Category: Boom Sprayers

Main category for sprayers with horizontal booms

Ten Tips for Spraying in the Wind
Choosing the right time to spray can be tricky. Our gut tells us that spraying when it’s windy is wrong. The experts tell us that spraying when it’s calm is wrong. So when can you actually spray?
I’ve always advised my clients to spray in some wind, because it has a few advantages. The main one is that wind helps disperse the spray upward and downward, diluting the spray cloud fairly rapidly. Another advantage is that winds tend to be reasonably steady in their direction and velocity (or at least that can be forecast), so downwind areas can be identified and potential impacts are known or predictable. It helps if it’s sunny, because that improves the dispersion of the cloud even more.
First, let’s define “windy”. The classic wind scale is the Beaufort Scale, intended for the sea, but also used on land. The upper limit for spraying is probably Force 3 or Force 4, with upper limits of 20 – 25 km/h or so. The Beaufort Scale calls these “Gentle or Moderate Breezes” (they had to save the alarming words for hurricanes), and the scale provides good visual clues such as what wind does to flags, leaves, or dust.
Spraying under breezy conditions can be done fairly safely if you follow specific steps. The idea is to understand what the risks are and to manage them.
The cornerstone is to use a low-drift spray and match it to a pesticide that will work well with larger droplets. But there are other important aspects to consider. Below are the top ten to think about:
- Choose a herbicide that can handle large droplets. Glyphosate products are well suited to coarse droplets. But glyphosate commonly has contact actives in the mix, members of Group 6, 14, and 15, and these are less likely to perform well with big droplets than those that contain Group 2 and 4 mixes. Actives with soil activity also have more tolerance for larger droplets.
- Use a low-drift nozzle and operate it so it produces a Coarse (C) to Very Coarse (VC) spray quality, as described by the manufacturer. Dicamba labels call for Extremely Coarse (XC) to Ultra-Coarse (UC) sprays, and Enlist requires at least Coarse. To achieve these you may need to purchase new nozzles. Low-pressure air-induced nozzles operated at about 50 – 60 psi will generally be very low-drift, but lower drift models are available. If you need a finer spray, produce it either by increasing the pressure or moving to a finer tip. Do this when the weather improves, for contact modes of action.
The name, symbol and range of droplet sizes used to describe the median droplet diameter produced by nozzles according to ASABE S572.3
- Keep your boom low. Lowering the boom ranks as the second-most effective way to reduce drift, after coarser sprays. But there’s a limit. For low-drift sprays, you need at least 100% overlap (more for PWM), which is for the edge of one nozzle pattern to spray into the centre of the adjacent pattern. In other words, the spray pattern should be twice as wide as your nozzle spacing at target height. For most nozzles, a boom height of close to 20 inches is enough to achieve this overlap. That’s pretty low by current standards from suspended booms on self-propelled sprayers, so being too low for a good pattern will only happen due to boom sway.
- Maintain reasonably slow travel speeds. These reduce the amount of fine droplets that hang behind the spray boom, reduce turbulence from sprayer wheels, and they also make low booms more practical. An added bonus is less dust generation.
- Know what’s downwind and what harms it. Survey the fields on all sides of the parcel you’re treating. When you have a choice, avoid spraying fields that have sensitive areas downwind such as water, shelterbelts, pastures, people, etc. If you can’t avoid being upwind of these areas, make sure you check and obey the buffer zone restrictions on the label. These will also give you an idea if the product can cause harm in water or on land, or both.
- Let the weather help you.
  1. Take the wind from the side if you can. Going straight into the wind creates a lot of extra drift.
  2. Spray when the sun shines if you have a choice. Early morning, late evening, or cloudy days increase the distance that drift moves. When it’s sunny, the drift cloud disperses quickly and causes less damage.
- Consider a dicamba tip for special situations, even if you don’t use dicamba. If you’re in a situation where quitting and waiting is a poor option, these tips allow you to finish the job with minimal drift risk and with only slight reductions in product performance due to poor coverage.
- Use a low-drift adjuvant. Specific products such as Interlock or Valid have been shown to reduce driftable fines (<150 microns) by between 40 – 60%, without adding significant volume in coarser droplets. The response will depend on the nozzle and the tank mix, but can be very noticeable.
- Study drift and how it forms and moves. It’s about more than wind speed and droplet size. Knowledge in this area can help you work out the best strategies.
- Invest in productivity. You may not need it every day, but on occasions when you have a small window to avoid bad weather, it pays dividends.
- If you feel that drift is unavoidable and someone might be impacted by it, talk to those people first. It’s one of the most important things you can do.
Keeping pesticide sprays on target continues to be one of our top responsibilities.
June 8, 2021
Spraying Asparagus in Fern
This research was performed in 2012 and since then there have been considerable advances in application technology for asparagus in fern that should be considered. Be sure to read the epilogue at the end of this article.
Introduction
Diseases such as purple spot can have major economic impacts for asparagus growers, and the best line of defence is spraying the appropriate control products. The good news is that asparagus growers know this. The bad news is that there are few things harder to spray than asparagus in fern.
Asparagus infected with purple spot.
Asparagus in fern can stand 1.5 m (5 ft) high by 1.0 m (3 ft) diameter and is typically planted on 1.2 m (4 ft) centres. Asparagus in fern has a very dense canopy full of needle-shaped leaves. This dense canopy slows air movement, making conditions still, humid and very difficult for a spray droplet to penetrate.
Spraying asparagus in fern.
Spray coverage is a combination of two factors: the area of the target contacted by spray droplets, and the distribution of spray droplets over that target. For most insecticide and fungicide applications, reasonable coverage is reflected by 10-15% surface area covered paired with an even distribution of approximately 85 medium sized droplets per square centimeter. This is not a rule, but a guideline.
In order to determine the best way to spray, we have to be able to compare the coverage achieved. To do this, we used water sensitive paper, which is yellow until contact with spray turns it blue. Three sets of three targets were placed in approximately the same location for each pass.
Water sensitive paper arranged on stands, ready to be placed in the fern.
Water sensitive paper orientation and location in asparagus canopy relative to sprayer direction.
We tested five popular nozzle types, at two ground speeds using three carrier volumes to answer three questions:
1. Does spray volume impact spray coverage?
2. Which nozzle style gives the best coverage?
3. Does travel speed impact spray coverage?
Does spray volume impact spray coverage?
Five different nozzle types were used to spray three volumes onto the targets at 16 kmh (10 mph). This was repeated three times and target coverage was determined both as droplet deposits per cm² (see Figure 1) and total % covered (see Figure 2).
Figure 1. Average deposits per cm^2 for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).
Figure 2. Combined average percent coverage for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).
Cards in each position consistently received a significantly higher average deposit per cm² and significantly higher average percent coverage at higher spray volumes. The relatively low coverage in the middle position was anticipated given the orientation of the targets to the sprayer.
Therefore, it would appear higher volumes result in better coverage, at least up to 280 L/ha (30 gpa). Generally, there is a threshold where exceeding a given carrier volume results in a diminishing return.
Which nozzle gives the best coverage?
Coverage from five different nozzles was compared: the Hollow cone, Flat fan, Dual flat fan, Guardian Air and Air-induced hollow cone. Given that 280 L/ha (30 gpa) resulted in the best coverage, the following figures illustrate droplet deposits per cm² (see Figure 3) and total % covered (see Figure 4) at 280 L/ha (30 gpa).
Figure 3. Average deposits per cm^2 for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).
Figure 4. Average percent coverage for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).
The graphs show that each nozzle followed a similar trend, with more droplets at the top of the canopy, less or par at the bottom of the canopy, and considerably less in the middle of the canopy (which is not surprising given the orientation of the target around the stem).
The trend in droplet density from highest to least coverage is:
1. Hollow Cone
2. XR flat Fan
3. Guardian Air
4. Dual Flat Fan
5. Air Induced Hollow Cone
The percent coverage data was less clear. The top two nozzles for each position were:
Top Target:
1. Guardian Air
2. All other nozzles approximately the same
Middle Target (around the stem):
1. XR flat Fan
2. Hollow Cone
Bottom Target:
1. XR flat Fan
2. Hollow Cone
It can be argued that the target at the top of the canopy is easiest to spray, and therefore does not have as much importance as the middle and bottom targets. As such, it would appear that the XR flat fan and Hollow cone nozzles give the best overall coverage. It is debatable whether the higher droplet count from the Hollow cone is more important than the higher percent coverage of the XR flat fan.
Does travel speed impact spray coverage?
Hollow cone nozzles and XR flat fan nozzles were used to spray targets at two travel speeds and three volumes. Target coverage was determined both as droplet deposits per cm² (see Figure 5) and total % covered (see Figure 6).
Figure 5. Average deposits per cm^2 for Hollow cone and XR flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).
Figure 6. Average percent coverage for Hollow cone and XR Flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).
The variability in deposit density and percent coverage from medium/fine droplets created by the hollow cone nozzles make it difficult to determine statistical significance, but the trend suggests that higher ground speeds improve coverage in the middle and bottom of the canopy. This is likely due to the wake of the sprayer and the vortices created by its passage stirring fine droplets into the canopy.
Overall recommendations
The data suggest that coverage was improved when the sprayer travels at 16 kmh (10 mph) rather than 8 kmh (5 mph). Coverage was also improved at higher spray volumes, where 280 L/ha (30 US g/ac) provided the best overall coverage for all nozzles. As for the best nozzle, this depends on the application; the hollow cone created higher droplet densities than the XR flat fan, but the XR Flat fan created higher percent coverage. Higher droplet densities may be preferred when controlling disease with contact products, but spray drift becomes a significant concern. Higher percent coverage might be preferred with locally systemic products where complete coverage is less of a concern and preventing spray drift is a priority.
Epilogue
This work was performed in 2012. Since then there have been significant advances in sprayer design for spraying asparagus in fern. Dr. Torsten Balz (Bayer Application Technology Manager) kindly provided an example of such a sprayer (see below) and a video link to watch it in action. Drop arms that bring the nozzles closer to the target at all canopy depths are an ideal solution as long as the row spacing allows clearance without snagging the drops. Further, there have been developments regarding the use of hollow cones in an overhead broadcast application. Over- and under-laps in the hollow cone swath lead to double-dosing and gaps respectively that are referred to as “Technical Strip Disease”. Combined with considerable drift potential, hollow cones are not recommended.
Air-assisted drop arms greatly improve coverage uniformity in asparagus in fern. Photo kindly provided by Dr. Torsten Balz.
Special thanks to Max Underhill Farm Supply (Vienna, Ontario) for use of their sprayer and their assistance both spraying and placing water sensitive papers in the field. Thanks to Mr. Ken Wall of Sandy Shore Farms Ltd. (Port Burwell, Ontario) for providing the site and hosting the associated workshop, and thanks to TeeJet Technologies for their donation of parts and supplies.
June 3, 2021
Fundamentals of Spray Drift
The year 1989 marked my first spray drift trial under the watchful eye of Dr. Raj Grover and John Maybank. We evaluated the performance of several spray shrouds, Flexi-Coil, AgShield, Brandt, and Rogers, and wanted to measure just how effective they were. But in my heart I wasn’t interested in drift. I wanted to study herbicide efficacy. Anyway, I thought, we’ll do this trial and I’m pretty sure we won’t have to revisit the topic.
It’s now thirty-two years later and spray drift has interwoven itself into all my projects, remains one of the most powerful drivers of regulatory activity, is likely the most visible consequence of poor stewardship, and will stay as one of the dominant creators of public opinion around modern agricultural practice.
Drift has not gone away. And yet our understanding of it is far from complete.
Spray drift is defined as the wind-induced movement of the spray cloud away from the treated swath. Droplet drift can occur for all sprays, and it happens within minutes of the spray pass. Its cousin, vapour drift, is limited to active ingredients that are volatile, that is, they can evaporate from dry deposits after application. Vapour drift happens also starts at application but can persist for days after the spray application is complete.
Droplet Drift
Droplet drift can be divided into two phases that are separated by about 1 second and that are measured differently. “Initial drift” happens first and refers to the product that leaves the treated area immediately after atomization. It is airborne, is caused by air movement strong enough to displace droplets from their intended trajectory, and can be measured by placing air-samplers (any device that can capture droplets in air) close to the downwind edge of the spray swath.
Figure 1: Initial vs Secondary drift. Once the drift cloud leaves the treated swath, the relative strengths of turbulence and sedimentation determine the amount that remains airborne and the amount that lands downwind.
Secondary drift describes the airborne spray cloud that continues to move downwind from the swath edge, where it either remains aloft or deposits on the surface below it. It is typically measured using samplers placed on the ground that capture sedimenting spray droplets. The difference in method is important because it goes to the heart of the problem of understanding spray drift.
Figure 2: Droplet drift occurs when displacement energy exceeds droplet energy. The droplet’s combination of mass and velocity cannot withstand the energy presented by moving air.
Initial drift is actually quite easy to understand because its creation is intuitive. The displacement of droplets from the spray plume is a function of balancing two types of energy. The first, droplet energy, is the product of droplet diameter and velocity. The more energy in the droplets, the more difficult they are to displace, and that’s why larger, heavier droplets or fast-moving air assist are useful drift reducing tools. The second, displacement energy, comes from relative air movement, either from forward travel speed or wind and the associated turbulence. More wind or turbulence means more power to displace.
Figure 3: Initial drift follows an expected response to greater wind speeds and coarser sprays. Data from a pull-type sprayer travelling 13 km/h with 60 cm boom height.
Because initial drift is easier to understand, our most common advice for reducing drift is based on maximizing droplet energy and minimizing displacement energy. Lower booms, larger droplets, slower travel speeds, shrouds, or properly implemented air assist all help reduce initial drift. It makes sense that creating less initial drift will also reduce downwind deposition arising from secondary drift.
Figure 4: Management of initial drift is intuitive. We reduce drift by adding energy to the droplet and by protecting the droplet from exposure to moving air.
Downwind Deposition
After leaving the spray swath, the moving secondary drift cloud has two main options. It can deposit or it can remain airborne. Basic physics suggest that all objects eventually fall to the ground, and since smaller objects need more time, they drift further. But when atmospheric turbulence and topography are considered, it’s not quite that simple. These two complicating factors control what proportion of the drift cloud remains airborne, and what proportion deposits.
Drift trials show that about 20% of the initial drift amount returns to the surface within the first 100 m or so of the sprayer. The rest remains and rises in the atmosphere where it evaporates and gets mixed further.
Figure 5: The majority of secondary drift remains airborne. Data are for Medium spray quality from a pull-type sprayer with 60 cm boom height and 13 km/h travel speed
It happens quickly. Just 5 m downwind of the spray swath, the cloud is already 4 m tall. At 100 m downwind, we’ve measured its height to be 30 m.
The proportion of the spray that remains airborne depends on the spray quality and the nature of the atmosphere. If it’s windy and sunny, or if the spray is finer, turbulence sends more into the air. If it’s cloudy and the wind is low, we have little atmospheric mixing. As a result, a smaller proportion will remain airborne and more will sediment, and overall, we may actually have more potential to damage downwind areas.
When we graph spray drift deposit data from a windy day, the deposit amount decreases exponentially with downwind distance. Usually, drift damage follows the same pattern. The larger droplets that contain the majority of the dose deposit first. The smaller droplets go further and are more likely to mix in the atmosphere and rise with thermals.
Figure 6: Deposited drift decreases logarithmically with distance. Top, linear axes. Bottom, log axes.
Under temperature inversion conditions that are common on calm summer evenings, overnight, and early mornings, the damage from the drift cloud does not decrease the same way. The cloud containing the buoyant mist lingers over a large area. Without atmospheric mixing and its resulting dilution with time and distance, large areas can be damaged.
The Effect of Turbulence on Deposition
We’ve established that the more atmospheric mixing we have, the less spray will deposit on the ground, at least in the short term. How does this affect our thinking on the role of wind?
When we evaluated drift data from a number of trials, we always saw more initial drift with higher wind speeds, as expected. However, the downwind deposit did not usually increase significantly. We attributed this observation to turbulence generated by wind which lifted more of the initial drift higher into the atmosphere. To be clear, deposited drift did not go down with higher wind. It just didn’t rise as fast as initial drift.
Figure 7: The effect of wind speed on airborne drift (top line) vs deposited drift (bottom line) from a high clearance sprayer travelling 23 km/h and emitting a Very Coarse spray.
The effect of turbulence can be viewed as a good thing because it protects downwind objects. Rapid dilution reduces immediate drift damage. We can use turbulence to protect objects on the ground. It’s certainly better than the alternative, emitting sprays when the atmosphere can’t dilute them, such as in an inversion. In that case, downwind areas remain at risk for a long distance, and for a long time.
But we have to also consider what happens to airborne spray droplets. Some pesticides degrade in sunlight and stop being a problem. But others are more stable and may persist in the atmosphere for days or longer. During that time, they may move significant distances, ultimately returning to the earth’s surface in precipitation or in dust. Even though the atmosphere has diluted them, these deposits are measurable, and will show up in environmental monitoring of air, soil, and water. We may not be able to find out where they originate, but the public knows who to blame. Agriculture.
Vapour Drift
Vapour drift is another issue altogether. It can persist for hours or days after application, as long as the volatile product remains on a surface and conditions that allow formation of vapours persist. Vapour pressure is related to surface temperature, and losses increase with warmer surfaces. Some products enter the vapour phase when in contact with water, and release vapour after a rainfall.
In situations where vapour is released for several days after application, it becomes impossible to control its subsequent movement. For droplet drift, if we know the wind direction at the time of spraying, we know where the impact is likely to be. But vapour movement depends on conditions that may occur between now and three days from now, and these could include high temperatures, various wind directions, and even inversions in which vapours accumulate. Ultimately, the best way to avoid off-target vapour movement is to avoid using volatile products.
The Public Good
Spray drift is one of agriculture’s most important stewardship challenges, and our industry needs to continue to improve its track record. Sprayers have a difficult task of converting a relatively small volume of liquid into a spray that offers good target coverage yet doesn’t move off the treated area. Favourable weather combined with droplet size management are at the heart of making this system work, but there isn’t a lot of wiggle room. Once again, an emphasis on sprayer productivity is one of the most fruitful areas to invest in, as this makes the best of the sometimes rare conditions in which spraying conditions are optimal.
May 19, 2021

Methods for Applying Fungicides in Corn

This work was performed with Albert Tenuta (OMAFRA) and David C. Hooker (University of Guelph, Ridgetown).

Objective

Gibberella ear rot is a significant disease that reduces the quality of grain corn, especially with the accumulation of mycotoxins (such as Deoxynivalenol (DON)) produced from the causal pathogen(s). Infection occurs through the corn silk channel when ideal temperatures (~27°C) and high humidity are present. Cool, wet conditions after pollination favour disease development and determine the degree of infection. With crop management practices providing only modest improvements in disease control, strategies to increase the efficacy of fungicides are important to investigate. Research has shown that the timely application of fungicide labelled to suppress the disease can reduce mycotoxins, but only by ~50%. We wondered if changes in the method of application could give better results.

It is reasonable to assume that improvements in spray deposit uniformity and increases in overall spray coverage (up to some threshold) at the infection channel (i.e. the silks) should result in improved efficacy. Water sensitive paper is an excellent tool for the qualitative evaluation of spray coverage. However, recognizing the complicated relationship between dose and coverage, we also looked at the deposition of copper sulphate as a surrogate for active ingredient .

Our primary objective of this study was to compare various sprayer systems and nozzle configurations by evaluating both spray coverage and copper sulfate deposition at the silks.

Experimental Design

The test field of hybrid corn had a stand of ~80,000 plants/ha. It was located at Ontario’s U of G Ridgetown Campus and was managed similar to a grower’s field (e.g. fertility, etc.). In August of 2019 we evaluated nine sprayer rigs (or nozzle configurations) in a randomized block design.

The ground rigs were calibrated to deliver a spray volume of 190 L/ha and the aerial systems to deliver 47 L/ha. In order to achieve the target spray volume, the ground rig speed varied from 9.5 to 13 km/h, depending on nozzle configuration. The aerial applicators used the same nozzle configuration, travel speed and altitude as in their commercial field applications.

Sprayer	Nozzle Set	Notes
John Deere	Yield Center 360 UNDERCOVER drop pipes 75 cm (30″) spacing, each equipped with two Turbo TeeJet (TT) nozzles.	Drop pipes were centred between corn rows with nozzles adjusted to spray ~horizontally and directly at the corn silks.
John Deere	Pentair Hypro Guardian Air nozzles on 50 cm (20″) spacing.	Boom positioned to create 100% spray overlap at tassel height.
John Deere	Turbo TeeJet Induction (TTI) nozzles on 50 cm (20″) spacing.	Boom positioned to create 100% spray overlap at tassel height.
John Deere	Turbo TeeJet (TT) nozzles on 50 cm (20″) spacing.	Boom positioned to create 100% spray overlap at tassel height.
New Holland (front-mounted boom)	Wilger 60 degree conventional flat fan nozzles on 40 cm (16″) spacing.	Boom positioned to create 100% spray overlap at tassel height.
New Holland (front-mounted boom)	Wilger 60 degree conventional flat fan nozzles alternating with custom-made Wilger 40 degree conventional flat fan nozzles on 40 cm (16″) spacing.	40 degree nozzles were positioned between corn rows (interrow) while 60 degree nozzles were positioned over the tassels.
Hagie (front-mounted boom)	Drop hoses terminating with TeeJet Duo Nozzle bodies equipped with Turbo TeeJet Induction (TTI) nozzles were alternated with TeeJet XR110 nozzles.	Drop hoses were centred between corn rows but nozzles were not aimed directly at the corn silks (aimed down 45 degrees and spray parallel to ground rather than perpendicular). They alternated with the AI nozzles positioned over the tassels.
Helicopter	Air Induction TeeJet Turbo TwinJet (AITTJ) nozzles directed backwards.
Airplane	CP-111T nozzle bodies with CP256-4015 40 degree flat fan tips on 15 cm (6″) spacing.	Wingspan was 14.2 m with a 10.6 m boom width.

The field was divided into four replicated blocks (REP 1-4 in the image below) which corresponded with a single pass of the sprayer. The sprayers alternated direction with each pass over the four blocks. Depending on the ground rig, a single pass through a block might include more than one set of nozzles. For example, in the image below, a John Deere sprayer carried a different nozzle set on each of four sections, leaving the centre boom section off. Therefore, each block was subdivided into four experimental units that corresponded with each nozzle set. Further, to account for variability, each experimental unit was further subdivided into five ranges. Four water sensitive papers (yellow rectangles) were oriented sensitive-side up and fastened to random corn plants directly on top of silks at each of the five intersections between range and treatment for a total 20 papers. This was replicated four times for a final count of 80 papers per treatment.

The experimental unit covered by a nozzle set was four corn rows wide (~3 metres). Space was left between each boom section to provide a buffer and no nozzles were placed on the centre boom section. Four water sensitive papers (yellow rectangles) were fastened to random corn plants directly on top of silks at the intersection of each range and for a total 20 x 4 = 80 papers. The chevrons indicate sprayer direction.

Test plots at University of Guelph, Ridgetown Campus

Evaluating Coverage

Each sprayer applied copper sulphate (Plant Products Inc., Leamington, ON) at 2 kg/ha as a chemical tracer. Agral 90 was added to the spray solution at 0.1% (v/v) to better emulate a typical fungicide application. After spraying, each water sensitive paper was allowed to dry, collected and then digitized using a DropScope (SprayX, Sao Carlos, Brazil). Droplet density and percent surface covered were evaluated within the detection limits of the equipment. Dose (represented by deposit volume) was more relevant to this study than percent surface covered, so a spread factor was used to convert area covered to volume. Once the papers were scanned they were subjected to flame emission spectroscopy (FES) (Actlabs – Activation Laboratories Ltd., Ancaster, ON) to determine the amount of copper deposited.

DropScope digitizing water sensitive paper

Results

Deposit area and volume

Note that papers were placed singly, oriented face-up. This was a missed opportunity to explore abaxial (down-facing) coverage and may have created a small experimental error wherein deposition from copper sulphate would be accounted for on both sides, but would only resolve on one side for area and density analysis. The results from evaluating water sensitive paper suggest trends and serve as quality checks for the experiment.

The percent area covered on water sensitive papers was affected by nozzle configuration (P<0.0001). Ground rigs produced ~4.0-12.0% area coverage, while aerial produced ~0.7-1.0%. It is not appropriate to compare ground and aerial spraying using water sensitive paper. Water sensitive paper does not reliably resolve deposits under ~60 µm and therefore underestimates the deposits from aerial applications because their spray quality tends to be finer. Further, these figures have not been normalized to reflect the differences in sprayer volume (190 L/ha for ground versus 47 L/ha for aerial).

The nozzle configurations with the highest percent area covered were produced by the 360 Undercover drop pipes and the TeeJet drop hoses (~9.5-12.0%). Coverage variability increased with percent area covered, but the lower 95% confidence limit with the pipes and hoses still exceed the upper limit of all overhead broadcast nozzles.

When area covered was converted to volume, estimated deposit volume on water sensitive papers was also affected by nozzle configuration (P<0.0001). The estimated volume calculated from deposit area showed fewer statistical differences across nozzle configurations compared to area data. However, once converted, there was no statistically significant difference in the volume deposited by drops or most broadcast methods.

Copper deposition

FES residue analysis (i.e. evaluating the amount of copper deposited on targets expressed as mass density) complements the water sensitive paper data. There are some differences that should be noted:

All applications sprayed the same amount of tracer per planted area. As such, depositions are more fairly compared with no need for normalization.
FES can resolve copper deposits as low as 0.5 µg/sample and may be more sensitive than the WSP method, which does not reliably resolve deposits under ~60 µm.
WSP will only resolve coverage on one surface. However, when these papers are subjected to FES, deposits on both sides of the paper will be accounted for, providing a more accurate result.

As anticipated, there was no correlation between the area coverage or volume estimates and the FES-derived copper deposition data. Estimated copper mass density on water sensitive papers was affected by nozzle configuration (P<0.0001). Analysis showed 56% more copper deposited from the 360 Undercover nozzles (1.75 µg/cm²) compared to the next highest deposition (1.12 µg/cm²) which was from the drop hose configuration (P<0.05). We feel the TeeJet drop hose configuration would have performed better still had the nozzles been directed at the silks, and the alternating broadcast nozzles been omitted and flow redistributed to the nozzles on the drops (see below).

Copper deposition from the airplane was similar to ground rigs with broadcast overhead nozzle configurations. The airplane deposited ~2x the copper as did the helicopter. It is assumed this is because the rotary atomizer nozzles on the airplane produced a much finer spray quality than the TTI nozzles on the helicopter. This increased the number of droplets considerably and has been shown to produce better coverage, particularly at such low sprayer volumes. Learn more about droplet size and behaviour here.

Average copper deposition from the Guardian Air nozzle set was similar to all other ground sprayer overhead broadcast setups, but had the highest variability (Between 0.4 and 1.12 µg/cm²). Comparatively, the lower 95% limit of the 360 Undercover drop pipe deposited 3.4x the copper as the lower limit of the Guardian Air.

Conclusions

The best deposition was produced from the Yield Center 360 Undercover drop pipes, followed closely by the TeeJet Duo nozzle body on drop hoses.
The deposition from ground sprayers with overhead broadcast nozzles was ~30% less than that of the two drop nozzle systems tested.
The deposition from Guardian Air and TTI nozzles were among the lowest of broadcast nozzle configurations with higher variability, but differences tended not to be statistically different (P=0.05) compared to other broadcast nozzles.
The deposition from the airplane was similar to the ground rig overhead broadcast applications, but the helicopter deposited the lowest amount of copper overall, likely due to droplet size (see image below).

Helicopter with air induction TeeJet Turbo TwinJet (AITTJ) nozzles directed backwards.

Next steps

In the summer of 2022 we re-evaluated promising nozzle configurations from this study, as well as other application methods (see bulleted list below).

Include various RPAAS (remote piloted aerial application systems) designs.
Include the Agrotop Beluga drop hose (Greenleaf Technologies, Louisiana, USA) with two nozzle bodies to span the silking zone of the canopy.

We used water sensitive paper as a qualitative indicator, but folded them to get adaxial and abaxial data. We also used copper deposition to indicate dose. Once the results are analyzed we’ll write a companion article to this one.

In 2021 and 2022 a separate study was performed to evaluate the efficacy, ease-of-use and return on investment of the Beluga drop hoses in corn. An article describing that work can be found here.

Thanks to the agrichemical companies, students, equipment owners and operators that donated their time and equipment to make this study possible.

Bonus

Watch these very cool slow-motion videos of the airplane and helicopter applications. Note that there is no difference in how the spray behaves once released; It deposits as a function of wind, gravity and momentum and is not “blown in” by the helicopter.

April 21, 2021

Venting Liquid-Filled Pressure Gauges
Liquid-Filled or Dry?
Small-plot agricultural sprayers should have a pressure gauge on the wand or boom to ensure accurate application rates. Most are added after-market and the operator has the choice of buying liquid-filled or dry gauges.
Glycerine- or silicone-filled gauges are preferred because they dampen pressure spikes, pulsation and mechanical vibration. Compared to dry gauges, they are available in higher ranges and are less prone to moisture problems (which cause corrosion, accuracy and visibility issues).
We use 100 psi (~7 bar) liquid-filled gauges for our handheld sprayers. Only recently did we acknowledge the sticker affixed to the glass advising the user to cut the nipple off the rubber plug located at the top. Preferring to avoid messy leaks, we have always left it intact.
We wondered what impact, if any, this was having…
What are Vents?
Expensive gauges have mechanical vents that can be opened prior to use and closed to retain liquid when stored. More commonly, there is a rubber plug with a protrusion (referred to as a nipple).
Why Vent?
Mechanical, liquid-filled gauges are sealed to keep the liquid in. When there are temperature fluctuations, the liquid expands or contracts and creates “case pressure”. This exerts a force that interferes with the pressure reading.
According to Marshall Instruments, case pressure can offset the accuracy by approximately 1 psi (0.07 bar) for every 35˚F (20˚C) temperature change, but is only noticeable when measuring lower pressures (0-15 psi or 0-1 bar). Nevertheless, they advise all gauges should be vented prior to use.
The plug can be removed to allow the user to refill the gauge, maintaining an air space of about ½” at the top of the window. If the nipple is cut off, the gauge is permanently vented and will leak if the gauge is not kept vertical.
Testing
We performed an experiment to see if typical working temperatures had a practical impact on the accuracy of an unvented gauge. We suspended an unvented, liquid-filled gauge upright in a water bath at approximately 15˚C, 30˚C or 45˚C (59˚F, 83˚F or 113˚F) until it equilibrated. The high temperature may seem unreasonable, but gauges left in trucks on summer days get far hotter.
The gauge was quickly removed and placed in a manometer (Ametek T-975) where it was subjected to pressures of 15, 30 and 45 psi (1 bar, 2 bar and 3.1 bar) and readings recorded. This was repeated five times. We then vented the gauge and repeated the process.
Results
At first, there appeared to be very little difference in average accuracy of vented and unvented gauges. Accuracy refers to the closeness of a measured value to a standard or known value. Perhaps there was some small increase in the pressure reported by an unvented gauge, but very little practical difference.
However, when we look at variability we get a different picture. Variability is a measure of precision, which refers to the closeness of measurements to one another. The graphs show that an unvented gauge has greater variability (less precision) at lower temperatures and lower pressures.
A good way to think of accuracy and precision is using the classic archery bulls-eye metaphor. The unvented pressure gauge is best represented by the third image, where it is accurate (on average) but not precise (variable).
Real-World Example
What does this mean in practice? Consider someone spraying a small plot using a TeeJet XR8002 nozzle on a CO₂-powered hand boom at 30 psi. The difference in output between 30 psi and 40 psi is about 0.003 gpm / psi.
An unvented pressure gauge used on a hot day may read 1.5 psi lower, causing you to overcompensate and raise the pressure 1.5 psi higher than intended. That would result in 0.0045 gpm (0.5%) more applied. Compensating for an unvented gauge on a colder day might be closer to 0.009 gpm (1%) more applied.
Assuming a walking speed of 3.1 mph (5 km/h) and a swath of 20” (50 cm), the nozzle should emit about16.3 gpa at 30 psi. Unvented in the heat, that’s 16.7 gpa. At 33 psi, that’s 17.15 gpa. That’s almost 1 gpa more than intended. Potentially, the lack of precision could make a significant difference.
Conclusion
- Liquid-filled gauges are preferred over dry gauges.
- To ensure precision, the gauge should be vented prior to use.
- Permanent venting on a hand-held sprayer causes leaks, which is a nuisance, so we suggest simply lifting the edge of the plug with a screwdriver or fingernail to vent the gauge prior to each use.
This work was performed by OMAFRA summer student, Aidan Morgan.
April 20, 2021