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# Boom sprayer calibration tips

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NOTE: If the tank is not completely empty when refilling, use the amount of water required to refill the tank, not the capacity of the tank itself when determining acres treated per tank. For example: If you have a 300 gallon tank but you have 75 gallons of spray left in it when you refill, you will use 225 gallons in your calculations instead of the total tank capacity.

225 gal. refill/15 gal./A. = 15 A./refill

15 A./refill x 2 pts/A. = 30 pts./refill

You must add 30 pints of chemical to the tank.

Sometimes, chemical manufacturers give recommended rates in terms of active ingredient (A.I.) to be used per acre rather than the amount of total product per acre. In these cases, calculate the amount of material to be applied as shown in examples 2 and 3 for dry chemicals and liquid chemicals, respectively.

#### Example 2

The application rate of the chemical is 2 pounds A.I. applied per acre. The material to be used is a wettable powder containing 50 percent A.I. Determine the quantity of chemical to add to the tank:

Lbs. of material per A. = 2 lbs X 100/50 = 4 lbs./A.

4 lbs/A. x 20 A./tank = 80 lbs./tank

Example 3

The chemical you are using is liquid. The recommendation calls for 1 pound A.I. per acre. You have purchased a formulation that contains 4 pounds A.I. per gallon. Determine the amount of product needed per acre.

Gal.of product needed per A.= 1 lb.A.I./A. /4 lb.A.I.gal = 0.25gal./A.

Next, calculate the amount of chemical to add to each tankful:
0.25 gal./A. X 20 A./tank = 5 gal./tank

#### Example 4

(Band Spraying) You want to apply a herbicide on a 12-inch band on rows spaced 36 inches apart. The herbicide label recommends 3 pounds of material per acre on a broadcast basis. The sprayer has a 300 gallon tank, and the application rate measured with the calibration method explained previously for band application is 5 GPA. Determine the amount of chemical needed per tank:

• First, determine how much chemical will be used when applied on 12-inch bands.

12-in. band/36-in row X 3 lbs./A. = 1 lb./A.

•  The rest of the procedure to determine the chemical required per tank is the same as explained earlier for broadcast applications.

300 gal. per tank/ 5 gal. per tank = 60 A./tank

60 A./tank X 1 lb./A. = 60 lbs./tank

Thus, you will need to add 60 pounds of chemical product to the 300 gallon tank.

Mixing Chemicals

Mixing the pesticide thoroughly and carefully is an important step in good sprayer operation. Incomplete mixing results in varied application rates - too heavy at times, too low otherwise. Some chemicals, when mixed improperly with others, form a thick, mayonnaise-like mixture that will not spray properly and is difficult to clean out of the sprayer. Always read the label for proper mixing sequence and test the compatibility of chemicals in a small container before mixing.

Generally, when preparing the spray mixture, fill the tank more than half full of water and pour in the correct amount of chemical while the pump is running. Then, finish filling the tank. When using wettable powders, make a slurry in a separate container and then add the slurry to the tank to ensure good mixing.

Other Considerations

Here are some other considerations for calibrating your sprayer:

• Getting the right amount of chemicals on the ground is not enough to achieve effective pest control. How the chemical is deposited on the spray target is as important as the amount deposited. Make sure that all nozzle tips are properly aligned. Some nozzles require overlapping adjacent spray patterns. Check the nozzle catalog to determine the overlap required for a given type of nozzle.
• A common cause of non-uniform coverage is clogged nozzles. Watch the nozzles periodically while spraying to detect clogging. Always carry extra nozzles in your tool box, and replace bad nozzles with good ones immediately.
• In most cases, the pressure gauges on sprayers do not represent the actual pressure at the nozzle tip. Therefore, check the pressure at the nozzle tip when calibrating your sprayer.
• Safety is extremely important when working with chemicals. Always wear gloves and protective clothing when handling chemicals and calibrating sprayers. For safety reasons, use water instead of actual chemical mixtures when calibrating.

However, some carriers, such as liquid fertilizers, are much denser than water and may cause the nozzle flow rate to vary from the rate obtained with water. In this case, determine the average nozzle output using the actual chemical mix in the field, away from the farmstead.

Useful Formulas

• To determine the actual travel speed in the field:
Distance (feet)/ Travel (seconds) X 0.68 = Travel speed (mph)
• To determine the appropriate travel speed (MPH) for a desired application rate (GPA):
a. GPA2 X MPH2 = GPA1 X MPH1

b. MPH2 = GPA1 X MPH1 / GPA2
• To determine the appropriate pressure (PSI) for a desired application rate (GPA):
a. GPA2/GPA1 = (sq.rt. PSI2)/sq.rt.PSI 1

b. PSI2 = PSI1 X (GPA2/GPA1)2

GPA2, GPA1: Desired and measured application rate, respectively (gal./A.).

MPH2, MPH1: Desired and measured travel speed, respectively (miles/hour).

PSI2, PSI1: Desired and measured spraying pressures, respectively (lb./in.2).

Acknowledgment

The author acknowledges the useful suggestions given by T.G. Carpenter and J.A. Gliem of the Department of Agricultural Engineering, Ohio State University.