Category: Boom Sprayers

Main category for sprayers with horizontal booms

  • Comparing Water Sensitive Paper Brands

    Comparing Water Sensitive Paper Brands

    Introduction

    Spray coverage describes the degree of contact between spray droplets and the target surface area. This metric can be used to predict the success of an application. One of the easiest methods for visualizing coverage is to use water sensitive paper (WSP), which is a passive, artificial collector that turns from yellow to blue when contacted by water.

    WSP is often used to evaluate iterative changes to a spray program. Placed strategically throughout a target canopy, or directly on the ground, achieving uniform, threshold coverage translates into improved efficacy, reduced waste, reduced off-target contamination and reduced risk of pesticide resistance development. WSP were also used to develop a system that measures the area covered by the effective radial distance in an attempt to relate the area covered by a stain to a larger area where sufficient pesticide activity is taking place.

    WSP tends to underestimate the spreading effect that can occur on plant surfaces (especially when surfactants are used), but they are effective as a relative index.

    A brief history of WSP

    In 1970, a journal article described a new method for sampling and assessing spray droplets. Photographic paper treated with bromoethyl blue created a yellow surface that changed colour when it encountered moisture. The pH-based reaction was fast and irreversible, leaving a distinct blue stain to mark the deposition.

    Ciba-Geigy Ltd. made water sensitive paper commercially available in 1985 (later as Novartis in 1996 and as Syngenta since 2000). It is produced in several formats, but aluminum foil packages of 50, 76 x 22 mm (1 x 3 in.) papers are the most popular. Odds are if you’ve ever used water sensitive paper, it originated from Syngenta in Switzerland. In 2023 I noticed that the papers now say “made in Germany.”

    Change of manufacturing location?

    In recent years, two new options have been made commercially available: Innoquest’s SpotOn Paper (United States) and WSPaper (Brazil). At the time of writing, there has been no impartial comparative evaluation of these three products.

    Once dry, the blue stains on WSP are irreversible and papers can be stored for long periods of time. However unstained portions will continue to react to moisture from humidity, dew, or fingerprints, so care must be taken in their handling and storage.

    Comparing WSP brands

    The three commercially-available brands of WSP were subjected to a series of comparisons. The intention was not to rank these products, but to determine if they performed in a similar fashion and to alert users to any significant differences.

    Packaging and Appearance

    Each package was donated for the study. The SpotOn (SO) papers had a “sell-by” date of November 2023, the Syngenta (SY) papers (provided via Spraying Systems Co.) were dated February 2021 and the WSPaper (WS) was their newest formulation (white package, not silver), received June 2021. The comparison was performed on July 5, 2021.

    WSP packages.

    Each product was a foil or plasticized bag of 50, 26 x 76 mm papers. SO and WS had a re-sealing feature similar to that of a sandwich bag. SO also included a package of silica gel desiccant to capture moisture and a pair of plastic forceps to facilitate handling.

    Users are encouraged to label papers to ensure they know their relative position and sprayer pass for later analysis. It was possible to write in ink on the faces of the SY and SO papers, but not WS. It was possible to write on the back of all brands.

    The three papers were different shades of yellow. Further, in the author’s experience, the colour can be visibly different between batches of the same brand. In the case of larger experiments where more than 50 papers are required, it would be prudent to ensure papers are not only from the same manufacturer, but the same production batch. This would not be an issue when subjectively comparing papers, but when using software that employs colour thresholding to identify deposits, it could create artifacts. Presently, only Syngenta has a batch number (found on a sticker on the back of the bag).

    Bleed-through

    WSP is often placed in foliar canopies which are subject to dew and transpiration that can cause the papers to react prematurely. This can be particularly limiting when moisture soaks through the backs of papers. Each brand of paper was placed face-up on a drop of water to see if the water would bleed through.

    Three brands were placed on a single drop of water. Within five minutes, WSPaper and Syngenta brands wicked the water through, causing a colour reaction. SpotOn did not, although the yellow surface darkened. When a drop of water was applied to the face, the SpotOn paper still produced a blue stain.

    WS quickly curled as the water wicked in from the edges. Within five minutes the water soaked through from the back as well. Within five minutes SY also curled, but the colour reaction was entirely due to water soaking through and not wicking along the edges of the paper. SO did not curl and there was no colour reaction save a minor wicking reaction at one edge. It did however produce a dark yellow patch. In order to see if a colour reaction was still possible, a single drop of water was placed on the face and the colour reaction was distinct and instantaneous.

    Note: Others have since replicated this experiment and reported that the response depends on the amount of water used and how long you leave it. We repeated our experiment with higher volumes and longer wait times (see image below). Ultimately, no brand of WSP is water proof from the back. Nevertheless, with small volumes of water (such as from dew) the original assessment of each brand is still valid.

    A replication of the bleed-through experiment with the same batch of papers was performed with higher water volumes and a longer duration. Eventually, all three brands bled through. (SpotOn left, WSPaper middle, Syngenta right).

    Deformation and drying time

    Users of water sensitive paper may be familiar with its occasional tendency to curl when one side is sprayed. In extreme cases, this movement could create smears if the paper contacted other wetted surfaces in dense foliage. The degree of curling was significantly different by brand, with SY becoming convex when wet and then flexing back into a concave form once dry. WS deformed as well, but only to a minor degree. SO did not appear to deform at all. Syngenta has noted that the degree to which their papers curl depends on the batch. Their manufacturing process has changed over the years in response to regulatory requirements and minor adjustments are still occasionally made.

    Once dry, each brand of WSP tended to curl to different degrees. Syngenta curled the most and SpotOn the least if at all.

    There was no appreciable difference in the time it took for any brand to dry. This is based on attempts to smear papers every 30 seconds. All were dry in under five minutes.

    Experimental design

    While there is considerable variability inherent to spraying, every effort was made to maintain consistent conditions. Papers were sprayed in a closed room with no appreciable air currents (21.5 °C and 64% RH). Papers were paired randomly, side-by-side on a plastic sled. The sled was pulled at 2.5 kmh (~1.5 mph) through the centre of a spray swath produced by a TeeJet XR80015 positioned 50 cm (20 in.) above the targets. The nozzle operated at 2.75 bar (40 psi) to produce ~270 L/ha (~29 gpa) with Fine spray quality. Six passes were made, producing four sprayed papers for each brand.

    All papers were dry to the touch after two minutes. They were removed to a cooler, low humidity space and were digitized and analyzed using the SprayX DropScope (v.2.3.0) within an hour of spraying. We noted that while WS and SO fit easily into the DropScope port, the SY papers were sometimes slightly wider and had to be forced. Learn more about how to digitize and analyze WSP in this series of articles.

    Screen capture from DropScope’s smartphone app.

    The “ground” option was selected, and each brand of paper was processed using its specific spread factor. DropScope has a detection threshold of 35 µm. This is appropriate as the smallest droplet diameter that can be resolved by any brand of WSP is ~30 µm (Syngenta, Innoquest, SprayX – Personal Communication).

    Percent surface covered

    The average percent surface covered was calculated with standard error of the mean for each paper. WS and SO produced similar values between 30 and 35%. While all three brands exhibited similar variability, SY approached saturation at approximately 80% coverage. Therefore, WSPaper exhibited a slightly higher degree of spread than SpotOn, while the Syngenta paper exhibited a significantly higher degree of spread.

    For reference, it can be difficult to determine if a stain represents a single deposit or is the result of multiple overlapping deposits. This becomes a problem when the surface of the WSP exceeds 20% total coverage. Further, it becomes increasingly difficult to distinguish a stain from the background, unstained surface when papers exceed 50% total coverage.

    Average percent surface coverage by brand.
    DropScope-digitized images of three brands of WSP. The Syngenta and SpotOn papers were sprayed simultaneously while the WSPaper was sprayed in a subsequent pass. WSPaper exhibited a slightly higher degree of spread than SpotOn, while the Syngenta paper exhibited a significantly higher degree of spread.

    Deposit density

    The average deposit density is a count of discrete objects (i.e. stains) per cm2. WS appeared to resolve the highest count, followed by SY and then SO. The process for determining what is a discrete object, and not the result of anomalies such as overlapping deposits, elliptical deposits or imperfections in the paper itself is complicated and computationally heavy. The algorithms employed by DropScope treated each paper consistently. So, while some differences are attributed to variations in spraying, they also reflect the paper’s innate ability to resolve individual deposits.

    Average deposit density was highest for WSPaper, then Syngenta, then SpotOn. Variability was similar in all cases.

    Droplet diameter

    It is not the intent of this article to determine if WSP should be used to extrapolate the original droplet size. The many assumptions and inconsistencies inherent to this process are well known. Nevertheless, some researchers do use WSP in this manner, so a comparison was warranted.

    DropScope bins deposit diameters by size to produce histograms of deposit size by count. These stain diameters are used to extrapolate DV0.1, DV0.5 (VMD), DV0.9 and NMD, which describe the population of droplets that produced the stains. DV0.5 is the Volume Median Diameter, or the droplet diameter where half the volume is composed of finer droplets and the other half by coarser droplets. Number Median Diameter (NMD) is the droplet diameter where half the total droplets are finer, and half the total droplets are coarser.

    Each brand of WSP will permit a certain degree of spread when a droplet of water contacts the surface. This spread factor is specific to the brand of paper. Further, the spread factor is not constant for all droplet sizes; Finer droplets will spread less than coarser droplets.

    When processing data using DropScope, selecting the appropriate spread factor makes a significant difference to the output. For example, here are the same four SY papers processed using the Syngenta-specific spread factor as well as the spread factors intended for SpotOn and WSPaper.

    The same four Syngenta papers were processed by DropScope using the Syngenta-specific spread factor as well as the SpotOn and WSPaper spread factors. The resulting VMD and NMD were very different.

    Therefore, each brand of water sensitive paper was analyzed using its brand-specific spread factor (according to DropScope), to produce the following graph.

    Three brands of WSP processed by DropScope using their specific spread factors. VMD differed by as much as 30%.

    SY produced a VMD higher than that of WS, and both were higher than SO. There was less variability in the NMD, but this was expected given the high droplet count on the finer side of a hydraulic nozzle’s droplet size spectrum.

    Conclusion

    Water sensitive paper has immeasurable value in agricultural spraying. It is far more important to encourage its use than to quibble over brands. However, when these tools are used for more rigorous evaluations of spray coverage, brand-specific variability must be addressed.

    The differences in how each brand responds to moisture (i.e. discolouration and deformation) may factor into which brand is most appropriate for a given situation. Further, there appear to be significant differences in how each brand resolves coverage. Once again, this may be irrelevant for those spray operators who occasionally use WSP to inform their spraying practices, but for consultants and researchers it is suggested that they use a single brand for an experiment, with papers produced in the same batch run.

    Syngenta, Spraying Systems Co., SprayX, WSPaper and Innoquest are gratefully acknowledged for their contribution of materials and time informing this article.

    2026 Update

    If there’s one thing that stays the same, it’s that nothing stays the same. Formulations and manufacturing processes change. According to SprayX, manufacturers of the DropScope, all three of the papers described in this article (written in 2021) have changed in recent years. Some have improved and others can create potential errors in digitizing coverage. The following points may require a deeper understanding of how WSP is digitized and analyzed. Refer to this series of three articles.

    Be aware of the following best practices when using WSP:

    • Be aware of package expiration dates. Expired paper will work differently from new paper, creating an artifact in analysis.
    • Papers with bright, reflective surfaces can cause an underestimation of deposit counts (specifically the smallest deposits).
    • Best results are obtained when using water for testing. Adjuvants and pesticide co-formulants have minor impacts on spread, but can also change the how the paper changes colour, making thresholding difficult.
    • Beware papers that create stains with bright borders and faint (hollow) centres (see image below). This can lead to an underestimation of volume median diameter. If your camera or scanner permits, examine the coverage in binary (e.g. black and white) for more accurate results.
    • Do not sample the edge of the WSP (leave at least a mm) to avoid edge effects such as wicking and partial impacts. Some scanners have a setting, or you can select the area manually.
    • Note the physical shape of the paper itself. Inconsistencies in the length and width (cutting errors) can make papers difficult to use in certain scanners, and curled papers cause changes in perspective and focal distance that can lead to errors.
    • When not using a sealed camera or scanner (e.g. DropScope or flatbed), changes in the camera angle, shadows, lighting conditions, and make/model of cellphone camera will affect the results. Be consistent.
    Stains with faint centers may not register correctly with some software. This could be due to adjuvants in the liquid, or issues with the coating itself. Other issues might include inconsistent coatings that are either too thick or to thin affecting the reaction to water.
  • How to Properly Set Up a Crop Sprayer

    How to Properly Set Up a Crop Sprayer

    Article reprinted with kind permission from an original article written by Oliver Hill in the February, 2017 edition of Farmers Weekly. Photos ©Kathy Horniblow.

    Crop spraying is one of the most important and highly skilled jobs undertaken on any arable farm, but it is facing increased public scrutiny. This is why it is vital that the kit you use as a means to apply pesticide to crops is in prime working order and is set up correctly to deliver the product safely and accurately to its target. Optimum sprayer set up will help to maximize the efficacy of applied products, reduce spray drift and keep machinery in good condition.

    For this best practice guide to sprayer set up, Farmers Weekly teamed up with former Farm Sprayer Operator of the Year Iain Robertson. Mr. Robertson is assistant arable farm manager at David Foot Ltd, a 2,200ha mixed farm south of Dorchester in Dorset, growing wheat, barley, beans, oilseed rape and maize as forage for the farm’s three dairy herds. The machine used for this guide is a Bateman RB26 self-propelled sprayer and while most of these checks and tests are universally applicable to all sprayers, it is also important to refer to the handbook of the manufacturer of your specific machine.

    Watch the video tutorial with Mr. Robertson and then see the step-by-step guide below for more detail.

    Pre Start Checks

    Before firing up the engine, the first thing to do is your pre-start checks – that means checking your machine’s vital fluids like fuel, hydraulic oil, hydrostatic oil, engine oil and coolant levels. If yours is a self-propelled sprayer, chances are you’ll need to get up on to the back of the machine to check some of these.

    “While I’m up on the back of the sprayer I also have a quick look in the top of the tank to make sure that it is nice and clean and the tank rinse nozzles have worked properly – cleanliness is next to godliness,” says Mr. Robertson. Next, move on to the tires. Use a pressure gauge to check all tires are at the correct pressure and refer to the manufacturer’s guidelines. If you’ve got a trailed sprayer, don’t forget to check the tractor tire pressures as well.

    Aim for tires to be run at the lowest pressure recommended for the load to be carried. This will help with boom height and stability and also helps tires act like a shock absorber to ride out bumps. If using a trailed sprayer, use a spirit level to ensure that the drawbar is level. Mr. Robertson says he tries to work around the machine in a methodical, clockwise manner to ensure that he doesn’t miss anything.

    Coming to the pumps, check that they have got enough oil, check that any tool boxes have enough spare parts and any equipment needed and make sure you are carrying a spill kit with absorbent granules and a spade in case the worst happens and there is a spillage. Make sure all parts are lubricated daily and that any grease nipples are cleaned before and after use to avoid them collecting dirt and blocking.

    Check all hydraulic hoses, spray lines and air lines for any signs of wear that could result in problems while operating.

    It’s best to run the sprayer at a minimum of 5 bar to check for leaks. Also check the spray tank is fixed down securely, all straps and bolts are tight.

    Boom checks

    Once opened out, check the boom has good movement in the x- and y-axis. All machines are different so check with your manufacturer as to how the boom is set up. Mr Robertson’s Bateman has tie rods and stock bots that can be adjusted to set the boom up to ride well.

    Check the tie rod nearest the back of the machine is slightly loose when moving and that the front rod is tight. Next, check for up and down movement by gently pushing the boom down by about 50cm and letting go. The boom should return to the central position without too much bouncing around.

    “We want a little bit of movement but not excessive so that you can ride over the bumps as you go along without over- and under-dosing the crop,” says Mr. Robertson. Boom height is one of the most critical factors when spraying and the ideal height is 50cm above the crop. One of the easiest ways to work this out is by using a cable tie that is cut off at the correct length to use a visual aid from the sprayer cab.

    Don’t forget to measure from the tip of the nozzle to the crop, not the spray line.

    Good sprayer cleanliness is important, so make sure the system is rinsed through at the end of each day with clean water to make sure there’s no residue left in the boom. If your machine’s boom doesn’t have recirculation, remember to take the end caps off occasionally and flush out the whole boom.

    Nozzle checks

    Check that the nozzles are aligned both vertically and horizontally, according to the NSTS guidelines. Loosen clamps to adjust any nozzles that need realignment.

    Check the nozzle output at least twice a year by running the sprayer with clean water at 3 bar pressure. Time the output of each nozzle for 30 seconds. If nozzles have been used previously, it’s best to check their output against that of a new pair. Mr Robertson advises using a measuring cylinder rather than a jug to measure the flow rate as a jug is less accurate “because you get a bigger variation over the wider surface area”.

    With an 03 nozzle running for one minute at 3 bar pressure, the output should be 1.2 litres/minute as a rule of thumb but refer to the nozzle manufacturer’s output chart for the expected flow rate. “An easy way to remember this is: at 3 bar your nozzle size multiplied by four will give you your target litres/minute output. It works for all nozzle sizes.” If the output varies more than 4% of the average, or if the spray pattern visually doesn’t look correct, you need to change the nozzle set.

    After checking the output, cross-reference this figure with the rate controller – you may need to adjust the flow figures to ensure that the two correlate. If a nozzle becomes blocked while spraying, Mr. Robertson says he will swap it for a new one and then clean it later using a toothbrush or airline. Never blow through a nozzle with your mouth.

    Nozzle choice

    The choice of nozzle is highly dependent on the sort of job you’re doing. “Timing is crucial but using the right nozzle at the right time will make the job so much easier, cut drift and mean that you’re getting more of the product where you want it to go. If you aim at it you will hit it,” says Mr. Robertson.

    His nozzle of choice is an 03 size and he prefers to use the Defy 3D nozzle alternated forwards and backwards across the boom for pre-emergence work and T0 applications as well as the T3 ear spray. “In less than optimum conditions I may prefer to use the Amistar/Guardian Air, a fine induction nozzle. I would use this at T1 and T2 and also in sub-optimum conditions.”  This nozzle has a 3-star Local Environmental Risk Assessment for Pesticides (LERAP) rating and is 75% drift reducing.

    A water volume of 100 litres/ha is a good rate for spring fungicide application. It provides enough coverage for good disease control and allows maximum efficiency from the sprayer.

    Forward speed

    The third and final part of reducing spray drift is forward speed. Depending on nozzle size and water volume, aim to travel at 12kph.

    Mr Robertson says he finds that this speed gives a good overall output and means you don’t get shadowing or turbulence behind the machine.

    Tips and tricks

    One of the biggest risk of contamination is at fill up. “A fantastic, cheap trick that I learned through Farm Sprayer Operator of the Year is to take a 200 litre plastic drum and cut it in half to create two drip trays to catch any spillages under the induction hopper and the tank overfill.” This eliminates point source contamination, he says.

    “Finally, there’s a plethora of information out there on the internet, loads of good apps to download. The technology is there to help us do the best job possible and make our job as safe as possible.”

  • Operator Safety: How to Avoid Pesticide Hazards

    Operator Safety: How to Avoid Pesticide Hazards

    A Veteran Applicator’s Questions about Pesticide Handling

    Time and again, after years of working with dozens of different chemicals, I would wonder to myself “How dangerous is this chemical?”, “Is glyphosate as safe as they say it is?”, “How do I find out what type of safety gear I need while handling this chemical?”

    Beyond the agrichemical dealer, ag. consultants, and university or government ag. extension specialists, a quick internet search reveals many sources of pesticide information. Collectively they identify the active ingredient(s) in formulated products, they detail which pests are best controlled by the pesticide, and they provide instruction for application. But it’s more difficult to find consistent, practical information about safe pesticide handling. Sometimes it’s excessive to the point of being impractical (try finding actual “chemical proof” gloves), and sometimes it’s minimal and vague – it depends where you look. No matter the level of precaution, pesticide safety is time consuming and involves some fussing, but it is the hallmark of responsible pesticide use. Just as we ensure that we are applying “safe rates” when spraying chemicals, we must also ensure we are respecting our own well-being while handling chemicals.

    In Canada, the Pesticide Regulatory Directorate (PRD) is charged with protecting human health and safety by monitoring pesticides that are sold in this country. According to the Federal Pest Control Products Act all pesticides sold in Canada must be registered with the PRD. There’s a very nice overview of how that process works here. It is during this registration process that pesticide handling precautions are identified for the label. Further classification may take place under provincial acts.

    All pesticides are designed to disrupt, repel, control or kill living organisms, but when it comes to safe handling, insecticides receive the most attention. This is because herbicides and fungicides target biochemical pathways that only exist in plants or fungi. However, most pesticides can be hazardous if they are not handled correctly. The handling precautions that appear on the label are based on five factors.

    Five factors that affect handling precautions:

    1. Pesticide Family

    This factor is the broadest way to categorize potential risk to the handler. Generally, herbicides and fungicides are considered safer than insecticides, but there are notable exceptions. Do not rely solely on the pesticide family when making decisions on pesticide handling.

    2. Pesticide Mode of Action

    The mode of action gives further detail into how a pesticide should be handled. Modes of action that inhibit biochemical pathways that exist in the target pest, but not in mammals (people, in particular), have lower acute toxicities. Examples include herbicides that inhibit enzymes involved in amino acid synthesis or in photosynthesis – these enzymes do not exist in mammals. However, once again, there are always exceptions. Do not rely solely on mode of action when making decisions on pesticide handling.

    3. Pesticide Formulation & Route of Entry

    Pesticide formulation affects how a product can potentially be absorbed into the body. Emulsifiable Concentrates (ECs), for example, have higher rates of absorption than solutions or dry products. When it comes to the route of entry, dermal contact is considered safer than inhalation or ingestion. However, not all parts of your skin are created equal, and the point of dermal contact on the body matters a great deal.

    4. Pesticide Toxicity

    Taken collectively, the first three factors form the overall toxicity of the pesticide. The level of toxicity cannot be predicted – it has to be tested. The LD50 (defined below) values that are reported for a pesticide come from standardized experiments such as animal feeding. Although the chosen species (usually white rats for mammalian endpoints) are known to be similar to humans in their response, there is still the possibility of error. Nevertheless, toxicity forms an important basis for establishing handling precautions.

    5. Operator Exposure

    People handle toxic substances every day. Household bleach, for example is surprisingly toxic, and yet it can be readily found on kitchen shelves in many homes. The risk of being harmed by a toxic product can only be determined by the likelihood of exposure. While it is possible someone might accidentally consume a hazardous dose of bleach, it’s improbable. Exposure does not just refer to a single exposure to a substance – repeated exposures to small doses of a toxic substance can have a cumulative effect. The goal when handling any pesticide is to minimize exposure, but it becomes even more critical when that pesticide is highly toxic. Together, exposure and toxicity form the basis for risk.

    Risk = Hazard x Exposure

    Studies have shown that exposure is greatest for handlers of agricultural pesticides during the mixing and loading phase of spraying. During this phase, the risk to the handler may be increased due to:

    • physical stress
    • the denial of risk
    • a negative opinion of personal protective equipment (PPE)

    The main method of pesticide exposure is dermal, and many of the surfaces on a piece of equipment are already contaminated.

    Health effects of pesticides: Acute and Chronic

    Acute: short term

    High exposure, resulting in immediate reaction due to a high dosage of pesticide exposure. The severity depends on the toxicity of the molecule and entry into the body (dermal, oral, eyes, etc.). The most common acute reaction is skin irritation, although in certain cases respiratory, digestive, and neurological systems may be affected. Organophosphate (e.g. Lorsban, Malathion) and carbamate (e.g. Sevin, Lannate) insecticides inhibit the cholinesterase enzyme, which is found in humans and affects nerve function. Frequent users of these insecticides undergo regular blood tests to ensure their levels are normal.

    Chronic: long term

    Chronic affects are more prolonged as they are usually due to lower doses of pesticide exposure over a longer period of time. Although some rare cancers and disruption of the reproductive system have shown to be related to this type of exposure, when the general population and farming population have been compared in studies, the farming population has shown an under-representation in the majority of cancers. In the cases were reproductive malfunctions were observed, a different cause of the malfunction, such as genetic offset, was most often observed in these situations. However, cancer types such as skin cancer and brain cancer were overrepresented in the farming community. A study in France has shown that the onset of neurological disorders in Agriculture communities shows a strong connection between Parkinson’s disease and exposure to pesticides.

    Label Information

    The majority of information needed to safely handle pesticides is found on the label. Pesticide labels are legal documents, meaning they can be enforced by the federal government. The problem is that most sprayer operators rarely look at the label as they are not very reader friendly and easy to skim through. Most pesticide boxes even have the recommended rate, or acres/case on the side of the box now, so there is even less reason to look at the label.

    LD50– the dose of pesticide in mg per kg of the test animals body weight that is lethal to 50 percent of the group of test animals.  For example, if the pesticide has an acute oral LD50 value of 1000 mg/kg, and the test animals each weigh 1 kg, then 50 percent of the animals would die if they each ate 1000 mg of pesticide at once.  A 100 kg animal would need to ingest 100,000 mg (100 g) of the pesticide for the same effect.  LD50 is often expressed by the route of entry – dermal, inhalation, acute oral (ingestion) are the main examples.

    Degree of Risk and Hazard Symbols
    Degree of Risk and Hazard Symbols

    Two Factors that Determine the Appropriate Level of PPE

    1. The Hazard Rating (above) incorporates the minimum protection generally required for a substance with the rating.
    2. The Label Recommendations will usually give the additional specific protective clothing and equipment needs for an applicator.

    Degree of Exposure

    This increases as the length of each pesticide application increases. As the number of pesticide applications increases, the time between exposures decreases. If an operator becomes exposed to spray, dust or fumes the degree of exposure increases. Essentially, more protective wear is needed as the degree of exposure becomes greater.

    Knowledge

    This encompasses all of the above information. In order for a pesticide applicator to avoid injury or the chances of adverse effects on the body, a pesticide applicator must be knowledgeable about pesticides. It can be overwhelming for an applicator to sort through all of the information on the label or on-line regarding pesticides. So much so, that most often applicators avoid the information altogether. Ongoing training and learning will ensure that they are effective in their work. Many aspects of pest control change continuously, as new studies are conducted on the effects of pesticide exposure.

    A Safety Data Sheet (SDS) is available for each pesticides registered, and these are usually linked on manufacturers’ websites. It can be eye-opening what types of toxicity tests are done, and what the results are.

    Denial that pesticides can potentially cause harm is also a major flaw in the behaviour of applicators. Maintaining a safe work environment and practicing personal safety will reduce the chances of an applicator experiencing serious injury throughout their farming career.

    Unknowns

    There is very little certainty in toxicology. For one, most testing is done using acute oral and dermal dosing. Basically, toxicologists expose test animals to the neat active ingredient and watch what happens. There is a lot of missing information – what about formulant like solvents, and surfactants? What about synergies in tank mixes? Some, but not all of these, undergo testing. We also have much less information on chronic (long-term) effects, and can only simulate these in quasi long-range tests. In addition, toxicological methodologies and statistical approaches can vary, and we should not be surprised that some reports disagree, and that there are outright conflicts between toxicologists and epidemiologists (scientists that study patterns of health in populations). Regulators are aware of these shortcomings and often use safety factors to account for them. But those of us that use these products regularly, the message is simple: be cautious, and protect yourself.

    Avoid Cross-Contamination

    Disposable nitrile gloves are the product of choice for handling pesticides. But one of the most common problems with the use of gloves is cross-contamination. You’re handling product with your gloves on, touching containers, hoses, valves, and couplers. When you’re done, you climb back into the cab where you take off your gloves. Later, someone climbs up into the cab to talk to you, using the railing and operating the door handle without gloves. Guess what’s on their hands? Even later, you put away the hose without gloves and return to the sprayer. Now it’s on the steering wheel and all the levers. There are a few solutions:

    • Double-glove so you can take the dirty outside glove off and still be protected.
    • Wipe down surfaces that you might touch with gloved or bare hands daily.
    • If using non-disposable gloves, avoid lined gloves and rinse the insides out daily.

    Learn More

    If you would like to learn more about pesticide safety, or to obtain pesticide application training, the Pesticide Applicator License can be obtained from the Ministry of Agriculture. This course offers in depth, valuable safety information for applicators, as well as general knowledge for pesticide applicators. The Pesticide Regulatory Directorate provides workers, employers, and the general public with a wide range of pesticide information. The PRD can be contacted from anywhere in Canada toll free at: 1-800-267-6315

    Download this Quick Reference Guide for commonly used herbicides. Print, laminate and post it at the fill station or pesticide storage area for easy reference. Also, grab a copy of Health Canada’s “Stay Safe when using Pesticides” factsheet.

    Sources

  • Sprayer Loading and the Jar Test

    Sprayer Loading and the Jar Test

    The time and attention spent during sprayer loading is a worthy investment. It ensures that the products in the tank perform as intended and reduces the chance of incompatibilities.

    The label

    Pesticide labels are always the first point of reference. Labelled mixing instructions should be obeyed even if they contradict conventional practices (see Mixing order, below). Consult this article on tank mix compatibility for more information on how to quickly and easily consult labels for each of your tank mix partners.

    The carrier

    Typically, the carrier is water, and understanding its role in pesticide performance is another article (or several). We’ve provided some links here for further reading.

    • Take some time to read Les Henry’s 2016 Grainnews article called “The Coles Notes of Water Chemistry“.
    • You can also read about pH and water hardness. It should be noted that pH and the resultant hydrolysis that can affect product half-life is typically an insecticide issue (not fungicide or herbicide). The famous fungicide example is Captan, which has a half-life of 32 hours at pH 5, but only 10 minutes at pH 8. Michigan State did a great summary (in 2008 and on US product formulations) which you can find here.
    • Finally, learn how to read a water quality report, here.

    Carrier volume

    Products dissolve better in higher volumes. The sprayer tank (vat, inductor, etc.) should be at least ½ full or water before adding the first product. In the case of a fertilizer carrier, it may look like water, but it contains high levels of salts that tie up free water and reduce solubility. For fertilizers, a higher initial volume of ¾ full is required.

    Note the undissolved residue collected on these swatches of red filter material. Products dissolve faster and better in higher carrier volumes.

    The incomplete dissolution of products can leave hard-to-clean residues, plug fluid lines, and result in a non-uniform application that reduces efficacy. The risk of incompatibility is greater with low carrier volumes and high product rates (especially dry formulations). This is a common problem in regions that use low water volumes to apply multiple tank mix partners.

    Carrier and product temperature

    Both carrier and product temperature affect mixing. Imagine mixing sugar in hot tea versus iced tea – more sugar dissolves more quickly in hot liquid. Here are three common temperature-related issues:

    • Dry formulations and liquid flowables take more time to disperse (consider using a pre-mixed slurry).
    • Emulsified concentrates and oil might form gels rather than milky blooms.
    • Water soluble packages might not dissolve completely and could plug filters and nozzles – or clog the pump intake.
    Note the undissolved residue collected on these swatches of red filter material. Products dissolve faster and better when carrier and products are warmer.

    Note: Water and fertilizer are very different carriers. Beware of carrier-specific incompatibilities

    Agitation

    Keep agitation running throughout mixing and spraying. Aim for a “simmer” on the liquid surface rather than a “rolling boil.”

    Low agitation can cause products to settle, making them difficult or impossible to resuspend later. Conversely, aggressive agitation (especially in half-full tanks) can cause foaming, pump suction loss, or product separation / clumping.

    Pace

    Adding products too quickly can cause product separation / clumping or poor suspension, leading to tank mix incompatibilities. While loading quickly improves operational efficiency, complex mixes require patience; Sometimes over five minutes between additions, especially in cold water or when using dry products.

    To save time without sacrificing quality, consider pre-hydrating dry products or using a separate nurse tank to pre-mix loads for quick transfer. Remember: even if dry products look dissolved, they may still need more time.

    Product formulation

    Product formulation is a complicated science. In the 1950s a formulation might have three active ingredients and an inert filler. See the historic formulation index card shared by Dr. M Doug Baumann (formally with Syngenta, Honeywood).

    Today, a product can include as many as 40 ingredients with formulation testing lasting two to four years! Generally, only 25% of the volume is water, 50% is active ingredients and the remaining 25% is co-formulants. This is why the more products you add to the tank, the higher the risk of antagonism. This is also why operators should carefully consider the cost benefit of generics, which may include the active ingredient, but do not tend to include the co-formulants.

    Illustration based on a slide by Dr. Samantha Francis, Formulation & Application Technology Lead at the Syngenta Honeywood Research Facility.

    Mixing order

    Tank mixing order is critical for chemical compatibility. While common acronyms like w.w.w.W.A.L.E.S., W.A.M.L.E.G.S., and A.P.P.L.E.S. serve as reliable guides 95% of the time, always defer to the pesticide label for specific instructions.

    Expanded generic mixing order:

    1. Water: Fill tank 1/2 full (or 3/4 if fertilizer carrier).
    2. Agitation
    3. Water-Soluble Bags (WSB): Allow to fully dissolve.
    4. Wettable Powders (WP)
    5. Water Dispersible Granules (WDG, WG, SG)
    6. Liquid Flowables (F, FL, SC, SE, CS, DC, EW)
    7. Emulsifiable Concentrates (EC, MEC, OD)
    8. Solutions (SN, SL, Liquid Fertilizers/Micronutrients)

    Adjuvants:

    1. Water Conditioners (e.g. anti-foamers, compatibility agents): Add before pesticides.
    2. Activator Surfactants (e.g. NIS, COC): Add after pesticides or by formulation type along with pesticides.
    3. Drift Retardants: Add last.

    Examples of mixing errors

    Micronutrients like sulfur (e.g. ATS) added to nitrogen-based formulations (e.g. UAN) can cause physical incompatibilities. This became a problem during “weed-and-feed” applications in Ontario corn in the late 2010s, and working with the registrants, we found a solution.

    What follows is not only a good example of why mixing order is critical, but why growers should get into the habit of performing jar tests. Learn more about a real-world ATS example here.

    Left: ATS and UAN premixed, followed by Primextra created curds.
    Centre: UAN, followed by low-load ATS followed by Primextra worked.
    Right: UAN followed by Primextra followed by high-load ATS worked.

    Mixing errors are just as likely in small plot work as in commercial sprayers. Watch this short video by Mike Cowbrough describing his experience with mixing order for Elevore and glyphosate.

    The jar test

    A jar test is a small-scale version of tank mixing used to check for physical incompatibility. Always wear PPE and work in a well-ventilated area away from ignition sources.

    Jar test steps:

    1. Prepare: Read all labels for formulation details, water quality requirements (pH/hardness), and mixing order. Shake liquid containers to ensure consistency.
    2. Initial Carrier: Fill a 1-litre glass jar with 250 ml of water (or 375 ml if using oil/fertilizer).
    3. Add Products in Order: Add chemicals following the standard mixing sequence, stirring constantly. Scale rates to match your tank concentration (e.g., 1 kg per 1,000 L equals 0.5 g in a 500 ml test).
    4. Wait and Observe: Allow 3–5 minutes between additions—especially for dry products—to ensure full dispersion. If testing water-soluble bags, include a small piece of the film.
    5. Final Volume & pH: Top the jar up to 500 ml with your carrier. Check the pH with a digital meter and add adjusters if required by the label.
    6. Evaluate: Let the jar stand for 15 minutes.

    The mix is likely incompatible if it generates heat, forms gels or scum, or if solids settle out (excluding wettable powders). Note: Jar tests only identify physical issues; they do not guarantee biological efficacy or crop safety.

    Compatibility kits

    When performing a jar test you must maintain the same product-to-carrier ratio as in a full-sized sprayer tank. This math is made easier with commercial compatibility kits such as the one from Precision Laboratories (below).

    Compatibility Test Kit: Five pipettes, three bottles, gloves, instructions. ~$10.00. (Photo: Precision Laboratories)

    Such kits contain a few plastic “jars” and disposable micropipettes. By following the instructions included with the kit, you can easily reduce large labelled volumes (e.g. 1 kg of product in 1,000 litres) of multiple products to small volumes at the same ratio. In this case we assume the final volume would have been 1,000 L, and so we reduce all the quantities accordingly to get 500 ml. The following mixing order is provided as an example.

    OrderIngredientQuantity for 500 ml or 500 g of product labeled for 1,000 L of final spray volume
    1Compatibility agents5 ml (1 teaspoon)
    2Water soluble packets, wettable powders and dry flowables. Include a 1cm2 cutting of PVA packaging.15 g (1 tablespoon)
    3Liquid drift retardants5 ml (1 teaspoon)
    4Liquid concentrates, micro-emulsions and suspension concentrates5 ml (1 teaspoon)
    5Emulsifiable concentrates5 ml (1 teaspoon)
    6Water-soluble concentrates or solutions5 ml (1 teaspoon)
    7Remaining adjuvants and surfactants5 ml (1 teaspoon)

    Records and delayed reactions

    Maintain detailed mixing records for traceability and to track performance. These records help you replicate successes and avoid future failures.

    Labelled jar tests are also valuable; by leaving them in the chemical shed overnight, you can see if products separate or solidify over time. This indicates whether a mix can safely sit in the sprayer or if it requires immediate rinsing. For example, one grower’s Enlist and Manzinphos mix appeared fine until it sat during a rain delay. It turned into “lard,” clogging the entire system and requiring a manual teardown. They even had to dig some of the substance out with screwdrivers (see the picture of the filter below). An overnight jar test likely would have predicted this problem.

    Some physical incompatibilities are not immediately apparent. This occurred overnight while the partially-full sprayer waited out a rain event.

    Closed transfer

    As a brief mention, an expansion of closed transfers systems for loading pesticides is on the horizon in North America. They have great potential to make loading more efficient, reduce operator exposure and reduce point-source contamination. Depending on the design, however, the operator may not be able to open pesticide containers to obtain samples for jar testing. This would be a great loss.

    For more information

    Learn more about physical and chemical incompatibility in our article on Tank mix compatibility. Be sure to download a copy of Purdue University’s 2018 “Avoid Tank Mixing Errors”. Finally, if you have questions about a specific product, contact the manufacturer, who have likely already performed the testing with common tank mix partners and can advise you.

    This article was co-written with Mike Cowbrough, OMAFA Weed Management Specialist – Field Crops

  • Cleaning Your Sprayer

    Cleaning Your Sprayer

    We all know the importance of cleaning out a sprayer. It protects a sensitive crop. It protects people working with the sprayer. It protects the sprayer and its components. But cleaning the sprayer is a pain. Here are some tips to make it easier.

    Some herbicide label instructions are cumbersome, requiring many flushes with full tanks of water. Many applicators look for shortcuts and hope they get away with it. It doesn’t have to be guesswork. The following is a checklist that may help.

    Be Prepared

    A few supplies can help ensure a clean sprayer tank.

    • A defoaming agent saves water and time
    • A cleaning agent (commercial products, or simple household ammonia) is useful, and recommended, for Group 2 products except the imidazolinones.
    • A supply of clean water, preferably with its own pump, and a pressurized spray hose helps clean the sprayer inside and out.
    • A wash-down nozzle (whose flow requirements can be met by the clean water pump) can automate the tank wash-down.
    • A bucket and brush for rinsing screens is very useful.

    Products to Watch:

    The products most frequently implicated in sprayer contamination are two members of the Group 2 modes of action: the sulfonyl ureas (e.g., thifensulfuron (Refine) and tribenuron (Express)), and the triazolopyrimidines (e.g., florasulam (Frontline, PrePass) and pyroxsulam (Simplicity)). Since these herbicides dissolve better at higher pH, proper cleanout usually requires ammonia, a weak base that raises the solution pH. The third member of Group 2 products, the imidazolinones (imazethapyr (Pursuit), imazamox (Solo, Odyssey), imazamethabenz (Assert), imazamox (Ares,  Adrenalin, Altitude or Viper)), tend not be implicated in as many residue issues, and don’t require ammonia for cleanout.

    Be Prompt and Thorough

    Remove pesticide from mixing and spray equipment immediately after spraying – it makes the job easier. The main areas of concern are the tank wall, sump, plumbing (including boom ends), and filters. First, spray the tank completely empty while still in the field. It’s sometimes OK to cover previously sprayed areas – all herbicides must be crop-safe at twice the label rate to be registered by the PMRA. Take care with residual products that may create problems down the road. Reduce the rate or choose a fallow field to be certain. Second, add 10 x the sump’s remnant of clean water, circulate, ensuring agitation is on, and spray it out in the field as well. Repeat. These two rinsing steps will take care of the majority of the cleaning and won’t take very long. The less remaining volume there is in your tank after the pump draws air, the less water is needed to dilute this remainder to an acceptable concentration. Having a clean water tank on the sprayer and a wash-down nozzle makes this job easier.

    Visual Inspection

    Herbicide residue may precipitate out of solution in some parts of the sprayer or plumbing. A thorough visual inspection can identify these problem areas and ensure that they are cleaned properly.

    Tank Wall

    Removal of residues from tank walls is best accomplished with a direct, pressurized spray. Make sure all parts of the wall have been in contact with clean water. Use a wash-down nozzle if it provides complete and vigorous coverage of the interior tank surface.

    Sump

    Empty the sump as completely as possible by spraying it out. Any spray liquid or herbicide concentrate remaining in the sump area will be re-circulated in the sprayer. The only way to remove any remaining herbicide is through dilution by repeatedly adding water, and leaving as small a remainder as possible.

    Plumbing and Boom

    Plumbing can be a significant reservoir of herbicide residue. Removal from plumbing can be achieved by pumping clean water through the boom while ensuring that all return and agitation lines also receive clean water and all residue is flushed out. This may require opening and closing various valves several times, and repeating the process with new batches of clean water. Boom ends can extend up to 6” beyond the last nozzle at each end of each boom section. These ends must be flushed to removed trapped residue. A useful product that does this automatically is the Pentair Hypro Express Nozzle Body End Cap, or better yet, consider recirculating booms.

    Dilution

    The most effective use of a volume of rinse water is to divide it equally across several repeat washes. Assuming a 10 gallon sump remainder, three washes with 30 gal each are as effective as two washes with 70 gallons each, and equal a single 600 gal wash.

    It’s even more efficient to use a separate clean water pump, introducing clean water as the rinsate is sprayed out. This saves water and time, and results in even more dilution.

    Filters

    Nozzle screens and in-line filters can be a significant reservoir for undiluted or undissolved herbicide and are one of the most overlooked parts of sprayer decontamination. Remove all filters and nozzle screens and thoroughly clean these with fresh water. Run clean water through plumbing leading to the screens.

    Nozzle Bodies

    Nozzle bodies can harbour herbicide mixture. When cleaning a spray boom, rotate through all nozzles in a multiple body to ensure clean water reaches all parts of these assemblies. Remove screens that may have been used with herbicide.

    Tank Cleaning Adjuvants

    Adjuvants such as ammonia can assist the tank decontamination process, especially with sulfonyl urea and triazolopyrimidine-containing products. Ammonia does not neutralize herbicides, but it does raise the pH of the cleaning solution which helps sulfonyl urea herbicides dissolve. When decontaminating after an oily (EC) formulation, the use of a wetting agent such as AgSurf will assist in removing oily residue that may trap SU herbicide on tank and hose material. Commercial tank cleaning products that contain ingredients for removing persistent deposits are available.

    Tank and Boom Material

    Both plastic and stainless steel are common tank and wet boom materials, and both can be cleaned using the above procedures.  However, stainless steel is easier to clean, and this means that less time may be required. Consider the choice of materials a productivity factor in your next purchase or upgrade decision.

    Rinsate Disposal

    Always spray out the tank in the field. Do not drain the tank while stationary unless you are certain it is free of pesticide and that you are away from sensitive areas and waterways. Consider a continuous rinse system. Consider building a biobed for safe disposal of dilute pesticide waste.

    Sprayer cleanout will probably never be the easiest job on the farm. But looking at it in a smarter way can prevent frustration and save time.