Category: Nozzles & Droplets

Articles helping with field sprayer nozzle selection

  • Developing Criteria for the Ideal Agricultural Spray – a Biologist’s Perspective

    Developing Criteria for the Ideal Agricultural Spray – a Biologist’s Perspective

    Originally published in: Wolf, T.M. and Downer, R.A. ILASS Americas, 11th Annual Conference on Liquid Atomization and Spray Systems, Sacramento, CA, May, 1998

    Note to reader: It’s been nearly 23 years since we wrote this paper at the invitation of organizers of the Institute for Liquid Atomization and Spray Systems Conference. At the time, custom operators, not farmers, bought self-propelled sprayers. Air-induction tips had just been introduced. Pulse-Width Modulation was only beginning to be available. GMO crops were available but not widely adopted. Buffer Zones were more rumour than policy. How badly out of date are the thoughts we mulled over?

    Abstract

    The goals of an agricultural spray application are to provide effective control of the pest at low cost without adverse environmental impact.  A spray must transport effectively from the atomizer to the target, be intercepted and retained by the target, and form a biologically active deposit.  Improvements in efficiency are elusive because of interactions between successive stages in dose transfer.  Progress will depend on atomizers providing increased control over droplet size and velocity spectra without sacrificing mechanical simplicity: (a) elimination of the interdependence of flow rate and spray quality, (b) control over size span at any given nominal diameter, (c) reversal of present relationship between droplet size and velocity.  Such an atomizer would drive a new research thrust to improve spray efficiency

    Introduction

    Polydisperse sprays provide consistent results yet suffer from inherent inefficiencies in dose transfer.  Drift potential and poor spray retention at the extreme ends of their spectra are classic examples of this inefficiency, and environmental aspects of spray application have been criticized as a result (Pimmentel and Levitan, 1986).  Yet, despite ongoing research, efficiency breakthroughs remain elusive (Hislop, 1993).  Due to the interdependency of the factors governing dose transfer, progress in one area (i.e., greater retention with finer sprays) has often been at the expense of spray drift, and vice versa (Young, 1986).  Theoretical improvements in efficiency with monodisperse sprays (Controlled Droplet Application, CDA) have not translated into widespread adoption due to drawbacks in consistency and robustness of the results.  After 50 years of research, the same compromises which have been discussed since the early days of spray application are apparently still unresolved. 

    Nozzle designs have certainly improved – wider pressure ranges, improved spray patterns, more options for achieving various spray qualities, better quality, longer wearing materials, and lower costs are all important for the end-user.  But the basic atomizer – the hydraulic flat fan nozzle generating a polydisperse spray – has hardly changed over the years. 

    A New Start?

    The questions posed in this paper are:  If a biologist could design the ideal spray, what would it be?  What are the criteria for achieving the best result in the most efficient manner?  Such a discussion represents a unique opportunity to think about what we know about sprays and their biological impact, providing atomizer design information to meet our future needs. 

    Unfortunately, biologists still know relatively little about the impact of kind of spray quality on efficacy.  General statements can be made relating spray quality to herbicide, insecticide, or fungicide effectiveness, but for the most part, the ideal spray or subsequent deposit has still not been defined for most situations (Hislop, 1987). The situation reflects the lack of choice in spray atomization, creating a catch-22:  not being able to easily produce customized sprays has made it difficult for biologists to identify (without confounding factors) the ideal spray for any particular situation.  Further, the need by the industry for a simple, reliable, and standard application system has inherently hindered efforts to optimize the system.  All stakeholders will need to be flexible to present a fertile environment for improvements to take hold. 

    “Integrated Spray Management”

    In this era of integrated pest management, cropping systems are optimized to provide the most effective pest management strategy on a case-by-case basis with minimal crop protection agent (CPA) use.  This underlying philosophy can be extended to spray application.  When CPAs are used in such systems, they, too, must rely on diverse strategies to make them more efficient.  Within this philosophy, a single standard application technique for all pests will not be acceptable.  Two developments are needed to put such a development into action:  (a) an application system capable of delivering a wide variety of spray qualities (droplet sizes, spans, velocities) at a range of carrier volumes; and (b) the knowledge to utilize specific spray qualities under identifiable conditions. 

    Application Objectives

    During the development of such a new application philosophy, the objectives for spray application must remain clear.  They are to deliver a CPA in its most effective form to the pest, with no off-target effects, at the lowest possible cost, i.e., effective, economical, and environmental. 




    Figure 1: Typical droplet number and volume spectra for an agricultural hydraulic flat fan nozzle

    The status quo for most post-emergent CPA applications is the hydraulic flat fan nozzle.  As we know, such a nozzle produces a heterogeneous mix of fine and coarse droplets (Figure 1) with a droplet speed and size relationship (Figure 2).  This nozzle has frequently been criticized for inefficiency because only a small portion of spray is optimally targeted (Adams et al., 1990).  At the same time, it has been applauded for consistency because a portion of its size and velocity spectrum (although not necessarily the same one) is usually appropriate for the pest complex at hand.




    Figure 2: Typical velocity spectrum for an agricultural hydraulic flat fan nozzle.

    The most frequently documented drawbacks of the hydraulic nozzle are driftability of fine, and poor retention of coarse components.  An additional drawback is interdependence of flow rate and droplet size for any given nozzle, i.e., at the same work rate, lower carrier volumes are applied with finer sprays.  Research into droplet size effects has been difficult because no variable can be held constant while another changes.  Keeping dose constant, studies of carrier volume have to accept a simultaneous change in travel speed or droplet size, droplet size studies have to contend with changes in droplet density, and droplet density studies must alter active ingredient concentration.  Given the complexity of the problem, few researchers commit themselves to solving these dilemmas. 

    Maximizing Effectiveness – No Easy Answers

    For any given spray mixture, an atomizer controls spray pattern, droplet size, and droplet velocity.  Spray patterns determine spatial uniformity.  Droplet size and velocity in turn affect spray fate by controlling canopy penetration spray interception, spray retention, spray coverage, evaporation rate, etc.  Considering the variety of active ingredients, formulations, concentrations, environments, pests, and plant canopies present, it is not surprising that the scientific body of evidence is often contradictory (Knoche, 1994).  It should also come as no surprise that there is no single “best” droplet size to optimize these factors. 

    Basic principles:  In order to better understand why a single ideal spray cannot exist, a brief review of the principles of spray drift, interception, and retention are appropriate. Larger droplets are driven mostly by inertial and gravitational forces (Spillman, 1984).  As such, they tend to have vertical trajectories from which they cannot easily be displaced.  This makes them a good choice for drift reduction, and also for canopy penetration into vertically oriented canopies, such as cereal grains. Collection efficiency by a target is a function of target size and orientation – horizontally oriented, larger objects will be favoured by larger droplets.  Spray retention is a function of leaf surface wettability and microstructure, as more difficult to wet species will be more likely to reflect larger droplets (Hartley and Brunskill, 1958). 

    Small droplets, on the other hand, are more subject to viscous drag, have shorter stop distances, and can therefore move with local air turbulence to reach shadow regions (Nordbo, 1992).  Thus the finer sprays have a propensity for displacement from their flight path by air turbulence, but they also are better able to penetrate dense broadleaf canopies because they can move around larger objects. Small, vertically oriented objects such as stems and petioles have the best collection efficiency for small droplets. 

    Upon depositing successfully on a target, the deposit must be in a form which exerts the desired biological effect.  Given the same spread factor, deposits with greater volumes remain wet longer, providing more opportunities for uptake into the leaf.  Small droplets provide more efficient coverage per unit volume, but dry rapidly, which may limit their uptake. 

    Uptake and translocation of active ingredients by biological targets are physical processes driven by concentration gradients.  Concentrations of active ingredients and surfactants per unit leaf area are a function of carrier volume, droplet size, and spread factor.  Less than optimum concentrations can result in reduced uptake and translocation (Wolf et al., 1992).

    Further complications arise due to the heterogeneous nature of weeds.  Individual regions of weed plants have unique anatomical and physiological features that can affect retention, uptake, and translocation processes on a spatial level.  For example, Merritt (1982) showed that for wild oats (Avena fatua), younger leaves and the basal region of leaves absorbed more difenzoquat than older leaves.

    All these factors conspire to complicate the quest for optimization in a field setting. 

    The Ideal Spray

    Based on the previous discussion, it may be obvious that a single droplet size cannot meet all demands within such a complex system.  Therefore our focus must shift from a theoretical optimum solution, as was the basis for controlled droplet applicators (Bals, 1980) to one which emphasizes flexibility. 

    One advantage of speaking on behalf of biologists is that one can feign complete ignorance about atomization, and propose seemingly ludicrous ideas.  Perhaps a prerequisite to a fresh approach is such ignorance. 

    Biologists need a spray to not only implement optimum application, but as a means with which to learn how to optimize the process in the first place.  Further, since there is no single optimum spray quality to meet all application scenarios, the most important feature in a spray is flexibility.  The following features will be important:

    Spray quality independence:  The first criteria is the ability to adjust spray quality easily, without affecting carrier volume or droplet velocity, and vice versa (Figure 3).  A shift towards a coarser or finer spray can then be achieved without introducing other confounding effects.  Some progress has already been made in this area (Giles and Comino, 1990).

    Figure 3: Shift in droplet size spectra from medium to fine or coarse qualities, achievable without a change in carrier volume.

    Relative span factor flexibility: The relative span factor of the spray should be adjustable (Figure 4).  It will be important to narrow the broad spectrum sprays produced by flat fan nozzles to determine the importance of specific droplet sizes.  While such research was conducted during the 1970s and 1980s with controlled droplet applicators (CDAs), the unique droplet velocity associated with such atomizers would question results if they were to be applied using hydraulic atomizers.

    Figure 4: Narrowing the span of the droplet size spectra, while preserving its polydisperse nature,  will be useful to strike a balance between specific droplet sizes and spray heterogeneity.

    Velocity control:  The third criteria is for improved droplet velocity control.  The droplet velocity dependency on size has meant that in the absence of air assist, smaller droplets are always moving slower.  This factor has reduced the efficiency of their collection and made them more drift prone.  Additionally, the larger droplets, being faster moving, were more likely to rebound from targets.  Acceleration of small droplets is a strategy for reducing spray drift and enhancing collection efficiency, but greater velocity for larger droplets may reduce the efficiency of their retention by the target.  If the droplet size – velocity relationship were reversed, then smaller droplets would be less drift prone and larger droplets would be less likely to rebound (Figure 5). 

    Figure 5: Droplet velocity spectrum for a typical agricultural hydraulic spray, accelerated with air assist to reduce drift potential of smaller droplets, and with smaller droplets travelling faster than larger droplets to maximize transfer efficiency.

    Spray heterogeneity:  Spray heterogeneity will remain important in an optimized system, especially in the absence of specific knowledge on droplet function by size class.  In this sense, a polydisperse spray does more than provide insurance for changing conditions, it adds diversity to static conditions which strengthens the overall effect.  While a quantitative dose-based approach to CPA delivery is often appropriate, it under-emphasizes the role of deposit structure and spray redistribution, where quality is more important than quantity (Wolf, 1996).  For example, let us assume that canopy penetration is maximized with a spray of 400 µm VMD, with a relative span factor of 0.7.  In such a spray, fine droplets contribute relatively little to overall dose.  However, their ability to redistribute in the canopy, targeting areas left untouched by the larger droplets may be more important than their total dose contribution would suggest.  In this way, they provide benefits which are total dose independent.  A heterogeneous spray would ensure that these benefits remain. 

    Deposit uniformity:  Efforts at optimizing dose transfer are compromised if spatial dose uniformity cannot be maintained within the treated area.  High deposit variability has been associated with reduced control of insects (Uk and Courshee, 1982; Cooke et al., 1986).  As such, uniformity remains a fundamental requirement for spray application and should not be compromised with new atomizer designs. 

    Environment as a Priority

    Spray must land on the intended target, be it a plant, insect or ground, and in some cases on the optimal pest part, i.e., specific leaves, leaf sides, stems, etc.  Off-target placement not only represents inefficiency, but also undesired environmental input.  With any application system, an important criteria is the ability to manage off-target impacts. 

    Past solutions to spray drift or droplet rebound has been two-fold:  (a) eliminate those droplets which do not impact on the target efficiently, or (b) protect them from displacement.  For spray drift, the elimination of small drops through production of coarse sprays has been successful (Edwards and Ripper, 1953).  The challenge is to provide drift protection without compromising the advances made in the previous exercise of maximizing effectiveness.  The protection of fines with barrier (shrouds) is an effective strategy for reducing drift, and provides the advantage of maintaining a spray quality established to meet separate criteria (Wolf et al., 1993).  Another successful strategy has been to assist transport of fines with an external energy source (air or electrostatics).  This also allows the preservation of an optimized spray quality, with the added advantage of modifying the droplet velocity spectrum in favour of canopy penetration. 

    Nozzle design may offer some opportunities for the reduction of rebound.  Novel atomization systems such as venturi or twin-fluid nozzles, which offer air-inclusion in droplets, may reduce rebound of larger droplets.  If larger droplets are required, but retention is of concern, such approaches may be useful.  Spray adjuvants can also play important roles in this area (Downer et al., 1995)

    Economical Considerations

    Underlying any attempt to provide effective pest management is an economical consideration.  The producer must see a benefit in making a technical investment.  Any atomizer solution must therefore not only meet the technical requirements for optimizing dose transfer, it must also be a cost-effective and practical system.  A system which is complicated to use is not likely to be widely adopted.  Without strategies for implementation by the end user, innovations in delivery are merely theoretical exercises. 

    Putting it into Practice

    During a typical work day, an applicator may be called to treat crops for a range of pests with broad-spectrum products.  These pests will likely be present in a range of densities, some above and others below an economic threshold.  There may also be a range of canopies present, some broadleaves, others grasses, some dense, others sparse.  Depending on the area, there may have been a range of environments under which pests became established, or during which application is made.  Each field will also have a range of bordering ecosystems with unique trespass sensitivities. 

    There will obviously be a limit to the degree of customization that is possible.  But some efforts will be rewarded.  The applicator uses GPS technology to collect or recall relevant data – sensitive areas, high and low infestation levels, or changes in canopy structure.  With the new atomizer, the applicator can emit the most effective droplet size, velocity, span, and dose appropriate for the pest or canopy on a site-specific basis.  The use of spray quality classification systems such as those developed by the BCPC and ASAE will guide optimization efforts, but in the end, these classification systems will be too broad to fine-tune the system.  A higher resolution, multi-parameter scheme which is sensitive enough to represent the criteria laid out in this paper will be necessary. 

    Possible difficulties emerge when the system resists optimization.  For example, it would be comparatively easy for the applicator to control a broadleaf weed in a grassy canopy, as the size spectrum which optimizes grass canopy penetration is also likely to target the broadleaf weed effectively.  If a tank mix is used to control both grassy and broadleaf weeds in this canopy, the applicator now needs a more heterogeneous spray, where a finer component targets the grassy weed, and the coarser component still effectively transfers dose to the broadleaf weed.  As the situation increases in complexity, the simultaneous optimization of several criteria will be increasingly difficult. 

    Conclusions

    Only an integrated approach involving all stakeholders (engineers, chemists, biologists, etc.) can result in improved application of CPAs.  Individual goals and concerns must be communicated and reconciled in new design efforts.  This paper represents a wish list from biologists’ perspectives.  While greater flexibility and control are important objectives in our opinion, consideration must also be given to mechanical complexity and cost, possible interactions with formulations exhibiting a range of physico-chemical properties, biocontrol agents, and practical strategies for adoption.  A continued willingness to establish and maintain lines of communication and cooperation between these disciplines will be pivotal to success.

    Acknowledgments

    The invitation by the ILASS Program Organizing Committee to make this presentation is gratefully acknowledged. 

    Citations

    1. Adams, A.J., Chapple, A. C., and Hall, F.R.. 1990.  Agricultural sprays: lessons and implications of drop size spectra and biological effects. In: L.E. Bode, J.L. Hazen, and D.G. Chasin (eds.) Pesticide Formulations and Application Systems, ASTM STP 1078. American Society for Testing and Materials, pp. 156-169
    2. Bals, E. J.  1978.  The reasons for C.D.A. (Controlled Drop Application).  Proceedings of the 1978 British Crop Protection Conference – Weeds, pp 659-666.
    3. Downer, R.A., Wolf, T.M., Chapple, A.C., Hall, F.R., and Hazen, J.L.  1995.  Characterizing the impact of drift management adjuvants on the dose transfer process. In: R.E. Gaskin (ed.) Fourth International Symposium on Adjuvants for Agrochemicals. New Zealand Forest Research Institute, Rotorua, NZ, pp. 138-143.
    4. Edwards, C.J. and Ripper, W.E.  1953.  Droplet size, rates of application and the avoidance of spray drift. Proceedings of the 1953 British Weed Control Conference, pp. 348-371.
    5. Giles, D.K., and Comino, J.A.  1990.  Droplet size and spray pattern characteristics of an electronic flow controller for spray nozzles.  J. Agric. Engng. Res. 47:249-267.
    6. Hartley, G.S. and Brunskill, R.T.  1958.  Reflection of water drops from surfaces. In: J. F. Danielli, K. G. A. Parkhurst, and A. C. Giddiford, eds., Surface Phenomena in Chemistry and Biology, Pergannon Press, London, pp. 214-223.
    7. Hislop, E.C.  1993.  Application technology for crop protection:  an introduction. Pages 3-12 In: G.A. Matthews and E. C. Hislop (eds.) Application Technology for Crop Protection. CAB International, Wallingford, UK.
    8. Hislop, E. C. 1987. Can we define and achieve optimum pesticide deposits? Aspects Appl. Biol. 14:153-172.
    9. Knoche, M.  1994.  Effect of droplet size and carrier volume on performance of foliage-applied herbicides.  Crop Prot. 13:163-178.
    10. Merritt, C.R. 1982.  The influence of form of deposit on the phytotoxicity of difenzoquat applied as individual drops to Avena fatua. Ann. Appl. Biol. 101:517-525.
    11. Nordbo, E. 1992. Effects of nozzle size, travel speed and air assistance on deposition on artificial vertical and horizontal targets in laboratory experiments. Crop Prot. 11:272-278.
    12. Pimentel, D. and Levitan, L. 1986.  Pesticides: Amounts applied and amounts reaching pests. BioScience 36:86-91.
    13. Spillman, J.J.  1984.  Spray impaction, retention and adhesion: an introduction to basic characteristics.  Pestic. Sci. 15:97-106.
    14. Wolf, T.M.  1996.  Spray application into standing stubble – an exploration of physical and physiological components.  Ph.D. Dissertation, Department of Agronomy, The Ohio State University, 192 pp.
    15. Wolf, T.M., Grover, R., Wallace, K., Shewchuk, S.R., and Maybank, J.  1993.  Effect of protective shields on drift and deposition characteristics of field sprayers.  Can. J. Plant Sci. 73:1261-1273.
    16. Wolf, T.M., Caldwell, B.C. McIntyre, G.I., and Hsiao, A.I.  1992.  Effect of droplet size and herbicide concentration on absorption and translocation of 14C‑2,4‑D in oriental mustard (Sysimbrium orientale). Weed Sci. 40:568-575.
  • Don’t try this tempting shortcut

    Don’t try this tempting shortcut

    There’s a call that I’ve been getting for 20 years now. It came again this week. Someone has a twincap with two small air-induced tips, and they’re applying herbicides and fungicides with low water volumes, often 5 gpa, sometimes less. They call because they want to know how much wind they can spray in. Is 30 km/h OK? They want my blessing.

    I don’t need to hear much more. Some nozzles are sold entirely on the premise that they provide superior coverage – more droplets per square inch – and that this improved coverage permits the reduction of water volumes. Furthermore, the claim goes, when water is reduced, the spray concentration increases and the whole darn package just works a lot faster and better.

    This line of thinking is as old as spraying itself. Applicators seek pesticide performance as well as productivity, and this approach gives them both. The proponents are well aware of their customers’ desires, and sell into it. “Use these tips and cut back on water. Any more than this just runs off anyways. You’ll get better coverage and better performance, get more spraying done.” It’s a convincing argument. Get an edge on your neighbour, the person who’s not in on the secret and is wasting time and water.

    Why don’t I embrace it? There are a few reasons.

    First, it doesn’t tell the whole story. Invariably it involves a twin nozzle setup. Use two nozzles, get more droplets, right? If that were true, believe me, I’d be advocating for quintuples.

    Fact is that the only factors that change droplet numbers are droplet size (spray quality) and water volume. Want more droplets at the same water volume? Make the spray finer. Want to keep spray quality and add droplets? Add water (not nozzles).

    The easiest way to improve coverage at the same volume is to use a finer nozzle, or to increase spray pressure. Depending on how far you go, you could make the spray finer and cut water, and still have more droplets per square inch.

    The hardest way to improve coverage is to purchase a twincap and buy two nozzles, each of them half the size. True, within any given nozzle type, smaller sized tips usually generate finer sprays. But why bother with two tips? They’re more expensive and plug more.

    If someone asks me how to improve coverage without changing water volume, I usually tell them to speed up a few mph. The rate controller will increase pressure and the spray gets finer. If speeding up is not possible, get one size smaller nozzle and run at higher pressure, same speed. Or keep nozzle and speed, and add some gpa, pressure will go up. It’s that easy. No twins necessary.

    Second, the twin nozzle/low volume approach exaggerates the value of the twin nozzle for herbicides. With small plants and relatively open canopies in the early season, plus our high booms and travel speeds, the twin tips are not adding a lot, if anything at all, to coverage. It remains a sum of droplet size and water volume, the angle is not important at this stage. Deposit is by turbulence and wind, most of the time.

    Third, low volume believers ignore a few potential problems. Drift is a big one. Low volume, fine spray operators are surrounded by nervous neighbours. They have fewer hours per day during which drift is acceptably low. And they definitely should not be on the field when wind is at 30 km/h. Basically, they’re a bit uncomfortable (at least they should be) and get less done per day.

    Another potential problem is evaporation. Most sprays, even when applied at lower volumes, are still 90% or more water. The same volume of water evaporates much quicker when atomized into smaller droplets. This has two main downsides: On their way to the canopy, small droplets evaporate and become even more drift prone, and may not impact at all. Those that impact evaporate shortly thereafter. Research has shown that pesticide uptake is better from wet than dry deposits.

    When Delta T (dry bulb minus wet bulb temperature) is high, evaporation can be so strong that it reduces pesticide performance or causes solvent burn. Fine sprays make it worse.

    I also hear about the use of oily adjuvants to control evaporation from small droplets. This could be even more dangerous. Small droplets drift, and evaporation to dryness is actually helpful in reducing the impact of that drift. How? It makes the small droplets disappear, with their remnants dispersing into the turbulent atmosphere. With oily adjuvants, the small droplets stick around and stay potent and their drift damage is much worse.

    Lastly, the practice is possibly off label. Water volume and spray quality label statements are designed to offer good performance and acceptable drift risk. While that part of the label is often a bit dated, it does provide better support from the manufacturer should something go wrong.

    If you’re spraying under hot, dry and windy conditions, the low volume, fine spray approach is irresponsible. Use sufficient water (7 to 12 gpa) to allow low-drift sprays, at least Coarse to Very Coarse, in some case, even coarser.

    Agronomists provide the best possible information for their clients, based on scientific evidence and experience and in accordance with their professional code of ethics. Sometimes the news we deliver aren’t what the customer wants to hear. But we have to represent the interests of all of us, collectively. I find that pretty important.

  • What Nozzle is This? (Field Sprayers)

    What Nozzle is This? (Field Sprayers)

    Us this handy visual guide to identify a mystery nozzle you may find on a field sprayer. We’ve included the most common low-drift nozzles found on North American, European, and Australian sprayers. The list does not contain any conventional flat fan nozzles.

    It’s in alphabetical order by manufacturer.

    First, a reminder of the ISO colour coding of nozzles by nominal flow rate, and their approximate output at normal speeds and nozzle spacings.

    ISO Flow rate colour coding and benchmark application volumes for US and metric units

    Also recall that most nozzles have markings that identify their fan angle (usually 30, 40, 65, 80, 90, 110, 120, 130, or 150 degrees, with 80 and 110 being most common) or flow rate (in US gpm, as shown in figure above).

    Albuz (manufactured in France)


    Albuz AVI (also John Deere ULAC)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray quality: VC
    Sizes Available: 01 – 10

    Albuz AVI Twin
    Type: Air-Induced Twin
    Average Pressure: 60 psi
    Average Spray quality: VC
    Sizes Available: 01 – 06

    Arag (manufactured in Italy)

    Arag Compact Fan Air (CFA)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray quality: C
    Sizes Available: 01 – 04
    Arag Compact Fan Air Ultra (CFA-U)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray quality: C-VC
    (intended for 2,4-D label compliance in Australia, available in 01 – 03 sizes only)
    Arag Twin Fan Low Drift (TFLD)
    Type: Pre-Orifice, suitable for PWM
    Average Pressure: 60 psi
    Average Spray Quality: VC – XC
    Sizes Available: 02 – 05

    Billericay Farm Systems (manufactured in UK)

    Billericay Farm Systems Air Bubble Jet (ABJ)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: M-C
    Sizes Available: 01 – 06
    Billericay Farm Systems EasyJet (known as Pulzar in UK)
    Type: Pre-Orifice, suitable for PWM
    Average Pressure: 60 psi
    Average Spray Quality: M-C
    Sizes Available: 01 – 08

    Greenleaf / Agrotop (manufactured in Germany)

    Greenleaf AirMix (made by Agrotop)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 01 – 06
    Greenleaf SoftDrop (made by Agrotop)
    Type: Pre-orifice, suitable for PWM
    Average Pressure: 60 psi
    Average Spray Quality: XC – UC
    Sizes Available: 04 – 10
    Greenleaf TurboDrop-XL (TDXL, made by Agrotop). TDXL-D appears same, but has larger exit size and produces coarser sprays for dicamba
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: TDXL, C-VC, TDXL-D, XC-UC
    Sizes Available: 01 – 15 (08 for -D)
    Greenleaf TADF (made by Agrotop). TADF-D appears same, but has larger exit size and produces coarser sprays for dicamba
    Type: Air-Induced Asymmetric Twin
    Average Pressure: 60 psi
    Average Spray Quality: TADF, C-VC, TADF-D, XC-UC
    Sizes Available: 01 – 15
    Greenleaf Dual Fan (DF, made by Agrotop), asymmetric twin.
    Similar to Hypro TwinCap, assembly can house two nozzles to produce a twin spray.
    Greenleaf Low Drift Dual Fan for PWM (BPDF)
    Uses AirMix nozzles with air portion removed.
    Spray Quality M – XC
    Sizes Available: 06 – 12

    Hypro Pentair / John Deere (manufactured in UK and USA)

    Hypro Guardian (Also John Deere LDX)
    Type: Pre-orifice, suitable for PWM
    Average Pressure: 40 psi
    Average Spray Quality: M
    Sizes Available: 015 – 08

    Hypro GuardianAIR (GA, also John Deere Low-Drift Air, LDA)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 015 – 05
    Hypro Ultra Low-Drift (ULD, also John Deere ULD)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C – VC
    Sizes Available: 015 – 08
    Hypro Ultra Low-Drift Max (ULDM)
    Type: Air-Induced, approved for PWM by Hypro
    Average Pressure: 60 psi
    Average Spray Quality: UC
    Sizes Available: 04 – 08
    Hypro GuardianAIR Twin (GAT, also John Deere GAT)
    Type: Air-Induced Twin
    Average Pressure: 60 psi
    Average Spray Quality: M-C
    Sizes Available: 02 – 08

    Hypro 3D (also John Deere 3D)
    Type: Pre-Orifice, suitable for PWM
    Average Pressure: 40 psi
    Average Spray Quality: M
    Sizes Available: 015 – 08
    Hypro TwinCap. Assembly can house two nozzles to produce a twin spray.

    John Deere LDM
    Type: Pre-Orifice, suitable for PWM
    Average Pressure: 60 psi
    Average Spray Quality: C – VC
    Sizes Available: 03 – 10
    John Deere LDM showing characteristic twin pre-orifice

    Lechler (manufactured in Germany)


    Lechler ID
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C – VC
    Sizes Available: 01 – 10

    Lechler ID3
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C – VC
    Sizes Available: 01 – 10

    Lechler IDTA
    Type: Air-Induced Asymmetric Twin
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 02 – 08

    Lechler IDK (Also Hardi MiniDrift)
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 01 – 10

    Lechler IDKT (Also Hardi MiniDrift Duo)
    Type: Air-Induced Twin
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 015 – 06

    MagnoJet (manufactured in Brazil)

    Magnojet MUG
    Approved by EPA for Dicamba in US
    Type: Air-Induced
    Average Pressure: 70 psi
    Average Spray Quality: UC
    Sizes Available: 015 – 05

    TeeJet (manufactured in USA)

    TeeJet AIXR
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: C
    Sizes Available: 015 – 10
    TeeJet AI
    Type: Air-Induced
    Average Pressure: 60 psi
    Average Spray Quality: VC
    Sizes Available: 015 – 15
    TeeJet TurboTeeJet (TT)
    Type: Pre-orifice, suitable for PWM
    Average Pressure: 40 psi
    Average Spray Quality: M-C
    Sizes Available: 01 – 12

    TeeJet TurboTwinJet (TTJ60)
    Type: Pre-orifice Twin, suitable for PWM
    Average Pressure: 40 psi
    Average Spray Quality: M-C
    Sizes Available: 02 – 10

    TeeJet Air-Induced TurboTwinJet (AITTJ60)
    Type: Air-Induced Twin (approved for PWM by TeeJet)
    Average Pressure: 60 psi
    Average Spray Quality: C-VC
    Sizes Available: 02 – 15
    TeeJet TurboTeeJet Induction (TTI)
    Type: Air-Induced (approved for PWM by TeeJet)
    Average Pressure: 60 psi
    Average Spray Quality: XC-UC
    Sizes Available: 015 – 15

    TeeJet Twin TurboTeeJet Induction (TTI60)
    Type: Air-Induced Twin (approved for PWM by TeeJet)
    Average Pressure: 60 psi
    Average Spray Quality: XC-UC
    Sizes Available: 02 – 08
    TeeJet AI3070
    Type: Air-Induced Twin
    Average Pressure: 60 psi
    Average Spray Quality: C-VC
    Sizes Available: 015 – 05
    TeeJet AccuPulse TwinJet (APTJ)
    Type: Pre-orifice Twin, suitable for PWM
    Average Pressure: 60 psi
    Average Spray Quality: XC- UC
    Sizes Available: 015 – 08

    Wilger ComboJet (manufactured in US and Canada)


    Wilger ComboJet
    Available as ER,SR, MR, DR, and UR models. Appear similar, requires inscription to differentiate
    Type: Pre-orifice, suitable for PWM
    Average Pressure: 50 psi
    Average Spray Quality:
    ER: M
    SR: C
    MR: VC
    DR: XC
    UR: UC
    Sizes Available: 01 – 25
    Adaptor for Combojet tips on TeeJet connector
  • Nozzle Selection for Boom Sprayers

    Nozzle Selection for Boom Sprayers

    Picking the correct nozzle for a spray job can be a daunting task.  There is a lot of product selection, and a lot of different features.  We try to break the process down into four steps.

    1. Identify Your Needs

    Before making any assumptions about the right nozzle for you, review your needs and objectives. Are you trying to reduce drift? Do you want better coverage? Are you moving towards more fungicide application? Do you need a wide pressure range?

    It’s always a good idea to review your experience with your previous nozzle. What, if anything, would you like to change?

    2. Identify Flow Rates

    Most spray operations fall into one of three categories, (a) pre-seed burnoff (3 to 7 US gpa); (b) in-crop early post-emergence (7 to 10 US gpa); (c) late season application to mature canopies (10 – 20 US gpa).

    To find the right nozzle size, you need to know the application volume, the travel speed, and the nozzle spacing. Most sprayers have 20” nozzle spacing, but some have 15” spacing. Use these metric or US units charts to find the right flow rate for common nozzle spacings. Various on-line calculators from Hypro, Greenleaf / Agrotop, Lechler, or Wilger or their apps, are also helpful.

    If you use our chart, the top row lists water volumes. The columns contain travel speeds. Travel speed is somewhat flexible and can change throughout the field.

    Let’s assume the water volume is 7 gpa, and the desired application speed is 13 mph. Move down the “7 gpa” column, searching for 13 mph. You will encounter 13 mph about 5 times: 02 nozzle @ >90 psi, 025 nozzle @ 60 psi, 03 nozzle @ 40 psi, and 035 nozzle @ 30 psi (the 035 size is only offered by some manufacturers) and the 04 nozzle at about 25 psi.

    Nozzle chart, in US units, solving for 7 gpa at 13 mph. Five nozzles can produce the required flow, each at different pressures.

    Note that for the smaller nozzle sizes, the spray pressure is perhaps too high, and for the larger sizes, it is too low. Select a size that allows optimum nozzle performance and travel speed flexibility. In this example, the 025 size is optimal, producing an expected pressure of about 60 psi. The column for the 025 nozzle can now be used to predict the travel speed range from 30 psi to 90 psi, about 9 to 16 mph. For the 03 nozzle, the minimum speed would be 11 mph, too fast for some.

    For Pulse Width Modulation (PWM), slightly different rules apply. See here for instructions.

    3. Select the Nozzle Model

    For general spraying, we recommend intermediate spray qualities ranging from Medium to Very Coarse.

    These intermediate spray qualities offer good coverage at reasonable water volumes and good drift control. Their spray quality can be tailored with pressure adjustments to suit specific needs. For images, see here. In alphabetical order:

    Air Induced:

    There is plenty of selection in this popular category, all manufacturers offering similar specs and performance.

    Pulse Width Modulation:

    PWM nozzle selection is improving, but some gaps in availability remain.

    All nozzles should be operated near the middle of their pressure range, for air-induction this is 50 to 60 psi or higher, a bit less for non air-induced types. This allows maximum flexibility when travel speeds change or when spray quality is adjusted with pressure.

    For fusarium headblight, consider a twin fan nozzle.

    Keep your booms no more than 15” to 25” above the heads for best results.

    Air Induced:

    There is an excellent selection of twin fans from most manufacturers.

    Pulse Width Modulation:

    Relatively poor selection, limited flow rate ranges or spray qualities available for some models.

    For finer sprays (lower water volumes), simply increase spray pressure or consider a non-air-induced design.

    There has always been a large selection of finer sprays on the market, remnants from a time when drift was less important. Very few offer flow rates above 06 or 08, decreasing utility for PWM systems.

    Notice that conventional flat fan tips and most pre-orifice tips are absent from these lists. These nozzles are not recommended for herbicides because they produce sprays that are too fine for acceptable environmental protection (ASABE Fine and Medium). The added coverage afforded by such sprays only has value with low water volumes, and in those instances is more than offset by their higher drift and evaporation. An exception is the use of insecticides with contact mode of action targetting small insects such as flea beetles or aphids. In thes cases, finer sprays (ASABE Fine or Medium) may be required to provide effective tragetting.

    Very high flows are sometimes needed (11010 and above, usually for PWM). When this occurs, conventional flat fans have merit because the higher flow rates of any nozzle usually create coarser sprays, and even conventional tips will create sufficient coarseness to prevent drift.

    For the best drift protection, consider these tips.

    The advent of the dicamba-resistant trait in soybeans has spawned interest in very low drift tips that comply with the label requirements for these products. Although superior for drift control, they are not well suited for low volume or low-pressure spraying, nor for contact herbicides or grassy weeds, as spray retention and coverage may be poor. But they are very valuable when drift control is paramount and when higher volumes can be used to maintain adequate coverage.

    The following advice is based on the rules at the time it was written. These may be suitable for 2,4-D application in Australia under the newest APVMA guidelines (check spray quality to be sure it is VC or coarser). Many are also suited for Dicamba in Canada (must be XC or coarser), or dicamba in the US (must be on approved lists such as this one for Xtendimax or this one for Engenia, but caution is advised, some low pressure limits make them impractical. Always check that spray quality can be achieved at pressures that offer travel speed flexibility.

    Air Induced:

    Excellent selection. This market has received much attention in recent years.

    Pulse Width Modulation

    Before making a selection, check the nozzle’s recommended pressure range and the spray qualities within that range from the manufacturer info. The target pressure for these tips may differ from your expectations.

    4. Tweak and Confirm

    Under field conditions, the spray pressures which produce the desired water volumes can vary from the charts. Make sure you trust your pressure gauge reading and know the pressure drop from the gauge signal to the nozzles, particularly with PWM, where the solenoid adds additional drop. Add the pressure drop to your target pressure reading. If using a rate controller, use the pressure gauge as your speedometer to ensure optimal nozzle performance. Adjust travel speed until the nozzle pressure meets with your spray quality and pattern goals. If that speed is too slow or fast…you have the wrong size nozzle and/or water volume.

    Spray pressure is more important than travel speed – make your pressure gauge your speedometer.

  • The Pressure-Spray-Coverage Relationship

    The Pressure-Spray-Coverage Relationship

    Pressure is integral to nozzle performance. Reducing hydraulic pressure reduces nozzle flow rate, increases median droplet size, and typically reduces spray fan angle. Increasing pressure increases nozzle flow rate, reduces median droplet size and typically increases spray fan angle.

    You can watch this Exploding Sprayer Myths video to learn how pressure, boom height and nozzle spacing interact. In extreme cases, too low a pressure can collapse the fan angle enough to reduce overlap and compromise coverage, as explained in the video at the end of this article.

    Pressure affects all aspects of spray quality. Using a flat fan nozzle as an example, a lower pressure increases the median droplet diameter, reduces the droplet count, reduces the nozzle rate and typically reduces the spray angle. Alternately, a higher pressure decreases the median droplet diameter, increases the droplet count, increases the nozzle rate and typically increases the spray angle. Always plan to operate a nozzle in the middle of its recommended range so it can handle small changes in pressure during spraying (such as from a rate controller, or changing PTO speeds on hilly terrain).
    Using a flat fan nozzle as an example, a lower pressure increases the median droplet diameter, reduces the droplet count, reduces the nozzle flow rate and typically reduces the spray angle. Alternately, a higher pressure decreases the median droplet diameter, increases the droplet count, increases the nozzle flow rate and typically increases the spray angle.

    Always plan to operate a nozzle in the middle of its recommended range so it can handle small changes in pressure during spraying (such as from a rate controller, or when changing PTO speeds on hilly terrain). Don’t operate an air induction nozzle below 2 bar (30 psi), even if it’s rated lower in the manufacturer’s nozzle table. Most AI nozzles perform best at >4 bar (60 psi).

    Pressure can be used on-the-fly to make minor changes to flow rate while spraying. This is how rate-controllers work to compensate for changes in ground speed and maintain a constant overall rate per planted area.

    However, pressure should not be used to make significant changes to flow rate. It takes a 4x change in pressure for a 2x change in flow rate, so it’s inefficient. Operating pressures at the upper or lower limit of a nozzle’s range can have undesirable impacts on nozzle wear, median droplet size and swath uniformity.

    For a more in-depth discussion of the relationship between spray pressure and nozzle performance, and how rate controllers work, check out this article.

    Note: It is far better to simply switch nozzles when a significant change in flow rate is required.

    In 2015, we ran demonstrations at Ontario’s Southwest Agriculture Crop Diagnostic Days. The 20 minute sessions were designed to explain:

    Although manufacturers of air induction nozzles often rate their performance as low as 15 psi, such a low pressure collapses the spray pattern and the resulting gaps reduce coverage. Additionally, the spray quality at such low pressures is coarser than at higher pressures, reducing the number of droplets available. This further reduces coverage potential.

    This video covers the key speaking points from that demonstration.