821.11 Calibration

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Definition: Calibration ensures that your equipment delivers the correct amount of herbicide uniformly over the target area.

When: The calibration of spray equipment is to be done prior to the spray season, after any alterations of spray equipment. Equipment calibration is to be routinely checked.


1. Proper calibration is an essential part of any herbicide application dependent on:

a. Constant volume
b. Constant speed
c. Constant pressure
d. Proper application rate (ex. ounces per acre)

2. The speed, volume, and pressure that the sprayer is calibrated must be the same as those during applications

3. Accurate rates are critical for successful results

Important information about an herbicide application is gained by calibrating a spray system.


How much volume is released on a given area or in a given time.


1. How much product to add to tank for area to be treated.

2. How many tanks it will take to complete a large area.

3. How much to mix for small areas.

4. Applications can be done without left over mixed product.

Keep accurate records:

1. Acres treated

2. Amount applied


A. Check spray system. Use only water.

Always check if equipment is working properly. Use water only in the tank to test operation of all booms and handguns.

1. Check for leaks, cracks in hoses, proper pump operation, etc.
2. Check spray bar or boom for proper nozzle spacing and operation.
3. Perform a test application with water on your lot at your desired speed and pressure.
4. Make a visual observation of the spray pattern to see if it dries evenly. If not make needed adjustments before beginning actual applications.
5. Recheck pattern after adjustments are made.

Make sure all nozzles are putting out the same amount. Operate sprayer at desired pressure (ex. 30 psi). Catch water from each nozzle for the same amount of time (ex. 30 seconds). Add all nozzles together and divide by the number of nozzles to get average output. All nozzles should operate with no more than 5% difference.

B. Calibration methods. Use only water.

1. Mark a distance (ex. 500 ft.). Fill tank, set operating pressure (ex. 30 psi), drive marked area at desired speed (ex. 8 mph).

Hand Sprayers – Mark area (ex. 20 ft. x 20 ft.), spray area as if actually applying product

2. Using a stopwatch, track the time taken to travel marked area. Operate boom at desired pressure and catch liquid from nozzles for same time it took to travel marked area.
a. Hand Sprayers – Measure amount of water needed to refill sprayer
Tip: Hand sprayers can be calibrated using the same method on a smaller area
Output from one nozzle can be caught and multiplied by the number of nozzles. This method is slightly less accurate.
Divide the number of ounces caught by 128 to get the gallons used.
Calculate gallons sprayed as follows:
\mbox{Gallons per Acre} =\frac{\mbox{(Gallons Used)}}{\mbox{(Test Area in Acres)}}
The speed, pressure and volume used during calibration must be used during the application.


A. Multiple nozzle spray bars - Even distribution.

1. Time water is caught________seconds.
2. Nozzle 1 ___________oz. Nozzle 7 __________oz.
Nozzle 2 ___________oz. Nozzle 8 __________oz.
Nozzle 3 ___________oz. Nozzle 9 __________oz.
Nozzle 4 ___________oz. Nozzle 10 _________oz.
Nozzle 5 ___________oz. Nozzle 11 _________oz.
Nozzle 6 ___________oz. Nozzle 12 _________oz.
3. Total ___________oz.
4. Divide total oz. by # of nozzles.
___________oz. / ________nozzles = ___________Avg. output
5. Figure 5% error of operating range. Any nozzle not performing within this range (+ or -) should be checked and replaced if needed.
__________Avg. output x .05 = __________ 5% error.

B. Gathering Information

1. Desired speed ____________mph
a. Truck#_____________
b. Gear ____________ High / Low (circle)
c. RPM_____________
2. Operating pressure___________psi
3. Test distance____________ft.
4. Time to travel test distance ___________seconds
5. Catch water for same time took to travel test distance at desired pressure.
__________ounces used divided by 128 oz. = _________ gallons used.

C. Gallons per acre (GPA)

1. Test Area ________ = (Test Distance________ x Pattern Width) / Acre (43,560 sq. ft.)
2. Gallons Per Acre(GPA) ____________= (Gallons Used) / (Test Area)

D. Convert miles to acres. Multiply miles to spray by the number of acres in a mile at desired width.

1. _________ miles x 2 (both sides) = _____________ miles
2. _________miles x _________ acres/mile = ___________ acres to spray

Table 821.11.1 Area Covered to Acres per Mile

Width (ft.)Acres/Mile
2 .24
6 .72
8 .97
16 1.93

E. Calculate gallons needed to complete spray operation.

_________GPA x __________acres = ____________ gallons needed

F. Calculate amount of herbicide to add to tank or needed for whole job.

________acres x ________rate per acre = ___________product needed

G. Calculate acres per tank.

_____(Tank capacity gallons)/ ____ (gallons per acre) = ____ acres/tank

Mix only amount needed to complete job. Avoid the need to store unused mixtures in spray tank.

H. Conversions

128 oz. = 4 quarts = 1 gallon
32 oz. = 1 quart
16 oz. = 1 pint
43,560 sq.ft. = 1 acre
5,280 ft. = 1 mile

Special Recommendations:

A. Read the label.

B. Any inconsistency in the application rates warrants a re-calibration of equipment.

Backpack Sprayer Calibration:

The following step-by-step method of calibrating a backpack or hand-gun sprayer involves very little math or formulas. It is based on the following principle:

One gallon = 128 fluid ounces and your calibration area to be sprayed is 1/128th of an acre, thus fluid ounces collected = gallons per acre

1. Clean sprayer and nozzle thoroughly. Then, fill the spray tank with clean water. Spray with water only to check to see that the nozzle forms a uniform spray pattern. If the pattern is uneven, check to make sure the nozzle is clean and replace if needed. Adjustable nozzles should be set and marked to permit repeated use of the selected spray pattern. If necessary, add a marker dye to the water to more easily see your spray pattern.

2. Measure an area 18.5 ft. by 18.5 ft., which is 1/128th of an acre. If possible, this should be done in the field on which you will be spraying.

3. Time the number of seconds it takes to spray the measured area uniformily with water using gentle side-to-side sweeping motion with the spray wand similar to painting a home or automobile. Record the number of seconds required to spray the area. During application be sure to maintain a constant sprayer pressure and cover the entire area. Repeat this step and take the average of the two times.

4. Spray into a container for the average time calculated in Step 3. Be sure to maintain constant sprayer pressure while you spray into the container.

5. Measure the number of fluid ounces of water in the bucket. The number of fluid ounces collected from the bucket is equal to the number of gallons of water per acre the sprayer is delivering. Volume sprayed in fluid ounces = gallons of water per acre.

6. Add the proper amount of herbicide to the tank based on label directions.

Table 821.11.2 Rates per Acre

DMA 4 IVM 2 qt. Selective and Aquatic Label Fumes Drift Off R/W
Aquatic Glyphosate 1 - 2% solution Safe, Versatile and Aquatic Non-Selective do not add surfactant is spraying over water
Krenite S 6 qt. Safe, Selective Rate and Time Critical
Plateau or Panoramic 3-5 oz. Safe, Selective -
Outrider 1 oz. Low Rate Johnsongrass control
Escort or generic ¼ - 1/3 oz. Low Rate -
Vastlan 2 qt. Low odor -
Total Veg Control – Custom Mix 2 qt. Low Rate season long control Non selective – Total Vegetation Control
Perspective 3 – 4.75 oz. Dry, broadleaf control Great for fall applications
Milestone 5-7 oz. Broadleaf control Use in PGR mixes or stand alone
Method 2 – 4 oz. for general weed control and 8 oz. for stands of target species Broadleaf Control Use in PGR mixes or stand alone
Basal Bark oilRTUPre-mixed and ready to use Dormant season and cut stump treatments
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