Category: Boom Sprayers

Main category for sprayers with horizontal booms

  • Recirculating Booms – Introduction to the Concept

    Recirculating Booms – Introduction to the Concept

    Listen to the audio version of this article here

    A lot of people are intimidated by sprayer plumbing. One look at the spaghetti bowl of spray mix and hydraulic hoses and valves, and they walk away. It hasn’t helped that much of it is concealed under the frame and all of it is in the same black colour, so figuring it out on your own is almost impossible.

    Belly of a typical sprayer, showing black hydraulic and spray hoses.

    Let’s quickly review the basics. In all sprayers, the liquid in the tank is drawn out from the bottom and pressurized by a pump. The pressurized liquid is split into two main paths. One goes to the spray boom to hydraulic atomizers (nozzles). The other goes back to the tank to agitate the liquid and act as a pressure bypass when the booms are off. Bypass throttling changes pressure. That’s it.

    Sprayer plumbing diagram (Source: TeeJet).

    By the way, has anyone ever thought of some colour-coding or labelling the hoses and valves on a sprayer? We’d definitely appreciate that.

    Conventional boom sections

    Most North-American sprayers feed the pressurized liquid to the boom, where the flow is subdivided into physical sections that define the various portions of the boom that can spray at any one time. Older sprayers might only have two sections, the left and the right boom. Wide booms now have anywhere from 5 to 13 sections, each about two to four metres wide. Each section has a pressure feed to its middle, and each section terminates at two dead ends, at which we place caps or valves for flushing.

    A conventional plumbed boom with two sections. Each section has two terminal ends that require cleaning. Boom can only be flushed or primed by spraying or by opening boom end caps.

    Sprayer with nine sections, each controlled by its own valve and each running a dedicated feed hose.

    Two partial boom sections, each showing a central feed line and a capped boom end.

    Sectional boom end showing 10 cm of capped pipe beyond last nozzle body.

    Boom end with valve to facilitate draining and flushing.

    Any liquid that enters this type of boom must exit at the nozzle or the boom end. It must be sprayed out or drained. This poses three distinct problems.

    • If the boom contains water or a previous spray mix, the boom needs to be primed with the new product before spraying. We need to spray or drain the existing product out.
    • If we want to clean the boom or flush it with water, again we need to push the existing liquid out.
    • If we have dead spots in the boom section, such as a boom end, we need to take special care to flush those out as well.

    These characteristics complicate cleaning, create waste or contamination, and take time.

    Recirculating booms

    In a recirculating boom, the spray mixture enters the boom at one end and exits at the other, returning to the spray tank. In most cases, the left and right wing each has its own feed and return. Sectional control is achieved via individual valves (air or electric) placed on the nozzle bodies.

    There are two main types of recirculating booms on the market.

    The first system routes the pressurized mixture into the boom and shuts off the return line during spraying. When the nozzles are shut off for a turn, the return line opens automatically and the boom flow is pushed past the nozzles back to the tank. When the nozzles spray again, the return line closes to pressurize the boom. 

    Recirculating boom system offered by Pommier. One end of boom is pressurized, the other end is return. Return flows when boom spraying is shut off. Boom can be primed or flushed without spraying.

    This is the system used by Pommier, the French aluminum boom manufacturer who first introduced recirculating booms to North America.

    Pommier recirculating boom.

    Pommier boom showing stainless steel supply and return lines, as well as air-activated shutoff valve on nozzle body.

    The second type of system contains a 3-way valve, connected to the return line and the pressure side of the pump. This valve provides the option of either allowing the return line to go back to the tank, as above, or to also allow pumped flow to the return side so that the boom is pressurized at both ends.

    Recirculating boom that allows return line to be either pressurized by pump, or return to tank.

    Top view of D.O.T. Connect sprayer recirculating boom setup. Lower line is pressurized by pump. Upper line is return. Three-way valve allows return line to either go back to tank, or be pressurized by pump.

    Tidy setup of pressure and return lines on D.O.T. Connect system.

    This feature may be useful with long booms along which pressure drop is more likely to occur, or when very high flows are required, and was introduced to North America by the Dutch manufacturer Agrifac, about which we wrote here and reprinted Mick Robert’s article from Pro Operator here. A similar system is available from Rogator (starting in 2018) via their C-Series featuring LiquidLogic. It has also been used on the Connect sprayer, developed by Pattison Liquid Systems, for the D.O.T. autonomous platform.

    The main advantages of this design are that it provides the option of additional pressure to the spray boom to avoid pressure drop, and to allow any spray mix in the return line to be pushed and sprayed out to the boom for rinsing in the field. This lowers the remaining volume that needs to be diluted.

    Agrifac recirculating boom showing return loop at boom end.

    Boom end on Rogator Liquid Logic system. Note Hypro Pro-Stop E shutoff valve.

    Features

    Recirculating booms offer advantages in terms of preventing soil and water contamination and also in terms of simplifying the boom cleaning process. The design provides an opportunity to graduate to a better resolved sectional control as well due to the requirement for individual nozzle shutoff valves. 

    Due to shorter and less complex lengths of plumbing needed, stainless steel can be used for the return lines which decreases the potential for pesticide residue being adsorbed.

    To rinse a boom with product mix still in the tank, simply draw water from the on-board clean water tank and push it to the boom without activating any nozzle bodies. The mix in the boom is returned to the tank and replaced with water, nothing is sprayed or drained. The tank contents may become slightly diluted depending on the duration of the rinse.

    To rinse the tank as part of the sprayer cleanout, first spray the tank empty. Then introduce clean water into the product tank via the wash-down nozzles and spray that out. As always, either use several batches of  small clean water volumes, or a continuous rinse system, to dilute the remainder most effectively. There may be additional volume to dilute from the return lines compared to a conventional system, depending on the type of recirculating system is used. However, boom ends no longer exist and this saves effort and ensures a more thorough rinsing.

    To prime a boom that contains water, simply open the return lines back to the tank and allow the new mix to flow through the boom. Again, some dilution of the tank will occur due to the water in the boom.

    The value of spray-free rinsing and priming adds up. Each prime, for example, consumes about 30 US gallons before the spray reaches the last nozzle of the longest section. Much of that product ends up on the ground, probably while the sprayer is stationary, and probably in a similar place on the field year after year.

    Since a recirculating boom requires a powered individual nozzle shutoff, this adds some cost. However, the opportunity of improved sectional control via virtual sections is significant (most monitors offer 16 virtual sections that can be configured). Well-configured virtual sections can save several percent from overlaps.

    Recirculating booms remove many of the contamination problems associated with conventional plumbed sections. They save time, money, and reduce environmental impact. We think they should be offered on sprayers.

    Here’s a link to a nice article on recirculating booms written by Spencer Myers for the Manitoba Co-operator. A video that goes with the article can be found here.

  • Techniques to Improve Spray Productivity

    Techniques to Improve Spray Productivity

    Click here for an audio version of this article

    In almost all agronomic practices, timing is key. There are certain, and often small, windows of opportunity for getting a task done without losing yield potential or product quality. Weed specialists talk about early weed removal, pathologists talk about symptom monitoring, and entomologists remind us of economic thresholds. Acting at the right time is fundamental.

    Sometimes I’m asked about comparing two different methods of spray application. I usually dodge these questions by advising to choose the one that gets the job done on time. “An average application at the right time is much better than an excellent application at the wrong time” is how I put it. Sure, I’m dodging, but I really believe that. It’s mostly in the timing.

    Everything we do carries with it some time inefficiencies. Some are rooted in technology, others in habits. It’s the habits that are easier and cheaper to address. That’s why, when evaluating how to improve a spraying operation, I advise to start with a stopwatch and notepad, not a sprayer brochure.

    A stopwatch and notepad provides your path to greater productivity.

    Remember, if you want to improve a system, you first need to understand it. And to understand it, you need to measure it.

    So, do a time accounting.  You need to know how your time is used on a spray day. Note the time spent preparing for the job (loading supplies, double checking label instructions, transporting, etc.). The big users of time are sprayer transporting, filling and cleaning, but there are very many small time users and those can add up. This time is doubly important because these tasks occur during the spray day, when the weather is good and you should be maximizing spray time.

    Make your own time accounting sheet, including every detail or possibility.

    Even within any one operation, time can be subdivided. How much time is spent on a turn? Since a 120’ sprayer will make about 22 of these per half mile, that can add up. Even a spray monitor can play a productivity role if it quickly and consistently locks onto its swath. Needing to stop and back up while it searches for a signal can be costly.

    On our farm, we sometimes used custom operators to get the cereals off. I recall how aggravating it was to watch the 8820 inch ahead of my N6. Surely it must be throwing a lot over, I thought (it was). But I usually caught it at the truck, where my unloading speed was over 1 minute faster. Redemption, briefly.

    That same principle applies to these small efficiencies. A well-designed tender truck can speed loading and more than make up for lower spray productivity of a smaller sprayer.  A lighter sprayer load and flotation tires can save a ton of time if it means the difference between getting stuck or cruising through that spot. A set of extra-coarse nozzles that can be rotated into place in just two minutes can help finish a field if the weather changes, or allow a margin to be sprayed, saving a return trip.

    Extra nozzles to allow spraying in higher wind speeds without increasing drift are a productivity tool.

    A custom operator shared some very useful tips with me a few years back. He optimized the small things, such as re-locating the switch to deflate his suspension airbags after driving onto the trailer, to the platform beside the cab. He’d deflate while descending the steps, and by the time the tie-down straps were thrown across, the unit was ready to be cinched down. No waiting. He also opted for a slightly wider aftermarket boom so he had an even number of spray passes per quarter, saving another 2 minutes or so per field.

    The same operator made me aware of the importance of knowing exactly how much spray is in the tank at any one time. The majority of spray monitors are simply not accurate enough. A factory sprayer can count down from a full tank using its flow meter, but that requires two things to be accurate, the filled amount (entered by the operator, usually from a sight gauge) and the flow meter itself. Point is, when we fill the last load of a field, we don’t want too much left over, but we’d still rather not run out. By using the AccuVolume from Simon Innovations, he was able to fill accurately and he was also able to exactly monitor his liquid usage. If he had two passes left, and knew he needed exactly 150 gallons (also considering when his pump drew air), he could monitor that and make small adjustments to the application rate, if necessary, to get there. It’s a big deal because contending with a larger remainder is wasteful and takes time to deal with. The AccuVolume also helps make multiple small volume batch cleaning more accurate, and therefore easier.

    The AccuVolume measures your tank contents, to the nearest gallon, regardless of slope position. It’s a time saver.

    A small addition to the tender truck such as an electric hose reel or a swing arm that carries, say 20’ of hose, helps deal with the weight of a full 3” line. Or an air-line at the pump end can be used to blow the remaining water into the tank. Time, and mess, are saved. Still pumping product? Induction using a venturi is much faster.

    An electric hose reel makes handling 3″ plumbing manageable.

    Preventing problems is probably a better use of time than dealing with them. Take tank mixes, for example. With more products in the tank, and adjuvants such as conditioners, fertilizers, or low-drift products making their way in, anticipating mixing problems may require a jar test. Get the tools, and learn how to do them. It’s important to use the actual tended water in these tests, at the temperature it will be, because that, and water quality such as hardness and bicarbonates, can affect mixing. And don’t over-agitate, as that can create its own problems, especially as the tank runs down.

    Consider a hot tank. If extra labour is available, it removes a lot of time pressure for mixing dry, or multiple products. At filling time, simply pump it over and go.

    A hot tank gives you more time to mix properly, and makes transfers faster. (Some additional labour required).

    Consider improvements in the plumbing to save time. The new Hypro Express End Cap features a ball valve for flushing (existing Express End Caps can be retrofitted), and this valve can soon be fitted with the ProStop E (electric) valve. Flushing can then be done from the cab, saving time and mess. It’s a small change, but it brings joy.

    A new valve addition is available for the Express End Cap. Manual (shown) or electric available.

    The importance of time on a spray day can also be viewed economically. Let’s say a large area needs to be sprayed today, and the weather forecast calls for rain overnight. The rain will stop spraying for 5 days. What is the yield potential lost in those five days if weed or disease pressure is high? If 100 acres don’t get treated, what is the lost revenue? (for example, if 3 bpa is lost, at $6/b, that’s $18/acre or $1,800.) That’s what that hour is worth. Tell your boss.

    Getting more done means getting more done on time. Evaluate your habits and technologies on that basis.

    Evaluate your spray productivity with our

  • Do Labels Help us Apply Pesticides Properly?

    Do Labels Help us Apply Pesticides Properly?

    It happened three times this spring.  As is often the case, I was contacted by growers who wanted help with herbicide application.  In most of these calls, the discussion revolves around the proper choice of nozzles for a specific task, perhaps some questions on spray pressure, water volume and travel speed.

    But these three were different.  Instead of being seasoned applicators, all three were new to the business.  And more importantly, they had done their homework by looking at product labels before calling.

    Labels give us important information on product rates, crop and weed staging, mixing order, sprayer cleaning, and personal and environmental protection.  They’re very valuable there.  But they also provide application information, and that’s where the problems begin.

    Perseverance Required

    I have to commend my three clients:  they showed great tenacity by actually finding application information on a pesticide label in the first place.  This document is so mired in legalese protectionist language at the front that it discourages all but the most persistent.

    And often, the application information comes in several parts, interspersed among other information.  Mixing instructions.  A little later, application. Somewhere nearby, buffer zones.  Another paragraph for cleaning.  Rainfastness?  Keep looking.

    It forces the reader to skim through the document, hunting for relevant information.

    But once my clients found application instructions, they obviously questioned if they should believe it, or else they wouldn’t have called.  The application statements on many labels, simply put, are from long ago, and it’s obvious.

    Consider the following two label excerpts, the first from a product initially registered in the mid 1980s and still available, the second from one registered about 30 years later:

    1980s:

    Application should be made using a minimum of 55-110 litres of water per hectare, at a pressure of 275 kPa, or 310 kPa if using check valves, and at a ground speed of 6-8 kph.

    The use of 80° or 110° flat fan nozzles is recommended for optimum spray coverage.

    Do not use flood jet nozzles, controlled droplet application equipment or Sprafoil® equipment.

    Application of the spray at a 45° angle forward and higher water volumes will result in better spray coverage and penetration of the crop canopy.

    Uniform, thorough coverage is important to obtain consistent weed control. Higher water volumes should be used under dense crop and weed canopies to ensure thorough coverage of the target weeds.

    2010s:

    Apply in a spray volume of 46.8 – 93.5 L/ha unless otherwise specified in tankmix partner section of this label – at 207-345 kPa (30-50 PSI) pressure to ensure proper weed coverage.

    Flat fan nozzles of 80° or 110° are recommended for optimum coverage.

    Do not use floodjet or controlled droplet application equipment or Sprafoil® equipment.

    Nozzles may be oriented 45° forward to enhance crop penetration and to give better weed coverage.

    Uniform, thorough coverage is important to obtain consistent weed control. Higher water volumes should be used under dense crop and weed canopies to ensure thorough coverage of the target weeds.

    Thirty years apart, but remarkably similar.

    Crop protection companies spend about 10 yrs. and $250 million to produce a new pesticide and register it for use.  Having made this commitment, it would be most useful to see a small further investment to provide current application information that is relevant to applicators.

    After all, these applicators purchase the active ingredient to provide a return on this multi-million dollar investment, to the tune of about 2 billion dollars per year in Canada alone. They deserve good application information.

    Imagine this scene:

    “Doctor, thank you for this new high tech pharmaceutical engineered to help me with my serious illness.  How should I take it?”

    “Not sure.  Here, read this cough syrup label I found in my drawer.  Should be pretty close.”

    It’s clearly ridiculous

    Let’s dissect these labels to see how they could be improved.

    Flat fan nozzles of 80° or 110° are recommended for optimum coverage…

    Our sample labels refer to what we assume are conventional flat fan nozzles.  While popular in the 80s, these have all but disappeared from sprayers over the course of the past 20 years or so.  We haven’t recommended them since then because they drift too much. They’ve been replaced by low-drift nozzles, either pre-orifice, or air-induction.

    Nozzle fan angles are now generally 110 degrees or more, and frankly, the difference between 80 and 110 degrees is not that important.  What’s important is proper overlap, achievable with a visual assessment followed by boom height and pressure adjustments.  Unfortunately the label is silent on that.

    Application should be made … at a pressure of 275 kPa, or 310 kPa if using check valves…

    A nozzle’s recommended operating pressure depends on the specific nozzle model and on the spray quality (average droplet size) required. With literally many dozens of nozzles now available to each applicator, general pressure suggestions are likely to be wrong, and are more of a liability than a help. And they force label non-compliance when over-ruled by a nozzle manufacturer’s recommendations.

    Speaking of spray quality, growers crave to know at what spray quality a product should be applied for best performance and lowest drift. Some labels refer to spray quality (e.g. “apply with a Coarse spray”), but this is with reference to spray drift and buffer zone distances, not efficacy, and that distinction is not made.  Knowing the right quality for efficacy would help applicators choose the right nozzle and pressure to meet that criteria.

    Higher pressures if using check valves?  Nobody has brass screens with check valves anymore.  Sprayers have had modern diaphragm check valves for a generation, and those don’t produce pressure losses.

    And we all know that six to eight km/h is hardly a common speed these days.

    Do not use floodjet or controlled droplet application equipment or Sprafoil® equipment

    Sprafoil nozzles have not been produced in Canada for about 25 years, in fact their manufacturer is no longer in business.  Controlled droplet atomizers, while becoming more popular again on aircraft, were last seen on ground sprayers in the 1980s. Even then, total installed numbers were probably in the single digits.

    As for FloodJet nozzles, those went out of style for herbicides in the late 70s, and were replaced by the very successful TurboTeeJet nozzles shortly after.

    Nozzles may be oriented 45° forward…

    Nozzles are rarely tilted 45 degrees forward for herbicide application anymore.  Maybe that’s because spray booms aren’t built that way today, or because modern booms on self-propelled sprayers are now about 30” (75 cm) above ground, and we travel at about 15 mph (22 km/h).  So the forward tilting, though shown to be effective for grassy weeds at 5 mph (8 km/h) and 20” (50 cm) boom heights, as researched in the 1970s, isn’t relevant for herbicides with higher booms.

    Uniform, thorough coverage is important to obtain consistent weed control.

    Statements advocating for good coverage are nice, but they aren’t useful.  Everybody knows we want good coverage.  What applicators need to know is how they should measure coverage, and what good coverage actually is.  Can we use water-sensitive paper?  How much of the target should be covered?  How many droplets should be in each square centimetre?  How can we measure that in the field, right now? How does it depend on the crop canopy, on weed stage, and on spray quality? The more information an applicator gets, the higher the chance of success.

    Apply in a spray volume of 46.8 – 93.5 L/ha…

    The only statement that survives our little examination is about water volume. Water volume is important.  But even there we have a problem.  The volume is in L/ha.  This is useful in some parts of Canada, but not in the west, where producers communicate primarily in US gallons per acre.  And in the west, provincial guidelines have generated this odd hybrid of L/acre, which few people use for spray volume.  But 46.8 to 93.5 L/ha?  How is that level of precision justified? (I know that this is a conversion from 5 and 10 US gpa…so why not just say so?)

    A Solution

    The problem with having outdated or impractical information on labels is that it creates disrespect.  Since labels are documents enforceable by federal law, applicators want to comply. At this time, they can’t, and probably shouldn’t, if they want to do the job right.

    A vision for a good label should be one that respects the needs of the applicator.  Such a label:

    • places the information that applicators need at the top;
    • is updated regularly to reflect modern practice and useful advice;
    • helps a new applicator work out how to apply the product with any equipment;
    • identifies a spray quality that offers good coverage and low drift;
    • makes reference to research that supports variations in the application guidelines;
    • is available electronically, readable on a mobile device, i.e., not pdf.

    This label would protect the environment and bystanders, and would foster better pesticide performance.

    This label is easy to generate.

    This label would be read by applicators.

    What’s it going to take?

    Additional:

    This article created a great deal of discussion. We decided that if we were going to point out issues with the current labelling system, we should also propose a way forward. Read about our Label Summary Sheet proposal.

  • Evaluating Electrostatic Spraying in Carrot

    Evaluating Electrostatic Spraying in Carrot

    This research was performed with Dennis Van Dyk, OMAFA Vegetable Crop Specialist.

    In 2018, MS Gregson introduced a line of electrostatic sprayers (the Ecostatik) in Canada. While electrostatic technology has been used in agriculture since the 1980’s, this is the first time ground rigs have been so readily available to Ontario (possibly Canadian) growers.

    The 3-point hitch Ecostatik can be configured for vertical booms or for banded/broadcast applications. The largest version has a 150 gallon tank, 10 gallon rinse tank and 72 nozzles on 7.5″ centres on a 60 foot boom. That model requires a 75 HP tractor, but 100 HP is preferred. The manufacturer claims the Ecostatik uses 50% less spray mix, gives superior underleaf coverage, and loses less spray to the soil compared to conventional methods.

    Ecostatik 3-point hitch electrostatic sprayer. 14′ boom model pictured.

    Objective

    In the summer of 2018 we evaluated and compared the electrostatic sprayer to conventional application methods at the University of Guelph’s Holland Marsh Research Station. Our goal was to assess spray coverage and physical drift in a vegetable crop.

    Treatments

    • Treatment 1: Conventional Hollow Cone (HC) at 53.5 gpa (500 L/ha).
    • Treatment 2: Conventional Air Induction (AI) flat fan tip at 50 gpa (468 L/ha).
    • Treatment 3: Ecostatik at 11.8 gpa (110 L/ha): electric charge on.
    • Treatment 4: Ecostatik at 11.8 gpa (110 L/ha): electric charge off.

    Sprayer set-ups

    Conventional Sprayer

    • 11.5 ft (3.5 m) boom with 20” (50 cm) nozzle spacing set 18” (45 cm) from nozzle to top of crop.
    • Treatment 1: D3-DC25 HC @ 140 psi and 3 km/h. SC-1 SpotOn calibration vessel (SC-1) gave an average flow of 1.36 L/min (0.36 gpm). Very Fine spray quality.
    • Treatment 2: AI11003 AI @ 80 psi and 4 km/h. At 50 psi, SC-1 gave an average flow of 1.21 L/min (0.32 gpm). Very Coarse spray quality.

    Ecostatik Sprayer

    • 15 ft (~4.5 m) boom with 7.5” (19 cm) nozzle spacing set 18” (45 cm) from nozzle to top of crop.
    • With tractor set to 2,100 rpms, avg. air speed was measured using a Kestrel wind meter. The turbulent nature of the air precluded testing with a Pitot meter. At 5″ from the nozzle: 71.5 mph (32 m/s). At 10″: 37.5 mph (16.6 m/s). At 18″ (target distance): 21 mph (9.4 m/s).
    • The MaxCharge nozzles contained TeeJet CP4916-16 flow regulator orifice plates. At 25 psi they should have emitted 0.020 gpm. However, the SC-1 indicated a consistent 0.034 gpm from multiple nozzles. We postulate that the air assist created a low pressure environment that increased flow. Extremely Fine spray quality.
    • Treatment 3: Electric charge of -16 µA (tested using a voltmeter set to 200 µA) and speed of 3.7 km/h.
    • Treatment 4: Electric charge off and speed of 3.7 km/h.
    The Ecostatik boom
    Testing electrostatic charge with a voltmeter. Hair standing on end was a fun extra.

    Experimental Design

    Fluorimetry

    We used the fluorescent dye Rhodamine WT as a coverage indicator. This allowed us to take tissue samples to evaluate deposition, rather than rely on analogs like water sensitive paper. Further, the dye is detectable in parts per billion concentrations, making it sensitive enough for detection in drift studies.

    • The conventional sprayer received 40 gallons (151.5L) of water dosed with 303.5 mL dye (i.e. 2 mL / L).
    • The electrostatic sprayer 20 gallons (75.75 L) of water dosed with 151.5 mL dye (i.e. 2 mL / L).
    • A sample of the tank mix was collected from the nozzle prior to each application. It was later used to calibrate the fluorimeter for samples taken during that application.
    • Tissue samples were removed and dried to establish their dry weight.
    Rhodamine WT pooling on carrot (and weeds) as boom charged prior to application.

    Spray Coverage

    We chose to spray carrot on 20″ (50 cm) spacing on August 30, when the crop canopy was densest and represented the most challenging target. Our targets were leaflets located about mid canopy depth, and 1″ lengths of stem just above the crown. A diagram illustrating the experimental design appears later in the article.

    Fluorimetry lab station. Inset: A typical length of stem and a leaflet with a Sharpie for scale.
    Drawing a tank sample prior to application. Carrot canopy was mature and very dense.
    • 12 m blocks were randomly flagged for each treatment. There were 3 blocks per treatment. 4 treatments * 3 replications = 12 blocks.
    • Temperature, windspeed, humidity and time were recorded prior to each application.
    • Three plants were randomly sampled from each block. These sub samples were averaged to get a single data point. 3 replicated blocks x 4 treatments x 6 subsamples = 72 tissue samples (36 leaflets and 36 stems).
    • Samples were collected 60 seconds after spraying ended, placed in sample tubes pre-filled with 40 mL of water and immediately placed in the dark.

    Drift

    We also performed an analysis of physical drift for each treatment.

    • 4″ lengths of pipecleaner mounted vertically ~12″ above the crop canopy as drift collectors.
    • They were placed in a straight line from the middle of the boom at 1 m, 2 m, 4 m, 8 m and 16 m downwind.
    • Samples were collected 60 seconds after spraying ended, placed in sample tubes pre-filled with 40 mL of water and immediately placed in the dark.
    Spray coverage spray drift trial block design.

    The following graph shows the coverage observed in µL rhodamine per dry weight of tissue sampled. Bars represent standard error. Each treatment represents three passes (n=3) where each pass included three sub-samples averaged to offset the high variability inherit to spraying. While statistical analysis did not prove significant, there were strong trends. The AI nozzle deposited more dye on the leaves, while the HC and both electrostatic applications were par. Stem coverage achieved in conventional applications was approximately double that of the electrostatic. However, note that the electrostatic system only applied 1/5 of the volume sprayed conventionally.

    When the data is normalized to depict a 500 L/ha application for all treatments, a different story emerges (see below). Now foliar coverage is 25-100% better for electrostatic applications than conventional. Stem coverage is twice that of conventional. Unexpectedly, the uncharged electrostatic treatment outperformed the charged treatment on the leaves. This might be the result of variability in the application, or the result of coronal discharge which can occur when pointy leaves repel charged droplets. This suspicion might be supported by the similar coverage achieved on the stems in both Treatment 3 and 4. You can read more about the Corona Discharge Effect in this article.

    Regarding drift, we will focus on the normalized data (where all treatments are adjusted to 500 L/ha). An analysis of variance indicated with 95% confidence that the electrostatic treatments drifted significantly more than conventional (approximately 5x more rhodamine detected). Particle drift follows an inverse square rule, where levels decline with distance, but the decline is only minor in all treatments. This may be a function of weather conditions, coupled with the limited distance investigated.

    Winds averaged 6.5 km/h gusting up to 10 km/h at boom height. Temperatures were between 15-17°C and relative humidity at ~70%. These conditions are conducive to drift as droplets are less likely to evaporate and in the case of Very Fine droplets, travel great distances. Many drift studies extend to 300 m from the point of application, whereas we were unable to monitor beyond 16 m. The downward trend would likely have been observed were we able to sample further downwind.

    Observations

    Our data supports the manufacturer’s claim that the electrostatic sprayer has the potential to match the coverage from a conventional application while using 50% less water and pesticide. It is unclear whether the electrostatic charge plays a role in this coverage, or if it is the result of the Very Fine spray quality and air assist (which have been demonstrated to improve canopy penetration). Further, it is unclear whether the charge may actually have been detrimental in the carrot crop. Claims of improved coverage uniformity were not explored in this study, but observations of water-sensitive paper in soybean (see image below) did indicate consistent under-leaf coverage, even at 50% application volume.

    The five-fold increase in drift potential is a significant barrier for this technology. The spray cloud is comprised of like-charged particles that expand in three dimensions, which improves coverage uniformity and penetration into the canopy, but also causes droplets to expand up and out of the canopy. Air assist is used to propel them downward, but the turbulent 9.4 m/s windspeed seemed excessive, even for a dense carrot crop.

    It is possible that focussing and reducing that airspeed may also reduce drift without compromising coverage. Presently, the air shear design of the Ecostatik’s MaxCharge nozzles prevent the operator from reducing the air speed without compromising spray quality. And, even if air speed could be reduced, the spray quality must remain Very Fine to achieve an optimal mass-to-charge ratio, and will therefore always carry an inherently high drift potential.

    Thanks to Kevin Van der Kooi for spraying, and Laura Riches, Tamika Bishop, Terisa Set, Christine Dervaric, Claire Penstone and Aki Shimizu for sample collection. Special thanks to Cora Loucks for assistance with statistical analysis and Martin Brunelle of MS Gregson for providing the Ecostatik for evaluation.

  • Air-Assist Improves Coverage in Field Corn

    Air-Assist Improves Coverage in Field Corn

    Why aren’t there more air-assist boom sprayers in Canada? I can understand why field croppers might hesitate to pay for the feature because it’s only been in recent years that fungicide applications have become a regular part of their annual spray program. But, high-value horticultural muck crops like onion and carrot, or field vegetables like tomato and peppers have been a great fit for many years.

    One operation near Dresden, Ontario was thinking the same way when they bought a used 2010 Miller Condor with a Spray-Air boom from Indiana. In the past, they employed a trailed Hardi sprayer applying 40 gpa using Turbo TeeJets alternating front-to-back in their field tomato and onion crops. They felt they could achieve better coverage with the air assist feature.

    On June 19 the onion and tomato canopies were still too sparse to be a good testing ground (and the ground was very wet). So, we decided to run coverage trials in a stand of 3 foot high corn on 30 inch centres.

    The Spray Air boom features a series of air shear nozzles on 10 inch centres. A liquid feed line meters spray mix to the orifice, where high-volume air is directed at the flow via two Cross-Flow jets. This shreds the liquid into spray and shapes a 60 inch flat fan pattern. The operator can select from a range of air speed/volume settings that affect spray quality (lower air means Coarser and fewer droplets and a smaller fan angle).

    This particular boom also carried a set of hydraulic nozzles, so the operator could elect to turn off the Spray Air feature and employ a conventional application. This would be appropriate if applying a herbicide using air induction nozzles. In this case, the sprayer was equipped with TeeJet FullJet cones.

    The first thing we noticed was that the air was not distributed evenly across the boom. We inspected the baffles that join each boom section, but found no problem.

    We then suspected the Spray Air combination nozzles might be occluded with debris (it did come all the way from Indiana). This turned out to be the case, so we popped them out and cleared the Cross Flow jets of any obstructions.

    We then measured the air speed produced by the boom. A Pitot meter proved to be too finicky to get a consistent reading, so we used a Kestrel wind meter held 12 inches from the nozzle. The operator moved between the six air settings in the cab, producing the following air speeds. Note that these speeds were much slower than the 100+ mph (160+ km/h) speeds noted in the Miller brochure. The owner has since told me that they found a number of air leaks in the boom that they have been diligently repairing, and as a result he’s operating at a lower air setting.

    Air SettingApproximate Airspeed at 12”
    14 mph (6.5 km/h)
    26.5 mph (10.5 km/h)
    38.5 mph (13.5 km/h)
    412.5 mph (20 km/h)
    515.5 mph (25 km/h)
    617.5 mph (28 km/h)

    We used water-sensitive paper wrapped around dowels to illustrate potential spray coverage.

    They were placed perpendicular to the spray at three depths in the corn canopy: High, Middle and Bottom. This provided an indication of panoramic coverage and represents a very difficult-to-wet target. In the last two trials, we also added a horizontal target at the Middle (not shown) and Bottom position to illustrate overall canopy penetration, and two at the High condition, angled at 45º into the sprayer’s path and 45º away from the sprayer’s path. These gave an indication of the highest potential coverage available to the canopy. Papers were later unfurled and digitally scanned. The papers were analyzed using DepositScan to determine the total percent coverage, and the droplet density.

    Trials took place between 8:30 and 11:00. Temperature slowly climbed from 20ºC to 23ºC (~ 70ºF). Relative humidity dropped from 69% to 60%. With the exception of Trial 1, we sprayed in a tail wind of 7.5 mph (12 km/h) gusting up to 10 mph (16 km/h). Travel speed was 7 mph (11 km/h).

    In the first five trials we made single, progressive adjustments to the spray settings that we assumed would improve coverage. Finally, we compared what we felt were optimal settings with the Spray Air (Trial 5) to optimal settings for the conventional hydraulic nozzles (Trial 6). Details are as follows:

    TrialAir settingSpray Volume (gpa)Boom Height (inches)
    121420
    23.51420
    361420
    46146
    56206
    6No Air – Fullcones206

    You can watch the passes in the following video. Note the boom height and the trailing spray.

    The following two graphs show the coverage obtained in the High, Middle and Bottom positions for all six trials. The first graph is percent coverage, and the second is droplet density.

    In trial 1 the air was insufficient to properly atomize the spray mix (as seen in the video) and this is evident in both graphs. By increasing the air in trials 2 and 3, we see that coverage increases in the High and Middle positions, but declines a little in the Bottom position. When we lower the boom closer to the canopy in Trial 4, we see increased coverage again in the High and Bottom positions, but lose ground in the Middle. We then increase our water volume for exceptional gains in the Middle and Bottom position, but at the expense of the High. Throughout these changes, overall coverage trended up. Finally, when we turn off the Spray Air system, and switch to the Fullcones, which were set to spray the same volume via the rate controller, there is a drastic reduction in coverage in all positions.

    Let’s look at the additional papers placed for Trials 5 and 6 in the following graphs.

    Even when papers were oriented to intercept the spray as much as possible, The Spray Air system provided superior coverage compared to the hydraulic nozzle.

    This leads us to conclude that there is an advantage to air assist in overall coverage and canopy penetration. Further, it demonstrates that such a system requires careful calibration to ensure it is being used optimally. Water volume, air settings and travel speed should all be reconsidered when the environmental conditions change (e.g. temperature and wind) and when spraying different crops, at different stages of growth.

    Two weeks after this trial, the corn grew too high for the Miller boom, but the grower moved into his onion and tomato and was very pleased with the overall coverage the Spray Air was providing. He’d also replaced the fullcones with 110 degree AI flat fans for herbicide spraying.

    I’d like to see more air-assist booms in Canada.