallon sprayer to achieve 32 oz. active ingredient per acre.

Image: GoatThroat Pumps

Measuring, dispensing and storage

1. Read label for required Personal Protective Equipment (PPE)
2. Start with your sprayer half full
3. Dispense small amounts into measurable containers
4. If mixing and loading larger quantities of pesticides on a regular basis, consider purchasing a pump to reduce exposure. 
5. Use a level surface for physical measurements
6. Return excess to the original container
7. Triple rinse product containers before recycling
8. Rinse water can be added to your sprayer
9. Top off sprayer with water after you've added your rinse water
10. Keep spray products locked up in a temperature controlled room

Application verification

Image: Ken Rost

Use water sensitive paper to confirm:

• Droplet size
• Whether your spray is drifting to unintended areas
• Whether you’re getting good coverage

Droplet size considerations

Contact pesticides: Good coverage is necessary for effective management. Small droplets provide good coverage, but are more likely to drift, so use small droplets only when necessary. 

                            

 

Systemic Pesticides: Since systemic pesticides are absorbed by the plant and remobilized throughout its tissues, small droplets are not necessary. Large droplets are less likely to drift. 

                                   

 

By:
Natalie Hoidal, Extension Educator, UMN Extension
Ken Rost, Frost Inc.