Calibrating your field sprayer
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Calibrating Your Field Sprayer. Montana State University Pesticide Safety Education Program. Proper Calibration Offers. Better Pest Control Environmental and human safety Effective use of time Inadequate control = more treatments. Calibrating your Sprayers.

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Calibrating Your Field Sprayer

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Calibrating Your Field Sprayer

Montana State University

Pesticide Safety Education Program


Proper Calibration Offers

  • Better Pest Control

  • Environmental and human safety

  • Effective use of time

  • Inadequate control = more treatments


Calibrating your Sprayers

  • You need to spray 1 pint / Acre of Insecticide.

    • HOW?

    • Cannot just spread 1 pint over an acre without a carrier can you?


How much to dilute?

  • Its easier to spread 20 gallons of water (with 1 pint added) over 1 acre than it is to spread 1 pint by itself.

  • The goal…….

  • Find out how many gallons it takes your sprayer to cover one acre


Clean your Sprayer

  • Toxic spray equipment

    • Clean with ammonia and water (2 quarts per 25 gallons)

    • Rinse with water

  • Replace nozzles, and filters


Determine GPA(4 tools/methods)

  • Backpack Sprayer

    • 128th acre method

    • Long hand method

  • Boom Sprayer

    • Calibration Strip Method (Preset Distance)

    • 5940 Method


Backpack Sprayer (GPA) 128th Acre Method

  • Use water when calibrating

  • Use same nozzles and filters as when spraying

  • Measure an 18 ½ by 18 ½ ft area.

  • Spray area with water and time how long it takes

    • Constant speed and constant pressure

  • Spray water into a container for same amount of time.

  • Ounces = Gallons Per Acre Applied


Sample ScenarioUsing 128th Acre Scenario

  • Takes 10 seconds to spray 128th Acre

  • In 10 seconds you spray 10 ounces.

  • What is the GPA output?

10 GPA


Long Hand ScenarioGPA for Backpack Sprayer

1 - If you have a different sized section that you spray

2 - Measure out known area sq ft / 43,560

3 - Spray known area and time yourself

4 - Spray into bucket for same length of time

5 - Measure amount sprayed and convert to gallons

6 - Multiply number found in step #5 times the number found in step #2.


Sample ScenarioLong Hand Scenario

  • Known area is 66 x 66’ (4,356 sq. ft)

  • 43,560 / 4,356 = 10

  • It took you 2 minutes to spray area

  • Collect 4 gallons in 2 minutes

  • 4 gallons * 10 = 40 gallons per acre


Boom Sprayers

  • No matter what method of calibration is used, you need to….

  • check nozzle spacing

  • check output across the boom.


Check nozzle spacing and height


Boom Level or Nozzle Angle Correct


Worn Spray Tips


Verify that all nozzles are equal


Nozzle Output

  • Check nozzle output for 1 minute and get average

  • If each nozzles output is not greater or less than 5% off of average, all is well.

  • How?


5% error level

  • To find 5%

  • Find your average…48 oz

  • Move the decimal place one space to the left. 48. = 4.8 This is a 10% error

  • Divide by 2 = 2.4.

  • This is 5% error

  • Now add 2.4 to 48 for +5%

  • Subtract 2.4 from 48 for

  • 5% Error range = 45.6 and 50.4

  • Any nozzle output between 45.6 and 50.4 is OK!


GPA for Boom Sprayer cont..

  • Nozzle output is same.

  • 18” = 227’ course length

  • 20” = 204’ course length

  • 30” = 136’ course length

  • 40” = 102’ course length

    • Or 340 / spacing in feet

  • Drive course in gear and rpm you will use when spraying and time yourself


  • GPA for Boom Sprayer cont..

    • Conduct 2 or 3 times and get average

    • Collect liquid from 1 nozzle for this amount of time

    • Ounces of liquid collected = GPA


    or GPA for Boom Sprayer can be calculated by

    • Gallons applied per strip= GPA

    • Test strip in Acres


    Sample Scenario Boom Sprayer

    • 18” wide nozzles, 6 nozzles

    • What to do?

    • Travel 227’ and time

    • 30 seconds

    • Measure amount delivered in that 30 seconds

    • 15 ounces in 30 seconds

    • 15 GPA


    How much pesticide to add to the tank

    • Determine how many acres that can be sprayed with a given GPA.

      • Volume in Tank / GPA = Acres

  • 300 GALLONS / 30 GPA = 10 acres


  • How much chemical do you need?

    • 2 pints / Acre

    • You will be spraying 10 acres

    • 10 pints of product


    5940 method

    • GPA = GPM X MPH X W / 5940

    • GPA = Gallons Per Acre

    • GPM = Gallons per Minute collected from a single nozzle (Make sure all nozzle are within a 5% range.)

    • 5940 is a constant

    • MPH = Field Speed

    • W = 1) width between nozzles or2) width of a broadjetswath in inches.


    What about field speed?

    • MPH = GPM * 5940 / GPA * W


    Sample Scenario5940 find speed needed

    • 1 nozzle / minute output = 0.2 gallons

    • GPA needed is 20 GPA

    • Width of nozzles is 12”

    • MPH = GPM * 5940 / GPA * W

    • = 0.2 * 5940 / 20 * 12

    • = 4.95 mph


    GPA is given or required!Need GPM for each nozzle!

    • Then you can purchase appropriate nozzles in GPM

    • Rearrange formula once again

    • GPM = GPA * W * MPH / 5940

    • GPM = 20 GPA * 30” * 5mph / 5940

    • 0.505 or 0.5 GPM nozzles needed


    Sample Questions

    You have an output of 20 GPA

    You need to spray 300 acres

    #1 - How much volume will you need?

    6000 gallons

    You need to apply 2 oz / acre of Warrior 1E.

    #2 - How much do you put in tank?

    600 oz of Warrior


    Questions Continued

    You are calibrating your hand sprayer and it took you 15 seconds to spray 1 18 ½ by 18 ½ ft area.

    #3 – What is your GPA?

    15 GPA

    With this 5 gallon backpack sprayer, you intend to apply 1 oz / acre of product.

    #4 - How much do you place in your backpack tank?

    Can only treat 1/3 acre at a 15 GPA rate, so 1/3 rate or 1/3 oz


    5940 example

    • You have checked all your nozzles and the average is 64 ounces per minute (OPM). All nozzles are within 5% of this average.

    • 64 OPM = 0.5 GPM (64 ounces ÷128 oz./gallon)

    • Your field speed is 5 MPH

    • Your nozzles are spaced 20”apart

    • GPA = GPM X 5940 = 0.5 GPM x 5940= 2970

    • MPH X W5 MPH x 20 100

    • GPA = 29.70 or 30 GPA


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