Author: Jason and Mark

  • Safe and Effective Pesticide Application using Drones

    Safe and Effective Pesticide Application using Drones

    Remote Piloted Aerial Application Systems (RPAAS) or Unmanned Aircraft Spray Systems (UASS) are generally referred to as drones. They are an increasingly common tool for pesticide delivery in modern agriculture. They offer flexibility and access to difficult terrain, are capable of broadacre and patch applications, and facilitate air-assisted applications over perennial canopies. As with all application technologies, careful attention to fundamentals, safety, stewardship, and regulatory compliance remain the cornerstones of responsible use.

    This document summarizes current best management practices for pesticide handling and application using drones. It is intended to support training and adoption for operators from a wide range of backgrounds. Given the rapid evolution of drone design and the changing regulatory landscape, key considerations are addressed without being overly prescriptive.

    Categorization and the Canadian Legal Environment

    Drones can be divided into three design categories (Figure 1):

    • Rotary-Wing: Single or multi-rotor, these drones employ vertical take-off and landing (VTOL) and can hover during spraying. They have relatively short flight times and low volumetric capacity.
    • Fixed-Wing: Resembling crewed airplanes, these drones require a runway for take-off and landing. They have relatively long flight times, operate at higher speeds and have more volumetric capacity.
    • Hybrid: Encompassing a range of designs including, for example, parasail-wing and VTOL-wing, this design combines aspects of rotary drones with the speeds, flight times and volumes of fixed-wing designs.
    FIgure 1 – Common drone designs

    Drones are also categorized by weight, which is used to define their legal use:

    • Small Drones (250 g to 25 kg): Typically have tank sizes up to 12 liters and speeds less than 25 km/h (10 m/s).
    • Medium Drones (25 kg to 150 kg): Typically have tank sizes ranging from 12 to 70 liters and a maximum speed of 25 km/h (10 m/s).
    • Large Drones (>150 kg): Typically have tanks >70 liters and a maximum speed of 72 km/h (20 m/s).

    Pesticide use is regulated by both federal and provincial governments to protect human health and the environment. Anyone applying pesticides must ensure they are properly licensed and comply with all applicable federal and provincial requirements, including those related to the sale, use, transportation, storage, and disposal of pesticides. Provincial rules vary, and it is the responsibility of the operator to understand and follow the requirements in their jurisdiction. 

    Transport Canada: Certification

    Drone pilots must follow Canadian Aviation Regulations (CARS) Part IX. Drones must be registered and marked, and the pilot must carry valid pilot’s certification.

    Table 1 lists each pilot certification (that is, Basic, Advanced, and Level 1 Complex) and permitted category of operation for small, medium and large drones. It is based on Transport Canada’s “Drone Operation Categories and Pilot Certificates: Overview (2025-11-04)”.


    Table 1 – Drone Operational Categories and Pilot Certificates

    BasicAdvancedLevel 1 Complex3
    Age minimum for certification1141618
    Fly in visual line-of-sightYYY
    Closer to or over people2NYY
    Small dronesYYY
    Medium dronesNYY
    Large drones4NNN
    Controlled airspace (air traffic control permitted)NYY
    Sheltered operators (small drones only)NYY
    Extended visual line-of-sightNYY
    Beyond visual line-of-sightNNY
    1In Canada, you must be at least 16 years old to apply pesticides.
    2Flying at an advertised event is considered a special operation, requiring permission.
    3Operating a drone over 150 kg in Canada is classified as a high-complexity, specialized operation requiring a Special Flight Operations Certificate (SFOC) from Transport Canada.
    4Operations with large drones are medium-complexity special operations and require permission.

    Health Canada: Pesticide Labels

    Pesticide labels are legal documents. They define application rates, equipment settings, mixing instructions, environmental precautions, personal protective equipment (PPE), restricted-entry intervals, and disposal instructions. As pesticide labels are updated to reflect drone applications, it is recommended operators consult the Pesticides Regulatory Directorate (formerly known as the Pest Management Regulatory Agency) pesticide label search for the most recent version. The pesticide must be registered for use on the target crop and pest and be permitted for application by drone.

    Tendering Considerations

    Staging Area

    Select a staging area for filling, take-off and landing that is safe for the operator(s) and equipment. It should present clear lines of sight and support efficient operations. Ideally, the staging area should be identified and prepared prior to the spray day.

    • Survey the area for obstacles, environmentally sensitive areas and areas of human activity.
    • The staging area should be upwind of the target site to reduce operator exposure to drift.
    • Check for relevant Notice to Air Missions (NOTAM) and ensure the airspace is not restricted.
    • Bystanders must be at a safe minimum distance, as defined by the nature of the operation.

    Tendering System

    A drone tendering system is a required component. At minimum, they achieve four things:

    • They supply onsite power.
    • They store water and chemicals.
    • They have a mixing and dispensing capability.
    • They transport the drone(s).

    Drone tendering systems vary in size, complexity, cost and capacity, depending on the nature of the operation. For example, licensed exterminators (that is, those paid to spray properties other than their own) may have additional needs beyond what is listed here.

    Mixing

    Drone tanks are small and lack agitation. Therefore, most tendering systems include a nurse tank for pre-blending and agitating batches of spray mix. This helps ensure that active ingredients dissolve and disperse fully, that suspension products stay mixed and that the target site receives a consistent mix.

    The act of mixing (and filling) carries the highest risk of operator exposure and environmental contamination. PPE requirements must be observed, and operators should avoid distractions or hurried work. Mix only the amount required for the task; leftover pesticide mixes create disposal problems and safety risks.

    1. Fill the nurse tank halfway with clean water. Backflow prevention (for example, a valve or air gap) protects the water source.
    2. Measure and add the pesticide, following the mixing order on the label and allowing time for each tank mix partner to dissolve and disperse. Tank mixing must be permitted on the label of each tank mix partner. Mixing multiple products at high concentration greatly increases the possibility of physical and/or chemical antagonism. If compatibility is in question, contact the manufacturers for guidance and conduct a jar test well in advance of spraying.
    3. Rinse jugs and measuring tools into the nurse tank.
    4. Top up with water and maintain agitation throughout the operation.
    5. Transfer the spray mix into the drone tank using the most closed system available.

    Filling and Battery Management

    Rotary-wing drones carry relatively small spray volumes, so refills and battery swaps occur frequently. Large models, for example, might have a 10-minute flight cycle, where the refilling and battery swap processes are simultaneous and comprise less than 2 minutes.

    Filling

    Haste and inattention increase the chance of spills, overflows and leaks during refilling. This represents unnecessary point source contamination and operator exposure and must be avoided. While drone refills currently involve quarter-turn-valved faucets, or gas-station-style automatic fuel nozzles, neither are ideal. Industry is developing alternatives. Ensure filling is performed with the most closed system available.

    Batteries

    Batteries, like the drone, carry spray residue and must be handled using PPE. Some battery chargers feature water baths, misters or air conditioning. If water-cooled, treat the water as pesticide‑contaminated and dispose of accordingly. Batteries charge more efficiently and last longer if charged in a cool, ventilated location. Charge according to the manufacturer’s instructions.

    Operator Comfort and Safety

    Drone operations are physically and mentally taxing. Attention to operator comfort improves safety and efficiency. Even seemingly minor accommodations have positive impacts:

    • Folding chairs combat operator fatigue.
    • RV awnings, umbrellas, foldable Bimini-style tops or flip-up doors provide shade.
    • Wear ear protection and consider lower-decibel equipment (for example, inverter gas generators are comparatively quiet, and electric pumps are even quieter).
    • Enclose or locate loud components far from the filling area to reduce noise and emission exposure.

    Elevated Platforms and Flight Decks

    While “beyond visual line-of-sight” operations are allowed under specific, authorized conditions, most current regulations require operators to maintain a visual line-of-sight with the drone. This supports swath alignment, obstacle avoidance, an ongoing assessment of drift risk, and general operational safety.

    Operating from an elevated platform can help maintain visual line of sight and improve connectivity between the flight controller and the drone. Real-Time Kinematic (RTK) is a satellite positioning technique that enhances GPS/GNSS data to provide centimeter-level accuracy (usually 1-2 cm) in real time. An RTK platform will improve connection reliability and drone accuracy. Satellite internet providers can supplement connectivity in regions with unreliable cellular coverage. Be aware that network latency varies with provider.

    The drones themselves represent a hazard. The safest approach is for the pilot to control the drone from an elevated platform while a partner performs refill and battery-swap procedures on the ground. However, if operating off a flight deck:

    • Long flight decks keep landings and lift-offs at a safer distance.
    • Decks with pull-out platforms or hydraulic wings can increase the operating area and can be adjusted to account for adjacent roads and the slope of the ground.
    • A security rail around the landing area can prevent a drone from slipping off; A falling drone is expensive, but falling or sliding into an operator is a disaster.
    • An enclosed operations area can improve operator safety and comfort.

    Cleaning

    Proper cleaning prevents cross‑contamination, maintains equipment lifespan, and avoids crop injury from residues. Perform cleaning away from open water and ensure rinsate is disposed of responsibly. Follow the pesticide label and adhere to the manufacturer’s instructions on allowable cleaning methods. The following recommendations do not supersede either resource.

    Triple‑Rinse Procedure

    Multiple, small-volume rinses are more effective than a single, large-volume one. Follow the triple-rinse procedure:

    1. Ensure the drone tank is as empty as possible.
    2. Fill the drone tank 1/4 full of clean water and, with a partner, agitate by rocking the tank (if removable).
    3. Flush the rinse water through the plumbing and nozzles.
    4. Repeat the process twice more.

    Employ a similar procedure to remove residues from the nurse tank plumbing systems. Important reminders when cleaning:

    • Use a cleaning agent in the second rinse if recommended by the label. Soaking may be required.
    • While the drone exterior should be rinsed, avoid pressure washing (to protect electronics) unless explicitly permitted by the manufacturer.
    • Commercial drone residue removers are available to assist in keeping the drone clean.
    • Wash or dispose of PPE according to label and local regulations.

    Swath Width and the Operational Use Case

    Swath width is the total width of the area covered in a single pass. Swath width is a fundamental variable for mission planning, ensuring the pesticide is applied at the correct rate and (in the case of broadacre operations) as uniformly as possible. A drone’s swath width is highly variable and affected by several factors, collectively referred to as the “Operational Use Case”. These factors include:

    • Drone design (for example, atomizer type and location relative to the rotors)
    • Operational settings (for example, altitude and travel speed)
    • Meteorological conditions (for example, wind speed, wind direction, relative humidity)

    Operational Settings

    When configuring a rotary-wing drone for a mission, pilots select operational settings on the controller. The three settings that have the most influence on droplet behaviour, and consequently swath width, are droplet size, flight speed and altitude. A single change alters several other influencing factors, but the cumulative impact on swath width and drift potential is clear (Table 2).

    Table 2 – Effect of rotary-wing drone operational settings on swath width and drift potential.

    VariableChangeEffect on Swath WidthEffect on Drift Potential
    Droplet sizeCoarserNarrowsReduces
    Droplet sizeFinerWidens1Increases
    Flight speedFasterWidens2Increases2
    Flight speedSlowerNarrowsReduces3
    AltitudeHigherWidens1Increases
    AltitudeLowerNarrowsReduces3,4
    1Coverage uniformity and overall number of deposits within the swath reduced due to offset and drift.
    2Current evidence suggest that at high speeds (> 10 m/s) there may be a plateau where there is little or no further change to swath width or drift.
    3Lower speed and/or lower altitude will increase the influence of downwash on droplet behaviour.
    4Low altitude may not permit sufficient overlap of the spray from each nozzle, creating gaps in coverage.

    Meteorological Conditions

    Spray released from a drone (or any aerial sprayer) is highly susceptible to environmental conditions. Drift potential increases when:

    • conditions are calm (inversion risk)
    • windspeed is too high (physical drift)
    • conditions are changeable (gusting and wind direction)
    • conditions are hot and relative humidity is low (droplet evaporation)

    Operators must observe label recommendations, local laws, and use good judgment to minimize drift potential. Practical methods include:

    • increasing droplet size
    • increasing volume
    • adjusting passes (particularly along buffer zone) to account for swath offset
    • halting operations when conditions favour movement toward sensitive habitat / crop / residential areas.

    Be aware that drift-reducing adjuvants have an unpredictable impact on the droplet size produced by current rotary atomizer designs. Until rotary atomizer design is standardized and tank mixes can be evaluated, do not assume adjuvants will work as intended.

    Downwash

    When a rotary-wing drone hovers, each rotor draws air from above and accelerates it downward in a high-velocity blast. The result is a vertical component referred to as the “downwash” and the turbulent splash of air that hits the ground and spreads laterally is the “outwash”. Droplets released beneath a drone at hover are almost completely entrained by the downwash. The majority get driven to the ground and then move laterally along the outwash, while a small portion (likely smaller droplets) recirculate back up through the rotors (see Figure 2a).

    Most rotary-wing drones have fixed-pitch rotors, so the entire drone must tilt forward to enter low-speed flight. This causes the column of downwash to tilt backward. While the downwash is created by lift, “wake turbulence” is created at the tips of the rotors as high-pressure air beneath the rotor wraps around to the low-pressure area above. As the drone flies at low speed (~3 m/s) the wake can be visualized as a pair of counter-rotating, cylindrical vortices that trail behind. Spray is still mostly entrained by the downwash on a downward and rearward vector with deposition aligning closely to the flight path. However, a portion will get caught in the wake (see Figure 2b).

    Figure 2 – A. Rotary-wing drone at hover creates a high-energy downwash directly below the drone.
    B. Rotary-wing drone at low-medium flight speed trails a lower-energy downwash and creates a rotor wake.

    The effect of higher speed flight has not yet been fully characterized. However, there is evidence that the downwash will detach from the ground, directing the spray further back and with lower energy. This exposes droplets to deflection by wind and shifts a greater proportion of the spray into the rotor-tip vortices (that is, the wake). This makes higher speeds undesirable, as they result in increased drift and an unstable and unpredictable swath. There is evidence that at some point this relationship with speed may plateau, where there is no further change to swath width or drift.

    Practical Impact

    Operational settings, meteorological conditions and the downwash have a cumulative effect on droplet fate. Consider the following operational use case: A rotary-wing drone spraying back and forth over rolling topography will experience changing wind speed and relative direction. The drone will respond by changing drone pitch, rotor speed and pump flow to maintain the desired altitude, travel speed, and application rate. Meanwhile, the drone gets lighter as it sprays, thereby reducing the magnitude of the downwash. Ultimately, this results in a swath width that expands and contracts and may shift back-and-forth or be consistently offset along the flight path (Figure 3).

    Figure 3 – Swath width and swath position along the flight path is variable.

    Evaluating Swath Width

    A drone’s swath width for a given operational use case must be determined through testing. The drone is first calibrated according to the manufacturer’s instructions. Swathing methods vary, but generally the drone is flown into the prevailing wind over a series of samplers (for example, discreet samplers like water sensitive paper or continuous samplers like string or bond paper). Multiple passes are required to capture the variability that occurs along the flight path (Figure 3).

    A rotary-wing drone does not deposit droplets uniformly across its swath. There are fewer droplets at the extremes and more directly beneath the drone. This can be envisioned as a bell-shaped curve with a tight span and a high peak (Figure 4).

    Figure 4- Methods for testing swath width

    Many drone manufacturers report an idealized swath width that represents the distance between the furthest detectable deposits. However, variability within the swath (that is, the amount of active ingredient deposited, the percent-area covered, and/or density of deposits) implies that the efficacy of the application will also be non-uniform, leading to further considerations.

    Effective Swath Width and the Agronomic Use Case

    The relatively sparse coverage at the extremes of the measured swath width may be insufficient to elicit the desired biological result. The Effective Swath Width (ESW) represents the segment of the total swath width that results in pesticide efficacy. In some use cases, the two widths can be similar, but in the case of a fungicide application, the ESW is typically only a fraction. The difference is influenced by the “Agronomic Use Case” which includes factors such as:

    • Minimum effective dose: This is a complex relationship between coverage, spray mix concentration and pesticide mode-of-action that results in an effective result while minimizing the environmental impact.
    • Target location (for example, a pest within a dense canopy or a weed on relatively bare ground)
    • Spray mix rheology (that is, the interaction of spray mix viscosity and atomizer design on droplet size)

    Minimum Effective Dose

    Consider a systemic herbicide and a contact fungicide. A systemic herbicide mixed according to the label will kill weeds with less volume per hectare and less target coverage than is required for some fungicides and insecticides. Therefore, a systemic herbicide can still be effective at the extremes of the swath, and while not ideal, higher residues in the middle of the swath are not a liability. Conversely, a contact fungicide requires relatively higher coverage and may not be effective at the extremes of the swath. Therefore, two missions with identical operational use cases, but different agronomic use cases, can present the same swath width during testing, but have different effective swath widths.

    Target Location

    Spray coverage diminishes with canopy depth. The degree depends on crop morphology and planting architecture. Simply put, a plant canopy filters out spray droplets, and this occurs both vertically and laterally.

    Spray Mix Rheology

    Most conventional hydraulic nozzle designs adhere to an international standard. This allows the operator to determine the size of droplets produced for a given operating pressure and flow rate. Droplet size is a not only a critical factor in mitigating drift and improving spray coverage, but it is often a defined pesticide label requirement.

    Currently, most rotary-wing drones employ rotary atomizers. This atomizer design is not standardized, and as a result, the droplet size selected on the controller will not necessarily produce the desired results. Studies have shown that changes in tank mix partners, concentrations, the inclusion of adjuvants, the flow rate and the atomizer design can produce droplets far larger or far smaller than intended.

    Further, some atomizers are prone to “flooding” when the flow rate exceeds the atomizer’s capacity, and this produces a volume of larger, less-effective droplets.

    Until rotary atomizers are standardized, operators can only select the desired size and infer the results based on in-flight behaviour and observing the size of the stains left on samplers during swath width testing.

    Practical Impact

    Taken collectively, research has shown a 20 to 30% reduction in ESW for corn, wheat and soybean fungicide applications compared to swaths measured on open ground. Conversely, herbicides sprayed on bare earth or sparse vegetation can produce an efficacious response 20% wider than the measured swath width (see Figure 5). The impact of agronomic use case on ESW must be considered during mission planning.

    Figure 5 – Measured swath width versus effective swath width for different agronomic use cases

    Route Spacing and Boundary Passes

    During mission planning, operational settings are entered into the controller. Route spacing should not be confused with ESW. Route spacing describes distance between passes over the target area, but this does not affect ESW, which is a constant. If a banded application is desired (for example, spraying over planted rows of perennial canopies, but not alleys) the route spacing should be wider than the ESW. If a uniform broadcast operation is desired, the route spacing should be less than the tested swath width and approximate the ESW (see Figure 6).

    Figure 6 – Matching route spacing to effective swath width results in a relatively uniform, broadacre application

    Kinematics

    Depending on the operational use case, rotary-wing drone speed and swath width share a direct relationship. This means swath width increases during acceleration and decreases during deceleration.

    Conventional crewed aerial applications reach the desired speed before spraying the target area. Ideally, rotary-wing drones would do the same, but software limitations currently prevent the separation of flight area from target area. As a result, it can take 25 meters or more for larger drones to accelerate to target speed. Additional headland passes may be required to ensure coverage is not compromised at the beginning and end of flight passes (see Figure 7).

    Figure 7 – Swath width changes due to acceleration and deceleration.

    Recordkeeping

    Detailed recordkeeping will help operators better understand how operational and agronomic use cases affect the outcome of a spray mission. Quality records also help mitigate against any allegations of misapplication, such as a drift complaint. The following items should be recorded, but the list is not exhaustive:

    • Product name(s), rate(s) and water volume.
    • Sprayer operational settings (altitude, speed, route spacing, droplet size to supplement a digital record of the mission)
    • Swath measurements
    • Weather conditions
    • Note of buffers and sensitive areas
    • Crew names and roles
    • Unusual events or corrections
    • Results (return to site to assess efficacy)

    Conclusion

    Drone technology is advancing rapidly, and best management practices will continue to evolve with new research and more experience. However, the principles in this document—proper preparation, careful mixing, responsible application, diligent maintenance, environmental awareness and swath testing—apply regardless of model or agronomic use case.

    Operators must ensure they are properly licensed and comply with all applicable federal and provincial requirements, including those related to the sale, use, transportation, storage and disposal of pesticides. With thoughtful planning, practice and recordkeeping, drones can be a safe and effective means of crop protection.

    References

  • Categorizing air-assist sprayers by air-handling design

    Categorizing air-assist sprayers by air-handling design

    Air handling systems

    Air handling systems can be specialists or generalists; some are designed to do one thing very well while others are more adaptable but not as precise. Fan type plays a big role in determining a sprayer’s abilities. Their native characteristics make them better suited to certain scenarios.

    This may seem contradictory, but we are not saying that the fan alone defines or limits the entire sprayer. Fans operate within a larger, engineered air handling system. Also, the operator has control over how that sprayer is configured and used. This means it is equally important to consider how the air exits the sprayer – not just the fan type that generated it.

    Fan types

    • Radial fans: Radial fans produce high volumes of moderately turbulent air, and relatively low static pressures. They are often associated with fixed vanes and straighteners inside the fan housing to reduce initial turbulence.
    • Turbines: Turbines may look like radial fans but they’re designed to spin faster and they have blades designed to compress air. They are used in sprayers that have ducts, towers, cannons, or other more complex volutes.
    • Straight-through axial fans: These fans produce high volumes of the most turbulent air. With their comparatively short throw and wide air wash, they should be positioned close to the target.
    • Tangential (aka Cross-flow) fans: Tangentials produce the most laminar air, forming a very high volume, low velocity jet sometimes called a “curtain” or “knife”. They have a comparatively long throw and rely on the canopy to induce turbulence.
    • Centrifugal (aka Squirrel cage) fans: Centrifugal fans have a side-discharge arrangement that turns air 90 degrees. They can produce high pressures and are nearly always paired with an air-shaping volute.

    We are proposing defining air-assist sprayers for perennial crops according to their air handling systems. Ultimately, the defining characteristic of each design is the net vector of the air they generate. We have provided silhouettes for clarity, but these generic designs are not intended to imply a manufacturer.

    Low profile radial

    The oldest and perhaps most recognizable air handling design, the Low Profile Radial (LPR) sprayer generates air in a radial pattern from one or more axial fans or a volute connected to some other fan style. This is the classic airblast sprayer.

    Defining characteristics

    • Wide range of adjustable air energies from virtually zero to high.
    • Minor adjustability of air vectors via deflectors and moveable outlets.
    • Net air movement is lateral and upward.

    Cannon

    The Cannon (CN) sprayer generates and channels air through a single volute and delivers the spray as a compact, point-source jet. 

    Defining characteristics

    • High air energy characterized by high velocity and low volume.
    • Extensive adjustability of air vector via a vertical duct with positional outlet and deflector(s).
    • Usually a single-sided sprayer used to spray over and through multiple rows.

    Fixed tower

    The Fixed Tower (FT) sprayer generates air from one or more axial fans, multiple straight-through radial or tangential fans. It may employ flexible tubes, tapered bags or solid ducts to redirect air laterally from a fixed central tower. It may feature additional flexible ducts or adjustable deflectors at the top of the tower to spray over and beyond the adjacent rows. 

    Defining characteristics

    • Wide range of adjustable air energies from virtually zero to high.
    • Minor adjustability of air vectors via deflectors and moveable outlets.
    • Net air movement is lateral compared to LPR sprayers.

    Targeting tower

    Similar to the FT, the Targeting Tower (TT) sprayer can focus air vectors with a wider range of adjustability, shaping the lateral air output more precisely to the canopy. TT generates air from one or more radial fans or multiple tangential or straight-through axial fans. It may employ flexible tubes or solid ducts to redirect air generally laterally. 

    Defining characteristics

    • Medium to high air energy.
    • Moderate to high adjustability of air vectors. Airflow can be subdivided into individually-adjustable sections.
    • When the tower exceeds canopy height, net air movement is lateral to slightly downward.

    Wrap-around

    The Wrap-Around (WA) sprayer surrounds the target rows with air sources. This creates multiple converging and/or opposing airflows within the row. 

    Defining characteristics

    • Straight-through axial fan systems are either electric or hydraulic with a wide range of air energies.
    • Low to high adjustability of air vector via deflectors, moveable air outlets, or fan position adjustments. May also have an adjustable frame.
    • Net air movement is ideally neutral to slightly downward.

    Summary

    In adopting this system of classification, we believe the process of optimizing sprayer configuration and calibration can be made less complicated. A universal language facilitates clear communication between growers, industry and consultants/specialists.

    We acknowledge that there may be rare sprayers that don’t fit these categories. There are commercial examples of air-assist sprayers that combine features from these air-handling designs (e.g. hybrids of LPR and FT designs)… but let’s keep things simple.

  • Rate Controllers on Air-Assist Sprayers

    Rate Controllers on Air-Assist Sprayers

    There are many advantages to using rate controllers, but their primary role is to maintain a constant application rate. All sprayers change speed on hills, at row-ends, or in response to surface conditions. Since flow from an uncontrolled sprayer is constant, the application rate varies significantly (up to 40% in hilly conditions). Rate controllers compensate for changing speed by adjusting flow.

    Hilly operations create highly variable application rates. Changes in travel speed can translate to 40% variability in rate applied. Rate controllers adjust flow to compensate.

    Pesticide is not saved directly (since increased uphill rates already cancel out reduced downhill rates), but consider the pesticide label. Labels that list a range of rates are contingent on pest pressure and crop size, but also compensate for poor coverage from low-performing equipment. When coverage uniformity is improved, experience has shown that operators can safely spray at minimal rates.

    Experience has also demonstrated that when coverage uniformity is improved, pack-out benefits follow. Even a modest improvement represents a quick return on investment. Equally important, a more consistent application reduces the risk of higher residue levels on the uphill and improves crop protection on the downhill.

    Now, if you are wondering if a rate controller is right for your operation, or if you should just stop reading now, consult this handy decision support matrix:

    This decision support matrix will help you decide if a rate controller is right for your operation. Spoiler alert: It probably is.

    Rate controller categories

    The following table categorizes controllers based on how they control flow. The categories are successively more expensive and complicated, but there’s commensurate value. For example, while not specified here, high-end rate controllers offer value-added features such as as-applied mapping (a powerful management tool).

    DescriptionProsCons
    Good:
    Monitors and adjusts pressure. Uses math to assume flow.    		-Fewest moving parts.
    -Simple interface.
    -Lowest cost.    		System monitors pressure, but does not register flow. For example, if nozzle flow is restricted, back pressure increases. The controller will compensate to correct pressure, implicitly reducing flow, but the operator is not alerted to the actual problem.
    Better:
    Monitors and adjusts flow, not pressure.    		Alerts operator to changes in flow. Operator usually sets the percent error threshold a little high to ignore transient changes.System will not register pressure deviations. At threshold speed, pressure may drop too low. This can cause inconsistent check valve operation and spray pattern collapse. With tall booms, the top nozzles may close completely.
    Best:
    Monitors flow and pressure and adjusts flow.    		-Best likelihood of a consistent application.
    -Alarms or automatic compensation of flow and pressure (user sets hard stops).
    -Provides a low tank level warning.
    -Stores preset calibrations to quickly switch between blocks.    		-Highest cost.
    -Steepest learning curve.
    -More “wire-wiggling”.
    -Operators often choose to over-apply at low speeds as a tradeoff for uniform output and consistent atomizer performance.

    Rate controller adoption and components

    As we write this, less than 10% of air-assist sprayers have rate controllers. In the dark old days of the 1980’s, air-assist operators were ill-advised to install high flow, low pressure field sprayer controllers. That history of mismatched components and subsequent bad experiences continues to hinder widespread adoption.

    Today’s components, however, are specific to air-assist sprayers and have made installations easier and more successful. Do your homework and speak with the manufacturer (not necessarily the local dealer) to ensure the controller, and all its components, meet your needs. Let’s describe the components so you’re prepared to have the conversation:

    • Console
    • Flow meter(s)
    • Flow control valve (including electric boom shut-offs)
    • Speed sensor
    • Wire harness
    Examples of rate controller components.

    Console

    The console is the interface. The user enters criteria about the sprayer, the planting, and calibration data and receives information about sprayer performance. Select a console designed for air-assist sprayers and not field sprayers. Controllers intended for horizontal booms perceive swath in two dimensions, but air-assist controllers account for multiple vertical booms or boom sections in the swath (see the following figure).

    Field sprayer rate controllers used in vertical crops must be “tricked” when programming swath. Leading air-assist rate controllers can assign flow to zones on a single vertical section (left) and adjust swath (sometimes called width) for multiple booms (right).

    Flow meter

    With rate controllers, flow is detected by one or more flow meters positioned pre-manifold. The relief valve becomes more of a safety device, defining the high pressure limit and bypassing flow if required. Most rate controllers use a flowmeter with no ability to monitor pressure. While still effective, adding a pressure sensor ensures nozzles are operating in the desired pressure range.

    Turbine or paddle meters are inexpensive and acceptably accurate. They require periodic cleaning because some chemistry can accumulate and interfere with their moving parts. Filtration helps to minimize this issue. Magnetic or ultrasonic meters have no moving parts, higher resolution, wider metering ranges and aren’t affected by the viscosity of the spraying solution or entrained foam. However, they are considerably more expensive than mechanical meters.

    Flow control valve

    Unlike boom control valves that are open or closed, flow control valves are capable of a range of adjustments. Valve actuation is controlled by 12 volt servomotors. The level of precision depends on the style of valve.

    • Butterfly valves: Simple, inexpensive, and typically for pressures <10bar (150psi). Some have minor leak-by when closed. Control is less precise as the valve opens because the orifice gets geometrically larger. This gives a narrow metering range.
    • Calibrated ball valves: Versions available for all pressures. May be simple flow through balls with similar metering limits to a butterfly. A better ball design is also available that offers a linear flow rate through the entire adjustment range, offering more stable rate control over the entire flow range. Several manufacturers offer these. All ball valves offer zero flow when closed.
    Left- A butterfly valve. Right- A ball valve. Notice how a small change in the opening angle translates into a large change in the orifice size; this is difficult to control manually. Servomotors not pictured.

    Compared to field sprayers, air-assist sprayers travel slower and use lower flow rates. It is a mistake to employ valves intended for high-flow, high-speed sprayers.

    • Speed: Valves are rated by connection size (½”, ¾”, etc.) and opening time (e.g. 1-14 seconds are common). Many rate controllers can be programmed to optimize adjustments for the speed and size of the valve.
    • Precision: As control valves open over their 90° range, the ability to control flow is less precise. Slower valves give less precision, but greater stability.
    • Size: Valve size should accommodate maximum flow and no more. If the valve is too large, it can only meter flow over the first few degrees of opening. For example, let’s say a valve capable of 200 L/min (50 gpm) and rated 1 second is used. Your sprayer meters 0-20 L/min (0-5 gpm). This means the whole metering range happens in the first tenth of a second. Even lightning-fast consoles will give unstable readings (aka hunting) as the computer overshoots the target in an effort to comply.

    Control valves are “service parts”. Seals, moving parts and abrasive liquids mean they will require regular care and eventual replacement. It’s a wise precaution to make them accessible and easily removable. We suggest installing them with quick-connects (see top-right of the previous collage of rate controller components above) to make field-maintenance fast and easy.

    Speed sensor

    Speed can be based on GPS, engine tachometer readings, radar, or wheel rotations. Newer rate controllers may even take the speed directly from the tractor’s data feed. Price, reliability and crop conditions are all factors you should consider in the choice.

    • GPS: Easiest to deploy, very accurate (especially RTK-GPS) and reasonably priced. However, overhead canopy can block satellite signals. Some controllers compensate for the GPS losses with sophisticated internal kinematic devices that measure the inertia of the sprayer and calculate speed when the GPS is not reliable.
    • Wheel rotation speed sensors:  An entry-level sensor, it’s typically a reed switch or Hall effect sensor that detects either the lug nuts or magnets installed on the rotating wheel. More magnets improve accuracy. Its exposure makes it prone to physical damage, and readings change with tire radius (which changes as the tank empties, on soft ground and with temperature). This is why wheel sensors are calibrated in the alley, with the tank half full and both tires at the same pressure.
    • Radar speed sensors: Employing the Doppler effect to measure speed, radar is the most accurate sensor. They are unaffected by terrain, slope or tank volume. They can be mounted anywhere in sight of the ground. They are, however, the most expensive and are typically not repairable if they fail.
    • Tachometer speed sensors: Largely obsolete, they measure the tractor’s tachometer speed and convert it to travel speed. Difficult to install and prone to the same inaccuracy as wheel sensors.
    • Interface sensors: Relatively new, some rate controllers interface with tractor electronics to receive speed data. ISOBUS, the standard interface language that agricultural electronics are increasingly adopting, makes this data exchange more common.

    Wire harness

    It may seem we’re drilling deep to mention wires, but standards are changing. Many controllers employ traditional analog wiring, but they are being made obsolete by the newer ISOBUS option.

    • Traditional Analog: Simple wires with automotive or custom plugs designed to match components. Relatively inexpensive and sometimes field repairable, analog wiring carries signal voltage (and power) to and from the controller to drive valves and receive analog sensor data. Communication is one-way: Sensor to controller, controller to valves.
    • Modern ISOBUS: Bus systems are more like a computer network, where digital signals travel back and forth between the controller and each component. Components that require power are wired directly to a battery. This results in a greatly simplified harness. The controller’s single ISOBUS wire “daisy chains” all components to relay commands and receive status, which makes system monitoring and diagnosis easier and more effective.

    Conclusion

    Rate controllers are a worthy consideration for your existing or future air-assist sprayer. Assess your needs and work with a knowledgeable dealer or manufacturer that can assemble and install a system appropriate for your operation.