Integrated pest management is an approach to plant care that uses all available tools to ensure healthy growth. It involves the use of cultural, genetic, mechanical and biological control methods to manage plant pests and pathogens. However, if these approaches fail to provide control, many plant pest problems can be solved by the judicial use of pesticides. 

If your equipment is calibrated and in good working condition, and you are following the pesticide label instructions, you can effectively reduce or eliminate non-target exposure while providing the necessary control of the target pest. 

This article discusses a quick and easy method for calibrating a hand-powered backpack sprayer. Calibration is important so that you understand the amount of product that is being delivered by your sprayer. Applying too little product may result in poor performance, and applying too much product is not only a waste of money but can lead to non-target effects in the environment.

The 10 steps below outline the 1/128th rule for calibrating your backpack sprayer.

1. Mark off a calibration plot that measures 1/128th of an acre (example: 8.5 feet by 18.5 feet).

2. Fill the sprayer to normal capacity with water.

3. Pump the sprayer to the pressure normally used for herbicide applications. (Hopefully, your sprayer has a pressure gauge! If not, do your best to maintain a consistent pressure.)

4. Spray water over the plot area while maintaining normal (and constant) operating pressure and walking speed. Coverage will depend on what is stated on the label. Some pesticides may require that the product be sprayed lightly on the target area while others may need to be sprayed until runoff.

5. Record the time in seconds it takes to spray the plot area (example: time = 30 seconds).

6. At the same constant pressure, by pressure gauge or constant pressure on the handle, spray into a bucket for the same time (number of seconds) it took to spray the plot area.

7. Measure the volume of water in fluid ounces (example: volume collected = 25 fluid ounces). The number of fluid ounces collected is equal to the number of gallons that would be applied to one acre if the sprayer is operated at the same pressure and walking speed used in the plot area. In this case, the sprayer is applying 25 gallons of water per acre. This quick conversion from fluid ounces per 1/128th acre to gallons per acre (gpa) works since there are 128 fluid ounces in 1 gallon of water.

8. Determine the total volume of your tank (example: 4 gallons).

9. Divide the tank volume by output = number of acres treated per tank (example: 4 gallons divided by 25 gpa = 0.16 acres).

10. To find out how much pesticide product to add to your sprayer, multiply the herbicide application rate (given on the product label) times the number of acres treated per tank (example: 2.0 ounces of product x 0.16 acres = 0.32 ounces of product should be added to 4 gallons of carrier).

For more information on calibrating spray equipment, refer to the article “Single-Nozzle Backpack or ATV Sprayer Calibration” at bit.ly/sprayercal

— Dr. Kevin Korus is the Agriculture and Natural Resources Extension Agent for UF/IFAS Extension Alachua County. Contact him at kkorus@ufl.edu or 955-2402.