In early July 2016, a farm supplier contacted us on behalf of a client with a history of disease control issues in his field pepper operation. He wanted us to calibrate their sprayer and diagnose spray coverage to see if there was room for improvement. Improved coverage doesn’t necessarily mean improved efficacy, but generally it’s a reliable indicator. When we arrived at the field the winds were gusting over 15 km/h, which had the potential to create a massive drift issue. We were only spraying water, so it was decided that if we managed decent coverage in those conditions, there would be no need to worry on an acceptable spray day.
Field pepper in Southern Ontario in mid-July
The grower traditionally ran two different settings on his sprayer. They were relatively low volumes for a vegetable operation, but the crop was still small at this stage, so we did not propose raising the volume:
TeeJet AITX 11008’s on 50 cm (20″) centres at 11.25 kmh (7 mph) and 3.44 bar (50 psi). That’s 3.35 L/min (0.89 gpm) per nozzle for a total rate of 350 L/ha (37.5 gpa).
TeeJet ConeJet TXVK18’s on 50 cm (20″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s 1.6 L/min (0.42 gpm) per nozzle for a total rate of 275 L/ha (29.5 gpa).
To test the coverage with these settings, we folded a piece of water-sensitive paper over a leaf to cover both surfaces, and wrapped one around a hollow tube to mimic a plant stem (see figure). Three plants were papered for each sprayer pass. Papers were collected, digitized and analysed for percent-coverage and droplet density. When diagnosing coverage for a horticultural crop, a distribution of 85 medium deposits/cm2 and 10-15% coverage is a reasonable standard for most applications.
Location of water-sensitive papers in situ.
The first condition (the AITX tips) averaged 17% coverage on upper leaf surfaces (37 deposits/cm2). These were coarser droplets at relatively low volume, so it was no surprise that we didn’t achieve 85 deposit/cm2 target. When using such large droplets, it is more important to achieve an even distribution and the 10-15% surface coverage (we achieved 17%). There were no deposits on the underside of the leaves (See figure 1), but that was also expected as coarser droplets tend to follow a downward vector that is not conductive to under-leaf coverage.
Figure 1 – Water-sensitive papers from three plants sprayed in Condition 1. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
The second condition (the ConeJets) provided better coverage. The fine droplets produced covered an average 17.5% coverage with a distribution of 99 deposits/cm2 on upper surfaces, and 23% coverage with a distribution of 185 deposits/cm2 on lower surfaces. Panoramic stem coverage was improved as well (see figure 2). This is excellent coverage, but the finer droplets were highly prone to drift (see below). With no form of drift control, this set up is undesirable.
Figure 2 – Water-sensitive papers from three plants sprayed in Condition 2. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.With no form of drift control, the finer droplets produced by hollow cones create unacceptable spray drift, even in moderate wind conditions.
This led us to propose a more directed boom arrangement: We set up a hollow cone over the row (the grower’s original ConeJet) and a drop hose suspended in each alley with two TeeJet XR 8004 flat fans positioned on an angle (i.e. not vertical or horizontal to ground). This gave sufficient height to span the canopy with as little direct waste on the ground as possible. As the crop grows, the nozzles would need to be twisted into a more vertical alignment.
ConeJet TXVK18’s alternating with drop hoses with TeeJet XR 8004’s.
We did not use an air induction fan to avoid the Very Coarse spray quality and we used 80° instead of 110° to ensure the spray did not overshoot or undershoot the plant. Here are the details of the third set up:
3. TeeJet ConeJet TXVK-18’s on 100 cm (40″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s 1.6 L/min (0.42 gpm) per nozzle. Also, two TeeJet XR 8004’s per drop on 100 cm (40″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s ~4.5 L/min (1.2 gpm) per drop hose. Together, set of nozzle for a total rate of 523 L/ha (56 gpa).
This set up raised the volume considerably and aimed spray directly at the sides of the plant. Coverage was excessive and in a few cases exceeded what the diagnostic software could reliably resolve (see figure 3). Since the plants were still small at this stage, it was decided we would let them “grow into the volume” and come back to check coverage once they were at full size.
Figure 3 – Water-sensitive papers from three plants sprayed in Condition 3. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
When we returned in mid-August the plants had reached full maturity. In this final coverage trial, we added a second water-sensitive paper to each plant to span the height of the crop canopy, which had grown considerably.
The same pepper plants ~5 weeks later had more than doubled in size.
Coverage was reduced compared to how we left things in July, but appeared to be sufficient on key surfaces (see figure 4). The papers showed upper leaf-surface coverage of 63%-to-offscale and deposit distribution of 137 deposits/cm2-to-offscale. Coverage on the lower leaf surfaces was greatly reduced to 4-4.5% and 36-90 deposits/cm2. Panoramic stem coverage was present, but minimal. Applying higher volumes would likely have improved matters.
Figure 4 – Water-sensitive papers from three plants sprayed in Condition 3, ~5 weeks later. Percent coverage and deposit density are calculated for the leaves, and a visual inspection is made of the stems.
When asked about the drop hoses, the grower reported “They are a bit of a nuisance because they take extra time to put on, and they get caught in the bush at the back of the field. But if they increase our coverage, then they’re worth the extra effort.”
Final thoughts
Adding drop hoses to a vegetable sprayer may be unconventional, but if fungicide coverage is a concern, and the drops will fit between rows, they might be worth a try. Carefully consider the volumes you use because they should reflect the size of the plant canopy you are trying to protect. Finally, water-sensitive paper provides excellent feedback to help you decide if your field volume, nozzle rates and nozzle positions are providing acceptable coverage.
We always admire the photos of sprayers in tulips produced by the Netherlands. Rose protection in Ontario is equally beautiful.
Nursery growers apply pesticides to a diverse range of plant species. In a perfect world, sprayer operators would adjust their sprayer set-up to match each crop, but this is rarely done because of time constraints and a lack of guidance. Adjustments in product rate and spray distribution should reflect the plant size, row spacing and developmental stage of the crop and pest. Any such adjustments should be performed using a reference point for coverage and a strong history of efficacy.
To demonstrate the value of sprayer optimization, we marked out three, 65m x 6.5m blocks in a field of roses. One block was an untreated control. One block was the grower’s traditional set up of hollow cones (D4D45) on 50 cm centres at 300 psi and 3.0 mph (841 L/ha). The third block was the experimental condition where we used an optimized set up of hollow cones (D3D45) on 50 cm centres at 150 psi and 3.0 mph (388 L/ha). We validated this condition using an iterative process to dial in the coverage indicated by water-sensitive paper.
Setting up water-sensitive papers in the rose blocks.Rule-of-thumb fungicide coverage on water-sensitive paper.
One application of Folpet + Nova was made on Sep 19, 2011. Roses were photographed before and after the treatment. The photographs were digitized and the amount of powdery mildew appearing on the upper surfaces was determined as a percent of the total visible leaf area. Six replications were randomly selected from each block.
Visual record of randomly selected roses prior to treatment (September 9).Visual record of randomly selected roses immediately following treatment (September 20).
There was no significant difference in the amount of mildew presented in the two sprayed blocks one day after the application (September 20). Eight days after application (September 27), there appeared to be better control in the optimized sprayer set up condition versus the grower’s standard set up. The large standard error bars in the grower’s condition made this statistically insignificant. It is unclear why the untreated block presented with the least visual mildew at this point. This preliminary work demonstrates the value of customized application settings and their potential to conserve pesticide, water, and fuel without compromising pesticide efficacy.
Results of optimizing sprayer set up on the visual occurrence of powdery mildew on rose leaves. Bars represent standard error of the mean. Unclear why control block presented less mildew on Sept 27.
The Ontario Farm Innovation Program and the grower co-operator are gratefully acknowledged for making this research possible.
The Fundamental Relationship, a concept by Professor D. Ken Giles (Emeritus), UC Davis Biological and Agricultural Engineering Department, is a way of talking about calibration without numbers and formulas. It is valuable for teaching concepts important to calibration. Since it is a relationship, it describes the variables needed and how they relate to each other.
We see here that land rate is inversely proportional to application rate. Thus, when land rate (either speed or swath width or both) are increased (and no other factors change), application rate is decreased. Likewise, flow rate is directly proportional to application rate. Thus, when flow rate is increased (and no other factors change), application rate is also increased. When flow rate is decreased (and no other factors change), application rate is also decreased.
The Fundamental Relationship is also a good way to do the math of calibration because nothing needs to be memorized. As long as the units are checked, you can’t go wrong. The Fundamental Relationship works for any sprayer calibration, as long as the units are tracked correctly and the flow rate correlates to the land rate, i.e., the land rate used is the swath that the nozzles (flow rate) are covering.
So, if the flow rate (GPM) used in the formula is for ½ of an airblast set up, the swath width in the land rate calculation would be ½ of the row width. If, for example, it is for a weed sprayer with 2 nozzles, the swath width would be the width the 2 nozzles are covering. Remember to think about this as what area is being covered by the spray:
Flow rate units are straight forward: gallons/minute.
Land rate can be a bit tricky because no one thinks in terms of acres covered per minute.
Land rate is tractor speed × swath width covered by the nozzles used to calculate flow rate.
Land rate in the above needs to be calculated in the units “ac/min”. Since there are 43,560 ft2 in an acre, the easiest way to calculate is to use the swath width in feet, and the speed in ft/min. Multiplied, this then will give you land rate in ft2/min, which can then be converted to ac/min.
Using MPH as Speed
When you measure speed in the field, those who have a speedometer on their tractor will tell you their speed in MPH. To go from a land rate with speed as MPH to ac/min, the following unit conversion is used when multiplying the speed in MPH times the swath width in feet:
Note: speed should always be measured and verified. Speedometers are notoriously incorrect!
Calculating nozzle flow rate (GPM):
You can also use the Fundamental Relationship to calculate the flow rate needed for a desired spray volume (application rate) when you have a set land rate (speed and swath width). This is necessary to help you choose your nozzles. Tractor speed is first determined by checking the coverage-using water sensitive paper or another coverage indicator like kaolin clay, and the fan (using ribbons in the canopy), to go as fast as safely possible while still getting adequate coverage. Swath width for any given field is set. What is left then is to calculate the GPM needed to achieve that application rate at that speed and swath width. This will allow you to select your nozzles based on individual nozzle GPM for a certain pressure.
To get the required GPM for one side of the sprayer, you multiply by ½:
GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]× 1/2
GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]
I’ve seen some folks round up the 990 to 1,000, which makes the above formula easier to remember.
Why I think the “495 formula” is bad for calibration
In my experience of teaching calibration math, folks often want to fall back on the formula they have used instead of trying the Fundamental Relationship. The problem I have with the “495 or 990” formulae, is that with using ground speed in MPH, often the step of measuring speed, a critical step for optimizing spray coverage, is eliminated.
Ground speed is assumed, the speedometer is assumed to be correct, and the entire step of measuring and setting speed is omitted-big mistake! Setting speed using flagging tape in the canopy and looking at the “Fan : Speed : Canopy” interaction is probably the most important step of calibration and optimizing coverage. So, if you must use the “495 formula”, please actually measure your ground speed!
Measuring speed manually
Typically, at least 100 feet are marked off to measure actual speed with a stopwatch. If you measure actual tractor travel time for a 100 foot length, you will likely find most common spraying speeds are timed in seconds. These can be converted to minutes, and then used in the formula for speed as ft/min which is then multiplied by the swath (or row) width in feet to obtain ft2/min, which can then be converted to ac/min.
If swath width is 6 feet, the land rate (or area the nozzles are covering) is calculated as:
264 ft/min × 6 ft = 1,584 ft2/min
In acres covered per minute, we divide by 43,560 ft2/ac to obtain a land rate of 0.036 ac/min. To travel 100 feet at this speed, it takes 0.37 minutes or 22.7 seconds. So, it is not uncommon to time 100-foot tractor runs in 21-23 seconds (which is why you need a good stopwatch). These runs are best done on the type of terrain to be sprayed; and it’s always good to take several times and average.
Remember that the speed is written as distance travelled/time. Sometimes when measuring speed, I’ve noticed that it will be written as time/distance travelled, which gives the wrong number. Track units!
Establishing an airblast nozzling solution is an involved process. We must first define the working parameters and flush out any special circumstances. Then we use an iterative approach to identify suitable nozzle combinations that require minimal changes to the sprayer.
This article outlines my process step-by-step and then applies it to a hypothetical orchard scenario. If readers wish to delve deeper into the variables or the reasoning, several links to supporting articles are provided. Be aware that nozzling the sprayer is the penultimate step in establishing optimal sprayer settings. Operators should first adjust air settings, which includes identifying a suitable travel speed. The last step in setting up any sprayer is to verify you are achieving threshold spray coverage.
Step One: Establish sprayer parameters
Is there more than one sprayer available? In diverse plantings, it may be more efficient to assign a sprayer to blocks that require the same nozzling solution.
How many nozzle positions are there on one side of the sprayer? If the nozzle bodies are roll-over style the operator can alternate between two different nozzles in each position. Some designs have twice as many nozzle bodies as needed. The intent is to assign two unique nozzle solutions in an alternating A-B set-up. This additional capacity gives us some flexibility if needed.
Is this a tower or a low-profile axial sprayer? Generally, we distribute nozzle flow evenly over a tower boom but distribute ½ the flow in the top 1/3 of the boom on a low-profile axial sprayer (depending on canopy shape and density). Air-shear and one-sided sprayers are special cases that are not addressed in this article.
What is the average travel speed, and can the operator easily change it? This process assumes the selected speed achieves a reasonable work rate while optimizing the interaction between sprayer air and the canopy.
What is the average operating pressure, and can the operator easily change it? For sprayers with positive displacement pumps, pressure is easily changed via the regulator. Not so for sprayers with centrifugal pumps. Pressure-based rate controllersempower an operator to dial in their desired volume and are easiest of all .
Step Two: Establish target parameters
What is the row spacing (or spacings)? Some operations include a variety of canopy morphologies and planting architectures.
What is the target volume (or volumes)? Operators often use a range of volumes to reflect the product being applied and the canopy area-density. This process assumes the volume will provide threshold, uniform coverage without misses or excess.
Step Three: Are there any environmental, geographical or adjacency concerns?
Each operation is unique, including conditions that may influence nozzling. For example, open water, sensitive crops, or residential areas adjacent and downwind of the planting may warrant drift-reducing nozzles or require the operator to only spray inward from one side of the sprayer. In another example, dry and windy conditions may require nozzles that produce a coarser spray quality will improve their survivability. Rolling hills and uneven alleys may cause sway that prevents the upper-most nozzles from consistently reaching the target.
Step Four: Find out why the operator is re-nozzling
The answer may reveal the operator’s willingness and ability to make changes to sprayer settings. For example, if their objective is to improve the match between sprayer and canopy it implies a willingness to take a more active role in spraying. Conversely, a less experienced operator might be satisfied with a more robust (i.e., wasteful) set up that does not require many changes between blocks.
Step Five: Determine the highest and lowest boom flow requirements
The following formulae relate travel speed, row spacing, and the desired volume sprayed per planted area to the output from a single boom. I recommend downloading this Excel-based calculator to make the process easier.
US Imperial Formula Output from single boom (gpm) = [(Sprayer Output (gpa) × Travel Speed (mph)) ÷ 990] × Row Spacing (ft)
Metric Formula Output from single boom (L/min) = [(Sprayer Output (L/ha) × Travel Speed (km/h)) ÷ 1,220] × Row Spacing (m)
Using the formula with the appropriate units, enter the highest desired volume, the fastest travel speed and the longest row spacing. This will give the highest rate of flow the boom must satisfy.
Repeat this process using the lowest desired volume, the slowest travel speed and the shortest row spacing. This will give the lowest rate of flow the boom must satisfy.
The ultimate objective is to select a combination of nozzles that can produce these two flows, distributed sensibly along the boom, with no gaps or excessive flow relative to the target. Ideally, the operator should be able to alternate between these two flows with as few changes as possible.
Step Six: Satisfy the highest flow
This step requires a nozzle manufacturer’s catalogue and a calculator (or the downloaded Excel spreadsheet). We must assume the range of available nozzle positions are oriented to span the target canopy with no over- or under-spray.
Divide the highest flow requirement by the number of available nozzles. Hypothetically, a nozzle size that produces this flow would satisfy the highest flow requirement while providing an even distribution along the boom.
Using the nozzle manufacturer’s catalog, find the flow table for the nozzle you want. Generally, a molded hollow cone nozzle is the preferred choice (e.g., TeeJet’s TXR ConeJet or Albuz’s ATR). If drift is a concern, there are also air induction (AI) hollow cones available. AI nozzles are most effective in the top two or three nozzle positions where drift potential is highest. However, they may require higher flow than calculated to compensate for a reduced droplet count.
Find the operating pressure (it may be in either the column or row heading) and find a flow rate in the body of the table that is as close as possible to your calculated ideal. It’s almost never an exact match, so choose the option that is less than the target rate – not higher.
Imagine placing that nozzle in every available position. Add up all the rates to determine how close you are to the ideal flow. It will likely be less. To compensate, replace the top nozzle on the boom with a higher rate and re-calculate the total flow. Repeat this process, substituting for nozzles with a higher rate, moving top-down along the boom until the flows match.
You have now satisfied the demand for the highest flow.
It is important to note that this process assumes the flow distribution along the boom should be relatively even, perhaps skewed towards the top. However, it is sometimes appropriate to distribute the flow differently to reflect each nozzle’s distance-to-target and the density of the corresponding portion of canopy it needs to spray. This tends to be the case when pairing low-profile radial sprayers with large or trellised canopies, and you can read more about that process in this article.
Step Seven: Satisfy the lowest flow
This is the art-and-compromise part of the nozzling process.
Confirm that the range of available nozzle positions still corresponds to the target. Quite often, the lowest flow is intended for smaller canopies. If so, we may no longer have as many nozzle positions to work with.
Imagine the sprayer is still nozzled for the highest flow per the last step. Leaving the highest effective nozzle on, imagine turning off every second nozzle. Add up the flows and determine how close you are to the lowest rate of flow. It is often still too much. Do not turn off any more nozzles or you may create gaps in the swath.
Instead, return to the nozzle catalogue and re-calculate the flows for the same nozzles, but using a lower operating pressure. Can you make that work? If not, you may have to go back further in the calculation (Step five) and recalculate the lowest flow required using a faster travel speed. This will reduce the demand for flow.
If none of those options are viable you will have to consider re-nozzling. Perhaps that’s swapping a few nozzles to lower rates. Hopefully this only requires the operator to flip a roll-over position, but it may mean using a wrench to remove caps and swap nozzles.
Once you’ve satisfied the lowest flow, the hardest part of the process is complete.
Step Eight: Satisfy the other permutations
The last step is no different than what we’ve already done. Go back to Step Five and calculate the flow for each spraying situation. That is, each unique combination of row spacing, travel speed and target volume. Using the nozzles already on the sprayer, adjust the pattern of nozzles in use (and pressure and/or travel speed if required) until each unique flow requirement is satisfied.
Step Nine: Record the setups, nozzle the sprayer and test the coverage
Be sure to clearly record the sprayer settings required to achieve each flow. Purchase the nozzles and take the time to test each set up using water sensitive paper to ensure coverage is achieved.
A working example
Let’s apply this process in a hypothetical orchard. I’ve included a screenshot of the spreadsheet I use to record the final nozzling solution (below) but feel free to design your own. It includes the nozzling solution for this example.
Our orchard is a 50 acre operation with both 11 and 15 foot row spacings. They have one tower sprayer with 15 nozzle positions on one side and they are not roll-over bodies. The operator wants to apply a 40 gpa volume (concentrated) and a 100 gpa volume (dilute). Their preferred travel speed is 4.5 mph and preferred operating pressure is 140 psi, but they are willing to change them if required.
We use the Excel calculator to work out the ideal highest and lowest demands for flow:
I usually shut off the lowest nozzle position because it almost never aims at the target. Let’s divide the high flow of 6.8 gpm by 14 available positions to give us an average output of 0.48 gpm per nozzle. This operator wants to use TeeJet TXRs, so using their table (below) we see that at 140 psi the Orange ’02 is too low and the Red ‘028 is too large. If we drop the operating pressure to 120 psi, the Red ‘028 is much closer at 0.465 gpm, so let’s do that.
A quick check gives us our current boom flow: 14 positions × 0.465 gpm per nozzle is 6.51 gpm of boom flow. We wanted 6.8 gpm, so let’s go up to the Grey ’03 in the top three positions. Now it’s 4 × 0.517 gpm + 10 × 0.465 gpm = 6.72 gpm. That’s close to our ideal 6.8 gpm, so let’s lock that down. If you want to see what this is in gpa, you can plug the value into the Excel calculator to discover it’s 99.6 gpa. Pretty darn close to our target 100 gpa.
Now using that nozzling arrangement, let’s see if we can satisfy the lowest flow requirement by shutting off every second nozzle position, leaving the highest position on. Doing so reduces us to two Greys and five Reds, totaling 3.36 gpm. That boom flow is much too high compared to the 2.0 gpm we need. However, in our hypothetical orchard, this block has shorter trees so we don’t need the highest nozzle. That drops us to only one Grey and a new total of 2.84 gpm. Good try, but it’s still too much.
Let’s reduce the operating pressure from 120 psi to 100 psi, which is as low as I like to go. According to TeeJet’s table, the Grey produces 0.473 gpm and the Red produces 0.426 gpm at this pressure. This gives us a new total of 2.60 gpm. Still too high! Well, let’s raise our travel speed from 4.5 mph to 5.0 mph and recalculate the lowest flow for Situation D:
This still won’t do it, and driving that fast (even if it’s possible) would change our air settings too drastically. Having exhausted all the easy options we have no choice but to re-nozzle the sprayer for the original lowest flow requirement.
Returning to the TeeJet table we see the best fit is to spray at 100 psi using one Red TXR80028 and five Orange TXR8002s. It’s a lucky break that our 1.98 gpm has come so close to the 2.0 gpm of flow we wanted.
Now let’s work out the best arrangement for the other permutations, Situation B and C. We need 5.0 gpm and 2.7 gpm, respectively. For Situation B, let’s use the nozzling solution from Situation A. We see that shutting off four nozzles gets us very close at 4.81 gpm or 97.3 gpa where we wanted 100 gpa. As for Situation C, let’s work from the nozzling for situation D. By adding a few more nozzles from that set, we can manage 2.71 gpm or 40.2 gpa.
Finally, we record all the settings (refer back to the spreadsheet image). We will need four Grey TXR8003s, ten Red TXR80028s and six Orange TX8002s per side, so 40 nozzles in total (plus a few spares for each rate). We will need to spray at 120 psi for Situation A and be prepared to shut off a few nozzles for Situation B. Situation C will require 100 psi and an entirely different nozzling and we will have to shut a few of them off for Situation D. Not only have we determined a nozzling solution, but we have revealed an efficient order for spraying the blocks that will require as little manual change to the sprayer as possible.
Summary
There is no one right answer to the question “which nozzles do I need” but there are certainly wrong answers. Bear this in mind when you buy a sprayer and the dealer offers you a factory-standard nozzle setup. Apply this process to your operation and be sure to use water sensitive paper to confirm the coverage and to make informed changes where required.
