April 1997 - Volume IV, Issue 4

Back Pack Sprayer Calibrations

David M. Kopec, Extension Turfgrass Specialist

In the January and March 1997 issues, we learned how to calibrate a lawn drop spreader and a lawn rotary (centrifugal) spreader. In this issue we will calibrate the home garden back pack sprayer. We will cover how to use the back pack sprayer for spot treatments and use the back sprayer for an entire ground area application.

The back pack (hand pump sprayer) is usually used for "spot treatments" of herbicides and insecticides in turf and landscapes. There are several ways to safely and accurately apply chemicals using this type of equipment. They often come with an adjustable nozzle. This allows either the application of a medium droplet mist, or a directed stream application.

Many "back pack" application directions for products are specified on the product label as (1) amount of product, per each gallon of spray, or (2) spray till wet, or till runoff occurs. In this case, simply apply the proper amount, per each gallon of final spray solution.

A liquid insecticide is required to control yellow aphids on Oleander. The label calls for mixing 5cc of "Spectracide" (diazinon) per gallon and "spraying till runoff."

(1) Add 2 gallons of water (8 quarts or 7570 cc) to the spray tank.

(2) Add 10cc (1/3 of a liquid ounce). Shake well.

Pump up the sprayer and apply a medium droplet spray to the Oleander foliage, paying attention to the infested areas (shoot tips).

Similar instructions are common on product labels for "directed spray applications," which are applied directly to the pest-site only. Examples include non-selective weed control agents like Round-up or Finale. Others include directed sprays for broadleaf weed control in lawns. Examples include 24-D, Turflon Ester, MSMA, Dimec, etc. In this case you are spraying the weeds only.

If you use a back pack sprayer to apply a pesticide to an entire ground area, then it is necessary and best to perform a calibration.

Calibrating a Back Pack Pump Sprayer

(1) Measure a known size area. A 10' x 10' area is 100 ft2.

(2) Add 2 gallons to a back pack sprayer. Add a spray marker in the tank. Pump the sprayer to a working pressure and maintain it during application.

(3) Spray evenly as possible across the 10' x 10' area, stop.

(4) Measure the remaining water in the tank.

(5) Subtract (2 gallons - remaining water). This gives you the amount of water applied per 100 ft. If you multiply this by 10, you will get the amount applied per 1000 square feet.


A herbicide, SURFLAN, is being applied to a bare gravel area in a xeriscape. The label rate is 2 quarts of product, per acre (43000 sq. ft.).

Spray Volume Calculation:

In the 10' x 10' area, you sprayed 1 quart of water. This means you applied 1 quart per 100 ft2. This is the same as 10 quarts per 1000 ft2. This is the same as 2.5 gallons per 1000 ft2. This is the same as 108 gallons per acre (43000 ft2).

Mixing the proper amount of product:

The label called for 2 quarts of SURFLAN per acre. This is the same as 4 pints of SURFLAN per acre. This is the same as 1892cc of SURFLAN per acre. This is the same as 44cc per 1000 ft2 (1892cc/43). Note that one "cc" is the same as one "ml."

From the information above, perform the calculation below.

44cc/1000 ft2 = 17.6 or 18cc per each gallon of water

2.5 gal./1000 ft2

Approximately 18cc of SURFLAN is needed for each gallon of spray solution. This achieves a label rate of 2 quarts of product per acre (43cc per 1000 ft2), when your total delivery volume is 2.5 gallons per 1000 ft2 (same as 108 gallons per acre).

Lastly, in order to estimate the right amount of chemical and water for the job site, do the following.

(1) Job site is 12' x 22' = 264 square feet. We know already that we spray 2.5 gallons per 1000 ft2, therefore ...

2.5 gallons ----------- 1000 ft2

(x) gallons ----------- 264 ft2 (job site)

Solve for (x) . (2.5 x 264) / 1000 = 0.66 gallons.

1 gallon -------------- 3785cc

0.66 gallon ---------- (x)cc

Solve for (x) . (3785 x 0.66) / 1 = 2498cc, or more easily 2500cc

2500cc of water are needed for this 12' x 22' job. Each gallon of water gets 18cc of pesticide. Therefore...

(1 gallon) 3785cc -------------- 18cc of pesticide

2500cc -------------- (x)cc of pesticide

Solve for (x) . (2500 x 18) / 3785 = 11.8 or 12cc of pesticide

Therefore, we need 12cc of pesticide, mixed in 2500 cc of water to treat our 12' x 22' area.

Products mentioned are used for discussion purposes only and does not imply endorsement. Exclusion of similar products is not intentional, not does it imply product efficiency.

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