Calibration

Pesticide Environmental Stewardship April 23, 2012|Print
Learning Modules for Pesticide Applicators:

 

Calibration of Application Equipment

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Calibration precisely determines the output of the application equipment under controlled conditions. The pesticide manufacturer spends millions of dollars to determine the rate at which the pesticide should be applied. Proper pesticide application is applying just enough pesticide to give effective control. Unlike the weather, for example, the application rate of the equipment is one factor that is under absolute control of the applicator. Calibrating your equipment is the first step in controlling the application. Calibration will also identify faulty equipment components and provide the applicator with the confidence that comes with a job well done.

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Key points on this page

 

  • Understand the importance of and how to calibrate different types of pesticide application equipment.
  • Learn the important facts involved in sprayer preparation.
  • Know how to check for mistakes.

Why Calibrate?


The effectiveness of any pesticide depends upon the proper application and placement of the chemical. The purpose of calibration is to insure that your chemical application machinery is uniformly applying the correct amount of material over a given area. Although you may have the right chemical mixture, it is still possible to apply the wrong amount. Insufficient application results in an uncontrolled pest problem. Too much applied pesticide results in pollution, environmental and human health problems, and lost profit. Pesticide delivery can change with equipment wear, gauge error, nozzle error, wheel slippage, speedometer error, and friction loss. Always pay close attention to make sure your machinery is properly calibrated.

Some reasons to consider calibration:

 

  • It is estimated that 60% of sprayers have a calibration error greater than + or - 10 %.
  • 43% of sprayers have greater than + or - 10% variation in discharge from individual nozzles.
  • 32% have inaccurate travel speed.
  • 27% have improper boom height for the nozzle spacing and nozzle discharge angle.
  • 13% have inaccurate pressure gauges. Many of the gauges indicate too low pressure.
  • 8% have inadequate hose size to supply nozzles, causing pressure to drop in the system.

Liquid Application

 

Finding Gallons per Acre Known Area Method


One method of determining overall sprayer performance does not require any arithmetic. You just mark out an acre. (An acre is a square 209 feet on a side or a rectangle 100 feet by 436 feet, or a similar area totaling 43,560 square feet). Fill the spray tank with water and spray the acre as if you were applying the pesticide. Measure the amount needed to refill your tank. This is your rate per acre. If it takes 9.9 gallons to refill the tank, then you are spraying at the rate of 9.9 gallons per acre. Calibration checks using this method are good to use throughout the growing season to monitor sprayer performance. However, this method cannot tell you anything about the condition of individual nozzles on the sprayer. Examination of individual nozzles will not only give you information on the output from each nozzle, but this information can also be used to adjust the rate of delivery.

Boom Sprayer Calibration Method


Boom sprayers meter the pesticide solution out of several nozzles along a long pipe or other structure called a boom. Each nozzle or group of nozzles delivers the same amount of pesticide to the site as the other nozzles along the boom. When using a boom sprayer, the following cleaning and calibration steps are recommended.

Sprayer preparation

 

  • Thoroughly clean all nozzles and screens to ensure proper operation.
  • Check all nozzles to see that they are the desired make and model.
  • Make sure that all spray patterns are uniform from each nozzle. Replace nozzles that do not have uniform spray patterns.
  • Be sure that all nozzles have the same volume of delivery. This can be checked by placing similar containers under each nozzle. Use a graduated measuring cup marked in fluid ounces. All containers should fill at the same rate. Replace any nozzle whose flow rate is 5% greater or less than the average flow rate of all of the nozzles. Make accurate speed and pressure readings as well as cup measurements.
  • Select an operating speed (usually three to five mph). When spraying, be sure to use the same speed used for calibrating.
  • Select an operating pressure. Adjust pressure to desired psi while the pump is operating at normal speed. Make sure water is flowing through the nozzles.

Sprayer calibration

 

  • Measure a course according to nozzle spacing. In the table below, for example, if your nozzle spacing is 20 inches, measure a course 204 feet long.

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At the chosen spraying speed, measure the time in seconds it takes the sprayer to cover the measured distance. Do several runs. For best accuracy make sure you can read the time to at least the nearest second. A one second error in speed measurement could result in an application error of 5%.

With the sprayer motionless, operate at the selected pressure and pump speed. Catch the water from several nozzles for the same number of seconds it took you to cover the measured distance.

Determine the average output per nozzle in fluid ounces. The ounces collected per nozzle equals the gallons per acre applied for one nozzle per spacing. It is important that your collection device allows you to make measurements to the nearest ounce for best accuracy. NOTE: For directed spraying applications where two or more nozzles per spacing are used, multiply the average nozzle output by the number of nozzles per spacing to get the number of gallons applied per acre.

Band Sprayer Calibration Method


Band spraying is the application of a pesticide to a strip along a crop row.

Sprayer calibration

 

  • Follow the method above for calibration of boom sprayers. However, the rates of application are for broadcast spraying and must be adjusted for the particular band width and row spacing used.
  • Calculate the number of gallons applied per sprayed acre in the band by using the following formula:

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Sprayed acres - the sum of the area of the treated bands.

Field acres - the total area to be treated.

Example

Application is 10 gallons per field acre in 12 inch bands on 24 inch rows. What is the rate per treated acre?

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The rate per sprayed acre is 5 gallons.

Air Blast Sprayer Calibration Method


Step 1: Nozzle Flow Rate

Nozzle orientation, high volume, and pressure of the air blast sprayer make it difficult to catch the nozzle output. Place tubes or hoses over the nozzles and allow them to drain into buckets. Collect the liquid for 60 seconds. Measure the water in the buckets after the 60 seconds. This step results in the applicator knowing how much liquid will be applied in one minute, as well as finding faulty nozzles.

Step 2: Ground Speed

The spray application rate varies with ground speed. It is best to determine your forward speed when traveling over actual field conditions and pulling the sprayer with approximately a half full spray tank. In orchard applications, you will probably be working with tree row volume (TRV) calculations, where the volume of the tree foliage dictates how much liquid you will be applying. In row crop applications, the application rate will be on an area basis. In this situation it will be necessary to estimate the sprayed width. In either situation, it is important to know exactly how much liquid is coming out of each nozzle. Never rely on your speedometer for the actual mph measurement. Wheel slippage and variation in tire size, due to wear, can cause as much as a 30 percent difference between the actual speed and the speed indicated on your speedometer. Speed under field conditions can be found by using a test course. Map out a course 88 feet long, which is 1/60 of a mile (88 ft./5280 ft.) Drive the course at your normal spraying speed. From a running start, record the number of seconds it takes to drive the 88 feet. Divide the number of seconds recorded into 60 and the result will be miles per hour.

Example

If you record 15 seconds while driving 88 feet, the field speed is 60/15 = 4 mph.

Hand Sprayer Calibration Method


It is just as important to calibrate manual sprayers as it is powered sprayers. Generally, these sprayers are calibrated by determining the amount of liquid required to adequately cover the intended target.

Step 1: Area Measurement

Measure and mark off an area 20 feet by 50 feet (1000 sq. ft.). Practice spraying the area with water. The most uniform method of application over a horizontal area is to spray the area twice, walking and swinging the nozzle back and forth, with the second application at right angles to the first application.

Step 2: Liquid Measurement

Once you are able to maintain a uniform spray pattern, fill the sprayer with water to a known mark and spray area. Refill the sprayer, measuring the amount of water required to fill to the original level. The amount of water needed to refill the tank is the amount used per 1000 sq. ft.

Example

One gallon of water was added to a one gallon hand-operated sprayer. After spraying a 100 square foot test area, it was determined that 8 ounces of water was needed to refill the tank to the one gallon mark. At this application rate, how many square feet of carpet could be treated with one gallon.

spray used = 8 ounces on 100 sq. ft.

one gallon of water = 128 ounces

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16 X 100 sq. ft. = 1600 sq. ft. could be treated with one gallon of liquid.

Changing Delivery Rate


If your sprayer is delivering less than or more than enough spray to each acre, you can change the rate by using one of three methods:

  • You can change the pump pressure. Lower pressure means less spray delivered; higher pressure means more spray delivered. This is usually not a good method because a pressure change will change the nozzle pattern.
  • You can change the speed of your sprayer. Slower speed means more spray delivered; faster speed means less spray delivered. Doubling the ground speed of the sprayer reduces the application rate by one-half. Speed change may be practical for small changes in number of gallons, but not for large delivery changes.
  • You can change the discs or jets in the nozzles to change the amount each nozzle delivers. The larger the hole in the disc, the more spray delivered. This is usually the preferred method.

Granular Application


Granular application equipment comes in many different forms, but each must be calibrated carefully. The use of this type of equipment varies from small units for home lawns to units built for covering wide swaths for field work. Calibration of granular application equipment requires you to measure the amount of granules spread over a known area. You must calibrate using the pesticide granule to be applied, because each granule flows differently. You also must recalibrate each time you switch types of granular pesticides. Run the calibration test over an area where the granules can be collected (i.e. tarp covered area, concrete driveway). Speed is not a critical factor when the granular application equipment is ground driven. However, the equipment should be operated at a speed that will allow an even flow of material.

Step 1: Area Measurement

The area used for calibration of your granular application equipment will depend on the type of equipment used. At least 1000 sq. ft. is recommended for a drop spreader and 5000 sq. ft. for a rotary spreader. Avoid contamination of the area that will later be treated.

If it is not possible to spread over a measured area, then place a bag or catch pan under your spreader to catch the chemical. The catch container must not interfere with the delivery of the chemical.

Step 2: Chemical Measurement

Collect and weigh the amount of chemical spread over the known area. The application rate will be in weight of material collected for the area covered (usually per 1000 sq. ft. or per acre).

Example 1

You are applying insecticide from a chemical box on a corn planter, using a 12 inch band. A bag is placed under the drop tube to collect the granules. The planter is driven a total of 1000 ft. One ounce of insecticide was collected in the bag. What was the application rate in ounces per treated acre?

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Example 2

You wish to apply turf chemicals using a push-type drop spreader. A 1000 sq. ft. area (20 ft. by 50 ft.) is measured on smooth concrete. The chemical is added to the spreader and is spread over the measured area. After spreading is finished, the material is swept up and it is determined that 6 ounces of chemical was delivered. What was the application rate?

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Check for Mistakes


After your chemical application equipment is calibrated, you should check it often. Be sure that you are treating the same amount of area (acres, square feet, etc.) for each tank-full, as you had figured on. If you find that you are treating more for each area or less area than you figured on, you should stop the application immediately and recalibrate. If you have figured wrong or your application equipment changes its delivery rate, you should be able to catch it before you make a major mistake.

Remember the facts behind calibration and it will become simple and easy. A well-calibrated sprayer makes for an effective job, as well as saves on materials and money.

Calibration – Self Study Questions

 

  1. When you have the right mixture in your spray tank, can you still apply the wrong amount of pesticide?
  2. What is the delivery rate?
  3. Why is an air blast sprayer difficult to calibrate?
  4. Once your sprayer is calibrated, does it always remain the same or should you recheck it often?
  5. If your sprayer were delivering less spray to each acre than you want it to, how would you usually change the rate?
  6. What must you measure to calibrate granular application equipment?
  7. Must you calibrate granular application equipment each time you change granules? Why?
  8. What facts must you know for the “Finding Gallons per Acre — Known Area Method” method of sprayer calibration?
  9. A 10 ft. sprayer with six nozzles on 20-inch centers is used to apply herbicides on a golf course fairway. At the desired speed setting, the sprayer traveled across a 204 ft. course in 40 seconds. How is the application rate calculated using this information?
  10. Thirty-two ounces of water was collected from one spray nozzle in 30 seconds. What is the nozzle delivery rate in gallons per minute (GPM)?
  11. Are speedometers accurate enough to be used in calibrating pesticide equipment?
  12. Explain how speed can be measured using an 88 foot course.

Answers to Self Study Questions -- Calibration

 

  1. Yes. Non-calibrated application equipment will apply the pesticide at an unknown rate. Unless calibrated, it could be under or over applying the pesticide.
  2. Delivery rate is the total amount of pesticide delivered on the target over a period of time.
  3. Nozzle orientation, high volume, and pressure of the air blast sprayer makes it difficult to catch the nozzle output.
  4. It must be rechecked often. Nozzles can wear or become plugged, thus changing the delivery rate.
  5. Change pump pressure, speed, or nozzles.
  6. You must measure the amount of granules spread over a known area.
  7. Yes, because each granule flows differently.
  8. The number of square feet in an acre, the speed of your sprayer, the width of your spray boom, and the delivery rate of your sprayer.
  9. Catch the spray from one nozzle in a container for 40 seconds (time it takes to travel speed course). The ounces of water collected represent the application rate in gallons per acre.
  10. Delivery rate = 32 ounces (wet)/30 seconds x 1 gallon/128 ounces x 60 seconds/1 minute = 0.5 GPM
  11. No. Wheel slippage and variations in tire size often make speedometers inaccurate.
  12. From a running start, record the time it takes to drive 88 feet. Divide the number of seconds recorded into 60 and you have calculated the miles per hour.

(RDG1182008)


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Disclaimer: Please read the pesticide label prior to use. The information contained at this web site is not a substitute for a pesticide label. Trade names used herein are for convenience only; no endorsement of products is intended, nor is criticism of unnamed products implied. Most of this information is historical in nature and may no longer be applicable.