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Publication #SS-AGR-108

Single-Nozzle Backpack or ATV Sprayer Calibration1

B. A. Sellers, J. A. Ferrell, G. E. MacDonald, and Dennis C. Odero2

Many growers have isolated patches of weeds that should be controlled to prevent their spread. In this case, spot spraying with a herbicide would be the most economically feasible approach. Some herbicide labels allow for spot-treatments. However, the recommended amount is often given in % volume of herbicide per volume of water, or a certain amount of herbicide per 1,000 square feet.

Before adding any herbicide to the spray tank, it is extremely important that the output of the sprayer is known. That is, it must be properly calibrated. This allows for reduced herbicide costs and optimum weed control. A simple calibration test for a single-nozzle backpack or ATV sprayer is shown in Table 1. No math is required for this calibration, and the end result is a known output volume for your sprayer in gallons per acre (GPA).

Hints for calibration:

  • Keep speed constant. This will ensure that you are walking the same speed at all times.

  • Keep the nozzle at the same height at all times—a height that is comfortable.

  • Modify the wand by adding a pressure gauge. Try to keep the pressure as constant as possible. Do not let the pressure fall below 10 psi.

Next the amount of herbicide to be added to the spray tank needs to be calculated. To do this multiply the amount of herbicide needed for 1 gallon by the number of gallons in the spray tank.

Example: A sprayer is calibrated with an output of 40 GPA and the tank holds 10 gallons. If the desired herbicide rate is 1 quart per acre, from Table 2, the amount of herbicide for 1 gallon of water is 4.75 tsp. Since the spray tank holds 10 gallons, 40.75 (41) tsp are needed, which is approximately equal to 7 fl oz.

Useful Conversions:

1 teaspoon = 0.17 fl oz

1 tablespoon = 0.5 fl oz

3 teaspoons = 1 tablespoon

1 pint = 16 fl oz = 32 tablespoons = 2 cups

Tables

Table 1. 

A no-math method for calibrating single-nozzle backpack or ATV wand sprayers for spot spraying herbicides.

Step 1

Measure a calibration plot that is exactly 18.5 feet by 18.5 feet.

     

Step 2

Spray the calibration plot uniformly with water. Repeat 3 times and record the average number of seconds needed to spray the entire plot.

Time Required

____

Seconds

Step 3

Spray into a clean bucket for the amount of time recorded in Step 2.

     

Step 4

Measure the number of ounces of water in the bucket.

Volume Sprayed

____

Ounces

Step 5

The number of ounces collected from the bucket is equal to the number of gallons per acre the sprayer is delivering.

Output Volume

____

Gallons/Acre

Step 6

Determine the volume of the spray tank.

Tank Volume

____

Gallons

Step 7

Determine the number of acres covered in one tank. Divide tank volume (gallons; Step 6) by output volume (gallons/acre; step 5).

Area covered per tank

____

Acres

Step 8

Determine the amount of herbicide to add to the tank from Table 2.

Herbicide/Acre

____

tsp, tbsp, mL, oz, cups

Table 2. 

Amount liquid herbicide to add to 1 gallon of water. Abbreviations: tsp=teaspoon, fl oz=fluid ounces.

Volume

(GPA)

Recommended Herbicide Rate per Acre

1 pint

1 quart

2 quarts

3 quarts

4 quarts

20

5 tsp

10 tsp

3.25 fl oz

4.75 fl oz

6.33 fl oz

30

3 tsp

6 tsp

2 fl oz

3.25 fl oz

4.25 fl oz

40

2.33 tsp

4.75 tsp

1.66 fl oz

2.33 fl oz

3.25 fl oz

50

2 tsp

3.75 tsp

1.25 fl oz

2 fl oz

2.5 fl oz

60

1.66 tsp

3.25 tsp

6.33 tsp

1.66 fl oz

2 fl oz

70

1.33 tsp

2.75 tsp

5.5 tsp

1.33 fl oz

1.75 fl oz

80

1.25 tsp

2.33 tsp

4.75 tsp

7.25 tsp

9.5 tsp

90

1 tsp

2 tsp

2.25 tsp

6.33 tsp

8.5 tsp

100

1 tsp

2 tsp

3.75 tsp

5.75 tsp

7.66 tsp

Footnotes

1.

This document is SS-AGR-108, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date January 2006. Revised April 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

B. A. Sellers, assistant professor, Range Cattle Research and Education Center; J. A. Ferrell, assistant professor, Agronomy Department; G. E. MacDonald, associate professor, Agronomy Department; and Dennis C. Odero, Extension weed specialist and assistant professor, Agronomy Department, Everglades Research and Education Center; UF/IFAS Extension, Gainesville, FL 32611.

Use herbicides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.