Category: Speciality Sprayers

Main category for all sprayers that are not horizontal booms

  • Perspective on Rates, Volumes and Coverage

    Perspective on Rates, Volumes and Coverage

    This short article is a thought exercise designed to give some perspective on chemical rates, carrier volumes and the foliar area we expect them to protect.

    Imagine we are spraying the fungicide Captan on highbush blueberry. In Canada, the label rate is to apply 2kg/ha (28.5oz/ac) of planted area. Captan is 80% active ingredient, so a quick unit conversion tells us our objective is to apply 160mg of active ingredient per m2 of planted area. Let us suppose we will use 500L of carrier per hectare (53.5 gal/ac), which converts to 50mL/m2.

    Now let’s say the blueberry patch is mature and well pruned. Each plant has a footprint of 1.2m by 1.2m (4ft by 4ft) and is 1.5m (5ft) high. The Leaf Area Index (LAI) is the one-sided green leaf area per unit ground surface area (LAI = leaf area / ground area) in broadleaf canopies. Assuming a conservative LAI of 2, that’s 2.88m2 (65ft2) of leaf surface area per plant. We double that figure since we want to spray both sides of the leaves, and then assuming the bushes are planted on 3m (10ft) alleys we arrive at a total foliar surface area per planted area of 3.25m2/m2 (3.25ft2/ft2).

    A grower with his mature, well-pruned blueberries. 4′ x 4′ on 10′ alleys.

    Let’s take these figures and convert them to something we can picture. An average grain of rice weighs 29mg and there are 15mL in a single tablespoon. What this means is that a sprayer operator’s goal is to dissolve active ingredient with a weight equivalent to 5.5 grains of rice in 3.5 tbsp of water and distribute it evenly over 3.25m2 (35ft2) of surface area!

    Now that’s perspective.

    This photo shows how much foliar surface area exists in a square meter of mature highbush blueberry. In the centre is the typical amount of active ingredient and water that must be distributed over that area. It’s amazing what we ask of an air-assist sprayer.
  • What’s the Relationship Between Vapour Drift and Inversions?

    What’s the Relationship Between Vapour Drift and Inversions?

    Drift symptoms can take a few weeks to be discovered, and to figure out the cause, people need to reconstruct the conditions during the application in question. Wind direction is the easiest. But when we consider factors like inversions, volatility, calm conditions, and others used to explain the movement of pesticides, it can quickly become quite confusing.

    Let’s review how and why pesticides move.

    There are about six main ways that pesticides can move off-target.

    1. Droplet drift at the time of application;
    2. Vapour drift at or after the time of application;
    3. Pesticide movement in water (precipitation or runoff) after application;
    4. Dislodgeable residues from plant surfaces after application;
    5. Pesticide-containing soil movement after application;
    6. Pesticide residue in sprayers applied to another site.

    Whenever we find pesticides in a place where they do not belong, usually first indicated by plant symptoms specific to that herbicide, we need to find out the possible reasons and take steps to prevent that from happening again. We’ll focus on the first two items from the above list because those two are the most common.

    Droplet Drift: Sprayer nozzles produce droplet sizes ranging from 5 to 1000 µm, some up to 2500 µm. All nozzles, even the venerable low-drift tips recommended for dicamba application, will have a fraction of their volume in driftable droplets, say, less than 150 to 200 µm. For the low-drift sprays, that fraction is indeed very low, only a few percent of the total spray volume. For conventional nozzles, the driftable fraction may be 10 to 20% or more if high pressures are used.

    Tiny droplets have no energy of their own and move with the air mass they’re released into. If it’s windy, they move downwind. If the air is turbulent, they move up and down. If the atmosphere is stable, the buoyant fraction stays aloft and concentrated. So in order to understand their movement, we need to understand the atmosphere.

    Vapour Drift: Some chemicals are inherently volatile. This means they convert from the liquid or solid phase to a vapour phase on their own in accordance with temperature. Water is a great example, it is highly volatile. It is also able to sublimate, which means it can convert from a solid directly to a vapour without going through the liquid phase. An example of that is freezer burn, in which ice cubes shrink due to water escaping as a vapour.

    Volatile pesticides can also sublimate. On landing on a leaf or soil, a significant portion of a droplet is absorbed or adsorbed. Some fraction may dry on the leaf surface. This remaining solid can volatilize (form a vapour) for hours or days after application. The rate of evaporation is driven by two factors, (a) the background vapour pressure of the substance in the atmosphere, and (b) the surface temperature of the object the chemical is resting on. For water, the atmospheric vapour pressure can be expressed as relative humidity. Droplets evaporate slower when the atmosphere is already full of water.

    Pesticide evaporation is driven primarily by surface temperature. The background concentration of pesticide in the air is much lower than saturation, and has no effect. Pesticide evaporation is not directly affected by relative humidity because vapour pressures are independent of each other. In other words, most active ingredients will evaporate at the same rate whether the RH is 30% or 100% (it’s actually a bit more complicated than that. See the Note on Evaporation at the bottom of this article). This will be on the test, kids.

    Vapour losses can be minimized by choosing low-volatile pesticides and also by making the application on cooler days. We also need to watch the forecast and avoid spraying when tomorrow or the day after is forecast to be hot.

    Sometimes a rainfall can affect vapour losses, prompting a release of pesticide into the atmosphere. This behaviour can be predicted by the Henry’s Law Constant of a chemical.

    Inversions:  There are two types of turbulence, mechanical and thermal. Mechanical turbulence results from air encountering friction as it moves across a landscape. Taller objects and stronger winds result in greater mechanical turbulence. This turbulence creates small eddies that allow different layers of the atmosphere to communicate with each other and transfer momentum and contents up and down. More mechanical turbulence means more mixing and more sedimentation and dilution of a contaminant. In other words, the downwind impact of drift particles is reduced with greater mechanical turbulence. Mechanical turbulence happens whenever it’s windy, day or night, and it tends to counteract thermal turbulence.

    Thermal turbulence is more powerful than mechanical turbulence for dispersion of pollutants. Driven by the solar heating of the earth’s surface, that causes the lower atmosphere to be much warmer than the air higher up. The atmosphere normally cools the higher you go (at about 1°C/100 m, called the dry adiabatic lapse rate), but when it’s sunny, the gradient is greater. In other words, it cools faster because the air at the ground is warmer.

    Thermal effects move large parcels of air up and down, and we call this an unstable  or a turbulent atmosphere. When parcels of air rise and fall great distances, we get a powerful diluting effect which is usually associated with a breeze but can also happen under calm conditions. An unstable atmosphere is great at dispersing drift, minimizing its downwind impact. This can only happen during the daytime, is most powerful when it’s sunny, and almost never happens at night.

    By the way, a neutral atmosphere occurs when the rate of air cooling with height equals the adiabatic lapse rate described above. A neutral atmosphere can occur on cloudy days just before a rain, or on windy nights. There are no thermal effects in a neutral atmosphere, and the only dispersion occurs due to mechanical turbulence (windy conditions).

    A stable atmosphere (inversion) happens when there is no solar heating of the soil. In other words, it can only happen when the sun is low in the sky or at night. In this case, soil cools off and the cold soil cools air near it. As a result, the air temperature rises with elevation. Since it’s normal for air to cool with elevation (at the dry adiabatic laps rate mentioned earlier), the temperature profile is now…inverted. Hence the name “inversion”. To be clear (write this down kids, it’s on the test), an inversion describes an atmospheric condition in which (potential) temperature rises with elevation. That’s it. It rarely happens during the day, but is common on clear calm nights. (btw, “potential temperature is the temperature adjusted by its normal rate of cooling with height. To have thermal effects, the rate of cooling needs to be different from this rate.)

    The atmosphere is called stable because there is no thermal mixing. Air parcels stay put. Suspended particles such as tiny droplets stay put. Drift clouds stay concentrated, potent. If you make a fire, smoke hangs around. Cool, dense air is near the ground, and moves laterally very slowly, and might run downhill, like water, in a sloped setting. This situation is dangerous because it can move pesticide particles or vapours great distances without them becoming diluted or dispersed. An additional danger is that relative humidity is higher at night, delaying evaporation of water from the droplets. They stay potent.

    In Summary: Pesticides move in the atmosphere and are rapidly diluted by mechanical, and especially thermal, turbulence. That is why we like to see spray applications on sunny days with a nice breeze, which moves the product in a predictable direction and dilutes any drift rapidly along the way. We minimize particle drift through the usual measures such as the use of low booms, protective shields, slow travel speeds, and coarser sprays. We avoid spray application of volatile pesticides on or preceding hot days to minimize the risk of vapour drift. We do not apply pesticides when the atmosphere is stable (inversion), which usually means from just before sunset to just after dawn on a clear night.

    OK, that’s the basics. Now let’s explore some common questions.

    1. Can all pesticides move as particles and vapours? All pesticides that are atomized through a nozzle can move as particles. Only pesticides that are considered “volatile” can form significant amounts of vapour and move in that form. Dicamba is volatile. New dicamba formulations such as Xtendimax, FeXapan, and Engenia are much less volatile than older formulations, but they’re still capable of moving as vapours. Glyphosate and many other pesticides are not considered volatile and are not known to cause vapour drift.
    2. Are inversions only a problem for dicamba? Inversions affect droplet drift from all pesticides equally. The key difference is the amount of harm that any given droplet or vapour cloud can impart. Dicamba can harm conventional soybeans, many vegetable crops, and many trees and shrubs at extremely low doses. That means that even a weak inversion or a small amount of drift can cause great harm for long distances. In comparison, most other products are not as harmful to most of our crops in such small doses (I’m generalizing, forgive me). Tiny amounts may never be noticed, but they are there. Dicamba lets us notice these tiny amounts.
    3. Does vapour drift move only by inversions? No, although its movement is more damaging under inversions. Vapour drift clouds form above a recently sprayed canopy on hot days when leaf or soil surfaces contain a volatile product. On a sunny day (no inversion), this vapour will likely disperse rapidly downwind, causing diminishing damage with increased distance in relation to the sensitivity of the non-target plant. But towards evening, the dispersion (caused by thermal turbulence) ends as the sun sets and the atmosphere becomes stable. Now, the residual vapour cloud above the crop is no longer diluted, and may move in an unpredictable direction based on the slope of the land or a very gentle evening breeze. This movement may be significant, extending for miles in some cases, and potentially causing harm along the way.
    4. How long after application can vapour drift occur? Under most conditions, vapour losses diminish rapidly and will likely be gone within a few days as the pesticide is taken up by plants, metabolized, converted to a non-volatile form, etc. For some products, a light rainfall event can release a new wave of vapour drift because these products would rather be vapours than be dissolved in water, in accordance with their Henry’s Law Constant.
    5. Do some products drift further than others? Yes and no, but mostly no. Spray drift is a physical process governed by the behaviour of droplets in the atmosphere. Droplet diameter determines its mass and this mass controls the time it takes the droplet to sediment to the ground. The substance dissolved or suspended in that droplet has no bearing on this behaviour. But there are two key exceptions to consider. First, we know that some formulations generate more fine droplets than others even when atomized through the same nozzles. The greater abundance of small droplets will create more drift damage at any given distance, and also extend further downwind. And secondly, some formulations change the rate of water evaporation from the droplets. As a result, droplets moving downwind may shrink faster, in effect making them more drift prone and causing them to move further downwind. The same droplet size drifts the same distance, but droplet size changes. Question for the final: If you spray dicamba and glyphosate on the same day using the same nozzle, and the formulation has no impact on droplet size or evaporation, which one drifts further over a soybean crop? The answer is at the bottom of this article.
    6. Do calm conditions indicate an inversion? Inversions are defined as a temperature profile, not a wind condition. But the two are associated. An inversion is most pronounced and persists the longest under calm conditions, and because it suppresses atmospheric mixing, an inversion does prevent a windier upper atmosphere from reaching the ground. But it can be calm in the middle of the day with an unstable atmosphere. The calm condition eliminates mechanical turbulence, and therefore reduces the dispersion of the spray cloud. Calm conditions are also undesirable because the winds that follow a calm period are often unpredictable in direction, force, or duration. So it’s not a great idea to spray when it’s completely calm, even on a sunny day.
    7. Can inversions occur during the day? Yes, but it’s rare. Sometimes a large cold air mass moves into an area, say from a cool body of water, pushing warm air above it. So technically the air at the ground is cooler than the air above it, suppressing dispersion through that cap. Another situation is an inversion layer that forms at the top of a transpiring plant canopy. The air at ground level is warm, and cools suddenly where the crop evaporates water from its leaves. Air temperature rises with elevation above this transpiring layer, then cools again in accordance with an expected profile. So we have a thin layer in which vertical mixing is suppressed. This is most common in dense, thick canopies with adequate soil moisture on hot days.
    8. Is there an inversion every night? No. Cloud cover suppresses the rapid cooling of the soil, and the air at soil level stays warmer longer. Wind mixes the cold air layer into a warmer air layer, returning a more neutral condition. Inversions are most likely on clear nights with little wind. Recent data in inversion frequency from Missouri and North Dakota shows that inversions occur on the majority of nights, but the frequency depends on the location.
    9. Can drift be eliminated? Yes, we can eliminate spray drift by atomizing the spray in droplets (or, for dry soil-active products on carrier particles) large enough to resist movement in wind. We would need to be sure that absolutely no fine droplets or particles are produced, and that they don’t dislodge after application. That will require different atomizers and significantly more water volume and possibly new adjuvants. Some will argue that drift can also be eliminated by protecting the fine droplets with shields or air assist, but again, the protection would need to be 100%. Drift control has not been a high enough priority for these technologies to be developed and made available to applicators. Vapour drift can be eliminated by not applying volatile products.

    Pesticide movement in the atmosphere is complicated. But pesticides don’t just move as a result of vapour or droplet drift. Consider all the options when investigating an affected field. And let’s all work together to better understand pesticide movement and to prevent it.

    Answer: Both drift equally. But assuming the beans are susceptible to both herbicides, the dicamba damage will appear further downwind due to the greater sensitivity of the beans to this herbicide. This does not mean it drifted further.

    Note on Evaporation: There is some discussion about the role of relative humidity on vapour loss. Although we stated that RH plays no direct role in pesticide volatility, we need to qualify that.

    (a) Many pesticides dissolve in water. More water moves to plant or soil surfaces during periods of low RH, and this can carry dissolved pesticide with it. The supply of pesticide that can evaporate is thereby replenished.

    (b) Evaporation is driven by temperature and the concentration gradient between the source and the atmosphere. In still air, the air layers closest to the evaporating surface are most concentrated with evaporated pesticide, slowing further evaporation. Air movement will remove these layers, increasing the rate of evaporation.

    (c) co-distillation may occur for some pesticides. This means that the pesticide dissolved in water may evaporate with water, liberating it into the atmosphere. When co-distillation occurs, low RH would increase pesticide losses as well.

    We still have much to learn about these phenomena, especially as it affects new formulations.

  • Categorizing air-assist sprayers by air-handling design

    Categorizing air-assist sprayers by air-handling design

    Air handling systems

    Air handling systems can be specialists or generalists; some are designed to do one thing very well while others are more adaptable but not as precise. Fan type plays a big role in determining a sprayer’s abilities. Their native characteristics make them better suited to certain scenarios.

    This may seem contradictory, but we are not saying that the fan alone defines or limits the entire sprayer. Fans operate within a larger, engineered air handling system. Also, the operator has control over how that sprayer is configured and used. This means it is equally important to consider how the air exits the sprayer – not just the fan type that generated it.

    Fan types

    • Radial fans: Radial fans produce high volumes of moderately turbulent air, and relatively low static pressures. They are often associated with fixed vanes and straighteners inside the fan housing to reduce initial turbulence.
    • Turbines: Turbines may look like radial fans but they’re designed to spin faster and they have blades designed to compress air. They are used in sprayers that have ducts, towers, cannons, or other more complex volutes.
    • Straight-through axial fans: These fans produce high volumes of the most turbulent air. With their comparatively short throw and wide air wash, they should be positioned close to the target.
    • Tangential (aka Cross-flow) fans: Tangentials produce the most laminar air, forming a very high volume, low velocity jet sometimes called a “curtain” or “knife”. They have a comparatively long throw and rely on the canopy to induce turbulence.
    • Centrifugal (aka Squirrel cage) fans: Centrifugal fans have a side-discharge arrangement that turns air 90 degrees. They can produce high pressures and are nearly always paired with an air-shaping volute.

    We are proposing defining air-assist sprayers for perennial crops according to their air handling systems. Ultimately, the defining characteristic of each design is the net vector of the air they generate. We have provided silhouettes for clarity, but these generic designs are not intended to imply a manufacturer.

    Low profile radial

    The oldest and perhaps most recognizable air handling design, the Low Profile Radial (LPR) sprayer generates air in a radial pattern from one or more axial fans or a volute connected to some other fan style. This is the classic airblast sprayer.

    Defining characteristics

    • Wide range of adjustable air energies from virtually zero to high.
    • Minor adjustability of air vectors via deflectors and moveable outlets.
    • Net air movement is lateral and upward.

    Cannon

    The Cannon (CN) sprayer generates and channels air through a single volute and delivers the spray as a compact, point-source jet. 

    Defining characteristics

    • High air energy characterized by high velocity and low volume.
    • Extensive adjustability of air vector via a vertical duct with positional outlet and deflector(s).
    • Usually a single-sided sprayer used to spray over and through multiple rows.

    Fixed tower

    The Fixed Tower (FT) sprayer generates air from one or more axial fans, multiple straight-through radial or tangential fans. It may employ flexible tubes, tapered bags or solid ducts to redirect air laterally from a fixed central tower. It may feature additional flexible ducts or adjustable deflectors at the top of the tower to spray over and beyond the adjacent rows. 

    Defining characteristics

    • Wide range of adjustable air energies from virtually zero to high.
    • Minor adjustability of air vectors via deflectors and moveable outlets.
    • Net air movement is lateral compared to LPR sprayers.

    Targeting tower

    Similar to the FT, the Targeting Tower (TT) sprayer can focus air vectors with a wider range of adjustability, shaping the lateral air output more precisely to the canopy. TT generates air from one or more radial fans or multiple tangential or straight-through axial fans. It may employ flexible tubes or solid ducts to redirect air generally laterally. 

    Defining characteristics

    • Medium to high air energy.
    • Moderate to high adjustability of air vectors. Airflow can be subdivided into individually-adjustable sections.
    • When the tower exceeds canopy height, net air movement is lateral to slightly downward.

    Wrap-around

    The Wrap-Around (WA) sprayer surrounds the target rows with air sources. This creates multiple converging and/or opposing airflows within the row. 

    Defining characteristics

    • Straight-through axial fan systems are either electric or hydraulic with a wide range of air energies.
    • Low to high adjustability of air vector via deflectors, moveable air outlets, or fan position adjustments. May also have an adjustable frame.
    • Net air movement is ideally neutral to slightly downward.

    Summary

    In adopting this system of classification, we believe the process of optimizing sprayer configuration and calibration can be made less complicated. A universal language facilitates clear communication between growers, industry and consultants/specialists.

    We acknowledge that there may be rare sprayers that don’t fit these categories. There are commercial examples of air-assist sprayers that combine features from these air-handling designs (e.g. hybrids of LPR and FT designs)… but let’s keep things simple.

  • 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.

  • Pesticide Safety for Student Workers

    Pesticide Safety for Student Workers

    This article is based on a presentation by Dr. Melanie Filotas, who delivered it as part of the 2019 agriculture summer student orientation day.

    Most crops are sprayed with organic or synthetic pesticides at some point during the growing season. Use caution before entering any area where crops are grown (e.g. corn field, nursery, greenhouse, orchard etc.). Always confirm that it is safe to enter.

    Most crops receive some form of chemical input during growth. Be aware of what has been applied.
    Even organic operations apply controlled products that may make it unsafe to enter for a period of time.

    You can be exposed to pesticides if you enter a treated area before pesticide residues break down and vapours dissipate. The minimal time that must elapse before being permitted to enter is called the Restricted Entry or Re-entry Interval (REI).

    REIs are data-driven and established by the federal government. They are defined as: “The period of time that agricultural workers, or anyone else, must not do hand labour in treated areas after a pesticide has been applied.” Hand labour can be any task involving substantial contact with treated plants, plant parts or soil, including planting, harvesting, pruning, and scouting.

    Things you should know about REIs:

    • REIs can range from one hour to several days
    • If a pesticide label does not indicate a REI, the default is 12 hours
    • REIs can vary with the product, crop and type of activity (e.g., scouting, harvesting, etc.)
    • REIs can change over time so always refer to the most recent label
    • If a tank mix (multiple products) was applied, observe the most restrictive REI

    Before visiting an operation to work in the field:

    • Tell your supervisor where you will be that day
    • Ask the grower or spray applicator what was sprayed. Records may be posted, but verbal confirmation is preferred
    • Look up the REI for the product on the crop you will be entering
    • Check with your supervisor on any products with special instructions beyond the REI

    Do not enter the field until the REI has ended. Pesticide REIs can be found in local production guides, or on pesticide labels.

    Local production guides summarize REIs.
    Local production guides list REIs by crop, by product applied, and by activity.

    If local production guides are not available, registered pesticide labels can be found using Health Canada’s Pesticide Label Search service online. In the United States, most labels can be found on the EPA’s Pesticide Product and Label System website.

    Health Canada’s online pesticide label search.

    Miscommunication can sometimes happen. Learn to recognize the signs of spraying. When in doubt, leave the planted area and call the grower to confirm or call your supervisor.

    • In some cases you can look for fresh tracks in the operation, but be aware they may not have been made by a sprayer
    • Some products have a distinctive odour
    • It can be difficult to see a sprayer operating, particularly in orchards, but they can be heard. Do not wear earbuds or headsets while in a production area
    • Look for foliar residue. This is an indicator, but does not always mean it is unsafe to enter
    Fresh wheel tracks may indicate recent spraying.
    Some products have a distinctive odour.
    It may be difficult to see a sprayer operating in the vicinity, such as in this orchard. However, they can often be heard. Do not wear a headset or earbuds in a production area.
    Residue on leaves may indicate a recent application, as in the left photo. However, it could also be unrelated. On the right is calcium magnesium precipitation from irrigation water. (Photo credit [right]: Jennifer Llewellyn)

    There are many potential symptoms of pesticide exposure: headache, fatigue, irritation of the skin, eyes, nose or throat, loss of appetite, dizziness, nausea or vomiting, diarrhea, decreased muscle coordination, and blurred vision. Each product has a Material Safety Data Sheet (MSDS) that will provide details on exposure symptoms and treatments.

    While sometimes confused with symptoms arising from sun stroke or dehydration, if you suspect pesticide exposure it is always best to be prudent and get medical help immediately. Contact your local poison centre or 911.

    Summer work in crop production can be rewarding and enjoyable, but always use caution and be safe.