The goal of any spray application should be to get the maximum result for the minimum cost.

Minimizing Crop Damage

Crop damage can result in several ways:

  • If the spray application is not effective, the insects or disease can damage the crop.
  • When the wrong chemical or incorrect application rate is used the crop can be stressed or damaged.
  • Spray drift onto adjacent fields can also result in unintended chemical application and damage.
Maximizing Crop Yield

Weeds or insects that compete with or stress the crop reduce the yield. Effective spray application eliminates the pests so the maximum crop yield can be achieved.

Spraying to control diseases or fungus is another means to maximize the crop yield.

Minimizing spraying (and re-spraying) costs

An effective application ensures that chemical costs are minimized and re-spraying (and additional cost) is not required.

This also includes off-target spray (or particle drift) which can cause damage to both the crop or other nearby susceptible crops, areas, waterways, or animals.

For Optimal Spray Application Results, seven key factors should be considered and taken into a spray plan:

Chemical Choice

Selecting the chemical, or combination of chemicals, that will achieve the desired result is vital to maximizing the application result and minimizing the cost. Use of multiple chemicals (e.g. tank mixing) can reduce application costs by letting you apply several chemicals in a single application. However, chemical compatibility must be considered.

Information on chemical selection is available from chemical companies, chemical suppliers, crop guides, agriculture extension divisions and agricultural consultants.

Application Rate

Determining the correct application rate for both the chemical and the water is important. You must select the correct amount of chemical for the application as well as the appropriate amount of water for the volume of chemical used.

An additional consideration that will affect application rate is droplet size. Typically, the larger the desired droplet size, the higher the required application rate. Please refer to the Droplet Size section for more information.

Information on application rates is available from chemical companies, chemical suppliers, crop guides, agriculture extension divisions and agricultural consultants.

Application Timing

To ensure the most effective spray application:

  • Apply the chemical at the growth stage of the target recommended by the chemical manufacturer.
  • Apply the chemical under the best climatic conditions possible – if the target is stressed from heat, cold or drought the chemical may not perform optimally.
  • Depending on water quality, or chemicals sprayed, water quality modifiers or adjuvants may provide improved application consistency and results.
Sprayer Controls & Capability

To ensure the most effective spray application:

  • Auto-rate vs. Pressure Controlled Spray Systems
      • Auto-rate equipped sprayers monitor the sprayer speed and liquid flow to the spray booms and automatically adjust the flow or pressure to compensate for changes in sprayer speed. When selecting a spray tip you need to consider the range of speeds at which the sprayer will operate and ensure that the spray tip can accommodate.
      • An additional consideration is that: as the sprayer speeds up, the system pressure increases and the droplet size decreases and; as the sprayer slows down, the system pressure decreases and the droplet size increases.
    • Spray systems that utilize a constant pressure setting (except Blended Pulse Width systems – see below) to determine the application rate apply a constant amount of spray volume (gallons or liters per minute), regardless of changes in sprayer speed. When spraying at a slower speed, the application rate will be higher than the intended rate. When spraying at a higher speed, the application rate will be lower than the intended rate.
  • Pulse Width Spray Systems
    • Sprayers equipped with Blended Pulse Width spray systems (eg. Capstan PinPoint, Case AimCommand, Raven Hawkeye, John Deere ExactApply, Intellispray, etc.) utilize a solenoid valve on the nozzle body which turns the spray on or off many times a second. This allows you to:
      • Get a much larger speed and application rate range for a given size spray tip.
      • Spray at a constant pressure while changing speed which allows you to maintain a constant droplet size.
  • Pressure Capability
    • Note the maximum operating pressure of your sprayer and select a spray tip with a suitable operating range.
  • Pump Output Capability
    • If you want to apply a high volume of liquid (high application rate), check that the total flow from all the nozzles at the highest sprayer speed does not exceed the pump output capacity of the sprayer.
Droplet Size

Droplet Size – Definition & Terminology

  • Individual droplets are measured in microns (a human hair is approximately 100 microns in diameter).
  • The spray from a nozzle is made up of a wide range of droplet sizes and is sometimes represented by the median droplet size of the spray distribution (Volume Median Diameter).
  • The VMD means that half of the total spray volume consists of droplets larger than the VMD and the other half of the total spray volume consists of droplets smaller than the VMD. A large percentage of the droplets are near the VMD.
  • The larger the micron or VMD number, the larger the droplet size.
  • Droplets smaller than 141 microns are much more susceptible to drift and droplets larger than 600 microns may not deposit effectively.

Droplet Size – ASABE Classification Categories

In an effort to make droplet size easier to understand and work with, the American Society of Agricultural Engineers (ASAE) established standard categories and colors for droplet size ranges. Please note that the classification category color codes do not correspond to Spray tip colors.

Droplet Size – Smaller Droplets vs. Larger Droplets

Choosing the best droplet size for your spray application is often a trade-off between coverage and drift control.

  • Smaller droplets = better coverage
    • More droplets in same volume of water
    • Smaller droplets deposit (“stick”) on the target better and are less likely to roll off
    • More likely to drift
  • Larger droplets = better drift control
    • Fewer droplets in same volume of water
    • Larger droplets don’t deposit (“stick”) on the target as well and may roll off
    • Less likely to drift


Droplet Size – Size vs. Quantity

The total volume of spray on both leaves shown on the right is the same. Only the droplet size is different.

Note – In an actual spray application there would be a range of droplet sizes produced by the nozzle.

Droplet Size – Spray Nozzle Considerations

Although the VMD for a spray nozzle can give indication of its output, all spray nozzles spray a wide range of droplet sizes. While VMD can be helpful in comparing nozzles tested on the same testing equipment, VMD will differ for the same nozzle when tested on different laboratory testing equipment (Example, an MR110-04 will have a different VMD if it was tested on a PDPA versus a Malvern laser, despite being the same nozzle). For this reason, ensure if VMDs are compared between nozzles that they were tested on the same underlying equipment.

Drift control nozzle models are specifically designed to produce larger droplets. Common drift control nozzle types are:

  • Closed Turbulence chamber – Utilize a pre-orifice and exit orifice on either side of a uniquely shaped “closed chamber” where the droplets are formed (e.g. COMBO-JET®).
  • Air Induction – Utilize a small “port” on the nozzle that allows air to mix with the spray to form the droplets.


  • Variable rate – Utilize a needle and seat, or elastomer orifice to vary the rate in response to changes in the spray system pressure. Different nozzles produce a different droplet size range.


  • Dual-Chamber Closed Turbulence chamber – Utilize a pre-orifice and exit orifice on either side of a uniquely shaped “closed chamber” where the droplets are formed (e.g. COMBO-JET® UR Series). The patented UR series is a spray nozzle that produces very little driftable fines due to its design.


80 degree nozzles generally have a larger VMD than 110 degree nozzles.


Droplet Size – Coverage vs. Drift Control

Some chemicals are more effective when applied with a certain droplet size / VMD spray, while others are just as effective when applied with larger droplets.

Within chemical groups, contact products (Mode of Action groups 6, 10, 22) usually benefit more from greater volume than from smaller droplets. Systemic products (Groups 2, 4, 9) are more flexible. Group 1 is systemic, but not as much as others, and it also targets grassy weeds, so finer sprays are better. Mode of Action tables are available from crop guides, agriculture extension divisions and agricultural consultants. The recommended VMD / droplet size information may be shown on the product label or is available from the chemical manufacturer.

If you are tank mixing to spray both grassy and broadleaf weeds, this creates a challenge with single spray tip application systems because you can only spray one VMD (droplet size). While all spray tips produce a range of droplet sizes, which offsets this problem somewhat, the largest percentage of the droplets produced will be in a certain droplet size range and will only be most effective on one category of weed.

Multi-tip application systems (COMBO-RATE nozzle bodies) provide a solution to this problem because they allow you to spray with more than one spray tip (and droplet size) at a time.

Droplet Size – Coverage vs. Drift Control

  • Drift Factors and Considerations
    • Wind speed is the greatest drift factor. If using reference of % driftable fines from charts, assume that figure will double when wind is in excess of 12mph.
    • Spray nozzles – for a given size of spray nozzle and pressure:
      • A nozzle with a larger orifice produces larger droplets than one with a smaller orifice. Most nozzles produce smaller droplets / VMD at higher pressures.
      • A 110 degree nozzle has a nominally smaller VMD than an 80 degree nozzle (for the same size of nozzle, operating at the same pressure).
      • Drift control nozzles produce larger droplets.
      • The closer the nozzle is to the ground, the less susceptible the spray is to drift.
    • Droplet size
      • Small droplets drift more easily than large droplets.
      • At higher temperatures, when humidity is low, small droplets may drift due to air inversion
    • On auto-rate controller equipped sprayers, the VMD decreases when you speed up and increases when you slow down, due to the flow rate / pressure change required to compensate for the change in speed.
    • The spray is moving at the same speed and direction as the sprayer when it exits the spray nozzle.
  • How to Minimize Spray Drift
    • Spray at the highest recommended application rate (water volume).
    • Spray at the lowest recommended nozzle pressure.
    • Use the largest size nozzle that gives the required flow.
    • Use a drift reduction nozzle model.
    • Spray at the lowest height recommended for the nozzles being used.
    • When near adjacent fields, slow down and reduce the pressure (an auto-rate control automatically reduces the pressure as the speed reduces).
Spray Tip Selection

Spray Tip Selection – General Considerations

  • While the information provided in Tipnology can be applied to many types of spray application, it is most specifically intended to apply to broadcast spray application. Broadcast spray application is where the complete field is sprayed (as opposed to row crop).
  • For broadcast spray applications, spray tips which produce either an 80 or 110 degree flat fan pattern are the most widely used.

Spray Tip Selection – Before Selecting a Spray Tip

  • Carefully read the chemical label and / or other information to determine the recommended application rate and droplet size.
  • Note the application units (US gallons, Imperial gallons, Liters, etc.).
  • Determine if you have a standard or pulse width modulation (PWM) spray system.
  • Note your nozzle spacing.
  • Note your nozzle degree (80 or 110).
  • What type of spray nozzle mounting do your nozzle bodies utilize – Radialock (COMBO-JET ®) or conventional – square lug (Tee Jet & Hypro)?
  • Consider the pressure and flow output capability of the sprayer.
  • Consider the spray application wind conditions.
  • To maximize coverage and drift control, select a nozzle that will produce the largest VMD recommended for the product being applied.
  • A lower pressure will produce a larger VMD / droplet size for a given spray nozzle.
  • An operating pressure near the middle of the nozzle’s range will give the best pattern and allow for pressure adjustment to accommodate speed variations.
    • If the pressure is too low the edges of the pattern will start to collapse, resulting in poor overlap.
    • If the pressure is too high the nozzle will produce finer droplets at the edges of the pattern than the center, which may result in increased drift.
  • An auto-rate controller will increase or decrease the pressure to compensate for changes in speed. The nozzle operating pressure range needs to accommodate the sprayer speed range.
  • If you are spraying with two spray tips per nozzle body location, determine how the flow to each tip is controlled (standard vs. pulse spray modulation system) and use the appropriate Spray tip selection procedure

Spray Tip Selection – Best way to start

  • Regardless of what means used to search for spray tips (Tip Wizard is the most ideal, while charts would be less ideal), consider the easiest way to filter out nozzles that might not work:

STEP 1: Size your spray tip

As the tips ability to put out the required application rate is critical, the first step would be ‘sizing’ the spray tip.

This includes ensuring the flow rate of the nozzle and pressure it is spraying at will work for your application.

If you are typically travelling reasonably slowly 8-10MPH, then you might be fine spraying at 35-40PSI, as you do not require a large pressure window for when you are slowing down in the field to turn and avoid obstacles.

If you are travelling faster speeds like 15-18MPH, you may require to use a nozzle that allows you to spray most of your fields safely at higher pressures (e.g. 60PSI), which provides you a pressure window to still have consistent application when you need to slow down (which might bring your pressure down to ~35PSI).

Also, focusing on sizing the nozzle as a first step simplifies the process as it will give the clearest idea of whether a nozzle will work for your application before you have to consider the spray quality/drift/coverage.


STEP 2: Qualify the spray tip

Assuming you found a spray nozzle that works for your intended travel speeds and pressures, you will have 4-5 series of spray nozzles to choose from (ER/SR/MR/DR/UR).

With the application label’s requirements, a few of the nozzles might be filtered out immediately, leaving perhaps 2-3 functional nozzle series that might be considered. In many cases, unless the application requires serious drift reduction above all else, the UR series will be discounted, leaving 1-2 series for serious consideration.

With the nozzles left in consideration, there are factors in the tip charts for %<141µ and %600µ. These factors can make it very easy to differentiate which nozzle is going to perform the best for an intended application.

While each chemical is different, a few general rule of thumbs can be used as a starting point to know where a balance between drift reduction (%<141µ) and Coverage (%<600µ) might be.

How to use %<141µ :

The %<141µ is the % of spray that is ultimately very small, to the point of being called driftable fines. Driftable fines are small enough that the droplets might evaporate before contact, be held up by inversion, or travel off-target by environmental factors like sprayer speed and wind. Ultimately, an applicator will be keen on minimizing driftable fines.

With many systemic chemicals that do not require absolute levels of coverage, trying to maintain a %<141µ below 10% might be a good target.

With many contact chemicals that require higher levels of coverage and are less drift-sensitive, try to maintain a %<141µ below 15%.


How to use %600µ:

The %<600µ is the % of spray that is small enough to be reasonable for coverage. Spray droplets that are larger than 600µ are typically less effective for application as they might either roll off a leaf (resulting in missed coverage) or they will ultimately use up a lot of the chemical & carrier volume ineffectively.

As far as a starting rule of thumb to consider:

For many systemic chemicals, try to maintain %<600µ higher than 80%. For applications that require very low levels of drift, consider that you will find your %<600µ might end up far below 80%. Often, for these applications, a higher water volume is required by label to attempt to offset the lower level of coverage.

For many contact chemical applications, as coverage is most important, maintaining a %<600µ above 90% might be ideal. In some higher volume applications, given the tip size is larger, using multi-tip spray options might be the only way to maintain exceptional levels of coverage with those higher water volumes.


Using %<141µ & %<600µ to Compare the last few tips:

Overall, now that there might be only 2 feasible nozzles to choose from, there is a means to quantitatively have confidence in picking one over the other.


If you take the %<600µ (which might be a stand-in for expected level of coverage) and subtract the %<141µ (which might be a stand-in for driftable fines in ideal conditions), you will be left with an ‘effective spray volume’ factor that might make it clear which nozzle is the best.


For example, if an SR series had 96%<600µ and 22%<141µ, it can be said to have ~96-22 = 74% effective spray volume

If the MR series in that same size had 92%<600µ and 8%<141µ, it can be said to have 92-8 = 84% effective spray volume.


Even though the SR series shows it has a higher level of coverage factor, when the amount of driftable fines it will create to get to that level, using the MR series might be a more consistent spray nozzle for the application.

KEEP IN MIND: If the two nozzles are nearly identical in effective spray volume, ensure the driftable fine levels are acceptable before you pick one over the other. If driftable fine levels are too high for your field conditions and drift susceptibility, then do not pick that nozzle. You might be marginally less coverage with the coarser nozzle, but you’d be doing your due diligence in ensuring a nozzle is correct for the real-life conditions you are spraying into.

Sprayer Calibration

Sprayer Calibration – Why Calibrate?

  • Worn or blocked nozzles don’t apply the correct rate, or don’t apply the spray evenly.
  • Rate controllers ensure that the correct total amount of flow is supplied to the number of boom sections turned on. However, this does not ensure that the individual nozzles are applying the correct rate or applying the spray evenly.
  • You can have worn or blocked nozzles and the rate controller will compensate by increasing or decreasing the flow so that the total flow to the boom sections remains correct.
Graduated container

  • Calculator
  • Stop watch or
    • wrist watch with second hand

Sprayer Calibration – Steps

Step 1- Check your speed – speedometers can give erroneous readings due to wheel slippage and/or variances in tire size. To verify the speed, follow the instructions in your sprayer or rate controller manual, use your GPS system to verify or:

  1. Make sure sprayer is tank is half full of liquid.
  2. Place 2 markers 300 feet or 100 meters apart on a section of a field that is representative of spray application driving conditions. Make sure there is enough distance to bring the sprayer up to speed before the first marker.
  3. Bring the sprayer up to average sprayer speed and when you pass the first marker start timing.
  4. When you pass the second marker stop timing.
  5. Calculate your actual speed using the applicable formula below.


MPH = Distance traveled(ft) x 0.68
Km/h = Distance traveled(m) x 3.6

Use the actual speed when checking nozzle calibration or selecting spray nozzles.


Step 2 – Check the individual nozzle application rate


Using a jug, stopwatch and calculator:

  • Turn on sprayer in test mode.
  • Collect the output from a nozzle in a graduated container and measure the time it takes. (Note – the larger the amount of spray collected / the more time taken, the more accurate your measurement will be).
  • Do this for 3 or 4 additional nozzles randomly along the boom. Determine the flow rate from each of the nozzles using one of the applicable formulas below.

Sprayer Calibration – Results and Actions

  • If all the nozzles checked are higher or lower than the intended flow or application rate, your spray system needs to be adjusted.
  • If individual nozzles vary by more than 10% from the intended flow or application rate, they need to be cleaned or replaced.
  • As a yearly inspection, even testing a few nozzles on each boom section to verify the consistency of wear would be a good test. If nozzles are consistent from the few nozzles on each boom section, proceed to assume they are relatively consistent. If they are not consistent, test the entire booms nozzles, and verify average wear & wear consistency, replacing nozzles as required.
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