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

Calibrating Your Field Sprayer

Montana State University

Pesticide Safety Education Program


Proper calibration offers

Proper Calibration Offers

  • Better Pest Control

  • Environmental and human safety

  • Effective use of time

  • Inadequate control = more treatments


Calibrating your sprayers

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

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

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

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 128 th acre 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 scenario using 128 th acre scenario

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 scenario gpa for backpack sprayer

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 scenario long hand scenario

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

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

Check nozzle spacing and height


Boom level or nozzle angle correct

Boom Level or Nozzle Angle Correct


Worn spray tips

Worn Spray Tips


Verify that all nozzles are equal

Verify that all nozzles are equal


Nozzle output

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

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

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 cont1

    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

    or GPA for Boom Sprayer can be calculated by

    • Gallons applied per strip= GPA

    • Test strip in Acres


    Sample scenario boom sprayer

    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

    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

    How much chemical do you need?

    • 2 pints / Acre

    • You will be spraying 10 acres

    • 10 pints of product


    5940 method

    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

    What about field speed?

    • MPH = GPM * 5940 / GPA * W


    Sample scenario 5940 find speed needed

    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

    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

    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

    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

    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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