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Ministry of Agriculture and Lands

Pesticide Application Equipment

Calibration

  1. Introduction
  2. Set-up
    1. Selecting Spray Volume
    2. Adjusting Spray Volume for Target
    3. Selecting Nozzle Pressure
    4. Selecting Air Volume (Airblast Sprayer)
    5. Determining Sprayer Swath Width
  3. Measuring Delivery Rate
  4. Adjusting Delivery Rate
  5. Calculating How Much Pesticide to Add to the Spray Tank
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Introduction 

Calibration helps ensure good pest control. It also helps prevent crop damage from pesticides, high pesticide residues, and environmental contamination. Calibration can also save you money by preventing over-application of expensive pesticides and reapplication when too little was used.

Calibrate all application equipment to ensure a pesticide will be applied accurately and uniformly at the recommended rate. Calibration involves:

  1. Preparing the equipment so it is working properly
  2. Measuring the delivery rate
  3. Adjusting the equipment to change the delivery rate
  4. Calculating how much pesticide to add to the sprayer tank

Calibrate equipment regularly (at least once per year) to make sure the output is not changing. Also calibrate equipment when it is new and when making changes that affect the delivery rate. Proper calibration will minimize, if not eliminate, left over mixed pesticides in the sprayer tank which can be very difficult to properly dispose of.

Details on calibration procedures are given below. (Also refer to the Pesticide Applicator Course for Agricultural Producers.)

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Set-up 

Flushing out an airblast sprayer Measuring RPM
Before calibrating, flush water through the spraying system to remove grit that could clog nozzles.  Measuring the RPM on the PTO

During set-up check that the sprayer nozzles, forward speed and spray pressure are correct for the applied pesticide, the weather and the crop conditions. Check the equipment to ensure all parts are in good condition and working properly (see the sprayers operating manual). The sprayer must apply the pesticide uniformly across the width of the boom and over the whole field.

The proper set-up of a sprayer will take more time than all the other steps involved in calibration. The Calibration Worksheets at the end of this section give a thorough checklist to use for your sprayer set-up.

You must choose which nozzles to use, nozzle pressure, tractor throttle setting and gear (forward speed) before you can move on to the second step in calibration, Measuring Delivery Rate. The last page of the Calibration Worksheet gives formulas for checking the speed of your tractor gears. Recording the speed of each gear used for spraying will help to make adjustments in the sprayers delivery rate. To use the calibration formulas you must also determine your sprayers swath width.

Measuring air speed Checking nozzle output
Measuring air speed from and airblast sprayer Checking nozzle output

Selecting Spray Volume  

Before calibrating your sprayer, you should know how much spray mixture should be sprayed in your field. Read the pesticide label for recommendations on the amount of spray mixture (spray volume). The spray volume will depend on crop, stage of growth, the pest, the pesticide, weather, soil conditions and the method of application.

Spray Volumes for Herbicides
For herbicides, spray volumes range from 50 to 1000 L/ha (20 to 400 L/acre). Refer to the product label for specific recommendations. Pesticide application rates and spray volumes for herbicides are normally given as a broadcast treatment as if the entire field is sprayed. However, for some crops, herbicides are applied in bands along the rows spraying only a part of the field. Therefore, to spray only bands and not the entire field, the amount of area actually treated must be calculated to determine how much herbicide to add to the sprayer.

Spray Volumes for Insecticides and Fungicides
For fungicides and insecticides, use spray volumes of 300 to 1000 L/ha (120 to 400 L/acre). Use just enough water to obtain thorough coverage of the leaves without run-off for foliar sprays. Early in the season when growth is light, 300 L/ha (120 L/acre) of water may be adequate. In situations where foliage is dense and coverage is critical, use at least 1000 L/ha (400 L/acre) of water. For drenches (high-volume, low-pressure sprays directed to the soil for control of soil-borne pests), use at least 2000 L/ha (800 L/acre).

Use of drop pendants will permit lower spray volumes than a conventional straight boom. Airblast sprayers may be operated at lower spray volumes than hydraulic boom sprayers. To maintain effective coverage of the foliage, lower spray volumes require finer droplets to cover the same area. Finer droplets will be more prone to drift in windy conditions. In hot dry weather low ambient relative humidity may cause the water in fine droplets to evaporate before the pesticide reaches the target. This is another cause of drift. Sprayer operators should carefully monitor the foliage including the lower stems and undersides of lower leaves to ensure thorough coverage. Water sensitive spray cards are available to help check coverage and monitor spray drift.

Water sensitive spray cards
 Tower sprayer with flagging tape
Use water sensitive spray cards to help monitor spray coverage and spray drift. Flagging tape can be used to help determine the direction of air flow during calibration.

Adjusting Spray Volume for Target 

Spray Volumes for Perennial Crops
Perennial crops such as fruit trees and berries increase greatly in size from the time they are planted to when they reach maturity. The spray volume needed to get good coverage of the plant (roots, stems and leaves) changes as the plant grows. Application rates on labels for pesticides applied to perennial crops (i.e. trees and berries) are usually set for mature plants. Less spray should be used for smaller plants. It may also be necessary to adjust the spray volume for annual crops as the canopy develops during the growing season.

Changing Spray Volume for Different Sized Plants
There are several different approaches for selecting the spray volume for crops that change in size. These include: 1.Reducing the volume proportionately to size of the plants, 2. Closing upper nozzles or, 3. Using tree row volume. After the volume is selected, confirm it when measuring delivery rate (below).

1. Reduce the spray volume by the same proportion that the young plants are smaller than a mature plant. A simple way of comparing size of plants is to compare heights. If the young plants are one half the height of mature plants, then use one half the spray volume. If the sprayer will cover 5 acres of mature plants with a full tank then it will cover 10 acres of half-size plants. Add enough pesticide to the tank so that the concentration stays the same. For example, the same spray mixture can then be applied to 5 acres of mature blueberries or 10 acres of half-size blueberries.

2. Closing the upper nozzles on the boom. If the fields have both large (mature) and small bushes or trees, set up the nozzles on the sprayers boom to give even coverage on the large bushes. Then check the nozzle setup in the smaller bushes. Close the top nozzles with blanks if they spray over the top of the smaller bushes. Special nozzle bodies are available that allow the nozzles to be shut off by simply turning the body. Some growers connect the top section of the boom to the pump through a separate hose and boom valve. This provides control from the tractor seat.

Comparing the number of nozzles used for small plants to the number used for large mature plants provides the size of reduction in spray volume (assuming the nozzles are of the same size). For example, if 10 nozzles are used to spray a mature bush and only 6 nozzles are used for a small bush, then the small bush would be sprayed by only 60% (6 nozzles/10 nozzles) of the spray volume used on the mature bushes. If 5 acres of mature bushes are covered with a full tank, then (5 acres x 10 nozzles/6 nozzles = ) 8.33 acres of smaller bushes (6 nozzle bushes) would be sprayed by the same full tank.

3. Another way to reduce spray volume is to use tree row volume or comparing the surface area of the targets. In tree fruits, tree row volume (the volume that the tree canopy occupies) is used to approximate the surface area of the trunks, limbs and leaves. Small blueberry bushes are not only shorter but they are also smaller in diameter than large mature plants. The volume of foliage reduction is greater than the reduction in height for small plants compared to large mature plants. If plant height alone is used as the basis for spray volume reduction the effect is to use spray volumes somewhat greater than actually required to give similar coverage on mature plants.

Selecting Nozzle Pressure 

Pressure gauge Measuring pressure at the nozzles
This pressure gauge is suitable to use when the spray pressure is between 100 and 500 PSI. Measuring the pressure at the nozzles on an airblast sprayer

Herbicides are generally applied with flat spray nozzles at low pressures (200 to 275 kPa or 30 to 40 psi) to keep drift to a minimum. Do not use higher pressures unless they are specifically recommended. Some new nozzles are available which work over extended pressure ranges including pressures as low as 100 kPa or 15 psi.

Insecticides and fungicides are applied with disc-core nozzles at pressures up to 2000 kPa (300 psi) depending upon the pest to be controlled and the density of the foliage. For example, some foliar insect and disease pests are more efficiently controlled using drop-pendant nozzles on the boom at high pressures to penetrate and cover the foliage. Other soil pests require a drench using large water volumes at low pressures applied to the soil. The drenches would generally be applied with flat spray nozzles.

The pressures recommended on pesticide labels refer to the pressure at the nozzles. Check both the pressure at the pressure guage at the regulator and at the nozzles. If there is a difference between these two pressures, adjust the pressure at the regulator so that the correct pressure is at the nozzle.

Many nozzle manufacturers report nozzle outputs with pressures in bar not kilopascals (kPa). One "bar" is equal to 100 kPa. Pesticide labels report pressures in kPa. Use a pressure gauge on the sprayer marked in both psi and kPa (or bar) so both units can be read directly from the gauge. The maximum pressure on the pressure gauge should be twice the maximum spray pressure used to protect the gauge from damage and allow it to be read accurately. Be careful not to damage the pressure gauge by exposing it to excessive pressures when using a high pressure pump.

Selecting Air Volume (Airblast Sprayers) 

Airblast sprayers designed for tree fruits are capable of moving large volumes of air at high velocities that can deliver the spray droplets into the tops of the fruit trees spaced 6 m (20 feet) or more apart. If the same sprayer is used for smaller trees or bushes, or closer spacing, the air volume may need to be reduced to prevent the spray mixture from blowing through the plants. Some sprayers are equipped with gear boxes in the fan drive allowing the operator to choose a slower fan speed. Another option provided by manufacturers is a variable pitch blade where the angle of attack and air volume can be adjusted. Some growers adjust fan speed by reducing the tractor throttle from the 540 rpm PTO setting. Reducing the throttle setting will change forward speed and sprayer pump output, both of which will affect the sprayer delivery rate. To maintain the same forward speed a higher gear and lower throttle setting can be used, however the pump must still deliver enough spray mixture at the lower rpm. A better option is to choose a sprayer with a smaller fan more suited to spraying small plants that are grown close together.

Determining Sprayer Swath Width 

Swath width is the width of treated area over which spray droplets or granules are distributed in one pass of the applicator. In a broadcast spray, it is the nozzle spacing multiplied by the number of nozzles and for band treatments it is the sum of the treated band widths. For row crops it is the row spacing (from center-to-center) multiplied by the number of rows. Swath width is usually measured in meters or feet. The swath width is used in sprayer calibration to calculate the sprayers delivery rate. As the sprayer swath width is based on the treated area, the delivery rate will also be based on the treated area when band spraying herbicides.

When blow-through cannot be adequately reduced with airblast sprayers on small plants, some growers use alternate row spraying by skipping every other row. If uniformity or coverage are critical then spraying should be carried out on every row. Note that when alternate row spraying, the effective swath width of the sprayer is two rows wide.

When sprayers are set-up during calibration, check to make sure that the driving pattern used in spraying does not cause skipsareas of the field not sprayed between successive passes of the sprayer. The sprayer boom may also overlap the first pass when spraying the next strip or swath. Both skips and overlaps can be caused by not matching the nozzles on the boom to the driving pattern of the sprayer. With skips and overlaps, either pests will go uncontrolled or high spray residues can occur which may be dangerous to humans, plants and the environment. While spraying, the true swath width of the sprayer is determined by the driving pattern of the sprayer through the field.

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Measuring Delivery Rate 

There are two basic methods used to measure sprayer delivery ratesthe test area method and the timed output method. The test area method uses fewer calculations, however, it can take longer to carry out. If an entire acre or hectare is used as the test area, the measured discharge of water is the delivery rate per acre or hectare and no calculations are required. The most common problem with the test area method is measuring the amount of spray water discharged. If too small a test area is used or it is not covered with enough passes the actual amount of water discharged is too small to accurately measure in the tank. The tractor and sprayer tank should be parked in the exact same location and the water must settle in the tank after stopping, before measuring the tank level again. The timed output method can avoid these problems, however it will require more calculations.

Test Area Method

  1. Mark out a test strip at least 60 m or 200 ft long.
  2. Fill the tank about half full with water and start sprayer nozzles and agitation. Then set the pressure to what you want. Use the same throttle RPM youll use in the field.
  3. Choose a tractor gear to get the desired forward speed.
  4. Record the volume of water in the tank before the test. Mark where the sprayer is parked so you can return it to the same position to measure the water sprayed (level ground is best).
  5. Drive towards the first marker at the correct speed, and open the boom valve as you pass it. Check the sprayer pressure. Close the boom valve as you pass the second stake.
  6. Repeat until at least 10% of a full tank is sprayed. Record the number of runs.
  7. Return to the water filling site and park in the same place as in Step 4. Measure the amount of water remaining and record the number of litres discharged during the test.
  8. Calculate the test area by multiplying the test strip length by your swath width by the number of runs.
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Adjusting Delivery Rate 

If the measured delivery rate of the sprayer is different than the spray volume listed on the pesticide label or recommended in the production guide, it can be adjusted in three ways:

  1. Nozzle size should be changed if large changes in delivery rate are needed. Check with the nozzle supplier or agricultural advisor. Obtain a catalogue listing nozzles and nozzle outputs in litres per minute (L/min).
  2. Forward speed changes will adjust the delivery rate. Slower speeds increase the amount sprayed in a field, and faster speeds reduce the amount. If the delivery rate is 112 L/acre at 6 mph, then by halving the speed to 3 mph, the delivery rate is doubled to 224 L/acre.
    Speed changes are usually made by using a different gear in order to keep tractor RPMs and spray pressure constant and within the range recommended for the sprayer pump. On airblast sprayers the air-velocity and volume will also be constant with constant PTO rpm.
  3. Spray pressure should be set for the correct droplet size. Changing pressure is recommended only for very small changes in delivery rates. Otherwise the droplet size will change and cause drift or runoff problems. Since pressure must be increased four times to double the delivery rate, this is not a good way to adjust delivery rate.

After making the adjustments, measure the delivery rate again.

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Calculating How Much Pesticide to Add to the Spray Tank

When the sprayer delivery rate is known, then calculate how many acres can be sprayed by a full tank and how much pesticide to add to the spray tank. Section 4a of the Calibration Worksheet shows how to calculate how much pesticide to add to either a full tank or partial tank Be very careful to accurately measure the area to be covered by the last tank to minimize left over spray mixture in the tank when you are finished spraying.

Also see:

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