Author: Jason Deveau

  • Greenhouse Foggers

    Greenhouse Foggers

    Greenhouse application equipment spans from the humble squirt bottle, to gas-powered foggers, to robots equipped with hydraulic vertical booms. The variety of spray equipment available reflects a variety of needs, just as a carpenter’s toolbox contains different tools designed to do different things. In order to get the most out of foggers and misters, it’s important to understand how they differ from “conventional” hydraulic spraying.

    A greenhouse robotic vertical boom sprayer.
    A greenhouse robotic vertical boom or “tree” sprayer

    Mechanical and Chemical Spread

    For many greenhouses, water is the carrier that dilutes and delivers the chemistry to the target. Water has a high surface tension and tends to bead on target surfaces. Dr. Heping Zhu (USDA, Ohio) created some amazing videos using controlled water droplets and both waxy and hairy leaves. In first video we see how water beads up on a waxy leaf, and as it evaporates, the area touching the leaf surface remains small. In the second, we see the droplet get hung up on a trichome (leaf hair) and evaporate while suspended above the leaf surface.

    Neither situation is desirable since the goal of spraying is to maximize the level of contact between droplet and target. Contact can be increased via mechanical spread or chemical spread (see figure below).

    The degree of chemical spread can be increased by adding adjuvants such as non-ionic surfactants to reduce surface tension. In the videos below we see the same controlled droplets with the same volume of liquid, but they now include a non-ionic surfactant. In the first video we see a greater degree of contact with the waxy target surface as the droplet spreads. In the second, the droplet does not get caught by the trichome, but splashes down onto the surface. Some product labels advise the inclusion of adjuvants and others are already formulated with them. In the case of surfactants, be aware of the potential for run-off and phytotoxicity.

    Mechanical spread requires us to break a single, larger droplet into several smaller volumes to increase the degree of contact. This approach usually comes with a caveat about evaporation, but this is rarely a concern in a humid greenhouse. As for the risk of drift, once again, in greenhouses it is a different story than conventional spraying. Spray drift is desirable! Lateral air movement is very important to encourage plant canopy penetration and prevent droplets from merely settling on upward-facing plant surfaces. While some equipment generates its own air, the air currents in the greenhouse are often the primary means for suspended droplets to circulate throughout the space. In either case, air could be considered the carrier instead of water. Too little air flow, or gaps in circulation, will reduce coverage. Too much air flow (specifically, greenhouse air circulation) may cause plants to exhibit stunting.

    Spray Quality (ISO)

    Here’s how ISO/DIS (5681:2019 Equipment for crop protection — Vocabulary 3.2.1) defines the spray quality produced by misters and foggers:

    • (3.2.1.13) MIST: “Spray with volume median diameter between 50 µm and 100 µm.”
    • (3.2.1.14) FOG: “Aerosol spray with volume median diameter under 50 µm where the droplets are effectively suspended in air with little or no settling by gravity.”

    These droplets do not behave like coarser droplets. For more information on droplet movement, survivability, and transfer efficiency, download Purdue Extension’s “Adjuvants and the Power of the Spray Droplet”.

    Water sensitive paper has limited utility when diagnosing coverage from foggers. Sophisticated optical scanners may be able to detect deposits as small as 25 µm, but this is open to debate. Manufacturers do not support the use of papers when quantifying deposits less than 50 µm , and some draw the line at 100 µm.

    In the following image, papers were used to diagnose coverage (from clean water) in a poinsettia greenhouse. The two papers on the right were located in the canopy and sprayed using a thermal pulse fogger and a hardware store style hand pump. The paper on the left was held directly in the path of the fogger while using the smallest nozzle provided with the unit. The spray enveloped the paper (and the person holding it). Close inspection showed tiny deposits, and the SnapCard app detected 4.5% coverage, but this greatly underestimates the actual deposition and does not account for the droplet count.

    UV dyes are the preferred method for analyzing coverage from foggers.

    Fogging and Misting Equipment

    Greenhouse spray equipment can be classified by droplet size, but also by the spray volume they employ.

    High Volume (HV)

    These applications are performed at pressures ranging from 500 to 4,285 kPa (75 to 700 psi) employing flow rates of 3.9 to 5.7 L/min (1 to 1.5 US g/min). They use standard label rates to accomplish a dilute application by broadcasting droplets larger than 100 microns. The goal is to cover all surfaces without incurring run-off. Examples of HV application equipment include backpack sprayers, trailed sprayers and boom sprayers. Practice and self-calibration are necessary to achieve the desired results when using manual HV sprayers.

    Targeted Low Volume (LV)

    These applications are performed at high pressures around 20,685 kPa (3,000 psi) employing flow rates approaching 1 L/min (0.26 US g/min), covering 93 m2 (1,000 ft2). They apply reduced rates over a given area and create droplets between 25 and 100 µm. These are concentrated sprays that do not result in wet foliage. LV applications are particularly good in high-humidity environments, when it is desirable to minimize the moisture on leaves. Examples of LV application equipment include aerosol cans.

    Ultra-Low Volume (ULV)

    These applications employ flow rates approaching 2 L/min (0.52 US g/min), covering 930 m2 (10,000 ft2). They require concentrated solutions, but apply reduced rates per area using droplets less than 25 µm. ULV applications will not raise greenhouse humidity and are a good choice when days are short and nights are long. They are also an excellent way to apply disinfectants for complete space sanitation before starting a new crop. It is important to ensure vents are closed and fans are off during sanitation. Examples of ULV application equipment include total release cans, auto foggers and thermal pulse foggers.

    PulsFOG hand-held ULV cold fogger

    Thermal pulse foggers are unlike other ULV equipment and warrant special consideration. The design of the pulse fogger has remained virtually unchanged since the 1940’s. Smaller, 24 hp machines are used in smaller operations but range up to large 175 hp machines. Tank size ranges from 10 to 50 L, where 10 L should be enough to cover 4,645 m2 (50,000 ft2) in about 10 minutes, depending on crop density. Their range is about 35 m (115 ft) from the point of release.

    Thermal Pulse foggers do not create aerosol using air shear – they use combustion (80 to 100 explosions per second) to shatter spray into a fog and propel it via positive pressure. Heat is a by-product of the engine, making it an unsuitable method for applying biological products.

    However, water-cooled foggers such as Dramm’s Bio Pulse Fogger reduce the exhaust temperature below 100 °C to make the application bio-rational. This has the added advantage of making droplet sizes more consistent and preventing spray from evaporating too quickly before it diffuses to the target.

    Dramm Bio Pulse Fogger.
    Dramm Bio Pulse Fogger

    Using a Fogger

    Dramm recommends that operators use approximately 1 L of carrier in 5 L of spray mix, but a higher proportion of carrier would be required for more viscous products. Start with a full tank of clean, high grade gasoline and once the fogger has been started, run it continuously until the application is complete. Leave it running even when moving between Quonset huts (see below).

    Know when to use a pulse fogger versus an auto fogger. Auto foggers are convenient because the operator can set them and leave. However, in the case of multiple huts, it is more efficient and timely to use a thermal pulse fogger.
    Know when to use a pulse fogger versus an auto fogger. Auto foggers are convenient because the operator can set them and leave. However, in the case of multiple huts, it is more efficient and timely to use a thermal pulse fogger.

    Do not leave the manual fogger running unsupervised as an auto fogger: If they stay stationary, or aim directly at the canopy (as in hydraulic spraying), they could drench and potentially damage nearby plants.

    When fogging, aim between the plants, such as the alleys and between hanging plants. This allows the fog to expand and permeate canopies for the best coverage. When spraying is done, be sure to release the pressure created in the spray tank to prevent accidental back flow into the gasoline tank.

    And, because it’s convenient to include the math in this article, here are the formulae for calculating greenhouse volume to help you determine rates.

    Care and Maintenance

    HV, LV and ULV equipment requires model-specific cleaning and maintenance, according to manufacturer’s instructions. Even when sprayers are kept in prime condition, they are only as good as the operator’s understanding. When the wrong product is applied by the wrong machine using the wrong method, operators risk poor control, crop damage and increased potential for pesticide resistance. For more information, read the instructions that came with your sprayer, or contact the manufacturer.

    Thanks to Louis Damm and Dr. Heping Zhu for their contributions to this article.

  • Spraying Asparagus in Fern

    Spraying Asparagus in Fern

    This research was performed in 2012 and since then there have been considerable advances in application technology for asparagus in fern that should be considered. Be sure to read the epilogue at the end of this article.

    Introduction

    Diseases such as purple spot can have major economic impacts for asparagus growers, and the best line of defence is spraying the appropriate control products. The good news is that asparagus growers know this. The bad news is that there are few things harder to spray than asparagus in fern.

    Asparagus infected with purple spot.
    Asparagus infected with purple spot.

    Asparagus in fern can stand 1.5 m (5 ft) high by 1.0 m (3 ft) diameter and is typically planted on 1.2 m (4 ft) centres. Asparagus in fern has a very dense canopy full of needle-shaped leaves. This dense canopy slows air movement, making conditions still, humid and very difficult for a spray droplet to penetrate.

    Spraying asparagus in fern.
    Spraying asparagus in fern.

    Spray coverage is a combination of two factors: the area of the target contacted by spray droplets, and the distribution of spray droplets over that target. For most insecticide and fungicide applications, reasonable coverage is reflected by 10-15% surface area covered paired with an even distribution of approximately 85 medium sized droplets per square centimeter. This is not a rule, but a guideline.

    In order to determine the best way to spray, we have to be able to compare the coverage achieved. To do this, we used water sensitive paper, which is yellow until contact with spray turns it blue. Three sets of three targets were placed in approximately the same location for each pass.

    Water-sensitive paper arranged on stands, ready to be placed in the fern.
    Water sensitive paper arranged on stands, ready to be placed in the fern.
    Diagram defining where water-sensitive papers were located relative to the fern and the sprayer.
    Water sensitive paper orientation and location in asparagus canopy relative to sprayer direction.

    We tested five popular nozzle types, at two ground speeds using three carrier volumes to answer three questions:

    1. Does spray volume impact spray coverage?
    2. Which nozzle style gives the best coverage?
    3. Does travel speed impact spray coverage?

    Does spray volume impact spray coverage?

    Five different nozzle types were used to spray three volumes onto the targets at 16 kmh (10 mph). This was repeated three times and target coverage was determined both as droplet deposits per cm2 (see Figure 1) and total % covered (see Figure 2).

    Figure 1. Average deposits per cm^2 for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).
    Figure 2. Combined average percent coverage for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).

    Cards in each position consistently received a significantly higher average deposit per cm2 and significantly higher average percent coverage at higher spray volumes. The relatively low coverage in the middle position was anticipated given the orientation of the targets to the sprayer.

    Therefore, it would appear higher volumes result in better coverage, at least up to 280 L/ha (30 gpa). Generally, there is a threshold where exceeding a given carrier volume results in a diminishing return.

    Which nozzle gives the best coverage?

    Coverage from five different nozzles was compared: the Hollow cone, Flat fan, Dual flat fan, Guardian Air and Air-induced hollow cone. Given that 280 L/ha (30 gpa) resulted in the best coverage, the following figures illustrate droplet deposits per cm2 (see Figure 3) and total % covered (see Figure 4) at 280 L/ha (30 gpa).

    Figure 3. Average deposits per cm^2 for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).
    Figure 4. Average percent coverage for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).

    The graphs show that each nozzle followed a similar trend, with more droplets at the top of the canopy, less or par at the bottom of the canopy, and considerably less in the middle of the canopy (which is not surprising given the orientation of the target around the stem).

    The trend in droplet density from highest to least coverage is:

    1. Hollow Cone
    2. XR flat Fan
    3. Guardian Air
    4. Dual Flat Fan
    5. Air Induced Hollow Cone

    The percent coverage data was less clear. The top two nozzles for each position were:

    Top Target:

    1. Guardian Air
    2. All other nozzles approximately the same

    Middle Target (around the stem):

    1. XR flat Fan
    2. Hollow Cone

    Bottom Target:

    1. XR flat Fan
    2. Hollow Cone

    It can be argued that the target at the top of the canopy is easiest to spray, and therefore does not have as much importance as the middle and bottom targets. As such, it would appear that the XR flat fan and Hollow cone nozzles give the best overall coverage. It is debatable whether the higher droplet count from the Hollow cone is more important than the higher percent coverage of the XR flat fan.

    Does travel speed impact spray coverage?

    Hollow cone nozzles and XR flat fan nozzles were used to spray targets at two travel speeds and three volumes. Target coverage was determined both as droplet deposits per cm2 (see Figure 5) and total % covered (see Figure 6).

    Figure 5. Average deposits per cm^2 for Hollow cone and XR flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).
    Figure 6. Average percent coverage for Hollow cone and XR Flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).

    The variability in deposit density and percent coverage from medium/fine droplets created by the hollow cone nozzles make it difficult to determine statistical significance, but the trend suggests that higher ground speeds improve coverage in the middle and bottom of the canopy. This is likely due to the wake of the sprayer and the vortices created by its passage stirring fine droplets into the canopy.

    Overall recommendations

    The data suggest that coverage was improved when the sprayer travels at 16 kmh (10 mph) rather than 8 kmh (5 mph). Coverage was also improved at higher spray volumes, where 280 L/ha (30 US g/ac) provided the best overall coverage for all nozzles. As for the best nozzle, this depends on the application; the hollow cone created higher droplet densities than the XR flat fan, but the XR Flat fan created higher percent coverage. Higher droplet densities may be preferred when controlling disease with contact products, but spray drift becomes a significant concern. Higher percent coverage might be preferred with locally systemic products where complete coverage is less of a concern and preventing spray drift is a priority.

    Epilogue

    This work was performed in 2012. Since then there have been significant advances in sprayer design for spraying asparagus in fern. Dr. Torsten Balz (Bayer Application Technology Manager) kindly provided an example of such a sprayer (see below) and a video link to watch it in action. Drop arms that bring the nozzles closer to the target at all canopy depths are an ideal solution as long as the row spacing allows clearance without snagging the drops. Further, there have been developments regarding the use of hollow cones in an overhead broadcast application. Over- and under-laps in the hollow cone swath lead to double-dosing and gaps respectively that are referred to as “Technical Strip Disease”. Combined with considerable drift potential, hollow cones are not recommended.

    Air-assisted drop arms greatly improve coverage uniformity in asparagus in fern. Photo kindly provided by Dr. Torsten Balz.

    Special thanks to Max Underhill Farm Supply (Vienna, Ontario) for use of their sprayer and their assistance both spraying and placing water sensitive papers in the field. Thanks to Mr. Ken Wall of Sandy Shore Farms Ltd. (Port Burwell, Ontario) for providing the site and hosting the associated workshop, and thanks to TeeJet Technologies for their donation of parts and supplies.

  • Methods for Applying Fungicides in Corn

    Methods for Applying Fungicides in Corn

    This work was performed with Albert Tenuta (OMAFRA) and David C. Hooker (University of Guelph, Ridgetown).

    Objective

    Gibberella ear rot is a significant disease that reduces the quality of grain corn, especially with the accumulation of mycotoxins (such as Deoxynivalenol (DON)) produced from the causal pathogen(s). Infection occurs through the corn silk channel when ideal temperatures (~27°C) and high humidity are present. Cool, wet conditions after pollination favour disease development and determine the degree of infection. With crop management practices providing only modest improvements in disease control, strategies to increase the efficacy of fungicides are important to investigate. Research has shown that the timely application of fungicide labelled to suppress the disease can reduce mycotoxins, but only by ~50%. We wondered if changes in the method of application could give better results.

    Gibberella ear rot

    It is reasonable to assume that improvements in spray deposit uniformity and increases in overall spray coverage (up to some threshold) at the infection channel (i.e. the silks) should result in improved efficacy. Water sensitive paper is an excellent tool for the qualitative evaluation of spray coverage. However, recognizing the complicated relationship between dose and coverage, we also looked at the deposition of copper sulphate as a surrogate for active ingredient .

    Our primary objective of this study was to compare various sprayer systems and nozzle configurations by evaluating both spray coverage and copper sulfate deposition at the silks.

    Experimental Design

    The test field of hybrid corn had a stand of ~80,000 plants/ha. It was located at Ontario’s U of G Ridgetown Campus and was managed similar to a grower’s field (e.g. fertility, etc.). In August of 2019 we evaluated nine sprayer rigs (or nozzle configurations) in a randomized block design.

    The ground rigs were calibrated to deliver a spray volume of 190 L/ha and the aerial systems to deliver 47 L/ha.  In order to achieve the target spray volume, the ground rig speed varied from 9.5 to 13 km/h, depending on nozzle configuration. The aerial applicators used the same nozzle configuration, travel speed and altitude as in their commercial field applications.

    SprayerNozzle SetNotes
    John DeereYield Center 360 UNDERCOVER drop pipes 75 cm (30″) spacing, each equipped with two Turbo TeeJet (TT) nozzles.Drop pipes were centred between corn rows with nozzles adjusted to spray ~horizontally and directly at the corn silks.
    John DeerePentair Hypro Guardian Air nozzles on 50 cm (20″) spacing.Boom positioned to create 100% spray overlap at tassel height.
    John DeereTurbo TeeJet Induction (TTI) nozzles on 50 cm (20″) spacing.Boom positioned to create 100% spray overlap at tassel height.
    John DeereTurbo TeeJet (TT) nozzles on 50 cm (20″) spacing.Boom positioned to create 100% spray overlap at tassel height.
    New Holland (front-mounted boom)Wilger 60 degree conventional flat fan nozzles on 40 cm (16″) spacing.Boom positioned to create 100% spray overlap at tassel height.
    New Holland (front-mounted boom)Wilger 60 degree conventional flat fan nozzles alternating with custom-made Wilger 40 degree conventional flat fan nozzles on 40 cm (16″) spacing.40 degree nozzles were positioned between corn rows (interrow) while 60 degree nozzles were positioned over the tassels.
    Hagie (front-mounted boom)Drop hoses terminating with TeeJet Duo Nozzle bodies equipped with Turbo TeeJet Induction (TTI) nozzles were alternated with TeeJet XR110 nozzles.Drop hoses were centred between corn rows but nozzles were not aimed directly at the corn silks (aimed down 45 degrees and spray parallel to ground rather than perpendicular). They alternated with the AI nozzles positioned over the tassels.
    HelicopterAir Induction TeeJet Turbo TwinJet (AITTJ) nozzles directed backwards.
    AirplaneCP-111T nozzle bodies with CP256-4015 40 degree flat fan tips on 15 cm (6″) spacing.Wingspan was 14.2 m with a 10.6 m boom width.

    The field was divided into four replicated blocks (REP 1-4 in the image below) which corresponded with a single pass of the sprayer. The sprayers alternated direction with each pass over the four blocks. Depending on the ground rig, a single pass through a block might include more than one set of nozzles. For example, in the image below, a John Deere sprayer carried a different nozzle set on each of four sections, leaving the centre boom section off. Therefore, each block was subdivided into four experimental units that corresponded with each nozzle set. Further, to account for variability, each experimental unit was further subdivided into five ranges. Four water sensitive papers (yellow rectangles) were oriented sensitive-side up and fastened to random corn plants directly on top of silks at each of the five intersections between range and treatment for a total 20 papers. This was replicated four times for a final count of 80 papers per treatment.

    The experimental unit covered by a nozzle set was four corn rows wide (~3 metres). Space was left between each boom section to provide a buffer and no nozzles were placed on the centre boom section. Four water sensitive papers (yellow rectangles) were fastened to random corn plants directly on top of silks at the intersection of each range and for a total 20 x 4 = 80 papers. The chevrons indicate sprayer direction.
    Test plots at University of Guelph, Ridgetown Campus

    Evaluating Coverage

    Each sprayer applied copper sulphate (Plant Products Inc., Leamington, ON) at 2 kg/ha as a chemical tracer. Agral 90 was added to the spray solution at 0.1% (v/v) to better emulate a typical fungicide application. After spraying, each water sensitive paper was allowed to dry, collected and then digitized using a DropScope (SprayX, Sao Carlos, Brazil). Droplet density and percent surface covered were evaluated within the detection limits of the equipment. Dose (represented by deposit volume) was more relevant to this study than percent surface covered, so a spread factor was used to convert area covered to volume. Once the papers were scanned they were subjected to flame emission spectroscopy (FES) (Actlabs – Activation Laboratories Ltd., Ancaster, ON) to determine the amount of copper deposited.

    DropScope digitizing water sensitive paper

    Results

    Deposit area and volume

    Note that papers were placed singly, oriented face-up. This was a missed opportunity to explore abaxial (down-facing) coverage and may have created a small experimental error wherein deposition from copper sulphate would be accounted for on both sides, but would only resolve on one side for area and density analysis. The results from evaluating water sensitive paper suggest trends and serve as quality checks for the experiment.

    The percent area covered on water sensitive papers was affected by nozzle configuration (P<0.0001). Ground rigs produced ~4.0-12.0% area coverage, while aerial produced ~0.7-1.0%. It is not appropriate to compare ground and aerial spraying using water sensitive paper. Water sensitive paper does not reliably resolve deposits under ~60 µm and therefore underestimates the deposits from aerial applications because their spray quality tends to be finer. Further, these figures have not been normalized to reflect the differences in sprayer volume (190 L/ha for ground versus 47 L/ha for aerial).

    The nozzle configurations with the highest percent area covered were produced by the 360 Undercover drop pipes and the TeeJet drop hoses (~9.5-12.0%). Coverage variability increased with percent area covered, but the lower 95% confidence limit with the pipes and hoses still exceed the upper limit of all overhead broadcast nozzles.

    Yield Center 360 UNDERCOVER drop pipes

    When area covered was converted to volume, estimated deposit volume on water sensitive papers was also affected by nozzle configuration (P<0.0001). The estimated volume calculated from deposit area showed fewer statistical differences across nozzle configurations compared to area data. However, once converted, there was no statistically significant difference in the volume deposited by drops or most broadcast methods.

    Copper deposition

    FES residue analysis (i.e. evaluating the amount of copper deposited on targets expressed as mass density) complements the water sensitive paper data. There are some differences that should be noted:

    • All applications sprayed the same amount of tracer per planted area. As such, depositions are more fairly compared with no need for normalization.
    • FES can resolve copper deposits as low as 0.5 µg/sample and may be more sensitive than the WSP method, which does not reliably resolve deposits under ~60 µm.
    • WSP will only resolve coverage on one surface. However, when these papers are subjected to FES, deposits on both sides of the paper will be accounted for, providing a more accurate result.

    As anticipated, there was no correlation between the area coverage or volume estimates and the FES-derived copper deposition data. Estimated copper mass density on water sensitive papers was affected by nozzle configuration (P<0.0001). Analysis showed 56% more copper deposited from the 360 Undercover nozzles (1.75 µg/cm2) compared to the next highest deposition (1.12 µg/cm2) which was from the drop hose configuration (P<0.05). We feel the TeeJet drop hose configuration would have performed better still had the nozzles been directed at the silks, and the alternating broadcast nozzles been omitted and flow redistributed to the nozzles on the drops (see below).

    Copper deposition from the airplane was similar to ground rigs with broadcast overhead nozzle configurations. The airplane deposited ~2x the copper as did the helicopter. It is assumed this is because the rotary atomizer nozzles on the airplane produced a much finer spray quality than the TTI nozzles on the helicopter. This increased the number of droplets considerably and has been shown to produce better coverage, particularly at such low sprayer volumes. Learn more about droplet size and behaviour here.

    Average copper deposition from the Guardian Air nozzle set was similar to all other ground sprayer overhead broadcast setups, but had the highest variability (Between 0.4 and 1.12 µg/cm2). Comparatively, the lower 95% limit of the 360 Undercover drop pipe deposited 3.4x the copper as the lower limit of the Guardian Air.

    Conclusions

    • The best deposition was produced from the Yield Center 360 Undercover drop pipes, followed closely by the TeeJet Duo nozzle body on drop hoses.
    • The deposition from ground sprayers with overhead broadcast nozzles was ~30% less than that of the two drop nozzle systems tested.
    • The deposition from Guardian Air and TTI nozzles were among the lowest of broadcast nozzle configurations with higher variability, but differences tended not to be statistically different (P=0.05) compared to other broadcast nozzles.
    • The deposition from the airplane was similar to the ground rig overhead broadcast applications, but the helicopter deposited the lowest amount of copper overall, likely due to droplet size (see image below).
    Helicopter with air induction TeeJet Turbo TwinJet (AITTJ) nozzles directed backwards.

    Next steps

    In the summer of 2022 we re-evaluated promising nozzle configurations from this study, as well as other application methods (see bulleted list below).

    • Include various RPAAS (remote piloted aerial application systems) designs.
    • Include the Agrotop Beluga drop hose (Greenleaf Technologies, Louisiana, USA) with two nozzle bodies to span the silking zone of the canopy.

    We used water sensitive paper as a qualitative indicator, but folded them to get adaxial and abaxial data. We also used copper deposition to indicate dose. Once the results are analyzed we’ll write a companion article to this one.

    In 2021 and 2022 a separate study was performed to evaluate the efficacy, ease-of-use and return on investment of the Beluga drop hoses in corn. An article describing that work can be found here.

    Thanks to the agrichemical companies, students, equipment owners and operators that donated their time and equipment to make this study possible.

    Bonus

    Watch these very cool slow-motion videos of the airplane and helicopter applications. Note that there is no difference in how the spray behaves once released; It deposits as a function of wind, gravity and momentum and is not “blown in” by the helicopter.

  • Venting Liquid-Filled Pressure Gauges

    Venting Liquid-Filled Pressure Gauges

    Liquid-Filled or Dry?

    Small-plot agricultural sprayers should have a pressure gauge on the wand or boom to ensure accurate application rates. Most are added after-market and the operator has the choice of buying liquid-filled or dry gauges.

    Glycerine- or silicone-filled gauges are preferred because they dampen pressure spikes, pulsation and mechanical vibration. Compared to dry gauges, they are available in higher ranges and are less prone to moisture problems (which cause corrosion, accuracy and visibility issues).

    We use 100 psi (~7 bar) liquid-filled gauges for our handheld sprayers. Only recently did we acknowledge the sticker affixed to the glass advising the user to cut the nipple off the rubber plug located at the top. Preferring to avoid messy leaks, we have always left it intact.

    We wondered what impact, if any, this was having…

    What are Vents?

    Expensive gauges have mechanical vents that can be opened prior to use and closed to retain liquid when stored. More commonly, there is a rubber plug with a protrusion (referred to as a nipple).

    Why Vent?

    Mechanical, liquid-filled gauges are sealed to keep the liquid in. When there are temperature fluctuations, the liquid expands or contracts and creates “case pressure”. This exerts a force that interferes with the pressure reading.

    According to Marshall Instruments, case pressure can offset the accuracy by approximately 1 psi (0.07 bar) for every 35˚F (20˚C) temperature change, but is only noticeable when measuring lower pressures (0-15 psi or 0-1 bar). Nevertheless, they advise all gauges should be vented prior to use.

    The plug can be removed to allow the user to refill the gauge, maintaining an air space of about ½” at the top of the window. If the nipple is cut off, the gauge is permanently vented and will leak if the gauge is not kept vertical.

    Testing

    We performed an experiment to see if typical working temperatures had a practical impact on the accuracy of an unvented gauge. We suspended an unvented, liquid-filled gauge upright in a water bath at approximately 15˚C, 30˚C or 45˚C (59˚F, 83˚F or 113˚F) until it equilibrated. The high temperature may seem unreasonable, but gauges left in trucks on summer days get far hotter.

    The gauge was quickly removed and placed in a manometer (Ametek T-975) where it was subjected to pressures of 15, 30 and 45 psi (1 bar, 2 bar and 3.1 bar) and readings recorded. This was repeated five times. We then vented the gauge and repeated the process.

    Results

    At first, there appeared to be very little difference in average accuracy of vented and unvented gauges. Accuracy refers to the closeness of a measured value to a standard or known value. Perhaps there was some small increase in the pressure reported by an unvented gauge, but very little practical difference.

    However, when we look at variability we get a different picture. Variability is a measure of precision, which refers to the closeness of measurements to one another. The graphs show that an unvented gauge has greater variability (less precision) at lower temperatures and lower pressures.

    A good way to think of accuracy and precision is using the classic archery bulls-eye metaphor. The unvented pressure gauge is best represented by the third image, where it is accurate (on average) but not precise (variable).

    Real-World Example

    What does this mean in practice? Consider someone spraying a small plot using a TeeJet XR8002 nozzle on a CO2-powered hand boom at 30 psi. The difference in output between 30 psi and 40 psi is about 0.003 gpm / psi.

    An unvented pressure gauge used on a hot day may read 1.5 psi lower, causing you to overcompensate and raise the pressure 1.5 psi higher than intended. That would result in 0.0045 gpm (0.5%) more applied. Compensating for an unvented gauge on a colder day might be closer to 0.009 gpm (1%) more applied.

    Assuming a walking speed of 3.1 mph (5 km/h) and a swath of 20” (50 cm), the nozzle should emit about16.3 gpa at 30 psi. Unvented in the heat, that’s 16.7 gpa. At 33 psi, that’s 17.15 gpa. That’s almost 1 gpa more than intended. Potentially, the lack of precision could make a significant difference.

    Conclusion

    • Liquid-filled gauges are preferred over dry gauges.
    • To ensure precision, the gauge should be vented prior to use.
    • Permanent venting on a hand-held sprayer causes leaks, which is a nuisance, so we suggest simply lifting the edge of the plug with a screwdriver or fingernail to vent the gauge prior to each use.

    This work was performed by OMAFRA summer student, Aidan Morgan.

  • Paint it black – Parody

    Paint it black – Parody

    Never fail, as spring turns to summer we get questions about algal growth in water tanks. There are lots of suggested solutions, but questions about pH antagonism and phytotoxicity seem to linger. In 2021/22 we ran trials to explore how well home-grown algicides like copper, bleach, and ammonia work, and whether they cause antagonistic responses when that carrier water is used on crops. You can see the results here.

    Anticipating those results, we wrote this parody on a Stone’s classic. Not long after it was brought to life by the brilliant minds behind Michigan’s epic podcast “The Vegetable Beet” (Go subscribe right now!). You can hear it in the link below, where Ben Phillips is accompanied by his daughter’s toy tambourine. Crank it up to 11!

    You can even download Ben’s sheet music here.

    I see a white tank and I want it painted black
    No algae anymore, I want my water back
    I see the cart drive up while spraying summer rows
    I have to dump it out until the algae goes

    I see my neighbours’ tanks and they’re all painted black
    With copper sulfate they claim algae won’t come back
    I see them turn their heads and quickly look away
    They see my algae grow in sunlight every day

    I look inside the tank to see if it is black
    I could park it in the shed, or in the shade out back
    Maybe then it’ll fade away and I can face the facts
    It’s not easy filling up when your filters plug with crap

    I wish that my green sea would turn a deeper blue
    If you try chlorine pucks it will clear up for you

    I’ll store my tanks away from that bright summer sun
    Then I’ll spray algae-free before the mornin’ comes

    I see a clean tank ‘cause I had it painted black
    No algae anymore, I got my water back

    I see the cart drive up while spraying summer rows
    Clear water coming out, and no more clogging woes

    Hmm, hmm, hmm
    Hmm, hmm, hmm
    Hmm, hmm, hmm
    Hmm, hmm, hmm

    I want to see your tank painted black!
    Black as night!
    Black as coal!
    I wanna see the bugs, knocked right out of the sky
    I wanna see it painted, painted, painted black, yea!