# How to Calibrate Herbicide Application Equipment

Aug. 4, 2014
The first step in calibrating liquid or granular spraying equipment is to read the entire label of the herbicide you are about to use.

The first step in calibrating liquid or granular spraying equipment is to read the entire label of the herbicide you are about to use. Then select the application rate listed on the label that fits the needs for managing that particular pest. The following steps and equations will help you calibrate several types of sprayers, from boom sprayers to handheld sprayers.

# Calibrating Boom and Boomless Sprayers

1. Fill the spray tank with water.
2. Choose spray nozzles with low drift properties.

Measure the swath width (SW) in feet to be sprayed with the nozzle(s).

3. Collect the water sprayed from all nozzles for the SW measured during 1 minute.

Record as GPM.

4. Determine sprayer speed (mph).

Determine time it takes the sprayer to travel 200 measured feet in seconds (SEC).

mph =            200 feet x 0.682
SEC

Determine gallons of output per acre (GPA):

GPA =            GPM x 495
mph x SW (in feet)

5. Add your herbicide at the desired rate per acre based on GPA output.

How to Determine Speed in Miles Per Hour Without a Ground Speed Indicator

1. Set out two markers 200 feet apart.
2. Select gear and throttle setting on the vehicle.
3. Measure time (in seconds) from running start to drive the 200 feet.
 Time Required to Travel 200 Feet at Various Speeds Time to travel 200 feet (seconds) Equivalent speed (mph) 45 3 34 4 27 5 23 6 19 7 17 8 15 9 14 10 11 12 9 15

The following chart provides area treated per mile lengths based on the width of the spray swath.

 Width of Area Covered to Acres Per Mile Traveled Width of strip (feet) Number of acres covered per miles traveled 2 0.24 4 0.48 6 0.72 8 0.96 10 1.21 12 1.45 16 1.93 18 2.18 20 2.42 25 3.02 30 3.63 50 6.04 75 9.06 100 12.1

Stationary Calibration Method

1. Fill spray tank approximately half full with clean water.
2. Measure swath width (SW) in inches or feet.
3. Collect the spray output from the nozzle(s) for 1 minute.

Measure volume collected in fluid ounces and divide by 128 to determine gallons per minute (GPM).

4. Select the speed in miles per hour that will be used for spraying.
5. Determine gallons per acre (GPA) being applied, using a large output nozzle or a cluster of nozzles.

GPA =          5940 x GPM
mph x SW (in inches)

---or---

GPA =            GPM x 495
mph x SW (in feet)

6. Determine chemical needed with the following equation:

Chemical need =  Chemical rate per acre x tank volume (in gallons)
GPA

Volume Calibration Method

1. Place sprayer on level ground and fill tank to a known level with clean water.
2. Mark the start of your calibrating course with a stake or other marking device and measure off the distance required to cover 0.25 acre. (Consult table below.)
3. When you get to the starting mark, open the valve and drive at the speed you will use when spraying.
4. Shut off the valve when you get to the mark at the end of your calibrating course.

Return the sprayer to level ground and carefully measure amount of water needed to refill the tank to the known level in step 1 above.

5. Multiply this amount by 4.

This gives you the quantity of water your sprayer delivers per acre.

 Table for Step 2 in Volume Calibration Method Width of boom swath (in feet) Linear feet traveled to cover 1/4 acre 2 5445 4 2723 6 1815 8 1362 10 1090 20 545 30 363

Handgun Calibration (by Area)

1. Put 50 to 100 gallons of clean water in the sprayer.

Choose the pressure setting and the nozzle you will use during application.

2. Set up a test spray area that is 10 feet wide and 43.5 feet long (equivalent to 1/100 of an acre).

Uniformly spray this area just as you would spray an actual site (same walking speed and pattern), being sure to time exactly how long it takes to spray the test area.

3. Take the handgun and spray into a bucket and collect the water for exactly the same length of time it took to spray the test area.
4. Multiply the amount (in gallons) of water you collected in the bucket(s) by 100 to get your carrier volume per acre.

Example: If you collected 3 quarts of water in the bucket after 45 seconds, multiply 100 by 0.75 gallon (3 quarts = 0.75 gallon) to get 75 gallons per acre.
5. Use the desired amount of herbicide to treat 1 acre at the carrier volume for which you just calibrated.

Realize the Difference With DuPont

DuPont herbicides can be great tools to help you provide uninterrupted power supply to the public while keeping encroaching brush out of rights of way. These herbicides also help you to manage the safety issues associated with uncontrolled weed growth along roadsides or the elimination of environmentally degrading invasive weeds.

DuPont is committed to providing the information and resources necessary to support the continued use of existing products as well as the development of new technology to meet future weed and brush control needs.

A full calibration and user guide is available at landmanagement.dupont.com, including a checklist for applying nonagricultural-use herbicides, techniques for calibrating liquid and granular spraying equipment, common conversion factors, and other useful information. See your DuPont representative for printed copies of the guide.

For more specific application guidance on how to incorporate DuPont herbicides in your brush or weed control programs, please refer to their federally approved labels or contact your local DuPont sales representative. To find label information for any DuPont herbicide, click here.