Author: Jason Deveau

  • Adjusting Sprayer for Alternate Rows

    Adjusting Sprayer for Alternate Rows

    An “Alternate Row Middle (ARM)” traffic pattern is where the sprayer passes down every second row. The intent is to improve work rate by cutting the driving time in half. The operator hopes to provide suitable coverage on both the sprayer-facing half of the canopy, and that half of the canopy facing the next alley. In our experience, this depends on sprayer design, and only works in very small/young plantings (or only for the first few applications of the season). Even then, the side facing the sprayer tends to get saturated in an effort to ensure a threshold dose reaches the far side. We’ve already captured the pros and cons of ARM in this article, and (spoiler alert) unless you’re using a wrap-around style design, it’s generally not the best approach for protecting an orchard, bush, cane or vine crop.

    So why on Earth would we be testing it here?

    We were contacted by an orchardist who planted a test block of Gala (est. spring, 2017) in an unusual way. He called it “V-Trellis Vertical Axis Cross”. Basically, he created an orchard architecture that only allowed equipment (e.g. platforms, sprayers) to pass down every second row. He figured it would save 35% of his labour costs. In the photo and illustration below, you can see the posts lean over the drivable alleys, creating a “V” shape.

    So, given that he couldn’t fit a sprayer down every row, we had no choice but to try to optimize sprayer settings for ARM applications. Note the six numbers in circles in the above illustration. They indicate where we would eventually place water-sensitive papers to diagnose spray coverage.

    Here are the settings the orchardist was using before we made any adjustments:

    • Turbomist sprayer with 11 foot high tower
    • Bottom-most nozzle was on and every second nozzle position skipped for a total of 5 nozzles active per side
    • Nozzles were TeeJet ceramic disc-core. Top to bottom: D3-DC45, D3-DC45, D3-DC45, D3-DC45, D3-DC25
    • 7 km/h (4.35 mph) travel speed per a speedometer app on a smartphone
    • Tractor engine speed was 2,150 rpm (PTO was ~ 540 rpm)
    • Fan set in low gear
    • Pressure was 190 psi
    • Ambient wind gusting to 8 km/h, temperature of 30°C, RH ~65%.

    And here is a video of what the sprayer was doing before we changed any settings. This is a single upwind pass, and as you can see, the spray blew through at least five downwind rows. Obviously, this was far too much air and spray volume.

    When we diagnose coverage in an every-row situation, we drive the alleys on each side of the target row (i.e. two passes). But, when diagnosing ARM spraying, we want to account for every drop of cumulative coverage from spraying upwind rows. So, we have to do three passes, as shown in the illustration below. In this top-down diagram, the sprayer travels the red line.

    In order to establish a baseline, we diagnosed coverage for the original settings using water-sensitive papers in the six positions indicated above. We folded them in half, so a sensitive side faced each alley. We sprayed water and later digitized the cards to determine the percent coverage on the papers. Remember, if 80% of the cards receive at least 10-15% surface coverage and a deposit density of 85 drops per cm2, it’s typically sufficient.

    Here are our results, with percent area-covered indicated in each position, as well as a representative scan of one of the papers. There’s no need to provide deposit density, which after about 30% surface coverage cannot be reliably determined.

    So, if the video doesn’t convince, then the papers certainly do: This was way too much air and spray mix.

    Next, we performed a series of air adjustments using ribbons (detailed here and here) which led us to reduce engine speed from 2,150 rpm to 1,300 using the Gear-Up, Throttle-Down method. Then we used the OrchardMax calculator to establish an ideal spray volume and guide us to which nozzle rates we should use:

    • Bottom-most nozzle was on and every second nozzle position skipped for a total of 5 nozzles active per side
    • Top nozzle was TeeJet AITX8002, followed by TeeJet TXR80015, TXR80036, TXR80015, TXR80015
    • 7 km/h (4.35 mph) travel speed per a speedometer app on a smartphone
    • Tractor engine speed was 1,300 rpm (PTO was ~ 300 rpm)
    • Fan set in low gear
    • Pressure was 100 psi
    • Ambient wind gusting to 4 km/h, temperature of 26.5°C, RH ~70%.

    The following video shows the coverage from a single pass (to be clear, no extra upwind pass). We eventually did three passes to capture the cumulative coverage, just like with the first sprayer settings. This video simply serves to show how in ARM applications, the sprayer-facing side always looks much better than the side facing away. Also note how much quieter the sprayer is, as well as the reduced blow-through.

    And here is the resultant, cumulative coverage from three passes. Once again, deposit density isn’t required as it exceeded our threshold in each position.

    In the end analysis, we saved the grower ~30% of their spray mix, greatly reduced noise and spray drift, and still achieved suitable coverage in the target canopy. So, does this mean ARM applications are redeemed? We refer you, kind reader, to our introduction where we said ARM can work in young plantings and early season applications.

    Note that the upwind side of the canopy received less coverage than the downwind side. As this new planting grows and fills, it’s going to be increasingly difficult to achieve sufficient coverage. Changes to the sprayer settings may be able to account for the imbalance, but they will also make the applications less efficient (i.e. more spray mix, more drift and coverage will still not be uniform). It remains to be seen if the spray inefficiency inherent to this orchard architecture is worth the estimated 35% savings in labour costs.

    It’s an economic decision. We’ll see.

  • Clean Your Nozzles

    Clean Your Nozzles

    When operators winterize their sprayers, they should remove all the tips and store them separately. Many store them in large pails with lids. Calibrating the sprayer just prior to winterizing will indicate if the nozzles should be stored, or replaced. Let’s assume each tip flow rate is within 5% of the average output and no more than 5% more than the manufacturer’s pressure tables. Yes, industry standard is 10%, but I always wonder how the spray quality suffers with that much wear. Nozzles are, comparatively, a cheap replacement and it’s not worth skimping. Learn more how to check nozzle flow rate, here.

    Just like any other part of the sprayer that comes in contact with spray liquid, nozzles (and strainers) should be cleaned regularly. And, just like any other part of the plumbing, the best way to do that is to dilute any residues via a series of rinses. For a more rigorous cleaning, one of the intermediate rinses should include a detergent, and soaking during this step is an excellent practice.

    The orifice of any nozzle is delicate, either machined or molded to exacting standards. Even small changes to the orifice shape results in distorted spray (e.g. spray comes out at undesirable angles), a change to the rate (typically more volume per minute) and a change in the spray quality (typically larger median droplet size). If foreign objects or residues remain in the tips, the subsequent spray job may be less accurate and even damage the tips.

    In the case of air induction nozzles, which are essentially the standard on most boom sprayers, debris and weed seeds can plug the air-intake ports. When that happens, the nozzle will not function as intended. So, while the occasional soaking of nozzles does a great deal of good, they may also have to be scrubbed. Don’t use picks or reamers! There are nozzle cleaning tools out there, but they’re basically toothbrushes so save your old ones (and mark them clearly). Soft bristles are the way to go for removing stubborn residues and cleaning any tip orifices, but we found a nifty new way:

    Occasionally we receive photos like the one below and we’re asked what we think. Well, just the same way we don’t recommend cleaning your sprayer overalls in the family clothes washer, we also don’t recommend the use of dishwashers for nozzles.

    Not a great idea. Certainly not if you intend to ever use this dishwasher for anything else. And where does the rinsate go?

    In an interesting experiment, Lucas Olenick of Wilger tried cleaning tips in a heated ultrasonic cleaner. We haven’t tested this and we don’t know what heat and vibration might do to poly and ceramic components, but surely it’s no more aggressive than hot, soapy water and a bristle brush. Lucas tried several durations with and without detergent and arrived at this recipe:

    “For tough, non-water-soluble pesticides, around 8+ hours in a heated ultra-sonic cleaner with (Dawn) dish soap to come out like brand new. Other solvents may speed this up, but I’d generally suggest against heating solvents at any concentration. For water-soluble pesticides, expect to be within the 3-6+ hours for the first time to be confident enough in not having to flow-test each of the nozzles. With any pesticides, ensure proper care in handling contaminated nozzles and rinsate after cleaning nozzles.”

    The mad genius of Lucas Olenick (@WilgerParts) who used dish detergent and a heated sonic cleaner to unplug tips. Be sure to dispose of rinsate safely. Photo credit: Lucas Olenick.

    Don’t have a heated sonic cleaner? No problem. Here’s a step by step:

    1. Wearing gloves, remove all nozzles, strainers, rubber gaskets and tips from the sprayer.
    2. Put them in a large plastic pail and cover them in warm water. Leave them to soak.
    3. Drain the pail, but be aware that the rinsate will have pesticide residue.
    4. Fill a second pail with a solution of the same commercial detergent used to clean the sprayer.
    5. With a toothbrush, scrub the caps, gaskets, strainers and nozzles to remove any residue. Some nozzles can be pulled apart to expose the mixing chamber and facilitate cleaning.
    6. Once scrubbed, leave all the parts to soak in the detergent solution.
    7. Drain the solution, which will contain trace amounts of pesticide, rinse the parts with water and reassemble the nozzles.

    While you’re at it, drop those filters and scrub them alongside the tips. This may seem extreme, but of all the technology on a sprayer, the nozzle has the biggest impact on the effectiveness and efficiency of the spray job. Take the opportunity over the winter months to clean and inspect the tips for damage so the sprayer is ready for calibration in the spring.

    Soak, scrub, rinse and store nozzles and nozzle strainers. You may replace them once the sprayer is clean, but I prefer to store then separately. Photo credit: Jason Boersma (@RVFBoys), Ridge Valley Farms, Ontario.

    Thanks to Jason Boersma (@RVFBoys), Ridge Valley Farms, Ontario, who sparked this article with his tweet: “Great job for a cold winter day, soak & clean all your tips to be ready for spring also saves on down time!”

  • Spray Drift Basics

    Spray Drift Basics

    This article is intended as a basic overview of what pesticide spray drift is and how to avoid it. If you want a more in-depth study of the physics of drift, head over here.

    Defining Drift

    Pesticide spray drift is the aerial movement, and unintentional deposit, of pesticide outside the target area. Aside from being illegal, there are a lot of compelling reasons for avoiding it. Drift can be measured in financial loss associated with wasted pesticide, wasted time and reduced crop quality/quantity. Plus, if an application is unsuccessful, the operator may have to re-apply, incurring further cost. Pesticide drift increases any risk of damage to human health, susceptible plants (e.g. adjacent crops), non-target organisms (e.g. wild and domestic animals, pollinating insects, etc.), the environment, and property.

    We’ll limit our definitions to two forms of pesticide spray drift: Particle Drift and Vapour Drift.

    Physical Drift is the initial off-target movement of pesticide droplets. This occurs at the time of application, and it is generally on a scale of tens-of-metres. There is a secondary component to physical drift wherein particularly small droplets (or the evaporated remains of droplets) stay aloft for longer periods of time, during which they can move laterally with wind or vertically with thermals and turbulence.

    Vapour Drift is the off-target movement of pesticide vapours. This is a function of product chemistry (vapour pressure) and surface temperature. Rainfall (rewetting) can also affect vapour loss. If vapour gets caught up in a light breeze, moves downhill during a thermal inversion, or is redistributed in precipitation, movement is can be on a scale of kilometres.

    Managing Drift

    Drift cannot be entirely eliminated, but sprayer operators can greatly reduce the degree and impact. Much of what follows relates predominantly to particle drift from horizontal boom sprayers, but it’s never wrong to follow these best practices. Research and modeling have shown that the three biggest factors under the operator’s control are:

    • Apparent wind speed (i.e. the sum of wind speed and travel speed)
    • Boom height (i.e. release height)
    • Droplet size (i.e. nozzle spray quality)

    Therefore, the degree and impact of drift can be greatly reduced by following these guidelines:

    • Reduce the distance between nozzle and target. For a herbicide application, that means lowering the boom to the lowest practicable height. There are exceptions, but a good rule of thumb is that the boom height should be approximately the same as the nozzle spacing.
    • Use the coarsest effective droplet size, generally achieved through the use of drift reducing nozzles such as air induction.
    • Work with the weather.  Labels will specify appropriate weather conditions for spraying. Change sprayer settings to account for hot, dry and windy conditions or halt the job until conditions improve. Generally, avoid spraying when the weather is against you.
    • Identify any vulnerable nearby crop, landscape or environmental area. Choose a spray day when winds are blowing away from these sites. Explore voluntary watchdog sites like DriftWatch to see if there are registered sensitive crops nearby. Planting windbreaks or utilizing riparian areas can also help manage wind and provide localized downwind protection.
    • Observe labelled buffer zones and recommended sprayer settings. In Canada, using optimal sprayer settings in the right environmental conditions may reward the sprayer operator with buffer-zone reductions.
    • Work with your neighbours.  Let them know your intentions. For example, greenhouse growers need to be notified to close vents during morning spray times to avoid any possibility of drift.
    • Understand the potential damage off-target herbicides can cause and make this part of your planning when selecting a herbicide. Where possible, choose herbicides with a low risk of volatility. Avoid products like dicamba near susceptible crops (grapes, tomatoes, peppers, sweet potato, tobacco, IP soybeans, etc.) or greenhouses. While not necessarily volatile, other synthetic auxins such as 2,4-D are extremely damaging to horticultural crops at very, very low doses.
    Buffer zones or No-Spray zones physically separate the end of the spray swath for the nearest downwind sensitive area.
    Buffer zones or No-Spray zones physically separate the end of the spray swath for the nearest downwind sensitive area.
    Consider planting windbreaks between your operation and sensitive downwind areas. Be aware that the windbreak should filter pesticide-laden air, not block it completely (~50 % porosity). Also be aware that there are potential impacts to nearby crop rows, such as creating shade as well as cool, still air conditions. Contact your local Nature Conservancy to discuss the right plants and management plan for you.
    Consider planting windbreaks between your operation and sensitive downwind areas. Be aware that the windbreak should slow and filter pesticide-laden air, not block it completely (~50 % porosity). Also be aware that there are potential impacts to nearby crop rows, such as creating shade as well as cool, still air conditions. Contact your local Nature Conservancy to discuss the right plants and management plan for you.

    Running an Airblast Sprayer?

    For airblast sprayer operators, the environmental factors that affect drift are the same, but the rules for optimizing sprayer settings are slightly different. Droplet size is less of an issue, and in some cases droplet size cannot be controlled. Air settings are the primary tool for reducing drift potential.

    • Adjust fan settings to produce the minimal effective air speed throughout the season.
    • Use deflectors to channel air into, not over or under, the target.
    • If possible, increase droplet size by using air induction nozzles or disc & core (or disc & whirl) nozzles that produce a coarser droplet size. Depending on canopy size, you could use them in every nozzle position, or only in highest nozzle positions.
    • Any sprayer design the brings nozzles closer to the crop (e.g. tower or wrap-around designs) will reduce drift.
    • Canopy sensors that turn boom sections on and off to match the size and shape of the canopy will reduce drift.
    It’s not only field sprayers that drift. Photo Credit – G. Amos and D. Zamora, Washington State.
    It’s not only field sprayers that drift. Photo Credit – G. Amos and D. Zamora, Washington State.
    Monitoring airblast drift using a tall pole with water-sensitive papers stapled along the length. This trial was run using only water so as not to expose the person holding the pole. Photo Credit – M. Waring, British Columbia.
    Monitoring airblast drift with ribbons and a tall pole with water-sensitive papers stapled along the length. This trial was run using only water so as not to expose the person holding the pole. Photo Credit – M. Waring, British Columbia.

    If You Suspect Drift

    If you suspect your crops or property have been damaged by pesticide drift, follow these steps (The contact info is specific to Ontario, so substitute your local authorities). The following information is based on this article in ONFruit which focuses on herbicide drift. Drift onto an organic operation would not necessarily cause visual injury, but steps are similar.

    1. Diagnose the problem

    • Is there evidence of a spray application (agricultural or vegetative management such as roadside spraying)?  Look for wheel tracks, weed symptoms, boom patterns and overlap on the headlands. Look for spray evidence in neighbouring fields, lawns, ditches, etc.
    • Familiarize yourself with the symptoms of drift injury on your crops.
    • Eliminate other possible causes. Disease, insects, nutrient deficiency, herbicide carryover, improper sprayer cleanout, and environmental stress can resemble drift injury.
    • Are there damage patterns? In the case of physical drift, damage is more pronounced on the upwind side of the damaged area, tapering away with distance from the source. In the case of vapour drift, damage can be uniform throughout damaged area and not necessarily downwind from the source. Pesticides can also move in cold air drainage and in surface run-off from rain events. If damage is patchy, it may be something else, such as soil pH or carryover (look where sprayer starts and stops).

    2. Contact the appropriate people

    • Talk to your neighbour or the sprayer operator. Ask what was sprayed, when it was applied and who performed the application.
    • Contact the Ministry of the Environment, Conservation and Parks District Office or Spills Action Center (SAC): 1-866-663-8477. The SAC is available 24/7 and they will then contact the appropriate Environmental Officer and pesticide specialist in your region. Local MECP offices can be found here.
      • It is extremely important to report as soon as possible because the concentration of herbicide drops quickly within the plant.  Do NOT wait until there are symptoms. Do NOT hesitate to call, even if you are unsure if it’s pesticide drift.
    • MECP officers can do a site visit, take samples of tissue and soil, and have them analyzed for suspect pesticides. Where appropriate, the offending applicator may face charges under Ontario’s Pesticides Act. Charges will be pursued only if off label use is identified from the information gathered.
      • Because of the wording of some of the labels and the difficulty of tracking down all the information needed, this has always been a very difficult thing to pursue in grower-to-grower drift incidents. 
      • The results from the MECP lab are available for the grower and, if enough information is collected, the grower is encouraged to pursue civil court if insurance and/or cooperation with the applicator does not work. According to the label of most pest control products, the applicator is liable for any damage caused by the misapplication of a pesticide.
    • Contact your (crop) insurance adjustor and advise the applicator to contact theirs. However, do not rely on your crop insurance; Insurance companies may not provide coverage for drift incidents. It is prudent to determine if you are covered before you need to file a claim.
    • Report the incident to the PMRA Voluntary incident reporting system
    • Report the incident to the manufacturer of the pesticide product. See the label for the toll-free number. Labels can be found on the PMRA label search.

    3. Document all details of the problem and consider lab analysis

    • Collect spray records. This includes yours (to ensure it was not your application), and the potential offending applicators’.
    • Collect weather records (temperatures, possible temperature inversions, wind speed, wind direction, rainfall) for the date of application).
    • Take timestamped, geolocated photos (most smartphones include this information automatically, but check your settings). Repeat photos several times through the season.
    • Document yield loss from the damaged area and an undamaged area. Choose a similar planting (same age, cultivar, rootstock, etc.). For perennial crops (e.g. vineyards, orchards, asparagus, berries) herbicides such as Group 4’s may necessitate documenting the effects for several years after the damage occurred.
    • Laboratory analyses of herbicide levels in plant tissue are often necessary to confirm the presence of herbicides, although symptoms may be helpful in diagnosing which herbicides caused the problem.
      • Research laboratories that will analyze crop samples for herbicide residues. Their requirements regarding sample size, labeling, storage, and shipping will vary, as will the list of pesticides they provide testing for and their minimal detection levels. Given the time-sensitive nature of pesticide detection, it would be prudent to know this information before need the service.

    Applicator Liability

    Anyone using pesticides is responsible for their safe application. For example, the Ontario Pesticides Act requires that licensed spray applicators carry a specialized liability insurance policy that provides appropriate coverage for their business. Operators who work on a “for hire” basis (e.g. a licensed spray applicator) or away from their own farm operation will need additional coverage. Where drift damages adjacent crops, insurance adjustors generally ask the following questions:

    • Was the damage to the applicator’s own crop? If so, it is unlikely that there will be coverage under any insurance policy.
    • Was the damage to a neighbour’s property? If so, the applicator’s liability policy may respond.
    • Was the product being applied according to label directions?

    Other Resources

    Managing spray drift is everyone’s responsibility. Extremely low, and often invisible, amounts of spray drift can be very damaging; even long after the application. For more information about drift mitigation, watch the following videos and download a copy of this Factsheet. 

    What is Pesticide Drift?- Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (2011)

    Equipment and Methods to Reduce Pesticide Drift- Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (2011)

    Preventing Pesticide Spray Drift- University of Missouri Extension (2013)

    Three simple ways to reduce drift. Thanks to Real Agriculture for filming and editing! (2014)

    Three simple ways to reduce drift. Thanks to Real Agriculture for filming and editing! (2014)

  • Optics on Airblast Sprayers – What They Can’t See

    Optics on Airblast Sprayers – What They Can’t See

    “Precision agriculture” is many things to many people. In the context of spraying, let’s define it as “detecting and responding to variability”. One example of precision ag is the use of crop-sensing optics to efficiently and accurately direct spray application. This is nothing new to field sprayer operators, but did you know that before Ken Giles published the first paper on pulse-width modulating nozzles in 1989, airblast sprayers already had crop-sensing technology?

    In the 1970s, Bert Roper noted the wastefulness inherent to citrus spraying. Losses to the ground of 30-50% and off-target drift of 10-20% of applied volume were (and still are) not uncommon for airblast sprayers. So, using Polaroid’s autofocus technology, and enlisting the help of a few engineers, they developed an ultrasonic sensor system that enabled a computer to “see” the target tree and engage nozzles accordingly. He and son Charlie built prototypes in their kitchen before proving it in their family groves, spraying 10 gal/ac instead of the usual 250 gallons. The first Tree-See system was sold to Cola-Cola in 1984.

    Figure 1 Tree-See on a Swanson sprayer (www.treesee.com)

    This technology is still used today; Sensors detect specific zones on the canopy and actuate boom sections, or individual nozzles, to only spray the target zone. But optics and machine learning are evolving. Now they can modulate flow from individual nozzles in response to changes in canopy density. To be clear, that’s not just “on/off”, but variable flow.

    Eventually, these systems will be able to identify and respond to specific pests (or pest damage) and adjust plant growth modifier rates based on canopy density or bloom counts. The possibilities are amazing. As an aside, interested readers can learn more about airblast sensors in this excellent article from Oregon State University which one of the authors later summarized for us here.

    Figure 2 LiDAR and control interface for a Smart Apply system fitted to a Turbomist sprayer

    However, as operators embrace this technology, they should be aware of the current limitations. Canopy-sensing optics are great at managing waste (their primary selling point seems to be pesticide savings), but this depends on crop morphology and planting architecture. It makes sense to not spray what isn’t there, but the gaps may not be as big as you think.

    Non-continuous canopies require the spray to lead and lag to some extent before and after passing the target to ensure sufficient coverage. Given the difficulty inherent to spraying to the tops of tall canopies, some specialists believe the top nozzles should never disengage. And, in the case of uniform canopies that form continuous hedge-like rows, the potential savings is greatly reduced.

    Further, all of these systems assume that application efficiency is primarily dependent on matching liquid flow rates to the profile (or perhaps density) of the target canopy. I don’t believe that’s true. At least, not entirely true. The impact of air settings on coverage efficiency and efficacy seems to have been marginalized.

    For example, these sprayers do not account for the spray’s ability to span the distance from nozzle to target (i.e., transfer efficiency). That depends on the droplet size, sprayer air settings and the environmental conditions – none of which are monitored by sprayer optics. They also cannot “know” if the spray gets intercepted by the target (i.e., catch efficiency) or if it deposits a biologically-active residue on the target surface (i.e., retention). Droplets must be retained by the target surface and not bounce or run off.

    What this means is that these sprayers, like any sprayer, can only promise “coverage potential”. Operators are still required to perform the following tasks:

    • Optimize air direction and air energy in relation to canopy size, travel speed and environmental conditions.
    • Use water-sensitive paper, or some other means of quantifying coverage, to ensure your target receives threshold coverage.
    • Monitor and adjust practices throughout the season in response to changing conditions.
    HOL’s Intelligent Spray Application (I.S.A.) system employing Weed-It sensors.

    So what’s missing? How do we progress beyond what is arguably a sophisticated rate-controller?

    In my opinion, I believe the pitcher needs a catcher – a closed-loop feedback system. Optics would identify the target, nozzle flow would respond, and then a digital spray sensor in the target canopy would detect and report coverage back to the sprayer so machine learning could make iterative adjustments in real-time.

    Spray-sensors are not a new idea, as wetness-detection systems have been used in forestry since the 70s. But, a sensor that can discern spray coverage would yield far more detail, and once again it seems Ken Giles is a pioneer in this concept. Such a sensor, integrated with sprayer optics and machine learning, could summarily account for all the unknowns that interfere with spray from the moment it’s released to the point that it (hopefully) lands. That’s some serious crop-adapted spraying.

    And yes, it would be fantastic if there were some manner of anemometer tied to a baffle or louvers in the spray head. Air energy could be balanced between up- and down-wind sides, and further adjusted to compensate for the distance to the canopy… but I’m dreaming in technicolour, now.

    Until then, sprayer eyes can only blindly dictate the release of spray into the airstream based on an assumed coverage constant (e.g., 1.2 oz./ft3). It remains for the sprayer operator to act as the brain, optimizing sprayer settings, quantifying coverage, and making changes to reflect conditions.

    Learn more about how to optimize the fit between your airblast sprayer and your target by downloading a free copy of our Airblast 101 textbook.

  • Spray Coverage in Field Tomato

    Spray Coverage in Field Tomato

    Spraying field tomato is difficult – period.

    In Ontario, early variety tomato canopies get very dense in July. The inner canopy is relatively still, humid, cool and a perfect environment for diseases such as late blight. It is challenging to deliver fungicides to the inner canopy and this can lead to inadequate disease control. Matters are slightly improved as the fruit grows and pulls the canopy open, and staked tomatoes might allow for the use of directed sprays, such as drop arms in staked peppers. But, there’s no getting around it – from a droplet’s perspective, it’s tough to get through the outer canopy.

    DSCF0002
    Imagine you are a spray droplet trying to get inside this canopy.

    Study 1 – Qualitative Observations

    In August, 2011 we worked in a market garden operation in Bolton comparing the spray coverage from four different nozzle configurations. We used the growers typical spray parameters: a travel speed of 4.5 km/h (2.8 mph), an operating pressure of about 4 bar (60 psi), a boom height of 45 cm (18 in) above the ground, and a sprayer output of 550 L/ha (~60 gpa). To monitor spray coverage, water sensitive paper was placed face-up in the middle of the tomato canopy. This diagnostic tool turns from yellow to blue when contacted by spray.

    Water-sensitive paper at top of tomato canopy - easy to hit.
    Water-sensitive paper at top of tomato canopy – easy to hit.

    This particular sprayer was equipped with an air assist sleeve that blew a curtain of air into the canopy at about 100 km/h (65 mph) as indicated by an air speed monitor placed at the air outlet. When properly adjusted, air-assist booms have a number of benefits:

    • They part the outer canopy giving spray access to the inner canopy.
    • They rustle leaves to expose all surfaces to spray.
    • They permit the use of smaller droplets, which are more numerous and adhere to vertical surfaces, by entraining them and reducing drift.
    • They extend the spray window by permitting the applicator to operate in slightly higher ambient wind speeds.
    Boom sprayer with air assist sleeve operating.
    Boom sprayer with air assist sleeve operating.

    We sprayed using the four different nozzle configurations, with and without air assist. Our goal was to make qualitative assessments (Good, Moderate, Poor), and here’s what we observed:

    Nozzle Type / Sprayer OutputWith Air AssistWithout Air Assist
    80 degree flat fans /~550 L/ha (60 g/ac)
    • Good coverage in upper canopy
    • Poor / Moderate canopy penetration
    • Low drift
    • Good coverage in upper canopy
    • Poor canopy penetration
    • Moderate drift
    80 degree air induction flat fans /~550 L/ha (60 g/ac)
    • Inconsistent upper canopy coverage
    • Poor canopy penetration
    • “No” drift
    • Inconsistent upper canopy coverage
    • Poor canopy penetration
    • “No”/Low drift
    TwinJet dual 80 degree flat fans /~550 L/ha (60 g/ac)
    • Good coverage in upper canopy
    • Poor / Moderate canopy penetration
    • Moderate Drift
    • Good coverage in upper canopy
    • Poor canopy penetration
    • Moderate/High drift
    Hollow cones /~750 L/ha (80 g/ac)
    • Good coverage in upper canopy
    • Moderate canopy penetration
    • Low drift
    • Good coverage in upper canopy
    • Poor canopy penetration
    • Very High drift

    The air induction nozzles performed poorly. Their Coarse/Very Coarse droplets impacted on the outer canopy, created run-off and resulted in very little canopy penetration. Medium droplets produced by twin fans and conventional flat fans were both inconsistent with inner-canopy coverage, but some advantage may have been observed with air assist. The TwinJets contributed to higher drift (likely because they were too high off the canopy) but otherwise produced coverage similar to the conventional flat fans. From these observations, the convention that spray shape (e.g. cone, fan, twin) has little or no impact on broadleaf canopy penetration holds true.

    Acceptable spray coverage deep in canopy (harder to hit) using hollow cone nozzles.
    Acceptable spray coverage deep in canopy (harder to hit) using hollow cone nozzles and air assist.

    After inspecting the papers deep in the canopy, we were surprised that air assist did not obviously improve canopy penetration. It did seem to help, but it wasn’t a slam-dunk. This may be because finer droplets (<50µm) are not easily seen on water sensitive paper. It might also be because we did not calibrate the air speed to the canopy: too little air and spray impacts on the outer canopy, while too much air forces leaves out of the way and spray is blown into the ground. It was obvious that drift was greatly reduced, so logically the spray had to have gone somewhere – we can only assume it entered the canopy.

    The best results were achieved with hollow cones and air assist. Theoretically, smaller droplets should improve the potential for coverage by sheer number, but they slow quickly and are easily blown off course. Winds were only about 5 km/h (3 mph) during the trials. Had they been higher, the no-air-assist condition would have resulted in poorer canopy coverage. While we feel the air assist improved inner canopy coverage, we attribute much of the performance to the spray volume of 750 L/ha (80 gpa), which was significantly higher than we used with the other nozzles. When we attempted lower volumes using the hollow cones (not shown) the inner canopy coverage was greatly compromised. Higher volumes are a demonstrated means for improving canopy penetration, so this observation is consistent with what was expected.

    The 2011 trial suggested that hollow cone tips used with high volume and air assist, improved canopy coverage and penetration. They are, however, very prone to drift and their use is not recommended without an air assist sleeve to counter the spray drift. Spray volumes over 500 L/ha are highly recommended.

    Study 2 – Quantitative Observations

    In July, 2016 we ran another study in Chatham-Kent. This operation was concerned about spray drift and recently changed from Hardi hollow cones on 25 cm (10″) centres to TeeJet Turbo TwinJets on 50 cm (20″) centres. They wanted to know if they had improved their coverage. We decided to test four nozzles at similar driving speeds and volumes.

    Once again, we used water-sensitive paper. This time we placed two pieces back-to-back (face up and face down) about 1/3 down into the canopy. Then we placed two more in the same orientation about 2/3 down into the canopy. We did this for three plants for each pass. The next four images show the visual drift and weather conditions for each nozzle. Note that only one boom section was nozzled (indicated by a white line) in each condition.

    Condition 1 – Turbo TwinJet (Coarse Spray Quality)

    2016_Tomato_Sprayers_TTJ

    Condition 2 – Hollow Cones (10″ centres – Fine/Medium Spray Quality)

    2016_Tomato_Sprayers_hollowcone

    Condition 3 – XR 110° FlatFan (Fine Spray Quality)

    2016_Tomato_Sprayers_XR

    Condition 4 – TeeJet 3070 (Coarse Spray Quality)

    2016_Tomato_Sprayers_3070

    It was very humid, making it difficult to place and retrieve the papers without smearing them. This made it tricky to discern differences in coverage, and the blurring prevented us from quantifying droplet density (i.e. number of drops per unit area). Nevertheless, papers were scanned and the percent coverage was calculated using the DepositScan software developed by the USDA’s Dr. Heping Zhu. The average percent-coverage (± S.E. n=3) is shown in the image below.

    2016_Tomato_Sprayers_Coverage

    Coverage on the upward-facing papers in the upper portion of the canopy showed excessive coverage for all nozzles but the 3070. Little or no coverage was detected on the downward-facing cards, but without air-assist or a directed application (e.g. drop arms), this was expected. It’s the deeper canopy that’s of particular interest. The only significant difference may lie in the XR flat fan which showed more coverage on the upward facing papers and some (however little) on the downward facing papers.

    This came as something of a surprise given that the XR produced a Fine spray quality and there was no air assist to guide spray into the canopy. I believe the high humidity and low winds played a role in this outcome by reducing evaporation and off-target drift. On a drier, windier day, we likely would not have seen this level of inner canopy coverage for either the XR or the hollow cone. By comparison, the Turbo TwinJet with its Coarse spray quality not only reduces off target drift, but would be more resilient in drier and windier weather and may very well have produced the best coverage by comparison.

    Take Home

    Drawing from both studies:

    • Properly calibrated air assist will reduce drift and has promise to improve canopy penetration/coverage.
    • Spray shape (e.g. twin, hollow cone, flat fan) does not seem to play a role in canopy penetration.
    • Spray quality larger than Coarse may negatively impact canopy penetration in tomato.
    • Coarse spray quality is perhaps the most versatile option when volume is sufficient (>500 L/ha).
    • Fine-Medium spray quality is only a viable option in high humidity and light winds. However, air assist is critical to counter drift, and high spray volumes (>500 L/ha) are still required despite the higher droplet count.
    • Underleaf coverage is exceedingly difficult to achieve, even with finer spray quality and air assist.
    This occurred in Ontario (date and location withheld). The sprayer missed the outer edge of the tomato field during a late blight application. An unintentional field check, and amazing to see the results.