Author: Jason Deveau

  • Wheat Head Coverage from Rotary Drones

    Wheat Head Coverage from Rotary Drones

    Editor’s Note: This work was performed in 2023. A more recent exploration into wheat head coverage was performed in 2025. This article is not obsolete as it introduces concepts and makes foundational observations. Read on, then read the 2025 article afterwards.

    Fusarium head blight is one of the most economically important diseases in winter wheat. Application timing is arguably the most critical aspect of effective crop protection. The application window stretches some two to five days following the point where 75% of the wheat heads are fully emerged and coinciding with the beginning of flowering (Figure 1). Product placement is the second most critical aspect, where the wheat head represents the primary target, and the flag and penultimate leaf are somewhat incidental, secondary targets.

    Figure 1. Winter wheat at T3 staging is optimal for fungicide application.

    This article describes the results of two experiments exploring wheat head spray coverage from a rotary drone. The first compares wheat head coverage from a drone to that of a helicopter (Figure 2). The second explores the effect of drone ground speed, and the related downwash, on wheat head coverage. All work was performed under PMRA research authorization. As of the date of this publication, there are no crop protection products permitted for application by RPAS in Canada.

    Figure 2. The helicopter spraying in background does not create a downwash. Note how the spray is not forced straight down but falls in a sheet subject to gravity and inertia. The rotary drone spraying in the foreground does create a downwash. Note how the wheat is displaced by the spray-laden air as the drone passes. At higher speeds, this downwash does adopt a down-and-back vector.

    Experimental Design

    Wheat field

    The wheat field was clay/loam located at 42°47’12.6″N 81°03’06.4″W near New Sarum, Ontario. Wheat was “common seed” planted on October 2nd, 2022, at 1.8 million seed/ac on 19 cm (7.5 in) row spacing. It was sprayed on June 5th, 2023, and at the time the wheat heads were about 0.7 m (2.5 ft) high.

    Treatments were laid out parallel with the planting direction in a randomized design. The helicopter pilot reported an effective swath width of 13.7 m (45 ft), which formed the basis for the treatment block widths (Figure 3). The helicopter made a single pass. The drone pilot reported an effective swath width of 4.5 m (14.75 ft). It made three passes per treatment block in the helicopter versus drone experiment but made only a single pass centred on the treatment block for the speed experiment.

    Both the helicopter and drone applied fungicide at label rate plus 0.125% Activate in a final volume of 50 L/ha (5 gpa). For the helicopter this was about 20 ac. per jug, and for the drone we created an equivalent tank mix using 450 ml fungicide and 37.75 ml Activate diluted with water to fill the 30 L spray tank.

    Figure 3. Treatment layout for both experiments. H: Helicopter. D: Drone. Yellow rectangles represent location of water sensitive papers on a 1.75 m (5.75 ft) spacing, centred on the treatment block. Flight paths were centred on the treatment block.

    Helicopter versus drone experiment

    For the helicopter treatments, five water sensitive papers (WSP) were spaced 1.75 m (5.75 ft) apart, centred on the treatment block. For the rotary drone passes, two rows of WSP were spaced 1.75 m (5.75 ft) apart, centred on the treatment block. Application volume was 50 L/ha (5 gpa)

    The helicopter had a 20 foot boom with CP-03-05 nozzles on 12” spacing, alternating between a 0.062 (smallest) orifice and a 0.172 (largest) orifice. Ground speed was 96.5 km/h (60 mph) and altitude ranged from 1.5-3 m (5-10 ft) above the wheat heads. The contractor company calibrated the helicopter according to their standard operating practices.

    The rotary drone was a DJI Agras T30 equipped with TeeJet TT110015’s. It flew at 5.1 m/s at 3 m above the wheat heads and applied three adjacent swaths of 4.5 m. The contractor company calibrated the drone according to their standard operating practices. A similar methodology can be found here.

    Drone speed experiment

    A single pass was made over three rows of WSP spaced 1.75 m apart, centred on the treatment block. The drone made two separate passes (n=2) for each speed. Samplers were retrieved and replaced after each pass and the same plot was used for all six passes. Application volume was 30 L/ha (3 gpa). Drone was refilled after every two passes to maintain a consistent weight.

    The rotary drone was a DJI Agras T40 programmed to apply an “Extra Coarse” spray quality at 3.5 m above the wheat heads with a swath width of 9 m. Ground speeds were 2 m/s, 4 m/s and 7.2 m/s and were visually confirmed by the RPAS controller. Once again, the contractor company calibrated the drone according to their standard operating practices.

    Target Locations

    For both experiments, SpotOn brand WSP from the same production run was pre-curled by wrapping it around a pencil, then wrapped around the wheat head and secured at the bottom by a small, spring back paper clip (Figure 4). This left approximately 1.5 x 1 inches (i.e. half) of the surface exposed to spray and provided an indication of panoramic coverage.

    The clip distorted the target by flattening it at the bottom and obscured a small portion of the target area, but this area was digitally removed during the analysis. By securing the WSP to the wheat head rather than a surrogate stake, the target moved naturally in the downwash of the drone. The papers were retrieved when dry, placed in individual plastic bags, flattened for scanning, and digitized using a DropScope within 24 hours of retrieval.

    Figure 4. Pre-curled water sensitive paper was wrapped around the bottom of the wheat head and secured with a spring back paper clip.

    Weather and Application Times

    Weather data was collected using a Kestrel 3550AG weather meter (Kestrel Instruments) in a vane mount positioned 1.5 m (5 ft) above the wheat heads. Wind speed fluctuated throughout the day, but wind direction remained relatively stable at 90 degrees to the flight path. Targets remained within the swath, despite any offset, as indicated by the consistent coverage observed on the windward WSP compared to other, downwind samplers in each pass.

    Application methodPass #TimeWindspeed (km/h)Temperature (°C)
    Helicopter18:452.017.0
    Helicopter210:004.517.7
    Helicopter310:204.819.9
    Agras T30110:204.819.9
    Agras T30210:455.219.7
    Agras T30311:008.620.0
    Agras T40112:258.221.6
    Agras T40213:004.822.4
    Agras T40313:305.222.8
    Wind direction remained a steady side wind (i.e. 90 degrees) to the flight path throughout day. Sky was clear (i.e. minimal to no cloud cover) throughout day.

    Results and Analysis

    WSP were scanned and digitized. Coverage was measured as percent surface covered (% area), and deposit density (# deposits/cm2). Given that only ½ of the WSP was exposed to spray, and the remining half was obscured during the wrapping process, the entire card was scanned, and the resulting coverage was doubled.

    Helicopter versus drone experiment

    For each helicopter pass, a single line of five WSP were averaged to a single data point. Therefore, n=3, but represents 15 WSP samplers. For the drone, two lines of three papers were placed in the block. Each line was averaged to a single data point, for n=2 per pass x 3 passes for a total of n=6, representing 18 WSP samplers. The following image (Figure 5) shows a digitized WSP typical of each method.

    Figure 5. Typical WSP from helicopter and drone applications at 5 gpa. Recall that only half the paper (the right half, in this case) was exposed following the wrapping process.

    The following histograms (Figure 6 and 7) illustrate the mean coverage for each application method, with standard error.

    Figure 6. Average wheat head coverage (percent area) by application method. Drone is n=6 and Helicopter is n=3. Bars represent standard error.
    Figure 7. Average wheat head coverage (deposit density) by application method. Drone is n=6 and Helicopter is n=3. Bars represent standard error.

    The drone covered an average 17% more surface area than the helicopter. The spray quality was visibly finer, as evidenced by the average 64% higher deposit count. As a matter of context, we ran a similar study four days later with a field sprayer running TeeJet AITTJ60’s on 38 cm (15 in) centres, 50 cm (20 in) above the wheat head. It applied 175 L/ha (19 gpa) compared to the 50 L/ha (5 gpa) applied by the helicopter and drone. The relative percent area covered is shown in Figure 8.

    Figure 8. Average wheat head coverage (percent area) by application method. Drone (5 gpa) is n=6, Helicopter (5 gpa) is n=3 and Field Sprayer (19 gpa) is n=6. Bars represent standard error.

    The more than fourfold difference in coverage from ground versus aerial application is significant, but given the relative concentrations of product applied (i.e. the same product rate) residue levels would likely prove equivalent for all treatments. Fungicide efficacy cannot be predicted from coverage data, but the convention is that the more surface area covered, the better the protection.

    Drone speed experiment

    The drone made two separate passes over each treatment block. For each drone pass, three lines of three WSP were placed in the block. Each line of three papers was averaged to create a single data point, for n=3 per pass and n=6 in total. The following histograms (Figures 9 and 10) illustrate the mean coverage for each application method, with standard error.

    Figure 9. Average wheat head coverage (percent area) by ground speed. Each speed is n=6. Bars represent standard error.
    Figure 10. Average wheat head coverage (deposit density) by ground speed. Each speed is n=6. Bars represent standard error.

    As an aside, note that the average is approximately 2% surface area for these 30 L/ha (3 gpa) applications compared to the 3.6% average at 50 L/ha (5 gpa) in the drove versus helicopter experiment, reflecting the results from many studies that show employing higher water volumes results in improved coverage until some point of diminishing return.

    The drone appeared to cover approximately the same surface area at all three speeds. However, when deposit density is considered, the slowest speed deposited 31% more droplets than the medium speed, which in turn deposited 23% more droplets than the fastest speed.

    One possibility is that higher speeds, which are known to create wider swaths, dispersed the spray over a larger area. Another possibility is that higher speeds, which are known to increase drift potential, left a greater proportion of droplets aloft, beyond the reach of the samplers. Yet another non-exclusive possibility is that deposit counts increased while overall surface coverage remained approximately equal because the diameter of the stain increased with speed. DropScope reports stain diameter, and this has been graphed alongside the deposit counts in Figure 11.

    Figure 11. Deposit counts share an inverse relationship with ground speed, but average stain diameter shares a direct relationship with ground speed.

    We see an inverse relationship between ground speed and deposit density, but a direct relationship between ground speed and stain diameter. This difference may appear small, but assuming stains are approximately circular, diameter can be used to calculate deposit area, per the following table.

    Drone Ground Speed (mph)Mean Coverage (%)Mean Deposit Density (#/cm2)Mean Stain Diameter (µm)*Mean Stain Area (µm2)
    4.52.088.4815,153.0
    92.261.388.36,124.0
    16.11.949.993.36,793.0
    *Assumes a circular deposit

    We see an increase in average deposit area of 16% and 10%, respectively, for each increase in speed. In previous trials conducted in corn in 2022 we saw a decrease in coverage and an increase in drift when drone ground speed was increased. We also observed that as the T40’s ground speed increased, the swath width appeared to increase. We did not measure effective swath width at different speeds, but if this observation is correct then droplet density by area would decrease at higher speeds. The loss of spray to drift and/or through increased swath width would explain why increased speed resulted in fewer deposits on the wheat heads.

    The increased deposit diameter is likely due to spread factor. Higher ground speeds would impart a higher droplet velocity and therefore cause droplets to spread more on impact. If this is the case, and had we conducted residue trials, we would predict an inverse relationship between ground speed and residue levels, despite having similar percent surface coverage. This observation underpins the importance of assessing deposition patterns as well as residue in coverage trials.

    Conclusions

    • For this use case, a drone applying 50 L/ha (5 gpa) produces a similar, if slightly higher, percent coverage on a wheat head compared to a helicopter applying the same volume. However, the deposit density is considerably higher.
    • Corroborating previous results in corn, drone application volume has a direct relationship with spray coverage.
    • For this use case, drone ground speed does not appear to affect the percent wheat head area covered, but there is an inverse relationship with deposit density. We theorize based on the direct relationship between ground speed and deposit spread, and prior evidence of increased drift with higher ground speed, that less active ingredient is deposited on the wheat head at higher ground speeds.
    • The relationship between downwash (i.e. dwell time, which is a function of downwash air energy and ground speed), wheat movement and coverage is unclear.

    Acknowledgements

    Thanks to Zimmer Air, Drone Spray Canada, Bayer Canada, Grower-Cooperator Adam Pfeffer and OMAFRA SEO student Vanessa Benitz.

  • Spraying from Seven to Seven (or) Drop Pipes Next Season – Parody

    Spraying from Seven to Seven (or) Drop Pipes Next Season – Parody

    We were long overdue for a new classic rock parody, so we decided to re-tackle one of the greatest rock ballads ever written. With the ongoing success of drop pipes (aka drop arms, drop legs, etc.) in corn, we’re promoting directed spraying in verse.

    If you’d like to read more about the research, check out this article, and this one too. Farmtario also wrote a nice summary from one of our 2022 demos.

    So, this was a tough one, but we feel good about how we laminated a new message over Zeppelin’s tricky cadence and rhymes. It helps if you play the actual song as you read. Rock on:

    There’s a grower who’s sure
    all corn glitters like gold
    and he’s spraying from seven to seven.

    When he’s done, then he knows
    that the products he chose
    will handle the pests that he sprayed for.

    Ooh ooh ooh ooh ooh
    And he’s spraying from seven to seven.

    He sees signs on them all
    but he wants to be sure
    ‘cause he knows bug poop means that they’re feeding.

    So, he stops for a look
    spits and wipes as he should
    sometimes all of his thoughts are misgivings.

    Ooh, it makes him wonder
    Ooh, it makes him wonder

    There’s a feeling he gets
    when the silks seem too wet
    and his scouting is slowly revealing.

    In his fields he has seen
    in the irrigation rings
    that tarspot’s in the plot where he’s standing.

    Ooh, it makes him wonder
    Ooh, it really makes him wonder

    Maybe he sprayed the corn too soon
    Or too late, it could be too
    ‘cause the timing defies common reason.

    And he goes back in the dawn
    to see what else has gone wrong
    and his checks echo pests that he’s after.

    Oh whoa-whoa-whoa, oh-oh

    If there’s cutworm in your corn row, don’t be alarmed now.
    It may have been coverage or timing.

    But there’s a new way, you can spray now, and in the long run
    there’s time to change the for the next season.

    And it makes him wonder
    Oh, whoa

    Overhead spraying is a no-go
    in case you don’t know
    drop pipes are calling you to try them.

    Diseases come in when the wind blows
    but did you know
    drop pipes cover stalks from end-to-end.

    So, as you drive on down the row
    overhead spray just won’t go
    deep into targets, we all know
    are hard to hit deep down below.

    Next year he can still have gold.
    Using drop pipes isn’t hard.
    Coverage will come to him at last.

    Quick to mount, one and all, yeah
    They barely rock as sprayers roll    .

    And he’s using drops from seven to seven.

  • Airblast Sprayers for Small Operations

    Airblast Sprayers for Small Operations

    Did you come here looking for advice on which sprayer is best for your small operation? Are you looking to ditch the backpack mist blower? Do you want to avoid repeatedly mounting and dismounting a 3-pt hitch sprayer from your only tractor? Are you concerned you’ll have to sell an organ to be able to afford one? We hear you, and we’ll try to help. Let’s set the stage with a few facts.

    Airblast sprayers stay in service for a long time; more than twenty five years is not unheard of. The majority of them are the generalist, PTO-driven low profile radial design with capacities ranging 150 to 1,200 gallons. Typical fan diameters are around 30″ and can produce >40,000 m3/h of air, making them a good fit for most pomme, citrus and tender fruit canopies. These sprayers come with a horsepower price tag of perhaps 45 hp or more. Many of these sprayers eventually enter the used sprayer market, making them an affordable option for small acreage specialty operations. But, affordability should not be the sole motivation when choosing a sprayer.

    Ontario, c.1980 and probably still out there spraying somewhere!

    The key to optimizing sprayer performance is to match the air settings to the the canopy you’re trying to spray. You can start reading about the process here. In the case of small and medium-sized canopies like vine, cane and bush crops, the fleet of gently-used sprayers we just described tend to produce too much air. There are options to improve the fit, like driving faster to reduce dwell time, or perhaps the operator can employ the Gear-up Throttle-down method. But, the best plan is to employ a smaller sprayer, which produces a more appropriate air volume, has a smaller profile, delivers better fuel efficiency and won’t break the bank.

    So, where are these sprayers? Unfortunately there aren’t many, and options are especially limited if you don’t own a tractor to power them.

    The budget-conscious grower may be tempted to buy a sprayer that does not have air-assist. We do not recommend this. Air is a critical component for spraying canopies consistently and efficiently. Caveat Emptor!

    We encountered a good solution in June, 2014, when we were invited to Durocher Farm in New Hampshire to see their new airblast sprayer. In years previous, spotted-wing drosophila (SWD) was a significant pest in this two acre, high bush blueberry planting. They claimed that since buying their new sprayer they no longer had any trouble with SWD. That’s quite an endorsement!

    The Carrarospray ATVM (200 L pictured)
    The Carrarospray ATVM (200 L option pictured)

    I’m not sure what I expected, but I was captivated by this miniature orchard sprayer. The toy-like size carried a zero-intimidation factor and I immediately wanted to start using it. Italian-made, Carrarospray’s hobby line is designed to be pulled behind vehicles without PTO. The ATVM is available in capacities from 120-400 L. The one I saw had a 400 L capacity, adjustable air deflectors, a fan speed gear box, and it was powered by a quiet and efficient pull-start Briggs & Stratton four-stroke engine. It even had a trash guard, a kick-stand and a clean water tank for hand washing. That’s a lot of features.

    Thanks to Kitt Plummer (Durocher Farm), Penn State, Univ. New Hampshire and Chazzbo Media for filming these 2014 videos:

    The sprayer was pulled (in this case) by a mower, so the grower not only sprayed, but mowed his alleys at the same time. It fit beautifully between the bushes, so the potential for physical damage to the berries was minimized. The air speed and volume was enough to displace the air in the blueberry canopy and replace it with spray-laden air with minimal blow-through. Combined with an appropriate spray volume and distribution over the boom, we found that the coverage it provided was excellent.

    Coverage from the top-centre of the bush. Card is 2x3 inches.
    Coverage from the top-centre of the bush.

    Since seeing this sprayer, we have had reports that importing it to Canada has proved challenging. But there are alternatives. A few companies here in North America offer economy-sized airblast models that are ATV trailed, or skid-mounted, or attached to a small tractor via a three point hitch. PBM’s Lil Squirt is a simple and versatile option. Available primarily in the western US from California through to Washington.

    PBM’s trailed Lil Squirt (Image from their website)

    Another option is the mounted, PTO-driven mistblower line from Big John Manufacturing in Nebraska.

    BJ 3PT mistblower from Big John Manufacturing (Image from their website)

    Or MM Sprayer‘s ATV sprayers, which come PTO or Engine-driven. The LG400 has a 106 gallon tank and a 20″ fan. I’d like to see deflectors, but you could easily add them. Here’s a 2024 pdf on features.

    Picture of the LG400 engine-driven model from www.mmsprayers.usa

    Or Wisconsin’s Contree Sprayer and Equipment. They carry the “Terminator” line. Skid mounted, one-sided air shear units with capacities from 15 to 100 gallons, this company offers a range of possibilities both PTO and gas-driven. Well worth a look.

    The “Terminator” skid-mounted mist blower from Contree Sprayer and Equipment (Image from their website)

    Then there’s the A1 Mist sprayer series, also out of Nebraska. They carry the Terminator line as well as an interesting two-sided volute option that employs conventional nozzles and allows one pass down an alley rather than two. This is a big productivity booster:

    A1’s two-way volute header. (Image from website)
    A1’s PTO-driven 60 gallon, skid-mounted “Terminator”. (Image from website).

    Then there are larger, PTO-driven, three-point hitch options. In fact, there are many options for this manner of sprayer, but they tend to be out of the price range for small operations, and they do require a tractor. That isn’t a deal-breaker, though, as they can sometimes be found used. Pictured below is British Columbia’s Major 193 (Slimline Manufacturing) and a Brazilian-made option (Jacto) distributed out of Quebec.

    Slimline Manufacturing (aka Turbomist) makes the Major 19P 3-pt hitch tower sprayer (PTO-driven)
    Jacto’s Arbus 200 3-pt hitch airblast sprayer (PTO-driven)

    When considering your options, give serious thought to your work rate, refill time and other factors that go into developing a robust spraying strategy. What’s a spraying strategy? That’s a farm’s overall management and operational plan for achieving safe, effective and efficient spray coverage. You can read more in chapter 8 of Airblast101, which you can download for free, here. And, just to play Devil’s Advocate, go small but not so small that the sprayer is underpowered.

    We staged this video in 2011 (spraying only water, so don’t mind the lack of PPE) to show how a sprayer can be too small for an operation. This 3-pt hitch GB cannot overcome the cross wind and the spray barely reaches the apple trees. Reducing travel speed and increasing pressure won’t cut it, either.

    Of course, other possibilities are emerging for crop protection in small acreage perennial crops. Multirotor drones are capable of delivering air-assisted spray from above the canopy. While it’s still a drift-prone and inconsistent means for broadcast spraying, it might lend itself to perennial row crops. Equipment design is evolving quickly and global research is underway to establish best practices. As regulators and agrichemical companies focus more on this method we may see drones as a cheap alternative to a tractor/airblast sprayer, with no compaction, no mechanical damage to fruit/berries, and no potential for splashing infection throughout an operations.

    DJI’s Agras T30

    Even further into the future, small autonomous sprayers may be viable, too. Very much in their early days there is great potential. One example is the XAG Revospray Ground 2 with it’s 150L capacity or the R150 with it’s 100 L capacity.

    The R150 – Image from https://hse-uav.com/. Modular system and ~32K USD (as of 2023)… if you can find one.

    It’s early days, but there are researchers looking at the spray pattern from these units. The image below may not be a fair indication because the nozzle used may not have produced as wide a swath as possible. Thanks to Dr. M. Reinke for the image.

    A test pass using food grade dye. You can see the waveform created by the two spray heads as they move up and down during travel.

    And recently, small autonomous platforms have become more common. Perhaps there’s an opportunity to place a gas powered sprayer on these platforms, or use them to pull a hitch-style sprayer. One such possibility is created by the Burro, shown below at the Ontario Fruit and Vegetable Convention in 2024.

    The Burro autonomous platform.

    Are you aware of a sprayer that’s not in this article? Let us know! Good luck and make sure you have only slightly more “sprayer” than you need.

  • Evaluating Methods for Controlling Algae in Carrier Water Storage Tanks

    Evaluating Methods for Controlling Algae in Carrier Water Storage Tanks

    This work was performed with Mike Cowbrough, OMAFA Field Crop Weed Specialist.

    In the early summer months, many field and specialty crop operations collect rainwater (or possibly pump water from holding ponds) into storage tanks for use as a carrier in spray applications. These tanks may be stationary, or they may be part of a nurse or tender truck that delivers both water and chemistry to the field as a means of improving operational efficiency.

    Poly tanks. Source: Purdue Extension publication PPP-77 “Poly Tanks for Farms and Businesses“.

    In the case of translucent poly tanks, which are commonly used because of their light weight, custom shape, and low price point, light exposure will grow algae. Algal populations multiply exponentially and will clog spray filters and negatively affect filling. In response, growers use home-grown algicides such as copper sulfate, lengths of copper pipe, household bleach, chlorine, bromine, etc. They do so with little or no guidance and therefore little or no consistency. Beyond the obvious questions surrounding efficacy, it is unknown whether these adjuncts create physical or chemical incompatibilities in the tank mix. If so, there is the potential for reduced efficacy and/or crop damage.

    We tested popular methods for algae control by inoculating a series of 10 L translucent plastic jugs with an algal population sourced from a southern Ontario holding pond. The population was left to acclimate and generally establish itself (aka colonize) before we introduced some form of control. Each jug was then gently stirred and emptied through a sieve for qualitative assessment.

    In a parallel experiment, we introduced the same algicides to fill water and conducted spray trials. 10 L volumes were mixed with a field rate of glyphosate and sprayed on RR soybeans. Weed control was assessed and soybean yield measured for each treatment.

    Algicide Efficacy Experiment

    In each treatment, tap water was mixed with a micronutrient growth media (from the Canadian Phycological Culture Centre at the University of Waterloo). This was an unsterilized 10% WC(ed) solution intended to provide micronutrients for algal growth while minimizing fungal and bacterial growth.

    The source algae were collected from the bottom of a holding pond from a farm in Guelph, Ontario. Algae were homogenized and equal parts added to each jug. The jugs were former 10 L pesticide containers thoroughly rinsed and sprayed with Five Star’s “Star San” non-rinse sterilizer. Tank solutions were gently bubbled (one bubble every 10-15 seconds) with air from an aquarium pump. Air was balanced using a manifold and introduced via diffusion stones at the bottom of each jug.

    Algae sourced from a farm’s holding pond near Guelph, Ontario. Algae was homogenized before inoculating treatment jugs with equal parts.

    Treatments

    Each treatment was tap water plus growth media inoculated with algae and exposed to a natural diurnal/nocturnal cycle unless otherwise indicated.

    1. Control (no algicide)
    2. Left in a shaded area (no direct sunlight)
    3. Household bleach (approximately 5.25% sodium hypochlorite)
    4. Container was spray-painted black to exclude light
    5. Ammonia
    6. “Scotch Bright” copper-coated scour pad. (copper is often introduced as copper sulfate at 1 cup / 1,000 US gal. or a short length of copper pipe)
    7. Bromine (sourced from a local pool supply store)
    Treatment NumberTreatment NameRate
    (/US Gal.)    		Rate
    (% v/v)    		Rate
    (/10 L final volume)
    1Control (no algicide)
    2Shaded
    3*Household bleach1/4 tsp0.000333.3 mL
    4Black container
    5*Ammonia solution1/4 tsp0.000333.3 mL
    6Copper-coated scour pad
    7Bromine1/32 ml0.0000040.04 g
    Table 1. * Bleach and ammonia should never be added together as they produce toxic chloramine gas.

    Method

    On July 12, jugs were loaded with water and growth media and inoculated with algae. They were bubbled gently for one week to establish a stable algal colony. On July 19, algicides were added, or transferred to shade or black-out conditions. On August 31 (approximately six weeks later), jug contents were gently stirred and filtered through white cloth for qualitative assessment.

    Building up algal population for each jug. Note air lines through lids for slow, intermittent bubbling. Algae was not moved to black container or to the shade until after the first week of acclimation.
    Almost six weeks after algicide was added, jug contents were gently stirred and poured through white cloth to collect algae and establish how easily the liquid passed through.

    Observations

    The results of all seven treatments, plus photos of the copper-coated scour pad.

    (1) Control. Liquid poured slowly through cloth. Algae was still alive and healthy. It formed some clumps but was not as thick as other treatments.

    (2) Shaded. Liquid poured fast and easily through cloth. Was particulate in texture rather than clumpy or gelatinous. Very little mass and entirely brown, suggesting it was dead.

    (3) Household bleach. Liquid poured easily through cloth until the clump of algae sitting at the bottom of the jug came out (i.e., most algae were not suspended). Thick mat of healthy-looking algae (note profile photo #3 below). Much greener and thicker than the control (1).

    (4) Black container. Liquid poured fast and easily through cloth. Algae retained a little green coloration (more than the shaded condition (2)) but was particulate and not as healthy as the control (1). We intended for this treatment to exclude all light, but it was still able to enter at the bottom where the jug wasn’t completely painted. This may have kept the algae alive.

    In an oversight, the jug was not completely painted. This left a source of light at the bottom edge that may have helped sustain algae.

    (5) Ammonia. Very difficult to pour liquid through the cloth (note profile photo #5 below). The only condition where a mat of algae was floating at the top of the jug rather than settled at the bottom. It was healthy, green and thick.

    (6) Copper. The most gelatinous of all conditions, the liquid took the longest to pass through the cloth filter. While the algae seemed brown and dead, the gel would be very problematic during sprayer filling and spraying. Note that the copper scouring pad (shown unrinsed) has nothing growing on it.

    (7) Bromine. Like the household bleach condition, liquid poured easily until the healthy mat of algae at the bottom of the jug came out (i.e., most algae were not suspended). Note profile photo #7 below.

    Profile shots of treatment 3 (Bleach), 5 (Ammonia), and 7 (Bromine).

    Spray Efficacy Experiment

    Ideally, adjuncts added to carrier water are inert. That means they don’t reduce a herbicide’s effectiveness on susceptible weeds or increase crop injury. For example, hypochlorite (found in bleach and in chlorinated water) reduces the biological effectiveness of low concentrations of isoxaflutole (the active ingredient in herbicides such as Converge and Corvus). However, when added to higher, agriculturally-relevant concentrations, the reduction in efficacy wasn’t considered significant (Lin et al., 2003). Conversely, bromide has been added to certain herbicides to improve performance (Jeschke, 2009).

    There’s precious little information about synergistic or antagonistic effects from adding bleach, ammonia, copper or bromine to herbicide carrier water. To learn more, we added each of these adjuncts to the standard rate of glyphosate (900 gae/ha – 0.67 L/ac). Using a CO2-pressurized plot sprayer, the solution was applied to <10 cm tall weeds at 150 L/ha (15 g/ac) in glyphosate tolerant soybean at the 2nd trifoliate stage of growth (Elora Research Station, Ontario).

    Visual crop injury was evaluated at 7 and 14 days after application. Weed efficacy was evaluated at 14 and 28 days after application. Soybeans yields were collected using a Wintersteiger plot combine and adjusted to a moisture content of 14%.

    Weed Control

    All treatments provided excellent control (>90%) of the weeds emerged at the time of application. Table 2 (below) presents the % visual control 28 days after application.

    Carrier Treatment
    (glyphosate 540 g/L at 900 gae/ha or 0.67 L/ac)    		Lamb’s-quarterGreen pigweedWitch grassGreen foxtail
    1) Control0000
    2) Shaded100100100100
    3) Household bleach100100100100
    3a) Household bleach – added prior to mixing9597100100
    4) Black container100100100100
    5) Ammonia100100100100
    6) Copper-coated scour pad100100100100
    7) Bromine100100100100
    Table 2. Visual control of lamb’s-quarter, green pigweed, witch grass and green pigweed at 28 days after the application of glyphosate 540 g/L at 900 gae/ha mixed with various carrier treatments intended to prevent algae growth. Treatment numbers correspond with the soybean injury and yield image below.

    Soybean Injury and Yield

    There was no noticeable crop injury from any treatment (figure below) and yields were not significantly different from the control treatment (Table 3). However, when bleach was added prior to mixing, we did observe a trend in reduced soybean yield. We’re unable to explain this observation, but suggest it may be an unrelated issue (such as field variability). There were no obvious signs of crop injury, and the treatment provided excellent weed control.

    Photographs of each plot 14 days after application. The number/letter in each inset image corresponds to treatments in Tables 2 and 3.
    Carrier Treatment
    (glyphosate 540 g/L at 900 gae/ha or 0.67 L/ac)    		Crop Injury
    (%)*    		Avg. Yield
    (bu/ac)    		Significance**
    4) Black container040.0A
    7) Bromine039.6A
    2) Shaded038.1AB
    3) Household bleach037.6AB
    1) Control037ABC
    5) Ammonia036.9ABC
    6) Copper-coated scour pad036.1 BC
    3a) Household bleach – added prior to mixing034.0 C
    Table 3. Visual control of lamb’s-quarter, green pigweed, witch grass and green pigweed at 28 days after the application of glyphosate 540 g/L at 900 gae/ha mixed with various carrier treatments to prevent algae growth. *7 days after application. **Duncan’s multiple range test. Soybean yields that don’t share a letter in common are significantly different.

    Discussion

    We elected to use an extreme situation where a single application of algicide was applied to an established, healthy colony. It’s possible that regular applications of algicide in a volume of water with little or no algae could maintain that condition.

    A treatment was considered effective if it slowed or halted algal growth, especially if it also degraded algal populations, causing them to become brown, thin, and/or particulate. Once in the spray tank, the shear forces created by circulation should disperse any dead or degraded algal masses, making it easier to pass them through filters and nozzles.

    The shade treatment appeared to kill algae as well as cause degradation. Second place went to the black-out treatment, where some light was unfortunately allowed in. This would have continued to fuel photosynthesis in the unpainted portion at the bottom of the jug. Conversely, the black exterior likely raised temperatures above >20 °C, which depresses most algal growth and may have contributed to the degradation.

    Copper appeared to kill the algae but also created a gel that would pose problems to filters. Unlikely to be bacterial, as copper is known to suppress bacterial growth, it could have been caused by diatoms; certain invasive species are known to form brown jelly-like material endearingly referred to as “brown snot” or “rock snot”. Alternately, and according to work by J. Rodrigues and R. Lagoa, alginate polysaccharide can form viscous aqueous dispersions (such as gels) in the presence of divalent cations (such as copper).

    No treatment appeared to reduce herbicide efficacy or affect crop health. However, unexpectedly, the household bleach added prior to mixing may have reduced soybean yield. Given the limited number of replications and the single plot location, we suspect this was a field effect, unrelated to the treatment.

    Take Home

    Based on these results, a combination of shade and light-excluding materials (e.g. black paint) would be the ideal approach to algae control. It’s cheap, effective, and doesn’t require periodic management. Buying black tanks is a good choice, or you can paint them. What you should paint them with is a matter of debate and there’s a very good Twitter thread on the subject if you’re interested.

    An Aside: Algae in Ponds and Dugouts

    We didn’t test this, but the question has come up and the best we can do is share some long-standing farmer wisdom. Some have used Aquashade dye to absorb the photosynthetic wavelengths and reduce algae buildup. Reputedly it is moderately successful. Another option is adding aluminum sulfate to the pond, and with a lot of agitation it should clarify in about 48 hours. Still others have added a few square barley straw bales to the water and found it to work surprisingly well (possibly an allelopathic response). Tie a rope to them and float them in the pond.

    Citations

    Jeschke, Peter. 2009. The unique role of halogen substituents in the design of modern agrochemicals. Pest Manag Sci, 2010; 66: 10–27

    Lin, C.H., Lerch, R.N., Garrett, H.E. and M.F. George. 2003. Degradation of Isoxaflutole (Balance) Herbicide by Hypochlorite in Tap Water. J. Agric. Food Chem. 2003, 51, 8011-8014

  • How to Spray Ginseng

    How to Spray Ginseng

    This article was co-written with Dr. Sean Westerveld, Ontario Ginseng and Herb Specialist.

    An effective ginseng protection program begins with observing the Integrated Pest Management (IPM) process:

    • diagnose the problem,
    • monitor the problem,
    • control the problem, and
    • monitor the results.

    When spraying is warranted, the operator should understand the basics of application technology. This not only includes the equipment, but the effects of changing spraying parameters (such as pressure or carrier volume), the impact of weather conditions (such as wind and relative humidity) and the product being applied (such as correct timing and safety requirements). The operator should also understand how to properly maintain, calibrate and orient the sprayer according to the nature of the target. Finally, monitoring the results requires the operator to respond to changes in the environment and target during application and to consider these factors when evaluating the outcome.

    The ginseng garden

    This is a four-year old garden, which represents one of the largest, densest ginseng canopies an applicator can spray. The six-foot wide beds in this particular garden are higher than most beds, making sprayer/tractor clearance an issue. It also means the distance-to-target from boom to canopy is less in the middle of the bed than it is nearer the alleys, making it difficult to ensure consistent coverage. Sprayer operators typically drive in the same direction over each bed, “training” the plants to bend in the same direction each time the tractor passes over the surface. This practice, combined with fenders on the tractor wheels, helps to minimize physical damage as the sprayer passes.

    Ginseng gardens have high beds.
    Ginseng gardens have high beds.
    In a four year old ginseng garden. Clearance is an issue.
    Clearance is an issue in a four year old ginseng garden.

    The sprayer

    This custom-built sprayer is a fairly standard design for most ginseng operations: Eight nozzles on each wing and nine on the centre boom. Spacing varies but this sprayer is on 11 inch centres, with the outermost nozzles on five inch centres and aimed outward towards the adjacent beds. Given the limited boom height, all nozzles are aimed back about 45 degrees to increase the distance to target and allow for overlap. The angle is critical to prevent gaps in the spray swath, but given the recommended practice of limited overlap for hollow cone nozzles, the 11 inch spacing may be a little shorter than required.

    Custom-made ginseng sprayer. A standard design.
    Custom-made ginseng sprayer. A standard design in Ontario.

    Spray coverage

    There is no hard and fast rule for spraying ginseng. The crop can receive 30 or more applications a year, most of which are fungicide applications. Tip: Monitoring the small plants inside the canopy is a good indicator of overall garden health.

    The following lists products available for use in Ontario at the time this article was published. The application target varies for each product, depending on the pest or disease the applicator wishes to control. As such, the application volume should reflect the location of the intended target. For example, a foliar-and-stem application should achieve consistent coverage of all leaf surfaces without incurring run-off. An application intended to reach the crown through the straw will require some run-off down the plant stem and should require a higher volume than a foliar-and-stem application. Many products will become immobilized if they dry onto the straw. Applications are best done to wet straw, followed by irrigation or rainfall to wash the product into the root zone. Applications for diseases like Rhizoctonia generally take place early in the season before the canopy closes, and higher volumes may not be required to achieve root coverage. In order to know how much is required for optimal coverage, read on.

    Table 1 – Spray target and relative volume by pest

    PestApplication Target – Specific ProductGarden AgeRelative Volume
    Alternaria and/or BotrytisFoliar and Stem – all productsSeedling – 2nd yearLow
    3rd – 4th yearModerate
    Phytophthora Leaf BlightFoliar and Stem – most productsSeedlingLow
    2nd-4th yearModerate
    Foliar – Aiette and PhostrolAllLow
    Phytophthora Root RotRoot – xylem-mobile root rot productsAllHigh
    Foliar – Aiette and PhostrolAllLow
    Phytophthora Leaf and RootRoot – xylem-mobile root rot productsAllHigh
    Foliar – Aiette and PhostrolAllHigh
    CylindrocarponRoot – all productsAllHigh
    RhizoctoniaRoot – most productsAllHigh
    Root – QuadrisSeedlingHigh
    PythiumRoot – all productsAllHigh
    AphidsFoliar and Stem/Berries – all productsAllModerate
    CutwormsStem – all productsAllLow
    Four-Lined Plant BugFoliar – all productsAllModerate
    LeafrollersFoliar and Stem – all productsAllModerate
    Root Lesion NematodesRoot – all productsAllHigh

    History of the ginseng boom in Ontario

    Historically, ginseng sprayer operators used brass hollow cone nozzles to spray ginseng. For reasons that are unclear, many then adopted the Casotti-style sprayer, which used higher volumes and an oscillating nozzle assembly to create a larger swath. This was determined to be overkill for ginseng, and it produced inconsistent coverage.

    Many growers (sadly, not all) switched back to horizontal booms and began using the Arag microjet assembly. Drop nozzles (aka drop arms, drop booms, drop legs, etc.) were positioned with disc-core hollow cone nozzles behind the wheels to direct spray into the canopy from below.

    Later, we demonstrated that the microjet mixing valve was difficult to set accurately, creating outputs +/- 50% the optimal rate. In response, a new variation on the Arag microjet was introduced, with a more reliable rate adjustment and a lower price tag (they are imported from Italy by a single North American distributor). The drop nozzles are absolutely critical for under canopy coverage, and growers have begun suspending them in each alley – not just behind the sprayer wheels. I predict the future boom arrangement will return to hollow cone nozzles, but in the form of molded poly nozzles with ceramic handling and drop nozzles with full cone disc-core assemblies. Air assist would be even better.

    Sprayer settings

    Most operators employ a ground speed of about 5 km/h (3.1 mph), operate at about 13.8 bar (200 psi) with nozzles spaced 25-30.5 cm (10-12”) spraying anywhere from 1,000 L/ha (107 gal./ac.) to 1,686 L/ha (180 gal./ac.). The application volume should reflect the stage of crop growth, the age of the garden and the target in question (see Table 1). Applicators should also consider droplet size (Table 2). This is difficult to control given that the majority use Arag microjets with the 1.5 mm orifice disc. In which case, pressure choice will affect median droplet size, with lower pressures increasing median droplet diameter and vice versa.

    Table 2 – The Impact of Droplet Size

    Droplet SizeDrops per areaRetentionCanopy PenetrationDrift Potential
    FineHighHighLowHigh
    MediumModerateModerateModerateModerate
    CoarseLowLowHighLow
    Two versions of the ARAG Microjet.
    Two versions of the ARAG Microjet.

    The older style Arag microjets with 1.5 mm diameter discs have highly variable outputs. We developed tables listing their rates with the mixing valve handle set in two positions. They can be found here. We have also developed tables for the newer Arag nozzles for the 1.0, 1.2 and 1.5 mm discs based on 28 cm (11”) spacing. They are listed in Metric and U.S. Imperial.

    Download the tables here: Metric (or) U.S. Imperial

    ARAG Microjet rates (Metric)
    ARAG Microjet rates (Metric)
    ARAG Microjet rates (U.S. Imperial)
    ARAG Microjet rates (U.S. Imperial)

    Timed output test

    Park the clean sprayer and get the pressure up to the desired level. Using a calibration vessel, perform a timed output test to determine each nozzle rate. I prefer the SpotOn SC-4 and a length of 1” braided line to direct the spray into the vessel. You will get wet, so ensure the water is clean and/or wear appropriate PPE.

    Timed output test. Prepare to get very wet. Sprayer must be clean and PPE is a must.
    Timed output test. Prepare to get very wet. Unless sprayer is sparkling clean, like this one, PPE is a must.

    At 200 psi, we took readings from each microjet and found that while they were more consistent than the older model, there was still a lot of variation from tip to tip. This required us to turn the valve on the nozzle to get a more consistent output, then take another reading, and repeat until we liked what we saw. It became tricky to adjust the rate without reducing the hollow cone pattern to a solid stream because only a slight turn of the nozzle was required. Once we had it, we tightened the lock nut and moved to the next nozzle. Table 3 is a record of the procedure.

    While calibrating, we noticed some of the nozzles would suddenly appear plugged, or dense lines could be seen in the spray cone indicating something was wrong. We cleaned them to discover bits of plastic from the poly tank. I asked about strainers, but they are not available for the microjets. I asked about in-line filters, but they aren’t rated for 200 psi. Filling the tank with clean water is very important, but even more so with these nozzles.

    Table 3 – Calibrating the new Arag microjets

    Nozzle PositionRates in gpm (bold represents final rate)Nozzle PositionRates in gpm (bold represents final rate)
    10.97, 0.96, 0.93140.77, 0.92
    21.07, 1.07, 1.26, 0.9150.76, 0.8, 0.95
    31.1, 1.1, 1.1, 0.93160.97, 0.95
    40.73, 0.92170.73, 1.0, 1.07, 1.0, 0.98
    50.92, 0.92180.83, 0.94
    60.94190.77, 1.0, 0.99, 1.1, 1.24, 10.8, 0.93
    70.88200.77, 0.88
    80.92210.71, 0.95
    90.95220.77, 1.07, 1.04, 1.1, 1.27, 1.0
    100.90231.06, 0.97
    110.86240.77, 0.97
    120.76, 0.83, 1.0, 1.0, 1.2, 0.92250.68, 0.95
    130.77, 0.92
    Average output: 0.93 gpm, standard deviation of 0.03 gpm.

    Ground speed

    Once the nozzles were adjusted, we filled the tank ½ full and measured out 25 m in the bed. We would normally do 50 m, but the row was too short. The sprayer operator drove the course and we measured the time it took to travel the 25 m distance. Pass one took 18.5 seconds and pass two took 18.3 seconds. That’s an average of 18.4, which we then double so it works in the formula = 36.8 s.

    ( 50 × 3.6 ) ÷ 36.8 s = 4.9 km/h

    Adjusting the drop leg nozzles

    This sprayer had drops behind the wheels and two more to hang in the adjacent alleys. This is excellent because research has shown considerably improved coverage with directed spray from drop arms. In my mind, these are not optional – they are mandatory!

    Drop nozzles in the alleys.
    Drop nozzles in the alleys.

    We swapped out the hollow cones we found in those positions for full cone disc and core (D5-DC35). Full cones increase the number of droplets that will clear the raised bed and enter the canopy. When adjusting them, be sure to minimize the portion intercepting the bed, while minimizing the spray escaping up through the canopy. It’s a fine line.

    Aiming drop arms in a ginseng garden.
    Aiming drop arms in a ginseng garden.

    Calculating sprayer output

    25 microjets at 200 psi = average of 0.93 gpm = 23.25 gpm
    8 × D5-DC35 at 200 psi = 1.4 gpm × 8 = 11.2 gpm
    That’s ~34.5 gpm for the boom.
    Ground speed was 4.9 k/hr or ~ 3mph.

    GPA = (GPM × 5,940) ÷ (mph ÷ nozzle spacing in inches)
    GPA = (34.5 gpm x 5,940) ÷ (3.0 mph × 11 inches)
    GPA = 204,940 ÷ 33
    62.1 GPA or about 580 L/ha.

    Diagnosing coverage

    Water sensitive paper, which turns from yellow to blue when contacted by moisture, was placed in the ginseng canopy. Two sets of papers were set out, with four papers in each set. The canopy was still wet with rain, which made placement difficult as the papers would accidentally contact water on the leaves and change colour prematurely.

    Water-sensitive paper wrapped around tubes for panoramic coverage.
    Water-sensitive paper wrapped around tubes for panoramic coverage.
    Position#1Clipped face-down on the underside of leaves at the top of the canopy.
    Position#2Clipped face-up on the upper side of leaves in the middle of the canopy.
    Position#3Clipped face-down on the underside of leaves in the middle of the canopy.
    Position#4Wrapped around a plastic tube and threaded over a wire flag, located at the foot of the plant to give panoramic coverage at the root.

    The sprayer passed over the canopy spraying water, and papers were carefully retrieved, allowed to dry and scanned.

    Panoramic papers in situ.
    Panoramic papers in situ.
    Flags mark the locations of papers.
    Flags mark the locations of papers.

    Generally, there were no “misses” whatsoever. Position 1 showed excellent coverage, with no indication of run-off and a high droplet count with even distribution. This is ideal for foliar applications, and under-leaf coverage is notoriously difficult to achieve. Positions 2 through 4 showed excessive coverage, with the exception of one of the position 3 papers, which was still adequate.

    Example of coverage and paper locations in canopy.
    Example of coverage and paper locations in canopy.

    Next steps

    Ideally, the operator would drop the pressure by 20 psi increments, reducing output until coverage failed. It is important to note that the operating pressure must never approach the lower end of the nozzle’s recommended pressure range, or the spray quality will be compromised and so will coverage.

    Once the coverage is considered a failure, the operator would return to the lowest output that did a good job, and the sprayer is calibrated for that crop (at that stage of growth).

    Note that the calibration must be performed for each significantly different crop. With the exception of an early-season drench intended to contact the entire root, an emerging one year old garden would need a very different prescription than a four year old garden with a fully-developed canopy. Plus, the weather conditions will affect coverage, so do not calibrate in conditions you would not normally spray in. Hot and dry and windy conditions produce very different coverage compared to cool, humid and still conditions.

    Once the operator knows what each garden requires, they will be able to mix their tanks using the same concentration of carrier to formulated product as they normally use, but likely go further on the tank. It will take some practice before the operator knows how much spray mix is required to finish the job.