Category: Speciality Sprayers

Main category for all sprayers that are not horizontal booms

  • Gear up – Throttle down

    Gear up – Throttle down

    In 1977, David Shelton and Kenneth Von Bargen (University of Nebraska) published an article called “10-1977 CC279 Gear Up – Throttle Down”. It described the merits of reducing tractor rpm’s for trailed implements that didn’t need 540 rpm to operate. In 2001 (republished in 2009), Robert Grisso (Extension Engineer with Virginia Cooperative Extension) described the same fuel-saving practice. Again, it was noted that many PTO-driven farm implements don’t need full tractor power, so why waste the fuel? He tested shifting to a higher tractor gear and slowing engine speed to maintain the desired ground speed. 700 diesel tractors were tested, and as long as the equipment could operate at a lower PTO speed and the tractor itself didn’t lug (i.e. overload), as much as 40% of the diesel was saved.

    How this applies to Airblast

    For airblast operators with PTO-driven sprayers and positive-displacement pumps, this has potential for reducing air energy. Gearing up and throttling down (GUTD) sees the operator reducing the PTO speed from 540 rpm to somewhere between 350-375 rpms, which not only saves fuel but more importantly slows the fan speed. This may be an option when air energy from the sprayer, even at higher travel speeds and a low fan gear, still overblows the target canopy.

    Some airblast sprayers, like this one, feature fan blades with adjustable pitch to increase or lower air volume and speed. It’s often a pain to try to adjust them, and most operators only try it once.
    Some airblast sprayers, like this one, feature fan blades with manually-adjustable pitch to increase or lower air volume and speed. It’s often a pain to try to adjust them, and most operators only try it once.

    A good time to try this out is early in the spraying season when (most) canopies are dormant and at their most sparse. For example, when applying dormant sprays in apple orchards, look to see if the wood on the sprayer-side gets wet, but does not creep around the sides. This suggests that the air, and much of it’s droplet payload, are being deflected. When the air speed is slowed, it will become more diffuse and turbulent on target surfaces, and this turbulence helps more droplets deposit in a panoramic fashion within (not past) the target canopy. Look to see if the wood is wet >50% around the circumference of the branches. You’ll get the rest when you spray form the other side.

    Limitations

    GUTD is not always appropriate. It requires airblast sprayers with PTO-driven positive displacement pumps (e.g. diaphragm). Airblast sprayers with centrifugal pumps would experience a drop in operating pressure and would have to be re-nozzled. Further, the pump must have sufficient surplus capacity to maintain pressure at low rpms.

    GUTD is not intended for air-shear sprayers that employ twin-fluid nozzles because dropping air speed below a certain threshold may compromise spray quality; the air needs to be fast enough to create and direct spray droplets

    The tractor must have sufficient horsepower (more than 25% in excess of minimally-required capacity) to permit the reduction in engine torque. This is especially important if the operator is on hilly terrain. If the tractor begins to lug (e.g. black smoke, sluggish response, strange sounds) you’ll be in trouble.

    Observations

    We first experimented with GUTD in 2013. We noticed how much quieter the sprayer was, and the fuel consumption was certainly reduced. One grower-cooperator switched to a GUTD spray strategy mid-way through their dormant oil application in pears. We saw the trees immediately began to drip. Panoramic coverage was improved significantly; once the operator passed down the other side of the target, capillary action and surface tension helped to give near-complete coverage.

    However, in one instance, the operator was already applying a low spray volume per hectare using air induction nozzles and their lowest fan gear. By further slowing fan speed using GUTD, coverage at the top of his cherry trees was compromised.

    In short, GUTD can work under the right circumstances. If you want to try it, use water-sensitive paper to establish a base-line with your current practice, and then evaluate coverage after you change your sprayer settings.

  • Drop Hoses Improve Coverage in Field Peppers

    Drop Hoses Improve Coverage in Field Peppers

    In early July 2016, a farm supplier contacted us on behalf of a client with a history of disease control issues in his field pepper operation. He wanted us to calibrate their sprayer and diagnose spray coverage to see if there was room for improvement. Improved coverage doesn’t necessarily mean improved efficacy, but generally it’s a reliable indicator. When we arrived at the field the winds were gusting over 15 km/h, which had the potential to create a massive drift issue. We were only spraying water, so it was decided that if we managed decent coverage in those conditions, there would be no need to worry on an acceptable spray day.

    Field pepper in Southern Ontario in mid-July
    Field pepper in Southern Ontario in mid-July

    The grower traditionally ran two different settings on his sprayer. They were relatively low volumes for a vegetable operation, but the crop was still small at this stage, so we did not propose raising the volume:

    1. TeeJet AITX 11008’s on 50 cm (20″) centres at 11.25 kmh (7 mph) and 3.44 bar (50 psi). That’s 3.35 L/min (0.89 gpm) per nozzle for a total rate of 350 L/ha (37.5 gpa).
    2. TeeJet ConeJet TXVK18’s on 50 cm (20″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s 1.6 L/min (0.42 gpm) per nozzle for a total rate of 275 L/ha (29.5 gpa).

    To test the coverage with these settings, we folded a piece of water-sensitive paper over a leaf to cover both surfaces, and wrapped one around a hollow tube to mimic a plant stem (see figure). Three plants were papered for each sprayer pass. Papers were collected, digitized and analysed for percent-coverage and droplet density. When diagnosing coverage for a horticultural crop, a distribution of 85 medium deposits/cm2 and 10-15% coverage is a reasonable standard for most applications.

    Location of water-sensitive papers in situ.
    Location of water-sensitive papers in situ.

    The first condition (the AITX tips) averaged 17% coverage on upper leaf surfaces (37 deposits/cm2). These were coarser droplets at relatively low volume, so it was no surprise that we didn’t achieve 85 deposit/cm2 target. When using such large droplets, it is more important to achieve an even distribution and the 10-15% surface coverage (we achieved 17%). There were no deposits on the underside of the leaves (See figure 1), but that was also expected as coarser droplets tend to follow a downward vector that is not conductive to under-leaf coverage.

    Figure 1 - Water-sensitive papers from three plants sprayed in Condition 1. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
    Figure 1 – Water-sensitive papers from three plants sprayed in Condition 1. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.

    The second condition (the ConeJets) provided better coverage. The fine droplets produced covered an average 17.5% coverage with a distribution of 99 deposits/cm2 on upper surfaces, and 23% coverage with a distribution of 185 deposits/cm2 on lower surfaces. Panoramic stem coverage was improved as well (see figure 2). This is excellent coverage, but the finer droplets were highly prone to drift (see below). With no form of drift control, this set up is undesirable.

    Figure 2 - Water-sensitive papers from three plants sprayed in Condition 2. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
    Figure 2 – Water-sensitive papers from three plants sprayed in Condition 2. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
    With no form of drift control, the fine droplets produced by hollow cones create unacceptable spray drift, even in moderate wind conditions.
    With no form of drift control, the finer droplets produced by hollow cones create unacceptable spray drift, even in moderate wind conditions.

    This led us to propose a more directed boom arrangement: We set up a hollow cone over the row (the grower’s original ConeJet) and a drop hose suspended in each alley with two TeeJet XR 8004 flat fans positioned on an angle (i.e. not vertical or horizontal to ground). This gave sufficient height to span the canopy with as little direct waste on the ground as possible. As the crop grows, the nozzles would need to be twisted into a more vertical alignment.

    ConeJet TXVK18’s alternating with drops with TeeJet XR 8004’s.
    ConeJet TXVK18’s alternating with drop hoses with TeeJet XR 8004’s.

    We did not use an air induction fan to avoid the Very Coarse spray quality and we used 80° instead of 110° to ensure the spray did not overshoot or undershoot the plant. Here are the details of the third set up:

    3. TeeJet ConeJet TXVK-18’s on 100 cm (40″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s 1.6 L/min (0.42 gpm) per nozzle. Also, two TeeJet XR 8004’s per drop on 100 cm (40″) centres at 7 kmh (4.5 mph) and 3.44 bar (80 psi). That’s ~4.5 L/min (1.2 gpm) per drop hose. Together, set of nozzle for a total rate of 523 L/ha (56 gpa).

    This set up raised the volume considerably and aimed spray directly at the sides of the plant. Coverage was excessive and in a few cases exceeded what the diagnostic software could reliably resolve (see figure 3). Since the plants were still small at this stage, it was decided we would let them “grow into the volume” and come back to check coverage once they were at full size.

    Figure 3 - Water-sensitive papers from three plants sprayed in Condition 3. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
    Figure 3 – Water-sensitive papers from three plants sprayed in Condition 3. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.

    When we returned in mid-August the plants had reached full maturity. In this final coverage trial, we added a second water-sensitive paper to each plant to span the height of the crop canopy, which had grown considerably.

    The same pepper plants ~5 weeks later had more than doubled in size.
    The same pepper plants ~5 weeks later had more than doubled in size.

    Coverage was reduced compared to how we left things in July, but appeared to be sufficient on key surfaces (see figure 4). The papers showed upper leaf-surface coverage of 63%-to-offscale and deposit distribution of 137 deposits/cm2-to-offscale. Coverage on the lower leaf surfaces was greatly reduced to 4-4.5% and 36-90 deposits/cm2. Panoramic stem coverage was present, but minimal. Applying higher volumes would likely have improved matters.

    Figure 4 - Water-sensitive papers from three plants sprayed in Condition 3, ~5 weeks later. Percent coverage and droplet density are calculated for the leaves, and a visual inspection is made of the stems.
    Figure 4 – Water-sensitive papers from three plants sprayed in Condition 3, ~5 weeks later. Percent coverage and deposit density are calculated for the leaves, and a visual inspection is made of the stems.

    When asked about the drop hoses, the grower reported “They are a bit of a nuisance because they take extra time to put on, and they get caught in the bush at the back of the field. But if they increase our coverage, then they’re worth the extra effort.”

    Final thoughts

    Adding drop hoses to a vegetable sprayer may be unconventional, but if fungicide coverage is a concern, and the drops will fit between rows, they might be worth a try. Carefully consider the volumes you use because they should reflect the size of the plant canopy you are trying to protect. Finally, water-sensitive paper provides excellent feedback to help you decide if your field volume, nozzle rates and nozzle positions are providing acceptable coverage.

  • Stop and Spray the Roses – More Efficiently!

    Stop and Spray the Roses – More Efficiently!

    Spraying roses.
    We always admire the photos of sprayers in tulips produced by the Netherlands. Rose protection in Ontario is equally beautiful.

    Nursery growers apply pesticides to a diverse range of plant species. In a perfect world, sprayer operators would adjust their sprayer set-up to match each crop, but this is rarely done because of time constraints and a lack of guidance. Adjustments in product rate and spray distribution should reflect the plant size, row spacing and developmental stage of the crop and pest. Any such adjustments should be performed using a reference point for coverage and a strong history of efficacy.

    To demonstrate the value of sprayer optimization, we marked out three, 65m x 6.5m blocks in a field of roses. One block was an untreated control. One block was the grower’s traditional set up of hollow cones (D4D45) on 50 cm centres at 300 psi and 3.0 mph (841 L/ha). The third block was the experimental condition where we used an optimized set up of hollow cones (D3D45) on 50 cm centres at 150 psi and 3.0 mph (388 L/ha). We validated this condition using an iterative process to dial in the coverage indicated by water-sensitive paper.

    Setting up water-sensitive papers in the rose blocks.
    Setting up water-sensitive papers in the rose blocks.
    Rule-of-thumb fungicide coverage on water-sensitive paper.
    Rule-of-thumb fungicide coverage on water-sensitive paper.

    One application of Folpet + Nova was made on Sep 19, 2011. Roses were photographed before and after the treatment. The photographs were digitized and the amount of powdery mildew appearing on the upper surfaces was determined as a percent of the total visible leaf area. Six replications were randomly selected from each block.

    Visual record of randomly selected roses prior to treatment.
    Visual record of randomly selected roses prior to treatment (September 9).
    Visual record of randomly selected roses following treatment.
    Visual record of randomly selected roses immediately following treatment (September 20).

    There was no significant difference in the amount of mildew presented in the two sprayed blocks one day after the application (September 20). Eight days after application (September 27), there appeared to be better control in the optimized sprayer set up condition versus the grower’s standard set up. The large standard error bars in the grower’s condition made this statistically insignificant. It is unclear why the untreated block presented with the least visual mildew at this point. This preliminary work demonstrates the value of customized application settings and their potential to conserve pesticide, water, and fuel without compromising pesticide efficacy.

    Results of optimizing sprayer set up on the visual occurrence of powdery mildew on rose leaves.
    Results of optimizing sprayer set up on the visual occurrence of powdery mildew on rose leaves. Bars represent standard error of the mean. Unclear why control block presented less mildew on Sept 27.

    The Ontario Farm Innovation Program and the grower co-operator are gratefully acknowledged for making this research possible.

  • If I had a Low Drift Nozzle – Parody

    If I had a Low Drift Nozzle – Parody

    Sung to the tune of “If I had a Rocket Launcher” by Bruce Cockburn

    Here comes the John Deere sprayer — second time today;

    All the insects scatter and hope it goes away;

    How many larvae murdered only Dow can say;

    If I had a low drift nozzle… I’d make somebody spray.

    I don’t believe in modes of action and I don’t believe in rates;

    I don’t believe in agronomists or their shiny steely spades;

    And when I talk with the survivors of that crappy bran bait;

    If I had a low drift nozzle… I would calibrate.

    On canola field margins one hundred thousand wait;

    Smash through truck radiators — or some less humane fate;

    Cry for bertha armyworm, sprayed with organophosphate;

    If I had a low drift nozzle… I would not hesitate.

    I want to raise every chirp — at least I’ve got to try;

    Every time I see them munching, with my compound eyes;

    Situation desperate, echoes of the hoppers cry;

    If I had a low drift nozzle… Some CCA would die.

  • Calibration – “The Fundamental Relationship”

    Calibration – “The Fundamental Relationship”

    The Fundamental Relationship, a concept by Professor D. Ken Giles (Emeritus), UC Davis Biological and Agricultural Engineering Department, is a way of talking about calibration without numbers and formulas. It is valuable for teaching concepts important to calibration. Since it is a relationship, it describes the variables needed and how they relate to each other.

    The Fundamental Relationship:

    Application Rate (gallons/acre) = Flow rate (gallons/minute) ÷ Land rate (acres/minute)

    We see here that land rate is inversely proportional to application rate. Thus, when land rate (either speed or swath width or both) are increased (and no other factors change), application rate is decreased. Likewise, flow rate is directly proportional to application rate. Thus, when flow rate is increased (and no other factors change), application rate is also increased. When flow rate is decreased (and no other factors change), application rate is also decreased.

    The Fundamental Relationship is also a good way to do the math of calibration because nothing needs to be memorized. As long as the units are checked, you can’t go wrong. The Fundamental Relationship works for any sprayer calibration, as long as the units are tracked correctly and the flow rate correlates to the land rate, i.e., the land rate used is the swath that the nozzles (flow rate) are covering.

    So, if the flow rate (GPM) used in the formula is for ½ of an airblast set up, the swath width in the land rate calculation would be ½ of the row width. If, for example, it is for a weed sprayer with 2 nozzles, the swath width would be the width the 2 nozzles are covering. Remember to think about this as what area is being covered by the spray:

    • Flow rate units are straight forward: gallons/minute.
    • Land rate can be a bit tricky because no one thinks in terms of acres covered per minute.
    • Land rate is tractor speed × swath width covered by the nozzles used to calculate flow rate.

    Land rate in the above needs to be calculated in the units “ac/min”. Since there are 43,560 ft2 in an acre, the easiest way to calculate is to use the swath width in feet, and the speed in ft/min. Multiplied, this then will give you land rate in ft2/min, which can then be converted to ac/min.

    Using MPH as Speed

    When you measure speed in the field, those who have a speedometer on their tractor will tell you their speed in MPH. To go from a land rate with speed as MPH to ac/min, the following unit conversion is used when multiplying the speed in MPH times the swath width in feet:

    1 mile/5,280 feet × 43,560 ft2/1 acre × 60 minutes/1 hour = 495
    Land rate (ac/min) = (Speed (mph) × swath width (ft)) ÷ 495

    Note: speed should always be measured and verified. Speedometers are notoriously incorrect!

    Calculating nozzle flow rate (GPM):

    You can also use the Fundamental Relationship to calculate the flow rate needed for a desired spray volume (application rate) when you have a set land rate (speed and swath width). This is necessary to help you choose your nozzles. Tractor speed is first determined by checking the coverage-using water sensitive paper or another coverage indicator like kaolin clay, and the fan (using ribbons in the canopy), to go as fast as safely possible while still getting adequate coverage. Swath width for any given field is set. What is left then is to calculate the GPM needed to achieve that application rate at that speed and swath width. This will allow you to select your nozzles based on individual nozzle GPM for a certain pressure.

    The Fundamental Relationship becomes:

    Flow rate (gallons/min) = Application rate (gallons/acre) × Land rate (acres/min)

    This is the flow rate for the ENTIRE sprayer (both sides, correlating to the swath width):

    GPM = GPA × Land rate

    OR if using MPH for speed:

    GPM = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]

    To get the required GPM for one side of the sprayer, you multiply by ½:

    GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495] × 1/2

    GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]

    I’ve seen some folks round up the 990 to 1,000, which makes the above formula easier to remember.

    Why I think the “495 formula” is bad for calibration

    In my experience of teaching calibration math, folks often want to fall back on the formula they have used instead of trying the Fundamental Relationship. The problem I have with the “495 or 990” formulae, is that with using ground speed in MPH, often the step of measuring speed, a critical step for optimizing spray coverage, is eliminated.

    Ground speed is assumed, the speedometer is assumed to be correct, and the entire step of measuring and setting speed is omitted-big mistake! Setting speed using flagging tape in the canopy and looking at the “Fan : Speed : Canopy” interaction is probably the most important step of calibration and optimizing coverage. So, if you must use the “495 formula”, please actually measure your ground speed!

    Measuring speed manually

    Typically, at least 100 feet are marked off to measure actual speed with a stopwatch. If you measure actual tractor travel time for a 100 foot length, you will likely find most common spraying speeds are timed in seconds. These can be converted to minutes, and then used in the formula for speed as ft/min which is then multiplied by the swath (or row) width in feet to obtain ft2/min, which can then be converted to ac/min.

    For example, at 3 MPH, you are travelling:

    3 mph × 5,280 ft/1 mile × 1 hour/60 minutes = 264 ft/min

    If swath width is 6 feet, the land rate (or area the nozzles are covering) is calculated as:

    264 ft/min × 6 ft = 1,584 ft2/min

    In acres covered per minute, we divide by 43,560 ft2/ac to obtain a land rate of 0.036 ac/min. To travel 100 feet at this speed, it takes 0.37 minutes or 22.7 seconds. So, it is not uncommon to time 100-foot tractor runs in 21-23 seconds (which is why you need a good stopwatch). These runs are best done on the type of terrain to be sprayed; and it’s always good to take several times and average.

    Remember that the speed is written as distance travelled/time. Sometimes when measuring speed, I’ve noticed that it will be written as time/distance travelled, which gives the wrong number. Track units!