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  • 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 registered for use in Canada and must comply with all applicable federal and provincial/territorial requirements. Provincial rules vary, and it is the responsibility of the drone 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 SFOC permission.

    Health Canada: Pesticide Labels

    Health Canada is responsible for approving the registration of pesticides across Canada. Pesticide labels are legal documents and set rules on how a pesticide can be used. 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 Health Canada’s Pesticides Regulatory Directorate (formerly known as the Pest Management Regulatory Agency) pesticide label search tool 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. Questions regarding product label interpretations and uses can be directed to the Pesticides Information Service at pesticides-info@hc-sc.gc.ca.

    Mission Planning

    Proper field mapping and mission planning leads to safe and successful flights. Map obstacles, no spray zones, buffer zones, sensitive area/crops, areas of human activity, terrain, etc. Be aware that these conditions may change if planning occurs too far in advance of the spray day. Always check for relevant Notice to Air Missions (NOTAM), ensure the airspace is not restricted, and be aware of any other aircraft operating in the area.

    Staging Area

    Ideally, the staging area should be identified and prepared prior to the spray day. Select a staging area for filling, take-off and landing that is safe for the operator, crew and equipment. Drones should never fly over, or too close to busy roads.

    • The staging area should present clear lines of sight and support efficient operations.
    • The staging area should be upwind of the target site to reduce operator exposure to drift.
    • Bystanders must be at a safe minimum distance, as defined by the nature of the operation.
    • When spraying large fields, moving to an alternate staging area can save unnecessary ferry time, increasing efficiency and reducing battery strain.

    Take-off and Landing

    The operator and crew must be a safe distance from the drone during take-off and landing. Flying over crew is prohibited. The operator should be focused on the drone during take-off and landing. Be prepared to use connecting points and perform a manual landing when needed.

    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.

    Water quality determines pesticide effectiveness; hardness, bicarbonate, pH, and turbidity can antagonize or degrade products. Water quality testing allows operators to correct potential problems before spraying. Higher spray volumes (that is, liters per hectare or gallons per acre) enable proper mixing and have been shown to improve spray coverage.

    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

    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

    Line-of-sight and Connectivity

    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 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 safest approach is for the pilot to control the drone from an elevated platform while a loader 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.

    Remember, the operator should be focused on the drone/controller when flying; Flight is not an opportunity for performing other tasks.

    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.
    • Cameras and Lidar will not function if they are covered in residue. 
    • 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.

    Thanks to Dr. Steve Li (Auburn University, College of Agriculture) and Dr. Michael Reinke (Michigan State University Extension) for their review of, and contribution to, this article.

    Resources

  • Spray Water pH

    Spray Water pH

    The scuttlebut on coffee row is that acidifying a spray mixture improves its efficacy. There are also claims that pesticides break down in the sprayer tank if the pH is too high.

    But it’s not that simple. Low pH has a strong impact on pesticide solubility, and that means mixing and cleanout are affected. Acidifying the mixture can have profound negative effects for many products.

    It’s important to know what you’re doing.

    What is pH?

    pH is defined as the negative log of the molar concentration of hydrogen ions in a water-based solution. The more abundant the hydrogen, the lower the pH. It’s a log scale, so every unit of pH refers to a 10-fold change in the concentration of hydrogen ions.

    Both very low (acidic) or very high (basic) pH can be caustic. But having a low or high pH doesn’t mean it will burn your skin or clothes right away, it might just be a bit unpleasant. But at the extreme ends, protection is needed.

    Why is pH Important in Spray Mixtures?

    In spraying, the main effect of pH is on the pesticide’s solubility. Solubility matters when mixing and becomes important during cleanout as well.

    A minor effect on pH, at least for herbicides, is on chemical breakdown, usually through hydrolysis, when the pH is too high. The effect on breakdown is rarely meaningful during any given spray day, but may play a role if a spray mix is stored overnight or longer.

    The Basics: Strong vs Weak Acids

    Strong acids like hydrochloric acid (HCl) ionize completely in solution. When added to water, only H+ and Cl– are present, there is no HCl. The water’s pH does not affect solubility of a strong acid.

    But weak acids do not completely ionize. The water pH affects the degree of ionization and therefore solubility.

    Most herbicides are weak acids. A weak acid is one that does not dissociate completely in solution. A typical example of a weak acid functional group is carboxylic acid (-COOH). In solution, compounds with a carboxylic moiety exist in an equilibrium, with some as -COOH (containing the hydrogen, also called “protonated”) and others as -COO– and H+. In the dissociated form, the acid is more water soluble than in its protonated form due to the negative charge that makes it ionic.

    Weak acids have a dissociation constant known as the pKa. When the solution is at the molecule’s pKa, the acid is 50% dissociated. When the solution has a lower pH than the pKa, there is less dissociation and the protonated forms of the molecule dominate. That has two important implications for herbicides.

    • the molecule becomes less water-soluble at lower pH
    • the molecule has fewer opportunities to interact with positively charged items

     pH Dependent Solubility

    Water-solubility is a two-edged sword. On the one hand, having a highly water soluble product makes it easier to dissolve in water. This pays dividends when mixing a batch or cleaning a sprayer because a product formulated as a solution will easily go into a true solution and will stay mixed. Examples are glyphosate, glufosinate, and salts of 2,4-D, MCPA, and dicamba.

    On the other hand, most pesticides need to enter a plant to reach their site of action. And a plant cell, with its waxy cuticle and oily membranes, creates an effective barrier for water, and for water-loving molecules dissolved in it. As a result, a formulation that allows the water-soluble product to interact with an oily barrier is needed.

    The products that can do this are surfactants. Acting like detergents, surfactants have regions in their structure that are oil-loving (lipophilic) and other regions that are water-loving (hydrophilic). Surfactants can therefore bind to both oil and water and provide a bridge for water-soluble products across oily barriers.

    That’s also one of the reason that the most water-soluble products such as glyphosate and glufosinate contain a lot of surfactants in their formulation, reducing the concentration of active ingredient in the jug and possibly leading to foaming with agitation.

    Pesticides have a wide range of solubilities, and for some, water pH will play an important role. Below is a table of some water solubilities of selected herbicides.

             Solubility (ppm)
    Trade NameActive IngredientMode of Action GrouppH ~ 5pH ~ 7pH ~ 9
    Selectclethodim1535,45058,900
    Ally 2metsulfuron25502,800313,000
    Expresstribenuron2482,04018,300
    Pinnaclethifensulfuron22232,2408,830
    Everestflucarbazone244,00044,00044,000
    Simplicitypyroxsulam21632,00013,700
    Frontlineflorasulam20.1694
    Varrothiencarbazone2172436417
    Raptorimazamox2116,000 >626,000>628,000
    Pursuitimazethapyr22,570 12,8707,500
    2,4-D2,4-D salt429,93444,55843,134
    dicambadicamba salt4>250,000>250,000>250,000
    Roundupglyphosate9>500,000>500,000>500,000
    Libertyglufosinate10>500,000>500,000>500,000
    Heatsaflufenacil14302,100 >5000
    Distinctdiflufenzopyr19635,90010,550
    Infinitypyrasulfatole274,20069,10049,000

    Compare the solubility at pH 7 to that at pH 5. For most of these herbicides, water solubility is worse at lower pH. That is because they are more protonated and become more lipophilic.

    I’ve placed a lot of Group 2 products in this table because those products are most often implicated in tank cleanout issues. All Group 2 products in this table, with the exception of Everest (flucarbazone-sodium) have lower solubility at pH 5 than they do at pH 7. For some, like pyroxsulam and floarsulam, it’s a big change. Those products, when acifified, are prime candidates for poor mixability and poor cleanout.

    When it comes to dicamba, low pH has another side-effect. It makes the molecule more volatile, increasing danger to sensitive plants nearby. For that reason, acidification of dicamba in its Xtendimax and Engenia formulations is not permitted.

    Note that the Group 4 examples, 2,4-D salt and dicamba salt, as well as glyphosate and glufosinate, are highly water-soluble and pH has very little effect on that.

    Particularly for glyphosate, the claim that it becomes more oily at low pH and will therefore be taken up more easily, is not supported by these data. Considering that the most acidic pKa for glyphosate (it has four acidic groups) is 0.8, pH would need to be much lower for any noticeable impact on oilyness.

    Tank Mixability

    Given today’s environment of herbicide resistance, applications with multiple mode of action tank mixes are very common. Acidifying a spray mix to benefit one herbicide may create problems for its tank mix partners.

    If there is a concern that spray water is too alkaline, it is recommended that the pH of the finished spray mix be measured. Since many herbicides are weak acids, they will lower the pH of the mixture by themselves. For example, the addition of glyphosate to water with pH 7.5 will drop the pH to about 5 or so, depending on the water’s buffering capacity.

    As a result, glyphosate tank mix partners that are pH sensitive may suffer in the presence of glyphosate, and pH may actually need to be raised.

    pH Dependent Half-life

    Herbicides

    There are a lot of claims that pesticides break down rapidly in alkaline spray water. And yet, in my career working primarily with herbicides, I do not recall this ever being a problem in practice.

    Below is a table of herbicides for which I could find half-life information, with the help of this comprehensive list produced by Michigan State University.

    ProductActive ingredientHalf Life
    AtrazineatrazineMore stable at high pH
    BanveldicambaStable at pH 5 – 6
    BromoxynilbromoxynilpH 5 = 34 d; pH 9 = 1.7 d
    Fusiladefluazifop-p-butylpH 4.5 = 455 d; pH 9 = 17 d
    Libertyglufosinate-ammoniumStable over wide range of pH
    GramoxoneparaquatNot stable at pH above 7
    ReglonediquatpH 5 = 178 d; pH 7 = 158 d; pH 9 = 34 d
    MCPAMCPApH 9 = < 5 days
    PoastsethoxydimStable at pH 4.0 to 10
    PrincepsimazinepH 4.5 = 20 d; pH 5 = 96 d; pH 9 = 24 d
    ProwlpendimethalinStable over a wide range of pH values
    RoundupglyphosateStable over a wide range of pH values
    TreflantriflularinStable over a wide range of pH values
    2,4-D2,4-DStable at pH 4.5 to 7

    Note that all of the herbicides are relatively stable. Some are a bit less stable at high pH, but none of the listed herbicides is in danger of breaking down on the day it is being applied. Only one is actually unstable at high pH – paraquat, a herbicide no longer registered in Canada and resticted in many other countries. Those with short half-lives experience them at quite high pH which are rarely seen in practice.

    Insecticides

    Insecticides are a different story. Several are very sensitive to pH. This table is again adapted from a comprehensive list published by Michigan State University, here.

    Trade NameActive IngredientHalf-life
    AdmireImidaclopridGreater than 31 days at pH 5 – 9
    Agri-MekAvermectinStable at pH 5 – 9
    AmbushPermethrinStable at pH 6 – 8
    AssailacetamipridUnstable at pH below 4 and above 7
    AvauntindoxacarbStable for 3 days at pH 5 – 10
    Cygon/LagondimethoatepH 4 = 20 hrs; pH 6 = 12 hrs; pH 9 = 48 min
    CymbushcypermethrinpH 9 = 39 hours
    DiazinonphosphorothioatepH 5 = 2 wks; pH 7 = 10 wks; pH 8 = 3 wks; pH 9 = 29 days
    Dipel/Forayb. thuringiensisUnstable at pH above 8
    DyloxtrichlorfonpH 6 = 3.7 days; pH 7 = 6.5 hrs; pH 8 = 63 min
    Endosulfanendosulfan70% loss after 7 days at pH 7.3 – 8
    FuradancarbofuranpH 6 = 8 days; pH 9 = 78 hrs
    Guthionazinphos-methylpH 5 = 17 days; pH 7 = 10 days; pH 9 = 12 hrs
    KelthanedicofolpH 5 = 20 days; pH 7 = 5 days; pH 9 = 1hr
    LannatemethomylStable at pH below 7
    LorsbanchlorpyrifospH 5 = 63 days; pH 7 = 35 days; pH 8 = 1.5 days
    Malathiondimethyl dithiophosphatepH 6 = 8 days; pH 7 = 3 days; pH 8 = 19 hrs; pH 9 = 5 hrs
    Matadorlambda-cyhalothrinStable at pH 5 – 9
    Mavriktau-fluvalinatepH 6 = 30 days; pH 9 = 1 – 2 days
    MitacamitrazpH 5 = 35 hrs; pH 7 = 15 hrs; pH 9 = 1.5 hrs
    OmitepropargiteEffectiveness reduced at pH above 7
    OrtheneacephatepH 5 = 55 days; pH 7 = 17 days; pH 9 = 3 days
    PouncepermethrinpH 5.7 to 7.7 is optimal
    PyramitepyridabenStable at pH 4 – 9
    Sevin XLRcarbarylpH 6 = 100 days; pH 7 = 24 days; pH 8 = 2.5 days; pH 9 = 1 day  
    SpinTorspinosadStable at pH 5 – 7; pH 9 = 200 days
    Thiodanendosulfan70% loss after 7 days at pH 7.3 to 8
    ZolonephosaloneStable at pH 5 – 7; pH 9 = 9 days

    Among insecticides, dimethoate, amitraz, and malathion stand out as breaking down rapidly in alkaline water. For these products in particular, it may be important to acifify the spray mix if there is any delay in spraying.

    Recommendations

    I’ve never been a fan of messing with solution pH unless recommended on the product label. Even when there is evidence that lower pH improves efficacy, consider the impact on tank mix partners.

    We’ve seen improvements in solubility and tank cleranout of Group 2 products with raised pH, and ammonia is the most cost-effective way to achieve that. But again, following label recommendations is strongly recommended. The consequences of changes in pH, particularly acifification, can be very detrimental. To be safe, consider doing a jar test before committing to a whole tank to a pH adjustment.

  • The Hidden Shape of a Drone’s Spray Swath: What 2-D Imagery Reveals

    The Hidden Shape of a Drone’s Spray Swath: What 2-D Imagery Reveals

    Most operators assume drone swath widths are wide, stable, and predictable. That confidence generally comes from three places:

    • Manufacturer specs, often broad, vague and dependent on working conditions, not to mention each drone model is different, and even two drones of the same model behave differently.
    • Single point calibrations (water sensitive paper, Swath Gobbler, etc.) that are useful and display a 1-dimensional point-in-time snapshot of the swath.
    • “Looks good from the ground.” Watching a plume from below often makes it feel wider than it is.

    But drones move through space and time; spray patterns evolve as they fly. What you think is happening in the two seconds you glance up is not what’s happening over a 50 metre pass. The following video shows a multi-drone comparison where three drones apply 20, 50 and 100 L/ha.

    Why Single Point Methods Fall Short

    This isn’t a criticism. Water sensitive paper (WSP) cards and tools like Swath Gobbler™ are valuable. But they are 1-D snapshots of a 2-D, time-evolving problem. WSP captures a moment, not a pattern. Swath Gobbler™ helps visualize centre mass but can’t show edge dynamics or how edges wander along the pass.

    Real deposition and uniformity depend on:

    • Flight parameters (altitude, speed, droplet size)
    • Ground or crop size and shape
    • Path stability and lane keeping of the aircraft
    • Continuous micro corrections the aircraft makes
    • Gusts, even in “light” wind
    • Onboard wind compensation behaviour

    We noticed an observation from the field: gusts → aircraft corrections → amplified drift. If a left-side gust pushes the aircraft, the autopilot often dips into the wind to hold course. The nozzles are mounted to the airframe, so that slight tilt can direct spray downwind, in the same direction the gust is pushing, amplifying drift rather than cancelling it.

    Hidden Message: Many operators are doing their homework. At SDEUC 2026, I was impressed by how many pilots were calibrating and said they “knew” their drone’s pattern. My data suggests your drone may be subtly lying to you – its pattern shifts as it moves through air over distance.

    What Happens Over 50 m: The Swath You Weren’t Expecting

    The setup matters, because without context, a lot of people will assume the pattern you’re about to see is an artifact. It’s not. It’s the result of a controlled, repeatable field experiment designed specifically to expose real-world swath behaviour.

    During August–September 2024, we conducted clopyralid herbicide application trials in soybean, a crop that is extremely sensitive to clopyralid. Even a trace amount causes clear visual symptoms four weeks after application, which makes soybean a perfect bio indicator of spray deposition. (I jokingly call this sensitivity the “touch of death” because it reveals every detail.)

    We used a DJI T50 to apply Lontrel™ XC (clopyralid) at the highest labeled rate (300 g ae/ha) across three water volumes (20, 50, 100 L/ha) over 100 m long field plots. From each pass, a continuous 50 metre analysis zone was extracted to see how the swath behaved over distance (Table 1).

    CategoryDetails
    CropCrop Soybean (highly sensitive to clopyralid, ideal for visualizing deposition)
    HerbicideLontrel™ XC (clopyralid) @ 300 g ae/ha (highest labeled rate)
    EquipmentDJI Agras T50 with rotary atomizers
    Spray Altitude3 m above canopy
    Water Volumes20 L/ha, 50 L/ha, 100 L/ha
    Droplet Size300 µm (rotary atomizer setting)
    Flight Speeds Achieved~7.0 m/s (20 L/ha), ~6.9 m/s (50 L/ha), ~4.2 m/s (100 L/ha)
    Plot Dimensions10 m wide × up to 110 m long (location dependent)
    Analysis WindowCentral 50 m (avoids acceleration/deceleration effects)
    Wind~5 km/h (cross wind)
    Data ExtractionDroneDeploy orthomosaic → continuous 2 D swath visualization
    Table 1 Key application parameters for the 50 m Swath Visualization trials

    Now, here’s what the swath actually looked like over 50 m (Figures 1 and 2):

    Figure 1 – 50 m continuous swath visualization, Trial 1. This stitched graphic shows annotations for upwind/downwind edges and width measurements.
    Figure 2 – 50 m continuous swath visualization, Trial 2. This stitched graphic shows annotations for upwind/downwind edges and width measurements.

    What becomes immediately obvious is that this is not the clean, geometric ribbon many expect. Here’s what the 50 m swath showed:

    • Despite all the drone consistently flying north to south in a straight line, the path of efficacy isn’t consistently straight, appearing to subtly be affected by the wind.
    • Within the path, the edges are also not straight, the upwind edge can often appear jagged. Each “tooth” could correspond to a micro correction the drone makes to hold course. The downwind edge adds a frayed or tattered look, not as clean of a boundary, likely caused by drifting spray.
    • The width changes along the pass. Some sections widen, while others pinch inward. It would be unlikely to see these 2-D effects with 1-D sampling such as WSP cards.
    • The plume tail wanders. The airborne portion of the spray oscillates left and right in response to gusts and minor stability corrections.
    • The pattern is asymmetric. Left ≠ right. Upwind ≠ downwind. A drone swath is not a mirror image, and each pass is different.

    The bottom line: A drone’s real swath is not a clean bar of colour, it’s an irregular coastline. And once you visualize it in 2-D over 50 m, the story becomes clear: swaths are dynamic, variable, dependent on conditions, and often narrower than manufacturer recommendations.

    Why I Think It Looks Like This

    It’s not that drones are bad sprayers; it’s that their reality is dynamic. 2-D imagery simply reveals what single point tools cannot:

    • Drones are constantly making tiny left/right/forward/back corrections to counter act the forces (mostly wind) acting on them.
    • The wind and the resulting corrections of the aircraft slightly change where the spray actually travels.
    • The downwash column shifts with the aircraft’s posture.
    • Even light wind (< 5 km/h) is enough to expose these shifts.

    The Wandering Swath and Jagged Edge Problem: Swaths Don’t Fit Together Like Shark Teeth

    This is where mis-set swath widths come back to bite. When you slide one measured swath against its neighbour, the non-linear path and jagged edges don’t interlock. Some spots show metres of overlap; others flirt with gaps. The following video shows us sliding a measured 2-D swath polygon until it just touches the neighbouring swath. Note how irregular edges force uneven overlap and occasional near misses.


    Operationally, if you rely on the widest advertised swath—or on a single clean snapshot—two things happen:

    1. Misses (especially with herbicides): escapes, patchy control.
    2. Dose non uniformity: some areas get 0x, others 2x.

    Sure, the average across 160 acres may equal the target rate, but field level uniformity is not icing-smooth.

    Practical Recommendations You Can Use Tomorrow

    These are observational, conservative, and based on what the 2-D data actually shows:

    1. Calibrate, test in your conditions, over distance

    Run a long test strip and evaluate coverage continuously (not just a few cards). Evaluate in many wind conditions, to best understand your swath variance given the situation.

    2. Tighten your swaths beyond what’s stated in the brochure

    Depending on the application and product, plan for more overlap than the manufacturer’s suggested swath width. Adjust from there with your own measurements.

    3. Different jobs, different risk tolerance

    • Herbicides: misses are costly → tightest spacing.
    • Fungicides: somewhat more forgiving but still benefit from stability and overlap.

    4. Faster (7 m/s) with lower water volume displayed more variable swath

    Higher water volumes direct in a large amount of water being pushed down within the downwash resulting in less drift and more consistency. This coupled with slower flight = fewer corrections = a straighter, more consistent swath.

    • At ~5 m/s, droplets fall mostly into the downwash beneath the drone, deposition is close to the flight line.
    • At ~9 m/s, the airframe tilts forward to hold speed. The nozzles are slightly tilted back and the spray is deflected backward, it trails the drone like Superman’s cape.
      • Downwash is no longer straight down.
        • Coupled with the flight speed, the downwash is no longer pushing the spray into the canopy.
        • Deposition lands farther behind the drone.
      • Small gusts now matter more.
        • A backward angled plume has more side profile for crosswind to grab. The following speed comparison (same drone, two speeds) illustrates this effect:

    5. Respect “light” wind

    The imagery shows meaningful edge change and drift even in 5 km/h. Even the ‘gusts’ in light wind move the swath. In relatively calm days continue to watch variability, plan overlap, and validate.

    Conclusion – Know the Swath You Actually Have

    Drone spraying is promising and can be very effective and is getting better fast. Fit the setting with the task. If there is less room for error (herbicide), tighten those swaths to prevent misses caused by the wandering swath. Swaths are often misunderstood when we only look at single points.

    When you test over distance and see the 2-D pattern:

    • Coverage becomes more reliable
    • Reduces misses
    • Efficacy gets consistent
    • Confidence rises

    The first step to improving application is knowing the real shape of your swath. Tighten spacing, higher water volumes, slow down when you can, validate in your own conditions, and keep learning as the technology evolves. Spray drone technology is rapidly evolving, and many of today’s limitations will be addressed with innovation.

  • Green-on-Green in Ontario: A Custom Operator’s Experience with See & Spray Premium

    Green-on-Green in Ontario: A Custom Operator’s Experience with See & Spray Premium

    In the summer of 2025, Todd Frey of Clean Field Services (Drayton, Ontario) and I participated in the Elora Weeds Tour. We discussed his new John Deere See & Spray Premium and the practical considerations for implementing green‑on‑green spraying in Ontario (Figure 1). With that first season squarely in the rearview mirror, I reached out to Todd to ask about his experience.

    To be clear, we had a lot of questions then and we still have questions now… but we’re optimistic. This article summarizes the original topics from the Weeds Tour, Todd’s 2025 learnings, and considerations for the year ahead.

    Figure 1 – JD See and Spray Premium at the 2025 Elora Weed Tour. Todd Frey (left) and Brendan Bishop

    Challenges Identified in 2025

    Label Language and MRL Constraints

    Optical spraying introduces uncertainties when interpreting pesticide labels written for broadcast applications. For example, an operator might elect to concentrate a herbicide beyond the common broadacre rate while technically adhering to the label. Depending on the active, this risks excessive residue levels that can cause crop replant issues. A few Canadian labels already address this grey area by specifying water-to-product ratios in addition to per‑hectare limits. Most do not.

    Australia’s experience offers a possible way forward: optical systems in Australia are commonly calibrated at 100 L/ha (~10 gal/ac), and labels specify whether they permit higher concentrations for spot and patch spraying. Additionally, most labels state the operator must revert to a conventional broadcast application when fields have more than 30% weed cover.

    Tendering and Mixing Logistics

    Estimating product and water needs is, perhaps, one of the most difficult operational challenges. Traditional field scouting cannot accurately predict how much spray solution an optical sprayer will apply. This leads to logistics issues, increased risk of unnecessary leftovers, and subsequent disposal/clean out problems.

    Nozzle Availability and Performance

    Nozzle choice is central to realizing the full benefit of precision application. Ideally, operators require low‑drift, narrow‑angle nozzles with an appropriate dynamic range (i.e. travel speed vs. flow rate) to spray small weeds efficiently. Perhaps it goes without saying that a stable boom is critical in this equation, but we’ll say it anyway. Nozzle options are currently limited and we’ve written about this subject in a previous article.

    Cost–Benefit Realities

    While herbicide savings are an obvious appeal, the actual economics are more nuanced. The See & Spray Premium model adds a $6/acre CDN fee for unsprayed acres, which can diminish savings in very clean fields. A fall broadcast herbicide application improves the success of spring green‑on‑green passes, but this added cost must be figured in. Of course, there are many other benefits to a fall burndown that shouldn’t be dismissed, and you can read about them here.

    On the other hand, perhaps good agronomy should be the motivating factor. Any savings from reduced broadcast spraying may allow operators to upgrade to more effective, higher‑value tank mixes, improving weed control and contributing to long‑term seedbank reduction. Regarding the later point, there have been recent studies that suggest using low sensitivity may adversely affect the seedbank.

    New Chemistry Possibilities

    It’s a stretch, but there could be a silver lining to increasing herbicide costs and resistance pressures: chemistries once considered too expensive for broadcast use could become economically viable for spot or patch applications. This would expand chemical options.

    The 2025 Experience

    Cost savings

    To evaluate performance under Ontario conditions, Todd conducted a structured trial on his own 125‑acre corn field. In 2024 the field received a fall application targeting annual grasses and broadleaf weeds. Todd’s intention was to leave perennial sow-thistle and Canada thistle for targeted control in the spring.

    He used the See & Spray Premium to apply Lontrel + glyphosate at 13 GPA. The John Deere Operations Center map (Figure 2) shows a distinct high‑pressure zone in red. This corresponds to 2–3 acres recently reclaimed for production —significantly weedier (Figure 3) than the remaining acreage (Figure 4). This work was performed using the Deere TSL8005 nozzle, with sensitivity set to 3 (medium) and buffers set to medium in both directions.

    Figure 2 – John Deere Operations Center weed pressure map
    Figure 3 – High weed pressure in the reclaimed section of the field
    Figure 4 – Low weed pressure in the majority of the field

    Download a copy of the as‑applied data. You’ll see the See & Spray treated only 25.8% of the field. If Todd had broadcasted Lontrel at 65 mL/ac and charged his typical $14.50/ac it would have cost $4,139.36. However, even with his premium spot-spray rate of $17/ac and passing on the $6/ unsprayed acre, the total cost was $3,507.96. This represents a net savings of $631.40, and the surprise twist: he used the 100 mL rate of Lontrel and still saved money.

    So, in fields with moderate but uneven perennial pressure, See & Spray Premium can produce meaningful savings while enabling more robust chemistry.

    Scouting Limitations

    As expected, visual scouting underestimated real weed density. Figure 4 might seem clean at first blush, but the cameras see a different story hidden in the stover (Figure 5). This is why predictive tank‑mix planning is unreliable.

    Figure 5 – Weeds may hide from a scout, but not from clever optics.

    Optimizing Tendering Through Job Planning

    Todd found that the best approach to minimizing leftovers was to group farms with similar pre‑emerge programs and weed spectra. He would then book them from the smallest to the largest fields, allowing leftover spray mix from smaller jobs to feed into larger ones. His goal was to finish with <5 acres worth and broadcast it at the end of the last job.

    This kind of planning starts with the fall burndown and should be firmly in place by March. It’s already challenging to accommodate last-minute requests during spring spraying, but this approach makes it particularly difficult.

    Customer Scheduling Challenges

    There was some frustration along the learning curve. A few customers experienced delays waiting on sprayer availability and then paid the premium on a field that ended up requiring a broadcast application. Experience will help refine expectations and scheduling.

    Looking Ahead: 2026 and Beyond

    In 2025, the See & Spray machines in Ontario sprayed mostly soybean, but in Todd’s region it was predominantly corn. One reason was that most of his soybean customers weren’t quite sold on the fall application. Todd has plans to get into soybeans in 2026, but his strategy involves IP beans.

    Traditionally, IP beans get a spring application timed to catch as many weeds as possible, perhaps too late for some and too early for others. Then Todd takes his phone off the hook as customers fret over burned beans while they inevitably grow out of the visual injury. But this time, Todd will make two targeted passes with a more expensive tank mix to do a better job of controlling weeds at the right stage, while avoiding burning the IP beans. If his projections are correct, he believes he can accomplish this more economically than a single broadcast pass.

    We’ll update this article with the outcome. Be sure to check back and see if he succeeds 🙂

    Conclusion

    Ontario’s early experience with green‑on‑green optical spraying suggests that while the technology is promising, it requires substantial logistical planning, label awareness, and nozzle optimization. Under the right conditions—particularly where weed pressure is irregular but significant—operators can achieve both economic savings and precise weed control.

    As adoption increases and equipment evolves, we’ll learn more about where spot and patch spraying technology fits in changing weed management programs.

    Thanks to Todd for sharing his experience and insights.

  • Drone Tendering – Considerations before Buying or Building

    Drone Tendering – Considerations before Buying or Building

    Much of this article is based on a session and tradeshow I attended at the 2026 Drone End-User Conference in Kansas City. I want to acknowledge the insightful information provided by the three session speakers, as well as the ~200 audience members that asked honest questions and shared their experiences. The speakers were Mr. Chase Plumer (Owner, ProBuilt Fabrication/ProDrone Spraying & Seeding, Seymour, IN), Mr. Klaytin Hunsinger (Owner, Hunsinger Ag Solutions, Rossville, IL) and Mr. Kyle Albertson (Owner, Albertson Drone Service LLC, Benton County IN).

    Tendering systems

    Drone-based crop protection is a rapidly growing industry and operator experience spans from novice to veteran. It follows that tendering systems are not a one-size-fits-all proposition. The best fit will be a configuration that is budget-conscious, reflects the size and nature of the operation, and accounts for future needs.

    We can categorize them by their complexity, cost and capacity.

    Entry-level tendering system: A starting point

    For those just getting started, focus on affordability (lower initial investment) and simplicity (basic components). Examples include skid or truck builds, which are removeable or permanent systems that either rest on a vehicle bed or are built on-and-around the vehicle. This is an operator-friendly system that is small and portable for easy access to diverse fields. It’s the least durable configuration, and not particularly efficient or upgradeable, but it will serve until you know what you really need and how you like to work.

    Mid-level tender system: Second year

    By year two, you might want a larger and more efficient configuration with additional storage and a few creature comforts to reduce operator fatigue. A truck build might suit, but this is more likely a trailed system that is still capable of being towed by a mid-sized (1/2 to 3/4 tonne) truck. Some operators feel enclosing the trailer reduces efficiency, while others appreciate the security and protection afforded by defined spaces.

    A mid level system has some capacity for modification, but isn’t designed to support multiple drones, and likely won’t have enough capacity to store a day’s worth of water, chemical, or fuel. The operator may wish to detach the truck to run for supplies. Or perhaps it makes more sense to run a truck with a skid-mounted tender system that trails a second, mid-level system to divide-and-conquer, or scale up for larger projects.

    Beware going too big, too quickly. A 30-foot gooseneck can get caught on hilly terrain, where a 20-foot flat bed with a straight truck might be better suited. Small to mid-size trailers also take less time to set up and tear down. Consider performing site recon before dispatching a mid-level tender system. This is an additional step, but it allows the operator to scope out potential hazards and is ultimately more productive because it prevents tender systems getting stuck or placed in inefficient or unsafe locations. For example, if a client is “plant-out, pick-in”, the fields are hard to service because there’s no way to access them with large vehicles. Pilots become landscapers, spending valuable time clearing an operations area.

    High-level tender system: Large scale and Commercial interests

    Made for efficiency, the limiting factor of this system is the drone’s productivity. This category is comprised of the largest gooseneck trailers, which may include an upper deck and enclosed areas. It has the highest capacity for water storage, can service multiple drones and has ample storage. Intended for large fields, the size of this unit can make it physically incapable of reaching smaller fields. While a one tonne truck might be able to tow it, an even larger vehicle might be more suitable. It may also be prohibitively inefficient given the time required for setup and teardown. Consider an operator that requires a 15 minute start-up and a 15 minute teardown to spray 250 acres at 50 ac/hr; At $20/ac, that’s roughly $500.00.

    Phiber’s DASH Carrier (image from website)

    Components

    Fundamentally, each tendering system has the same function, so they share the same basic components. Here’s an overview of common features and considerations.

    Trailer

    The trailer is (literally) the foundation of most tendering systems. Operators suggest building for your current budget but planning for future needs as best you can. Trailer size should reflect the nature of the farms you will be servicing and how best to access them. You should also consider the safest and most efficient workflow on and around the trailer before committing to a layout.

    Option 1 – Utility trailer

    AdvantagesDisadvantages
    Easy to get on/offLow ground clearance
    Less expensiveNarrow footprint for accessories (e.g. conventional tanks not fitting between wheel wells)
    Versatile (use for drones on season, and other tasks off season)Narrow if planning a top flight deck
    May be an insufficient trailer GVWR (Gross Vehicle Weight Rating). This is the maximum allowable total weight of a trailer when fully loaded.

    Option 2 – Flatbed gooseneck trailer

    AdvantagesDisadvantages
    More room for accessoriesMuch heavier. ¾ tonne truck likely not sufficient.
    Better ground clearanceHard to get into tight places (length dependent).
    Higher GVWRSet up / Tear down takes longer
    Potential for top flight deck. Typically, 102” wide, so top deck can be about the same.

    Option 3 – Enclosed trailer

    AdvantagesDisadvantages
    Protection from weather and elementsLimited clearance for large drones (e.g. 24’ long, 8.5’ wide)
    Increased security for equipmentHighest GVWR
    Could serve as mobile workspace / officeMost expensive
    Cleaner environment for charging batteries, and generators don’t need maintenance (e.g. filters changed) as often.Can get hot inside, both for people and battery overheating. Airflow on batteries is a necessity, and fans can only cool to ambient. Drone hasn’t got time to cool between fields.

    Vehicle

    Based on operator discussion, it seems many have a tendency to push their trucks to the limit… or beyond it. One operator uses a ¾ tonne truck to pull a 22-foot trailer with an upper deck. Another uses a 1 tonne (aka tonner) gas F350 which struggles to pull a 30-foot trailer. Others recommended the use of a single axle semi (e.g. a Kodiac or a Kenworth T300), which even used still has ample life left in it, and at ~15 to 17,000.00 USD is cheaper than buying a truck.

    Consider that if you run a two-person operation, you may want more than one vehicle. A smaller truck can be employed to run for parts or fuel, or as previously noted can be fitted with a skid mount and a 1,300 gal. poly tank to split up the duty.

    Tanks

    Tank size(s) will depend on how you choose to operate, how many acres you plan to do in a day, and the weight capacity of your truck and trailer. Again, there is no one solution, so consider the following scenarios before you commit.

    If you plan to hot load, perhaps you’ll just mix in a single, large tank. However, if you plan to switch between insecticides, fungicides and herbicides, one or two 100-gallon cone-bottom tanks with wash-down nozzles might make more sense. Then, you can carry clean water separately in a few repurposed IBC’s or go for the efficiency of a single, high-volume poly or stainless tank. Consider the most flexible and efficient arrangement.

    Will you have access to water, will you have water tendered, or will you carry enough for the day? Will you fill from a 3-inch connector or suffer the lost time and fill with a garden hose? Will your truck and your trailer handle that weight, and will the vessel(s) fit between the wheel wells? Are the tanks black or shaded to prevent algae and do you have a plan to baffle the volume, so it doesn’t slosh when you drive over uneven terrain? Larger poly tanks (e.g. ~1,000-gallon tanks) have spots molded in to accept baffles, but some operators noted it’s difficult to install them after-market. Slosh suppressors such as floating balls or lengths of poly French drain can help.

    Pumps and Lines

    While some prefab trailers offer pneumatic pumps, most must choose between electric and gas pumps, and there are pros and cons to both.

    Electric PumpGas Pump
    Low noiseHigh noise
    No exhaustExhaust
    Taxes the generatorDoes not tax the generator
    No fuelRequires fuel
    Low maintenanceRegular maintance
    May limit head pressureAmple head pressure

    Gas-powered pumps (e.g. Drummond or Predator transfer pumps) are relatively cheap, but some claim they have a high failure rate. This not only incurs downtime, but operators must deal with the chemical in the pump and lines during repair.

    Electric may be a better choice, if only to avoid the noise and exhaust, and some operators run them continuously to recirculate chemistry when not filling a drone. Consider the horsepower, gallons per hour and head pressure, especially if you are pushing flow to an upper flight deck.

    An AMT electric transfer pump on a mid-level tender system.

    You should be able to fill a drone in about a minute. Some operators have begun increasing fill line diameter from 1-inch to 1.5-inch but feel 2-inch lines are too heavy to warrant the few seconds saved during filling. This may not be a limitation, however, if they are part of a top flight deck arrangement, and not dragged along the ground.

    The auto shutoff function of a fuel-pump-style filler is preferred over a quarter-turn-style. The former contributes to foaming but some operators say that can be mitigated by using an anti-foam adjuvant and it’s less likely to create an overflow situation.

    Perhaps a metered flow valve that shuts off once a predesignated volume has been dispensed would be a workable solution. This would preserve speed, but without foaming or potential overflows.

    A loose line terminating in a quarter-turn valve fills quickly and with few bubbles, but is ultimately not ideal. It’s prone to causing overflows which increase the potential for operator exposure and cause point source contamination.
    A reeled hose and a fuel-pump style filler is a better approach. The hose can be recoiled to keep it from being underfoot, and the filler has a back pressure valve that shuts off when the drone is full. There is greater potential for foaming, but some suggest anti-foam adjuvants can help.

    Generator

    This proved to be a controversial subject at the conference. Many operators were unwilling to promote a single make or model, but the discussion resulted in some general guidance based on personal experiences. Generators will have a peak and a continuous performance rating. Ensure the sum total of all your draws does net exceed the continuous rating.

    Drones are getting bigger, and the number of electrically powered devices on the trailer is increasing. Smaller operations tend to employ mobile gas generators that produce less than 10 kW. Larger operations reported using 30 kW (or more) diesel standby generators to charge two drones, plus accessories, while ensuring room for future growth.

    A mobile gas generator (inverter or not) tends to be the cheaper, lighter alternative, depending on the wattage. They are a good choice for entry level systems and with regular maintenance will last longer, but are still a short-term proposition. Diesel generators tend to be more expensive, but are quieter, more fuel efficient and more reliable. A liquid propane standby generator is yet another option; Generally cheaper than diesel, consideration must be given to the weight and size of what is typically a 250-gallon propane tank.

    A few points raised by operators during the discussion:

    • Most standby generators do not need diesel emission fluid, while mobile generators do.
    • Many operators prefer the durability of mobile generators over standby generators. The former is built to be moved while the later presents issues with brackets, mounts and stators.
    • Warranties are advisable for inversion generators, as they are not easily repaired.
    • Standby gas generators (10 kW continuous / 13 kW surge) may require you to downrate the battery charger, or the heat can trip the breakers. It is not advisable to bypass breakers.

    Storage

    Storage is often overlooked but can be critical to efficiency. For example, if you plan to spray six, 50-acre farms in a day and it takes 10 minutes for set up and 10 for tear down, that’s two hours gone. Consider what you’ll need and where you’ll need it, and place storage accordingly to minimize downtime. PPE should be located near your flight deck or filling area. You’ll also want to consider carrying spare parts, such as an electronic speed controller, motor, pump and a full set or rotors.

    Batteries

    Some battery chargers feature water baths, misters or air conditioning, but at bare minimum batteries should charge in the shade and in a ventilated area (e.g. not enclosed in a storage or tool box). One operator vented air from a commercial blower fan to the batteries on the top flight deck.

    Connectivity

    A hotspot on your cellphone doesn’t always provide reliable service. Satellite internet providers such as Starlink or Xplore (depending on your location) might be a solution. If the controller drops a direct signal to drone, it can bridge to satellite to connect to the SIM card in most drones. Operators that use this system advise it’s best to rent the hardware (if possible) so if something damages it, you get a free replacement. 100 gb of monthly roaming has proven more than enough for most operators.

    Mounting solutions vary, but operators noted good experiences with companies such as Veritas Vans, which have a replacement policy. They warn against 3D printed options that tend to be produced using unsuitable filament materials. Operators that use magnetic mounts on their trucks have reported no issues. Some run wire through rear window or sliding door, and others pull the headliner down and run the power cord out through the third brake light.

    Operator safety

    Lastly but certainly not least, when it comes to the cost-benefit assessment of tender features, safety should always be a priority. Even simple comforts such as folding chairs combat operator fatigue, increase safety and happily also improve overall productivity. We’re none of us getting any younger.

    RV awnings, umbrellas, foldable Bimini-style tops or flip-up doors provide shade. Switching to lower-decibel equipment (e.g. inverter gas generators run at about 90 decibels and electric pumps are even quieter), enclosing loud systems, or positioning them far from the filling area, reduce noise and emission exposure. Chemical drift and exposure during filling should be considered, and PPE should be used and stored in convenient locations.

    Trailers that feature an upper flight deck sometimes include a central cable to tether belt harnesses. Stationary railings can help prevent falls, while a fold-up version provides clearance when backing the trailer into a shed.

    The drones themselves are a hazard. Long flight decks keep landings and lift-offs at a safe distance, and a protected cockpit area improves matters. 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 short 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. The simplest approach might be to operate on the ground.

    An enclosed area for operators on a two-platform gooseneck trailer.
    Kodiak’s retractable flight deck on their skid-mounted system

    Take home

    The speakers left the session with some summary advice.

    • Trailer first, equipment second.
    • Build for today and tomorrow.
    • Function over form (stability, balance and access over appearance, bearing in mind that if it is a business, it can’t look terrible, either).
    • Efficiency from day one. Run a stopwatch (when the crew isn’t watching). Find and change the limiting factor, if it’s changeable. The right trailer improves efficiency even before the first acre is sprayed.

    Thanks to the many speakers, attendees and trades people that contributed to this article. If you want to share pictures and specs for your tender system, let us know! If we get enough interest we’ll publish an article showcasing your tender systems so others can learn from your experience.