Author: Jason Deveau

  • Spray Equipment From the 2016 Great Lakes EXPO

    Spray Equipment From the 2016 Great Lakes EXPO

    Michigan’s Great Lakes EXPO is a massive horticultural convention that draws international speakers and more than 4,000 attendees to Grand Rapids every December. Like any large agricultural conference, it can be challenging to run back and forth between lecture rooms to hear key presentations. And, of course, there is always disappointment when you have to choose between two talks in concurrent sessions. When your head is full and your posterior is numb, you move onto the trade show floor.

    I think the trade show might be my favourite part; Who doesn’t like filling a bag with swag? Candies, foam vegetables, pens, DVD’s, colourful brochures and all manner of gimmicks designed to get your attention in a sea of vendors that vie for “just a minute of your time”. But for me, I only have eyes for the sprayers. And wow, were there a lot of sprayers at GLEXPO.

    This article is a photo journal of those sprayers (or features) that caught my eye. For some readers, these features might be old news, but for me they were insight into a different way of spraying. For example, Europe’s tolerance for spray drift is practically nil, and sprayer manufacturers have had to develop equipment that comply with that reality. Many such sprayers were present, so I had a chance to see, and ask questions, about their claims of less than 5% drift. At the other end of the spectrum, there were sprayers that proudly boasted being able to cover multiple rows in a single pass by boiling the spray over great distances… which while appealing to producers looking to save time, still makes me wince. But then, I’ve never tried to spray almonds in California, or citrus in Florida. Then there were sprayers claiming to cover multitple rows and reduce drift, which would be quite a trick. I reserve the right to be a skeptic.

    So, I’m not promoting or condoning any of the equipment or claims described here. I’m just sharing what I found interesting and I’m giving the reader a peek onto a trade show floor they might not otherwise have seen.

    Shrouded Herbicide Application

    There are lots of approaches to making in-row or under-row herbicide applications. The concept is simple enough: You want to get the product on the ground either under or between rows without hitting the crop itself. If you don’t care about hitting a mature orchard trunk, the boomless nozzle is a good choice with it’s massive droplets and variable swath. But if you want to avoid off-target movement as much as possible, you need shrouds.

    I’ve seen brushes used to great effect in asparagus because they match the contour of moderately uneven ground by dragging over it. Gaps may open in the shroud as the bristles part, but that issue may be offset by the possible advantage of physical redistribution of herbicide as it rubs over the target weeds like a weed-wicker.

    Then there’s the classic flexible curtain. Similar to the brushes, it’s intended to “just” touch the ground and should maintain a reasonable seal even if said ground is moderately uneven. I often wonder how difficult it is to clean all the surfaces on these systems, but since they are only ever used with herbicide, I won’t speculate how often operators actually decontaminate (or even rinse) them.

    Other variations include a hard carapace with no contouring lip. They should only be used with Coarse spray qualities or larger. Note the hefty spring on the boom for those inattentive moments where the operator might whack a trunk or fence post. The wing flexes away from the impact and snaps back into position, giving the operator time to put  down the cell phone and tweak the steering wheel. The adjustable nozzle body on the far end is a nice feature for adjusting the swath without changing nozzle spacing, but beware to maintain proper overlap.

    And, if you want the heartiness of a solid carapace, wouldn’t it be nice to be able to see through it so you can spot a plugged nozzle before it becomes a problem? This variation with its heavy impact bar, tight nozzle spacing (to reduce the potential for misses) and guide wheel (to maintain correct boom height) looks ready to handle anything.

    Airblast – Multi-Row, Ducted Systems

    In the never-ending quest to do more in less time, multi-row airblast systems are very appealing. Delivering air to the vertical booms in each row can be challenging. I’ve seen suspended axial fans (e.g. Gregoire, not pictured) but they’ve always struck me as overkill because of the volume and speed of the air they deliver, and because they need fairly wide rows to be accommodated. Their weight is also a concern, requiring scaffolding that must be strong and still somewhat flexible to handle the inevitable pitch and yaw translated from uneven ground to the boom.

    Lightweight conduits that channel air through ducts (like the Berthoud sprayer below) are a popular solution. They can be suspended to any length and telescope to any row width. Head pressure, and friction from sharp bends in the ducts can influence the air delivered, so the shorter the ducts and the less bends, the better. It was a surprise to discover the ducts in this sprayer are corrugated inside as well as out, but apparently it’s not enough to disrupt air flow significantly.

    This Berthoud sprayer offers many of the optional features I’ve seen on the Hol sprayer (not pictured) such as tandem axles, a hand wash tank, low residual volume tank, and built-in boom and tank rinse systems. What’s interesting is the light weight “Drop Legs” (i.e. the vertical booms) with dual-angled “airmist diffusers” (i.e. the air shear nozzles) for multi-row vineyard applications. The close-up below uses my hand for reference. There are options for two to four diffusers on each drop leg, and they can be single or double sided, giving a lot of flexibility to match the crop.

    How do you control flow? With a digital flow regulator. What if you want a different rate at each diffuser? Well, if I understand this correctly, instead of using a typical flow-metering disk placed in-line to restrict flow, you slot a conventional moulded hollowcone inline and use the nozzle manufacturer’s flow tables. And what if you are concerned about using a misting air-shear style nozzle? It appears they also offer an option to swap out the diffusers for air assisted swirl nozzles where the air flow is behind the nozzle to entrain the spray and limit dispersion. They look similar to the diffusers, except they have a nozzle cap between the slotted air outlets (not pictured).

    Ducted air handling comes in many shapes and sizes. Rather than terminating in a blade-shaped diffuser, Cima has hourglass shaped distribution heads that use the venturi principle to deliver airspeeds up to 180 mph at the nozzle. That’s fast, and while it would help entrain spray as it travels longer distances, I wonder what it does to crops close-up?

    In the centre of each head is the teardrop-shaped atomizer-style nozzle that produces a Very Fine spray quality between 100 and 150 µm in diameter. It was explained that the teardrop employs Bernoulli’s principle… and for the lay reader (like me), think of the teardrop the way you think of an airplane wing. Air moves over the contour at different rates, making a low pressure area at the tip. The upshot is that it creates lots of very small droplets that (according to the manufacturer) permit you to use much lower volumes that you would with an airblast sprayer using conventional hydraulic nozzles. As always, I suggest you let coverage be your guide to spray volume.

    Flow is controlled by an inline disc that allow the user to select from a series of flow-restricting orifices. Look back two photos and you’ll see them as yellow circles on the tower. The photo below is a stainless steel version from an AgTec.

    Air-Assist Horizontal Booms

    A ducted, vertical airblast sprayer is an air-assisted horizontal boom sprayer just waiting to happen. For vegetable and berry growers, air assisted spraying is an appealing prospect. Many still use axial airblast or cannon sprayers to spray row crops, but I don’t like that. It’s my opinion that while it may be effective, it’s not efficient because it’s not possible to consistently control drift or coverage. I prefer getting the air and nozzle closer to the crop, but sprayers that can do this are few and far between.

    There have been no after-market options I’m aware of for converting a horizontal boom to an air-assisted boom. That leaves only a few manufacturers of trailed boom sprayers to fill the need (e.g. the trailed Hardi Commander with Twinforce air or their new self-propelled Alpha evo). But this tradeshow opened other possibilities, as demonstrated by the Cima below. It uses all the same principles described above… it just aims down.

    Not interested in ducted air delivery on a three-point hitch system from France or Italy? No problem. How about a Florida company called Airtec that offers trailed air-assist booms up to 120 ft. I wasn’t able to photograph the sprayer at the show, so here’s a picture of one in the field (from their website), as well as several I took at a spinach operation in Ontario.

    Airtec offers a single axle, or a walking beam tandem axle reminiscent of the Argifac Condor. Note that the boom itself is the air conduit, which should open crop canopies, expose underleaf surfaces, entrain smaller droplets to reduce drift, and extend the spray window by allowing the operator to work in slightly windier conditions. I can’t speak to the manufacturer’s claims of reducing spray volumes (and by extension, chemicals), but you can read it on their glossy brochure.

    Each air outlet terminates in an hourglass-shaped duct, similar to the Cima and ostensibly creating the same advantage, as they also claim 180 mph windspeed at the nozzle. Again, I wonder if that can be dialed back, or adjusted to match the density of the crop canopy? Unlike the Cima teardrop shear nozzle, conventional hollowcone nozzles are used (see below). They can also be suspended to match the contour of the row (look back at the first photo) improving coverage in a manner similar to using drop arms or row kits.

    Airblast – Unconventional Fans

    Have you seen this man? Mark Ledebuhr is the co-author of the 2nd edition of Airblast101. He looks happy here… little did he know I’d one day lasso him into writing the new edition with me.

    Let’s get back to airblast sprayers. The majority do not use ducts to convey air to the target – they point and blow. Pictured below is the generous Mark Ledebuhr with a Proptec rotary atomizer. I call him generous because for several hours Mark led me through the tradeshow and introduced me to many of the vendors. Perhaps more importantly, he helped me interpret what they were explaining after we left each display. Developed with his father, the Proptec system suspends individual fans with rotary atomizers so each can be aimed and operated independently, offering a lot of targeting flexibility. The fans can be electrically or hydraulically driven. Some might be reminded of a Sardi fan (not pictured) but unlike that system which uses several conventional nozzles around the circumference of the fan, Proptec employs a rotary atomizer in the centre. Rotary atomizers can produce very, very small droplets and until GLEXPO I was only familiar with their use in aerial applications.

    I admit to a bias when it comes to airblast sprayers. In my mind, the further away the source of air and spray are from the target, the more opportunity there is to drift. Particularly when such small droplets are involved. I couldn’t find the Proptec video I saw looping at the tradeshow, but what I saw looked like tight columns of cycling spray, reminiscent of a tornado, firing into each row of a vineyard. I was told it was during a 15 mph wind, yet I didn’t see a lot of off target movement. A notable advantage to spraying down into the ground rather than sideways or up into the air. Here’s a good video I found of one operating in highbush blueberry (below). It seems I have a lot more to learn about this system.

    Then Mark and I went over to see Michigan-based Precise Manufacturing’s EX III cross-flow rotary atomizing tower system. I was reminded of the Curtec tangential fan towers that, like this sprayer, employ rotary atomizers and a peristaltic pump. For Curtec, it’s the AccuStaltic pump. For Precise, it’s the Extreme pump. More on that shortly.

    Here’s a video of the EX III operating (sourced from the Precise Mfg. website). Obviously, we’re not talking grapes, berries or high-density orchards, here. This is for big, dense targets like standard cherry, nut trees and citrus. The rotary atomizers throw spray in a circle, but the air from the tangential fans capture it and blow it all out towards the target in very laminar (i.e. not turbulent) air that carries it over long distances to the target.

    Back to the peristaltic pump. It can run dry, is self-priming, is anti-backflow, low maintenance and can handle pretty much any manner of spray mix (i.e. viscosity and corrosion are non-issues). Each atomizer has its own flow channel, and by changing the diameter of each tube you change the relative flow rate to each atomizer. Certainly not something you’d do every  day, but it does allow you to match flow to the canopy density.

    The Precise Touch Screen Controller is very intuitive and I liked how much control the operator has. Fan speed can be adjusted quite easily (although it would require a very knowledgeable operator to ensure the correct speed is selected). It tracks GPS position and logs where the sprayer empties and the rates used per acre. It also calculates a kind of tree-row volume by determining savings when the operator turns off nozzles that would otherwise blow over the tops of targets, or when overall flow is reduced by slowing the rpms of the pump.

    Airblast – Cannons

    Well, there were lots of cannon sprayers. Most airblast manufacturers have one in their lineup. Squirrel-cage style fans feed air into a tower that allows spray to come out laterally, and on a downward angle from the top of the sprayer. AgTec, pictured below, has long sold such a sprayer.

    The nozzles are air-shear style, relying on fast-moving air to shear the spray into finer droplets.

    They usually only have nozzles on one side and the cannon can be turned via a chain-driven gear, and aimed up or down from the cab. They are intended to spray larger areas to save the grower traveling every row, and to prevent physical damage to the crop as the sprayer passes (I’m thinking about knocking berries off, mostly).

    Nurseries use cannon sprayers quite often because they spray whips (i.e. young trees), shrubs, container crops, and all manner of crops in dense plantings and they try to spray them all with a single sprayer. Generally, there’s a lot of drift potential and erratic coverage from cannon sprayers – especially when operators try to cover too much ground in a single pass. I’m always skeptical when I can’t adjust air settings without impacting spray quality, and considering the bad practice of trying to apply too wide a swath, I have a hard time with cannon sprayers. I will note that the AgTec now has baffles that allow the operator to distribute air over the height of the tower (see the hand near the hydraulic piston in the image below). However, I don’t know what that does to spray quality in each section of the tower.

    Airblast – Classic Axial Fans

    And, of course, there were many classic axial airblast sprayers. Even then, however, there were features to set them apart from one another. British Columbia’s Slimline TurboMist was there, featuring their turbine fans and adjustable air outlets (not pictured). Italy’s Carrarospray was there, and I’ve written about them in the past because they make a tiny sprayer that I like in cane fruit and highbush blueberry. You can hitch it to a mower and mow while you blow.

    More interesting to me was their sprayer boasting two axial fans that run counter to one another. Carrarospray claims this counter-rotation creates more uniform air than a single fan… but I have no idea how.

    Then there was the Andreoli Eco with it’s stainless steel high-efficiency vane system. Reminding me of the Turbomist, the suction is in the front, so the sprayer is a little less likely to draw spray into the fan when one side is shut down for border spraying and when turning at the end of a row. Louvers covering the outlets would be better, but still, this is an improvement. They also claim to have a symmetrical airflow pattern, unlike older axial fans that move air up on one side and down on the other.

    The Rears Pul-Tank reminded me of just that – a tank! Heavy-duty, stainless construction and intended (with care) to last a long, long time. No special features to boast of. It would seem this sprayer adheres to old-school ideas about airblast spraying. Certainly, simple and strong are two appealing features to those operators that don’t want to be bothered with complications.

    And, lastly (not leastly), was the Air-O-Fan sprayer. Another solidly-built sprayer with a few interesting features. Not shown is the reverse-style propeller which like the Andreoli Eco, claims to draw from clean air, and not spray-laden air. This is undoubtedly the biggest trash guard I’ve ever seen to protect the fan blades from drawing in dirt and leaves (see below). Looks like a CAT steam shovel.

    Something that struck me was the air deflector blades inside the fan housing. In my experience, the nozzle bodies and blades are two separate components. But not here, and it makes so much sense! I’ve always taught operators to adjust the air speed/volume and direction first, then adjust nozzle direction and rates second. With this system, you aim the nozzles right along with the air. Expanded systems (e.g. for tree nut, citrus) can have as many as three nozzles per deflector blade.

    There was one other very exciting feature coming to this sprayer that I promised I wouldn’t reveal until they were ready, but I’ll just write “HVES” so you will remember you heard it here, first!

    Closing

    So, this was a massive, sprawling article. Congratulations for getting to the end and I hope it opens your mind to the possibilities for horticultural spray application. The GLEXPO tradeshow was a great experience and I’ll try to get back there in the future. Until then, I look forward to bringing some of this equipment to Ontario to try it out in our horticulture operations. There’s always more to learn.

  • How to evaluate airblast coverage

    How to evaluate airblast coverage

    Note: While there’s nothing wrong with this article, a more recent article on this subject can be found here.

    It’s nearing the end of a long morning of spraying and you just want to get it done. As the tank empties and you watch the last of the spray cloud waft through the row, you’re thinking about rinsing out and moving on… but did the spray land where you wanted?

    How do you really know if you hit the target?

    Maybe you’re content with the occasional “shoulder checks” you made from the cab while spraying. Perhaps you stop at the end of the row and get out of the tractor to look for wet foliage during.
    Maybe you plan to return once the product is dry and look for white residue.

    Taken with the sprayer operator’s smart phone, here’s the over-the-shoulder view of an early-morning spray application from the cab. You can’t see coverage, but gaps in the spray will show if nozzles are plugged. You can also check to see if you are overshooting or blowing through the target. Photo Credit – C. Hedges, ON.
    This early morning “shoulder check” was photographed by the operator using his smartphone.  You can’t see coverage, but gaps in the spray will show if nozzles are plugged. You can also check to see if you are overshooting or blowing through the target. Photo Credit – C. Hedges, ON.

    These are all good feedback practices, but a more accurate method is the use of water-sensitive paper, which turns from yellow to blue wherever spray touches it. You can easily see the distribution of the spray and the overall area covered, and it can be quantified so you can compare one sprayer set-up to another, or see the impact of weather, or even the effects of nozzle choice, pressure and  water volume.

    Water- (and oil-) sensitive paper: Cheap, simple and available on-line or in person from your favourite sprayer equipment store.
    Water- (and oil-) sensitive paper: Cheap, simple and available on-line or in person from your favourite sprayer equipment store.

    Draw a map

    Begin by creating a simple drawing of the tree, cane, bush,vine, etc. you wish to spray. Label the drawing with unique numbers that correspond to where you are going to place the papers. Write the numbers on the back of each paper so you can see where they came from after they are collected. You should also note the pass number, so you can differentiate between each sprayer setup and corresponding pass. You might make a change and want to see how it affects coverage, and it’s very easy to mix up the papers if you haven’t record everything clearly. Plan to do this for at least two plants upwind from the sprayer to ensure you will get an accurate representation of average coverage. Be sure to wear disposable gloves and avoid dew so the papers don’t react prematurely.

    Create a simple drawing of the target. Number positions on the drawing that correspond to where you plan to place the papers.
    Create a simple drawing of the target. Number positions on the drawing that correspond to where you plan to place the papers.

    Distribute the papers

    It is critical to distribute the papers evenly throughout each target canopy. They should be placed in key locations where pest damage has been an issue in the past (e.g. scab at the top of a tree, or spotted-wing drosophila at the bottom-centre of highbush blueberry), or anywhere coverage is notoriously difficult. Our preference is to place them at the top, centre and bottom of a tree canopy as well as laterally from the outer edge of the canopy beside the sprayer moving in towards the trunk.

    Number positions on the drawing that correspond to where you plan to place the papers. Label the papers as well so you know where they came from. Consider writing the pass number and the position (e.g. 1-1 would be Pass 1, Position 1) so you can evaluate the changes to the sprayer settings from pass to pass. (Figure 60) Later, all the information from the calibration can be entered into your spray records, like in this example.
    Number positions on the drawing that correspond to where you plan to place the papers. Label the papers as well so you know where they came from. Consider writing the pass number and the position (e.g. 1-1 would be Pass 1, Position 1) so you can evaluate the changes to the sprayer settings from pass to pass. Later, all the information from the calibration can be entered into your spray records, like in this mock-up.

    We use spring-back paper clips attached to alligator clips at 90 degrees to attach the papers to small branches. You can also staple them to the upper or lower face of the leaves (as long as they don’t cause leaf to droop). You can wrap them around stems for panoramic coverage or to monitor drenches. They can be stapled the trunk to show if spray is aimed into the canopy or being wasted. You can even skewer to the ground using wire flags to to illustrate poor lower-nozzle positioning and/or canopy run-off. Put them wherever you want to know about spray coverage!

    This home-made double-ended alligator clip holds papers at right angles. One end for the paper, the other end to a twig or wire flag.
    This home-made double-ended alligator clip holds papers at right angles. One end for the paper, the other end to a twig or wire flag.

    We typically orient them facing the alleys so their sensitive faces are square to the sprayer as it passes. We often use two in each location, oriented back-to-back facing each alley so you can resolve coverage from both sides. The important part is to ensure you are consistent. Mark the location in the canopy with some colourful flagging tape so you can find the papers after you spray, and if you wish to replace them with fresh papers to evaluate another pass, orient them the same way to make the comparison fair.

    Water-sensitive papers located in five positions in an Empire apple tree. Two papers were pinned back-to-back in each position, distributed evenly throughout the canopy, facing the alleys. One paper was located at the lowest branch to determine if the lowest nozzle position needed to be on. Another paper was pinned to the ground face-up under the tree to show any excessive waste. Be creative, but be consistent from pass to pass.
    Water-sensitive papers located in five positions in an Empire apple tree. Two papers were pinned back-to-back in each position, distributed evenly throughout the canopy, facing the alleys. One paper was located at the lowest branch to determine if the lowest nozzle position needed to be on. Another paper was pinned to the ground face-up under the tree to show any excessive waste. Be consistent from pass to pass.

    Spray, check and spray again

    Once the papers are in place, pass by on one side with both booms open (as you would normally spray). Be sure to start spraying well before passing the target, and keep spraying afterwards to ensure the resultant coverage represents an actual application. It is very informative to get out of the cab and examine the papers before passing by on the other side. You can learn a lot about how the wind is affecting the spay.

    Once papers are in place, pass by spraying with both booms open to emulate a typical spray day. Be sure to start spraying well before passing the target, and keep spraying afterwards to ensure the resultant coverage represents an actual application. It can be very informative to examine coverage at this point to see how wind is affecting the spray. Then, pass by on the other side to complete the application.
    Once papers are in place, pass by spraying with both booms open to emulate a typical spray day. Be sure to start spraying well before passing the target, and keep spraying afterwards to ensure the resultant coverage represents an actual application. It can be very informative to examine coverage at this point to see how wind is affecting the spray. Then, pass by on the other side to complete the application.
    An example of the coverage obtained on water-sensitive papers placed throughout an apple tree canopy, and on the ground beneath it.
    An example of the coverage obtained on water-sensitive papers placed throughout an apple tree canopy, and on the ground beneath it.

    Interpret the patterns

    You might notice the outer portions of larger canopies receive more spray than the inside. This is hardly surprising given that spray must pass through the outside to get to the inside. As a result, inner papers often receive proportionally less spray and should be the basis for determining if you have sufficient spray coverage. This is also why the label recommendation of “spraying to the point of runoff” is unhelpful: the outer portion of wide, dense canopies often begin to drip before the inner portion receives sufficient coverage. Further, how do you spray to the point of runoff? How do you know when to stop before it’s too late? Label language can be frustrating…

    When water-sensitive paper is sprayed to the point of run-off, the blue dye will drip. This is fine for a drench (dilute) application, but excessive for a typical concentrated application like foliar fungicides and insecticides.
    When water-sensitive paper is sprayed to the point of run-off, the blue dye will drip. This is fine for a drench (dilute) application, but excessive for a typical concentrated application like foliar fungicides and insecticides.

    When assessing coverage, don’t follow the droplet counts in the small guide that comes with the paper sensitive paper kit – they haven’t been updated for a very long time and are more appropriate for field crop applications – not airblast applications. Research and experience suggest that 85 discrete fine/medium-sized droplets per square centimetre and a total coverage of 10-15% should be sufficient for most foliar insecticides and fungicides. Remember, this is only a suggested threshold and in the case of coarser sprays, focus more on even distribution and the 10-15% coverage.

    It’s debatable, but 85 fine/medium-sized drops per square centimetre and about 10-15% total surface covered represents adequate airblast spray coverage for most foliar applications. It is less applicable for applications made with very coarse droplets, because there are fewer of them and they generally cover more area. In this case, focus more on the even distribution of spray and the 10-15% coverage. The extreme example of this is a drench (dilute) application of oil where total saturation is the goal.
    It’s debatable, but 85 Fine/Medium-sized drops per square centimetre and about 15% total surface covered on a minimum 80% of all papers represents adequate airblast spray coverage for most foliar applications. It is less applicable for applications made with Coarse/Very Coarse droplets, because there are fewer of them and they generally cover more area. In this case, focus more on the even distribution of spray and the 15% coverage. An extreme example of this is a drench (dilute) application of oil where total saturation is the goal. Conversely, ultra-low volume applications employ Very Fine droplets and a better metric is uniform, high droplet density rather than area covered.

    Make a change and try again

    There’s no easy way to define a threshold between sufficient and insufficient spray coverage. When you retrieve and examine the papers, think about how the product is intended to work: “Is it a contact, trans-laminar or locally systemic pesticide? What are the odds that an insect or spore will come in contact with residue? Will I be spraying again soon (e.g. fungicide) and will the spray already on the leaves have residual activity?” Regarding that last thought, protectant fungicide applications are often layered, so what one spray misses, the next will catch. Quite often, “sufficient coverage” is less than most sprayer operators think.

    If you are content with the coverage, record your sprayer settings to use them again in that block (in similar weather, and assuming the crop canopy doesn’t change significantly before the next spray day). If you are not content, make a change to the sprayer to improve matters, reset the papers, and go again. It can take time and some effort to get it right, but improved coverage and reduced waste are ample financial reward for your efforts.

    Other methods of evaluating coverage

    It should be noted that while water-sensitive paper is versatile, cheap and easy to use, it has its shortcomings. Placement and orientation of the paper is very important; it’s easy to hit papers on the outside of the canopy with the sensitive-side facing the sprayer. It’s considerably harder when they are at the very centre of the canopy, or hiding behind fruit. When the thin edge of the paper is oriented to the spray (i.e. oriented facing the ground), it presents very little surface and can be difficult to hit.

    Use enough air to only just ruffle the leaves. This exposes all surfaces, however briefly, to the spray. Too much air will align leaves with the spray, exposing only their thin edge and making coverage difficult. Too much air may also cause leaves to shingle (overlap), and create shadows like on the grape leaves shown here.
    Use enough air to only just ruffle the leaves. This exposes all surfaces, however briefly, to the spray. Too much air will align leaves with the spray, exposing only their thin edge and making coverage difficult. Too much air may also cause leaves to shingle (overlap), and create shadows like on the grape leaves shown here.

    Further, the papers won’t show the finest droplets (<50 µm), so there may be spray even though you can’t see it. Taken collectively with the product’s mode of action (i.e. contact or locally systemic), and any possible re-distribution by rain or dew, spray coverage becomes a good indicator for protection, but it isn’t definitive. While coverage is a good indicator, improved coverage does not always mean improved efficacy.

    Some sprayer operators use other methods to confirm their coverage. Kaolin clay is an inert compound that leaves white residue when dry. Red, yellow or green water-soluble, food-grade dyes will also indicate coverage. Even fluorescent dyes such as phosphorus can be sprayed at night and illuminated under black lights.

    Kaolin clay and fluorescent dies sprayed into fruit canopies give a lot of information about sprayer coverage, but are relatively inconvenient compared to water-sensitive paper.
    Kaolin clay and fluorescent dies sprayed into fruit canopies give a lot of information about sprayer coverage, but are relatively inconvenient compared to water-sensitive paper.
    Red food-grade dye sprayed from a horizontal boom to demonstrate downwind drift onto a white target. This was a messy experiment and my hands, and the sprayer, were pink for a long time afterwards. Photo Credit – J. McDougall, Ontario.
    Red food-grade dye sprayed from a horizontal boom to demonstrate downwind drift onto a white target. This was a messy experiment and my hands, and the sprayer, were pink for a long time afterwards. Photo Credit – J. McDougall, Ontario.

    Take home

    These methods give the sprayer operator a lot of information because they land on the actual target, not a piece of paper hung in the canopy. But, they require a lot of time and effort and are typically out of reach for most operators. Further, they do not allow multiple applications on the same canopy to compare the effect of sprayer settings on coverage – once the target is sprayed, it’s sprayed.

    No matter which method you choose to use, understanding how changes to you sprayer, or the impact of weather, affect coverage is a critical piece of information. Operators should make an effort to evaluate spray coverage. Here are a few videos describing the process:

    Using water-sensitive paper for airblast coverage diagnostics – thanks to Penn State, Univ. New Hampshire and Chazzbo Media (2014).

    Checking water-sensitive paper in an orchard. Tower is spraying only water during a calibration run (2013).

  • The Sprayer Operator – The Most Important Factor in Spraying

    The Sprayer Operator – The Most Important Factor in Spraying

    Spray application is one of the most important activities regularly done in any crop operation. It can also be one of the most expensive and time-consuming. Integrated Pest Management (IPM) is a multi-step process that helps sprayer operators make informed choices about when and what to spray. But, the decision to spray is not the end of the process.

    Spraying highbush blueberry in British Columbia just after a rain. Not ideal, but sometimes the window for application is very small. It’s not the ideal situation, but one strategy for spraying a protectant fungicide on wet leaves is to concentrate the tank mix and use less spray per hectare. The fewer, and more concentrated, spray droplets will dilute in the water already on the leaves and the possibility of run-off is reduced. This is a stop-gap measure, only. The spray will not dry or distribute as it was intended and this strategy will require an additional full-rate application as soon as the weather improves, as long as the label permits. It is often said there is no such thing as a wasted fungicide application.
    Spraying highbush blueberry in British Columbia just after a rain. Not ideal, but sometimes the window for application is very small. It’s not the ideal situation, but one strategy for spraying a protectant fungicide on wet leaves is to concentrate the tank mix and use less spray per hectare. The fewer, and more concentrated, spray droplets will dilute in the water already on the leaves and the possibility of run-off is reduced. This is a stop-gap measure, only. The spray will not dry or distribute as it was intended and this strategy will require an additional full-rate application as soon as the weather improves, as long as the label permits. It is often said there is no such thing as a wasted fungicide application.

    The sprayer operator now faces a lot of decisions about sprayer set-up and application method. These decisions determine if the application will be effective, and they also determine if it will be efficient. Efficient spraying saves money and reduces environmental impact. The goal is to be both effective and efficient.

    So what should the operator be aware of?

    A quick Google search reveals a seemingly endless number of sprayer articles by government, industry and academia (and many on this website!). There are differences in definitions, opinions on priorities vary, and classic sprayer wisdom is sometimes supported and sometimes debunked by current research. But, if you read enough of them you will find more similarities than differences, and common themes will emerge.

    Most agree that the objective of spraying is the safe and timely delivery of an effective, uniform dose of product to a target area. Any product not deposited on the target (e.g. spray drift, sprayer leaks, run-off, etc.) reduces efficiency and is called wastage. The literature points to six broad elements that affect spray efficiency and effectiveness. Sprayer operators should actively consider all six elements before, and during, each spray application.

    The six elements in the illustration overlap because changing one of the elements often means reconsidering others. For example, increasing droplet size to reduce drift potential also reduces the number of droplets sprayed. This may warrant higher spray volumes, which means you might require a more dilute tank-mix to maintain the rate-per-area. Only the sprayer operator’s decisions affect all the elements, which is why it’s pictured in the centre. Technology or technique can not compensate for an inattentive operator; an operator’s skill and willingness to do a good job impacts the overall efficiency and effectiveness of every spray application. Understanding how droplets behave (or misbehave) is essential.

    The six elements of effective and efficient spray application.

    Each element is comprised of many contributing factors. Some of these factors might fit under multiple elements and certainly we’ve reorganized this list many times over the years. No matter how they are presented, all of these factors (and more) contribute to the success of spray applications and they should figure into the operator’s considerations.

    The expanded six elements of effective and efficient spray application.

    So, as sprayer operators, we should all be aware of how the factors that affect an application. Take an active role! Don’t be afraid to get out of the tractor and make changes to your pressure or your nozzle choice. Check your coverage as you spray, and make adjustments as the weather changes. Finally, recognize when it’s a waste of time and spray, and know when to pack it in. The days of “set it and forget it” are no more!

  • Evaluating an Anti-Drift Adjuvant in an Airblast Sprayer

    Evaluating an Anti-Drift Adjuvant in an Airblast Sprayer

    Most pesticides are either pre-formulated with the required adjuvants, or the label specifies their addition. However, compelling claims by manufacturers create interest in tank mixing additional adjuvants to improve some aspect of pesticide performance. In a previous article we advised caution when using adjuvants in airblast sprayers (see here). Specifically, we stated that unless an adjuvant has been tested with airblast equipment, do not assume it will perform as it does in a boom sprayer. In the last year, we’ve received a lot of questions about anti-drift adjuvants, so we decided to test one of the more popular products.

    2016_orchard_spraying

    The Adjuvant

    According to the manufacturer, InterLock is a vegetable oil-based adjuvant intended to improve deposition, canopy penetration and drift reduction from both aerial and ground applications. Independent research has validated its ability to reduce the population of Finer droplets produced by a nozzle without shifting the entire droplet spectrum into a Coarser category. As such, InterLock is used extensively in aerial and field sprayer applications, but we wanted to explore its fit in airblast applications.

    There are fundamental differences in how an airblast sprayer functions compared to a field sprayer. An airblast sprayer operates at pressures considerably higher than field sprayers, and many use paddle agitation to churn tank mixes. Further, droplets are entrained by air and can be carried several meters before reaching their target. So, does the collective impact of paddle agitation, droplet shear and the increased opportunity for evaporation affect the adjuvants performance?

    The Trials

    Water sensitive cards were distributed throughout target trees in an apple orchard. We elected to use two models of airblast sprayer to eliminate the chance of sprayer-specific results. Both models applied either water or water-and-adjuvant. So, the four treatments were:

    Hol Sprayer: Water
    Hol Sprayer: Water-and-Adjuvant
    Turbomist: Water
    Turbomist: Water-and-Adjuvant

    Weather Conditions

    On the afternoon of May 30, 2016, the crosswind was 6-11 kmh (3.7-6.8 mph), the temperature was 27 ˚C (80.5 ˚F), and the relative humidity was ~50%. While warm, conditions were reasonable for spraying.

    Orchard and Targets

    We worked in high-density Honeycrisp apples planted in 2008 on M.26 rootstock. Row spacing was 5 m (16’), average canopy width was 1.2 m (4’) and average height was 3.3 m (11’). Water sensitive cards were located at the top, middle and bottom of each target tree, close to trunk. In each location, the cards were placed back-to-back with sensitive sides facing the alleys.

    We placed cards in two trees in the same row, and the sprayer passed down both sides to complete the application. We performed this twice per treatment. That’s four trees per treatment representing a total of 24 cards (comprised of eight per position).

    Sprayers

    As previously mentioned, we used two models of airblast sprayer. In both designs, nozzle bodies are outside the airstream, causing additional shear as nozzles spray into the air on an angle.

    A Hol sprayer with tower operated at 9.6 bar (140 psi) and driven at 5.6 kmh (3.5 mph). The sprayer was calibrated and spray was distributed to match the canopy. Nozzles were TeeJet AITX 8004s and TXR 80015’s spraying 10.2 l/min. (2.7 gpm) per side for a total rate of approximately 500 l/ha (53.5 gpa).

    A Turbomist with tower was operated at 11.7 bar (170 psi) and driven at 5.6 kmh (3.5 mph). The sprayer was calibrated and spray was distributed to match the canopy. Nozzles were TeeJet AITX 8004s and TXR 8002’s spraying 10.6 l/min. (2.8 gpm) per side for a total rate of approximately 500 l/ha (53.5 gpa).

    2016_hol_turbo_interlock

    Spray mix

    Sprayers were filled with water for the control trials, and then dosed with the equivalent of 250 ml per 500 L (8.5 oz in 132 US gal.) of spray mix, per manufacturer’s recommendation. We ensured lines were primed and sprayer was up to speed before spraying.

    Analysis

    Water sensitive cards were scanned and digitized to compare coverage and median droplet size using DepositScan software (created by Dr. Heping Zhu, USDA ARS, Ohio). Water sensitive cards have a limitation when quantifying average droplet size: once a card exceeds about 30% coverage, too many droplets overlap and their combined profile is wrongly counted as a single droplet. This can skew droplet size analysis.

    For the sake of an accurate comparison, we selected subsets of the overall data; we analyzed only those cards with 40% coverage or less, then refined our comparison to those cards with 30% or less, and finally cards with 20% or less. In each subset, the data remained fairly robust because they included at least one card from each canopy position (i.e. top, middle, low) and three from each treatment.

    In the following tables, the range of droplet sizes is represented by DV0.1, DV0.5 and DV0.9 in µm. Basically, this is the span of droplet diameters from the smallest 10%, to the median to largest 10% in microns. The standard error of the mean and the number of papers are also indicated.

    Data subset 1: Cards with 40% coverage or less

    Avg. DV0.1 (µm) ±SEMAvg. DV0.5 (µm) ±SEMAvg. DV0.9 (µm) ±SEM
    HolAdjuvant: 255±33 (n=8)
    Water: 254±24 (n=12)    		Adjuvant: 664±137 (n=8)
    Water: 736±114 (n=12)    		Adjuvant: 1,175±223 (n=8)
    Water: 1,391±204 (n=12)
    TurbomistAdjuvant: 252±38 (n=8)
    Water: 258±31 (n=9)    		Adjuvant: 545±86 (n=8)
    Water: 697±141 (n=9)    		Adjuvant: 964±168 (n=8)
    Water: 1,175±237 (n=9)

    Data subset 2: Cards with 30% coverage or less

    Avg. DV0.1 (µm) ±SEMAvg. DV0.5 (µm) ±SEMAvg. DV0.9 (µm) ±SEM
    HolAdjuvant: 221±30 (n=6)
    Water: 189±22 (n=6)    		Adjuvant: 553±127 (n=6)
    Water: 495±118 (n=6)    		Adjuvant: 1,007±245 (n=6)
    Water: 969±235 (n=6)
    TurbomistAdjuvant: 240±42 (n=7)
    Water: 192±22 (n=5)    		Adjuvant: 502±86 (n=7)
    Water: 433±89 (n=5)    		Adjuvant: 912±184 (n=7)
    Water: 759±187 (n=5)

    Data subset 3: Cards with 20% coverage or less

    Avg. DV0.1 (µm) ±SEMAvg. DV0.5 (µm) ±SEMAvg. DV0.9 (µm) ±SEM
    HolAdjuvant: 163±19  (n=3)
    Water: 172±28 (n=4)    		Adjuvant: 371±107 (n=3)
    Water: 472±176 (n=4)    		Adjuvant: 617±137 (n=3)
    Water: 904±315 (n=4)
    TurbomistAdjuvant: 240±78 (n=4)
    Water: 192±22 (n=5    		Adjuvant: 439±140 (n=4)
    Water: 433±89 (n=5)    		Adjuvant: 691±189 (n=4)
    Water: 759±187 (n=5)

    Conclusions

    In the first subset (i.e. 40% coverage or less) there was no trend to suggest the sprayer model made any difference in coverage. Nor did there appear to be any change in the droplet spectra produced by water or water-plus-adjuvant. In particular, there was no apparent increase in the DV0.1 when adjuvant was used, which we would expect to see if the Finest droplets produced by the nozzle were made Coarser. We hoped that by further subdividing the data to cards with 30% coverage or less, and then 20% coverage or less might resolve some trend, but there were no significant differences to speak of.

    These trials are not drift studies, so we cannot say that the adjuvant has or doesn’t have an effect on particle drift. However, according to the water sensitive cards, there is no apparent impact on droplet size or deposition. This suggests that some property of airblast application has reduced or negated the benefit of using the adjuvant. As such, the use of InterLock in an airblast sprayer cannot be recommended. It supports our position that unless an adjuvant has been tested with airblast equipment, you should not assume it will perform as it does in a boom sprayer.

    Thanks to Winfield for the educational donation of InterLock, to TeeJet for the nozzles and to Provide Agro for use of the Hol sprayer. Special thanks to Donald Murdoch of the University of Guelph for operating the sprayers.

  • How to Assess Spray Coverage in Vegetable Crops

    How to Assess Spray Coverage in Vegetable Crops

    Sprayer operators recognize the importance of matching their sprayer settings to the crop to optimize efficacy. For example, spraying a protective fungicide in field tomato should require a different approach from spraying a locally systemic insecticide in staked peppers. Knowing this, many operators make ad hoc changes and then wait to “see if it worked”. A process is required that empowers the operator to make systematic changes to their program and assess coverage immediately.

    Such a process would require some fundamental understanding of how droplets behave, the location of the target, and the physical structure of the crop. This would be tempered by broader concerns such as weather (e.g. wind, rain and inversions as they affect coverage and spray drift), pest staging, and sprayer capacity (i.e. the sprayer’s ability to cover the crop in the window of time available). Finally, there has to be a mechanism for the operator to make a single change, then assess the impact in a quick, convenient, and yet quantitative manner.

    There are always exceptions to a rule, but an operator looking to assess spray coverage might consider the following process:

    • Understand how the pesticide works. Not only do certain tank mixes and weather conditions affect pesticide efficacy, but the mode of action plays a big role. A contact product must hit the target, while a locally systemic offers more latitude and can withstand less coverage.
    • Use IPM to determine where the pest is, whether it’s at a stage of development where it is susceptible to the spray, and where the spray needs to be to affect it. For example, if the pest is deep in the canopy, or under a leaf, or in the flower, this is where spray coverage should be targeted and assessed.
    • Understand droplet behaviour.
      • Coarser droplets move in straight lines and are prone to runoff (especially on waxy and vertical targets). They rarely provide acceptable canopy penetration in dense, broadleaf canopies and do not give under-leaf or panoramic stem coverage. The Coarser the droplet, the fewer the sprayer produces, reducing droplet density. However, they are not prone to drift and can tolerate higher winds.
      • Finer droplets slow quickly and tend to move in random directions without some form of entrainment (e.g. air-assist). While they are not prone to runoff, they can get caught up on trichomes (leaf hairs) and may not reach the leaf surface. They provide improved canopy penetration and some under-leaf and panoramic stem coverage, but their lack of momentum leads some operators to use higher pressures to “fog them in”. Higher pressures are generally not advisable because they increase the potential for drift and often result in less spray available to the crop.
      • Consider the droplets’ point of view. Look along the droplets potential path from nozzle to target. If there’s something in the way, consider re-orienting the nozzle using drop-arms, or a nozzle body that can be adjusted to change the spray direction.
    • Understand the impact of water volume and travel speed. Higher volumes improve spray coverage by increasing the number of droplets. Slower speeds give more opportunity for spray to penetrate the canopy and reduce the potential for drift, leaving more spray available to cover the crop.
    • Use water-and-oil sensitive paper to assess spray coverage. The operator should pin or clip papers in the crop, in locations and orientations representing the desired target. Wire flags and flagging tape mark their locations:
      • Spray using water to establish baseline coverage.
      • Retrieve the papers and replace them with a new set in the same locations and orientation.
      • Make one change to the sprayer set-up and determine whether or not coverage was improved.
      • Continue to tweak the sprayer until coverage is improved. Sometimes, improving spray efficiency means maintaining coverage while using less spray.
      • Understand how much is enough. Knowing whether to drench the target, or be satisfied with a low droplet density depends on how the pesticide works and whether or not the pest is mobile. As a general rule for foliar insecticides and fungicides, 85 drops per square centimeter and 10-15% surface coverage on 80% of all targets should be sufficient.

    Now, a few caveats: Know that under-leaf coverage is VERY difficult to achieve and that improved coverage does not necessarily mean improve efficacy. Further, know that a systematic approach requires time and effort, and should only be performed in weather conditions the operator would spray in.

    Read about how a similar process was used to assess coverage in field tomato and in staked pepper. It may take time out of an already busy schedule, but performing this assessment is always worth it.