“If you can’t measure it, you can’t improve it”. While the source is nebulous (Peter Drucker, Lord Kelvin, or Antoine-Augustin Cournot), the sentiment is clear.
The status quo
In the world of crop protection, considerable resources are expended to distribute a pesticide over a target. And yet, sprayer operational settings and spray coverage are rarely assessed. As a result, too much time elapses between the application and observing the biological results to evaluate and correct equipment performance. The damage (be it waste or an inconsistent and sub-lethal dose) is done. All sprayer operators know this to be true, so why do precious few perform these assessments?
Perhaps, dear reader, you have personal experience assessing coverage and already know the answer. Perhaps you’ve performed the iterative dance that is placing, spraying, retrieving, assessing and re-placing water sensitive paper (WSP). Perhaps you’ve sprayed fluorescent tracers and hunted for faint glows at twilight using UV lights. Perhaps you’ve looked for residue from diatomaceous earth or fungicides. Or, perhaps, you’ve trusted in the falsely-comforting “shoulder check” and assumed dripping must mean you’ve hit the target.
Existing methods are complicated, subjective, messy and time-consuming. We need an alternative.
The alternative
Consider a permanent, solar-powered sensor that supplies real-time spray coverage data to your smartphone via a cellular connection. The output could be visualised in a simple and intuitive way, and immediately available to both sprayer operators and farm managers. If the sensor was relatively inexpensive, sufficiently hardy, and easy to deploy, its utility would only be limited by your imagination:
Stakeholders could confirm the correct functioning of their equipment before committing to the application. Decisions could be made to change operational settings, repair equipment, or delay until conditions improved.
The sensors would provide coverage data specific to their location and orientation. Units could be installed in difficult-to-spray regions such as treetops, or canopy-centres, or fruiting zones. Sensors could be placed where pest/disease pressure has been historically high, or where wind is a known issue.
Large operations could install them in a test-row, where sprayer operators would perform a gauntlet-style calibration run prior to a day of spraying.
Spray records could inform compliance audits, supplement insurance or CanadaGAP traceability requirements, or be used in agronomic assessments.
In 2025 I was approached by an Australian developer who claimed he had a device that did all of this. And, if that weren’t enough, it could also monitor certain meteorological factors such as pre-spray moisture levels and temperature and report post-spray evaporation rates. I could barely contain my excitement. A prototype was in my hands a few weeks later.
Prototype, 8-sided sensor located in a blueberry bush.Solar panel powering three, 8-sided prototype sensors spanning 10 meters of highbush blueberry.
Benchmarking the sensor
The Spray Doctor (working name for the prototype) started its life as a leaf wetness sensor, evolving into a spray coverage sensor piloted in 2023/24 in Australian and New Zealand grape production. The history of earlier iterations and company schisms is convoluted, and fortunately immaterial to our purposes. All I needed to know was that we weren’t starting from scratch. Several of the questions regarding how accurately the surface could detect spray deposition were already addressed by independent research.
The sensing surface is impregnated with an array of capacitive wetness sensors. The sensor responds to the surface area covered and not deposit density. Researchers reported a reliable response range between ~10% and 50% surface coverage. Given the arguable “ideal” coverage standard of 10-15% surface area, this includes the range of interest for most sprays.
Benchmarking against WSP was part of the foundational assessment. A droplet of water deposited on WSP produces a high angle of contact and very little spread, while the same droplet deposited on plant tissue tends to produce a lower angle of contact and more spread. This means the stain produced on WSP is smaller than would be produced on plant tissue, depending on how smooth, vertical or waxy the tissue surface was.
It was therefore surprising that WSP were found to report a higher degree of spray coverage during water-only sprays than the sensor. It seemed droplets more easily coalesced and ran off the sensor surface. This was ultimately interpreted as an advantage, because the sensor would better emulate how a leaf surface would respond to the influence of surfactants and spray quality.
Adding a surfactant to a spray solution improves droplet adherence, and/or reduces surface tension, improving the degree of contact on plant surfaces. Likewise, it was found that surfactants increased the degree of coverage reported by the sensor, and when actual chemistry was sprayed (e.g. sulphur powder or copper sulfate) there was an effect on the degree of coverage reported. This is unlike WSP, where adjuvants and chemistry do little to increase the spread.
And so, like every method for assessing spray coverage, the sensor has limitations and caveats. If you have some doubt as to the sensor’s accuracy, do not get distracted by the fine detail. Remember, most operators currently have no feedback whatsoever; even a binary response (e.g. hit or miss) would be welcome. The sensor is sufficiently sensitive and consistent to resolve coverage in a range relevant to most sprays, and therefore worth field testing.
The experiment
My role in this story was to work with a grower to evaluate the sensor’s ability to report coverage information in a clear and actionable way. There were three questions:
Does data from the sensor influence a sprayer operator’s behaviour?
Does that change in behaviour lead to improved spray coverage (implying more efficient and effective crop protection).
Could we “dial in” the hardware and the interface based on the grower’s feedback?
In part two, we share our experience installing and using the Spray Doctor, as well as supply answers to these questions. Stay tuned.
Thanks to Brandon Falcon (Falcon Blueberries) for volunteering his time and farm for this evaluation, and the developer for the in kind donation of the prototype Spray Doctor.
This case study is taking place on a 15 acre highbush blueberry operation in southern Ontario. In 2016, considerable pressure from spotted-wing drosophila (SWD) prompted the growers to make changes to their crop management practices and their spray program. They employed a three-pronged approach to improving crop protection:
Significant changes to canopy management and picking / culling practices
Investing in a new sprayer
Adopting the Crop-Adapted Spraying (CAS) method of dose expression
We have been tracking pesticide use, water use and yield compared to historic values. We also monitored spotted-wing drosophila catches both in crop and in wild hosts along the border of the operation for three years.
Canopy Management
In 2016 the operation made the following changes to their canopy management practices:
They performed their first-ever heavy pruning and planned to to maintain an ideal crop density by removing ~30% plant material annually. This more-or-less took place.
They regularly collected and buried culled and dropped berries.
They picked cleanly and more frequently.
Heavy pruning in 2016.Most years, bushes were pruned ~30% to maintain an ideal size and shape.Pickers were educated in how to pick cleanly and dropped / culled fruit was collected and buried.
There were initial concerns that such dramatic pruning would reduce production per acre and require trellising to prevent berries weighing down the smaller bushes. However, in 2017 (and thereafter) they found that the quality of the berries was greatly improved and noted fewer hours spent culling berries during packing. Financially, the growers felt they came out ahead.
Application Technology
In 2018 they replaced their old, inefficient KWH sprayer with a low profile axial with conventional hydraulic nozzles to permit greater control of the spray. The KWH design was intended for standard fruit trees. It produced >100 mph air and an Extremely Fine spray quality and was therefore a bad fit with the planting architecture and canopy morphology of highbush blueberry.
They considered a cannon-style sprayer hoping to spray multiple rows in a single pass but given the desire for improved coverage and reduced waste, they elected to drive every row using a low-profile axial.
Fore: An old KWH air shear sprayer. Rear: Low profile axial sprayer with conventional hydraulic nozzles.
The new sprayer was more reliable, quieter, and more fuel efficient. Further, the old sprayer leaked and the air-shear nozzles did not respond when shut down at the end of rows. Eliminating these sources of waste represented a savings of ~20% of the spray volume traditionally used per acre.
Crop-Adapted Spraying
The redundancy inherent to product label rates for three-dimensional perennial crops has long been recognized. In response, rate adjustment (or dose expression) methods have been developed to improve the fit between rate and canopy coverage (e.g. Tree-Row Volume, PACE+, DOSAVIÑA). Each has value, but their adoption has been slow because they are region- or crop-specific and they can sometimes be quite complicated.
CAS lends structure and repeatably to the informal rate adjustment methods already used to spray three-dimensional perennial crops (e.g. Making pro rata changes by engaging/disengaging nozzles in response to canopy height or altering travel speed in response to canopy density).
The CAS method relies on the use of water sensitive paper to confirm a minimal coverage threshold of 85 deposits per cm2 as well as 10-15% area covered throughout a minimum of 80% of the canopy. Using this protocol, we calibrated air energy and direction, travel speed and liquid flow distribution. This process is covered in detail here and in the new edition of Airblast101. In that first year we reassessed coverage every few weeks between April and June using water-sensitive paper.
Spray volume / Pesticide
By matching the sprayer calibration to a well-managed canopy, the growers were able to go from ~1,000 L/ha to ~400 L/ha of spray mix. The ratio of formulated product-to-carrier remained the same, but less spray was warranted per acre. Stated differently, the grower mixed the spray tanks per usual, but drove further on a tank.
This also saved an estimated 15 hours of filling/spraying time per year, which translates to reduced operator fatigue and exposure as well as reduced manhours and equipment hours.
The decision of what and when to apply was at the growers’ discretion. Chemistry was rotated and applications were made according to IPM in early morning (if there were no active pollinators) to avoid potential drift due to thermal inversions. The following image shows what those papers looked like in June of the first year.
Example of water sensitive paper coverage on a windy day (worst case scenario) in June, 2018.
Note how little spray escapes the target rows in the following video. The wind was too high for spraying, but we were only using water and saw it as an opportunity to test a worst-case scenario. Air-induction hollow cones were used in the top nozzle position on each side so droplets were large enough to fall back to ground if they missed the top of the canopies.
SWD monitoring
SWD represents a serious economic threat to blueberry operations. Traps were placed in the operation (three in the crop and one in an unmanaged wild host along a treeline) and monitored weekly. Traps were also placed in surrounding horticultural operations which were employing standard pest control practices. This not only provided regional information about SWD activity but allowed us to compare the level of SWD control from the Crop-Adapted Spraying approach.
In 2018 the comparison included up to 16 other sites that were berry and tender fruit.
In 2019 the comparison included 10-12 sites (depending on the week) and they were berry and tender fruit sites.
In 2020 the comparison included 4 other sites (blueberries, raspberries and cherries).
2020 & 2021 – Covid 19 and Heavy Rain
In agriculture, every year is an adventure, but 2020 and 2021 were exceptionally difficult and the circumstances should be considered when deciphering the results. Covid-19 has had a significant impact on global agriculture.
In 2020, fearing a reduction in the availability of seasonal labour, the operation pruned their bushes heavily. This was done to reduce the yield in order to make harvest manageable.
In 2021, labour was once again secure. Given the heavy pruning the year previously there was no need to prune again, so the crops densified. This coincided with abnormally high levels of precipitation to create significant anthracnose issues. Additional fungicide applications took place that raised costs, but the grower maintained CAS-optimized rates and sprayer settings.
Quantitative Results
Prior to replacing their sprayer, and adopting CAS, the operation sprayed about 78,260 L/yr. Their average savings in spray volume (water) has been 54,720 L/yr, or 70%.
In terms of pesticide savings, we compare each year to the 2017 baseline. In order to make for a fair comparison, we update pesticide prices each year using current costs. Therefore, the 2017 total has increased by about $2,600.00 (wow). Their average savings represents $5,575.00 CAD/yr or 62.5%.
Yield is more difficult to interpret due to mitigating circumstances in 2019 and 2020:
In 2016, prior to any changes, they harvested 12,076 flats (about 9lb of fruit each).
In 2017, following the canopy management changes, harvest increased to 18,335 flats (~50% increase).
In 2018, using CAS, harvest was essentially unchanged compared to 2017, which was excellent.
In 2019, harvest started a month late compared to previous years. Further, blueberry prices were low, and the operation elected to stop harvesting a month early. However, when those issues are factored in, the harvest was comparable.
2020 was particularly challenging for agriculture and with the possibility of reduced labour due to the pandemic, the operation elected to prune heavily and reduce their yield.
2021 saw unpruned bushes (following the heavy pruning in 2020) and abnormally high levels or precipitation which created anthracnose issues. As a result, more applications were made than any other year on record, but maintained the CAS-optimized rates and sprayer settings.
2022 was (thankfully) fairly typical. Low SWD, average anthracnose and no drama.
2023 was very much like 2022 with low SWD, average anthracnose and no drama.
2024 saw a LOT of rain. The season started and ended early, but yields were par. “Pivot” replaced “Tilt”.
2025 was pretty average all things considered. No drama whatsoever. “Inspire-Super” was added to product list.
Trap counts for SWD were only performed during three years of the CAS study, so we are only able to present 2018-2020 data. It should also be noted that while the presence of SWD in an operation represents an impact on yield, there is not necessarily a correlation between the number of SWD captured the amount of damage.
In 2018 and 2020, average counts were higher in the surrounding operations employing standard practices (STD) compared to the CAS trial. In 2019, average counts were higher in the CAS trial. When total average counts are compared, the difference is negligible. Berries were tested regularly by the growers and the damage due to SWD was within acceptable limits. It should also be noted growers monitored and reported satisfactory disease control throughout the study.
We have not applied any statistical rigor, but the trend suggests that the level of control provided by the CAS method was comparable to conventional methods. This conforms with our previous results in Ontario apple orchards and similar evaluations of optimized application methods world wide.
Qualitative results
Beyond the quantifiable results, the growers reported qualitative benefits:
Customers of the U-pick portion of the operation regularly enquire about pesticides. The operation’s reduction in pesticide use became a positive speaking point and aligned with the grower’s philosophy about reduced environmental pesticide loads.
While many blueberry growers experienced a market shortage of certain fungicides in 2018, this operation returned unused product to the distributor.
Growers reported less early-season disease damage, which saved considerable time on the packing line because there was less fruit to cull. Disease levels rose to typical levels later in the season, but there was still a net savings in labour.
Conclusion
The success enjoyed in this berry operation was a result of several canopy management and crop protection changes. This is a situation where the whole equaled more than the sum of its parts – it could only be achieved by making holistic changes to the operation. At the end of three years the growers themselves stated:
“Based on my experience losing multiple crops to SWD, I can say with absolute certainty it works. <The results are> superior to what I expected. What we are doing is successful.”
Here’s a narrated PowerPoint presentation of this study (includes data up to 2020):
The monitoring portion of this project was funded by Niagara Peninsula Fruit and Vegetable Growers Association, Ontario Grape and Wine Research and Ontario Tender Fruit Growers in collaboration with private consultants.
I work in agricultural extension and I’m always on the lookout for new methods to help me achieve my goals. A big part of my job is to research and teach efficient, effective and safe crop protection practices, so it follows that I have to be able to evaluate the quality of a spray application. Fundamentally, there are two ways to do it:
Wait to see if the pesticide did its job and protected the crop from weeds / bugs / disease.
Don’t wait. Confirm your spray is depositing where you want it before committing to the application.
Three guesses which approach I advocate. So, how do you check spray coverage in a way that’s quick, cheap, easy and informative? Again, there are choices, but rather than simply list them I’ll add a little insight in the form of pros and cons.
Reflects actual, whole-canopy coverage and off-target coverage at same time.
Expensive, hard to find, messy, time-consuming, hard to photograph, not repeatable, leaves unwanted residues (or can’t be used on edibles), may have to take place at night, may fade quickly… or is any of this actually true?
I’ve never been a proponent of spraying dyes because of the reasons I listed in the table. If I already have difficulty convincing a grower to leave the sprayer or tractor cab to place and retrieve water sensitive papers, what are the odds of them mixing a messy and expensive tank of dye and waiting until twilight to see the results?
On the other hand, dyes are compelling. Particularly if we change the perspective a little. What if we consider the use of dyes, not as a tool for a grower, but as a tool for agricultural extension or consultation (really, anyone that wants to research or teach the safe and effective use of crop inputs)? Several of the cons are minimized or even eliminated. Additionally, this new lens reveals several uses for dyes beyond spray coverage. This is not an exhaustive list:
Off-target (primarily drift) evaluation
Dermal exposure / PPE evaluation
Rinsate / sprayer cleanout evaluation
Sprayer loading / point source contamination evaluation
I decided to compare a few of these dyes. I enlisted the help of a local blueberry operation. Being October, all the berries have been picked so we could spray the bushes without any risk to the fruit. Plus the sprayer was clean and the growers were curious to evaluate their spray coverage.
Blueberry in Ontario in October.
Having secured a location, spray equipment, and operator, I needed dyes and some criteria for choosing them. First and foremost, I chose fluorescent dyes that glowed under UV (aka black lights). My thinking was that they would be more interesting in demos, and given that we might be spraying horticultural operations, I didn’t want obvious and persistent stains on the produce. At least not something easily seen in daylight before it broke down and/or was washed away.
My UV dye candidates had to be:
Moderately inexpensive.
Non-toxic (i.e. had an SDS that clearly permitted human exposure, were environmentally friendly and could be sprayed on edible crops).
Readily available in Ontario (e.g. quickly and cheaply shipped from within Canada or perhaps the US).
Available in formats that facilitated small volume batches (anywhere from 50 mL squirt bottles for indoor demos, up to 50 L volumes for field demos).
Clearly visible on plant tissue.
I found five likely prospects for the study. I won’t list prices, but none of them were over $100.00 CAD. Number 3 was a free sample and number 5 was gifted to me by a colleague more than 15 years ago. I looked up the SDS for that last one and was surprised that it was relatively inert. So, I used it.
I also purchased UV lights. When I was bequeathed the phosphor powder it came with heavy, ancient, black lights. They made an unsettling humming noise and required a power source, making them unwieldly for field work. I opted to try three battery powered versions instead. Again, I won’t list prices, but they weren’t unreasonable.
UV flashlight number
Name of light
Manufacturer
Wavelength / wattage
Batteries
1
Super Tac
Risk Reactor
395 NM / 850 µW/cm2 at 5 inches
Rechargeable battery provided
2
Mini Zoom
Risk Reactor
395 NM / 1 watt
1 AAA
3
V3 UV Flashlight with 68 LEDs
Amazon.ca
395 NM / 10 watts
3 AA
Regarding the recipes, one of my criteria was that the dyes could be mixed in relatively small batches. I chose 50 L as the high end because the airblast sprayer we were using (Turbo-Mist 30P) could still prime when only 50 L was added to the tank. This allowed us to mix as small a batch as possible, while still having enough to spray a row of berries from both sides. We left three rows between treatments to serve as buffers.
Turbo-Mist Model 30P before the dye-job.
I also had to consider the nature of the dyes. The Eco Pigment (Dye 3) is a hydrophobic powder and two colleagues warned me that it was notorious for plugging filters. So, it had to be mixed with a non-ionic surfactant (NIS) to help “wet” the powder prior to adding it to the tank. In fact, NIS seemed like a good idea for all my dye candidates, so I included Activate Plus (Sollio Agriculture, Winfield Solutions) in each recipe.
The candidates.
I added the dye, NIS, and a small amount of water to a Pyrex measuring cup on a digital scale, then rinsed the cup into a final volume of 50 L while filling the tank. I didn’t always follow the advice I received, so I’ll show you the ratios I was told and (right or wrong) what I ultimately did.
Dye number
Manufacturer- or colleague-suggested ratio
Amount of dye
Amount of NIS
Amount of water
1
1 part dye : 10,000 parts water
125 mL
65 mL
310 mL
2
1 part dye : 10,000 parts water
125 mL
65 mL
310 mL
3
1 gram dye : 1 mL NIS : 200 L water
65 grams
65 mL
425 mL
4
1 part paint : 100 parts water
500 mL
65 mL
0 mL
5
1 gram dye : 1.25 L water
65 grams
65 mL
425 mL
It took roughly 15 minutes to fill, prime, spray, and rinse out each dye. We started at 5:00 p.m., were done at 6:15, and then waited for sunset at 7:30.
50 L tank mixes going through circulation and paddle agitation.Draining the remains and rinsing the tank. It looks terrible, but these dyes are intended for environmental projects like tracing water courses.
We used a smartphone (Google Pixel 9a – 48 megapixel camera) to photograph each combination of dye and flashlight. It was tricky to find an angle where the black light illuminated the residue, but didn’t wash out the photo. In those cases where the dye was evident, it was always far more vibrant in person than through the lens of a camera. As for the results?
Lets start with the lights. We found that the high wattage of Light 3 showed dye more easily. This also happened to be the cheapest light, which was a pleasant surprise.
Dye 1 and 2 were disappointing. We couldn’t see anything on the plants. This dye is intended for monitoring plumbing and water courses, and the manufacturer states that the colour will disappear if the solution is mixed with chlorine. Perhaps mixing it with city water caused it to fade, but that’s likely to happen, so these dyes failed.
Dye 1 – Light 1, 2 and 3. A sad, single drop showed up for Light 3.Dye 2 – Light 1, 2 and 3. Again, a solitary deposit illuminated under Light 3.
Dye 3 was spectacular. Not only was it evident with every light source (including day light to some extent), but we were able to find it several rows downwind, on the sprayer nozzles, all over the tires and on the floor of the cab (which surprised the operator). I may have mixed this one too strong; It seemed to clump on the leaves, but perhaps that’s because they were exceptionally waxy.
Dye 3 – Light 1, 2 and 3.Dye 3 showed up everywhere… whether we wanted it there or not.A nice close up of Dye 3 on a leaf.A close up of Dye 3 on the boom.
Dye 4 came in second place. It wasn’t amazing, but it was visible. This is children’s tempera paint, used in daycares for finger painting and at universities for raves. I’ve used it in the past with mixed results, not only to spray canopies, but in classroom demos on cabbage leaves and as a surrogate tracer to hunt down where pesticide hides in sprayer plumbing. It’s OK in a pinch if you mix it at least 2x more concentrated than I did here.
Dye 4 – Light 1, 2 and 3.A nice close up of Dye 4 on a leaf.
Dye 5, like dyes 1 and 2, was a disappointment. I’ve seen it used in powder-form to demonstrate how dermal exposure can spread as you touch clothing, doorknobs, your face, and places where the occasional adjustment is required. But in a liquid solution, it wasn’t any good at all.
Dye 5 – Light 1, 2 and 3
Persistence
We followed up after the application to see if the dyes would persist. Twenty four hours after application, Dye 4 (our runner-up) was gone. This was no surprise given it was a water soluble paint and wasn’t terribly showy to begin with. However, Dye 3 (our winner) was still clearly in evidence. This is a hydrophobic, micro ground powder (~0.1 micron). That’s one reason it had to be mixed with a non-ionic surfactant. The following photos shows little or no change after 24 hours and a respectable dew:
Dye 3 after 24 hours.
Three days after application (DAA), we had a rain event. Four DAA this (blurry, sorry) image was taken:
Dye 3 after 96 hours and a heavy rain.
We see that the deposits did redistribute to drip points and the overall coverage was reduced, but it was still holding on. This means it likely shouldn’t be used on any horticultural crop that isn’t going to be washed. Or at least used long before any fruit, leafy green or vegetable contacted by the powder will be harvested. Not because it is unsafe (see safety data sheet) but because of the optics to buyers.
Conclusion
And so, I hope you have been inspired by this process. I’ve learned that the use of dyes for education and research is potentially powerful, relatively cheap, and more accessible than I originally thought. Certainly the growers were impressed by what they could suddenly see and it’s led them to reassess some of their practices. Just bear in mind the possible persistence, and remember to wear gloves when mixing.
Wear gloves. Trust me.
Thanks to Mark Ledebuhr, Helmut Spieser, David Manktelow, and Ben Werling for the helpful advice. Thanks to Brandon and Jordan Falcon for use of their spray equipment and their blueberry operation.
The decision on which application method is best for herbicides boils down to two main factors: (a) target type and (b) mode of action. In general, it’s easier for sprays to stick to broadleaf plants on account of their comparatively larger leaf size and better wettability compared to grassy plants. There are exceptions, of course – at the cotyledon stage, broadleaf plants can be very small and a finer spray with tighter droplet spacing may be needed. Water sensitive paper is a very useful tool to make that assessment. Imagine if a tiny cotyledon could fit between deposits – that could be a miss!
Some weeds are also more difficult to wet, and those may also need a finer spray or a better surfactant for proper leaf contact. An easy test is to apply plain water to the leaf with a spray bottle. If the water beads off or the droplets remain perched on top in discrete spheres, the surface is considered hard to wet. Most grassy weeds are hard to wet, while most broadleaf weeds are easy to wet.
Grassy weeds are an especially difficult target because they have smaller, more vertically oriented leaves, and almost without exception are more difficult to wet than broadleaf species. All these factors call for finer sprays for effective targeting and spray retention.
Broadleaf weeds usually have more horizontally oriented leaves which also happen to be larger. As a result, they can intercept larger droplets quite efficiently.
There are about thirty mode of action (MOA) groups among the herbicides with about ten accounting for the majority in Canadian prairie agriculture. It’s probably an over-simplification to categorize them into just two groups – systemic and contact. But that grouping goes a long way to making an application decision.
Contact products (MOA Group 5, 6, 10, 14, 22, 27) must form a deposit that provides good coverage. Good coverage is an ambiguous term that basically means that droplets need to be closely spaced and cover a significant proportion of the surface area because their physiological effects occur under the droplet, and don’t spread far from there. One way to generate more droplets is to reduce droplet diameter, another is to add more water. A reasonable combination of both is ideal because simply making droplets smaller creates issues with evaporation and drift.
Systemic products (MOA Group 1, 2, 4, 9) will translocate within the plant to their site of action after uptake. As a result, coverage is less important as long as sufficient dose is presented to the plant. In practice, this means coarser sprays and/or less water may be acceptable.
When two factors are combined, either in a tank mix or a weed spectrum, the more limiting factor rules. Application of a tank mix or product that is active on both broadleaf and grass plants will be governed by the limitation placed on grass targets. A tank mix comprised of both systemic and contact products is governed by the limitations placed on contact products.
A factor we should also consider is soil activity and the presence of residue. Studies have shown that soil-active products are relatively insensitive to droplet size. But if they have to travel through a layer of trash to get to the soil surface, more application volume is the best tool.
Below are some recommended spray qualities and water volumes for use in Canada. The spray qualities listed in the table can be matched to a specific nozzle by referring to nozzle manufacturer catalogues, websites, or apps. Note that Wilger also offers traditional VMD measurements on their site, allowing users to be a bit more specific if necessary.
This article was co-written with Dr. Sean Westerveld, Ontario Ginseng and Herb Specialist.
An effective ginseng protection program begins with observing the Integrated Pest Management (IPM) process:
diagnose the problem,
monitor the problem,
control the problem, and
monitor the results.
When spraying is warranted, the operator should understand the basics of application technology. This not only includes the equipment, but the effects of changing spraying parameters (such as pressure or carrier volume), the impact of weather conditions (such as wind and relative humidity) and the product being applied (such as correct timing and safety requirements). The operator should also understand how to properly maintain, calibrate and orient the sprayer according to the nature of the target. Finally, monitoring the results requires the operator to respond to changes in the environment and target during application and to consider these factors when evaluating the outcome.
The ginseng garden
This is a four-year old garden, which represents one of the largest, densest ginseng canopies an applicator can spray. The six-foot wide beds in this particular garden are higher than most beds, making sprayer/tractor clearance an issue. It also means the distance-to-target from boom to canopy is less in the middle of the bed than it is nearer the alleys, making it difficult to ensure consistent coverage. Sprayer operators typically drive in the same direction over each bed, “training” the plants to bend in the same direction each time the tractor passes over the surface. This practice, combined with fenders on the tractor wheels, helps to minimize physical damage as the sprayer passes.
Ginseng gardens have high beds.Clearance is an issue in a four year old ginseng garden.
The sprayer
This custom-built sprayer is a fairly standard design for most ginseng operations: Eight nozzles on each wing and nine on the centre boom. Spacing varies but this sprayer is on 11 inch centres, with the outermost nozzles on five inch centres and aimed outward towards the adjacent beds. Given the limited boom height, all nozzles are aimed back about 45 degrees to increase the distance to target and allow for overlap. The angle is critical to prevent gaps in the spray swath, but given the recommended practice of limited overlap for hollow cone nozzles, the 11 inch spacing may be a little shorter than required.
Custom-made ginseng sprayer. A standard design in Ontario.
Spray coverage
There is no hard and fast rule for spraying ginseng. The crop can receive 30 or more applications a year, most of which are fungicide applications. Tip: Monitoring the small plants inside the canopy is a good indicator of overall garden health.
The following lists products available for use in Ontario at the time this article was published. The application target varies for each product, depending on the pest or disease the applicator wishes to control. As such, the application volume should reflect the location of the intended target. For example, a foliar-and-stem application should achieve consistent coverage of all leaf surfaces without incurring run-off. An application intended to reach the crown through the straw will require some run-off down the plant stem and should require a higher volume than a foliar-and-stem application. Many products will become immobilized if they dry onto the straw. Applications are best done to wet straw, followed by irrigation or rainfall to wash the product into the root zone. Applications for diseases like Rhizoctonia generally take place early in the season before the canopy closes, and higher volumes may not be required to achieve root coverage. In order to know how much is required for optimal coverage, read on.
Table 1 – Spray target and relative volume by pest
Pest
Application Target – Specific Product
Garden Age
Relative Volume
Alternaria and/or Botrytis
Foliar and Stem – all products
Seedling – 2nd year
Low
3rd – 4th year
Moderate
Phytophthora Leaf Blight
Foliar and Stem – most products
Seedling
Low
2nd-4th year
Moderate
Foliar – Aiette and Phostrol
All
Low
Phytophthora Root Rot
Root – xylem-mobile root rot products
All
High
Foliar – Aiette and Phostrol
All
Low
Phytophthora Leaf and Root
Root – xylem-mobile root rot products
All
High
Foliar – Aiette and Phostrol
All
High
Cylindrocarpon
Root – all products
All
High
Rhizoctonia
Root – most products
All
High
Root – Quadris
Seedling
High
Pythium
Root – all products
All
High
Aphids
Foliar and Stem/Berries – all products
All
Moderate
Cutworms
Stem – all products
All
Low
Four-Lined Plant Bug
Foliar – all products
All
Moderate
Leafrollers
Foliar and Stem – all products
All
Moderate
Root Lesion Nematodes
Root – all products
All
High
History of the ginseng boom in Ontario
Historically, ginseng sprayer operators used brass hollow cone nozzles to spray ginseng. For reasons that are unclear, many then adopted the Casotti-style sprayer, which used higher volumes and an oscillating nozzle assembly to create a larger swath. This was determined to be overkill for ginseng, and it produced inconsistent coverage.
Many growers (sadly, not all) switched back to horizontal booms and began using the Arag microjet assembly. Drop nozzles (aka drop arms, drop booms, drop legs, etc.) were positioned with disc-core hollow cone nozzles behind the wheels to direct spray into the canopy from below.
Later, we demonstrated that the microjet mixing valve was difficult to set accurately, creating outputs +/- 50% the optimal rate. In response, a new variation on the Arag microjet was introduced, with a more reliable rate adjustment and a lower price tag (they are imported from Italy by a single North American distributor). The drop nozzles are absolutely critical for under canopy coverage, and growers have begun suspending them in each alley – not just behind the sprayer wheels. I predict the future boom arrangement will return to hollow cone nozzles, but in the form of molded poly nozzles with ceramic handling and drop nozzles with full cone disc-core assemblies. Air assist would be even better.
Sprayer settings
Most operators employ a ground speed of about 5 km/h (3.1 mph), operate at about 13.8 bar (200 psi) with nozzles spaced 25-30.5 cm (10-12”) spraying anywhere from 1,000 L/ha (107 gal./ac.) to 1,686 L/ha (180 gal./ac.). The application volume should reflect the stage of crop growth, the age of the garden and the target in question (see Table 1). Applicators should also consider droplet size (Table 2). This is difficult to control given that the majority use Arag microjets with the 1.5 mm orifice disc. In which case, pressure choice will affect median droplet size, with lower pressures increasing median droplet diameter and vice versa.
Table 2 – The Impact of Droplet Size
Droplet Size
Drops per area
Retention
Canopy Penetration
Drift Potential
Fine
High
High
Low
High
Medium
Moderate
Moderate
Moderate
Moderate
Coarse
Low
Low
High
Low
Two versions of the ARAG Microjet.
The older style Arag microjets with 1.5 mm diameter discs have highly variable outputs. We developed tables listing their rates with the mixing valve handle set in two positions. They can be found here. We have also developed tables for the newer Arag nozzles for the 1.0, 1.2 and 1.5 mm discs based on 28 cm (11”) spacing. They are listed in Metric and U.S. Imperial.
Park the clean sprayer and get the pressure up to the desired level. Using a calibration vessel, perform a timed output test to determine each nozzle rate. I prefer the SpotOn SC-4 and a length of 1” braided line to direct the spray into the vessel. You will get wet, so ensure the water is clean and/or wear appropriate PPE.
Timed output test. Prepare to get very wet. Unless sprayer is sparkling clean, like this one, PPE is a must.
At 200 psi, we took readings from each microjet and found that while they were more consistent than the older model, there was still a lot of variation from tip to tip. This required us to turn the valve on the nozzle to get a more consistent output, then take another reading, and repeat until we liked what we saw. It became tricky to adjust the rate without reducing the hollow cone pattern to a solid stream because only a slight turn of the nozzle was required. Once we had it, we tightened the lock nut and moved to the next nozzle. Table 3 is a record of the procedure.
While calibrating, we noticed some of the nozzles would suddenly appear plugged, or dense lines could be seen in the spray cone indicating something was wrong. We cleaned them to discover bits of plastic from the poly tank. I asked about strainers, but they are not available for the microjets. I asked about in-line filters, but they aren’t rated for 200 psi. Filling the tank with clean water is very important, but even more so with these nozzles.
Table 3 – Calibrating the new Arag microjets
Nozzle Position
Rates in gpm (bold represents final rate)
Nozzle Position
Rates in gpm (bold represents final rate)
1
0.97, 0.96, 0.93
14
0.77, 0.92
2
1.07, 1.07, 1.26, 0.9
15
0.76, 0.8, 0.95
3
1.1, 1.1, 1.1, 0.93
16
0.97, 0.95
4
0.73, 0.92
17
0.73, 1.0, 1.07, 1.0, 0.98
5
0.92, 0.92
18
0.83, 0.94
6
0.94
19
0.77, 1.0, 0.99, 1.1, 1.24, 10.8, 0.93
7
0.88
20
0.77, 0.88
8
0.92
21
0.71, 0.95
9
0.95
22
0.77, 1.07, 1.04, 1.1, 1.27, 1.0
10
0.90
23
1.06, 0.97
11
0.86
24
0.77, 0.97
12
0.76, 0.83, 1.0, 1.0, 1.2, 0.92
25
0.68, 0.95
13
0.77, 0.92
Average output: 0.93 gpm, standard deviation of 0.03 gpm.
Ground speed
Once the nozzles were adjusted, we filled the tank ½ full and measured out 25 m in the bed. We would normally do 50 m, but the row was too short. The sprayer operator drove the course and we measured the time it took to travel the 25 m distance. Pass one took 18.5 seconds and pass two took 18.3 seconds. That’s an average of 18.4, which we then double so it works in the formula = 36.8 s.
( 50 × 3.6 ) ÷ 36.8 s = 4.9 km/h
Adjusting the drop leg nozzles
This sprayer had drops behind the wheels and two more to hang in the adjacent alleys. This is excellent because research has shown considerably improved coverage with directed spray from drop arms. In my mind, these are not optional – they are mandatory!
Drop nozzles in the alleys.
We swapped out the hollow cones we found in those positions for full cone disc and core (D5-DC35). Full cones increase the number of droplets that will clear the raised bed and enter the canopy. When adjusting them, be sure to minimize the portion intercepting the bed, while minimizing the spray escaping up through the canopy. It’s a fine line.
Aiming drop arms in a ginseng garden.
Calculating sprayer output
25 microjets at 200 psi = average of 0.93 gpm = 23.25 gpm 8 × D5-DC35 at 200 psi = 1.4 gpm × 8 = 11.2 gpm That’s ~34.5 gpm for the boom. Ground speed was 4.9 k/hr or ~ 3mph.
GPA = (GPM × 5,940) ÷ (mph ÷ nozzle spacing in inches) GPA = (34.5 gpm x 5,940) ÷ (3.0 mph × 11 inches) GPA = 204,940 ÷ 33 62.1 GPA or about 580 L/ha.
Diagnosing coverage
Water sensitive paper, which turns from yellow to blue when contacted by moisture, was placed in the ginseng canopy. Two sets of papers were set out, with four papers in each set. The canopy was still wet with rain, which made placement difficult as the papers would accidentally contact water on the leaves and change colour prematurely.
Water-sensitive paper wrapped around tubes for panoramic coverage.
Position#1
Clipped face-down on the underside of leaves at the top of the canopy.
Position#2
Clipped face-up on the upper side of leaves in the middle of the canopy.
Position#3
Clipped face-down on the underside of leaves in the middle of the canopy.
Position#4
Wrapped around a plastic tube and threaded over a wire flag, located at the foot of the plant to give panoramic coverage at the root.
The sprayer passed over the canopy spraying water, and papers were carefully retrieved, allowed to dry and scanned.
Panoramic papers in situ.Flags mark the locations of papers.
Generally, there were no “misses” whatsoever. Position 1 showed excellent coverage, with no indication of run-off and a high droplet count with even distribution. This is ideal for foliar applications, and under-leaf coverage is notoriously difficult to achieve. Positions 2 through 4 showed excessive coverage, with the exception of one of the position 3 papers, which was still adequate.
Example of coverage and paper locations in canopy.
Next steps
Ideally, the operator would drop the pressure by 20 psi increments, reducing output until coverage failed. It is important to note that the operating pressure must never approach the lower end of the nozzle’s recommended pressure range, or the spray quality will be compromised and so will coverage.
Once the coverage is considered a failure, the operator would return to the lowest output that did a good job, and the sprayer is calibrated for that crop (at that stage of growth).
Note that the calibration must be performed for each significantly different crop. With the exception of an early-season drench intended to contact the entire root, an emerging one year old garden would need a very different prescription than a four year old garden with a fully-developed canopy. Plus, the weather conditions will affect coverage, so do not calibrate in conditions you would not normally spray in. Hot and dry and windy conditions produce very different coverage compared to cool, humid and still conditions.
Once the operator knows what each garden requires, they will be able to mix their tanks using the same concentration of carrier to formulated product as they normally use, but likely go further on the tank. It will take some practice before the operator knows how much spray mix is required to finish the job.
