Tag: spray quality

  • ExactApply Primer

    ExactApply Primer

    ExactApply is an application system capable of PWM, introduced by John Deere in August, 2017, with its first customer field season in 2018. ExactApply offers several unique features that differentiate it from the existing systems. Here is a brief description of its major components and capabilities:

    Nozzle Body Design:

    • The body contains a turret with six numbered nozzle locations, all pointed down, and two solenoids, one on either side of the body. Three nozzle locations are on short feeds (locations 1, 2, and 3), whereas the remainder are on long feeds (4, 5, and 6). The front locations and left solenoid is called “A”, whereas the right solenoid and rear location is “B”.
    ExactyApply nozzle body
    • Nozzles are paired so that A or B or both are capable of spraying at a time, depending on the selected mode. Pairs are 1 & 4, 2 & 5, and 3 & 6. The operator manually rotates the desired nozzle pair into position.
    • When a short feed (1, 2, or 3) is placed at the front of the body, the system is in Separated Mode. In this mode, the left solenoid controls the front nozzle and the right solenoid control the rear nozzle. Either or both can be used, in pulsing (PWM) or conventional mode, selected through the monitor.
    • When a long feed (4, 5, or 6) is placed at the front, the body is in Combined Mode. Now, all flow from the right and left solenoid can only exit the front nozzle. Very high flows are achievable in Combined Mode, making it suitable for liquid fertilizer application. It may not have other practical applications in Western Canada.
    View from left side of body (solenoids removed). Turret position #4 (tall feed) is in front, and #1 (short feed) is in back, placing the body in Combined Mode.
    • In Pulsing Mode, each solenoid pulses at 15 Hz, meaning it completes 15 open-and-close-cycles per second. The A and B solenoid timing is offset by 180 degrees, so that the B nozzle is in the middle of its on-cycle when the A nozzle is in the middle of its off cycle. In combined mode, this means that the system operates at 30 Hz.
    • Adjacent bodies are also 180 degrees out of sync with each other, similar to Capstan, Raven, and TeeJet bodies, so that whenever a nozzle is off, its adjacent partners are on (when operating at 50% DC and above). Another way of saying this is that all even-numbered bodies act together, and all odd-numbered bodies act together but half a cycle later. This results in a blended pulse that prevents skips.
    Plunger assembly inside solenoid. Black plastic portion can be removed, exposing poppet and spring.
    • The proportion of each cycle that the solenoids are open is known as the duty cycle (DC). At 100% DC, the valves are always open. At 50% DC, the valves are open 50% of the time. The minimum DC allowed by the system in default is 25%. This can be lowered to a smaller value within the monitor.
    Opened plunger assembly showing tip of poppet (right) and seat (left)
    Poppet inside plunger assembly is pulled back by magnet inside solenoid 15 times per second
    • DC is closely related to the flow rate of the nozzle. There are two ways of looking at this. An 08 sized tip operating at 40 psi will have a flow rate of 0.8 US gpm at 100% DC, about 0.4 US gpm at 50% DC, and close to 0.2 US gpm at 25% DC. This feature is primarily useful when sprayer speed is changed, requiring new flow rates without a change in spray pressure.
    • Pulsing Mode is not available for nozzles sized smaller than 02, or for air-induced tips.
    • Pulsing can be disabled to allow the use of air-induced or other tip technologies that may not function well when pulsed. This is called AutoSelect Mode.

    AutoSelect Mode:

    • AutoSelect Mode (“Auto Mode” in 4600 monitor) can be used to achieve three unique flow rates. “A” alone, “B” alone, or “A” & “B”. When properly staggered, a travel speed range similar to Pulsing Mode can be achieved, although pressure will rise within each nozzle as travel speeds increase, as in a conventional system.
    • In AutoSelect Mode, the user selects a tip for position A, and an incrementally larger tip for position B. The monitor requires that the user inputs minimum and maximum pressures for A, B, and A&B. Travels speeds corresponding to these tip and pressure choices are calculated, and the monitor warns the user when speeds don’t overlap. The user either changes minimum and maximum spray pressures, or selects a different sized tip to eliminate the gap.
    • AutoSelect Mode is useful when a certain specific tip is required which is not compatible with Pulsing Mode, for example drift protection with air-induced tips.

    Pulsing Mode Nozzle Selection

    At this time, John Deere nozzles best suited to the ExactApply’s Pulsing Mode are the LDM, LD, LDX, and 3D. Of these, the LDM most closely represents the spray quality of the LDA and ULD that John Deere operators are accustomed to. The remainder are considerably finer.

    ASABE spray qualities for Low-Drift Max (LDM) tips. Being Very Coarse at lower pressures, applicators are advised to use higher spray pressures (50 to 70 psi) when coverage is important.
    ASABE spray qualities for Guardian (LDX) tips. Note that the smaller sizes (03, 04, 05) produce finer sprays and will require pressures below 40 psi to have any reasonable drift reduction.
    ASABE spray qualities for 3D tips. As with LDX, the smaller sizes (03, 04, 05) produce finer sprays and will require pressures below 30 psi to have any reasonable drift reduction. Such low pressures may narrow the spray pattern.
    ASABE spray qualities for Low-Drift (LD) tips. As with LDX, the smaller sizes (03, 04) produce finer sprays and will require pressures below 40 psi to have any reasonable drift reduction.
    ASABE spray qualities for the Low-Drift Twin (LDT). Comprised of two same-sized LD tips assembled in a TwinCap.

    Proper sizing for PWM requires that tips be sized for about 20 to 40% extra capacity. In other words, at expected average travel speeds, the pulsing duty cycle should be approximately 60 to 80%. The following chart has a highlighted column at 70% duty cycle for that reason. Assuming an ExactApply operator expects to apply 5 gpa and travel at 15 mph on average, possible nozzle options (highlighted in yellow) are:

    03 at 60 psi

    04 at 30 psi

    05 at 20 psi

    06 at 15 psi

    Calibration chart for PWM systems. Nozzles are sized at about 70% Duty Cycle (grey column). Options for 5 gpa at 15 mph are highlighted yellow. Black highlights represent speeds >25 mph, not available.

    The best choice will likely be either of the first two options, as the third and fourth have spray pressures which are probably too low for good nozzle performance. The decision would depend on the spray quality obtained for each of the remaining two options.

    Of course, spray pressure can be altered to suit the operator’s spray quality requirements. This merely affects the available speed range as well as the DC at which the system operates at a given target speed, possibly affecting Pulsing Mode utility.

    The row of speeds adjacent to the selected nozzle and pressure identifies the approximate travel speed range that can be expected, from 25 to 100% DC.

    It’s important to know your current DC to be sure the system is operating properly, and also to take full advantage of turn compensation features. We’ve described a way to place a DC display module on your home screen here.

    Download an Excel version of this chart here.

    ExactApply Nozzles Pulse Mode-June 2020Download

    The application volume can be changed to suit the specific use, the chart’s speed values are updated automatically. Make sure the nozzle spacing at the top left is correct for your sprayer

    Pressure Drop across Solenoids

    PWM solenoids represent a restriction to flow, and may cause a pressure drop. John Deere has published the pressure drop, and it is shown in the above chart (download version only). The pressure drop is fairly low, only 2 psi for an 04 tip operating in separated mode at 40 psi. For an 06 tip, the drop is 3 psi, and for an 08, it’s 6 psi. a #10 tip has a 10 psi drop at 40 psi. These pressure drops must be added to the operating pressure of the sprayer. Pressure drop is important because the LDX, LD, and 3D tips will be operated at low pressures to obtain coarse sprays for drift protection. Operating an 08 tip at 20 psi (at which pressure it has s drop of 3 psi) will result in in a tip pressure of 17 psi. Since we are at the low end of a nozzle’s operating range, pattern stability may be compromised when the drop is not taken into account.

    Why 70% Duty Cycle?

    An operator of any PWM system needs to know their current duty cycle. On ExactApply, a module can be installed on the home screen that provides a visual display. We show how to do this here.

    There are five main reasons a nozzle should be sized to run at approximately 70% DC. The first is to provide speed flexibility. An operator may need to speed up somewhat, but usually not more than 30%. On the other hand, slowing down is much more common to accommodate challenging terrain, and a factor of two to three is possible (from 70% DC to 25% DC).

    Secondly, drift reduction through lower spray pressure usually requires less speed due to the associated lower flow rate. With some DC room to spare, the loss of flow can be corrected without requiring a speed change.

    Thirdly, spot spraying at a slightly higher rate is possible, again through DC alone.

    Fourth, Nozzle Rate Boost of up to 25% for up to six nozzle locations is possible within the monitor, but only if the system is operating at 75% DC or less.

    Finally, turn compensation, during which the outside boom travels faster than the tractor unit and the inside boom slower, requires this additional capacity. More on turn compensation here.

    AutoSelect Mode Nozzle Selection

    AutoSelect Mode allows for three flow rates to be used in succession: A, then B, the AB. The key to success is to use small size increments between A and B, and to use tips that have a wide pressure range.

    In the example below, the A location was an 02 tip and the B was an 03, for a total of 05. Pressure was not allowed to drop below 30 psi to retain good patterns. Pressure at switch over to the next largest flow rate therefore needed to be 80 psi to make the moves possible without pressure gaps resulting in over-application. As a result, the spray quality can be expected to fluctuate three times as the sprayer accelerates through A, B, and AB in succession.

    Nozzle selection should seek to emphasize the middle of the pressure range of either B or AB to avoid unnecessary fluctuations.

    Spray pressure and travel speed as Auto Mode moves through A, then B, then both A&B

    Download an Excel sheet that assists in nozzle selection for Auto Mode here.

    ExactApply Nozzles Auto ModeDownload

    Maintenance

    A maintenance kit comes with each ExactApply sprayer. It contains two spare plunger assemblies, clips, and pins, as well as a brush, an O-ring picker, and a torque driver.

    Maintenance kit

    The ExactApply body is fairly easy to take apart for servicing. Hair pins at the back of the unit secure each solenoid, and both pull out easily. The plunger assembly can be disassembled without tools. Take care not to drop the poppet spring!

    Reassembly of the plunger requires the use of the torque driver fitted with a 17 mm socket, included in the kit. Do not over-tighten the plastic component.

    Aside from the manual rotation of the turret to select a different nozzle combination, the only moving part in the ExactApply body is the poppet in the plunger assembly. This piece is the valve that controls flow rate, and opens and closes 15 times per second whenever pulsing mode is on, moving like a piston in a cylinder. Debris (sand, fertilizer crystals, etc.) can interfere with the seal of the poppet against its seat, and good filtration is important.

    In the first generation, metal flakes began appearing inside some plunger assemblies . A coating de-laminates off the sleeve and can cause the plunger to stick. This has been starting at 800 h of use. The springs have also been observed to break. This problem has been addressed in newer generations.

    Metal flakes interfering with plunger action
    Plunger damage showing likely source of metal flakes
    Broken plunger spring

    Certain formulations may build up a residue that interferes with poppet movement. It’s impossible to predict all possible formulation impacts, but oily formulations such as emulsifiable concentrates (EC, milky appearance) are likely to be more problematic than solutions (S, clear appearance). John Deere recommends a daily rinse of the boom through both the A and B valves with Erase, a tank cleaner product. Fortunately, the R series sprayer allow for boom flushes from the clean water tank even when the product tank has product in it.

    Each nozzle body contains ten O-rings and two sets of seals. The turret assembly has two large rings, and each plunger assembly has four. Care needs to be taken to prevent damage to these rings to prevent leaks.

    O-rings in nozzle body

    Some Recommendations

    The ExactApply system is very full featured and customers new to PWM can be overwhelmed by the number of choices at their disposal. Let’s simplify the system and make some basic recommendations.

    1. Pulsing mode is likely to be the most useful feature of the system. Plan to use this feature for most spraying operations.
    2. In Pulsing mode, select from John Deere’s LDM, LDX, LD, and 3D tips. The LDX, LD, and 3D offer similar Medium spray qualities and should be operated between 20 and 40 psi to produce lower-drift sprays. Check spray patterns at these pressures and ensure that 100% overlap is achieved (pattern width is twice nozzle spacing).
    3. The LDM (Low Drift Max) is coarser than the above nozzles (comparable to ULD or LDA) and is available in 03, 04, 05, 06, 08, and 10 sizes. This will be the tip of choice for pulsing mode and can be used at higher pressures to ensure good pattern formation.
    4. Separated mode can handle most flow rates, and offers the flexibility of choosing A (front tip) or B (rear tip) or both. This means turret 1, 2, or 3 will be in the forward (A) location.
    5. Equip the A location with your low volume tip (say, 5 gpa). Place the high volume tip (say 10 gpa) at the B location. Use both together for late season sprays into dense canopies (in this case, A&B=15 gpa)
    6. Twin tips for Fusarium Head Blight (FHB) can be achieved in five different ways.
      1. 3D tips in “A” or “B”, alternating their orientation along the boom (forward, backward, forward…). Pulsing Mode. (Since these tips are not very coarse, low pressures are needed to ensure that the angle of the spray persists more than a few inches).
      2. 3D tips in “A” and “B” on each body, front facing forward, rear facing backward, and operating in A&B. Pulsing Mode.
      3. LDT (Low Drift Twin) in “A” or “B”. LDT is a TwinCap with two LD tips installed. Pulsing Mode.
      4. LDM (Low Drift Max) in installed in a TwinCap in “A” or “B”. These are coarser sprays that will retain their direction longer and are well suited for FHB. Pulsing Mode.
      5. GAT (GuardianAIR Twin), an air-induced tip, running in either conventional “A” mode or in Auto Mode but sized for “B” (avoid operating in A&B to prevent pattern interference).

    Some recent recommendations: A customer wanted tips for 5, 10, and 15 gpa at 14 mph, and the 15 gpa was for FHB. He didn’t want to be too coarse. We recommended the LDM 03 at 60 psi (5 gpa) in “B”, the 3D 08 at 30 psi (10 gpa) in “A”, and both together, with the 3D facing forward, for FHB for 15 gpa. The sprays would be “Coarse”, a nice middle ground.

    ExactApply joins Capstan PinPoint II, Raven Hawkeye, and WEEDit Quadro, Agrifact StrictSprayPlus, and TeeJet DynaJet with PWM capable systems. Auto Mode is a version of nozzle switching first introduced into the market as Arag Seletron and Hypro DuoReact. It appears to be a full-featured system that is fully integrated into the new John Deere 4600 display but is also available as a retrofit on the older R-Series 2630-equipped sprayers.

  • The Misplay of our Generation

    The Misplay of our Generation

    We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run.

    –Amara’s Law of Computing

    We tend to overestimate the effect of a stewardship mistake in the short run and underestimate the effect in the long run.

    –Wolf’s Adaptation of Amara’s Law to Agricultural Stewardship

    August 9, 2017

    Since June of 2017, we’ve been hearing reports of widespread dicamba damage symptoms in soybeans throughout the US mid-south and midwest. It appears that millions of acres could ultimately be affected, and yield impacts are unknown at this time.

    For those new to the issue, dicamba is a broadleaf herbicide in the Group 4 mode of action group, a benzoic acid. It’s an important tool for herbicide resistance management for weeds like palmer amaranth (Amaranthus palmeri) and waterhemp (A. tuberculatus), populations of which have become resistant to Group 2 (ALS inhibitors), Group 5 (triazines), Group 9 (glyphosate), Group 14 (PPO inhibitors) and Group 27 (HPPD inhibitors) in some places.

    Dicamba is a volatile herbicide, discovered in 1942 and first registered in the US in 1967. Its primary use was in corn and other cereal crops, lawns, and rights of way, at comparatively low doses, and relatively early in the season.

    Calling a pesticide volatile means it can evaporate after application, either from a liquid or a dry deposit, for hours or sometimes days after application. The resulting vapor cloud can move unpredictably, depending on atmospheric conditions, and affect plants long distances away. Higher temperatures increase vapor loss.

    Starting this year, dicamba-tolerant soybeans and cotton (Xtend varieties) were sprayed with new lower-volatility formulations of dicamba, XtendiMax, Engenia, and FeXapan, to control certain broadleaf weeds (including the Amaranth species above) without harming the soybeans. Problem is, dicamba can harm non-Xtend soybeans and other plants, even at very low doses. And these registrations were for applications that occurred later in the season, at higher doses than before.

    I usually don’t get involved in people’s decision about whether to spray, or what to spray. But I do get involved when it comes down to how to spray. That’s my job. The real question to me is “can this product be used safely in cotton and soybeans?” Right now, the jury’s out on that one.

    In my business, our guiding principles are what some people have called the “Three Es of Application”, Efficacy, Efficiency, & Environment.

    We use sprays to control pests. That’s the only reason. We have to apply them so that they work, or else it’s a wasted effort. That’s the efficacy part. We also need to use our resources, time, money, etc., efficiently so the whole process doesn’t bankrupt us and we have time left for other important tasks.  That’s efficiency. And finally, we need to protect the environment, and that means making sure the product lands where it’s intended.

    None of these three priorities trumps the others. All need to be met to the best degree possible. And due to ever-changing conditions, we will typically change our approach to emphasize one or two of these three over the others, to have a working system.

    Simply put, pesticides belong on target surfaces covered by the swath of the sprayer, and nowhere else. If they do move elsewhere (something we’ve come to view as inevitable), regulators conduct risk assessments to ensure that this movement does not result in harm. If harm is possible, mitigating tools such as application timing, product rate, spray method, and buffer zones may be imposed. If those tools aren’t enough to ensure safety, regulators deny product registration. That’s their job.

    But even if no harm is done by trespass, the products still need to be on-target. That’s stewardship. It’s a principle whose adherence gives license for a technology to be used. It gives others faith in our competence. Practicing this principle when it’s easy prepares us for hard times.

    I respect our regulatory process, and know it to be increasingly conservative with regards to risk the less data there are. I worked for the PMRA (the Canadian pesticide regulatory agency) as an application expert for five years. I know the system isn’t perfect and can make mistakes.  I know the system can be political. Usually it’s by being too careful. With dicamba, it looks like the opposite happened.

    The reason we’re seeing dicamba leaf cupping everywhere isn’t because all applicators suddenly forgot how to spray. They didn’t suddenly get reckless. They didn’t wilfully ignore all the training that the dicamba manufacturers and state and provincial governments developed in preparation for the product launch.

    Instead, dicamba drift reports arose from a combination of extreme sensitivity and easily identified symptoms, as well as an unexpected (by some) amount of vapor drift. Even good applications appeared to create problems. Despite warnings from local experts, regulators and registrants didn’t see it coming.

    Experienced agronomists have suggested that the observed dicamba trespass of 2017 implicates both temperature inversions and vapor drift. And although the new product labels advise against spraying under inversion conditions, they don’t say a word about vapor drift, the conditions that give rise to it, or how to protect against its occurrence. Not one word. I’ve searched the Xtendimax, Engenia and FeXapan labels. Nada.

    Seems that the regulators and registrants felt confident enough in the reduced volatility of dicamba, based on their internal empirical data and modeling, that they didn’t need to mention it on the label. Calling that a mistake is an understatement.

    I’d call it the biggest spray application misplay I’ve ever seen.

    A part of the problem may be the enormous scale on which this new use of dicamba was introduced, over 25 million acres of Xtend crops. Scale-up errors are common in many industries. Emergent properties related to scale can’t readily be predicted by empirical data and models. Especially when the underlying data are scant.

    So what to do? The continued success of agriculture depends to continued access to safe crop production tools. Irresponsible use threatens that. And by irresponsible use, I don’t just mean application. I also mean registration, promotion, sale, and support. The whole stewardship package.

    When problems occur, we need to be quick on our feet to acknowledge them, to support those affected, and to try to understand the cause and prevent the situation from continuing or getting worse.

    The current industry response appears to be the exact opposite. What I’ve seen is full of denial, downplaying, innuendo, blaming, and entrenchment.

    Why is such an important issue in pesticide stewardship handled so poorly?

    The immediate victims of this situation are the producers that depend on new technologies. But the long-term victim is agriculture as a whole. The lack of humility and leadership by many of the proponents of this technology, those with no small financial stake in its continued use, hurts not just them, but all of us involved in farming. This is not stewardship. It’s not license. It’s short sighted and reckless.

    Over my career, spray application has generally become safer for the operator and the environment. A big part of our success has been the adoption of low-drift nozzles, the de-facto standard for modern pesticide application. The development of less toxic and less persistent pesticides has also been very important. We can avoid a lot of problems with good chemistry. I’ve been proud to tell this story.

    I want to stay proud of our story. And in this case, that requires admitting to mistakes that were made and taking corrective action that is in the best interest of our entire industry. Agriculture will persist longer than company brands and titles. It takes priority.

    It’s still too early to fully understand all the reasons for the widespread dicamba damage. But it’s not too soon to say that much of this could have been prevented with a smaller rollout, with greater collaboration with government and university experts during registration, and with more honest information on dicamba volatility on product labels. Call it Volatility Humility.

    We’ll all pay for the mistakes that were made. We’ll likely have more stringent and expensive registration protocols. More restrictive application parameters. Strained relationships. More distrust of agriculture.

    And as always, an ounce of sweet prevention would have been much better than the pounds of bitter cure that will surely be required to make this right.

  • Question of the Week: Fine Sprays for Fungicides?

    Question of the Week: Fine Sprays for Fungicides?

    The following question arrived from one of our prairie clients last week:

    “A retailer is promoting the use of hollow cone nozzles to be used on field sprayers (20” spacing) to apply fungicides which he claims out-perform any regular and twin fan tips. Claims:

    • create an extra fine droplet for maximum coverage on the canopy
    • use less water, less time spent filling
    • apply at 3.5 gpa
    • add vegetable oil to reduce drift

    “So his direction to a specific customer was to use the TEEJET CONEJET TXA8001VK nozzle at  80 psi – travelling at 10 – 12 mph to achieve a 3.4 gpa application rate with a ‘very fine’ droplet size.

    “What are your thoughts?”

    Here’s how I answered (edited for clarity):

    That recommendation sounds familiar – it originates from a consultant with experience in South America, where this idea is promoted to improve (aerial) spray productivity.

    I fundamentally disagree with his approach. Adopting and promoting it is not only illegal (contravenes every modern label’s water volume and spray quality requirements), it also puts a generation’s worth of stewardship efforts on drift management at risk.

    To be balanced, let’s explore the attractiveness of this approach. Finer sprays do provide superior coverage and save water. Every child knows this. Finer sprays also go places in the canopy where the coarser sprays can’t, for example very dense lentil canopies.

    Over the years, we’ve explored the performance of fine fungicide sprays in canola, pulses, and cereals in research trials with the U of S and AAFC. To our surprise, droplet size played only a small role in fungicide performance. Water volume was much more important. Droplet size management with pressure through a low-drift nozzle was enough to get the best disease control.

    The main drawbacks of very fine sprays are:

    1. The fine droplets evaporate to dryness very quickly, in seconds. As they shrink, their drift potential is increased even more, and once dry, the remaining particles work much less well. The proponent corrects for this by adding an oily adjuvant as an evaporation retardant. With oil, the fines remain liquid much longer. Although many products become more effective this way, they also become more phytotoxic and less safe for the applicator and bystander. Completely off label, completely risky for crop safety, unknown effects on MRLs, extremely unsafe for the environment and humans. Remember when people dissolved 2,4-D ester in diesel, back in the 40s and 50s and sprayed it with their brass 6501 tips? That’s what this is.
    2. Cone nozzles are designed for airblast sprayers and do not produce good pattern overlaps for boom sprayers. The proponent of this method actually recommends that the boom be raised to overcome the bad patterns and to (believe it or not) simulate aerial application. If this were done, the spray would be re-distributed by air-currents and come down wherever the wind blows it. Probably far away.  The concept of on-target, uniform application, the practice that makes product use acceptable, and the thing we try to achieve with flat fans at a low boom height, is completely lost.
    3. Producers will not have the support of pesticide manufacturers should a performance issue arise. Even worse, if regulators find out about this off-label practice, significant fines (fines for fines, get it?) can be charged under the Pest Control Products Act.
    4. Airborne spray drift with an air-induced spray like the AirMix, GuardianAir, AIXR and the like, applying 10 gpa, is about 1% of the applied amount, measured at 5 m downwind of the downwind edge of the swath in a 20 km/h wind. We’ve never measured hollow cone drift from a boom sprayer, but when we used a flat fan at 5 gpa, drift increased to about 8% of applied. I’d guess a high pressure hollow cone would easily double or triple that. Illegal and irresponsible.
    5. Travel and boom turbulence is a part of faster travel speeds. This would affect the finer droplets much more than the coarser ones, as we can imagine. It’s similar to drift. With a low-drift spray, the proportion of the total spray volume that is “fine”, say less than 150 microns, is about 5%. For a very fine hollow cone, it might by 50 to 75%. So a much greater proportion of the sprayed dosage would be susceptible to uncontrollable movement. This could be good, when turbulence redirects the spray to places that are unreachable by larger droplets. Or it could be bad, as turbulence pushes droplets away from an important target, creating a miss. On balance, bad. Very bad.

    These types of recommendations are concocted by people who want to tell a unique story that is popular with some. Their approach differentiates them from the rest of the crowd, an old and effective marketing trick. But these proponents do not have the best interests of the industry in mind.

    Our individual and collective agricultural practices must be respectful of others. Of safety. Of the law. Of the environment. We have lots of opportunities to make shortcuts…nobody’s watching most of the time. But that doesn’t make it right. It’s certainly not in ag’s long-term interest.

    When considering our agricultural practices, imagine describing them to a young non-farming person. Can you justify your actions? Do your practices make you proud? If not, you have work to do.

    Here’s a task: If your boom sprayer has nozzles that produce very fine sprays, take them off and throw them in the garbage. Might sound radical, but it’s the right thing to do.

  • Exploding Sprayer Myths (ep.8): Volume

    Exploding Sprayer Myths (ep.8): Volume

    In this episode of Exploding Sprayer Myths, we lay out four steps to determining the most appropriate spray volume required to achieve good coverage.

    1. Understand how the product works
    2. Understand the target
    3. Understand droplet behaviour
    4. Understand the plant canopy

    Joined by show-stealing Dr. Doug Baumann, and with the help of a lot of caffeine, we learn that there’s no silver bullet to choosing a spray volume.

    Special thanks to Syngenta, Honeywood, and to Real Agriculture.

  • Deciding on the Right Way to Spray

    Deciding on the Right Way to Spray

    “What is the right way to apply this pesticide?” It’s one of the classic questions. Applicators know that spray method determines the efficacy of the application as well as its environmental impact. And it has to use time and water resources efficiently to make sense.

    To answer the question properly, we need to take things one step at a time.

    1. Canopy: To start, we need to look at the canopy that our application will go into. If it’s an early season spray into a seedling crop, then the canopy won’t be much of a barrier. Lower water volumes can be possible. Droplet size will only depend on the target type and the pesticide mode of action.
    Small weeds require more smaller droplets to secure effective targetting

    If it’s a later application into the bottom of a maturing canopy, the foliage may intercept the spray before it reaches the target area. More water will likely be needed, and droplet size may become more critical for getting the spray to its destination. Dense canopies are a real challenge and lower-canopy deposition usually benefits from finer sprays because the small droplets can turn corners better.

    Dense canopies are very difficult for a spray to penetrate. Higher water volumes and smaller droplets are the key tools that help.

    2. Water Volume: Regardless of canopy, the range of application possibilities will depend on the water volume and spray quality combination. It’s math: assuming some constant amount of coverage on each leaf, more layers of foliage will require more water. Using less water volume will make it necessary to use finer sprays to keep droplet numbers constant. More water will allow coarser sprays. This decision has implications for drift, and by extension, affects the number of hours we can spray in a day. More drift tolerance means better application timing and overall productivity.

    The tradeoffs between water volumes and droplet sizes are seen in this figure. Once a certain threshold of coverage has been reached, a further increase in coverage may not provide any additional control.

    3. Target Type and Droplet Behaviour: Whatever spray we use, the target plant or insect needs to intercept, collect, and retain the spray droplet. This is where the fun begins. Target leaves may be vertical or horizontal, large or small. Their waxy surface may be easy-to-wet or difficult-to-wet. The general rules of thumb are that larger, more horizontal and easy-to-wet surfaces are better suited for coarser sprays – these are intercepted more efficiently and stick readily. That is a reason why most broadleaf weeds and crops are very compatible with low-drift sprays.

    Large targets (left) are most efficient at intercepting larger droplets (provided droplet bounce is not a problem) because smaller droplets may evade capture. Smaller targets are usually missed by larger droplets but are very capable of capturing smaller droplets.

    On the other hand, smaller, vertically oriented and difficult-to-wet plants require finer sprays for effective targetting. Larger drops tend to miss these targets or bounce off them. Most grassy, and some broadleaf weeds (especially at early growth stages) fall into this category.

    4. Mode of Action: There are nearly 30 modes of action on the herbicide world, and another ten modes for insecticides and fifteen for fungicides. The effect of droplet size and water volume on their uptake and translocation varies, and it’s probably not correct to generalize too much. There is one notable product, glyphosate. For this product, research has consistently shown that large droplets and more concentrated mixtures provide better uptake. But we’ve also seen problems when this is over-done, causing localized toxicity and limiting translocation.

    With many products, we’ve sometimes seen better performance with finer sprays due to improved coverage, yet at other times less performance due to rapid evaporation. On the whole, it’s probably still fair to say that contact modes of action require finer sprays and higher water volumes, even if there is the occasional exception. And systemic products can typically handle coarser sprays. We’ve always been surprised just how coarse we seem to be able to push the system before any loss of efficacy.

    What does it all mean? In spraying, we need to accommodate a lot of diversity. The average application is broad-spectrum, targeting large and small broadleaf and grassy plants. Many sprays are tank mixes of several modes of action. It’s impossible to prescribe a specific spray for each situation. We need a little bit of everything. And the spray should not be drift-prone. It’s easy to see that we need to aim for the middle to accommodate everything.

    The traditional flat fan nozzle, either in its conventional or low-drift form, generates a wide range of droplet sizes that can range from 5 µm to about 2000 µm. If we need fine droplets, they’re there. If we need larger droplets, they’re also there. The proportion of the total spray volume in each specific size fraction depends on the nozzle choice and size, the spray pressure, and the adjuvant mix in the tank. Overall, the system is very robust, and although it requires some tweaking, a well chosen average spray can achieve most tasks well enough.

    A typical spray quality chart shows the expected spray quality for a range of nozzle sizes and pressures. Spray quality measurements follow standards set by the ISO and ASABE, these change from time to time and therefore charts tend to become outdated.

    Our research has repeatedly shown that a Coarse spray is a good starting point that does most things well. It is acceptable to move into a Very Coarse or coarser category provided water volumes are also raised, and provided the target types and modes of action are suited for this change.

    It is rarely necessary to spray finer than Coarse, and when this is done, we recommend against spraying finer than a Medium spray. There is simply no advantage from product performance, and drift risk becomes unacceptable.

    Tweaking the System. In order to maximize the performance of your spray, and the efficiency of your overall spray program, here is some advice:

    1. Know the spray quality of your nozzles, and their response to spray pressure. Manufacturers publish this information in their catalogues and on-line. Make this your homework assignment.
    2. Use the coarsest spray that you can afford to. This will make the application safer, it will widen the weather window, and it will simply let you get more done in a day or a season. Coarse sprays work.
    3. Use spray pressure and water volume to fine tune the application for a specific purpose. If using a contact product, you can keep the same nozzle you used for a systemic product. Apply more water or use more spray pressure to generate more droplets.
    4. Do not skimp on water. Higher water volumes tend to make an application more uniform, robust, and crop-safe. Spray coverage improves. Canopy penetration improves. Coarser sprays are possible. The only exception to this rule is glyphosate, which works better in lower water volumes. But with higher glyphosate rates and more tank mixing, even that exception is disappearing.
    5. Learn as much as you can about how your pesticides work and where they need to be in your canopy. Apply your knowledge to select optimal water volumes and spray qualities.
    6. Be wary of people who advise very low water volumes in conjunction with fine sprays. They want to appeal to your need for efficiency, but do so at the cost of consistency and environmental stewardship. Plus these types of applications are illegal for many of our products.