This article was co-written with Jennifer Llewellyn, former OMAFA Nursery Crop Specialist
With more and more bio-rational products on the market, crop protection methods may require reassessment. Certain products require exacting water quality, cannot tolerate residues, and have half-lives that are both time- and temperature-critical. We’ve been getting questions about sprayer compatibility with some of these new products, so it seemed like a good opportunity to recycle this article from 2013.
Many horticultural commodities, such as turfgrass and nursery crops, include the application of live nematodes as part of their annual IPM program. We performed preliminary research into the claim that a grower’s nematode applications were becoming less effective. In the course of the investigation it was discovered that the nematode concentration (i.e. dose) sampled from the spray nozzle was diminishing over the course of the application.
(A) Tank-rinse assembly mounted through tank lid with a flow-regulating valve. (B) Close up of tank-rinse nozzle.
After eliminating potential sinks in the sprayer’s plumbing (e.g. filters, strainers, etc.) it was hypothesized that the nematodes were adhering to the interior of the poly tank. If this was the case, the concentration would drop as the level of spray mix dropped. To test the hypothesis, we installed a tank-rinse nozzle to sparge the inner walls of the tank throughout the application and to re-suspend any stranded nematodes.
A high capacity roller pump (Pentair series 1700C) was installed to operate the tank-rinse nozzle (Pentair Proclean Tankwash) during spraying. It was installed through a bulkhead fitting in the tank fill lid. During testing it was discovered that the tank-rinse nozzle shunted too much flow and pressure to maintain flow to the spray gun. A valve was installed behind the tank-rinse nozzle to restrict flow to the point where it gently rinsed the inner walls of the tank, restoring flow and pressure to the spray gun.
(A) Installing a high-capacity roller pump. (B) Tank-rinse nozzle, with valve, installed through tank lid. (C) Control manifold installed to plumb the return, the tank-rinse nozzle, spray gun and boom. (D) The entire installed system.(A) Nematodes, as-shipped, in a sponge. (B) Suspending nematodes for tank mixing. (C) Counting nematodes. (D) Undiluted, healthy nematodes in a stock solution via microscope ocular.
The 200 L tank was inoculated with a stock solution containing 25 million nematodes (125 nematodes / ml). 20 L of the spray solution was sprayed into a bucket every 10 minutes, whereupon 1 L of spray solution was immediately removed and 1 ml volumes were sub-sampled for counting.
In the first trial, nematode counts continued over a period of 2 hours and viability dropped by ~40%. It was assumed the damage was caused by prolonged circulation through the roller pump. In subsequent trials, the sampling duration reduced to 10 minutes (more realistically reflecting the time it took the grower to apply 200 L in the field). The tank was rinsed and re-inoculated for each trial. 1 ml samples were drawn from the spray gun, which operated continuously, with and without the tank rinse nozzle in operation.
Univariate analysis confirmed data normality and a GLM procedure was conducted for analysis of variance. Results indicate that nematode concentration dropped by ~15% without tank-rinse with minimal nematode damage observed. With the tank-rinse nozzle engaged, the concentration still declined slightly, but significantly less (<5%) (see graph below).
Nematode concentration over time for each condition.
The results suggest that a tank-rinse system that sparges the tank walls preserves nematode concentration throughout an application and may lead to more efficacious applications.
Horticultural Crops Ontario, Ground Covers Unlimited, Pentair (Hypro) and Nemapro are gratefully acknowledged for making this research possible.
The level of filtration required for any given spray operation depends on the materials sprayed and the nuisance factor: That is, the balance between lost productivity from plugged nozzles and the effort required to address them during rinsing.
There are opportunities to install strainers at the tank opening (usually a basket), the suction-side of the pump, each section line, and behind the nozzles. While we’ve yet to see an operation that uses all four (speciality or field operations), the suction strainer and line strainers are required bare-minimum.
This infographic explains how strainers are classified. Be aware that older strainers may use a different colour code (e.g. 50 mesh used to be red – now it’s blue).
To convert these ratings to actual size exclusion, we look at the Mesh Width (mm). An 80 mesh (yellow) leaves a distance of 0.18 to 0.23 mm between the wires. We can convert Mesh Width from mm to microns by multiplying it by 1,000, giving us 180 – 230 microns.
Each level of filtration should get progressively finer, ending with the nozzle strainers being slightly finer than the nozzle orifice. Nozzle catalogues will often advise you on which strainer is appropriate for the nozzle you are using.
When we ask why operators don’t use nozzle strainers, the response is either “Because they plug” or “It’s one more thing to clean”. Well, if your nozzle strainers are plugging, it’s likely because you have an agitation (see here) or mixing issue (see hereand here) further up the line. They can handle a lot before the spray pattern begins to suffer … but yes, you do have to clean them regularly so they can continue their good work.
Running water through any strainer often fails to remove plugs and debris, which are a source of contamination that can wreak havoc later on. They have to be removed and physically scrubbed during rinsing. We ran a demo to show why this irritating process is still a must-do (here).
If you use an airblast sprayer, you should use slotted (not mesh, which plug too easily) nozzle strainers. Beyond the obvious benefit of preventing plugged nozzles, the strainer shoulder plays a role in keeping the nozzle snug in the nozzle body. Without it, you may need additional gaskets to prevent leaks. Be aware that some nozzle strainer designs can plug a nozzle body. Learn more here.
If you use a field sprayer with clean carrier water, liquid formulations and large nozzles, you may never need nozzle strainers. But, if you’re using a lot of dry formulations, if your agitation is under-powered, or if your fill water is less than pristine (we’ve seen frogs in sprayer tanks) then you might consider them… even if they are a nuisance to clean.
“I’m an organic apple grower with constant nozzle-clogging problems. These problems occur when we use wettable powders such as micronized sulfur and Surround WP. We always premix before adding to the tank through its strainer. Our airblast sprayers have towers and employ mechanical agitation. The nozzle/filter combo is TeeJet TXR8001K Ceramic Conejet Visiflow Hollow Cone spray tips with TeeJet 4514NY10 50-mesh nylon slotted strainers. The nozzle strainers rarely make it through a full tank without having problems. Do I need to add an additional level of filtration or is there something that I’m missing?”
A clogged slotted strainer inside the nozzle body. Note that the inners of the check valve seem clear (a good thing).A clogged slotted strainer.
You can almost feel the frustration. When I receive grower enquiries, I first turn to the library of articles on Sprayers101 as well as the Airblast101 textbook. I was surprised to discover that we didn’t have anything that addressed this issue directly. So, I checked through university extension and industrial resources. Ultimately I couldn’t find what I was looking for, so let’s correct this oversight.
Possible causes
There may not be a single reason for why nozzles plug. It might be a combination of the following factors:
1. Product choice
While any tank mix can create clogs if they prove to be physically incompatible, there are two formulations that have a reputation for clogging nozzles.
Wettable powder (WP) formulations such as micronized sulfur and diatomaceous earth are notorious for clogging nozzles. WPs consist of a finely ground solid active ingredient often combined with wetting and bulking agents to help hold them in a dilute suspension. They tend to be dry products rather than liquids.
In a similar vein, suspension concentrate (SC) formulations also consist of a finely ground solid active ingredient, but this time they are suspended in a liquid and kept dispersed in the sprayer tank by wetting agents, dispersants, and thickeners. These formulations are known as “flowables” or “suspensions”.
By the way, for those thinking he should change products, he already uses Kumulus DF (or Microthiol Disperss), which are reputedly the least troublesome formulations… and smell better than other sulfurs.
2. Mixing practices
Pre-slurries are sometimes prescribed for SCs. I personally feel that pre-slurries create exposure risks and more things to clean, but this opinion is moot in the case of WPs: Micronized sulfur and diatomaceous earth are not soluble. They’re particles that are held in suspension by fluid flow or agitation, so there’s no point in a pre-slurry.
For those readers that cook, consider the corn starch metaphor. You’re making a sauce, and you choose to thicken it with a pre-slurry of corn starch and water. The particles disperse, but do not dissolve, so if you fail to use it immediately they settle to the bottom of the container. They must be forcibly scraped up and resuspended.
3. Agitation
Best practice is to fill the tank at least ½ full of water and engage agitation before you add anything. To extend the cooking metaphor, you want a simmer but not a rolling boil. Once filled, never stop agitating or WPs and SCs will settle and may not resuspend uniformly, if at all.
Your sprayer design may affect matters. Some hydraulic agitation systems flag if they have undersized pumps. If your pump is busy sending flow to the nozzles, it may not have sufficient capacity to run the agitation. When your sprayer is “empty”, is there a thick accumulation at the bottom? You may have insufficient hydraulic agitation. Mechanical (paddle) agitation does not suffer this issue because it is direct-driven off the PTO. Read more here.
4. Clean-out practices
Perhaps plugs are occurring because of the previous tank, not the current tank. WPs can leave a buildup of settled pesticide in the tank, suction strainer and nozzle strainers. If you aren’t diligent about rinsing at the end of each day, products will settle and harden. Micro sulfur particles, for example, are less than 10 µm in diameter and harden into a flakey shell that can break loose and cause plugs.
5. Flow restriction
Several things can restrict flow. Elbows, bends and fittings can increase friction, reducing flow. The greater the distance a fluid needs to travel, the more flow is reduced. The greater the head (a pump’s head is the maximum height that the pump can achieve pumping against gravity), the more flow is reduced. There is an excellent description of this relationship here.
So, if an operator is using nozzles with a particularly small orifice, plus nozzle strainers, on a vertical boom, liquid flow will be reduced. This allows particles to fall out of suspension and settle, forming further restriction to flow and eventually, plugs.
Possible solutions
Now, armed with these potential causes, let’s return to the grower. After some back-and-forth, he clarified that the clogs were a problem, but restricted flow was worse. An operator will stop to clean or replace a plugged nozzle, but may not notice reduced flow. This has the potential to affect several rows as well as leave unsprayed product in the tank.
My first proposal was to increase nozzle size. An ’01 tip is very, very small and even with slotted strainers (as opposed to mesh), that’s a lot of restriction. I suggested recalibrating for larger tip orifices. This is a rather involved process, but options included using every second nozzle (as long as there were no gaps in coverage), and/or dropping pressure, and/or increasing travel speed (as long as the spray still reached the tree top and canopy centre). I shared this Excel outputcalculator to help with the process.
Failing that, we discussed a plumbing project. Section 5.2.1 of Airblast101 describes a way to create a self-cleaning line filter that replaces nozzle strainers. That means instead of climbing a ladder to pull tips off a tower to reach the strainers, all filtration is conveniently located at ground level for easier (and more frequent) cleaning.
The outcome
The grower felt the numbers worked best running orange 02 TXR’s in every second position. He ordered new 50 mesh slotted nozzle strainers. His new operating parameters would be 5 nozzles/side, at 8.2 bar (120 psi) and 5.1 km/h (3.2 mph) for a total 51.5 L/ha (55 gpa). He noted some incompatibility issues running Braglia nozzle bodies (spec on his Rears sprayer), TeeJet TXR’s, TeeJet slotted strainers and TeeJet CP20230 caps. That was an important observation, and you can learn more about it here.
We felt good about this, but while there was an improvement, it didn’t solve the problem. There was still strainer clogging after the first tankload. So, he added inline filters and removed the tip strainers. The result:
“Yesterday I sprayed over 350 pounds (over 1,000 gal) of Surround WP and had no issues. I’m really excited about this new setup – it looks very promising. I’ve attached more pics if you’re interested (I don’t spend a lot of time scrubbing sprayers until after Surround season). Thanks again for all your help in this matter. – Joe Fahey, Peck & Bushel Fruit Company”
A 50 mesh inline filter assembly with a 1/4 turn ball valve for quick flushes.New filter plumbed and secured. Note the anti-rub wrap on the line – always a good idea.The new loadout. 02’s in every second position, with no tip strainers, and a new inline filter on each side of the sprayer.
Fantastic. Thanks to Joe for letting me share this story. Hopefully his experience will help you diagnose and solve any flow or nozzle plugging issues in your own operation.
Happy Spraying.
Epilogue
This article elicited some interesting comments. I’ll share two:
One grower proposed switching from a low profile axial sprayer to an air-shear system (there are a few examples here). In this case, the grower had a European make with hydraulic agitation. The grower re-plumbed theirs by installing a bigger pump and swapping the sparge system with a 3/4″ pipe oriented toward the bottom to sweep it out. When mixing, the agitation valve is left wide open. He says he doesn’t even bother with a tank basket; he dumps the Surround (as much as 2 x 50 pound bags in 1,000 litres) and has no plugging issues.
Another grower with considerable boom-sprayer experience was genuinely surprised this was even an issue. Self-cleaning filters have been commercially available for more than 30 years and most boom sprayers have them. This is a comment on the stagnation of the North American low-profile radial airblast design. Perhaps the long life of these sprayers (sometimes 40 years of service) makes iterative change slow, or perhaps most operators aren’t aware of new features, or perhaps change is a risky proposition in such high-value crops. This is a shame given that the first optic sensors were installed on airblast, not broad acre field sprayers. That comes as a surprise to many. But it seems to have been the exception and not the rule.
As Canadian farmers begin to adopt closed transfer systems (CTS), growing pains are to be expected. Instructions for installation and use are primarily European and field-sprayer centric. We’ve seen precious little in the way of practical advice for incorporating CTS into airblast operations.
This is a “live” article which we’ll update periodically. We encourage readers to contact us and share their observations and experiences (and photos) so we can all learn from them. We’re happy to keep contributions anonymous if that’s preferred.
This article does not intentionally imply any brand preference. Our experience is limited at this point and we are using any information we have access to. As the article grows, so will the combinations of sprayer and CTS. Also, we are not recommending or endorsing any of the following approaches. It’s still unclear if modifying the sprayer is the purview of the manufacturer / dealer of the sprayer or the CTS. At this point, we suspect it’s likely the owner that accepts any responsibility.
Does it matter where the CTS is relative to the sprayer?
If the system is gravity-fed, the coupler, the fill line and the connection to the tank must be higher than the fill level in the tank. Liquid won’t flow uphill unless it’s pushed from behind (pressure) or pulled (suction or siphon). Be aware this means the entire fill line should be above the tank’s fill level; sags will prevent fluid transfer. If we’re observing best practices, the tank should be half-full of water before you start adding products.
If the coupler uses suction from the sprayer itself, or employs a pump, relative height won’t affect filling. In this case it is likely part of a separate transfer system (i.e. not permanently mounted on the sprayer). It might be simple, or part of a larger and more sophisticated affair, but in either case it should be level, stable, and easily accessed without the operator having to reach or squat. Two examples are pictured below.
Here, a CTS is mounted to a hand cart so it can be wheeled into place and then put away. The sprayer provides suction via venturi to pull in the chemistry and a simple garden hose supplies municipal carrier / rinse water. Note the cinder (concrete) block used to stabilize the unit. Simple and effective.Here, a coupler is part of a larger tender system. Carrier / rinse water is pumped from an onboard tank, through the coupler, and then into the sprayer.
How do I plumb the CTS to the sprayer?
If the CTS is mounted directly on the airblast sprayer, it’s typically a smaller, gravity-fed coupler. The rinse / carrier water is often from an external source (e.g. water tank, tower, pond or municipal water), but there are cases where an onboard water source can be used.
Provide Agro has attached a gravity-feed coupler to the secondary tank hatch. This is above the fill line, sealed tightly, and it uses an onboard rinse / carrier water source. If considering cutting into a hatch, be aware of the filter basket or any onboard rinse system. Also, note that letting the lid flop open (or setting it aside) should not damage the coupler itself.No matter the rinse / carrier water source, it should match the manufacturer’s prescribed pressure range (generally between 3 – 6 bar or 45 – 85 psi) and have an anti-backflow device. There is no such device in this photo.
Some have suggested cutting a hole in the tank itself, above the highest possible fill line, and sealing the coupler in place. This is not simple. If you find a flat horizontal surface and you are equipped to cut poly, Fiberglas or steel (listed in ascending order of difficulty), doing so could undermine tank integrity and create potential for leaks. We won’t even entertain what would happen to your sprayer warranty… assuming someone still has one.
If the intent is to couple a fill line to the sprayer, the best approach is to tee a fitting into the suction-side of the sprayer plumbing to draw product in through the pump. Consider accessibility and safety first: Can you safely and easily reach the suction side of the sprayer plumbing? Is the PTO shaft too close for comfort? Will anything stick out past the sprayer that might create a risk of snagging a crop canopy or trellis? If a tee can be plumbed in, will it need to be secured to the chassis in some way to create stability?
There is no easy or universal answer to these questions.
On this sprayer, the only easily-accessed point is between the suction filter and pump. Creating a tee that would accommodate a dry poppet fitting is challenging.In the case of this 3-pt hitch sprayer, there is no simple way to access the suction side of the plumbing. Perhaps a tee could be added and the fitting extended up-and-out from under the chassis. Securing the fitting might require strapping it to the back of the tank, or to a mast of angle iron (or similar) attached to the chassis. Imagination required. Apply within.
As for the fitting, what style is best? A cam lever style fitting will work, but it will leak a volume of liquid when it’s detached. A quarter-turn valve will also be required on the sprayer, and preferably another on at the end of the feed line, so that’s two more valves in play when loading. And, for the sake of safety, best practice would to be to use a cam cap on the sprayer just in case the quarter-turn valve gets snagged and opens. Far safer and more efficient, a dry poppet style fitting will ensure minimal spillage when the hose is disconnected, with no additional valves or caps required.
Finally, what of the fill line itself? We’re seeking confirmation, but we have been told of a situation where the pump suction was sufficient to collapse the feed line. This is why some CTS manufacturers provide the hose and fitting with the units. At minimum, check the CTS manufacturer’s instructions and ensure the hose is rated for the degree of suction created by the pump.
Send us your experiences
And that’s all we have for now. We encourage you to reach out to us with your successes and failure and we’ll update this article for others to learn from.
Alternate Row (aka Alternate Row Middle [ARM]) spraying is an application method where the air-assist sprayer does not pass down every alley during an application. The sprayer operator is relying on the spray to pass through one or more rows and provide acceptable coverage to the entire canopy (or canopies) on a single pass.
Some state agencies promote this spraying strategy to various degrees, and many sprayer operators (whether they admit it or not) have used this method of spraying. I have advised it myself for very young and/or very sparse vineyard and orchard plantings, but never without confirming coverage. When I tell operators that I have serious reservations about alternate row spraying, they defend it. Here are the most common justifications I’ve heard over the years, and my response:
Justification
Reply
“I do not have enough spray capacity to spray every row when time is short.”
You need more sprayer capacity. Get another sprayer so you can get spray on in time or invest in a multi-row sprayer is possible.
“ARM spraying saves money and reduces environmental impact because I use less pesticide.”
Technically, if you travel every second row with a sprayer calibrated to travel every row, you have indiscriminately reduced your carrier and chemical inputs by half (or more). Without close monitoring you may compromise your efficacy.
“I only perform ARM spraying early in the season when canopies are empty, or only on young plantings.”
I grudgingly grant this one as long as coverage is closely monitored. I’ve prescribed it myself in young or sparse plantings where I couldn’t get the sprayer output low enough to prevent drenching the targets.
“The spray plume in the alley beyond the target row must mean the spray is providing adequate coverage. More is better!”
If the spray is blowing through the canopy, it isn’t landing in the canopy. Further, if the air speed/volume is too high, droplets can ‘slipstream’ past the target without impinging on them. I’ve removed water-sensitive paper from canopies with barely any spray on them despite the plume in the downwind alleys. It looks like a magic trick, albeit an unhappy one.
“Uncooperative weather doesn’t always leave me enough time to spray the entire crop, and it is the lesser of two evils to spray alternate rows than not at all. I’ll make sure I come back to spray the other rows later.”
Choosing to do half a job requires an understanding of the products’ mode of action. If you are spraying an insect at a particular stage of development, there’s no “coming back later” to get that generation – if you missed, your window has closed. If it’s a protective fungicide that offers no kick-back, then once the disease has infected tissue, the damage is done. Get the spray on as best you can, but if it washes away before it has a chance to dry sufficiently, be prepared to reapply at the earliest opportunity as long as the label allows it.
“ARM has always worked in the past.”
Would you mind picking my lotto numbers for me? You’re a very lucky person!
My reservations about ARM spraying come from published research and personal experience that show that coverage is almost always compromised when spraying from one side of a canopy. The spray must pass through the canopy to reach the far side, and the canopy filters droplets from the air as it passes through. This reduces the number of droplets available to cover the far side. In addition, high velocity spray will create “shadows” where any targets on the immediate far side of a leaf or branch become shielded and receive little if any coverage. Further still, fine droplets slow quickly as they leave the nozzle and take a long time to settle. As the entraining air slows and becomes erratic, the droplets float and change course, making their behaviour hard to predict.
The cumulative impact can be seen in this infographic I built in 2016. The orchardist was a dyed-in-the-wool ARM applicator and he was resistant to driving every row because it took so much time. I wanted to show that he could claw back some of the lost time by spraying less pesticide every row versus his current volume every second row. He would need fewer refills, and save a LOT of unnecessary pesticide. The water sensitive paper does the talking, and while I’d like to think I’ve convinced him, I’ll bet he’s still out there dicing with fate.
A very popular argument in favour of ARM spraying comes from orchardists that are shifting from semi dwarf to high-density plantings. They ask “How it is different to spray a four foot diameter tree from one side compared to an eight foot diameter tree from both sides”?
Well, we know coverage is reduced as a factor of distance. Spraying from one side gives a single opportunity to cover the middle and far side of a canopy, whereas spraying from both sides provides an opportunity for an overlap in coverage. Essentially, the centre of a canopy receives the cumulative benefit of two sprays. Coverage is therefore always improved when spraying from both sides, period.
Spraying from one side gives a single opportunity to cover the far side of a canopy. However, spraying from both sides provides an opportunity for an overlap in coverage. In other words, the centre of a canopy receives less spray than the outside, but is essentially sprayed twice resulting in a compounding effect.
Why, then, do some sprayer operators claim that alternate row applications work? Because sometimes, they do! Just because coverage is reduced doesn’t mean it isn’t sufficient to protect the crop. It simply means that the potential for poor coverage and reduced dose is dramatically increased by alternate row applications. A sprayer operator might perform alternate applications successfully for years before conditions conspire to defeat the application: unfavourable wind, poor timing, increased pest pressure, poor pruning practices, excessive ground speed, high temperatures, low humidity, insufficient spray volume, and several other factors might occur simultaneously and reduce coverage below a minimal threshold for control. This confluence of bad luck may not happen the first year, or the second, but eventually…
Product failure isn’t the only concern. Repeated reduced dosages may play a role in developing resistance. In those situations where the operator recognizes insufficient coverage, they may have to spray more often to compensate, negating any savings in time or product. Reduced dosage is a common error when a sprayer operator elects to use ARM.
If you still aren’t convinced, at least perform alternate row spraying the “right” way. Here are three situations that I’ve heard operators refer to as alternate row spraying. Situation 1 is most common, but to my mind only Situation 2 would be considered acceptable. Even then, confirming coverage is a must.
Situation 1:
The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.
The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.
Situation 2:
The sprayer is calibrated for double output compared to a typical every-row situation, and the operator drives alternate rows. The result is that the hectare gets the whole dose per application, but coverage is always inconsistent.
The sprayer is calibrated for double output compared to a typical every-row situation, and the operator drives alternate rows. The result is that the hectare gets the whole dose per application, but coverage is always inconsistent.
Situation 3:
Since the sprayer will only drive alternate rows, the operator mistakenly sets the sprayer to emit half the output compared to a typical every-row situation. The first application (solid line) covers different rows from the second application (broken line). The result is a quarter-dose per application, and if the operator chooses to spray a second time, the hectare will only ever get half-a-dose. Yes, this happens.
The sprayer has a typical calibration for spraying every row, but only drives alternate rows. The first application (solid line) covers different rows from the second application (broken line). The operator will claim to spray more frequently, but generally does not perform the second application unless there is high pest pressure. The result is half-a-dose per hectare per application.
So, my final word on alternate row applications is that they should be performed with extreme caution. I’ve used them myself in early season applications in new plantings, but never without confirming coverage with water-sensitive paper, and never in conditions that might further compromise coverage to the point that the application does not give control.
Caveat Emptor!
Well, I thought it was funny. My apologies to J. Luymes from British Columbia (pictured) and Obi Wan Kenobi (not pictured… or is he?)
