Author: Jason Deveau

DJI Agras T100 – First Impressions

On July 15, 2025, DJI Agriculture announced the global launch of the DJI Agras T100. Compared to its predecessor, the T50, it features a larger payload for spraying and spreading and can fly at approximately twice the speed. The rotary atomizer-style nozzles (which DJI refers to as sprinklers) produce comparatively increased flow with an option to increase from two to four for orchard operations. Designed for large-scale commercial growers, it also features a new single-side spraying function to assist with sharper field boundaries and infield obstacles.

On September 13 we performed some preliminary trials comparing it to the T50. We applied Roundup Transorb HC (PMRA research authorization 0054-RA-25) in plots over a 160-acre field of wheat stubble. While the results of this study will appear in a later article, we wanted to capture our initial observations.

160 ac wheat stubble field 7 DAA. Wind was a light 2-6 km/h with consistent direction throughout the study.

Weight and Dimensions

In Canada, Remote Piloted Aircraft (RPA) are regulated under the Canadian Aviation Regulations (CARs). Part IX of the CARs deals with RPA by operating weight and complexity of the operation to be conducted. Prior to recent amendments (which came into force in November 2025), Part IX covered up to and including 25 kg (55 lb) flown in visual line of sight (VLOS). Other operations like above 25 kg and Beyond VLOS operations required a Special Flight Operations Certificate.

The 2025 amendments to Part IX added operations of medium RPA that weigh more than 25 kg (55 lb) up to and including 150 kg (331 lb) and introduced rules for beyond visual line-of-sight (BVLOS), sheltered, and extended VLOS operations.

Left: DJI Agras T100. Right: DJI Agras T50.

	T50	T100
Empty weight	52 kg	75 kg (2 nozzles 77 kg (4 nozzles)
Max. takeoff weight (full liquid tank)	92 kg	175 kg (2 nozzles) 177 kg (4 nozzles)
Dimensions (arms & rotors unfolded)	2,800 × 3,085 × 820 mm	3,220 × 3,224 × 975 mm

If flown full, the T100 will be 25 kg beyond the medium RPA category. Therefore, Canadian pilots will have to apply for a Special Flight Operations Certificate (SFOC). Similarly, DJI notes that when using the T100 in Australia, pilots are to follow local regulations and keep the maximum takeoff weight at 149.9 kg.

The additional size and weight may make handling and transportation more challenging (e.g. lifting the RPAS out of a vehicle). Regarding spray performance, it remains to be seen if the greater weight of the T100 will appreciably increase the magnitude of the downwash, or perhaps this will be negated by the potential for greater travel speed (see Dwell time).

Tank and nozzles

Both the T50 and T100 have HPDE tanks (neither with agitation). The rotary atomizer nozzle (aka sprinkler) design has changed. According to DJI’s promotional video, the atomizers are “water cooled”. Our assumption is that the spray mix itself serves as a heat-exchanging coolant. This will come up later in this article.

	T50	T100
Liquid tank capacity	40 L	100 L
Atomizer model	2 or 4 LX8060SZ standard sprinklers	2 LX07550SX, standard sprinklers 2 LX09550SX, optional mist nozzles for orchard spraying
Atomizer flow rate	16 L/min (2 sprinklers) 24 L/min (4 sprinklers)	30 L/min (2 sprinklers) 40 L/min (2 sprinklers plus 2 misters)
Droplet size	50 – 500 μm	50 – 500 μm
Span between nozzles	1,570 mm (between rear nozzles)	1,834 mm (between rear nozzles)
Effective swath width	4 – 11 at 3 m altitude	5 – 13 m (no altitude specified)

DJI states that droplet size was “measured by a laser particle size analyzer, with a 50-micron diameter using the Dv50 standard”. It is notable that they do not refer to ASABE S572.3 or ISO 25358:2018, which are standards that define nozzle spray quality. Canadian pesticide labels will require compliance with these standards when the application of agricultural pesticides is eventually permitted.

It would be interesting to confirm if the new atomizers can actually produce the median droplet size indicated on the controller. Historically, and to differing degrees, RPAS rotary atomizers suffer from a “flooding” issue. This is a condition where flow to the nozzle overwhelms its ability to atomize the fluid, degrading the spray pattern and creating coarser, heterogenous spray.

DJI states that the effective spray width depends on the “actual working scene [sic]”. Compared to the T50, the T100 atomizers are not directly below the rotor hubs, are angled slightly outward and are set further apart. This may explain claims of a larger swath width than the T50.

However, our studies with the T50 have determined that when flight settings are optimized for low drift and consistent coverage, the ESW for in-canopy fungicide application is no greater than 7 m. This is likely wider for herbicide applications in stubble or on bare ground, but the risk of downwind drift (i.e. not displacement) makes claims of 11 or 13 m for the T100 unlikely. Swathing runs were performed using the Speed Track and Swath Gobbler methods (results will be reported when the burndown study is analyzed).

Observations during spray trial

According to DJI, both the T50 and the T100 can manage a maximum 30 L/ha (~3 gpa) at their respective maximum speeds. For the T50, this is 10 m/s (36 km/h) and for the T100 this is 20 m/s (62 km/h). This has obvious implications for greater efficiency, but we wondered what effect higher speeds might have on spray coverage and drift potential.

Succinctly, faster speeds leave droplets aloft for longer periods, subjecting them to wind, wake and vortices while reducing the influence of the downward-rearward downwash that might normally entrain and direct them to the ground. As a result, they tend to spread laterally in the direction of the prevailing wind. This is drift. To see if this was happening, our treatments included combinations of travel speed, altitude, programmed swath width and droplet size. Here’s what we saw.

Altitude

We generally fly the T50 between 3 and 3.5 m above the ground or crop canopy. Any higher creates unacceptable drift and any lower tends to leave a bimodal and inconsistent coverage pattern. However, the T100 controller advises an altitude of >5 m during “high speed operations”. Perhaps this relates to orchard operations, or it’s strictly a matter of safety for such a large drone operating at high speed. In any case, it seemed far too high for field applications.

To compare the T50 directly to the T100, we chose to fly three treatments at 3 m altitude, 6 m/s and 50 L/ha (5 gpa). There appeared to be a gap in the T100 swath between the nozzles that might indicate bimodal (non uniform) deposition. This gap disappeared when we later flew at 4 m and increased the speed of the drone. Despite what we observed during the application, a preliminary inspection of the aerial images taken of the treatment plots hasn’t revealed any obvious gaps in the burndown. We hope to learn more when we have higher resolution images and when the swath gobbler data is analyzed.

At 3 m altitude and slower speed (~10 m/s) there was a visual gap in the spray. This was not obvious at 4 m altitude and higher flight speed. It did not appear to leave a corresponding gap in weed control, likely due to secondary coverage from from subsequent passes.

Battery heat and endurance management

According to DJI, the T50’s DB1560 battery takes 9-12 minutes to fully charge and the T100’s DB2160 Intelligent Flight battery takes 8-9 to get to 95%. We did not have access to the recommended 3-phase generator and instead used an adaptor cable (pictured right in the following image) that allowed the use of a smaller generator at a cost of slower charging. We alternated between two batteries and did not use a battery cooling station (pictured left in the following image).

Left: Cooling station (from DJI website). Right: DB2160 battery being charged using a smaller generator and adaptor cable.

When spraying our 150 m long treatments, the drone flew four passes (two out-and-backs). During the 10 m/s, 50 L/ha (5 gpa) trials, the battery threw an “overheat” warning. We were only able to do a single out-and-back before replacing the overheated battery with a fresh one. The overheated battery was placed in an air-conditioned truck cab until it was cool enough to recharge.

This taught us that to manage battery heat, three batteries should be swapped, and the cooling station is likely not optional. Also, we gave further thought to the purpose of the water-cooled nozzles: We did not have an overheat issue during faster flights (15-18.5 m/s) and that may have been because the nozzle flow rate was considerably higher and kept the system cooler. In subsequent flights (and days), the drone sprayed at higher flight speeds and the overheat warning did not reappear. [Editor’s note] As of May, 2026, we have not encountered this overheat issue again.

Addendum

A few months after writing this article we were able to analyze the burndown data (here). There’s another possibility to explain the battery overheat phenomenon. Any operator can confirm that rotary drones expend a lot of power to remain in the air when they are full and when they are hovering. Flying at slow speed is a little more battery-efficient, but flying faster is better still. However, because rotary drones cannot achieve transitional lift, they are still not flying in a traditional sense. Rather, think of them as pushing hard off the ground, which is why they produce an extensive downwash. The faster they fly, the less the dwell time, which is the time the downwash is focused on one spot.

But this new generation of larger, faster rotary drones challenges those limitations. The T100 (and a few other brands such as the EAVision J150) are capable of far greater speeds than previous designs. There is a threshold (yet to be determined) where the drone surpasses translational lift and achieves proper flight. When that happens, the downwash is reduced or even eliminated, just as with a helicopter. This could explain why the overheat issue disappeared during faster flights. It might also explain why, beyond a certain speed, additional speed did not appear to affect swath width (see the burndown study).

This changes certain expectations about droplet movement beneath and behind the drone, as well as canopy penetration, drift potential and certainly, productivity. As drone design continues to evolve, the “rules” surrounding optimal operational settings must be reassessed. These observations are already changing research plans for 2026.

Flight speed and flow

Two of our treatments explored the effect of flight speed on swathing. The first set of three treatments set the T100 at max speed (20 m/s) spraying 30 L/ha (3 gpa) at 4 m altitude on an 8 m swath using 50, 250 and 500 µm droplets. Then, the next set of three treatments held droplet size at 250 µm and the dependent variable became speed at 10, 15 or 20 m/s.

We found the controller set limits on certain combinations of settings. For example, at 20 m/s we could not select any lower than a 200 µm droplet. In fact, the lowest combination of settings was 80 µm and 12.5 m/s. We thought this might be a drift mitigating measure, but it’s more likely a pump or nozzle flow limitation. We also found that we were unable to exceed 16.7 m/s when applying 30 L/ha (3 gpa) using 250 um droplets on a 10 m swath.

Once we started flying the treatments, we found the drone was not able to exceed 18.3 m/s over the 250 m treatment distance. It took roughly 200 m to get up to 18.3 m/s before the drone began to slow in anticipation of the end of the treatment block. This is not to suggest the drone was under- or over-applying up to that point, because it’s assumed the flow rate compensated for a changing travel speed. It does reflect observations with other rotary RPAS that they take some time (and distance) to achieve a consistent spray state.

Conclusion

The T100 shows promise for spraying larger fields more efficiently. Early indications suggest a higher travel speed and altitude will be required for battery management and to maintain consistent coverage over potentially wider swaths. However, research is required to determine how this will affect the balance between coverage, drift and productivity. The results of the burndown study can be found here.

Acknowledgements

Adrian Rivard and Stuart Hunter (Drone Spray Canada), Adam Pfeffer (Bayer Canada) and Mike Cowbrough (Ontario Ministry of Agriculture, Food and Agribusiness) are gratefully acknowledged for their participation, and both in kind and financial support of this study.

September 22, 2025

Circulating Spray Mix Through a Tank-Rinse Nozzle Maintains Nematode Concentration
This article was co-written with Jennifer Llewellyn, former OMAFA Nursery Crop Specialist
With more and more bio-rational products on the market, crop protection methods may require reassessment. Certain products require exacting water quality, cannot tolerate residues, and have half-lives that are both time- and temperature-critical. We’ve been getting questions about sprayer compatibility with some of these new products, so it seemed like a good opportunity to recycle this article from 2013.
Many horticultural commodities, such as turfgrass and nursery crops, include the application of live nematodes as part of their annual IPM program. We performed preliminary research into the claim that a grower’s nematode applications were becoming less effective. In the course of the investigation it was discovered that the nematode concentration (i.e. dose) sampled from the spray nozzle was diminishing over the course of the application.
(A) Tank-rinse assembly mounted through tank lid with a flow-regulating valve. (B) Close up of tank-rinse nozzle.
After eliminating potential sinks in the sprayer’s plumbing (e.g. filters, strainers, etc.) it was hypothesized that the nematodes were adhering to the interior of the poly tank. If this was the case, the concentration would drop as the level of spray mix dropped. To test the hypothesis, we installed a tank-rinse nozzle to sparge the inner walls of the tank throughout the application and to re-suspend any stranded nematodes.
A high capacity roller pump (Pentair series 1700C) was installed to operate the tank-rinse nozzle (Pentair Proclean Tankwash) during spraying. It was installed through a bulkhead fitting in the tank fill lid. During testing it was discovered that the tank-rinse nozzle shunted too much flow and pressure to maintain flow to the spray gun. A valve was installed behind the tank-rinse nozzle to restrict flow to the point where it gently rinsed the inner walls of the tank, restoring flow and pressure to the spray gun.
(A) Installing a high-capacity roller pump. (B) Tank-rinse nozzle, with valve, installed through tank lid. (C) Control manifold installed to plumb the return, the tank-rinse nozzle, spray gun and boom. (D) The entire installed system.
(A) Nematodes, as-shipped, in a sponge. (B) Suspending nematodes for tank mixing.
(C) Counting nematodes. (D) Undiluted, healthy nematodes in a stock solution via microscope ocular.
The 200 L tank was inoculated with a stock solution containing 25 million nematodes (125 nematodes / ml). 20 L of the spray solution was sprayed into a bucket every 10 minutes, whereupon 1 L of spray solution was immediately removed and 1 ml volumes were sub-sampled for counting.
In the first trial, nematode counts continued over a period of 2 hours and viability dropped by ~40%. It was assumed the damage was caused by prolonged circulation through the roller pump. In subsequent trials, the sampling duration reduced to 10 minutes (more realistically reflecting the time it took the grower to apply 200 L in the field). The tank was rinsed and re-inoculated for each trial. 1 ml samples were drawn from the spray gun, which operated continuously, with and without the tank rinse nozzle in operation.
Univariate analysis confirmed data normality and a GLM procedure was conducted for analysis of variance. Results indicate that nematode concentration dropped by ~15% without tank-rinse with minimal nematode damage observed. With the tank-rinse nozzle engaged, the concentration still declined slightly, but significantly less (<5%) (see graph below).
Nematode concentration over time for each condition.
The results suggest that a tank-rinse system that sparges the tank walls preserves nematode concentration throughout an application and may lead to more efficacious applications.
Horticultural Crops Ontario, Ground Covers Unlimited, Pentair (Hypro) and Nemapro are gratefully acknowledged for making this research possible.
August 25, 2025
Strainers (aka Filters)
The level of filtration required for any given spray operation depends on the materials sprayed and the nuisance factor: That is, the balance between lost productivity from plugged nozzles and the effort required to address them during rinsing.
There are opportunities to install strainers at the tank opening (usually a basket), the suction-side of the pump, each section line, and behind the nozzles. While we’ve yet to see an operation that uses all four (speciality or field operations), the suction strainer and line strainers are required bare-minimum.
This infographic explains how strainers are classified. Be aware that older strainers may use a different colour code (e.g. 50 mesh used to be red – now it’s blue).
To convert these ratings to actual size exclusion, we look at the Mesh Width (mm). An 80 mesh (yellow) leaves a distance of 0.18 to 0.23 mm between the wires. We can convert Mesh Width from mm to microns by multiplying it by 1,000, giving us 180 – 230 microns.
Each level of filtration should get progressively finer, ending with the nozzle strainers being slightly finer than the nozzle orifice. Nozzle catalogues will often advise you on which strainer is appropriate for the nozzle you are using.
When we ask why operators don’t use nozzle strainers, the response is either “Because they plug” or “It’s one more thing to clean”. Well, if your nozzle strainers are plugging, it’s likely because you have an agitation (see here) or mixing issue (see here and here) further up the line. They can handle a lot before the spray pattern begins to suffer … but yes, you do have to clean them regularly so they can continue their good work.
Running water through any strainer often fails to remove plugs and debris, which are a source of contamination that can wreak havoc later on. They have to be removed and physically scrubbed during rinsing. We ran a demo to show why this irritating process is still a must-do (here).
If you use an airblast sprayer, you should use slotted (not mesh, which plug too easily) nozzle strainers. Beyond the obvious benefit of preventing plugged nozzles, the strainer shoulder plays a role in keeping the nozzle snug in the nozzle body. Without it, you may need additional gaskets to prevent leaks. Be aware that some nozzle strainer designs can plug a nozzle body. Learn more here.
If you use a field sprayer with clean carrier water, liquid formulations and large nozzles, you may never need nozzle strainers. But, if you’re using a lot of dry formulations, if your agitation is under-powered, or if your fill water is less than pristine (we’ve seen frogs in sprayer tanks) then you might consider them… even if they are a nuisance to clean.
August 7, 2025
Why are my Airblast Nozzles Plugging?
This article was inspired by the following email:
“I’m an organic apple grower with constant nozzle-clogging problems. These problems occur when we use wettable powders such as micronized sulfur and Surround WP. We always premix before adding to the tank through its strainer. Our airblast sprayers have towers and employ mechanical agitation. The nozzle/filter combo is TeeJet TXR8001K Ceramic Conejet Visiflow Hollow Cone spray tips with TeeJet 4514NY10 50-mesh nylon slotted strainers. The nozzle strainers rarely make it through a full tank without having problems. Do I need to add an additional level of filtration or is there something that I’m missing?”
A clogged slotted strainer inside the nozzle body. Note that the inners of the check valve seem clear (a good thing).
A clogged slotted strainer.
You can almost feel the frustration. When I receive grower enquiries, I first turn to the library of articles on Sprayers101 as well as the Airblast101 textbook. I was surprised to discover that we didn’t have anything that addressed this issue directly. So, I checked through university extension and industrial resources. Ultimately I couldn’t find what I was looking for, so let’s correct this oversight.
Possible causes
There may not be a single reason for why nozzles plug. It might be a combination of the following factors:
1. Product choice
While any tank mix can create clogs if they prove to be physically incompatible, there are two formulations that have a reputation for clogging nozzles.
- Wettable powder (WP) formulations such as micronized sulfur and diatomaceous earth are notorious for clogging nozzles. WPs consist of a finely ground solid active ingredient often combined with wetting and bulking agents to help hold them in a dilute suspension. They tend to be dry products rather than liquids.
- In a similar vein, suspension concentrate (SC) formulations also consist of a finely ground solid active ingredient, but this time they are suspended in a liquid and kept dispersed in the sprayer tank by wetting agents, dispersants, and thickeners. These formulations are known as “flowables” or “suspensions”.
By the way, for those thinking he should change products, he already uses Kumulus DF (or Microthiol Disperss), which are reputedly the least troublesome formulations… and smell better than other sulfurs.
2. Mixing practices
Pre-slurries are sometimes prescribed for SCs. I personally feel that pre-slurries create exposure risks and more things to clean, but this opinion is moot in the case of WPs: Micronized sulfur and diatomaceous earth are not soluble. They’re particles that are held in suspension by fluid flow or agitation, so there’s no point in a pre-slurry.
For those readers that cook, consider the corn starch metaphor. You’re making a sauce, and you choose to thicken it with a pre-slurry of corn starch and water. The particles disperse, but do not dissolve, so if you fail to use it immediately they settle to the bottom of the container. They must be forcibly scraped up and resuspended.
3. Agitation
Best practice is to fill the tank at least ½ full of water and engage agitation before you add anything. To extend the cooking metaphor, you want a simmer but not a rolling boil. Once filled, never stop agitating or WPs and SCs will settle and may not resuspend uniformly, if at all.
Your sprayer design may affect matters. Some hydraulic agitation systems flag if they have undersized pumps. If your pump is busy sending flow to the nozzles, it may not have sufficient capacity to run the agitation. When your sprayer is “empty”, is there a thick accumulation at the bottom? You may have insufficient hydraulic agitation. Mechanical (paddle) agitation does not suffer this issue because it is direct-driven off the PTO. Read more here.
4. Clean-out practices
Perhaps plugs are occurring because of the previous tank, not the current tank. WPs can leave a buildup of settled pesticide in the tank, suction strainer and nozzle strainers. If you aren’t diligent about rinsing at the end of each day, products will settle and harden. Micro sulfur particles, for example, are less than 10 µm in diameter and harden into a flakey shell that can break loose and cause plugs.
5. Flow restriction
Several things can restrict flow. Elbows, bends and fittings can increase friction, reducing flow. The greater the distance a fluid needs to travel, the more flow is reduced. The greater the head (a pump’s head is the maximum height that the pump can achieve pumping against gravity), the more flow is reduced. There is an excellent description of this relationship here.
So, if an operator is using nozzles with a particularly small orifice, plus nozzle strainers, on a vertical boom, liquid flow will be reduced. This allows particles to fall out of suspension and settle, forming further restriction to flow and eventually, plugs.
Possible solutions
Now, armed with these potential causes, let’s return to the grower. After some back-and-forth, he clarified that the clogs were a problem, but restricted flow was worse. An operator will stop to clean or replace a plugged nozzle, but may not notice reduced flow. This has the potential to affect several rows as well as leave unsprayed product in the tank.
My first proposal was to increase nozzle size. An ’01 tip is very, very small and even with slotted strainers (as opposed to mesh), that’s a lot of restriction. I suggested recalibrating for larger tip orifices. This is a rather involved process, but options included using every second nozzle (as long as there were no gaps in coverage), and/or dropping pressure, and/or increasing travel speed (as long as the spray still reached the tree top and canopy centre). I shared this Excel output calculator to help with the process.
Failing that, we discussed a plumbing project. Section 5.2.1 of Airblast101 describes a way to create a self-cleaning line filter that replaces nozzle strainers. That means instead of climbing a ladder to pull tips off a tower to reach the strainers, all filtration is conveniently located at ground level for easier (and more frequent) cleaning.
The outcome
The grower felt the numbers worked best running orange 02 TXR’s in every second position. He ordered new 50 mesh slotted nozzle strainers. His new operating parameters would be 5 nozzles/side, at 8.2 bar (120 psi) and 5.1 km/h (3.2 mph) for a total 51.5 L/ha (55 gpa). He noted some incompatibility issues running Braglia nozzle bodies (spec on his Rears sprayer), TeeJet TXR’s, TeeJet slotted strainers and TeeJet CP20230 caps. That was an important observation, and you can learn more about it here.
We felt good about this, but while there was an improvement, it didn’t solve the problem. There was still strainer clogging after the first tankload. So, he added inline filters and removed the tip strainers. The result:
“Yesterday I sprayed over 350 pounds (over 1,000 gal) of Surround WP and had no issues. I’m really excited about this new setup – it looks very promising. I’ve attached more pics if you’re interested (I don’t spend a lot of time scrubbing sprayers until after Surround season). Thanks again for all your help in this matter. – Joe Fahey, Peck & Bushel Fruit Company”
A 50 mesh inline filter assembly with a 1/4 turn ball valve for quick flushes.
New filter plumbed and secured. Note the anti-rub wrap on the line – always a good idea.
The new loadout. 02’s in every second position, with no tip strainers, and a new inline filter on each side of the sprayer.
Fantastic. Thanks to Joe for letting me share this story. Hopefully his experience will help you diagnose and solve any flow or nozzle plugging issues in your own operation.
Happy Spraying.
Epilogue
This article elicited some interesting comments. I’ll share two:
1. One grower proposed switching from a low profile axial sprayer to an air-shear system (there are a few examples here). In this case, the grower had a European make with hydraulic agitation. The grower re-plumbed theirs by installing a bigger pump and swapping the sparge system with a 3/4″ pipe oriented toward the bottom to sweep it out. When mixing, the agitation valve is left wide open. He says he doesn’t even bother with a tank basket; he dumps the Surround (as much as 2 x 50 pound bags in 1,000 litres) and has no plugging issues.
2. Another grower with considerable boom-sprayer experience was genuinely surprised this was even an issue. Self-cleaning filters have been commercially available for more than 30 years and most boom sprayers have them. This is a comment on the stagnation of the North American low-profile radial airblast design. Perhaps the long life of these sprayers (sometimes 40 years of service) makes iterative change slow, or perhaps most operators aren’t aware of new features, or perhaps change is a risky proposition in such high-value crops. This is a shame given that the first optic sensors were installed on airblast, not broad acre field sprayers. That comes as a surprise to many. But it seems to have been the exception and not the rule.
June 20, 2025

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 6^th, 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.

Time	Rep and Treatment	Temperature (°C)	Wind Speed (km/h)	Wind Direction
10:21:51	1. RPAS 6 m/s	16.4	3.1	S
10:33:56	2. RPAS 6 m/s	17.7	6.2	S x SW
10:45:50	3. RPAS 6 m/s	18.8	4.0	S x SW
10:55:40	1. RPAS 10 m/s	18.6	2.1	SW
11:06:24	2. RPAS 10 m/s	20.0	0.5	S
11:16:00	3. RPAS 10 m/s	19.2	5.8	S x SW
11:29:54	1. Field Sprayer	21.1	0.0	S
11:41:12	2. Field Sprayer	19.9	1.7	S x SW
11:48:31	3. Field Sprayer	20.2	3.9	S

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 DropScope^TM (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).

Treatment	Pole Position	Threshold Coverage (count/cm²)	Under-dose (%)	Over-dose (%)	C.V. (%)	Swath (m)
RPAS 6 m/s	21-10	120	10.4	5.0	18.0	5.5
RPAS 6 m/s	10-1	120	5.7	14.1	26.0	5.0
RPAS 10 m/s	21-10	80	9.1	11.4	25.4	6.0
RPAS 10 m/s	10-1	35	17.2	14.1	43.4	6.5

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.

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.

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.

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.

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.

June 11, 2025