Category: Calibration

Horizontal boom sprayer calibration

  • Variable Rate Spraying

    Variable Rate Spraying

    Variable rate spray application is receiving a lot or attention with our increased ability to farm according to prescription maps.  For dry products such as seed or fertilizer, metering is relatively straight-forward and variable rate application has been possible for many years. However, liquid product application has been more complex and requires special approaches

    Hydraulic Pressure and Flow Rate

    In conventional liquid metering, the liquid is forced through a metering orifice that is placed in-line.  This could be an orifice plate for liquid fertilizer, or a flat fan nozzle for pesticides.  Rate control is achieved by altering the spray pressure. It is usually impractical to change the nozzle or metering orifice during an application.

    The main drawback to this approach is that spray pressure is not very effective at changing flow rates due to the square root relationship between spray pressure and flow rate.

    For example, with reference to the table below, one can see that doubling the spray pressure (say, from 30 to 60 psi) only increases the flow rate by 40%. Tripling the pressure (from 30 to 90 psi) increases the application volume by 73% (we can call that a factor of 1.73). As a result, the use of pressure alone doesn’t offer a large range of application rates, and we accept a factor of 2 to be the limit for fertilizer streamer and broadcast nozzles (meaning a four-fold pressure range) and a factor of 1.73 to be practical for broadcast pesticide sprays over a 3-fold pressure range.  Any wider application volume range would require adjustment to travel speed.

    Application Chart 2015 cropped

    With these inherent limitations in flow rate capacities from hydraulic pressure alone, applicators are often forced to use wide pressure fluctuations to achieve reasonable rate responses.  In some cases, this means that pressure needs can be too low for uniform distribution, or too high for pump or plumbing capacities.

    For Variable Rate application, we are less interested in travel speed range, and are more interested in flow rate range. The above chart can be used for both purposes. In the above example, rows under each application volume identify the travel speed range. These headings can be flipped, so the 10 gpa column (with mph values in it) can also be a 10 mph column (with gpa in it). the numbers don’t change. same is true for metric units, except the convenience of being in the same magnitude that makes the flip easy in US units is absent.

    There are a few options available that expand the flow rate range of liquid products.  A brief overview of the main options follows:

    Greenleaf / Agrotop

    TurboDrop Variable Rate (TDVR): This nozzle appears like the traditional TurboDrop family, but has an innovative dual orifice in its venturi. The first stage is always open, but the second orifice is held closed under spring pressure until a certain threshold is reached. This design achieves a 3-fold flow rate range between 40 and 140 psi. Below the 40 psi threshold, the spray pattern fan angle deteriorates quickly.

    TurboDrop VR tip provides about 3-fold flow rate range at any given speed, but requires higher pressures.

    TurboDrop Variable Rate Fertilizer (TDVFR): Because fertilizer streams do not need to atomize the spray or form a fan, the minimum pressure can be reduced, in this case to 10 psi. From 10 to 140 psi, this design offers a four- to five-fold range of flow rates. Three exits are offered, a streamer, a hose barb, and a quick connect.

    Three variants of the variable rate fertilizer orifice are offered by Greenleaf.

    VariTarget Nozzle

    This nozzle design uses a spring-loaded plunger to exert force on a flexible nozzle cap, deflecting it slightly.  The deflection changes the orifice size, allowing for a change in flow.  As a result, the flow rate response to a pressure change is increased dramatically. A single VariTarget nozzle equipped with a blue or green nozzle cap can deliver flows ranging from 0.2 US gpm at 20 psi to 1.2 gpm at 65 psi, for a stunning 6-fold change in application rate (link).

    VariTarget
    The VariTarget nozzle body

    The main drawback of this nozzle is the poor metering accuracy of the system. In calibration tests, flows from various new VariTarget nozzles operated at the same pressures varied by more than 10%.  While this amount of variability may be acceptable in liquid fertilizer application, it is not considered acceptable for pesticide application. Tightening or loosening the threaded spring cap even a little changes the flow.

    VariTarget Flow Chart

    TeeJet Variable Rate Fertilizer Assemblies

    These metering assemblies, introduced in 2016, offer an elastomer (EPDM) metering plate whose orifice diameter expands with pressure, offering a wider range of flows.  There are no moving parts in the assembly.  Four models are available (link).

    IMG_20160112_112250662

    PTC-VR:  Using a push-to-connect design for planters and toolbars, it offers versions that accomodate 1/4″, 5/16”, and 3/8” OD tubing diameters

    QJ-VR Hose Barb:  This unit offers hose barb diameters for 1/4″ and 3/8” ID hose.

    Both units feature a pressure range of 10 psi to 100 psi, within which a flow rate range of approximately 8-fold is possible.

    SJ3-VR: This unit generates three streams and operates over a pressure range of 20 to 100 psi, offering a flow rate range of about 3-fold.

    GPA ranges for specific travel speeds for TeeJet SJ3 VR

    SJ7-VR: Generating seven streams and operating over a pressure range of 30 to 80 psi, this unit allows a flow rate range of about 2.9.

    In all cases, the realized flow rate range is significantly greater than would have been achieved with pressure change alone. TeeJet has tested the flow rate variance among units operating at the same pressure and has found them to be acceptable, according to company representatives.

    Fertilizer banding has greater tolerances for application because pattern width is less important, and also because stream stability is less affected by pressure than spray pattern droplet size.

    Pulse Width Modulation (PWM)

    PWM utilizes conventional plumbing:  a single boom line and a single nozzle at each location.  Liquid flow rate through each nozzle is managed via an intermittent, brief shutoff of the nozzle flow activated by an electric solenoid that replaces the spring-loaded check valve.  Typical systems pulse at 10 or 15 Hz (the solenoid shuts off the nozzle 10 or 15 times per second), and the duration of the nozzle in the “on” position is called the duty cycle (DC) or pulse width.

    100% DC means the nozzle is fully on, and 20% DC means the solenoid is open only 20% of the time, resulting in the nozzle flowing at approximately 20% of its capacity. This is illustrated in the figure below.  The ability to control the duty cycle is referred to as pulse width modulation.

    PWM Schematic

    The system has a theoretical flow rate range of about four- to five-fold. Within this range, spray pressure, and the corresponding spray pattern and droplet size, stay roughly constant.  This makes it ideal for variable rate pesticide application, where spray patterns and spray quality are critical for performance.

    The main disadvantage of this system, compared to the variable orifice designs, is cost. Although highly accurate and dependable, commercial sprayer units are priced between $15,000 and $65,000 per sprayer, depending on features and boom widths. The available systems are Capstan PinPoint II and EVO (as a retrofit to any sprayer), Raven Hawkeye (retrofit to any sprayer, available as factory option on Case (AIM Command), New Holland (IntelliSpray) and most other brands, John Deere ExactApply, WEEDit Quadro, Agrifac StrictSprayPlus and TeeJet DynaJet (available as retrofit). See our in-depth article on PWM for more information on these systems.

    For ammonia and liquid fertilizer planters or toolbars, Capstan offers three different PWM products, N-Ject NH3, N-Ject LF or EVO LF. These systems offer more control over PWM pulse frequency and duty cycle and can achieve 8-fold rate ranges. 

    Flow rate ranges for Capstan N-Ject LF, on 30″ spacing

    At low frequencies and duty cycles, the mobiliy of the fertilizer in soil needs to be considered, as significant gaps in a stream can be generated.

    A variable rate for liquid fertilizer system for seeders, together with sectional control and turn compensation, is offered by Capstan EVO-LF. This system can generate 10 to 60 gpa at 4.5 mph on 12″ spacing.

    Dual Boom Systems

    A second boom fitted with different flow nozzles is installed, and is activated when the flow rate requirements can no longer be met with a single set of nozzles.  Once the second boom is activated, the spray pressure drops significantly and additional flow capacity can be realized.

    Dual boom system

    Dual or Quadruple Nozzle Bodies

    A similar approach to the dual boom is available as selectable nozzles in the same body from Arag (Seletron), Hypro (Duo React), John Deere (ExactApply) Amazone (AmaSelect), and others. These systems utilize a single boom and direct the flow through one of any two (Duo React, ExactApply, Seletron) or four (Seletron, others) nozzles, or several nozzles at the same time. 

    AmaSelect utilizes a unique switching system that allows the user to select only Nozzle 4, Nozzle 3, Nozzles 3 & 4, and Nozzles 2 & 4, making the placement of certain sized nozzles critical.

    Amazone AmaSelect nozzle switching system

    Similar pressure fluctuations as with a dual boom would be experienced, requiring careful selection of nozzle flow rates to avoid large pressure jumps. The system can also be used to manually change from one nozzle to another as needed. In the figure below, the pressure changes associated with the sequential use of 015, 02, and 035 flows are shown.

    Duo React

    Direct Injection

    Direct injection is an option for variable application of pesticides.  In this system, undiluted pesticide is placed into canisters on the sprayer, and plain water (or water plus adjuvant) is in the sprayer tank. The chemical is metered and introduced into the water on the pressure side at some distance upstream from the boom sections. The pesticide rate can be varied with the speed of the direct injection pump, offering a very high dynamic range of possible rates. For example, Raven’s Sidekick Pro (available as factory option on Case and John Deere sprayers, or as a retrofit to any sprayer) offers a 40-fold range of flow rates.

    20140123_145619

    After injection, an in-line mixer ensures that products are evenly distributed in the carrier.  The amount of lag in the systems will depend on the amount of spray mixture in the plumbing upstream of the nozzles, the total boom flow rate, as well as the boom section configuration.  With a variable rate map this lag can can be anticipated and accommodated.

    Pump technology has improved the metering accuracy over a range of viscosities. However, dry formulations remain a challenge as slurries can settle and create problems for the pump and screen components.

    Summary

    High dynamic flow rate ranges for agricultural sprays are challenging to achieve, but will become more important as interest in site-specific management increases.  Relatively inexpensive solutions are available for liquid fertilizer, whereas pesticide sprays require greater investments in technology to preserve spray pattern integrity. As mapping sophistication continues to grow, these application technologies will be integral to variable input prescriptions.

  • Compulsory, Standardized Sprayer Inspections

    Compulsory, Standardized Sprayer Inspections

    Spring always brings renewed interest in sprayer calibration. This is good, because a well-maintained and calibrated sprayer will protect crops more effectively and efficiently, as well as reduce the potential for off-target drift and point source contamination.

    Presently, there is no nationally-recognized standard for sprayer calibration in either Canada or the United States. As a result there are many methods, some more stringent than others, spanning activities relating to seasonal maintenance through to precise diagnostic measurements. This means an operator can be in compliance with programs such as CanadaGAP (a food safety traceability standard for fruit and vegetables), and yet only perform the most rudimentary adjustments.

    I was first made aware of “compulsory inspections” in 2009 when I started noticing certification stickers on certain European import airblast sprayers. Some Ontario tender fruit and grape growers familiar with the European standards asked why we didn’t enforce standardized calibration program as they do in Europe. I was surprised to hear a farmer ask for more paperwork, so it made me wonder, are Canada and the US overdue for a change?

    All sprayers, from large, commercial field and airblast sprayers, to the more humble home-grown sprayers (see below) benefit from regular servicing and calibration. And yet, sprayer calibration in Canada and the US remains largely voluntary and highly variable depending on the size of the operation, sprayer design and the willingness/skill of the operator.

    Canada and the US: Then

    In the mid 1980’s, University of Nebraska engineers and Successful Farming Magazine published a study showing that un-calibrated spray applications were costing US farmers ~$1,000,000,000 per year. The article was infamously called “The Billion Dollar Blunder”. You can download the original journal article describing the survey here.  It was estimated that fewer than 5% of applications were within 5% of the desired rates. Spray overlaps and poor calibration resulted in over-applications of more than 20%.

    At the time it was eye-opening and received a lot of attention. In 2006 the original study was revisited (see here), and even with advances in precision application, there was a disappointing lack of improvement. Bill Casady, University of Missouri Extension agricultural engineer, estimated that if 20 minutes of calibration can save 5% on 500 acres in an application sprayed at $25/ac ($61.75/ha), then the 20 minutes of effort worked out to $1,875 / hour. Now that’s a solid return on investment!

    Belgium: Then

    Belgium recognized and addressed this issue more than twenty years ago. In 1995, following the lead of the Netherlands and Germany, Belgium’s Ministry of Agriculture mandated that all spraying equipment (save backpacks) be inspected every three years. At the time, other countries such as Sweden, Hungary and Austria had similar, albeit voluntary, programs.

    Belgian farmers received letters asking them to make their sprayers available for testing by a Ministry-appointed institution, in locations no more than 10 kilometers from their operations. The institution’s trained technicians would subject the sprayers to a regimented, standardized inspection. When the equipment met the standard, they would receive a permit in the form of a sticker (see below) attached to the sprayer. The growers paid for this service, based in part on the size of the sprayer.

    In order to introduce the process to the Belgian farmer, a short documentary was produced. If you would rather not watch the preamble explaining why the prudent use of chemistry is critical to agriculture, and get right to the sprayer inspection process, skip ahead to 3:35.

    What follows is a brief outline of that 1995 process, which I’m told is similar to the process currently used in Belgium:

    1. Administrators perform visual checks to assess the general condition of the sprayer (e.g. obvious maintenance, safety and operational issues).
    2. Boom balance (where applicable), hinges, boom ends and boom sturdiness is checked.
    3. Nozzle spacing and orientation of nozzle bodies is inspected.
    4. All points of filtration are inspected.
    5. For boom sprayers, a spray pattern distribution used to be performed, but it wasn’t diagnostic enough. Instead, a pressure gauge / nozzle combo is used in each position to check for pressure fluctuation, and to ensure each tip had a flow rate within 5% of the average and no more than 10% deviation from the manufacturer’s rate.
    6. For airblast sprayers, the overall output of the sprayer is measured to determine nozzle wear using individual collectors clamped onto each position.
    7. For sprayers with rate controllers, calibrated collection bags are attached to a few nozzles and the sprayer drives a 100 metre course while spraying. The actual output is compared to the expected.
    8. Finally, the farmer receives a report outlining issues that need to be remedied before the sprayer is certified.

    SPISE: Today

    Today, collaborating European countries are members of SPISE – Standardized Procedure for the Inspection of Sprayers in Europe. Established in 2004 by founding members from Belgium, France, Germany, Italy and the Netherlands, the SPISE Working Group aims to “further the harmonization and mutual acceptance of equipment inspections”. They also work to continually improve the inspection / calibration process.

    Their website hosts a number of sprayer-related resources, but the SPICE Advice handbooks are perhaps most valuable to the sprayer operator. Click either image below to download them as PDF for airblast or field sprayers:

    This more current video by AAMS-Salvarani goes though the inspection and adjustment process for airblast sprayers. While there is no mention of air speed adjustments, many of the steps in this video correspond with the airblast adjustments relating to Crop-Adapted Spraying which has proven very successful in Canada.

    Canada and the US: Tomorrow

    Regular, third-party mediated inspections offer many potential benefits to the average operator. But, in order to realize gains in crop protection and environmental stewardship, perhaps there are two programs required: One to certify the sprayer and the other to certify the sprayer operator.

    1. A sprayer inspection program would focus on sprayer maintenance rather than calibration. Maintenance occurs at regular intervals to ensure spray equipment is operating optimally. Calibration is an ongoing process intended to match the sprayer to the conditions in which it’s operating, and that requires an educated sprayer operator.
    2. Sprayer operator education programs such as Ontario’s Grower Pesticide Safety Course, or Penn State’s Pesticide Applicator Certification Course already exist, but they are not offered in every state or province, and they are often voluntary or perhaps specific to a particular expertise (e.g. not applying to custom applicators or airblast operators).

    They could start as voluntary, pay-for-service pilot programs to see if operators appreciate how much better their sprayers are functioning, and to quantify how much waste is been reduced. They wouldn’t necessarily have to be government-run; Industry or Academia may be better conduits. So, what would be required to develop and implement these two programs?

    • We would need to agree on a robust and generic sprayer inspection protocol. We have several European examples to draw on.
    • We would need to agree on the minimal content for a sprayer operator course. Again, we have many to draw on, with the obvious understanding that the core curriculum would be amended to reflect various state and provincial requirements.
    • We would need a trained, third-party organization to take responsibility for overseeing and implementing the two programs.
    • And, of course, we would need the funds to initiate both programs before they would eventually become self-sustaining.

    So, are we dreaming in Technicolor? If responses to this article are any indication, there are those in western society that lash out at the idea of mandatory requirements. But there are supporters, too. Maybe we can learn from those European countries that have been doing this for more than 20 years.

    Thanks to Jan Langenakens of aams for reviewing this article, and providing the videos.

  • Pressure Spikes and Relief Valves on Air-Assist Sprayers

    Pressure Spikes and Relief Valves on Air-Assist Sprayers

    A properly-sized pump should produce more flow than is needed and work in conjunction with the atomizers to regulate that flow. Typical to high pressure pumps, a piston relief valve (aka regulator) should maintain the desired system pressure through the normal speed range of the sprayer, regardless of the number of booms (or boom-sections) that are on or off. This is achieved by balancing the sprayer pressure against the relief valve spring, which must move freely across a range of flows.

    But what does it mean when the pressure gauge briefly spikes off-scale when boom are turned on or off? This is bad for the gauge and will eventually cause it to fail. Quite often, pressure spikes are an indication of one of two things:

    • A dirty or stuck valve
    • An inappropriate spring size
    A pressure gauge spiking beyond its range.
    A pressure gauge spiking beyond its range.

    Relief valve maintenance

    Sometimes, pressure spikes indicate a need for valve cleaning and maintenance.

    • The regulator spring cavity may be packed with dirt, which limits valve travel. Clean the housing and spring, and then lubricate and adjust.
    • The regulator may be partially seized or sticky. If the regulator piston and cylinder bores are caked with spray they will ‘hold’ the valve until the pressure/spring balance overcomes the friction.
    • Sometimes valve, and/or the valve guide pin are seized. Disassemble them, clean all sliding surfaces, then lubricate and adjust.
    • Valve/seat wear may have created a leak. You may have already tightened the spring to compensate, but this loads the spring past the pressure balance point you want to spray at. This means that when the booms are shut off, the pressure increases until it reaches the ‘new’ spring balance point. Repair (or replace) the regulator, then lubricate and adjust. Be aware that any leak (external or internal) can contribute to this condition and tightening the spring isn’t the solution.
    • The spring may be damaged (e.g. bent, corroded, etc.). Replace the spring, lubricate and adjust.

    Note: Be sure to read the operator’s manual before you do anything. You should understand your sprayer’s design before you perform any maintenance, adjustments or calibration.

    Spring size

    Sometimes, the relief valve may be mechanically sound, but the spring may not be sized to match a reduced operating pressure. Relief valve springs match the maximum pressure range of the pump. Sprayers operated at lower pressure may be unable to compress the spring. This is common when people switch from disc-core nozzles operated at higher pressure to molded nozzles operated at lower pressure.

    This would manifest when one boom is shut off for single-boom operation; there may not be enough pressure to open the bypass. As a result, flow increases over the remaining boom.

    Recognizing this problem, some operators have teed-in a second relief valve capable of finer adjustments at lower pressures. Make sure you know what you’re doing if you’re considering this option.

    Technically, a spring can either be too weak, or too heavy:

    • The spring may be too weak for the pressure being used (i.e. any adjustment bottoms out). In order to obtain sufficient pressure the operator tightens the spring until it is virtually collapsed, essentially creating a fixed orifice. When the booms are closed the ‘fixed orifice’ doesn’t compensate and pressure rises to force the increased flow through that small orifice.
    • If the spring is too heavy for the pressure being used (any adjustment barely touches the spring when pump is turned off). In this case, the pressure being used will not deflect the spring, so the operator closes the regulator until the ‘fixed orifice’ creates sufficient restriction to flow to achieve the desired pressure. When the booms are closed the ‘fixed orifice’ doesn’t compensate and pressure rises to force the increased flow through, or until the spring begins to deflect.
    • In either situation the spring must be sized so it is in the centre-third of its flex range (i.e. rest state > fully collapsed) at the desired pressure. You can buy springs from the sprayer dealer or hardware supply. Try to maintain original length and diameter of the coil, while varying the diameter of the wire.

    Engineering

    In some cases, it is not a matter of valve maintenance, or spring size, but poor engineering. Consider the following:

    • The valve supply and return may be too small for the pump flow. Consult hose and fitting catalogs for flow capacities and lengths. Re-size the hoses and fittings appropriately, and then adjust the regulator.
    • There may be kinks or sharp bends in in the supply and return lines. Re-route the hoses and/or fittings to avoid kinks and sharp bends, and then adjust the regulator.
    • The relief valve may be too small for the pump flow. Consult a regulator catalog for flow capacities and replace the regulator with an appropriate size. Calibrate the regulator spring and adjust.
    • Relief valves have a ‘cracking’ pressure (that’s when the valve just starts to open). Well-designed regulators have small pressure changes from ‘cracking’ to full flow. That information is in their catalogs. Poorly designed regulators have large pressure changes between these two ratings and these regulators should be avoided.
    • The pump may be too big for system. This often happens when sprayers are upgraded and pumps are replaced. Consult the catalogs and reduce pump size or speed, or increase the sizes of the hoses, fittings and regulator.
    • There may be a hydraulic agitator jet on the regulator ‘tank’ line. An agitator jet applies considerable back pressure to a system, and when booms are closed the increased flow causes more than a linear increase in pressure.
    • Broadly, the sprayer system as a whole may be poorly engineered. Inspect and draw a flow path of the sprayer system. Examine where everything is going (or not going). Is it possible someone made changes that the manufacturer did not intend? Consult the manufacturer if you are uncertain. Sometimes, it will have to be re-engineered, which may require expert consultation.

    Note: Your pressure gauge can tell you a lot more than your operating pressure – it can indicate a problem with your regulator, pump, lines or overall sprayer engineering. Don’t ignore it – address it.

    Thanks to Murray Thiessen, Consulting Agricultural Mechanic, for his contribution to this article.

  • 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.

  • Sprayer Math for Banded Applications

    Sprayer Math for Banded Applications

    Where crops are planted in rows, growers can save on chemical costs and reduce potentially wasted spray by performing banded applications. A banded application is treating parallel bands (Figure one), unlike a broadcast application where the entire area is treated (Figure two). This means only a portion of the field or orchard/vineyard floor receives spray, so the total amount of product applied per hectare (or per acre) should be less for banded than for broadcast.

    Figure 1
    Figure 1
    Figure 2
    Figure 2

    Banded applications are used in many situations, including:

    • Applying herbicides right over a crop during planting, both for pre-emergent or post-emergent crops.
    • Applying insecticides/fungicides by “directed spraying” using drop hoses or row kits; the latter is pictured in Figure three.
    • Carefully spraying herbicide between the rows to control weeds in the alleys of an established crop (Figure one).
    • Applying herbicide under fruit trees or grape vines to control weeds (Figure four).
    Figure 3
    Figure 3
    Figure 4
    Figure 4

    It’s easy to make mistakes when calculating product rates for banded applications and these can be costly errors: too little means poor control and too much means wasted product and possible crop injury. This article describes how to calculate sprayer output and product rate for common banded applications.

    Step One: Determine broadcast volume

    Pesticide labels typically list broadcast product rates (e.g. amount of formulated product per hectare or acre). In this example, let’s say the label recommends a broadcast product rate of 500 ml of formulated herbicide applied using 100 litres of spray mix per hectare (i.e. added to 99.5 L water).

    Step Two: Establish sprayer settings

    Select a travel speed that is safe, gives decent efficiency and doesn’t compromise coverage. For this example, we’ll say the sprayer moving is at 8.0 km/h.

    Select a band width that completely covers the target row and some of the adjacent area where control is desired. Band width should be measured along the ground for soil-applied products or along the top of plants for post-emergence products. We’ll use Figure one for our settings: bands are 50 cm wide on 100 cm centres. We’ll say that a single nozzle swath can treat the band, and that we’re spraying 2 hectares of planted area.

    Step Three: Calculate the banded sprayer output

    We can calculate how much of the planted area actually receives spray using this formula:

    [band width (cm) ÷ row width (cm)] x total planted area (ha) = actual sprayed area (ha)
    [50 cm ÷ 100 cm] x 2 ha = 1 ha

    For completeness, here’s the US formula:
    [band width (in) ÷ row width (in)] x total planted area (ac) = actual sprayed area (ac)

    From this we now know that we should be able to go twice as far on a tank spraying a banded application as we would a broadcast, because we’re only spraying half the planted area.

    Step four: Calculate the nozzle output

    Use the following formula to convert the broadcast output into the banded output:

    [broadcast output (L/ha) x travel speed (km/h) x (swath width (cm) ÷ number of nozzles per swath)] ÷ 60,000 = nozzle output (L/min)
    [100 L/ha x 8 km/h x (50 ÷ 1)] ÷ 60,000 = 0.67 L/min

    For completeness, here’s the US formula:
    [broadcast output (gal/ac) x travel speed (mph) x (swath width (in) ÷ number of nozzles per swath)] ÷ 5,940 = nozzle output (gal/min)

    If multiple nozzles were contributing to the swath, such as in figure three or figure four, this formula will account for it. You still mix the labelled product rate at a ratio of 500 ml of herbicide to 99.5 L water, but as we determined in step three, we should be able to spray twice the planted area using a banded application as we would a broadcast application.

    Warning! Watch your units. You may be familiar with other formulae for calculating your output. Do not mix and match formulae or parts of formulae. For example, here is another Metric option for determining L/min. It employs different units so it requires a different constant:

    [broadcast output (L/ha) x travel speed (m/min) x (swath width (m)) ÷ number of nozzles per swath)] ÷ 10,000 (m2/ha) = nozzle output (L/min)

    Step Five: Use the nozzle catalogue to find the right nozzle

    Using a nozzle manufacturer’s catalogue, select a nozzle that gives the desired spray quality (usually coarser for herbicides) and will produce the 50 cm swath we’re looking for (which can be adjusted a little using boom height). Always choose to operate a nozzle in the middle of its pressure range.

    Step Six: Calibrate the sprayer (i.e. double-check)

    Follow your typical calibration process and make minor adjustments until the nozzle discharge per minute results in the desired banded output. A rate controller will handle this on larger sprayers, but if you don’t have one you can make small adjustments to speed and pressure until the desired output is achieved. Ideally, if your math was right, these changes won’t be needed.

    When performed correctly, banded applications are a great way to focus your efforts on the target, saving time and money.

    Here are a few additional resources if you’d like to learn more, or work with a few online calculators: