#  # Backpack Sprayer Calibration Worksheet

1. Divide 340 by the measured spray width to determine the calibration course.

Example: Spray width is 6 feet, therefore the course length is 57 feet.

340 ft / 6 ft = 56.6666, round off to 57 feet.

340 ft / ___ ft = ___ feet course length.

2. Tag a tree down the row that comes closest to the specified distance.

Example: Based on 5 feet tree spacing, mark the 11th tree from starting point to establish the calibration course.

57 ft / 5 ft = 11.4, round off to 11 feet.

Course length in feet ___ / tree spacing in feet ___ = ___ trees to count off.

3. Take an average of two trips to determine the time it takes to spray the course.

Example: Based on trips that took 16 and 18 seconds each, the average time to spray to the 11th tree is 17 seconds.

(trial #1 ___ seconds + trial #2 ___ seconds)/2 = ___ seconds.

4. Collect spray in a cup for number of seconds it took to walk the course. Number of ounces collected = number of gallons per acre (GPA) being applied.

Example: After spraying into a measuring cup for 17 seconds, you collect 7.5 ounces of water. 7.5 oz. per 340 square feet = 7.5 gallons per acre.

__ ounces collected = ___ gallons per acre.

5. Divide amount of herbicide you wnt to apply per acre by the GPA.

Example: For application in April, recommended Roundup® rate is 8 ounces per acre.

8 oz per acre / 7.5 gal. per acre = 1.06 oz Roundup® for each gallon water.

___ oz per acre / ___ gallon per acre = ___ oz. Roundup® for each gallon of water.

6. Determine ounces of Roundup needed per 3-gallong backpack load.

Example: 1.06 oz. Roundup® x 3 gallons = 3.18, round off to 3.2 oz Roundup® per three gallons of water.

___ oz. Roundup® X 3 gallons = ___ oz. Roundup® per 3 gallons of water.

7. Convert to milliliters

Example: 3.2 oz X 30 milliliters per oz = 96 milliliters® of Roundup in 3 gallons of water.

___ oz X 30 milliliters per ounce = ___ milliliters of Roundup in 3 gallons of water.

## Written By Dr. Jill SidebottomExtension Specialist (Mountain Conifer IPM) (828) 684-3562 jill_sidebottom@ncsu.eduForestry & Environmental Resources
NC State Extension, NC State University
Page Last Updated: 4 years ago