Category: Speciality Sprayers

Main category for all sprayers that are not horizontal booms

  • Rainfastness of Insecticides and Fungicides on Fruit

    Rainfastness of Insecticides and Fungicides on Fruit

    This article was co-authored by Kristy Grigg-McGuffin, OMAFA Horticulture IPM Specialist

    In view of the frequent heavy rains in many regions this season, understanding rainfastness, or the ability of a pesticide to withstand rainfall, is important to ensure proper efficacy. All pesticides require a certain amount of drying time between application and a rain event. Typically, residue loss by wash-off is greatest when rain occurs within 24 hours of spraying. After this point, the rainfastness of a product will depend on formulation, adjuvants and length of time since application.

    Rainfastness of Insecticides

    John Wise, Michigan State University has studied rainfastness of common tree fruit insecticide groups and his findings are summarized below. For the complete article, refer here. Note that some products listed in this article may not be registered for use in Canada. Check with your local supplier or in Ontario, refer to OMAFA Publication 360 for a complete list of registered products.

    According to Wise, the impact of rain on an insecticide’s performance can be influenced by the following:

    1- Penetration

    Penetration into plant tissue is generally expected to enhance rainfastness.

    • Organophosphates have limited penetrative
      potential, and thus considered primarily surface materials.
    • Carbamates and pyrethroids penetrate the cuticle,
      providing some resistance to wash-off.
    • Spinosyns, diamides, avermectins and some insect
      growth regulators (IGR) readily penetrate the cuticle and move translaminar (top
      to bottom) in the leaf tissue.
    • Neonicotinoids are considered systemic or
      locally systemic, moving translaminar as
      well as through the vascular system to the growing tips of leaves (acropetal
      movement).
    • For products that are systemic or translaminar,
      portions of the active ingredient move into and within the plant tissue, but
      there is always a portion remaining on the surface or bound to the waxy cuticle
      that is susceptible to wash-off.

    2- Environmental persistence and inherent toxicity

    Environmental persistence and inherent toxicity to the target pest can compensate for wash-off and delay the need for immediate re-application.

    • Organophosphates are highly susceptible to
      wash-off, but are highly toxic to most target pests, which means re-application
      can be delayed.
    • Carbamates and IGRs are moderately susceptible
      to wash-off, and vary widely in toxicity to target pests.
    • Neonicotinoids are moderately susceptible to
      wash-off, with residues that have moved systemically into tissue being highly
      rainfast, and surface residues less so.
    • Spinosyns, diamides, avermectins and pyrethroids
      are moderate to highly rainfast.

    3- Drying time

    Drying time can significantly influence rainfastness, especially when plant penetration is important. For instance, while 2 to 6 hours is sufficient drying time for many insecticides, neonicotinoids require up to 24 hours for optimal penetration prior to a rain event.

    4- Adjuvants

    Spray adjuvants that aid in the retention, penetration or spread will enhance the performance of an insecticide.

    The following tables can serve as a guide for general rainfastness to compliment a comprehensive pest management decision-making process. They are adapted from “Rainfast characteristics of insecticides on fruit” by John Wise, Michigan State University Extension.

    Based on simulated rainfall studies to combine rainfastness with residual performance after field-aging of various insecticides, including carbamates (Lannate), organophosphates (Imidan, Malathion), pyrethroids (Capture), neonicotinoids (Assail, Actara, Admire), IGRs (Rimon, Intrepid), spinosyns (Delegate) and diamides (Altacor), Wise recommends the following re-application decisions for apples. Additional work was done on grapes and blueberries; see Wise’s article for this information. Among the crops, variation in rainfastness of a specific insecticide occurs since the fruit and leaves of each crop have unique attributes that influence the binding affinity and penetrative potential.

    • ½ inch (1.25
      cm) rainfall:       All products with 1-day old residues could withstand ½ inch
      of rain. However, if the residues have aged 7 days, immediate re-application
      would be needed for all products but Assail, Rimon, Delegate or Altacor on
      apples.
    • 1-inch (2.5
      cm) rainfall:       In general, most products would need re-application following
      a 1-inch rainfall with 7-day old residues, whereas Delegate and Altacor could
      withstand this amount of rain on apples and would not need to be immediately
      re-applied. Some products such as Imidan on apples could withstand 1 inch of
      rain with 1-day old residues.
    • 2-inch (5
      cm) rainfall      : For all products, 2 inches of rain will remove enough
      insecticide to make immediate re-application necessary.

    It is important to note, not all products registered for the selected pests were included in this study. Refer to Publication 360 for a complete list of management options.

    Rainfastness of Fungicides

    There is no comparable research on rainfastness of fungicides and few labels provide this kind of information. A general rule of thumb often used is that 1 inch (2.5 cm) of rain removes approximately 50% of protectant fungicide residue and over 2 inches (5 cm) of rain will remove most of the residue. However, many newer formulations or with the addition of spreader-stickers, some products may be more resistant to wash-off. Avoid putting on fungicides within several hours before a rainstorm as much can be lost to wash-off regardless of formulation. As well, there are exceptions to the general rule in regard to truly systemic fungicides such as Aliette and Phostrol.

    The effectiveness of sticker-spreaders with fungicides is variable and product/crop specific. Penetrating agents don’t help strobilurins; in fact, some fungicide/crop combinations have been associated with minor phytotoxicity due to excessive uptake. Captan, which is intended to stay on the surface, is notorious for causing injury when mixed with oils or some penetrating surfactants that cause them to penetrate the waxy cuticle.  Consult labels for minimum drying times for individual products and recommendations for using surfactants. 

    Annemiek Schilder, Michigan State University suggests the following to improve fungicide efficacy during wet weather:

    • During rainy periods, systemic fungicides tend
      to perform better than protectant (or contact) fungicides since they are less prone
      to wash-off.
    • Applying a higher labelled rate can extend the
      residual period.
    • Apply protectant fungicides such as captan
      (Supra Captan, Maestro), mancozeb (Manzate, Dithane, Penncozeb) and metiram
      (Polyram) during sunny, dry conditions to allow for quick drying on the leaves.
      These types of fungicides are better absorbed and become rainfast over several
      days after application.
    • Apply systemic fungicides such as sterol
      inhibitors (Nova, Fullback, Inspire Super), SDHI (Fontelis, Sercadis, Kenja, Aprovia
      Top, Luna Tranquility) and strobilurins (Flint, Sovran, Pristine) under humid,
      cloudy conditions. The leaf cuticle will be swollen, allowing quicker
      absorption. In dry, hot conditions, the cuticle can become flattened and less
      permeable, so product can breakdown in sunlight, heat or microbial activity or
      be washed off by rain.

    Click here to refer to the complete article.

  • Pesticide Drift and Communication

    Pesticide Drift and Communication

    When it comes to information about mitigating pesticide drift, it’s plentiful and easily accessed. I have an archive of >30 articles written by Ontario Ministry of Agriculture staff spanning 1999 to present day. Many are on this website. In fact, there’s so much good information out there (see BeDriftAware) it feels like there’s nothing left to say. As a connoisseur (and author) of such materials, I’ve noticed they can be grouped into four common themes – see if you recognize any:

    • The Carrot: These articles describe the benefits of reduced drift, like solid neighbourly relations, reduced environmental impact, saving money in wasted pesticide and improved spray coverage.
    • The Stick: These articles feature insurance adjusters or regulators providing statistics from case studies on the financial, legal, and insurance impacts of drift. Not to mention the time it takes to deal with these issues.
    • The Heart: Many articles describe the frustration and emotional impact from the driftee’s perspective. Others chronicle the conflict, irritation and personal insult that come from being accused of drifting.
    • The Facts: Here we have technical specialists laying out math, such as weather models describing spray behaviour, buffer zones and drift reduction technologies like nozzles, shrouds and sprayer calibration.

    Beyond the written word there are also videos, PowerPoint presentations, workshops or demonstrations, government fact sheets, marketing brochures, social media content and smartphone apps. And yet, every May-July, the drift complaints seem to roll in regardless. For those that ask “why?” here are a few possible reasons:

    Why drift happens

    • Maybe the sprayer operator is pressed for time and chooses to ignore best practices in an effort to catch up. Haste can lead to mistakes.
    • Perhaps the sprayer operator is new and inexperienced, or falls into that small demographic without ready access to educational resources like ag meetings or the internet.
    • Maybe the operator is a veteran lulled into false security having successfully sprayed so many acres, for so many hours, for so many years. Why be so diligent when nothing bad ever seems to happen? Bad logic, but not uncommon.
    • Maybe the problem stemmed from poor communication. Perhaps the land is rented by one person, to a farmer that isn’t there, who has their fields sprayed by custom applicators, who don’t know what’s around the field.
    • Or, perhaps, even the best-intentioned sprayer operator can have bad luck.

    Where can drift take place?

    Agricultural spray (i.e. field crop or horticulture) has the potential to move between operations, or onto residential areas, or sensitive environmental areas. A single operation can even drift an incompatible chemistry onto itself. There are also residential applications (e.g. lawn care) that can negatively affect neighbours. Industrial applications such as roadside sprays can drift to agricultural or residential. Even organic operations spray products that can move outside the treatment area if conditions allow.

    It is important to recognize that every single spray application has the potential for off-target movement. That’s why it’s so important to know what and who is around the treated area.

    Communication helps

    Communication between neighbours can make a big difference, both in preventing drift damage and resolving matters should an incident occur. Here are two perspectives on the same chemical trespass incident. In the first, the parties do not know, and do not care to know, one another. In the second, the parties have communicated previously. Which scenario will be easier to resolve?

    1. A “field cropper that drives 20 miles per hour in high winds” is contacted by a MECP officer on behalf of a “vegetable grower that’s always complaining about spraying”. Accusations and defensiveness between the two parties escalate until they prevent them from speaking directly. Specialists, adjusters, and the officer find themselves acting as mediators. The process is slow and likely headed for court.
    2. Sarah knocks on Kevin’s door and says there might be something wrong with her crop – can he come have a look? She has (rightfully) contacted the MECP to collect samples just in case, and Kevin has all his spray records so they can figure it out. They call in a crop consultant and she contacts a university specialist to solve the problem and prevent it happening again. They follow the crop to yield to determine the impact and agree on a settlement between them.

    Regarding Scenario 1, it’s not my intention to slander field croppers or horticulturalists; I have actually heard parties involved in highly emotional drift disputes describe one another this way. My intent is to point out that you cannot label an entire industry based on the actions of an individual. When parties see each other in this fashion they are unlikely to work together to resolve the problem. No one will be satisfied with the outcome.

    Regarding Scenario 2, I have observed that once each party has a face and a name, it’s so much easier to find solutions. It doesn’t mean someone wasn’t at fault or that compensation isn’t required, but the dialogue facilitates a faster, easier and less emotional outcome. Obviously, in the case of repeated or large-scale incidents, communication may not yield satisfactory results. I’m hopeful, but not naive.

    Opening a dialogue

    Communication can be initiated from either direction: An applicator can inform a residential neighbour or fellow farmer with sensitive crops when and what they intend to spray. Likewise, the neighbour or sensitive crop grower can reach out to the applicator to let them know they are there and that they are concerned.

    There’s no need to wait until there’s a problem. Both parties benefit from keeping one another informed about when sprays go on and the state of any sensitive crops. And, if there is an issue, both parties should begin documenting conditions and suspected damage as soon as possible and over time during the resolution.

    Penn State produced a great article about speaking about pesticides with neighbours.

    Final thoughts

    So, the core of this article isn’t how to prevent drift, or what to do if you suspect it. That’s all been said and I’ve listed a few resources for reference at the end. This article is about being aware of drift potential and about opening lines of communication between those that share borders.

    So follow the links below to learn more about what you can do to mitigate drift. Then, go introduce yourself to your neighbours. Bring a pie. Everyone loves pie.

    Resources

    • Article – This link includes four videos and a factsheet about what drift is, how to prevent it and what to do if you suspect it.
    • Article – This link includes a video and a factsheet about surface inversions and drift.
    • Article – Spraying in the wind.
    • Video – The time of day can affect drift potential.
    • Video – Spray quality (i.e. droplet size) and how it relates to drift.
    • Two articles (one and two) on reducing travel speed and employing other means of improving productivity.
    • Article – Drift-reducing nozzles.
    • Website – This is a link to BeDriftAware, a collection of resources and tools to encourage the use of best application practices by farmers and sprayer operators to reduce the possibility of spray drift.
  • What’s with dew? – Tips with Tom #9

    What’s with dew? – Tips with Tom #9

    When warm air is cooled, it loses some of its moisture-holding capabilities. This change often occurs at night, when plants (and other objects) cool. Once the temperature of the surface of the leaves, for example, drops below the dewpoint, it causes water to condense, forming the shiny dew that causes so many to question early morning spray applications.

    The question is often: will the spray run off the plant or will it get so diluted that it doesn’t work anymore?

    In a dew chamber, work has shown that large spray droplets are more likely to run off a plant saturated with dew than their smaller counterparts. However, similar work showed that spray efficacy was not altered by droplet size.

    Wolf discusses this work and the potential answer to the seemingly conflicting findings. Wolf also explains how grassy weeds compare to broadleaves, the role of surfactants, and what to consider when making the decision to spray through dew or not.

  • Airblast Nozzles – Nozzle Bodies

    Airblast Nozzles – Nozzle Bodies

    Excepting air shear and centrifugal style nozzles, most airblast sprayers employ nozzle bodies designed to except hydraulic nozzles distributed evenly along the booms. Nozzle caps compress the nozzle against the body to force the spray mix through the nozzle orifice. Nozzle bodies are not all created equal.

    Double Outlet Roll-Over Nozzle Bodies

    Double outlet roll-over bodies (pictured below) allow the operator to quickly switch between two nozzles mounted in each position. This is convenient when alternating from dilute to concentrated applications, or changing the spray distribution from block to block.

    A typical brass roll-over style dual nozzle body with Cap and optional check valve.
    A typical brass roll-over style nozzle body with cap and check valve.

    The roll-over feature can act as a shut-off and facilitate fine-tuning the orientation +/- 15° from centre. When roll-overs are new there is an audible ‘click’ when they reach 15° to alert the operator that turning them any further will interfere with flow. This feature fails as bodies wear.

    Single Nozzle Bodies

    Some sprayers employ single nozzle bodies featuring screw or lever-style quarter-turn shut-offs. Some sprayers, like the Turbomist featured below, double the density of the bodies along the boom, arranged in an alternating A-B pattern. The operator shuts off each alternate nozzle, perhaps using the A’s for dilute and the B’s for concentrate applications. The density gives the operator the ability to “double up” in positions along the boom if more spray is required.

    Some sprayers do not use roll-over nozzle bodies. Instead, they double the density of the bodies on the boom for use in an alternating A-B pattern.
    Some sprayers do not use double outlet roll-over nozzle bodies. Instead, they double the density of single bodies along the booms for use in an alternating A-B pattern.

    Still others may affix the nozzle bodies to the deflectors (like the Air-O-Fan below), permitting the operator to orient the air and nozzles at the same time.

    The Air-O-Fan offers double-density by affixing two single nozzle bodies to each air deflector. The operator aims air and nozzles simultaneously and can select flow combinations using quarter-turn shut-offs.

    Check Valves

    In my opinion, it should be mandatory for nozzle bodies (or at least booms) to have diaphragm check valves. When pressure drops below ~15 psi the valves shut to prevent the boom from draining (see image below).

    Old FMC with nozzles bodies that do not have check valves. Once the pressure is off, the booms begin to drain through the lowest nozzle. This is a waste of pesticide and unnecessary environmental contamination.
    An older FMC with nozzles bodies that do not have check valves. Once the pressure is off, the booms drain through the lowest nozzle. This is a waste of pesticide and unnecessary environmental contamination.

    Booms don’t just drain in the yard. Operators shut off the outside boom when turning at the end of a row. Without check-valves, the boom drains through the bottom nozzle, wasting pesticide and causing repeated and unnecessary point-source contamination. Further, it takes a moment for the boom to refill, meaning the top nozzles may not be spraying at the beginning of each row.

    You may be tempted to purchase mesh nozzle strainers with built-in ball valves. They can work as an alternative to integrated nozzle body check valves, but they plug and fail with irritating regularity. The image below shows a creative method for installing check-valves on single nozzle bodies. The nozzles protrude and the check valve seems too close to the shut-off, but reputedly this works.

    An example of retrofitting diaphragm check valves on single nozzle bodies.

    Thread Types

    In North America, you will encounter four inlet thread types: NPT, BSPT, NPS and BSPP.

    National, Pipe Tapered (NPT) single-sided, brass roll-over nozzle body with check valve. Note the shallow cap pictured here.
    National, Pipe Tapered (NPT) single-sided, brass roll-over nozzle body with check valve. Note the shallow cap pictured here.
    British Standard, Pipe Tapered (BSPT) single-sided, brass roll-over nozzle body with a check valve.
    British Standard, Pipe Tapered (BSPT) single-sided, brass roll-over nozzle body with a check valve.
    National, Pipe Straight (NPS) single-sided, brass roll-over nozzle body with check valve. Note the deep cap pictured here.
    National, Pipe Straight (NPS) single-sided, brass roll-over nozzle body with check valve. Note the deep cap pictured here.
    British Standard, Pipe Parallel (BSPP) single-sided, brass roll-over nozzle body with a check valve.
    British Standard, Pipe Parallel (BSPP) single-sided, brass roll-over nozzle body with a check valve.

    The inlet thread sizes available are 1/4” female, 1/4” male and 3/8” male. 1/4” female is not available on the NPS or BSPP inlet thread types. If you are considering installing new roll-over bodies, know your boom’s thread type. The retrofitted Turbomist below, for example, required bodies with female fittings.

    A retrofitted Turbomist with check valves and female double outlet roll-over bodies.

    Molded Nozzles

    Another reason for installing new bodies is to convert from disc & core combination nozzles to single-piece, molded nozzles. They may not fit existing nozzle bodies. Check the diameter of the body outlet (where the nozzle rests) and the outlet cap (which compresses the nozzle against the body outlet). Your sprayer may currently use an unusual-diameter nozzle, like older FMC disc & whirls or European large-diameter pink ceramic disc & cores. Today’s ISO molded nozzles won’t fit in those bodies, so you’ll need to replace them.

    Old FMC roll-over bodies removed in favour of moulded-nozzle-compatible roll-overs with check valves.
    Old roll-over bodies without check-valves. These were removed to make way for better bodies.
    Older nozzle bodies can seize in the boom, requiring novel approaches to removing them. In this case, the mechanic is heating the fittings before unscrewing them. I took this picture with a zoom lens so avoid getting too close! If you plan to do this, please be very careful to do so in an open space, using PPE like gloves and a respirator. Years of residue build-up should be anticipated and respected.
    Older nozzle bodies can seize in the boom, requiring novel approaches to removing them. In this case, the mechanic is heating the fittings using “the blue wrench” to loosen them. If you do this, do not do what this mechanic did. Operate in an open space using gloves and a respirator. Years of residue build-up should be anticipated and respected.

    Be aware: that unlike disc and core, molded nozzles protrude and may hit the edge of the sprayer duct when rolled over, preventing them from turning freely

    Nozzle Body Caps

    Nozzle bodies DO NOT come with the nozzle caps; they are specific to the nozzle type and must be ordered separately. This was an unpleasant surprise the first time I ordered a set of bodies.

    The standard caps are threaded brass hex nut-style but there are also nylon wing-style caps that don’t require a wrench. Beware converting to quarter-turn systems for airblast sprayers. It can work, but nozzles may require additional gaskets and O-rings… and even then are known to leak if the cap diameter is too large (see below):

    Airblast pressure often exceeds 100 psi and can force the O-ring off the molded nozzle and cause leaks.

    Be aware: North American nozzle caps might not fit imported European bodies, and European nozzles might not fit North American cap diameters. The LipCo sprayer is one such example.

    Regarding the cap depths, sprayer operators must consider the how much “stuff” is between the nozzle body and cap. Gaskets, spacers, O-rings and strainers take up room that may warrant a deeper cap. Perhaps most critical is the nozzle itself. For example, brass disc-core are quite thin, but ceramic are much thicker. They require different cap depths.

    TeeJet’s molded cone nozzles come with an ‘A’ (Thinner) or ‘B’ (Thicker) shoulder. The shoulder is the lip around the nozzle base that is compressed against the nozzle body outlet. The B-shoulder is the ISO standard, and is preferred (see below). Shallow caps may not thread onto a nozzle body using a nozzle with a B-shoulder. Deep caps may bottom-out before compressing a nozzle with an A-shoulder, creating leaks. Be sure to note in the nozzle catalog which caps are recommended for the nozzle.

    Moulded hollow cone nozzles come in the thin shoulder (A-style) or thick shoulder (B-style) varieties. The B-style is the ISO standard and is preferred.
    Molded cone nozzles come in the thin shoulder (A-style) or thick shoulder (B-style) varieties. The B-style is the ISO standard and is preferred.

    Nozzle Strainers (aka Filters)

    Before we wrap up, here’s one more look-out. As mentioned, the nozzle strainer shoulder takes up some room between nozzle body and cap. It turns out there can be another concern.

    A hop grower contacted me. He had installed new nozzle bodies on his sprayer. He’d taken into account the shoulder depth and the cap depth. So why were his nozzles plugged? And why when he loosened the cap to finger-tight did they spray, but leak?

    We tried gaskets, O-rings, different cap depths and new nozzles – but no change. That’s when we noticed one side of the roll-over body had a plastic slotted strainer and the other had newer mesh strainer. The mesh strainers were longer and terminated in a disk of solid plastic. When we swapped the two strainers, we had flow! We realized the longer mesh strainers were being compressed against the orifice in the nozzle body, acting like a cork in a wine bottle.

    I prefer slotted over mesh because they are a bit more forgiving with dry formulations and hard water residue, but perhaps more critical is that they aren’t long enough to block the flow.

    Be aware that some strainers may be long enough to block flow in the nozzle body.

    Take Home Tips

    If you are considering installing new nozzle bodies:

    • Confirm the male or female fitting and thread type of your boom
    • Ensure bodies have check valves
    • Ensure roll-overs and check valves clear any obstructions with nozzles in place
    • Know the nozzle type you intend to use, and ensure cap diameter is appropriate
    • Know whether you will use gaskets, o-rings, spacers and strainers, and confirm the cap depth will accommodate everything.
    • Be certain the strainer you choose isn’t so long that it interferes with flow.
    • Consider buying a single nozzle body to install as a trial before buying an entire set of replacements.
  • Continuous rinsing for airblast sprayers

    Continuous rinsing for airblast sprayers

    Why Rinse?

    Airblast sprayers are not rinsed as frequently or as diligently as field sprayers. This is primarily because they are not used to spray herbicides, so residue carry-over doesn’t incur an immediately obvious penalty. The typical operator rinses prior to long-term storage or when cross contamination might cause some form of antagonism (e.g. dormant oil followed by Captan or sulfur).

    Learn more about the difference between rinsing and cleaning in this article.

    Aftermarket Rinsing Systems

    Airblast sprayers can be outfitted with rinsing systems that permit operators to rinse quickly, easily, and dispose of dilute rinsate in rotating locations.

    A Serial Rinse (SR) system, common on field sprayers, re-purposes the pump to transfer clean water from a saddle tank to the product tank via tank rinse nozzles. The operator introduces a volume of clean water to the remaining volume in the tank, circulates it through the system, and then sprays the rinsate in the crop. Repeating this process three times (i.e. the Triple Rinse) serially dilutes the remainder, resulting in a higher dilution factor than a single high-volume rinse.

    A Continuous Rinse (CR) system requires the addition of a dedicated rinse pump. In this case the operator introduces clean water to the tank via tank rinse nozzles while simultaneously spraying. While there is circulation from the bypass (and/or agitation) circuit, the remaining volume is diluted and essentially displaced by clean water.

    Objective

    Using a fluorescent dye tracer as an analog for pesticide, we wanted to explore the effectiveness and efficiency of both systems. We describe the fluorimetry method in this article. We installed a CR system in a 2,000 L H.S.S. tower sprayer, which unlike most North American airblast sprayers, already features a SR system (150 L clean water tank and two tank rinse nozzles).

    Installing a Continuous Rinse System

    Installing a CR option required us to address the same three criteria we have already discussed in previous articles on field sprayer installs:

    • Identifying a CR pump with sufficient flow to operate the tank rinse nozzles
    • Satisfying the electrical or hydraulic requirements of the CR pump
    • Matching the supply flow from the CR pump to the demand flow at the booms
    The Hol sprayer with an 18-nozzle ducted tower, 150 L clean water tank and two tank rinse nozzles. Inset: Rhodamine WT dye used as a pesticide analog for comparing residue levels.

    We mounted two electric Shurflo pumps in parallel to provide flow sufficient to match the typical demand at the booms without excessive electrical load.

    Parallel electric Shurflo pumps drew low amperage and provided sufficient flow to the boom.

    We found that while the CR flow spun the tank rinse nozzles weakly, the spray didn’t reach all interior surfaces. This was remedied by adding a deflector plate to the bottom of the nozzles to redirect flow.

    A brass disc mounted on the tank rinse nozzle deflected spray to all interior surfaces.

    We encountered a complication installing CR on an airblast sprayer compared to a field sprayer. Most field sprayers have rate controllers that permit the operator to adjust travel speed or ‘dial in’ a rate to match boom demand to CR pump supply. Unless the airblast sprayer already has this feature, the operator has to calculate in advance how best to match the flows.

    The calculation has to be performed for each unique output (e.g. dilute or concentrate nozzle arrangements). The flow from the CR pump is a known constant. The nozzle output is variable according to operating pressure, calculated using a nozzle guide. The operator can adjust pressure (bypass or pressure regulator), PTO-speed (on positive displacement pumps), or even alternate between booms or boom-sections to match the flows.

    Matching flow demand to supply using a nozzle catalogue.

    In our case, the operator was using 12 blue Albuz hollow cones in their orchard. We knew the CR pump output was 24.25 L/min. So, by setting the pressure to 6.1 bar prior to rinsing, we were spraying about 24.5 L/min. We parked the sprayer and watched to ensure the sump did not fill or drain during CR. Note in the following video how well the two flow rates were balanced (the camera was accidentally turned when we showed the vertical boom).

    During trials we noticed that as the sprayer climbed uphill the water level in the tank shifted and the pump drew a little air, causing the nozzles to briefly sputter. This was a welcome sight given reports that introducing a few air bubbles during continuous rinsing can be beneficial.

    Field Testing

    During testing, we filled the 2,000 L Hol sprayer with 500 L of water and a final concentration of 0.25 ppm rhodamine (0.5 mL dye per 500 L water). The clean water tank was filled to 150 L. We allowed the mix to circulate for two minutes before priming the booms by spraying for a minute. A 50 mL sample was then drawn from the manifold (see below) and later used to represent the starting concentration during the analysis. The sprayer then drove through the orchard, spraying until empty.

    Samples were drawn after the tank, before the manifold. Note the telltale Mancozeb coating the sprayer. PPE was worn.

    Serial Rinse testing: When the sprayer was empty, the operator left the cab to introduce 75 L of clean water to the main tank via the tank wash nozzles. The rinsate was circulated for one minute before the operator returned to the cab and sprayed the orchard until empty. A 50 mL sample was drawn from the manifold to represent the concentration half-way through the rinse. The process was repeated for the remaining 75 L of clean water and a second 50 ml sample was drawn to represent the final concentration. We did this twice. It took about 12 minutes to rinse the sprayer and the operator had to leave the tractor cab twice.

    Continuous Rinse testing: When the sprayer was empty, the operator stopped spraying and engaged the continuous rinse pump. After a few seconds, he continued driving and spraying rinsate. When 75 L had passed through the system, we paused to draw a 50 mL sample from the manifold to represent the concentration half-way through the rinse. The operator continued until the remaining 75 L was sprayed and a second 50 ml sample was drawn to represent the final concentration. We did this twice. It took about 5 minutes, 45 seconds to rinse the sprayer and the operator did not leave the tractor cab.

    Sample Analysis: A Turner TD 700 fluorometer was calibrated using samples from the tank. Samples were diluted when necessary to ensure they fell in range of the calibration curve (where there is a linear relationship between the concentration of Rhodamine WT and Raw Fluorescence Units (FSU)). This range spanned a maximum of 0.1 ppm and a detection limit of 0.01 ppm active ingredient. Having previously tested recovery accuracy of 95%, data was adjusted accordingly.

    Results of rinsate analysis. n=2.

    Observations

    While both methods diluted the residue significantly, the remainder following both Serial and Continuous Rinse was much higher than anticipated. This may be an artifact given that both concentrations are potentially below our detection limit, per the following:

    Assuming 10 L of residual spray volume left in the system once “empty”, 75 L added would give a dilution factor of 9 (according to the ). While the first 75 L of Continuous Rinse seems to remove more residue than a single addition of 75 L, both are higher than anticipated. A subsequent addition of 75 L should result in a dilution factor of 72. In this case, the remainder would be below our fluorometer’s detection limit, and could explain the results.

    Nevertheless, there were positive observations:

    • Continuous Rinse resulted in a more dilute rinsate with less water than Serial Rinse.
    • Continuous Rinse took less time than Serial Rinse.
    • The operator did not leave the tractor cab during Continuous Rinse.
    • Potentially, any remaining water from the Continuous Rinse system could be used to operate a spray wand to rinse the sprayer exterior before leaving the crop.
    • Both systems encourage improved airblast sprayer sanitation and reduce environmental impact from point source contamination.

    Thanks to ProvideAgro for performing the installation, Wilmot Orchards in Ontario for supplying the sprayer and running the trials, and OMAFRA summer student Aidan Morgan for assistance with the data analysis.