Category: Boom Sprayers

Main category for sprayers with horizontal booms

Evaluating Wheat Head Coverage from Two New Nozzles

We’ve written extensively about angled flat fan nozzles and their ideal operating parameters (i.e. pressure, boom height, droplet size, volume and travel speed) for spraying wheat heads. Generally, coverage on the sprayer-approach side of a wheat head (aka the advance side) is easier to achieve because droplets from a conventional flat fan geometry tend to follow a downward-forward vector. Imagine dropping a ball from the window of a moving car. An outside observer would see it travelling forward as it fell.

The back of the wheat head (aka the retreat side) and the sides are harder to hit. When we introduce a rearward angle to coarser, fast-moving droplets, the high momentum and downward-rearward vector deposits spray on the retreat side of the wheat head after the sprayer passes over. Mythbusters produced a cool video segment that illustrates this concept by matching the rearward velocity of a soccer ball to the forward velocity of a truck; the ball falls straight down. Of course, in our case we want it to shoot backwards.

A great deal of independent research has determined that low booms coupled with dual fans that produce coarser spray and higher volumes will optimize coverage on any vertical target. Asymmetrical nozzles that have a more aggressive rearward angle perform better still. Of course both of these claims assume a “reasonable” wind speed, because the finer droplets in the spray experience a comparatively lower degree of inertia. Inertia is a property of matter that describes the resistance of an object to changes in its state of motion and it’s related to the object’s mass. What this means is that smaller droplets slow quickly, are easily deflected by wind, and tend to deposit on the windward side of the wheat head.

So, maybe you already knew all that. What’s new?

Two asymmetrical tips have been introduced in recent years and we wanted to characterize their coverage (Figure 1).

The first is the “Fusarium Fighter” which is a combo-tip developed by Nozzle Ninja in Stettler, Alberta. It combines Pentair Hypro’s FC-3D100 (a non-AI tip with a 2 star rating from LERAP and a 100° wide fan) with ASJ’s, Compact Fan Low-Drift Coarse with its 120° wide fan. The 3D already has a 55° angle from vertical and the twin cap brings that to a very steep 65°.

The second is Pentair Hypro’s Asymmetric Ultra Lo-Drift AI Ceramic. This is the same as the Lechler IDTA where the front angle is 120° wide, angled 30° forward from vertical and sprays 60% of the spray volume. The rear fan is 90° wide, angled 50° back and sprays the remaining 40%.

Finally, and only to illustrate how symmetrical fans and finer droplets are perhaps not ideal for reliable wheat head coverage, we ran TeeJet’s TwinJet Twin TJ60-110VS. This is two 110° flat fans and the angle between them is 60° (30° fore and 30° back from vertical).

Figure1. Evaluating coverage from three nozzles in winter wheat.

For each treatment, five nozzles were positioned mid-boom on a Deere 410R to minimize any turbulence from the sprayer wheels and chassis and to reduce the degree of yaw. Extensions were used on all tips to ensure the spray did not impact the boom itself. All other nozzles were turned off. Nozzle bodies were on 50 cm (20″) centres and positioned 50 cm (20″) above the average wheat head. Travel speeds were selected to achieve 187 L/ha (20 gpa) at a pressure ideal for the tip in question and this is recorded in Table 1. Contractors and other such custom applicators may find these speeds low and the volumes high, but in this study we chose to emulate usage in smaller operations. The effect of travel speed on coverage is debatable but likely quite minor. More can be found on the subject in this article.

Nozzle	Spray Quality	Speed	Pressure
AULD-C 11003	C	6.6km/h (4.1mph)	483kPa (70psi)
FF (CFLD-C02 & FC3D11003)	VC & M	8km/h (5mph)	207kPa (30psi)
TJ60-11004	F	8km/h (5mph)	207kPa (30psi)

Table 1. Operating parameters for three nozzles applying 187 L/ha (20 gpa) to wheat heads.

The weather was 25°C, 40% R.H. and there was a very light and consistent tail wind of 2-4 km/h (1.2-2.4 mph). These were ideal conditions because it was not hot or dry enough to evaporate finer spray appreciably, and not windy enough to deflect the spray.

Water sensitive paper (Syngenta) was wrapped around the wheat head and held by a paper clip (see Figure 2). This gave a panoramic representation of coverage. Two more were mounted nearby on a length of rebar at wheat head-height; One faced the sprayer advance and one faced the retreat. Three such sets were positioned inline, spaced about 1 m apart and centered on the swath produced by the five nozzles. This was repeated 2x for each nozzle. Papers were retrieved, digitized and analyzed per the method described in this article.

Figure 2. WSP wrapped around a wheat head.

The resultant coverage is recorded in Table 2 and graphed in Figures 3 and 4.

Nozzle	Panoramic: Area covered (%) & deposit Density (#/cm²)	Advance: Area covered (%) & Deposit density (#/cm²)	Retreat: Area covered (%) & Deposit density (#/cm²)
AULD-C 11003	10.2% 130.4 deposits/cm²	7.9 % 56.1 deposits/cm²	11.1% 87.7 deposits/cm²
FF (CFLD-C02 & FC3D11003)	13% 97.5 deposits/cm²	9.0% 46.9 deposits /cm²	18.3% 72.4 deposits/cm²
TJ60-11004	22.3% 471.0 deposits/cm²	21.5% 320.9 deposits/cm²	11.4% 286.1 deposits/cm²

Table 2. Average coverage from three nozzles applying 187 L/ha (20 gpa).

Figure 3. Comparison of average percent area covered for three nozzles.

Figure 4. Comparison of average deposit density for three nozzles.

Unless you are experienced with interpreting coverage data, these numbers and graphs may not convey what coverage truly looked like. And since we saw some unexpected results, we felt it would be best to digitize the papers from each nozzle and create graphics to support our observations and opinions on how they performed. Each image shows six replications of each orientation. We’ll begin with the AULD in Figure 5.

The AULD was operated at a relatively high pressure to create the Coarse droplets recommended by the nozzle manufacturer. The steep rearward angle produced a higher degree of coverage on the retreat side compared to the advance. The streaky or tear-drop shaped deposits indicate a droplet that “scuffed” along the paper surface, almost but not quite in parallel. On the panoramic targets they tend to correspond with the sides of the paper, where the droplets are not aimed directly at the surface as in the “advance” and “retreat” surfaces. All in all, this nozzle performed well and created droplets large enough that we feel they would stay on course in a higher wind and not get tied up on the awns of the wheat head.

Figure 5. Digital scans of water sensitive papers from the AULD nozzle. Spray quality was C.

Next is the Fusarium Fighter. This nozzle was developed in Western Canada where, on average, sprayers tend to travel faster than they do in Ontario. Certainly this isn’t the case for all Ontario fields, but we chose to emulate usage in home farm operations where fields may be smaller and less level. This is relevant because faster travel speeds permit the use of a larger 3D nozzle to achieve 20 gpa, which in turn produces a coarser spray quality. In our trials, we traveled more slowly and that necessitated a smaller 3D that produced only a Medium droplet size. We hypothesized that those smaller droplets may not stay on course, but the papers show otherwise (Figure 6).

Figure 6. Digital scans of water sensitive papers. Spray quality was VC and M.

Coverage on the retreat side was very good and far outstripped the coverage on the advance side. In fact, the Very Coarse spray quality from the CFLD-C may be too large. Dropping from VC to C would create more droplets and a higher deposit density on the advance. We did see some gaps in the panoramic papers that likely reflect the lack of finer droplets which tend to move more erratically and contact the sides. Recall that we said weather conditions were ideal. It is still questionable how well a 3D producing a Medium spray quality would perform in windier conditions or on the boom ends where yaw tends to lift tips well above the ideal operating height.

Figure 7. All three tips operating on a stationary sprayer at 40 psi. The Fusarium Fighters (foreground), the TwinJets (middle) and the AULDs in the background.

Finally, the TwinJets (Figure 8). We used this nozzle only to demonstrate how the lack of an aggressive rearward angle and a Fine spray quality was not conducive to reliable wheat head coverage. Many studies have demonstrated that such a nozzle outperforms a single, conventional flat fan, but it is not the best choice of angled nozzles. Once again recall that these nozzles were positioned centre-boom where yaw and sprayer-induced turbulence were not an issue and in absolutely ideal environmental conditions.

We saw tremendous coverage on the advance side and while we saw comparatively less on the retreat side, it still performed well compared to the other nozzles. The panoramic targets also indicated suitable coverage, both as percent area covered and deposit density. BUT, if we have some questions about how the Medium spray from the 3D would perform in more challenging conditions, we are far more concerned about the fines from this tip. Having used this nozzle in past demonstrations we are well aware of how non-uniform and erratic coverage can be, and that translates to poor efficacy and increased drift. However, sometimes circumstances conspire to create exceptions, and the coverage we saw in this trial is hard to fault.

Figure 8. Digital scans of water sensitive papers. Spray quality was F.

This trial was not intended to rank nozzles, but to explore the merits of a few new designs and evaluate their respective coverage. If anything the results reinforce the need to operate angled sprays correctly and in appropriate weather conditions. Water sensitive paper remains a quick and easy method for sprayer operators to evaluate their own coverage and inform any corrective actions to improve results in their own unique circumstances.

Thanks to Dan and Paul Petker (Petker Farms) and Don Murdoch (Simcoe Research Station, University of Guelph) for providing the fields and operating the sprayers. Nozzle Ninja is gratefully acknowledged for the donation of AULD and Fusarium Fighter nozzles, and Spraying Systems Co. for the TwinJet nozzles and water sensitive paper.

July 25, 2023

Avoiding Skips from PWM Sprayers
Does this sound familiar?
“This year was the first year we used a growth regulator on our wheat. After heading, we noticed a wavy pattern of different plant heights between 30 and 45° to the operating direction. It was only a couple inches difference and was difficult to photograph. We sprayed 12 gpa at 9 mph using TT11005 nozzles alternating forward and back at 35 psi and a 70% duty cycle. I’ve talked to other operators in Canada and in Europe and several customers have reported seeing this pattern, no matter which model of PWM sprayer. What’s happening?”
Skips in cereal that are obvious to the eye can be difficult to photograph.
The pulse width modulation is very likely responsible for the waves. We have a number of articles describing how PWM works, but here’s a brief recap of the relevant bits.
A solenoid intermittently interrupts nozzle flow with a frequency between 10 and 100 times per second (depending on manufacturer). The proportion of the time the nozzle remains open is called the Duty Cycle. Each nozzle is linked to the neighbouring nozzles so that when one pulses on, the neighbour pulses off. So although you may only have half the nozzles spraying at any moment in time, sufficient overlap ensures there are no gaps in the pattern.
However, depending on the combination of frequency and duty cycle, it is possible to lose that overlap between nozzles. This can cause a checkerboard pattern that appears to repeat in a diagonal line. The following two images are from www.Capstanag.com and they illustrate an ideal overlapping pattern and a pattern that creates skips.
Here’s a 11008 at 10 gpa, 15 mph, 60% DC, 10 Hz, 21” boom.
Here’s an 8008 tip at 5 gpa, 15 mph, 30% DC, 10 Hz, 21” boom.
We can also sometimes see skips on the outer edges of sharp turns. In that case the outer boom section can be travelling two or three times as fast as the cab. In a conventional system, this would produce under-dosing in the outer region and over-dosing closer to the cab.
Some degree of skipping may be more common than we realize. It’s only when we spray products that produce obvious visual symptoms at low doses that we can see a biological response. In the case of plant growth modifiers used to prevent lodging in cereals, we have a perfect storm situation. A region of reduced spray overlap, applied at a time when the crop is elongating rapidly, perhaps on rolling ground from an unstable boom height, can all conspire to create regions of reduced dose with striking visual symptoms.
The following list describes conditions that can increase the potential for skips, and what you can do to avoid them.
1. Low duty cycles. Cycles less than 60% should be avoided.
2. Fast travel speeds. Faster speeds may help blend the spray in the swath a little, but too fast can create gaps and increase drift potential. At high travel speeds the system is usually operating at a high duty cycle unless an especially large nozzle size has been selected. Ideally, we want to run the duty cycle at 60-80%, but there are always exceptions. For example, according to Wilger, 90-92% is fine when you run at 20 gal/ac with their “15 gal tips”.
3. Low booms. The lower the boom, the less overlap. Raising the boom to 24″ above the crop may help, but beware of drift.
4. Narrow fan angles. Nozzle angles less than 110° reduce the degree of overlap and are less forgiving if the distance between nozzle and target decreases.
5. Low pressure. Avoid operating at pressures below 35 PSI. Due to pressure drop at the solenoid, 40 PSI on the monitor might mean 28 PSI at the nozzle. Some nozzle tables account for solenoid-induced pressure drop and some do not. Low pressure may be insufficient to establish the full 110° pattern, and the resulting marginal overlap not only means inconsistent dose, but inconsistent droplet size because droplets are coarsest at the edge of the pattern. And, if that’s not already enough, note that air induction nozzles intended for use with PWM tend to create messy patterns at low pressures and low duty cycles.
6. Especially coarse spray quality. Unless the label requires it, consider using spray qualities no larger than Very Coarse, particularly at low volumes. PWM frees the operator to use pressure independent of rate, so you may be able to accomplish this without swapping nozzles.
7. Products that are highly dose-dependent. This one is likely unavoidable, but be aware they are the products most likely to produce obvious visual symptoms. In the case of PGR’s, we have not (yet?) seen any evidence that skips translate to reduced yield. Weed misses or sub-lethal doses of fungicide or insecticide might be another matter.
June 28, 2023
Spraying from Seven to Seven (or) Drop Pipes Next Season – Parody
We were long overdue for a new classic rock parody, so we decided to re-tackle one of the greatest rock ballads ever written. With the ongoing success of drop pipes (aka drop arms, drop legs, etc.) in corn, we’re promoting directed spraying in verse.
If you’d like to read more about the research, check out this article, and this one too. Farmtario also wrote a nice summary from one of our 2022 demos.
So, this was a tough one, but we feel good about how we laminated a new message over Zeppelin’s tricky cadence and rhymes. It helps if you play the actual song as you read. Rock on:
There’s a grower who’s sure
all corn glitters like gold
and he’s spraying from seven to seven.
When he’s done, then he knows
that the products he chose
will handle the pests that he sprayed for.
Ooh ooh ooh ooh ooh
And he’s spraying from seven to seven.
He sees signs on them all
but he wants to be sure
‘cause he knows bug poop means that they’re feeding.
So, he stops for a look
spits and wipes as he should
sometimes all of his thoughts are misgivings.
Ooh, it makes him wonder
Ooh, it makes him wonder
There’s a feeling he gets
when the silks seem too wet
and his scouting is slowly revealing.
In his fields he has seen
in the irrigation rings
that tarspot’s in the plot where he’s standing.
Ooh, it makes him wonder
Ooh, it really makes him wonder
Maybe he sprayed the corn too soon
Or too late, it could be too
‘cause the timing defies common reason.
And he goes back in the dawn
to see what else has gone wrong
and his checks echo pests that he’s after.
Oh whoa-whoa-whoa, oh-oh
If there’s cutworm in your corn row, don’t be alarmed now.
It may have been coverage or timing.
But there’s a new way, you can spray now, and in the long run
there’s time to change the for the next season.
And it makes him wonder
Oh, whoa
Overhead spraying is a no-go
in case you don’t know
drop pipes are calling you to try them.
Diseases come in when the wind blows
but did you know
drop pipes cover stalks from end-to-end.
So, as you drive on down the row
overhead spray just won’t go
deep into targets, we all know
are hard to hit deep down below.
Next year he can still have gold.
Using drop pipes isn’t hard.
Coverage will come to him at last.
Quick to mount, one and all, yeah
They barely rock as sprayers roll.
And he’s using drops from seven to seven.
June 6, 2023
Calibrating a Plot Sprayer
It’s the rite of passage of many agricultural summer students across the world: applying experimental treatments to field plots using a research sprayer. The results of these experiments may be the basis of new product use registrations, or provide clues into future scientific studies. Needless to say, the application method needs to be bullet proof to ensure the results are reliable. Here are a few guidelines, starting with some tips:
Pro Tips:
1. When assembling a hand-held boom, ensure the threads are properly sealed using Teflon tape. More or less tape can be used to create a snug fit at the right part of the thread rotation.
2. Choose nozzle bodies with diaphragm shutoff valves. These valves stop flow below 10 psi and prevent dripping of the nozzles after shutoff, without pressure drop during operation.
3. Avoid the use of older style “check-valve strainers”. Although these also prevent drips, they create a pressure loss of about 5 psi which creates uncertainty around the actual spray pressure.
4. Install a trusted pressure gauge on the handle of the sprayer in clear view for the operator. This provides important information. Don’t believe the gauge on the regulator. Ours, for example, is stuck at 30 psi.
5. For hand-held booms, rotate the booms so that the nozzles point down, for each application. Different size people or height of crops will change this angle and make accuracy more difficult.
6. Set the boom height so that you achieve 100% pattern overlap. This means that a nozzle’s pattern width should be twice the boom’s nozzle spacing. Boom height will be close to 50 to 55 cm above target, depending on fan. Too low, and the pattern may cause striping. Your supervisor will see that all year long and think of you.
7. You can test the spray pattern by applying water to a concrete pad. At the right boom height, the entire boom width should dry at a similar rate.
8. Install a visual guide for boom height. For example, place a wire flag at the end of the plot, at the correct height. This will provide a handy reference of boom height as your arms get weary. Or hang a wire, zip tie, or chain from a spot that doesn’t interfere with your spray pattern (thanks ACC).
9. Minimize weight by using smaller bottles of CO₂. We use 20 oz paintball bottles, they are much lighter, last long enough, and can be legally refilled with liquid CO₂ or topped up with gas from a nurse tank in the field.
10. Spray out leftover mix in a designated part of the plot area. Do not pour any mix on the ground. Please. Consider a biobed on your research farm.
11. When completing a treatment, spray the boom completely empty so air comes out of each nozzle. This provides certainty that the next liquid at the nozzles is from the next bottle, be it water or another treatment.
12. When spraying dose responses of the same product, always start with the lowest dose. Again, spray out in a designated place until the boom produces air, no need to flush.
13. Construct a boom hanger from electric fence posts and coat hangers. Nozzles face down and can be serviced. The boom should never lie on the ground.
14. Use nozzle screens to prevent time delays due to plugging. Usually 50 (blue) or 80 (yellow) mesh is sufficient. Any finer mesh may interfere with some dry formulations. Note: Beware old screens – ISO mesh colours have changed. Learn more here.
15. It’s very useful to apply research sprays with low-drift nozzles. Air-induction tips are most effective. These reduce drift, and are also closer to the commercial spray quality used by producers.
16. 01 size (orange) air-induced nozzles are available from Albuz (AVI Twin and AVI), Arag (CFA, CFAU, AFC), Billericay (Air Bubble Jet), Greenleaf (AirMix and TurboDrop XL), Lechler (ID3 and IDK). No other major manufacturer produces this small size of tips in air-induction.
17. 015 size tips (green) and larger are produced by the above, as well as Albuz (CVI Twin and CVI), Hypro (GuardianAIR or ULD) and TeeJet (AIXR, AI, and TTI), within both manufacturers listed in order of increasing coarseness.
18. Always carry several other nozzles of the same size and type already on the boom. Should a nozzle plug, replace it, don’t clean it. Clean it later.
19. If a nozzle plugs and there is no extra nozzle, use compressed air to clean it. Compressed air electronics cleaners are available in most electronic stores.
20. If a plugged nozzle can’t be cleaned, simply place it at the end of the boom and continue. Plot ratings and yields are usually taken from the centre. Remind your supervisor of this.

21. Always de-pressurize a sprayer before disconnecting any liquid hoses. You can’t rely on check valves. If two people work together, make sure you practice and communicate this with each other.
Calibration:
1. Assemble the sprayer and run water through it to ensure it’s free from silt or residue. Repair leaks.
2. Install nozzles and ensure none are plugged and the pattern looks good.
3. While spraying water, set pressure to what you intend to spray with. (Note: boom pressure will be lower than regulator (attached to CO₂ canister) by a few psi, hence the separate pressure gauge on the boom. Also note that the set pressure will always be higher when the system is at rest.)
4. Obtain four containers of similar size that can hold about 500 mL, and place on ground at nozzle spacing. Using stopwatch, emit spray directly into all four for a set time, say 30 s.
5. Expected spray volume at 40 psi: 01 tip, 380 mL/min; 015 tip, 570 mL/min; 02 tip, 760 mL/min. In other words, from a 2 L bottle you’ll not get much more than 30 s spray time from 4 tips.
6. Measure collected volume from four tips using the same graduated cylinder.
7. Repeat, for total of three times.
8. Average three reps for each nozzle and convert to mL/min. Make sure all nozzles are within 5% of the average flow. Replace those that aren’t or place worst offender on outside edge of boom.
9. Advance to “Calculations”, but be prepared to conduct another calibration
Now for the fun part.
Calculations
There are three options for applying the correct amount. We’ll be using metric in these examples:
1. Use the average nozzle flow from the calibration (mL/min) and the target application volume (L/ha) to calculate the necessary walking speed (km/h);
  
  or
2. Use the flow from the calibration and a set walking speed to arrive at an application volume;
  
  or
3. Use a set walking speed and a set application volume to calculate a required calibrated flow.
Option 1:
Walking Speed = (60*flow)/(Volume*nozzle spacing)
If your nozzle flow was 330 mL/min and you wanted to apply 100 L/ha using a sprayer with 50 cm nozzle spacing, your required walking speed is 60*330/100/50 = 3.96 km/h
Option 2:
Application Volume = (60*flow)/(Speed*spacing)
If your nozzle flow was 330 mL/min and you wanted to walk 5 km/h using a sprayer with 50 cm nozzle spacing, your application volume is 60*330/5/50 = 79 L/ha
Option 3:
Required flow = (Speed *Volume*spacing)/60
If your speed is 5 km/h and you wanted to apply 100 L/ha using a sprayer with 50 cm nozzle spacing, your required flow is 5*100*50/60 = 417 mL/min
If you selected Option 3, you now need to return to your sprayer and find a nozzle, or a pressure, that delivers an average of 417 mL/min. You can use math to get into the ballpark with the nozzle you already have:
New Pressure = (required flow/calibrated flow)²*calibrated pressure
If your required flow is 417 mL/min and the calibrated flow is 330 mL/min, and you calibrated at 30 psi, then you should be close to your required flow at (417/330)²*30 = 48 psi
Now, return to your sprayer, set the pressure to 48 psi, and confirm this estimate.
We use Option 3 when comparing nozzles of the same size but from different manufacturers. It’s not uncommon for these to have slightly different outputs. Rather than adjusting our walking speed slightly, which is very difficult to do accurately, we change pressure slightly so all nozzles produce the same flow. This is also useful when comparing water volumes by switching to a larger nozzle.
Travel Speed:
The last step is to confirm travel speed. Say you want to walk at 5 km/h. The best way to calibrate walking speed is to measure a known distance (m) in the field you’ll spray. Wearing the gear and carrying the sprayer you will use to spray, walk this distance. Use a wire flag to mark the start and end points; when the boom hits the flags, start and stop the timer. Repeat until comfortable.
Time needed to walk distance:
Time (s) = Distance *3.6/required speed
Say your walking distance is 10 m, and you need to walk 5 km/h.
10*3.6/5 = 7.2 s
A simple spreadsheet that can be used for the calculations can be found here.
Congratulations! You’re done. Happy spraying! Remember to not worry too much about a 5% deviation from your expected application. That’s definitely an acceptable error, as long as you don’t allow too many of those to add up.
Low Volume Research (Aerial)
Some product uses are by air, and the label volumes for those are often 30 to 50 L/ha. Registrants need to provide efficacy data at those volumes. Ground application can be accepted as a surrogate for aerial as long as the volumes are correct.
Since the spray nozzles aren’t typically available below the 01 (orange) size and if they are, they usually plug so easily and make such a fine spray that they’re frustrating to use. The alternative, to travel faster, is also problematic on research plots.
We recommend that Turbo TeeJet nozzles be used for this purpose. They produce such a wide fan angle that a 100 cm spacing is justifiable. Simply cap off every second nozzle body. Booms need to be elevated to ensure overlap, for uniformity. The value of the small nozzles and wider spacings is the low total application volume that is now possible.
The TT tips can also be used at fairly low spray pressures (say 20 psi) further reducing their output.
Spray Quality of TeeJet Turbo TeeJet (ASABE S572.1). This tip is available in smaller sizes and, due to its wide fan angle, can be used at 40″ (100 cm) spacing, therefoe applying low water volumes.
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May 8, 2023
Air-Assisted Boom Sprayers
Air-assisted boom sprayers have been around since the 70s. More common in Europe than North America, they have demonstrated value in mitigating drift and improving canopy penetration. The majority of air-assist systems are found on three-point-hitch or trailed sprayers, which is fine (and perhaps even preferable) as long as clearance, travel speed and acreage aren’t limiting factors. In North America, trailed air-assist sprayers are used by some vegetable and strawberry growers, but air-assist in general is rare among field croppers. There are a few possible reasons for this:
- North American field croppers are predominantly concerned with work rate and prefer the larger, faster, self-propelled option.
- Air-assist is not ideal for herbicide applications to bare soil because unless it’s perfectly adjusted, it tends to bounce spray off the ground. A canopy is preferred to capture the spray and exhaust the air energy. This reduces the overall utility of air-assist.
- The air-assist feature is expensive and growers are either unaware or unconvinced of its value.
- There are few, if any, after-market air-assist upgrade kits available. This is because installations are bespoke; The apparatus is heavy, adds load to existing electrical and hydraulic systems and can interfere with boom folding. So, getting air-assist means purchasing a new (and perhaps unfamiliar) brand of self-propelled sprayer… and there aren’t many on offer.
Figure 1 – Dammann’s massive three-axel DT3200H S4 self-propelled air-assist sprayer at Canada’s Outdoor Farm Show in 2018.
Figure 2 – Agrifac’s AirFlowPlus (Image from Agrifac website)
Figure 3 – Agrifac’s AirFlowPlus depicting adjustable angle (Image from Agrifac website)
Figure 4 – This photo of a John Deere with air-assist was taken at a dealer’s lot in Southwestern Ontario in 2014. We have no idea what the history is, or who added the air-assist feature (it looks similar to a Miller Spray-Air with two blowers).
Air assist booms came to Western Canada in the early 1980s in the form of the “Spray-Foil” sprayer, later renamed Spray-Air. This sprayer was developed and manufactured in Carseland, Alberta. It used a shear-atomizer nozzle, a “foil”, that required a strong airblast to properly atomize a liquid feed that was introduced on the foil’s leading edge. As a result, it created a powerful airblast and a very fine spray. It was marketed as a way to reduce herbicide rates, an attractive feature during the times of drought, high interest rates, low commodity prices, and general economic malaise of farming on the prairies during the 1980s. Neighbours of Spray-Foils didn’t like the drift potential of the machines, and chemical companies objected to the claims of reduced water volumes (2 gpa) and lower product rates which contravened label directions. An unflattering test report of the sprayer by PAMI in Lethbridge resulted in a protracted lawsuit which helped cast the fate of the company. A Danish company licensed the design and sold it in Europe under the name Danfoil, where it continues to exist and @Nozzle_Guy saw it in person during the 2019 Agritechnica.
Figure 5 – A Spray-Air Trident pull-type made in Carseland, Alberta, for sale.
Eventually, Spray-Air rose from litigation and developed an improved nozzle with the assistance of the National Research Council (the “Shear Guard”) and introduced the Trident boom which gave users the option of atomizing spray with a conventional boom with or without air assistance, in addition the the native choice of shear-atomization. The sprayer chassis itself also continued to improve with a better overall design. Nonetheless, it was sold to Miller in the 2000s after a period of sales stagnation.
Figure 6 – A trailed one-sided Kyndestoft Air-Sprayer in Ontario field tomatoes (c. 2010)
Figure 7 – Everyone’s favourite sprayer, the Spra-Coupe, sporting a Kyndestoft Air-Spray system (1996, PAMI)
Figure 8 – An innovative prototype out of Alberta, the “Kaletsch fan sprayer” used pulleys to power the fans (1996, PAMI)
A fundamental problem with shear-atomization on sprayers like the Spray-Air is the requirement for significant air velocity for the atomization to occur properly. When the canopy cannot absorb that energy, air rebounds and creates drift. And if the operator cannot reduce the airblast strength without adversely affecting atomization, it leads to problems.
This photo (Figure 9) was submitted by Mr. L. Jones, a cash-cropper in ND, USA. It’s his JD4710 (circa 2004), which has 100′ booms and an 800 gallon tank. What’s interesting is that it has a Miller’s Spray-Air. This air-assist system is available on Miller’s Nitro and Condor line as well as New Holland sprayers (which are built by Miller). @spray_guy did some work with it on a Condor in field corn. It comes with their dual-flow nozzle system (Shear Guard™ PLUS Air Nozzles plus Dial-A-Drop™) for fungicides (applied at low volume) but you can also use conventional tips for coarser herbicide work.
Figure 9 – A JD4710 with Miller’s Spray-Air and conventional nozzles.
Mr. Jones says they use the flat fans when spraying a soil-applied herbicide. If it’s moderately windy, they engage the air to reduce drift. When they apply fungicide on wheat they use only enough air to move the heads as they pass over. Bystanders can see the spray enter the canopy and a portion rebounds, which they suggest (and hope) provides some underside coverage. That’s possible, but it’s generally better to keep all the spray in the canopy. This can be achieved by further reducing air speed, increasing travel speed, and/or aiming the air slightly backwards to increase the cross-sectional distance the spray has to travel and slow the spray velocity relative to the sprayer speed.
Generally, we’re proponents of using air when spraying. It opens the crop canopy, exposes otherwise-hidden surfaces, entrains and carries droplets to the target (reducing drift and improving coverage) and it extends the spray window by out-competing moderate winds. We have no proof, but wonder if it might also help alleviate the negative impact of tire and chassis turbulence on coverage uniformity under the boom. And, before you feel we’ve ignored a big benefit, we’d would be very cautious about using air-assist as a means for reducing carrier volume. The debate about finer sprays at less volume giving greater efficacy continues. While true at times, any benefit needs to be balanced with the downsides of potentially more drift and evaporation.
Here’s some 2018 footage from an assessment of canopy penetration in field pea using a Miller Nitro with Spray-Air. We see coverage extends deeply into the canopy, the degree of which shares an inverse relationship with depth (fairly classic). Note the heterogeneous mix of smaller and larger deposits from the air-shear nozzles. While some heterogeneity is good, this extreme span represents waste. The product tied up in the largest droplets could have been more gainfully employed as several smaller droplets. This pattern may be the result of using insufficient air energy, preventing the air-shear nozzle from fully atomizing the spray liquid.
In 2015 we felt air-assist needed some exposure, so we held a demonstration at Canada’s Outdoor Farm Show. Over three days we used water-sensitive paper to evaluate coverage in a soybean canopy (moderately dense, planted on seven inch centres) from a Hardi Commander (Figure 10) with and without air-assistance. We originally wanted to get our hands on a self-propelled Hardi Alpha Evo (Figure 11), but there were only two in North America at the time and neither were available. By the way, the Alpha Evo is now on the third iteration, but still uses the Twin Force air-assist system which allows the operator to change the angle of the air and the air speed. Each blower can be steplessly adjusted to a maximum output of 2,000 m³/h per m of boom and a maximum (and we’d wager, often excessive) air speed of 35 m/sec. You can watch a video explaining how to dial-in a Twin Force sprayer here.
Figure 10 – The Hardi Commander (118 foot boom) with Twin Force air-assist used in a spray demo at Canada’s Outdoor Farm Show.
Figure 11 – Hardi’s Alpha Evo self-propelled sprayer employs their their Twin Force air-assist system.
Figure 12 – Looking up from under the Hardi Alpha Evo boom. Air angle and speed can be adjusted.
The demo treatments
The sprayer was calibrated for 93.5 L/ha (10 gpa) at 2.75 bar (40 psi) at 9.7 km/h (6 mph). The boom was suspended 50 cm (20 inches) above the top of the canopy. On one side of the boom, we ran yellow mini drift nozzles (MD 11002’s) to create a Coarse spray quality, and on the other side we ran conventional yellow flat fans (F 11002’s) to produce a Fine spray quality.
Water-sensitive paper was attached to rods at three canopy depths: at the top, midway down and at the bottom of the canopy. Papers were oriented both face-up and face-down (Figure 13). Following each application, papers were collected for digital analysis using “DepositScan” which calculates the percent surface coverage and the deposit density. Both of these factors contribute to overall coverage.
We collected papers from three treatments:
1. Fine spray quality, No air assist
2. Coarse spray quality, No air assist
3. Fine spray quality, Air assist
Figure 13 – Water-sensitive papers were placed at three levels in a dense soybean canopy, facing up and down, for three treatments. Treatment 1 (Fine spray quality, No air assist). Treatment 2 (Coarse spray quality, No air assist). Treatment 3 (Fine spray quality, Air assist).
We held two demos per day at noon and 3:00 pm for three days, giving us six sets of papers to analyze for each treatment. The weather ranged from 25-29°C, 30-58% relative humidity and winds of variable direction from 3-11 km/h.
This was a simple randomized complete block design, but it was not a rigorous experiment. We simply took the opportunity to gather numbers from the demonstration. A more fulsome experiment would require many, many more passes under more stable conditions. For example, we set the angle of the air and nozzles to about 30° forward and the air speed at maximum, which wasn’t necessarily correct. Ideally, these settings should have been fine-tuned to match the forward speed of the sprayer, the density of the crop and the weather conditions. There was a lot of boom sway (watch the video below).
And so, caveats aside, the following graph illustrates the mean percent coverage and mean deposit density for papers in each treatment, for papers that were facing up (Figure 14). Standard error of the mean is presented alongside the average (x% ± y).
Results
Figure 14 – Average percent coverage (red) and deposit density (blue) for upward-facing water-sensitive papers in three canopy depths for each of three treatments. Averages rounded to the nearest 0.5 +/- standard error. “*” indicates significance with 95% confidence. Condition 1: Fine, No Air. Condition 2: Coarse, No Air. Condition 3: Fine, Air Assist.
Treatment 1 (Fine, No Air) reflects a typical coverage pattern for a dense canopy. Coverage declines as a function of canopy depth because spray droplets are intercepted by plant material before they reach the ground. This is particularly evident with broadleaf canopies that create shading. The coverage data doesn’t show it, but there was an obvious (and unacceptable) plume of spray drift during these applications (see Figure 15).
Figure 15 – The effect of air-assist on downwind drift from a Medium-Fine spray quality. Note that the nozzles and air are directed 30° forward. When sprayed over relatively bare ground, the air-assist bounces spray back up, as pictured here. However, when sprayed into a canopy with the correct air settings, bounce is virtually eliminated.
Treatment 2 (Coarse, No Air) follows the same coverage trend as Treatment 1. This treatment represents much larger, and fewer, droplets than Treatment 1, and yet the only obvious difference is reduced coverage in the middle of the canopy. There was little or no plume of spray drift during these applications.
Treatment 3 (Fine, Air) also followed the trend of reduced coverage as a function of canopy depth. Mean coverage was higher at the top of the canopy compared to the other two treatments. In fact, according to an ANOVA, deposit density was significantly higher in this canopy position than the other treatments, with 95% confidence. While mean coverage in the middle of the canopy was more than 2x that of Treatment 2, it was not statistically significant. There was no apparent difference at the bottom of the canopy. It is important to note that unlike Treatment 1, there was little or no spray drift plume during these applications.
Figure 16 – Upward-facing water-sensitive paper from mid-way into the canopy (position B) for Treatment 2 (Coarse spray quality, no air assist) and Treatment 3 (fine spray quality, Air assist). The difference in coverage is obvious.
DepositScan was unable to detect coverage on any of the downward-facing papers. However, close visual inspection did reveal differences. Unsurprisingly, Treatment 2 (Coarse, No air) did not produce any underside coverage; Large droplets do not change direction mid-flight unless acted upon by some other force. Droplets can bounce and shatter, but that did not occur here. The Medium-Fine droplets created in Treatment 1 (Fine, No Air) and Treatment 3 (Fine, Air) did leave trace coverage on the downward-facing surfaces. Generally no more than 10-30 deposits on the entire 1 x 3″ surface, representing less than 1% total surface coverage. It could not be determined if the air used in Treatment 3 improved underside coverage over that of Treatment 1.
Did air-assist make a difference?
Let’s start with the literature. Many experiments in peer-reviewed journals show that it does. A perfunctory literature review reveals improved coverage in the middle and lower portions of cotton, potato, soybean and wheat canopies. Some of these experiments were based on coverage using fluorescent dyes, and some with water-sensitive paper. Others were based on efficacy and report improved crop protection. The actual implementation was highly variable with some authors recommending angling the air and nozzles forward 20-25°. Others proposed 30° backwards. Most agreed (as do I) that the air speed should be set relative to the canopy density where higher speeds improved coverage deeper in the canopy, but did so at the expense of coverage in the higher canopy. Picture a bell curve on it’s side where the Y axis is canopy depth and the X axis is coverage; More air shifts the peak of the curve down the Y axis, into the canopy.
As for our demonstration, some interpretation is required. If an operator is spraying a contact product with limited or no translocative properties, then coverage becomes especially important. In order to improve coverage, higher volumes and finer droplets combined with slower travel speeds are often advised. This may be impractical, as most operators prefer to use less water and drive faster.
When we used Medium-Fine droplets with no air assist, coverage was good (Figure 14) and better than coverage obtained using Very Coarse droplets. However, spray drift was unacceptable (Figure 15). When air-assist was engaged, we reaped the coverage advantage of smaller droplets and drift reduction as good or better than what we saw with coarser droplets. Unexpectedly, we did not see an obvious improvement in coverage from the air assist. This begs the question “If the spray didn’t drift, where did it go?” This demo was a far cry from a formal mass accounting exercise, but my guess is it wasn’t effectively captured by our collectors and that a hefty fraction ended up on the ground. We would expect more uniform coverage under the boom, and some improvement in canopy penetration, but our ad hoc experiment wasn’t sophisticated enough to reveal it.
In the end, we feel there are advantages to the air-assist mechanism. The ability to employ a finer spray quality when required, while greatly reducing spray drift and combating inclement weather to extend the spray window are appealing features. Research has clearly demonstrated that deep-canopy spray coverage and overall efficacy are improved when this system is properly adjusted to match spray conditions. We’re not comfortable with suggesting it warrants lower carrier volumes (i.e. not dose) because of the expertise required to adjust the system. However, to be fair, experienced operators have accomplished it
We hope to see more air-assist options on boom sprayers.
February 10, 2023