Author: Jason Deveau

  • Characterizing RPAS Coverage at Four Cardinal Points on a Vertical Plane: Practical implications for spraying wheat at T3

    Characterizing RPAS Coverage at Four Cardinal Points on a Vertical Plane: Practical implications for spraying wheat at T3

    Global research into Remotely Piloted Aerial Systems (RPAS) is producing pesticide residue, drift and efficacy data that is helping to inform federal regulatory policy. It is reasonable to assume that Canada will ultimately sanction the use of RPAS for agricultural spraying. The first registered products will likely be fungicides intended for broad acre crops such as soybean, corn, and wheat.

    Those considering RPAS for agricultural spraying have expressed interest ranging from general curiosity to high demand. Successful adoption will be contingent on expectation management, which in turn requires education on the functional differences between RPAS and conventional application technologies.

    Quadrotor RPAS design dominates the current commercial landscape, with typical models featuring four rotary atomizers and 40 L tanks. There have been improvements in recent years, but these designs continue to suffer from a low rate of productivity (by North American standards for broad acre crops). This is due, in part, to low volumetric capacity and limitations with rotary atomizer design, which result in a debatably short effective swath width. Broadly, “swath width” refers to the minimal span consistently sprayed by a single pass, while “effective” indicates a spray coverage (i.e. deposition pattern and threshold dose) sufficient to achieve the desired result.

    Our research efforts have focused on identifying and evaluating variables that influence effective swath width. These include operational settings such as altitude, travel speed, volume applied and nozzle settings. They also include environmental factors such as meteorological conditions, crop morphology, and planting architecture. Establishing a combination of settings that account for these factors will inform operator practices and optimize the balance between RPAS effectiveness and efficiency.

    Study Objective

    Fusarium head blight is a significant economic threat in wheat. Fungicide application takes place at the T3 stage of development, with the intention of providing panoramic coverage of the wheat head. RPAS is being considered to apply these fungicides.

    The pursuit of productivity tempts operators to push operational settings to the point that spray coverage is compromised. This study will use operational settings based on the results of previous work and assign flight speed as the independent variable.

    Coverage will be assessed using water sensitive paper (WSP) positioned at the top of the canopy and oriented vertically in four cardinal directions to emulate the circumference of the wheat head. Isolating the resultant coverage in each cardinal direction may provide insight into droplet behaviour within the RPAS spray cloud and perhaps better assess effective swath width.

    Coverage from a conventional field sprayer will also be characterized. This represents the current standard and it will provide a basis for comparison.

    Materials and Methods

    Site

    The experiment was conducted at 45939 John Wise Line, St Thomas, Ontario (42.7320746, -81.0879887) on June 1, 2025. Common seed wheat was planted on October 6th, 2024, at 1.8 million seeds/ac on a 19 cm (7.5 in) row spacing. At the time of spraying, wheat was at the T3 stage of development, approximately 0.7 m (2.5 ft) high.

    Holder Design

    3D-printed holders were designed in Autodesk Fusion. They feature tabs that create a pressure fit (for quick WSP loading and unloading) and a back support (to prevent WSP movement in a downwash) to vertically position 1×3” WSP facing out on four cardinal points (figure 1). 21 poles were positioned on a 1 m spacing, leaving the tops coplanar with the wheat heads for in situ swathing. The square cross-section of the poles corresponded to a square depression in the WSP holder, ensuring the samplers were correctly aligned (figure 2). The gcode file to 3D print your own holders can be downloaded here. We used PLA filament with 3 walls and a 15% rectilinear infill to print 16 holders at a time on a Bambu P1S.

    Figure 1. 3D-printed WSP holder slotted onto a pole in the wheat field.
    Figure 2. Four WSP positioned vertically, facing four cardinal points, at wheat-head depth.

    Wind direction is indicated by the direction the wind is coming from, not the direction it’s blowing to. Therefore, a wind blowing in a northern direction is referred to as a southern wind. The WSP holders were aligned east to west, perpendicular to the prevailing southern wind. We established a trampled path ~0.75 m on the downwind side. This left the wheat canopy surrounding the samplers intact while still permitting access to the WSP holders (figure 3).

    Figure 3. 21 WSP holders on 1 m spacing with access ~0.75 away.

    WSP were given unique serial numbers to identify their position, and pre-loaded into the holders. 170 loaded holders were stored on raised grids inside four shallow plastic bins, arranged in the order they would be used (figure 4). This greatly expedited placement and retrieval, allowing for more repetitions to take place while optimal weather conditions held.

    Figure 4. WSP holders arranged in sequence in a storage bin. This allowed the pre-loading of serial numbered WSP prior to the day of the experiment.

    Application Method

    A DJI Agras T50 RPAS maintained and calibrated by the cooperator was fitted with four rotary atomizers. Previous work has demonstrated that higher rates of flow can have a detrimental effect on the spray quality from rotary atomizers, so distributing the flow over four nozzles was intended to prevent this. The atomizers applied a 250 µm spray over a 7 m swath width (corresponding with route spacing), as selected on the flight controller. Altitude was 3 m above the wheat heads, and flight speed was either 6 or 10 m/s (three repetitions each). Application volume was 50 L/ha, anticipating this to be a future label requirement.

    The RPAS flew a racetrack pattern over the samplers (figure 5). It flew with a prevailing tailwind between samplers 14 and 15, and then back with a prevailing headwind between samplers 7 and 8. We employed a DJI RTK-1 base station, which claims 1 cm horizontal accuracy.

    Figure 5. Racetrack flight path relative to WSP holders and prevailing wind direction.

    The RPAS was given sufficient distance (~40 m before and after the samplers) to reach the target speed, which was confirmed with a screenshot from the flight controller. The RPAS tank (capacity 40 L) contained municipal water with 0.125% v/v of NIS (Ag-Surf II). The level of liquid in the RPAS tank was maintained at 40 L throughout the trial to eliminate the effect of a changing payload.

    The field sprayer, maintained and calibrated by the cooperator, was a New Holland SP 275s. It extended the left boom over the samplers from position 1 through to 12 and made a single pass with a prevailing tailwind (three repetitions). It traveled at 4.5 m/s (16 km/h or 10 mph) spraying 187 L/ha (20 gpa) and rough terrain caused the boom height to fluctuate between ~25 cm and ~50 cm above the wheat heads. The nozzles were Greenleaf Technologies TADF 06 (greys) on a 50 cm spacing operated at 50 psi to produce a Coarse spray quality. The tank contained municipal water with 0.125% v/v of NIS (Ag-Surf II).

    Trial Procedure

    WSP holders were placed just prior to spraying while the RPAS or field sprayer was positioned ~40 m beyond the samplers. When wind conditions were deemed appropriate, a signal was given to initiate spraying. On pass completion, one minute elapsed before initiating collection to permit complete deposition of the spray and drying of the droplets.

    Weather Data

    Weather data was collected using a Kestrel 3550AG weather meter (Kestrel Instruments) in a vane mount positioned roughly 1 m below RPAS altitude. Data was logged as the RPAS or field sprayer boom passed the samplers (table 1). In the case of the RPAS, there was very little difference between the two passes per repetition, so values were averaged.

    TimeRep and TreatmentTemperature (°C)Wind Speed (km/h)Wind Direction
    10:21:511. RPAS 6 m/s16.43.1S
    10:33:562. RPAS 6 m/s17.76.2S x SW
    10:45:503. RPAS 6 m/s18.84.0S x SW
    10:55:401. RPAS 10 m/s18.62.1SW
    11:06:242. RPAS 10 m/s20.00.5S
    11:16:003. RPAS 10 m/s19.25.8S x SW
    11:29:541. Field Sprayer21.10.0S
    11:41:122. Field Sprayer19.91.7S x SW
    11:48:313. Field Sprayer20.23.9S
    Table 1. Time and weather conditions for each repetition. Data was captured as the nozzles passed over the holders. Wind direction is indicated by the direction it is coming from.

    Digitization

    WSP (Spot-On) were scanned using a DropScopeTM (SprayX). The software reported droplet density and percent area coverage, but only deposit density is considered in this report.

    Results

    Comprehensive Observations

    When the average deposit density from each of the four WSP per holder is added, we have a measure of total panoramic coverage. The mean total panoramic coverage from three repetitions of each treatment is shown in figure 6. For the RPAS treatments, distinct coverage peaks typical of RPAS applications correspond to the flight passes through poles 14-15 and 7-8. There is a slight spray displacement due to an occasional shift to a west wind (i.e. overall coverage shifted towards pole 1). However, the entire spray swath appears to have fallen within the range of the samplers. The back-and-forth flight pattern produced higher coverage at the interface between passes (pole 10) compared the extremes (beyond poles 19 and 3) suggesting some overlap. Deposit density was higher for the slower RPAS flight speed, and RPAS produced a higher deposit density than the field sprayer. Field sprayer coverage data is included for perspective but is generally not referred to unless it has some bearing on the evaluation of the RPAS coverage.

    Figure 6. Mean sum deposit in count/cm2 for each treatment. RPAS 6 m/s deposited an average 700 drops/cm2. RPAS 10 m/s deposited an average 400 drops/cm2. The field sprayer deposited an average 280 drops/cm2. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    Swath Width

    If the coverage at pole 10 represents the edge of each swath, then a swath width of ~6.0 m can be estimated based on similar coverage at poles 16-17 and 3-4. This is less than the programed value of 7.0 m.

    This inference is supported when these averaged values were entered in an Excel-based model that calculates swath width. The model sums deposits from adjacent swaths assuming a racetrack pattern. Threshold coverage is subjective but adhering to the objective of establishing a balance between over- and under-dosing with the lowest possible C.V., we calculated swaths between 5.0 and 6.5 m (table 2).

    TreatmentPole PositionThreshold Coverage (count/cm2)Under-dose (%)Over-dose (%)C.V. (%)Swath (m)
    RPAS 6 m/s21-1012010.45.018.05.5
    RPAS 6 m/s10-11205.714.126.05.0
    RPAS 10 m/s21-10809.111.425.46.0
    RPAS 10 m/s10-13517.214.143.46.5
    Table 2. Swath widths calculated from the average cumulative deposit density for each WSP holder.

    It was expected that the field sprayer would produce a somewhat trapezoidal coverage pattern, tapering up at pole 12 (boom extreme) and level to pole 1 (sprayer chassis). Instead, note the gradual increase in coverage from pole 12 to 1. This is likely the result of boom yaw, where the boom end rose higher than the point closest to the sprayer. If this degree of coverage represents the industry standard, it is notable that the average boom coverage is either on par with, or considerably less, than that of the RPAS.

    Deposit Density

    The RPAS was programmed to produce a 250 µm droplet size, while the field sprayer produced Coarse (~218-349 µm) droplets. Smaller stains were produced by the RPAS than the field sprayer (figures 7 and 8), and their circular/oval shape suggest both a smaller droplet volume and a somewhat perpendicular flight path. Droplets produced by the field sprayer left long streaks, which suggest higher droplet volumes and a more parallel flight path.

    Figure 7. Typical deposition pattern from a single WSP holder in the centre of the RPAS flight pattern. Considered from the perspective of the RPAS, WSP starting at the top and rotating clockwise are left side, retreat side, right side, and advance side.
    Figure 8. Typical deposition pattern from a single WSP holder nearer the field sprayer chassis. Considered from the perspective of the field sprayer, WSP starting at the top and rotating clockwise are left side, retreat side, right side, and advance side.

    When the overall average coverage is calculated the RPAS at 6 m/s deposited an average 700 drops/cm2 and an average 400 drops/cm2 at 10 m/s. The field sprayer deposited an average 280 drops/cm2. When volume remains constant, smaller droplet diameters produce a greater number of droplets than with larger droplet diameters, so more droplets would be expected from the RPAS. However, the RPAS applied only 50 L/ha while the field sprayer applied 182 L/ha. Therefore, the RPAS distributed a greater density of potentially higher-concentration droplets on each WSP holder compared to the field sprayer. Further, a slower flight speed deposited a higher density of stains than a faster flight speed.

    Effect of Travel Speed

    The 6 m/s treatment resulted in slightly smaller swath widths (1 m or 15% less) than the 10 m/s treatment. The positive relationship between swath width and flight speed has already been established. The positive relationship between flight speed and off target drift has also been established, which may account for the significantly fewer deposits (almost 50% fewer) in the swath at 10 m/s versus 6 m/s. When a higher deposit density is valued, such as in the case of contact fungicide application, the loss of productivity from a slightly smaller swath width is a reasonable compromise for the superior coverage within that swath.

    Coverage by Cardinal Point

    North Facing WSP

    This side of the WSP holder faced north, away from the prevailing south wind. The RPAS deposited far more on this face when traveling with the wind between poles 14-15, making this side face the RPAS retreat (figure 9). It suggests the RPAS blows down and back, even against a tail wind. This is supported when RPAS returned between poles 7-8 and deposited comparatively less on this face.

    Figure 9. Mean sum deposit in count/cm2 for each treatment on north facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    RPAS speed may have had an effect. With airblast sprayers, slower travel speeds produce greater dwell times, which increases the distance a droplet travels on a given trajectory. Logically, when flying away from the retreat face, higher speeds would impart a greater forward momentum on a droplet, cancelling out some of the backward momentum (watch a video here). If this were the case, there would be comparatively improved deposit density on the 14-15 pass for slower speeds and reduced coverage between poles 7-8 as it blew past the target. Figure 9 supports this hypothesis.

    South Facing WSP

    This side of the WSP holder faced south, into the prevailing south wind. Considering the 6 m/s treatment, we see more coverage on the 7-8 pass than the 14-15, because it represents the retreat side of the sprayer (figure 10). The differential is far less on this plane than the north facing (figure 9) because the prevailing wind likely blew spray into the WSP on the 14-15 pass. Nevertheless there is significantly more on 7-8.

    Figure 10. Mean sum deposit in count/cm2 for each treatment on south facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    This relationship is less clear for the faster 10 m/s treatment. There does tend to be higher deposit on the 14-15 pass as spray was blown into the collectors. However far more was expected on this face for the 7-8 pass as it represents both the retreat face and has the added benefit of wind. Further, there was far less coverage overall when compared to the slower flight speed. We have no explanation for the lack of coverage on the 7-8 pass and can only conclude that higher speeds left droplets airborne and were not conducive to coverage.

    West Facing WSP

    This side of the WSP holder faced west, into the slight west wind. We see coverage is almost exclusively on those WSP facing the drone (figure 11). In other words, as the RPAS passed between 14-15 and 7-8, coverage was positively skewed from this point. The skewed coverage was evident at both flight speeds, but overall coverage was higher for the slower speed. Once again, we cannot explain why there was significantly reduced coverage on the 10 m/s pass between poles 7-8 except to suggest the spray may have remained airborne.

    Figure 11. Mean sum deposit in count/cm2 for each treatment on west facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    East Facing WSP

    This side of the WSP holder faced east, away from a slight west wind. We see that coverage is almost exclusively on those WSP facing the drone in the upwind direction (figure 12). Overall coverage was slightly higher for the slower speed, but far less overall coverage compared to the west facing samplers (figure 11). This is likely because the light west wind caused spray to displace from pole 21 to pole 1, washing past the back (insensitive) sides of the WSP.

    Figure 12. Mean sum deposit in count/cm2 for each treatment on east facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    Summary

    RPAS can provide par or better panoramic wheat head coverage compared to a conventional ground rig when they are flown using reasonable operational settings in optimal environmental conditions. A moderate flight speed (~6-8 m/s), appropriate altitude (~3 m above wheat heads), and four rotary atomizers producing a Medium-Coarse (~250 um) droplet size can produce an in situ 6 m swath width at 50 L/ha. Higher flight speeds produce a marginally wider swath at the cost of reduced droplet density and increased drift potential.

    Assessing coverage using vertical WSP facing four cardinal points has provided further insight into the behaviour of spray from an RPAS. Droplets from any application technology tend to deposit with wind and gravity, but rotor downwash represents an additional variable unique to RPAS. That force, combined with a forward cant of the drone during flight, lead droplets to deposit on vertical surfaces that face the rear (retreat) of the sprayer as well as surfaces that face and intercept spray that radiates laterally from the flight path.

    Drone Spray Canada, Bayer Canada, volunteers Kurtis Pilkington and Natalie, and grower-cooperator Adam Pfeffer are gratefully acknowledged for their contributions to this study.

  • Celebrating 10 Years of Sprayers101

    Celebrating 10 Years of Sprayers101

    On May 29, 2015, we launched www.sprayers101.com. Actually, that date is practically correct, but not technically correct. To celebrate our anniversary, I thought I’d share the history of how of we got to where we are today.

    2013

    On December 21, 2013, I launched www.sprayers101.com… sort of. Back then, the website was different. I’d just developed a classroom -based course called “Airblast101” to teach applicators how to calibrate, operate and maintain their airblast sprayers. The website was a virtual and self-directed version for those that couldn’t attend in person.

    Screenshot of a template for the original Sprayers101.com website.

    The name “Sprayers101” sounded like a first-year university course, so it seemed an appropriate domain name. I could have called the site “Airblast101” but I had hope that the course might one day expand to include field crop, closed environment and aerial spraying systems. Being generic gave room to grow.

    After the launch, I lurked behind the scenes, addicted to Google Analytics (a diagnostic tool that lets us assess how the site was being used). It was a thrill to see a modest number of people around the Great Lakes and in British Columbia use this new resource. But they weren’t using it the way I’d envisioned. It was designed as an online course, so it was assumed the user would start at the first page and read it in order until they reached the end. Instead, they were jumping all over the place.

    Users would search for key words to find specific information, and once they had what they wanted, they left. This suggested the audience was more interested in a resource library. They were also interested in bite-sized morsels, not a long-term commitment.

    2014

    Around this time, I was fortunate to have been in communication with Dr. Tom Wolf. I took a flyer and proposed that we team up to re-create the website from the ground up. I knew it would benefit immensely from his experience as a global authority on application technology. Happily, Tom agreed and he brought an insight and creativity to the project that helped transform it. We worked for the next six months to develop and assemble new content as well as beta test website designs. Then we re-launched.

    Mock-up of the new Sprayers101.com concept.

    In the 17 months B.T. (Before Tom) I had a total 31,500 page views. Only six months A.T. (After Tom) we gained 70,000 more. We were on to something good. The numbers continued to climb as we added calculators, opinion pieces, research results and invited content from contributing authors.

    2015

    In 2014 Tom encouraged me to explore social media. By 2015 we were deeply involved in Twitter, using it to learn from farmers, discuss their issues and draw inspiration for some of our articles. Our handles “Nozzle_Guy” and “Spray_Guy” were entirely coincidental – seriously. There was another bump in website use in 2018 when we created “Exploding Sprayer Myths”, which are parody-based educational videos for our companion YouTube channel. Incidentally, we’re still hoping to one day find a legit educational reason to blow up a sprayer.

    2021

    In July, 2021 we decided to refresh and relaunch the site. Most of the changes addressed stability, improved smart phone access, and allowed us to cross-reference and re-organize content (an ongoing administrative task). We adopted a cleaner look and lost the drop-down menus to focus on a more powerful search engine to help users access the now 250+ articles.

    2025

    Today, ten years since we reimagined the site, sprayers101.com has grown beyond what might be considered “101”. It receives >250,000 page views annually from users all over the world. Of the 325+ posted articles, our most popular have been viewed more than 20,000 times. We have more than 2,000 subscribers. We’re often contacted by people who tell us how much it has helped their spraying practice, or how it’s been used to train new industrial, agronomic and regulatory staff.

    Our original goal was to provide the best information on agricultural spray application, and that remains true today; from humble backpack sprayers and fundamental skills through to drones and autonomous sprayers with optics, prescription maps and algorithms. The site is, and has always been, entirely impartial to preserve the integrity of the content we offer.

    Our heartfelt thanks to our readers, to our sponsors, and to our contributing authors.

    Happy Spraying.

    2026 ADDENDUM

    Just for completeness, and given that this article is something of a historical record, we relaunched the website in March of 2026. New features include:

    • All-new look and feel, including an animated logo
    • Bulleted, AI-generated summaries
    • Far better search engine with predicative text and the ability to search titles and tags
    • Referenced and printable articles
    • Better layout on mobile devices

    Looking forward to the next ten years.

  • Closed Transfer for Airblast Sprayers – A Learning Process

    Closed Transfer for Airblast Sprayers – A Learning Process

    As Canadian farmers begin to adopt closed transfer systems (CTS), growing pains are to be expected. Instructions for installation and use are primarily European and field-sprayer centric. We’ve seen precious little in the way of practical advice for incorporating CTS into airblast operations.

    This is a “live” article which we’ll update periodically. We encourage readers to contact us and share their observations and experiences (and photos) so we can all learn from them. We’re happy to keep contributions anonymous if that’s preferred.

    This article does not intentionally imply any brand preference. Our experience is limited at this point and we are using any information we have access to. As the article grows, so will the combinations of sprayer and CTS. Also, we are not recommending or endorsing any of the following approaches. It’s still unclear if modifying the sprayer is the purview of the manufacturer / dealer of the sprayer or the CTS. At this point, we suspect it’s likely the owner that accepts any responsibility.

    Does it matter where the CTS is relative to the sprayer?

    If the system is gravity-fed, the coupler, the fill line and the connection to the tank must be higher than the fill level in the tank. Liquid won’t flow uphill unless it’s pushed from behind (pressure) or pulled (suction or siphon). Be aware this means the entire fill line should be above the tank’s fill level; sags will prevent fluid transfer. If we’re observing best practices, the tank should be half-full of water before you start adding products.

    If the coupler uses suction from the sprayer itself, or employs a pump, relative height won’t affect filling. In this case it is likely part of a separate transfer system (i.e. not permanently mounted on the sprayer). It might be simple, or part of a larger and more sophisticated affair, but in either case it should be level, stable, and easily accessed without the operator having to reach or squat. Two examples are pictured below.

    Here, a CTS is mounted to a hand cart so it can be wheeled into place and then put away. The sprayer provides suction via venturi to pull in the chemistry and a simple garden hose supplies municipal carrier / rinse water. Note the cinder (concrete) block used to stabilize the unit. Simple and effective.
    Here, a coupler is part of a larger tender system. Carrier / rinse water is pumped from an onboard tank, through the coupler, and then into the sprayer.

    How do I plumb the CTS to the sprayer?

    If the CTS is mounted directly on the airblast sprayer, it’s typically a smaller, gravity-fed coupler. The rinse / carrier water is often from an external source (e.g. water tank, tower, pond or municipal water), but there are cases where an onboard water source can be used.

    Provide Agro has attached a gravity-feed coupler to the secondary tank hatch. This is above the fill line, sealed tightly, and it uses an onboard rinse / carrier water source. If considering cutting into a hatch, be aware of the filter basket or any onboard rinse system. Also, note that letting the lid flop open (or setting it aside) should not damage the coupler itself.
    No matter the rinse / carrier water source, it should match the manufacturer’s prescribed pressure range (generally between 3 – 6 bar or 45 – 85 psi) and have an anti-backflow device. There is no such device in this photo.

    Some have suggested cutting a hole in the tank itself, above the highest possible fill line, and sealing the coupler in place. This is not simple. If you find a flat horizontal surface and you are equipped to cut poly, Fiberglas or steel (listed in ascending order of difficulty), doing so could undermine tank integrity and create potential for leaks. We won’t even entertain what would happen to your sprayer warranty… assuming someone still has one.

    If the intent is to couple a fill line to the sprayer, the best approach is to tee a fitting into the suction-side of the sprayer plumbing to draw product in through the pump. Consider accessibility and safety first: Can you safely and easily reach the suction side of the sprayer plumbing? Is the PTO shaft too close for comfort? Will anything stick out past the sprayer that might create a risk of snagging a crop canopy or trellis? If a tee can be plumbed in, will it need to be secured to the chassis in some way to create stability?

    There is no easy or universal answer to these questions.

    On this sprayer, the only easily-accessed point is between the suction filter and pump. Creating a tee that would accommodate a dry poppet fitting is challenging.
    In the case of this 3-pt hitch sprayer, there is no simple way to access the suction side of the plumbing. Perhaps a tee could be added and the fitting extended up-and-out from under the chassis. Securing the fitting might require strapping it to the back of the tank, or to a mast of angle iron (or similar) attached to the chassis. Imagination required. Apply within.

    As for the fitting, what style is best? A cam lever style fitting will work, but it will leak a volume of liquid when it’s detached. A quarter-turn valve will also be required on the sprayer, and preferably another on at the end of the feed line, so that’s two more valves in play when loading. And, for the sake of safety, best practice would to be to use a cam cap on the sprayer just in case the quarter-turn valve gets snagged and opens. Far safer and more efficient, a dry poppet style fitting will ensure minimal spillage when the hose is disconnected, with no additional valves or caps required.

    Finally, what of the fill line itself? We’re seeking confirmation, but we have been told of a situation where the pump suction was sufficient to collapse the feed line. This is why some CTS manufacturers provide the hose and fitting with the units. At minimum, check the CTS manufacturer’s instructions and ensure the hose is rated for the degree of suction created by the pump.

    Send us your experiences

    And that’s all we have for now. We encourage you to reach out to us with your successes and failure and we’ll update this article for others to learn from.

    Happy Spraying.

  • Alternate Row Spraying

    Alternate Row Spraying

    Alternate Row (aka Alternate Row Middle [ARM]) spraying is an application method where the air-assist sprayer does not pass down every alley during an application. The sprayer operator is relying on the spray to pass through one or more rows and provide acceptable coverage to the entire canopy (or canopies) on a single pass.

    Some state agencies promote this spraying strategy to various degrees, and many sprayer operators (whether they admit it or not) have used this method of spraying. I have advised it myself for very young and/or very sparse vineyard and orchard plantings, but never without confirming coverage. When I tell operators that I have serious reservations about alternate row spraying, they defend it. Here are the most common justifications I’ve heard over the years, and my response:

    JustificationReply
    “I do not have enough spray capacity to spray every row when time is short.”You need more sprayer capacity. Get another sprayer so you can get spray on in time or invest in a multi-row sprayer is possible.
    “ARM spraying saves money and reduces environmental impact because I use less pesticide.”Technically, if you travel every second row with a sprayer calibrated to travel every row, you have indiscriminately reduced your carrier and chemical inputs by half (or more). Without close monitoring you may compromise your efficacy.
    “I only perform ARM spraying early in the season when canopies are empty, or only on young plantings.”I grudgingly grant this one as long as coverage is closely monitored. I’ve prescribed it myself in young or sparse plantings where I couldn’t get the sprayer output low enough to prevent drenching the targets.
    “The spray plume in the alley beyond the target row must mean the spray is providing adequate coverage. More is better!”If the spray is blowing through the canopy, it isn’t landing in the canopy. Further, if the air speed/volume is too high, droplets can ‘slipstream’ past the target without impinging on them. I’ve removed water-sensitive paper from canopies with barely any spray on them despite the plume in the downwind alleys. It looks like a magic trick, albeit an unhappy one.
    “Uncooperative weather doesn’t always leave me enough time to spray the entire crop, and it is the lesser of two evils to spray alternate rows than not at all. I’ll make sure I come back to spray the other rows later.”Choosing to do half a job requires an understanding of the products’ mode of action. If you are spraying an insect at a particular stage of development, there’s no “coming back later” to get that generation – if you missed, your window has closed. If it’s a protective fungicide that offers no kick-back, then once the disease has infected tissue, the damage is done. Get the spray on as best you can, but if it washes away before it has a chance to dry sufficiently, be prepared to reapply at the earliest opportunity as long as the label allows it.
    “ARM has always worked in the past.”Would you mind picking my lotto numbers for me? You’re a very lucky person!

    My reservations about ARM spraying come from published research and personal experience that show that coverage is almost always compromised when spraying from one side of a canopy. The spray must pass through the canopy to reach the far side, and the canopy filters droplets from the air as it passes through. This reduces the number of droplets available to cover the far side. In addition, high velocity spray will create “shadows” where any targets on the immediate far side of a leaf or branch become shielded and receive little if any coverage. Further still, fine droplets slow quickly as they leave the nozzle and take a long time to settle. As the entraining air slows and becomes erratic, the droplets float and change course, making their behaviour hard to predict.

    The cumulative impact can be seen in this infographic I built in 2016. The orchardist was a dyed-in-the-wool ARM applicator and he was resistant to driving every row because it took so much time. I wanted to show that he could claw back some of the lost time by spraying less pesticide every row versus his current volume every second row. He would need fewer refills, and save a LOT of unnecessary pesticide. The water sensitive paper does the talking, and while I’d like to think I’ve convinced him, I’ll bet he’s still out there dicing with fate.

    2016_ARM

    A very popular argument in favour of ARM spraying comes from orchardists that are shifting from semi dwarf to high-density plantings. They ask “How it is different to spray a four foot diameter tree from one side compared to an eight foot diameter tree from both sides”? 

    Well, we know coverage is reduced as a factor of distance. Spraying from one side gives a single opportunity to cover the middle and far side of a canopy, whereas spraying from both sides provides an opportunity for an overlap in coverage. Essentially, the centre of a canopy receives the cumulative benefit of two sprays. Coverage is therefore always improved when spraying from both sides, period.

    Spraying from one side gives a single opportunity to cover the far side of a canopy. However, spraying from both sides provides an opportunity for an overlap in coverage. In other words, the centre of a canopy receives less spray than the outside, but is essentially sprayed twice resulting in a compounding effect.
    Spraying from one side gives a single opportunity to cover the far side of a canopy. However, spraying from both sides provides an opportunity for an overlap in coverage. In other words, the centre of a canopy receives less spray than the outside, but is essentially sprayed twice resulting in a compounding effect.

    Why, then, do some sprayer operators claim that alternate row applications work? Because sometimes, they do! Just because coverage is reduced doesn’t mean it isn’t sufficient to protect the crop. It simply means that the potential for poor coverage and reduced dose is dramatically increased by alternate row applications. A sprayer operator might perform alternate applications successfully for years before conditions conspire to defeat the application: unfavourable wind, poor timing, increased pest pressure, poor pruning practices, excessive ground speed, high temperatures, low humidity, insufficient spray volume, and several other factors might occur simultaneously and reduce coverage below a minimal threshold for control. This confluence of bad luck may not happen the first year, or the second, but eventually…

    Product failure isn’t the only concern. Repeated reduced dosages may play a role in developing resistance. In those situations where the operator recognizes insufficient coverage, they may have to spray more often to compensate, negating any savings in time or product. Reduced dosage is a common error when a sprayer operator elects to use ARM.

    If you still aren’t convinced, at least perform alternate row spraying the “right” way. Here are three situations that I’ve heard operators refer to as alternate row spraying. Situation 1 is most common, but to my mind only Situation 2 would be considered acceptable. Even then, confirming coverage is a must.

    Situation 1:

    The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.

    The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.
    The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.

    Situation 2:

    The sprayer is calibrated for double output compared to a typical every-row situation, and the operator drives alternate rows. The result is that the hectare gets the whole dose per application, but coverage is always inconsistent.

    The sprayer is calibrated for double output compared to a typical every-row situation, and the operator drives alternate rows. The result is that the hectare gets the whole dose per application, but coverage is always inconsistent.
    The sprayer is calibrated for double output compared to a typical every-row situation, and the operator drives alternate rows. The result is that the hectare gets the whole dose per application, but coverage is always inconsistent.

    Situation 3:

    Since the sprayer will only drive alternate rows, the operator mistakenly sets the sprayer to emit half the output compared to a typical every-row situation. The first application (solid line) covers different rows from the second application (broken line). The result is a quarter-dose per application, and if the operator chooses to spray a second time, the hectare will only ever get half-a-dose. Yes, this happens.

    The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.
    The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.

    So, my final word on alternate row applications is that they should be performed with extreme caution. I’ve used them myself in early season applications in new plantings, but never without confirming coverage with water-sensitive paper, and never in conditions that might further compromise coverage to the point that the application does not give control.

    Caveat Emptor!

    Well, I thought it was funny. My apologies to J. Luymes from British Columbia (pictured) and Obi Wan Kenobi (not pictured… or is he?)
    Well, I thought it was funny. My apologies to J. Luymes from British Columbia (pictured) and Obi Wan Kenobi (not pictured… or is he?)
  • Airblast Spraying in Poor Conditions

    Airblast Spraying in Poor Conditions

    Some springs are tougher than others. This article was originally written in 2019, which was particularly challenging. The frequency and duration of rain events left limited opportunity for orchard sprays. Even then, the periods between rains were transitions between warm and moist conditions and cold fronts, which makes wind gusty and changeable. These same periods leave wet alleys prone to rutting and compaction, and conditions that favour spraying may also favour pollinator activity.

    In response, applicators get frustrated. Some may be tempted to spray in sub-optimal conditions and risk drift thinking even a little coverage is better than none. But the adage that “there is no wasted fungicide spray” does not apply here. Some may disagree, but spraying in wet and high-wind situations:

    • greatly reduces coverage and subsequently, crop protection.
    • may result in repeated sub-lethal doses that can encourage resistance.
    • greatly increases the degree of surface run-off and off-target drift, risking environmental, commercial and residential
      contamination.

    The argument itself may be moot because the decision to spray is not strictly a consideration of economics, productivity, and risk tolerance. When environmental restrictions exist on a pesticide label they are inviolate. That is, they are not suggestions but legal requirements. Statements might include:

    • Not spraying when rain is forecast within 12 hours following application. This is, in part, to prevent water-soluble products from moving in surface or channel run-off.
    • Not spraying in calm conditions (generally <3 km/h, as measured at the top or outside of the orchard). This is to prevent airborne spray from moving in unpredictable directions during a thermal inversion, or downhill with stratified air.
    • Not spraying in gusting or windy conditions (generally >10 km/h, but there is no Canadian standard). This is to prevent airborne spray from moving with the wind. This is of particular import when there are sensitive downwind areas that can bring buffer zones into play

    Technologies exist that extend the spray window, but they require long-term planning and may not be economical (or even completely proven). They are generally a combination of orchard architecture and sprayer design. Examples include:

    • Tented orchards (more common in Australia) designed to exclude pests and insulate against hail, wind and inversions.
    • Shrouded vertical booms (e.g. Lipco) designed for trellised orchards.
    • Solid-set emitters (more common in Europe and still experimental in parts of the northern US) that reduce drift and can spray large areas quickly.
    • Vertical towers with downward-oriented fans (e.g. Curtec Proptec or Sardi sprayers) that rely on the orchard itself to filter
      lateral/downward-directed spray.

    Assuming the pesticide label does not prohibit application, there are adjustments that can improve coverage and reduce drift in sub-optimal conditions, but only marginally. These are compromises that sacrifice time, money, effort and/or the level of crop protection. Further, they are only intended for sprayers with towers (i.e. not low-profile axial sprayers):

    • Convert to air induction nozzles (at least in the top two nozzle positions, and likely at one rate higher than you usually use).
    • Be certain to turn off any nozzles spraying excessively over the top of the canopy. A little can’t be helped and is actually a best practice to ensure spray reaches the treetop. Be reasonable.
    • Reduce fan speed to only reach just past the middle of the canopy on the upwind side.
    • Turn off the boom on the downwind side of the sprayer and adjust airspeed and nozzle rates for upwind alternate row spraying only. Especially on the last three downwind rows, which you may have to leave unsprayed entirely.

    The best advice is unpopular: Park the sprayer until conditions improve. Like hail, there are environmental factors that are out of the farmer’s control. They are inconvenient and highly frustrating, but do not be tempted to takes risks on what might ultimately result in poor coverage and accusations of pesticide drift.