Equipment | Preparation | Calibration | Application Rates | Work Crew | Keys to Success | PDF

Calibrating a Backpack Sprayer for Chemical Mowing

Examples for Each Step of the Calibration Procedure

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 dquare 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.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

Posted December 21, 2004