Today’s sprayer has to excel at a lot of things. It has to have capacity and low weight. It has to go fast but be comfortable. It needs wide booms that stay level over complex terrain. It has to deliver the right spray volume at the right spray quality for the job. It has to be easy to fill and easy to clean. And of course, it has to be reliable, affordable, and come with dealer support.
We’ve definitely made progress in many of these areas. But the overall package still leaves lots of room for improvement and doesn’t address some issues that are of importance to applicators. Is it time for a reset?
Let’s say cost is no object. Here’s where I think the industry could go.
Focus on spray delivery
Spraying is done to protect crops. We need to do it without harming the environment while being economical with the inputs. These three tenets make up the Application Triangle, sometimes known as the 3 Es of spraying: Efficacy, Environment, Efficiency. The triangle represents the need for balance. A gain in one or two areas often requires a loss in another. That’s why there has never been a so-called “silver bullet” in spraying.
Priority 1: Only spray when and where required. Site specific treatments and IPM have been slow to make their way to the spraying world partly because of the low cost of inputs, but also because of difficulties defining and mapping areas that require different rates or products. The machine learning revolution is changing that. Green on Brown or Green on Green sensing can do more than save inputs. They can generate maps that document the change of weed patches over time, identifying priority areas and threshold densities and flagging problems early.
Priority 2: Integrate air assist. Air carries small droplets towards the target, protecting them from displacement by travel-induced or ambient winds. Once there, air can improve target interception and retention. It has to be done right, though, as improper adjustment can result in the opposite outcome. The reason it’s high on this list is because it improves efficacy and environmental protection at a modest cost.
Priority 3: Improve droplet size control. Nozzle design has improved, but the overall range of spray qualities that is achievable for any specific nozzle remains narrow. Sprays can be made finer or coarser with spray pressure, but this has implications for pattern uniformity. Twin Fluid nozzles currently offer the widest range of spray qualities, allowing one nozzle to do it all. We simply need greater droplet size flexibility on the spray boom.
Priority 4: Use nozzle-specific rate control. At minimum, a sprayer needs a system that allows for individual nozzle rate control within a wide window, say 4:1. This allows consistent dosing over a wide speed range, turn compensation, or local adjustments to dose for specific (sensed) canopy conditions. By layering direct injection at the nozzle on top of this, the sprayer can change rate and volume independently. Being able to spray the right amount in the right spray quality at the right volume, where needed completes the opportunity created by pest and canopy sensing.
Create better infrastructure
The backbone of the sprayer, the frame, drivetrain, boom, tank, pump, and plumbing, are responsible for carrying and delivering the spray liquid. Poor management of these variables results in an unproductive, heavy machine.
Priority 1: Prepare booms for future. A limiting factor in sprayer performance is boom width and stability. Consistent and low boom heights are the cornerstone of good application, ensuring uniform distribution, reducing drift potential, and improving targeting within the canopy. But perhaps as importantly, stable booms are essential for accurate optical spot spraying and any other sensing tasks that will rise in importance. Set a standard for sway, say target height plus or minus 10 cm along the width of the boom, 90% of the time. Do the same for yaw. Accommodate brackets for sensors and wiring harnesses when designing the boom fold.
Priority 2: Improve plumbing. Poorly executed sprayer plumbing causes waste and decontamination headaches. Although rubber hoses attached to plastic fittings provide a very versatile and generic building block, they generate and hide countless niches in which pesticide mixtures or active ingredient residue can accumulate. A simplified design that incorporates more engineered stainless steel tubing, smooth directional and dimensional transitions, interior surfaces that don’t accumulate residues and generate more efficient flows – all these would improve many aspects of the spray operation. It needs to be goal oriented – i.e., zero waste in priming and cleaning, guaranteed decontaminated after a rinse cycle. Draining on the ground should not be necessary.
Priority 3: Save weight. Weight causes compaction and eats fuel. Advanced materials or techniques can save weight while preserving strength. Savings can be applied to capacity. We need to explore advanced materials and trussed or exoskeletal designs (see “Aerodynamics”).
Priority 4: Consider aerodynamics in chassis and boom design. Wind blowing past a tractor, tank or boom, or counter-rotating air from wheels creates turbulence that displaces small droplets within it, reducing uniformity. Cleaner air makes it easier to use smaller droplets, easier to implement air assist or any other drift-reducing technology. This is no small task, as air can come from any direction. But as units become larger and travel faster, this effect can’t be ignored. Monocoque designs that use aerodynamic exteriors to carry machine weight may provide an answer.
Provide quality control
Spraying can be a guessing game, hence the terms “Spray and Pray”. We don’t know the outcome for days or weeks, depending on the mode of action, and by the time the result is known, it is too late to do anything if it’s unsatisfactory. But we can do better in assuring some sort of standard.
Priority 1: Confirm pressure, flow, and patterns at nozzles. The average sprayer has one flow- and one pressure-sensor. It can confirm the flow of the entire spray boom but cannot do that at the nozzle level. PWM has helped, by inferring flow from duty cycle. But actual liquid flow, and its pressure, remain unverified at the spray tip. A visual inspection of the pattern is necessary, and this is not only impractical but also wasteful and potentially hazardous.
Priority 2: Characterize canopy. If we knew the crop canopy was dense or sparse, we could adjust the water volume or rate of the product accordingly. LiDAR (Light Detection and Ranging) can characterize the physical structure of an object that would indicate density or porosity for which a dose (or droplet size, or air) adjustment may be necessary. This is not some future technology. The iPhone 12 Pro has it. Even RGB image processing could do something very similar.
Priority 3: Confirm coverage and drift. Say we’ve characterized the canopy and adjusted the atomization to suit. Is it having the intended impact? We will need a way to verify that the settings of the sprayer result in the required canopy penetration and coverage, even drift, on-the-go. We would need sprayer-mounted sensors that see spray deposits or an airborne spray cloud. The verification must be fast enough to make corrections during the spray operation. This kind of quality control provides the feedback loop to the first priority, spray delivery. It creates a perfect environment for machine learning and continuous improvement.
Priority 4: Improve user interface. The complexity of modern equipment monitors is great if you’re familiar with their features. But if you’re a new user or less comfortable with layers of screens and buttons and warning beepers, navigating the monitor can be a game stopper. Can we have beginner modes? Or a system where the monitor more actively engages with the user, asking questions or reminding a novice of key settings? The friendliness of the interface is a sleeper issue, it seems less important at first look but can over-ride many equipment features because of the power of a positive user experience.
I challenge sprayer manufacturers to conceptualize and show us the ideal sprayer they’re working towards. The perfect unit may never reach us, as this proposal is rife with technological and cost barriers. But it is nonetheless important to identify priorities and identify possible ways to meet them. As we creep towards the solution with incremental improvements, recall that its not the size of the step that matters, it’s the direction.
It’s finally that time of year to put away the most-used piece of farm equipment, the sprayer. Winterizing is a necessary step, but also an opportunity to do a few extra things.
Winterizing
Before you do anything, walk around the sprayer and note any telltale signs of liquid leaks. Once washed, the helpful dusty surfaces are gone and slow, chronic leaks may go unnoticed.
Now it’s OK to clean and rinse the sprayer tank and wash the sprayer exterior.
Drain any remaining water from the product and the rinse tanks. These remainders will cause unwanted dilution of the antifreeze. After you drain filter housings, inspect and clean filters.
Choose your anti-freeze. Automotive anti-freeze works, but’s it’s toxic and you can’t spray or drain it on the ground. Liquid fertilizer is sometimes used, but it’s corrosive, crystallizes when cold, and is not recommended. The best product is RV Antifreeze. It’s friendly to rubber and plastic, considered non-toxic, and can protect down to the coldest temperatures. Some dealers carry specific sprayer antifreeze. Don’t use fertilizer (e.g. 28) to winterize – especially with PWM systems.
Add between 25 and 50 gallons of antifreeze to the product tank, or if you have one, to the clean water tank. Most larger sprayers need at least 25 gallons just to prime the plumbing.
If you have a rinse tank, start a normal rinse procedure. Run the product pump, drawing from the rinse tank and pushing the material through the wash down nozzles into the product tank. Once the rinse introduction is complete, an automatic rinse procedure may subsequently open various lines leading to the tank as it swirls the rinse solution through the tank. Familiarize yourself with the specifics of that process.
If rinsing valves are manually controlled, once the antifreeze is in the product tank, run the pump, drawing from the tank and circulating back to the tank via agitation. If you have any other bypass lines, such as sparge, make sure the valve is opened. Run for two to three minutes.
If you have an on-sprayer eductor system, run the antifreeze past it and activate the eductor wash process.
Now, it’s time to push the antifreeze to the boom. Treat this like a boom cleaning, making sure the antifreeze gets to each nozzle body. If you have high- and low-flow options, open them to ensure the bypass gets the antifreeze.
Activate one boom section at a time and ensure all nozzles have received the antifreeze. Open nozzle end caps and allow the antifreeze the push out the water that is trapped there. It helps if you first purge the system with compressed air, then you don’t need to wait for the clear water to gradually change colour as the antifreeze arrives.
For extra points, rotate the nozzles through each position. As with cleaning or servicing, a remote-control boom section controller is invaluable here.
Remember to activate the fence row nozzles if you have any. These usually have their own dedicated feed line coming off the outer boom section.
If you filled your anti-freeze directly into the rinse tank, briefly open the rinse and product tank fill valves to allow anti-freeze to push out any water. Don’t forget the front fill line.
It’s OK to leave any leftover antifreeze in the tank. Next spring, collect it for re-use in the fall. You’ll still need more but this saves you some.
Don’t forget to also winterize your spray tender and any other transfer pumps.
It’s always a good idea to grease fittings after equipment is washed, to displace any water that got in, and to lubricate other moving parts that should be protected from corrosion.
Inspecting and Reflecting
You’re going to be looking closely at a clean sprayer, and this is a good time to spend a few extra moments to ponder the big picture. But first:
Inspect the full length of all hoses. Look for kinks, rubbing, small leaks, loose or defective clamps, valves, nozzle bodies. Tighten what’s loose, replace what’s worn.
Check cabin air filter service interval. Most new sprayers have activated carbon filtration that requires regular replacement. Activated carbon starts deteriorating with any air contact, so if you get a new one, leave it wrapped in its plastic until you need it.
Download or record sprayer performance data. How many engine and spraying hours? How many acres? How much water? A typical sprayer may calculate your acres per hour, but uses spraying hours only which paints a rosy picture. Do the calculation using gross engine hours to get a better idea of time lost to idling, transporting. Compare to previous year, perhaps set some goals.
Check with the dealer to make sure you’ve got the latest controller software version. Many systems get an upgrade during the off-season, so check back in the spring.
Remove the flow meter from the system and ensure it runs free. Do not use compressed air to run the impeller, this can ruin it. Simply blow on it and ensure it runs freely. This is an important part of the sprayer, so some people store it separately over winter. Did it provide accurate information?
Top up the fuel tank to prevent condensation.
Don’t forget to mouse-and bird-proof.
Now:
Think back on the season. What went well? What went poorly? What repairs were needed? Which ones did you put off? Are you happy with your procedures for filling and cleaning? Did you hear or read about improvements that seem interesting? Reminisce by reading the notes you wrote on your cab windows.
Make a list of the improvements that would address the main issues you came up with during your reflection. Is it time for a better filling setup? Do you need a whole tender system, or just an upgraded fill pump or a better inductor? Is it time to add a continuous rinse system?
Replacements and Improvements
Some sprayer components simply wear out and need regular replacement. A rule of thumb for sprayer nozzles is about 30,000 acres for an average sprayer speed and boom width. But before you buy, make sure you know what you need. Were you happy with the spray performance? Did you have more drift than you wanted, or poor coverage? As our cropping systems change, we may need different nozzles to suit the purpose. Now is the time to think about that very coarse low-drift nozzle that would have allowed you to get the spray on before the rain that delayed you for 3 days. Or the higher volume spray that would have done a better job with desiccating the tall canola crop, speeding up harvest. Or the finer spray that works better with the contact products you need to manage resistance.
Pumps can also wear. An impeller replacement can revitalize a centrifugal pump and give back more pressure and flow. Or a new pump with run-dry seals can avoid downtime from a pump failure in the middle of a good stretch of weather.
We still see plastic boom lines on some sprayers. Replacing them with stainless steel eliminates warped lines and makes spray patterns more accurate, improves cleanout, and adds sparkle.
A wider boom can dramatically increase productivity. After-market booms are available in 135′ and larger widths. Aluminum construction keeps them light, and corrosion-free.
Pulse Width Modulation (PWM) can be retrofitted on any sprayer. This will offer improved sectional control resolution, turn compensation, and better droplet size control.
Spot spraying can be added to any sprayer, and this will save 50 to 75% of pre-seed product use. In the case of WEEDit Quadro, these systems now come with stand-alone PWM that will work for general broadcast spraying in crop, with all the features mentioned above. Trimble offers the WeedSeeker II, it’s also feature rich but doesn’t offer PWM.
Become part of a mesonet. Most crop imaging services and some agronomic service providers offer weather stations, and obtaining one can make you part of a large, high resolution network. Local monitoring of temperature, rainfall, and wind conditions improves spray decisions as well, and may even give you the ability to identify temperature inversions.
The sprayer will often be the first piece of equipment used in the spring. Preparing it for its next job starts now.
The self-propelled sprayer revolution is complete in western Canada. Almost all sales of new equipment are self-propelled. In fact, the once thriving sector of Canadian-made pull-type sprayers, and the innovations they brought to spraying, has disappeared.
In its place we have self-propelled sprayers that offer plenty of power, large tanks, high mobility and comfort, and of course, the clearance required for late-season sprays. These features come at a cost: high capital expense, weight, fuel consumption and drift potential if the speed or boom height are not controlled.
The self-propelled machines are nice; however, customers are becoming concerned about overall value. Sure, the sprayer is the most-used piece of equipment on the farm, with the average field being treated four to five times per year. Does that justify the $500 to $700 k purchase price?
To answer this question, we need to evaluate the alternatives. Even though we’ve lost most North American pull-type sprayer makers, a few, such as Top Air, are left. A new pull type, the Connect Sniper, is being offered by Pattison Liquid. In addition, there are now several European manufacturers looking at our market. These bring large capacity, sophisticated booms plumbing and a narrow transport width. Let’s look at the issues:
The Connect Sniper, manufactured by Pattison Liquid, offers recirculating booms, Raven Hawkeye pulse-width modulation, continuous rinsing, and 120′ Millenium booms. The WEEDit spot spray system is also available.
Capacity
Not a problem. Top Air features tanks up to 2400 gallons and 132’ booms. Amazone builds a 3000 gallon tank twin axle sprayer (UX11200) with 132’ booms. The 230 gpm on-board diaphragm pump can fill the sprayer in 15 minutes. The Hardi Commander offers tanks up to 2600 gallons with 132’ booms. The Horsch Leeb TD12 is at 3170 gallons with 138’ booms. Equipped with air brakes, these sprayers can be trailed at up to 50 km/h.
The Amazone UX 11200 has an 11,200 L (2960 US gal) tank and tandem, steering axles combined with up to 130′ booms.
Clearance
The pull-types themselves have adequate clearance for most crops. The limiting factor will be the tractor and the hitch point. The availability of a high hitch point, and an 80 mm ball, on European tractors, is a boon for this. Although it may be necessary to shield the low standard drawbar and belly, pull-type owners report no long-term effects from the lower clearance.
The Horsch Leeb TD12 offers a 12,000 L (3170 US gal) tank and up to 1.25 m ground clearance (Photo: Horsch.com).European tractors offer 80 mm ball hitches for larger implements with high mounting heights to gain extra sprayer clearance.
Tractor
The pull-type sprayer makes most sense if it allows the re-purposing of an existing tractor. The common yard tractor isn’t enough, as the high capacity sprayers may require >200 hp with front wheel assist, especially in softer ground or hilly terrain. Another requirement is that the track width match the sprayer, and the European standard of a 2.25 m track width (centre to centre) can be hard to match in North America. New rims on the sprayer can push the width out, but the resulting increased axle stress may be problematic; these issues should be considered in advance. Fortunately, powerful front wheel assist tractors are finding a place on farms, even as seeding tractors. The changing over from one implement to another during a busy time can be a hassle, with a dedicated rate controller requiring additional cab real estate. But with the lower capital cost of a pull-type, a new tractor that also has other utility on the farm may be justified.
Large pull types require large tractors that may not already exist on the farm. The ability to match wheel tracks and the convenience of monitor hookups are important considerations.
Productivity
We’ve long maintained that productivity gain through increased travel speed creates more problems than it solves. It is virtually unavoidable to use somewhat higher booms with faster speeds, and it’s been proven that spray drift potential increases with travel speed. Instead, the sprayer features that save time are faster fill and clean times (reduced downtime), larger tanks (fewer stops to fill) and wider booms. Wider booms are easier to keep steady with slower moving equipment.
So how do typical self-propelled sprayers stack up against pull-types?
We compared two sprayers, a large pull-type with 3000 US gallon tank and a typical self-propelled with a 1200 gallon tank. Travel speeds were 10 and 15 mph, respectively, and fill times were 15 and 10 minutes. The slower pull-type turned in one headland, whereas the self-propelled used two to allow room for acceleration after the turn.
On half-mile runs, our “Productivity Calculator” at agrimetrixapps.com showed 129 acres per hour for the self-propelled and a respectable 119 acres/h for the pull type. The value of fast but infrequent fills and the more efficient turns made the difference for the pull-type. Use the app to compare other tank sizes, travel- and fill-speeds, or boom widths.
Productivity of a 3000 gallon tank pull-type (left) vs a 1200 gallon self-propelled (right), given specific speed, boom width, and fill times.
The specific design features of a sprayer may create additional productivity. For example, the ease of tank rinsing and cleanout can save time. European sprayers typically have lower remaining volume values, which increases the speed of tank rinsing and can eliminate the need for dumping tank remainders on the ground. Ease of filter inspection may seem trivial, but it permits more frequent confirmation that the system is clean and thus avoids potential future problems. An on-board pressure washer on the Amazone makes boom hygiene easier. It’s important to account for all these seemingly small gains because they add up.
Service
The success of any agricultural equipment relies on the equipment durability, fast availability of parts and service. Any new market entry will need to establish a dealer network, parts distribution system and superior service. This is no easy feat in a time of dealer consolidation. But without a drive train, there’s less to go wrong in a pull-type, and many plumbing parts are generic or can be obtained in metric equivalents.
With fewer mechanical components, pull-type sprayers require less service and are less prone to breakdowns.
Cost and Value
Prices vary, but a pull-type sprayer will usually cost less than half of a similar-sized self-propelled sprayer depending on the options selected.
With European-influenced equipment, the plumbing system will be more sophisticated, often offering recirculating booms, steering axles that follow in the tracks of the sprayer, narrow transport widths for greater road safety, an improved boom suspensions and levelling performance. It is safe to say that in terms of features, these sophisticated machines offer good value and many good design ideas. Operating costs are almost certainly lower, with better fuel economy and less drivetrain trouble.
The pull-type sprayer continues to have an important place to fill on our farms. With trade and weather anomalies lowering farm income, farmers are wary of being over-capitalized. It is conceivable that lower-cost and feature-rich alternatives to self-propelled units will have a fit. They certainly make sense on smaller farms that may not be able to utilize the full performance of a self-propelled, or on a larger farm that needs extra capacity but doesn’t want to bear the capital cost of a second expensive sprayer. The inherently slower working speeds allow for lower booms, less drift, overall improved deposit accuracy and uniformity. They’re worth a closer look.
Authors: T M Wolf, B C Caldwell and J L Pederson. Originally published in Aspects of Applied Biology 71, 2004, in expanded form.
Abstract
Spray drift deposition into water bodies may pose environmental and health hazards, and buffer zones have been suggested as a means of mitigating water contamination. Field trials were conducted to determine the effect of nozzle type and riparian vegetation on spray drift deposition into wetlands. Three riparian vegetative types, minimal vegetation (grass), low vegetation (willow shrubs), and high vegetation (aspen trees) were compared with open field conditions. Spray was released upwind of wetlands with these riparian characteristics with conventional and air-induced low-drift nozzles. Low-drift nozzles reduced drift deposits by about 75% in the absence of any vegetation, and by 88 to 99% when vegetation was present. Dense willow shrubs resulted in anomalous downwind deposits, possibly because of air turbulence caused by low porosity characteristics. By considering vegetation effects, a 15-m buffer zone could be reduced to 5 to 7 m for conventional, and 1 to 4 m for low-drift nozzles without increasing deposits at the edge of the sensitive habitat. Both variables should be considered by regulatory bodies in their risk assessment procedures.
Introduction
Airborne transport is an important vector for movement of pesticides from agricultural land to receiving waters. In an effort to maintain low pesticide levels in water bodies in accordance with risk assessment protocols, the Pest Management Regulatory Agency (PMRA) is mandating minimum setback distances (buffer zones) from water bodies during a spray operation. Several additional variables can complement buffer zones in preventing spray drift, including low-drift sprays and riparian vegetation. Germany and the United Kingdom already account for these characteristics in their buffer zone regulations (Kappel and Taylor, 2002).
Vegetation has been shown to be effective at mitigating droplet spray drift in several recent studies and reviews (Richardson et al., 2002, Hewitt, 2001, Ucar and Hall, 2001) by reducing wind velocities and intercepting spray. The documented magnitude of the spray drift deposit reduction in these studies ranges from 50 to >95%, dependent on variables that include vegetation height, porosity and orientation relative to wind direction, and wind speed.
We studied the integrated effect of buffer zones, vegetative barriers, and low-drift sprays to determine the overall impact of spray drift deposition onto downwind water bodies.
Materials and Methods
Overview and Site Description
The study was conducted in 2001 on a farm field near Aberdeen, SK. Sprays were applied upwind of a water body, and drift deposits were collected on petri-plates placed near ground level. Experimental sites were chosen to represent different vegetation heights and types around the water body in question: low (uncut grass), intermediate (willow shrubs), and tall (aspen trees). These were compared to nearby open-field conditions. Two sprayer nozzle types were used in the study: conventional flat fan nozzles and venturi-type low-drift nozzles.
The grass barrier was comprised of a mix of grasses dominated by bromegrass (Bromus spp.) growing to a height of 75 cm. Willows (Salix spp.) were approximately 3 m tall with a density of about 0.15 m-2 and presented a fully foliated barrier for their full height. Willows extended for a width of about 7 m toward the edge of the water body. Trembling aspen (Populus tremuloides Michx.) were approximately 8 m tall, with foliation beginning 1.5 m above ground. Trees were present at a density of about 0.25 m-2 and extended for 8 m toward the water edge.
Figure 1: Site and sampler layout
Spray Equipment and Application Method
A Melroe Spra-Coupe 220 was used to make the applications. This sprayer was equipped with conventional flat fan nozzles (XR8003) and air-induced low-drift nozzles (TD11003) at 275 kPa, producing ASABE Fine and Coarse sprays, respectively. The spray boom was 10 m wide and nozzles were 75 cm above ground. Sprayer travel speed was 12.9 km h-1, at which the application volume was 100 L ha-1.
The sprayer tank contained a mixture of 2,4-D amine4 (4 g L-1) and Rhodamine WT5 (2 mL L-1), a fluorescent tracer dye which would be used to quantify the deposits. 2,4‑D acted to photostabilize the dye, and also provided a spray formulation with physico-chemical properties representative of agricultural pesticides.
Top row: Fine and Coarse sprays used in study Middle row: Tall and medium vegetation Bottom row: Short vegetation and open field
Application was made in a direction approximately perpendicular to the prevailing wind, with the downwind edge of the spray boom at the edge of the wetland’s riparian vegetation. This was usually about 15 m upwind of the edge of the water body (due to severe drought conditions, the wetland did not contain any water at the time of the trials). Three consecutive passes were made along the same swath in a 10-min period to obtain average meteorological conditions for all three vegetation types. Wind speed and direction, temperature and relative humidity were monitored during application using a portable micrometeorological station.
Sampler Layout
Downwind of the spray swath there were 3 parallel lines of eleven 15-cm diameter glass petri-plate samplers starting underneath the sprayer boom and extending 46 m downwind from the edge of the spray swath (Figure 1). Samplers were separated by 5 m within the line, and lines were about 2 m apart.
The deposition profile was also assessed under open field conditions, using the same sampler layout but on crop land with no riparian vegetation. These are referred to as ‘bare soil, or ‘reference’ samplers in this report and served as a baseline to determine the impact of the riparian vegetation.
Sample Collection and Analysis
Sample collection began 5 minutes after spray application was complete (See Table 2 for trial times). Beginning with the furthest downwind locations, petri-plates were covered with a plastic lid, and placed into dark boxes. Spray deposits on the samplers were washed off in the laboratory using 95% ethanol in three 15-mL washes. Final samples were made up to 50 mL. and two 20-mL sub-samples were collected in borosilicate vials and stored in the dark.
Within 24 h, subsamples were analyzed using a fluorescence spectrophotometer with excitation and emission wavelengths of 545 and 570 nm, respectively (Shimadzu Model RF-1501 spectrofluorometer equipped with Model ASC-5 auto-sampler). Instrument readings were converted to µg L-1 using standard curves and expressed as a percent of the applied dosage under the field sprayer.
The fluorescence spectrophotometer data were averaged over the three replicate sampling lines, adjusted for photolysis, and expressed as a percentage of the amount applied on-swath. Relationships of spray drift deposits with downwind distance were first visualized by plotting all data points, and then mathematically related through appropriate regression techniques.
Results
Meteorological Conditions
Weather conditions were favourable during the trials. Wind speed and direction were appropriate for the sampler layout and the experimental objectives. Mean wind direction varied by up to 44º from the ideal (270º) in 6 out of 12 trials, and was within 30º for the remaining 6 trials (Table 1). Mean wind velocities were consistently between about 17 and 21 km h-1 in all but one trial. Air temperature and relative humidity fluctuated between 14 to 22º C and 31 to 80%, respectively, on the trial dates.
Deposition Profiles
A visual review of the raw data suggested that a linear regression of the log of deposit amount and log of downwind distance would be appropriate. It was noted that for willow, the deposit profile tailed upwards after the 26 m mark. Based on a survey of the site, it was concluded that this tail was probably caused by the length of the spray pass exceeding the length of protection offered by vegetation. In other words, beyond the 26 m sample, drift had not been attenuated by a vegetative barrier. It is also possible that the airflow was deflected up over the low, non-porous barrier and returned to ground level beyond the 26 m distance (Carter et al., 2001).
Figure 2: Spray deposit profiles from Fine (top) and Coarse (bottom) sprays. The deposition data for the willow were regressed from 6 to 26 m, all others were taken to 46 m (see text for explanation).
As a result of the questionable data for this vegetation type, it was decided that it would be misleading to include the furthest downwind data points. Implications of this observation will be discussed later in the manuscript. All regressions were statistically significant, explaining between 61 and 99% of the observed variation. In 5 of 8 trials, more than 90% of variation was explained.
Drift Mitigation by Riparian Vegetation and Application Method
The predicted drift deposit at 15 m was calculated for all trials based on the regression parameters (Table 3). For the conventional sprayer on bare soil, the deposit amount was 0.322% of the applied dose. The distance at which this specific deposit amount would be achieved was then calculated for all other trials. This value is the buffer zone distance at which equivalent protection to the reference system was offered. Buffer zones could therefore be reduced by 55% (grass), 99% (willow) and 69% (aspen) using the conventional nozzle and 56% (bare soil), 74% (grass), 98% (willow) and 92% (aspen) for the low-drift nozzle.
Table 1: Buffer zone distances based on observed drift, calculated from regression.
The calculated buffer zone reductions were not equivalent to the observed drift reductions due to the unique regression slopes of each deposition line. For example, expected drift deposits at 15 m downwind on bare soil were reduced by 77% when the air-induced low-drift nozzles were used (Table 4), whereas buffer zone distances could only be reduced by 56% (Table 3). Furthermore, the effectiveness of the grass vegetation diminished with distance, reducing drift by 64, 50, and 28% at distances of 15, 25, and 45 m, respectively. Therefore, a complete deposition profile will be required for each vegetation scenario to accurately adjust buffer zones.
Table 2: Drift deposits expressed as a percent of the reference deposition line for two application methods, four vegetation types, and three downwind distances. All numbers are the mean of three separate experiments on the same location.
Riparian vegetation was typically more effective than low-drift nozzles in protecting water bodies from drift deposition. While grass reduced deposition by 28 to 64% from the conventional nozzle (depending on the downwind distance), willow and aspen reduced deposition by between 95 and 99% (Table 4). The willow was not considered at further distances since the data used for the regression were truncated at 26 m. Low-drift sprays provided some additional protection in all cases except for trees at the 45 m distance, where deposits increased slightly relative to the conventional spray.
Discussion
The aerodynamics of vegetative barriers are a complex phenomenon. Wind, upon reaching a solid barrier, is diverted up and over giving strongly turbulent conditions on the leeward side and a rapid return to free wind speed. For a permeable barrier like a hedge, the return to free wind speed is more gradual since some air filters through, reducing the pressure differential and allowing for less turbulence (Davis et al., 1994). Wind speed reduction is most pronounced for a distance of 5 H upwind and 30 H downwind at the 1 H height, where H is the height of the barrier (Rider, 1951). Nonetheless, there may still be an upward diversion of air (and spray drift) which may simply delay, not eliminate, sedimentation (Hewitt, 2001, Ucar and Hall, 2001), particularly for dense hedges (Carter et al., 2001). Richardson et al. (2002) did not, however, notice such a deflection up to 10 m height.
The reduction in drift deposition by riparian vegetation in this study is clearly significant, but is subject to some interpretation. These data were generated at a single site, and while this site was carefully selected to be representative and trials were repeated three times, it does not necessarily constitute an average result. There are clearly any number of possible arrangements of trees, shrubs and grass, plus any additional vegetative or landscape features which would influence drift deposition behaviour. However, due to the consistent nature of the data of this study, some confidence is attained in that the numbers are at least reliable for the given set of conditions. In this study, three spray passes were made along the same swath at the edge of the water body. Results could have been different had adjacent spray swaths been used, owing to the possible change in contribution of upwind swaths with the altered airflows under vegetated conditions.
Since the water body was dry, additional grass vegetation which had grown up could have made an effective collector of spray drift, possibly reducing deposit values beyond those that would have occurred in a water body. It is recommended that efforts be made to repeat these studies when water is present at normal values.
The mitigating effect of vegetation depends on the aerodynamic features of the vegetation, as well as the collection efficiency of their leaves, twigs, etc. This poses some difficulties because there are no absolute measures of these features. Permeability, for example, varies with wind speed owing to the movement of leaves, and winds speed itself varies with height (Davis et al., 1994). Collection efficiency of the vegetation varies similarly with target size, its movement, wind speed, and droplet size spectrum (Hewitt, 2001). However, there are opportunities for improved characterization with specialized equipment, such as that used by Richardson et al. (2002). Their LIDAR instrument was able to help calculate tree height and width, mean area index and mean area density. Work to further characterize vegetation will prove useful in future efforts to understand its mitigating potential.
Low vegetation such as grass has not received the recent attention of hedges and trees but has also been documented to reduce spray drift significantly. A study by Miller et al. (2000) documented significant reductions in airborne drift concentrations above uncut grass canopies, even at low plant densities. Bache (1980) documented similar reductions in spray drift when sprays were applied over a mature wheat crop compared to bare soil. Therefore the filtering effects of “low” canopies may be very significant and should be the subject of further study.
Riparian areas are regions of high biological activity and diversity, not only protecting adjacent water from outside influence, but also providing food and shelter for many species of wildlife. These areas must themselves be protected from harmful effects, which can include pesticides. Their efficient capture of sprays suggests some risk from pesticides capable of controlling perennial vegetation. Likewise, pesticide residues in this vegetation have the potential to be ingested by wildlife or be washed off with precipitation, resulting in movement into the water body. These effects must be considered when using vegetation to mitigate airborne drift.
Conclusions and Recommendations
Vegetative barriers reduced spray drift deposition from conventional or low-drift nozzles into water bodies by 24 to 99%.
Low-drift sprays reduced deposition by about 75%.
Of the vegetation types, shrubs and trees had similar effects, reducing deposition from open-field conditions by an average of more than 95%. Low-drift sprays improved on this reduction.
Calculated buffer zone reductions were less than drift deposit reductions. Accurate determination of buffer zone distances requires that the entire deposition profile be characterized.
It is suggested that both riparian vegetation and sprayer technologies are important components of water body protection. Both should be considered in BMP and regulation development whenever the impact of pesticide applications near water bodies is to be estimated or mitigated.
Acknowledgements
The technical assistance of Glenda Howarth, Jill Clark, Rachel Buhler, Murray Nelson, Trevor Linford, and Pam Reynolds is greatly appreciated. Financial assistance was provided by the Rural Quality Program of the Agri-Food Innovation Fund, administered by the PFRA. The authors wish to thank Darrell Corkal and Clint Hilliard of PFRA for their enthusiasm, support and guidance directed towards this project, and Raymond Malko for making his land available for the trials.
Citations
Bache, D. H. 1980. Transport and capture processes within plant canopies. Spraying Systems for the 1980’s. BCPC Monograph No. 24, 127-132.
Carter, M. H., R. B. Brown, K. A. Bennett, M. Leunissen, V. S. Kallidumbil, and G. R. Stephenson. 2000. Methods for reducing buffer zone requirements for pesticide spraying adjacent to wetland environments. Sainte-Anne-de-Bellevue, Quebec: Proc. 2000 National Meeting, Expert Committee on Weeds / Comité d’experts en malherbologie [on-line: http://www.cwss-scm.ca/pdf/ECW2000Proceedings.pdf].
Davis, B. N. K, M. J. Brown, A. J. Frost, T. J. Yates, and R. A. Plant. 1994. The effects of hedges on spray deposition and on the biological impact of pesticide spray drift. Ecotoxicology and Environmental Safety 27:281-293.
Hewitt, A. J. 2001. Drift Filtration by natural and artificial collectors: a literature review. Special publication by Spray Drift Task Force, 12 pp. [on-line: http://www.agdrift.com]
Kappel, D. and W. A. Taylor. 2002. Buffer zones and “low drift” equipment. Hardi International Discussuion Paper, available from Hardi International A/S Helgeshøj Allé 38 DK-2630 Taastrup.
Miller, P. C. H, A. G. Lane, P. J. Walklate, and G. M. Richardson. 2000. The effect of plant structure on the drift of pesticides at field boundaries. Aspects of Applied Biology 57:75-82.
Richardson, G. M., P. J. Walklate, and D. E. Baker. 2002. Drift reduction characteristics of windbreaks. Aspects of Applied Biology 66:201-208.
Rider, N. E. 1951. The effect of a hedge on the flow of air. Quarterly Journal of the Royal Meteorological Society 78:97-101.
Ucar, T. and F. R. Hall. 2001. Windbreaks as a pesticide drift mitigation strategy: a review. Pest Management Science 57:663-675.
Wolf, T. M. 2000. Low-drift nozzle efficacy with respect to herbicide mode of action. Aspects of Applied Biology 57:29-34.
Site-specific treatments have long been a goal in agriculture. It makes sense to provide inputs or treatments at rates that reflect the local situation. And to a large degree, those capabilities have been available for fertility and seed inputs for some time, with input zones reflecting soil types or topography.
Typical prescription map for nutrients (Source: Field Crop News)
But the
sprayer world has not seen as much site-specific treatment. One reason is that
pest maps are time-consuming to generate and their usefulness may be
short-lived. Or perhaps weeds are fairly ubiquitous, and it usually makes sense
to treat an entire field. Another reason could be that sprays are relatively
inexpensive compared to fertilizer or seed.
For
spraying, we need to re-define site-specific.
While
traditional zone maps (corresponding to, say soil type and/or elevation or
slope position) allow unique treatments on a scale of acres, new sensors have
allowed sprayers to basically leapfrog this approach and treat each square foot
uniquely. These sensors identify plants directly and create an immediate
treatment response.
Optical Spot Spray(OSS) principle (adapted from WEEDit)
The idea, and technology, has and been around agriculture since the early 1990s, with the Concord DetectSpray and later the Trimble WeedSeeker. For various reasons, these two never became widespread in North America, although a significant market formed in Australia and New Zealand. New cutting edge technologies are about to change this.
Green on Brown
Two main manufacturers have occupied the traditional Green on Brown Optical Spot Spraying (OSS) space, the Trimble WeedSeeker and WEEDit. Both have been available for over 10 years and are well established and proven reliable. WeedSeeker uses the Normalized Difference Vegetation Index (NDVI) principle to detect green on a non-green background. It employs one sensor per nozzle and the nozzle is either on-or off based on what the sensor detects. The WEEDit system is manufactured in the Netherlands by Rometron (https://www.weed-it.com/), and is widely adopted for use in Australia and South America. It is now making inroads into North America. The most recent version is named Quadro.
WEEDit spray booms contain sensors placed at 1 m intervals. These scan the ground ahead of the boom, identify the presence of plants, and trigger the nozzle in line with the plant. The newest Quadro sensor contains four channels so that its resolution is actually 25 cm (10″) wide. The boom therefore contains a nozzle every 25 cm, and this nozzle has a correspondingly narrow fan angle that treats just this space.
Hypro even spray (banding) nozzle with 30 degree fan angle. 30 and 40 degree nozzles are currently installed on WEEDit on 10″ spacing. 30 degree fan achieves approximately 8″ to 10″ band at target height. Boom stability is important
The detection principle is based on the quality of light that is reflected from living plant tissue compared to everything else. A red (older generation) or blue (newest generation, Quadro) light is emitted, and chlorophyll-containing plants reflect a unique wavelength that differentiates them from ground or dead plant material.
Older generation WEEDit sensors were placed at 1 m intervals and had five channels, each covering a 20 cm band. There were 180 nozzles on a 36 m (120′) boom.
The
response time of the system is very fast. Triggered by small solenoids, a
sprayer travel speed of up to 15 mph is possible when the sensor looks 1 m
ahead. Furthermore, the software allows the user two important controls: first,
the sprayed distance before and after a detected plant can be buffered between
5 and 20 cm, resulting in a sprayed patch between 10 and 40 cm long. This could
be useful when boom heights fluctuate and placement of the sprayed patch shifts
accordingly. Second, the user can select from among four sensitivity settings.
Higher sensitivity can detect smaller weeds but will also result in more false
results.
WEEDit Quadro sensor
One
reason the system has been successful in the southern hemisphere is the long
growing season that may require multiple spray passes outside of the crop each
year, and in which the weeds are relatively large at treatment time and
therefore easier to detect.
Water sensitive paper can be used to show whether a target has been detected (and therefore sprayed).
In North
America, the pre-seed spray window is relatively narrow and weeds may be very
small or just be emerging. The risk of a miss due to non-detection is therefore
greater. Fortunately, the WEEDit system has a feature that addresses this risk.
PWM valve for WEEDit, capable of instantaneous response at 10 to 50 Hz
The solenoids that trigger an individual nozzle are pulse-width modulated (PWM). This means that the application rate is adjusted according to travel speed via a duty cycle. And it offers an innovative capability: The entire boom can be programmed to spray a defined fraction of the full dose, to a maximum of 50%, as a background broadcast rate (called “Dual Mode” or “Bias”). The smallest weeds that escape detection are likely to be susceptible to this lower dose. Larger weeds are then detected and sprayed with an individual spot spray at the full dose. Dual Mode is typically set to about 25%; overall savings are less, but control is improved for those very early season situations.
A WEEDit Quadro boom can also be operated in “Cover Mode” for broadcast spraying where it functions as a full PWM system with turn compensation.
Currently, several hundred WEEDit sprayers are operating in Australia, and they’ve been available in Canada and the US since 2017. in 2019, Croplands, an Australian sprayer manufacturer owned by Nufarm, started representing WEEDit in Canada. It is available as a retrofit on existing booms, and can be ordered with a WEEDit Millennium aluminum boom that contains mounting brackets and wiring harness channels. Savings compared to broadcast spraying range from 65 to 85%.
In early 2021, John Deere announced its entry into the Green on Brown space with See & Spray Select™. This system is built around the ExactApply nozzle body and uses RGB cameras to differentiate green plants from non-green background colours. It will be in fields in 2022 according to John Deere. Similar RGB-based systems are in development by other manufacturers. Although their performance has not been compared side by side with WEEDit or WeedSeeker, initial specs suggest that the RGB systems are slower and are less able to detect small plants. Nonetheless, the future looks very promising.
In 2021, Hardi Australia announced a new product, called GeoSelect. This system does not have boom-mounted sensors, and instead sprays according to a prescription map developed by a drone. The advantage of this system is that the amount of herbicide needed is known in advance of spraying, and the knowledge of weed distribution in the field can allow for a more efficient coverage plan to be used. This system allows for spraying under any light condition, and adjusts for boom sway to ensure accurate placement. Drone map development is the responsibility of the applicator.
Green on Green
Green on Green spraying, which detects weeds within a crop and differentiates them from that crop, is advancing and the earliest commercial releases are now available in Australia, offered by a partnership between Bilberry and Agrifac (WeedSmart podcast here), as well as Bilberry and Goldacres with Swarmfarm. Others, notably the SmartSprayer from Amazone in partnership with Xarvio and Bosch and Greeneye Technology are entering field testing with commercial sized units in 2021 and 2022, respectively.
Opportunities for Optical Spot Spraying
Taken as a whole, optical spot spraying offers a number of opportunities for weed management.
Cost
Savings: OSS has
an appealing rate of return on investment. On a 5000 acre farm, a pre-seed
treatment of glyphosate plus tank mix for resistance management may cost
$10/acre, or $50,000 per year. At an average savings of 75%, that represents
$37,500 per year. Add other non-crop uses, such as post-harvest, and savings
increase. With eventual weed recognition in-crop, virtually all herbicide
treatments are candidates for such savings.
Herbicide
Resistance Management: Delaying the onset of herbicide resistance requires the use of multiple
effective modes of action in a tank mix. Cost is a deterrent to this practice.
With OSS, these tank mixes become affordable.
Efficiency: With 75% product savings, a tank
of product will last longer. The time lost to hauling water and product, as
well as filling the sprayer, will decrease. For example, WEEDit users are
spraying a full day on a single load. Or they may choose to use a much smaller
load, decreasing equipment weight.
Pre- and
Post-Harvest: Whether
for desiccation or weed control, site-specificity of late season sprays can
also be based on living tissue. Only regions in the field requiring the
desiccant are treated. Perennial or late-season weeds are selectively
controlled pre-harvest. Since herbicide rates in these applications are
typically higher, savings are significant.
High
value crops: Row
crops requiring multiple fungicide applications per season, such as potatoes,
can benefit from OSS. Sprays applied prior to canopy closure can thus avoid
gaps between plants, saving product.
Producer Innovation: One user of the WEEDit system in Saskatchewan developed an innovative use. Having missed a pre-seed spray, the applicator was faced with large weeds in a 1-leaf RoundupReady canola crop. By turning down the sensitivity of the system so the canola crop did not trigger the sensors and turning on Dual Mode, he was able to broadcast spray the field at a low glyphosate dose (sufficient to control the small weeds) and then apply a full dose to the larger weeds, triggered by the sensor.
Equipment Innovation: Since individual zones or weeds require unique doses or products, technologies like direct injection, remote nozzle switching, multiple smaller tanks and booms, and PWM will make more sense and grow. But the whole concept of detection and treatment can be moved away from pesticides to mechanical control or other techniques such as lasers, as does Carbon Robotics.
License
to Farm: OSS
makes intuitive sense not only to applicators, but also to the public at large.
Showing and using these technologies demonstrates stewardship practices that
are easy to communicate and understand.
Artificial Intelligence Scouting
Another approach is pioneered by several companies, for example Dronewerkers in the Netherlands (https://www.dronewerkers.nl/english/) Taranis (http://www.taranis.ag/), and Xarvio (https://www.xarvio.com). These companies have developed plant recognition algorithms that are currently able to identify over 100 different species. Each species can be divided into several growth stages. Taranis has launched a business in North America that scouts fields by high-resolution drone imagery, and then provides customers with maps that highlight potential agronomic issues such as weeds, disease, or insect damage.
Example of information available from artificial intelligence scouting. In this case, plant and foreign material information by species, relative abundance, and growth stage.
Resolution of the output can be species-specific (lambsquarters vs redroot pigweed), or by coarser resolution (broadleaf vs grass). The resulting output then shows the plant density at each location.
Weeds in a soybean crop (courtesy of Taranis)
Xarvio Scouting is a product in their Field Manager line (https://www.xarvio.com/en-CA/Scouting). App-based, the agronomist or producer takes pictures of their crops and the app is able to recognize weeds, diseases, insect feeding damage, as well as nitrogen status. The app is aware of other users in the area and basically crowd-sources emerging agronomic issues as they arise, communicating them back to the user.
The Xarvio Scouting app can identify certain weeds, diseases, and insect feeding damage from pictures taken while scouting (Screenshot from Xarvio.com).
The agronomic value of this information is clearly very high. Imagine knowing the distribution of weeds by species before and after treatment. Although we can already assess this when we walk fields, by conducting the task via drone we are measuring on a wide scale, permitting an accurate quantification of the treatment effect so its value can be assessed. This level of measurement intensity was not possible before. Yield loss models for time of removal of certain weeds at certain growth stages can be applied across the entire field, and economic analyses allows follow-up treatments to be tailored to specific portions of the field.
Green-Eye Technology artificial intelligence can differentiate these ragweed plants from the pea crop. (Courtesy Green Eye Technology).
Or
imagine following specific patches of weeds over time, to monitor the
effectiveness of a certain cultural practice, or be alerted to the
establishment of a resistant population while it’s still feasible to contain
it.
Heat maps can be generated to document weed patches, and perhaps monitor their size over time. (Courtesy Green Eye Technology).
When this information is converted to a prescription map, rate and tank mix composition (or cultural controls) could be varied as necessary by zone, or weeds could, in the future, be sprayed individually. Perhaps future autonomous robots could be deployed more efficiently.
Identification of plant symptoms in canola (Courtesy of Taranis)
Development and improvement of these technologies is ongoing rapidly. Finally, we may have all the pieces that can bring site specific weed, disease, and insect management to market.
