Author: Jason Deveau

Spray Coverage in Carrot, Onion and Potato
This research was performed with Dennis Van Dyk (@Dennis_VanDyk), vegetable specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs.
Prior to 2017, Syngenta introduced the UK to the Defy 3D nozzle, which is a 100° flat fan, designed to run alternating 38° forward or backward along the boom. They prescribed a boom height of 50 to 75 cm, 30-40 psi, and travel speeds of 10 to 14 km/h in cereals and vegetables. Compared to a conventional flat fan, they claimed that the angle and Medium-Coarse droplets promise less drift and improved coverage.
In 2017, Hypro and John Deere began distributing the Defy 3D in North America. Our goal was to explore coverage from the 3D in vegetable crops. We compared the nozzle’s performance to common grower practices in onion, potato and carrot in the Holland Marsh area of Ontario.
Experiment
We used a technique called fluorimetry. A fluorescent dye (Rhodamine WT) was sprayed at 2 mL / L from a calibrated sprayer based on protocols generously provided by Dr. Tom Wolf.
Tissue samples from the top, middle and bottom of the canopy were collected from random plants.
The samples were rinsed with a volume of dH2O and this rinsate was then tested to determine how much dye was recovered.
The tissues collected were dried and weighed to normalize the samples to µL of dye per gram dry weight to allow for comparison.
In addition, we used water-sensitive paper as a check in key locations in the canopy to provide laminar and panoramic coverage. Papers were digitized and coverage determined as a percentage of the surface covered.
In carrot and onion, we compared a hollowcone, an air-induction flatfan, and alternating 03 3D’s at 500 L/ha (~40 cm boom height, ~3 km/h travel speed, ~27ºC, 3-9 km/h crosswind, ~65% RH).
In potato we compared the alternating 05 3D’s to a hollowcone at 200 L/ha (~55 cm boom height, ~10.5 km/h travel speed, ~22ºC, 6-8 km/h crosswind, ~65% RH).
Water-sensitive papers were originally intended as a coverage check, and not as a source of analysis, but their use revealed interesting information. The following images are the papers recovered a single pass in each crop.
Carrot
Onion
Potato
Results
The following table represents the percent coverage of these paper targets. Papers were digitized using a WordCard Pro business card scanner and analysis made using DepositScan software. This table is small, but you can zoom in for a quick comparison. The following three histograms show the same data graphically for carrot, onion and potato, respectively. Remember, this only represents a single pass, so don’t draw any conclusions about coverage yet.
Carrot
Onion
Potato
It was interesting to note differences in coverage observed on the papers versus the results of the fluorimetric analysis. It was anticipated that while water-sensitive paper serves for rough approximation of deposition, fluorimetry would be far more accurate. This is because of the droplet spread on the paper, and the evaporation and concentration of a spray droplet en route to the target. Again, here is a small table, and again, the next three histograms show the same data graphically for carrot, onion and potato, respectively.
Carrot
Onion
Potato
Observations
While water-sensitive paper is an excellent diagnostic tool for coverage, fluorimetry allows for greater resolution. The high variability in coverage meant little or no statistical significance, however the means suggested the following:
- In carrot, the 3D deposited more spray at the top of the canopy.
- In onion, the hollowcone spray had a higher average deposit, and penetrated more deeply into the canopy.
- In potato, the hollowcone deposited more spray at the top, with little or no difference mid-canopy.
Each nozzle performed well at the top of the canopy, which is quite easy to hit. Certainly they exceeded any threshold for pest control. With the possible exception of hollowcone in onion, nozzle choice had only minor impact on mid-bottom canopy coverage. And so, if coverage is not a factor for distinguishing between these nozzles, we should consider drift potential. Due to the comparably smaller droplet spray quality, the hollowcone is far more prone to off target movement. This leads us to select the AI flat fan or the 3D as the more drift-conscious alternatives.
Future analysis would benefit from a larger sample size to reduce variability, and the inclusion of an air-assist boom to better direct spray into the canopy.
Applitech Canada (Hypro / SHURflo) is gratefully acknowledged for the 3D nozzles. Thanks to Kevin D Vander Kooi (U of G Muck Crops Station) and Paul Lynch (Producer). Assistance from Will Short, Brittany Lacasse and Laura Riches is gratefully acknowledged. Research made possible through funding from Horticultural Crops Ontario.
November 6, 2017
The Vermorel Nozzle – Humility in the Face of History
It’s a rainy Friday in 2017 and I decided to deal with the articles, factsheets, manuals and other sprayer-related documents that have been piling up on my desk for a year.
My filing strategy is based on some advice I got from Dr. Bernard Panneton (Application Tech Guru) back in 2009. He said to read each document and then file them according to content, not by author or date. That way when I need something, I can search up the subject and find everything that might be relevant. More than 1,200 files later, the system works. No Dewey Decimals in my office, thank you.
What I’ve noticed as I sift through this eclectic pile of wisdom, is that many of the application methods I experiment with, or generally promote, are rarely entirely novel. Crop protection has evolved considerably (think pulse width modulation, crop sensing and remote piloted aerial application systems), but the fundamentals of spraying haven’t changed that much.
Case in point.
I just found a photocopy of a 1906 book called “Ginseng – It’s Cultivation, Harvesting, Marketing and Market Value, with a Short Account of Its History and Botany“. Great title. We obviously appreciated florid language in technical manuals 100 years ago. Here’s an excerpt that caught my eye:
“When applied to plants, the finest nozzle obtainable must be used. The Vermorel is perhaps the best. Now make no mistake: this spray must be a spray, not a dribble, nor a drizzle, nor a squirt, but a mist. It must look like a little fog at the end of the hose and must reach every part of the plant, particularly the undersides of the leaves, mind, just enough so it won’t trickle off.”
Poetry. And to make my point, it’s similar to what I’d tell a ginseng grower today. Granted, I’d lead them into a lower-range-of-Medium droplet size and help them achieve the described coverage using drop arms. But what on Earth is a “Vermorel nozzle”? That’s not one I have in my motley collection.
I turned to Virginia Tech’s Museum of Pest Management. I hope they’ll forgive me for lifting their content, but it’s too wonderful not to share. They note the contributions of Charles Valentine Riley. Born in London, England in 1843. He was a multi-talented Renaissance man. He was a pioneer of entomology in the United States and is often referred to as the founder of biological control in America.
Charles Valentine Riley
Two of his greatest contributions to pest management included founding the field of biological control and the invention of the Riley spray nozzle (1889). The Riley nozzle was sold as the Vermorel nozzle. It produced a fan pattern and was the primary nozzle used in pesticide application in the United States and Europe well into the 20th century. The auspicious Mr. Riley died in a bicycle accident in 1895.
The Vermorel nee Riley Nozzle
It was Riley’s nozzle, and the invention of some other early European pesticide application devices, that inspired W.B. Alwood (publisher of orchard spraying techniques c.1899) to import these devices and adopt them to Virginia conditions. The rest is history.
I tell you this because of what I found beneath the book touting the Vermorel; A 2015 TeeJet brochure for their TXVK hollow cone nozzles. I’m aware that the engineering behind the TXVK molded poly body and ceramic orifice is considerable compared to the humble Vermoral. But on closer inspection the fundamental designs aren’t so different. That realization both surprised and pleased me and compelled me to write this article.
I’m not certain what my point is. I suppose it’s just good to be reminded that the next time you want to invest time, money and effort into a “new idea” you might consider a little historical research. Odds are, you’re not the first person to recognize the problem, or propose a solution. A little time in the archives also instills respect for those that were there first. Let’s not waste time repeating their efforts, but stand on their shoulders and advance what they’ve already pioneered.
And if anyone has one of Riley’s Vermorel nozzles, I’d love to add it to my collection. Drop me a line.
August 23, 2017
Should Backpack Sprayers be Used to Test Airblast Products? – Part 2
In Part One of this article, we showed that approximately 40% of minor use label expansions and registrant submissions rely on data from hand booms and guns. We also showed that a hydraulic backpack or knapsack will not give the same coverage as an airblast sprayer, and we concluded by suggesting that small plot researchers use spray equipment that reflects grower practices.
Unfortunately, practical logistics prevent most researchers from using a full-size airblast sprayer. They may not have access to such a sprayer, and if they do, it takes considerable time to mix and clean between treatments. Further, treatments are often only a single row, or even a single plant. It takes too much pesticide, too much time, and too much plot space to justify using a full-sized airblast sprayer, even if the relevance of the results are questionable.
Would another method of application better emulate an airblast application but retain the convenience of a hand boom or gun?
The motorized backpack mistblower
Using the same methods used to compare airblast to hand boom spray coverage in the previous article, we compared airblast sprayer coverage to that of a motorized backpack mistblower in grape, raspberry and peach (July, 2013). Once again, coverage was analyzed as overall percent coverage (see first graph) and droplet density (average droplets per square centimeter – see second graph).
Comparison of average % coverage in peach, raspberry and grape using a mistblower and air blast sprayer emitting he same volume
Comparison of droplets per square centimetre in peach, raspberry and grape using a mistblower and air blast sprayer emitting the same volume
Results and Observations
The mistblower met, or in the case of droplet density, exceeded the coverage obtained using an air blast sprayer in most crops. The results led to a few observations:
- The significantly-higher droplet density is a function of the Finer spray quality produced by the mistblower (see water sensitive papers below). This may still represent a confound between small plot work and large scale airblast applications.
- Drift between proximal treatments may be an issue given how far the mist was blown. This should be considered when planning plots.
- While not shown here, spray coverage was more consistent throughout each canopy, of each crop, when using the mistblower. This is likely because the operator was able to aim the output as they swept the spray over the canopy, thereby ensuring all surfaces were hit from multiple angles.
- While we always try to be brand-neutral, it should be noted that we’ve used multiple Solo mistblowers over the years, and all of them required significant maintenance (no matter how they were cleaned and stored). It was very difficult to find brand parts and repair expertise in Ontario. The Stihl brand currently has far more dealers, and more accessible parts, and has not caused us any difficulties (yet).
- Always use the highest grade gasoline in two-stroke engines to avoid ethanol gumming up the carburetors!
- Always calibrate mistblowers by volume because raising and lowering the boom will affect the flow rate.
Conclusion
Hand booms, and likely hand guns, are not appropriate for testing agrichemical products intended for use with an airblast sprayer. Data derived from these methods should be questioned. An airblast sprayer is the best choice for any such research, but a mistblower is a viable alternative. Transparent, standardized operating protocols for testing products intended for use in airblast sprayers should be required.
Thanks to Vaughan Agricultural Research Services Ltd. for their assistance in the research performed for this article.
March 27, 2017
Should Backpack Sprayers be Used to Test Airblast Products? – Part 1
Peer-reviewed journal publications claim there is a significant difference in spray coverage and deposition patterns when an agrichemical product is applied using an airblast sprayer versus a hydraulic hand boom. An airblast sprayer creates Fine droplets that shear in entraining air and are carried into a plant canopy. Properly calibrated, the air opens the canopy to expose all target surfaces to the spray. By comparison, a hand boom relies on pressure to propel fine droplets into a canopy, and while there is some air-entrainment surrounding the spray, it cannot travel as far or displace as much canopy. As a result, most of it impacts on the outer surfaces of the canopy.
Knowing this, it is surprising that so many products intended for use with airblast sprayers are applied by researchers and consultants using hand booms or the high-pressure arborist-style handgun (see ‘Survey of Submissions’).
Survey of Submissions
This graph represents a random selection of 150 minor use label expansion studies and registrant submissions from Canada and the USA spanning 1990 to 2011. It shows the application method by crop.
In 2012, we performed some research with the following goals:
- To demonstrate the difference between spray deposition and coverage when using a hand boom versus an airblast sprayer.
- To create a sound basis for questioning and potentially improving how agrichemical products for orchard, bush, and vine are tested in Canada.
Using water-sensitive paper to diagnose spray coverage, airblast sprayer application was compared to hand boom application in highbush blueberry, apple and grape.
Target locations in highbush blueberry.
Target locations in apple.
Target locations in grape panel.
Sprayers were calibrated to emit the same volume per planted area via hollow-cone nozzles. Volumes selected were based on typical application volumes for Pristine or Captan (commonly sprayed in Canada). While there is no standardized protocol (and there should be) we followed typical practices of 500L/ha for grapes, blueberry and apples until plant growth warrants higher carrier volumes. At that point, many researchers go up to 1,000 L/ha. Coverage was quantified by collecting and digitally scanning water-sensitive papers to calculate overall percent coverage (see graph) and droplet density (average droplets per square centimeter – see graph).
Overall percent coverage
Droplet density
Conclusion
In all cases, airblast applications deposit > %50 more spray than a hand boom. In the case of grape, you’ll note there are three bars. This is because spraying 1,000 L/ha with the airblast sprayer drenched the targets (it was late in the season and the canopy was sparse), making it impossible to discern droplet density. When we reduced the output to 375 L/ha, we were able to register droplet density, which was still significantly higher than that produced by the hand boom at 1,000 L/ha. This raises significant questions about the validity of efficacy and residue studies performed with hand booms when growers apply the same products using airblast sprayers.
When this data was shared at extension conferences, it was sometimes noted that many researchers choose to spray the target until it is drenched, ensuring the dose administered to the crop reflects what was intended. This does not, however, invalidate the fact that a growers spray equipment and practices are significantly different, and the dose and spray distribution they achieve will not reflect the original research.
The recommendation is that researchers use the same equipment to test products as the growers use to apply them. But, recognizing the difficulties associated with performing small plot experiments with full-sized airblast sprayers, an alternative is needed. That topic will be addressed in part two of this article.
Horticultural Crops Ontario, the grower co-operators and former OMAFRA summer student Carly Decker are gratefully acknowledged for making this research possible.
March 22, 2017
Canopy Management for Improved Airblast Coverage
Managing the canopy of any perennial crop (e.g. pruning, hedging, leaf stripping, etc.) is an important consideration. The benefits are manifold: It affects the health of the plant, the quantity and the quality of the yield. It allows light and air to circulate and it keeps the crop manageable. From the perspective of an airblast sprayer operator, the reason for canopy management is quite simple:
If you can’t see it, odds are you can’t spray it.
Picture this: It’s late April, and an apple grower and I are calibrating his sprayer. We achieve excellent spray coverage in the target block, shake hands and part ways. In late May I get a phone call from the grower. I assume it’s time to adjust his settings to match the growing canopy, but no… he had called to say he suspected apple scab in one of his blocks. Since I was the last person to adjust his sprayer, the unspoken implication was that I’d better come fix matters.
As I drove back out to his orchard, I considered what the problem might be:
- Bad product choice?
- Poor application timing?
- Spraying in inclement weather?
- Cutting rates?
- Resistance? (a long shot)
Maybe it was ego, but I couldn’t believe it would be the calibration. We left ample volume to provide sufficient coverage to get the grower to petal fall. We ensured the spray swath was higher than top of the tallest tree, accounting for wind and an uneven alley. We did everything right to match the sprayer to the canopy and leave enough buffer to get to petal fall.
When I arrived, he took me to a block I hadn’t seen before. We didn’t calibrate the sprayer to match this particular group of trees, but he figured since they were about the same height, the sprayer would do its job. It was immediately obvious to me what the problem was, but I knew if I simply told him outright, the lesson might not stick. And so, with respect to that old proverb, I taught him to fish rather than give him one. We spent the next few hours trying to fix our alleged calibration problem by exploring:
- Slower ground speed
- Higher fan gear
- Higher rpms to increase fan speed
- Changes to deflector settings
- Air induction nozzles in top positions
- Higher sprayer output
Of course, none of these adjustments had any great impact on coverage because the problem was that the alley had grown so tight that branches were brushing the cab of the tractor (see picture).
If the canopy is brushing against the tractor, it may intercept spray before it expands fully. Essentially, it temporarily blocks nozzles.
Closed canopies and tight alleys will almost always compromise spray coverage.
The canopy was so dense you couldn’t see the trunk! I asked the grower to move the sprayer down the row to a tree I saw that was far less dense that the others. We returned the sprayer to our original calibration settings and achieved excellent coverage once again. The only solution was to prune the trees, and once his workers did this, coverage improved considerably. An airblast sprayer can only do so much. Sometimes it comes down to canopy management.
An orchardist taught me this trick: If you want to know if spray will penetrate a canopy, you should be able to see the trunk.
An orchardist taught me this trick: If you want to know if spray will penetrate a canopy, you should be able to see sunlight through the shadow at high noon.
Row Spacing in Specialty Crops
Canopy management isn’t just an orchard issue. For high bush blueberry crops, coverage problems may stem from insufficient pruning. How can spray reach the lower, inner portion of a mature bush to control spotted-wing drosophila if the canopy is too thick?
Sometimes it’s not the canopy, but the plant and/or row spacing. Many nurseries arrange container crops, shrubs, whips and cedars as tightly as possible. This may optimize how many plants will fit on a given area, but it compromises sprayer access (due to the reduced number of alleys) and may cause plants to block one another from the spray. Nursery sprayer operators often use cannon sprayers to throw spray over and through all those rows of plants, but cannon sprayers produce excessive coverage at the beginning of the swath and increasingly erratic coverage as a function of distance.
A cannon sprayer attempting five rows of cedars. This sprayer will eventually spray in from the other side, but experience has shown that coverage will be compromised in the centre rows and excessive in the outer rows. Spraying multiple rows may save time, but coverage is almost always erratic.
Calibrating a cannon sprayer can greatly improve coverage consistency. Before calibration (above) the sprayer was equipped with full cone nozzles in the upper boom positions and excessive air was employed in an attempt to force spray through the canopy. Although the sprayer would eventually pass down the far side of the five rows, only the water-sensitive papers in the tops of the trees indicated suitable coverage, and a great deal of spray simply blew away. After calibration (below) considerably less air and spray was used, and coverage on water-sensitive papers placed lower in the trees and facing the sprayer was more consistent. Remember, the sprayer would eventually pass down the far side, resulting in similar coverage on the remaining papers. Don’t bite off more than your cannon sprayer can chew – the further spray travels from the sprayer, the harder it is to achieve consistent coverage.
Coverage can be improved by reducing the distance the spray has to travel (i.e. leaving more alleys and reducing the density of planted rows).
A Jacto cannon sprayer in a nursery. Many nursery and berry operations elect to spray multiple rows in one pass, but be aware that spray coverage suffers the farther away from the sprayer it goes. Independent research has shown that coverage is not reliable at half the distance typically claimed by many cannon sprayer manufacturers. This is a function of canopy density and weather. Always confirm coverage with water-sensitive paper. Photo Credit – M. Lanthier, British Columbia.
The results of a cannon sprayer calibration in a container crop nursery. The cannon sprayed 1,000 L/ha and tried to cover too many rows in a pass. The water-sensitive paper showed insufficient and inconsistent coverage. When it was recalibrated to spray 550 L/ha, but drive more rows, the water-sensitive paper showed considerable improvement.
I also suspect that staggering plant spacing from row to row to reduce mutual shading might allow spray to penetrate more easily. As I write this, we’re planning to explore this concept in cedars.
This is speculative, but the when nursery shrubs, trees and container crops are planted in perfect grids, mutual shading probably prevents spray from penetrating deeply into the planting. By staggering the spacing, spray may be able to penetrate more easily between rows. This can be accomplished without reducing the number of plants per hectare significantly.
In the end, try to see the spray target from the droplet’s point of view. If you can easily see where you want the spray to go, you’ll do well. If you can’t see the target, it’s far more challenging.
February 20, 2017