Author: Jason Deveau

  • Boomless Nozzle Performance

    Boomless Nozzle Performance

    NOTE: This article has proved very popular, and subsequently we received emails with additional information. The article has now been expanded to include work performed by Dr. Bob Wolf et al.

    Part 1:

    Boomless nozzles are used for vegetative management activities where it’s not practical, or sometimes even impossible, to use a horizontal boom. Consider highway easements and ditches, railways, and infrastructure like buildings, powerline poles or fence posts. In these cases, the booms would hit uneven ground, trees and other obstacles. Enter the boomless nozzle.

    Unlike a typical flat fan nozzle, these nozzles direct spray laterally in one or two directions, creating a very wide spray pattern. Some field sprayers use a smaller version such as an off-centre or uneven fan to either extend the booms’ coverage (e.g. to get around fence posts) or give the pattern a discrete edge and not spray beyond the booms length.

    There are many varieties of boomless nozzle available, but they don’t give the same performance.

    Using a spray pattern table, Helmut Spieser and I compared coverage patterns from three popular tips:

    • The Boom X Tender
    • The Boom Buster
    • XP BoomJet

    The Boom X Tender

    With seven rates to choose from, this nozzle claims up to 13′ throw from tip to the edge of the swath. When we ran the tip at 40 psi we noticed a lot of inconsistency in the pattern, where it clearly had variation in flow along the swath. Note the red arrows in the image.

    2

    These inconsistencies made themselves known when we observed the pattern produced on the spray table. We achieved a 7.5′ swath at 40 psi, 16″ above the table with the XT024 (yellow) tip. The coverage wasn’t very even.

    3

    The Boom Buster

    There are fourteen nozzles to choose from, each delivering different flows and according to the manufacturer, spanning up to 31′ from the tip to the edge of the swath. An interesting feature when we ran this nozzle was that the fan extended back ~15°, which might eliminate the need for a centre nozzle if two were operated at the same time with sufficient overlap.

    4

    We achieved a 7′ swath at 40 psi, 16″ above the table and the coverage described a fairly consistent curve. It did taper at the far end, but did a respectable job. It was obvious some overlap at the 15° end would help level out the response, and when paired with a second tip facing the opposite direction, this would work well.

    5

    The XP BoomJet

    The BoomJet mounts 90º to the swath, and with five rates to choose from claims a swath up to 18.5′ from tip to edge.

    6

    We mounted the (B) 1/4XP20L (You have to specify left or right) 16″ above the table and at 40 psi we achieved a 6′ swath. There was an odd dip in the coverage pattern not far from the tip. We suspected it might be an artifact, but after multiple attempts it persisted. Other than that dip, the pattern was quite consistent. Had we adjusted the angle to reach a 7′ swath, it may have tapered as much as the Boom Buster.

    7

    Observations

    Given the range of possible rates and swath distances, the overall consistency of the swath, the conventional nozzle mount, and the 15º overlap, Helmut and I chose the Boom Buster. The BoomJet was a close second, with a consistent pattern save the odd dip, but the 90º mount while making it possible to elongate or shorten the swath was a bit finicky and could pose a snagging risk. The Boom X Tender ranked third because of the inconsistent coverage.

    Part 2:

    Nozzle mounted on the front bumper of a County Highway Spray Truck used to spray ditches in Kansas.

    Boomless nozzles are often used on all-terrain vehicles (ATV’s) equipped with small-capacity spray tanks and they’re popular for for eliminating weeds in pastures and rangelands as well as along roadsides. In 2009, Kansas State University published a factsheet evaluating the efficacy of boomless spray nozzles and describing how they can best be used. What follows is a summary of the findings from their field trials.

    Considerations for using boomless nozzles

    1. Pick a nozzle that best fits the mode of action of the herbicide being used.
    2. Select spray width to achieve uniform distribution.
    3. Both the height of the vegetation, and the prevailing wind, will interfere with the width of the spray swath.
    4. As with any hydraulic nozzle, pressure should be optimized to achieve the desired droplet size and swath width while reducing drift potential.

    Field Trials

    Applications were tested on small (growth stage prior to jointing and 4-5 inches tall) and large (growth stage after jointing and 24-30 inches tall) wheat crops planted in 20 foot wide strips. The nozzles tested were the BoomJet (XP) , Boom X Tender (XT) , Boom Buster (BB) and the Combo-Jet (WCJ). Glyphosate and paraquat were applied a typical ATV-mounted set-up. The treatments were replicated three times and water sensitive paper was used to analyze droplet size.

    The Combo-Jet nozzle group.

    Results

    The mode of action, coverage and droplet size affected the results in both short and tall wheat. As expected, glyphosate served as the 100% control and paraquat efficacy ranged depending on the nozzle (see Graph 1). The XT gave the best performance with paraquat.

    Graph 1 - Percent Control in Large Wheat
    Graph 1 – Percent Control in Large Wheat

    Spray (control) uniformity was about equal with glyphosate, but with paraquat, on a scale of 1-10 with 10 being the highest level of control, the XT and BB tied for best (Graph 2).

    Graph 2 - Spray Uniformity in Large Wheat
    Graph 2 – Spray Uniformity in Large Wheat

    Swath width was considerably less than manufacturers claimed in the tall wheat (Graph 3). Based on width of control, the WCJ had the widest swath.

    Graph 3 - Swath Width in Large Wheat
    Graph 3 – Swath Width in Large Wheat

    Swath width was somewhat less than manufacturers claimed in the short wheat (Graph 4). Based on width of control, the XT had the widest swath.

    Graph 4 - Swath Width in Small Wheat
    Graph 4 – Swath Width in Small Wheat

    Median droplet size ranged from 684 to 799 microns (Graph 5). If we assume the preferred range for coverage/weed control is 300-500 microns, all nozzles were on the high end. It should be noted that this does reduce drift potential.

    Graph 5 - Droplet Size as VMD (microns)
    Graph 5 – Droplet Size as VMD (microns)

    Percent coverage ranged from 37.5 to 27.0 for paraquat and 28 to 21.3 for glyphostate (Graph 6).

    Graph 6 - Percent Coverage
    Graph 6 – Percent Coverage

    Observations

    The wind direction and height of the spray stream likely affected the results. To achieve the manufacturer-rated swath width, nozzles would have to be mounted higher on the ATV than is practical, and this would lead to increased drift potential. It was noted that the large orifices common to boomless nozzles made it difficult to pressurize with pumps typically used on ATV’s and a more powerful pump (e.g. a roller pump) might provide better swath width.

    While there are many parameters to consider, and counter to the lab trials performed in Part 1, the results from Part 2 suggest the Boom X Tender and Boom Buster gave better overall performance.

    Checking the Boom Buster spray pattern.

    Overall Conclusions from Part 1 and Part 2

    It can be frustrating testing nozzles. What works wonderfully one day might not be worth the materials they’re made of the next. Obviously there was no clear “winner” at the end of this article, but that’s just as well, because perhaps that’s the wrong take home message.

    Instead, remember that any nozzle can be used incorrectly. Mind the pressure, swath width and environmental conditions to get the most out of whichever nozzle you choose to use. Take time to confirm that everything is working optimally, and go back to ground-proof the results so you know what worked and what didn’t.

  • Strategies to Spray the Top of a Perennial Canopy

    Strategies to Spray the Top of a Perennial Canopy

    Orchardists, nurserymen and hop growers share something in common – they want to get spray to the top of a tall plant canopy with as little waste as possible. The tops of trees, for example, are a primary site of infection as they filter spores from the air, so fungicide coverage is critical. Spraying the tops of high canopies (e.g. too high for over-the-row style sprayers) can be a difficult proposition.

    Here are a few considerations:

    • Wind moving through a planting, as a general rule, is twice as fast at the top of a canopy as it is at the ground. Wind carries spray off target.
    • The further the distance a droplet travels, the smaller it gets as it evaporates and the less momentum it has. The likelihood of it hitting the target is greatly reduced.
    • The top of a canopy typically has far less plant material than the rest of the canopy. Relatively speaking, there’s not much there to hit.

    In order to overcome these challenges, the traditional axial orchard sprayer is nozzled with a larger proportion of spray distributed at the top of the boom. The idea is to increase the odds of some spray making it to the top of the canopy. Often, full-cone nozzles are used to accomplish this. Of course, if an estimated 10% of the spray actually impinges on the top of the canopy, the rest goes… well, somewhere else. This shotgun approach is hardly an efficient use of chemical.

    Another strategy is to crank the PTO rpm’s up to 540, throw the fan in high gear and blow the spray as high as possible. The problem is, by increasing air speed and volume to carry spray to the top, the rest of the canopy (far closer to the sprayer) gets overblown and spray shoots right through. Some overspray might hit the next row, but most ends up on the alley floor. If you doubt it, consider how white your pant-legs get when you walk an orchard after spraying kaolin clay.

    Others, mistakenly, might elect to raise the operating pressure to >150 psi in the hope that pressure will drive the droplets in a straight line at higher speeds. Most airblast sprayers using hollow cone patterns create very fine spray quality, even at 100 psi. Raising pressure means the droplets get even smaller, and tiny droplets have very little momentum. Increasing pressure just makes the problem worse.

    Here’s what we propose.

    Deflectors

    If using an axial sprayer, employ air deflectors at the top of the air outlet to channel air (and spray) more effectively. The commercially-available deflectors are often just flat sheets, and air hits the surface and spills over all edges. Image pouring water onto a dinner plate – it just splashes over any which way. Better to replace those deflectors with a set that feature side-walls to channel the air. Anyone with access to a break and some sheet metal can make their own, but ensure they do not stick out beyond the wheel of the sprayer or they could snag plants and trellises. Always aim to overshoot the canopy top by a small factor to compensate for unexpected gusts of wind – better to overshoot a bit than to miss.

    Commercial deflectors may or may not have channeling side walls. Inset: Homemade deflectors can do a great job.Commercial deflectors may or may not have channeling side walls. Inset: Homemade deflectors can do a great job.
    Commercial deflectors may or may not have channeling side walls. Inset: Homemade deflectors can do a great job.
    The original Munckhof deflectors were reversed, and a larger set of extensions were fabricated and attached.
    The original Munckhof deflectors were reversed, and a larger set of extensions were fabricated and attached.

    Towers

    Better than deflectors, some sprayers move the air and nozzles closer to the target via ducted tower assemblies. They work very well, but they must be as tall as the target you intend to spray. Even then, an uneven alley can cause them to rock and you might still miss some upper targets. Operators using adjustable towers or ducts might angle them back to aim the air (and spray) on a slight upward angle rather than parallel to the ground, and that can compensate for a slight height difference, but it begins to defeat the purpose.

    Nozzle body on upper tower deflectors. Still some air assist and a good idea, but use air induction nozzles.
    Nozzle body on upper tower deflectors. Still some air assist and a good idea, but use air induction nozzles.

    Extra Nozzle Bodies

    Some creative operators have attached additional nozzle bodies to the tower’s top deflector plate to aim it up in the top of the canopy. Still others have extended the wet boom itself higher than the tower. Unfortunately, although the nozzle is closer to the target (good) the benefit of air assist has been greatly reduced (bad). Air induction nozzles might help on boom extensions, per below.

    Wet booms can be extended to reach high canopies, but may no longer benefit from air assist. Consider using air induction nozzles in these positions.
    Wet booms can be extended to reach high canopies, but may no longer benefit from air assist. Consider using air induction nozzles in these positions.

    Air Induction Nozzles

    Consider using air induction nozzles in the top two positions of each boom (totaling four per sprayer), with or without towers. There are three advantages:

    1. Coarser droplets have more mass. They move in straight lines and are less likely to be deflected by wind before they reach the target.
    2. Coarser droplets can be propelled by pressure, so unlike finer droplets they rely less on being carried by sprayer air.
    3. Coarser droplets that miss the target do not continue upwards; they fall back out of the air into the orchard, reducing off-target drift potential.

    No matter which strategy, or combination of strategies, you use to hit the top of the canopy, always confirm coverage using water-sensitive paper. Further, recognize that it’s very difficult to compete with high winds, so know when to wait it out.

    Controlling your spray at the top of the canopy means better coverage and less waste. Plus, people won’t see this (wait until the ~50 second mark).

  • Flag the Technology – Matching Herbicide to Genetics

    Flag the Technology – Matching Herbicide to Genetics

    We like to keep things simple ’round here and this poka-yoke from Arkansas is both simple and effective. What’s a poka-yoke?

    “Poka-Yoke”: a Japanese term that means “mistake-proofing”. It’s a mechanism that helps an equipment operator avoid (yokeru) mistakes (poka) by preventing, correcting, or drawing attention to human errors as they occur. Thanks, Wikipedia.

    The problem

    An aerial applicator has to spray a lot of fields. They consult their work orders, the plane is loaded, they spray and repeat. However, depending on which herbicide trait was introduced to which crop, accidents can happen. Imagine the mess when you spray a crop with glyphosate… and it isn’t a glyphosate-tolerant crop? This problem promises to become more of an issue as we introduce glyphosate+2,4-D and glyphosate+dicamba-tolerant crops. It may look like the right soybean plant, but you DO NOT want to mess up by spraying the wrong chemistry on the wrong genetics! You think a bit of residue in the lines can cause trouble…

    Yellow flags designate this field as a Clearfield rice field (Photo from UofA FSA2162)
    Yellow flags designate this field as a Clearfield rice field (Photo from UofA FSA2162)

    The solution

    In 2011 the University of Arkansas came up with a “quick and inexpensive” way to prevent this from happening. They used six-foot, colour-coded bicycle flags. Each colour or pattern represented a specific herbicide tolerance, as shown here. Aerial operators were given a copy of this visual key and the growers placed a couple of appropriate flags at the edge of the field on the approach vector at planting.

    The result

    Aerial applicators got one final check before they started to spray… just in case. In 2014 the innovative people behind this concept reported that it prevented countless acres of accidentally-damaged crops. Several (honest) aerial operators admitted to pulling up just before they started to spray because they realized there was a mismatch between what was in their tank and what the field was supposed to receive.

    Corn field with glyphosate (white) and glufosinate (bright green) stacked technology. (Photo from UofA FSA2162)
    Corn field with glyphosate (white) and glufosinate (bright green) stacked technology. (Photo from UofA FSA2162)

    The challenge

    This is the kind of elegant, simple tool that we all should be using for ground rigs as well as aerial sprayers as we begin to plant more crops with stacked traits. Canada, the US, Australia, anyone using these genetics, could benefit. We should consider adopting this method, complying with Arkansas’ existing colour scheme and adding to it as required. Seed companies and agrichemical companies should find a way to bundle the flags with the chemicals and seeds for the buyer.

    Read more about the Flag the Technology method from this University of Arkansas factsheet.

    …and one more time with gusto: “poka-yoke“.

  • Hol Spraying Systems – Canadian airblast gets an upgrade

    Hol Spraying Systems – Canadian airblast gets an upgrade

    The first modern airblast sprayer was developed in the mid 1900’s, but competed with existing equipment before it was adopted by the majority. As you can see below, we’ve come a long way. As application technology continues to evolve and grow, so does the array of choices facing growers.

    An Ontario orchard spray crew c.1910. Pump pressure was maintained by the two operators at the right. The spraying rate by the above method could cover 1.2 to 1.6 hectares (3 to 4 acres) per hour. Image from www.farms.com
    An Ontario orchard spray crew c.1910. Pump pressure was maintained by the two operators at the right. The spraying rate by the above method could cover 1.2 to 1.6 hectares (3 to 4 acres) per hour. Image from www.farms.com

    Provide Agro (a subsidiary of N. M. Bartlett Inc.) had been considering introducing a new airblast sprayer to Canada for more than ten years. After deciding not to get into the manufacturing game, they explored importing sprayers from Europe and Australia. In late 2014 they recently invited me to see their choice: the H.S.S. CF airblast sprayer built by Holland-based “Hol Spraying Systems”.

    It’s not often I get to see a “new” airblast sprayer design. To be fair, H.S.S. has been building similar sprayers in Holland for more than 20 years, so technically it was new-to-me.

    We met at a local apple orchard in Simcoe, where we ran the sprayer through a series of light duties. The first thing we did was explore the sprayer’s features, both optional and standard. As the ambassador to Canada, this particular model had all the bells and whistles. Here is a list of features and observations I feel are worth relating. It’s important to note that this list is in no way an endorsement, nor are any omissions intended to be a condemnation.

    The H.S.S. CF sprayer. Outwardly this PTO-driven sprayer appears very different from Ontario’s typical fleet of airblast sprayers. Notably the flexible ducts and gantry comprising the tower, and the double axle. However, it operates using the same principles as our more familiar sprayers and following a brief inspection of welds and fastens (and given its more than 20 year history in Europe) it appears to be very durable.

    Each duct is paired to a nozzle body, and that means each air outlet can be adjusted individually. The tower structure can be customized to match everything from vines to high-density orchards and even has an optional woolly aphid attachment for directing air and spray up-and-into the canopy. For taller crops like hops and semi-dwarf trees, a second fan can extend the tower to 5.5 m.

    Anyone that’s been stuck in wet weather can appreciate the value in this adjustable double axle. Weight is distributed to reduce compaction and hopefully, the creation of ruts. This feature is standard, but you have the option to upgrade to hydraulic adjustment. I’m not sure how often an operator would want to adjust the axle length, but there it is.

    The H.S.S. CF has a lot of features that promote operator safety by reducing the potential for exposure. One convenient feature is the access port separate from the tank fill port. No need to remove the basket to examine/clean the interior, and no need to remove the basket and come in contact with (potentially) concentrated pesticide residue.

    Many large field sprayers feature tank rinse nozzles to facilitate sprayer cleanout following an application. Finally, airblast can boast this feature as well. The 150 L clean water tank supplies enough water to the tank rinse nozzles for a triple, low-volume rinse in the field with no need for a pressure washer or a nurse tank. This prevents residue buildup and reduces operator exposure – and it’s standard!

    An optional feature is the tank level sensor, which can be tied to the agitation. If you are using a foamy tank mix, agitation won’t turn on until a preset tank level. I’m not certain about this option because proper tank suspension requires agitation from the beginning – just use a defoamer. Note the tank basket has a hose attached to the bottom… read on.

    There’s a standard hydraulic jet at the bottom of the tank basket to assist in proper mixing. I don’t know if it precludes mixing a slurry, or if it will improve pesticide bag dissolution, but I have to assume it helps. I trust there’s a safety feature to prevent this nozzle from operating while the hatch is open, but I’m not certain.

    This final standard feature may seem small, but it further reduces the potential for operator exposure. The onboard clean water source is separate from the spray tank and the tank-rinse supply and provides a convenient hand-wash station.

    Other features include solenoid shut-offs for boom sections, a rate controller and a small-radius draw bar.

    An important function of any airblast sprayer is air handling. Too often, tower sprayers have inconsistent air speeds (and presumably air volumes) over the length of the air outlet. Sometimes this can be compensated for using the small deflectors in the tower, or in extreme cases, replacing conventional hollow cone nozzles in “dead spots” with air induction hollow cones that produce coarser droplets and tend to fly farther under pressure. Using a Pitot meter, we examined the airspeed from each air outlet. The PTO was set to 400 rpm and the fan gear was in low.

    Nozzle:Ground234567Top
    Left70 mph85 mph90 mph85 mph80 mph85 mph80 mph85 mph
    Right75 mph90 mph90 mph90 mph80 mph90 mph85 mph85 mph

    There were no obvious dead spots, and the left and right sides of the tower seemed about equal. The bottom two positions were notably slower than the rest, but given the distance to the target in that position, and the fact that ambient wind is slower at the ground, it’s interesting, but not necessarily a concern.

    We arranged a set of water-sensitive targets in the canopies of semi dwarf apple trees to get a sense of the sprayer coverage. Admittedly, it was very humid and there was little wind that day, so coverage is much easier to achieve because so little spray evaporated or was blown off course before reaching the target. We ran different combinations of PTO speed and fan gear. These images are from 540 rpm and low fan gear using red Albuz nozzles (1.5 L/nozzle/minute @ 6 bar) spraying about 400 L/ha at about 5 kph. On a drier and windier day, higher volumes would be needed.

    There were no obvious misses, even when papers were oriented parallel with the ground (exposing their narrow edge to the sprayer, such as in the paper on the right). This isn’t conclusive, but it does show that the sprayer had no trouble penetrating the canopy, and with further tweaking should be able to provide suitable coverage throughout the canopy. Personally, given the upward orientation, I would use the woolly aphid nozzle for all applications, particularly for drenches. More on that later.

    One notable quality was the “quiet” operation of the sprayer. Applicators are familiar with the loud whine created by most airblast sprayers; at lower rpm’s and in low fan gear, the tractor seemed as loud (or even louder) than the sprayer operation. You can watch a video of one of the spray passes at the bottom of this article.

    So the big question: “How much?”. You’ll have to contact the dealers to find out more, but I will say that stripped down to standard features, it’s comparable to some of the more expensive sprayers in Ontario. Don’t be dissuaded because I believe the expense is warranted given the features, with particular note of the on-board tank rinse system and adjustable air ducts.

    So is this the sprayer for you? Well, if you’re in the market for a new sprayer, always start by prioritizing your goals. Perhaps work-rate is a priority, so look to sprayer capacity to reduce the number of refills and consider over-the-row technology (where possible) to reduce the number of passes. Perhaps the crop is adjacent to sensitive areas or residential homes and drift control is a priority; consider adjustable air direction and adjustable air speed.

    When compiling a prioritized list, reflect on the positives and negatives of your current sprayer and talk to fellow growers about their experiences. It may come down to personal preference, but consider the following points. These points are in no particular order; they come from many articles I’ve read on the subject of considering new equipment purchases and from talking to dealers, mechanics and sprayer owners:

    • Necessity – Is a new sprayer really needed? Manufacturers have a number of retrofit kits available to upgrade and improve sprayers. If poor pesticide performance has led to the decision to purchase a new sprayer, be sure it’s related to the technology, and not to an operating error.
    • Crop Type and Acreage – Consider the size of the operation and the size, shape and density of the crop(s). Can the sprayer adapt to provide adequate coverage throughout the growing season and in the long-term? How flexible is the sprayer when spraying different products onto different targets?
      • Sprayer Capacity and Filling – Fewer refills means a higher work rate, but increased capacity also means more weight, so consider the effects on navigation, turning radius and soil compaction. Is the tank easy to fill?
    • Cleaning, Calibrating and Maintenance – Moving between crops sometimes requires complete cleaning and decontamination of the tank, lines, nozzles and any shrouds or ducts. Clean water reservoirs, tank-rinsing nozzles and overall accessibility should be considered. Review the steps required to winterize and to calibrate the sprayer. Is it easy to access parts? Is operator exposure minimized
    • Horsepower – This is an important consideration for airblast sprayers because fans move a lot of air and liquid. Tank agitators require power, too. Consider selecting from the higher range of manufacturer-recommended horsepower to improve longevity. Remember, however, that fans typically don’t have to operate at the maximum rated rpm’s, particularly early in the season.
    • Nozzle Technology and Operating Pressure – Consider the range of nozzle-types intended for use and ensure the sprayer can provide sufficient pressure. While more expensive, diaphragm and piston pumps have fewer moving parts in contact with the spray solution, reducing cleaning time and operator exposure.
    • Spraying Conditions – A sprayer has to be reliable, even in adverse conditions, so consider the operating environment. Night spraying, uneven terrain, high winds, dry conditions – many environmental factors can impact sprayer performance and may warrant special consideration. Investigate deflectors, shrouds and the structural framework and durability of the sprayer.

    Since its introduction in late 2014, growers have been slowly adopting this sprayer in Ontario and the northern US. Some high-density operations have purchased the optional over-the-row boom system that allows them to spray multiple rows at once. Here at at the Simcoe Resource Station, we’re hoping to run the HOL sprayer in apples for the 2016 season to see if the optional woolly apple aphid (WAA) nozzle has any impact on scale, mites and of course, WAA control. Moreover, we plan to run that nozzle all season long to see if its upward angle improves underleaf coverage and canopy penetration.

  • When is Fungicide Coverage Critical? Always!

    When is Fungicide Coverage Critical? Always!

    Introduction

    A local strawberry producer was just beginning his harvest when the entire field was suddenly stricken with anthracnose. He would have done almost anything to save it, but he could only watch in frustration as the disease quickly devastated his crop. While he was telling me this story, he was wringing his hands; I’m sure he didn’t realize he was doing it. It had been more than a month since the crop was lost and he was obviously still very upset. Let’s put on our deerstalker hats and consider what might have caused the trouble.

    Strawberry anthracnose. Photo by Pam Fisher, OMAFRA.
    Strawberry anthracnose. Photo by Pam Fisher, former berry specialist with OMAFRA.

    Most of the fungicides we apply in horticulture are protectants, not curatives. What that means is that the fungicide has to be in place before disease has a chance to take hold. Once it establishes a beachhead, you can typically only hold it at bay, not eradicate it. So, if you’re guilty of waiting too long between fungicide applications, the problems may have already begun. This is exacerbated when you don’t achieve the necessary spray coverage. Put the two together and mix in rainy and warm conditions and diseases like anthracnose can spread at alarming speed.

    Method

    I focus on the sprayer part of disease management, so I have to assume that inoculum is being controlled as much as possible (e.g. culling infected plants, drip irrigation, etc.). I asked the grower about his sprayer and his spraying schedule. He admitted to pushing the limits between fungicide applications, and being uncertain about the spray coverage he was achieving with his conventional flat fan nozzles.

    Strawberry Sprayer
    Strawberry Sprayer

    In cases like this I try to find gentle ways of introducing the idea of using more water, increasing the frequency of applications, or buying new nozzles, because there is time and expense involved and many growers don’t want to hear that. However, when I started my soft sell routine, he looked me straight in the eye and said he’d lost tens of thousands of dollars in revenue so a few nozzles or a couple more applications were not a pressing concern. There’s a point in any endeavour when you’ve committed so much time and money that you’ll do pretty much anything to see it come to fruition (pun intended). He was willing to do whatever it took. This was my kind of guy.

    So, in preparation for next year, we diagnosed spray coverage from five different sprayer set ups. Let me point out, as I always do, that spray coverage analysis does not necessarily extend to control. They correlate well, but if you aren’t using the right product or your timing is off, even the best coverage won’t help you. Caveats aside, here’s what we tested:

    Setup1:

    Broadcast application using a horizontal boom with TeeJet Twinjet 8006’s at 8.3 bar (120 psi) on 50 cm (20 in) centres. We calculated a nozzle rate of 3.9 L/min (1.03 gpm), so at 5.0 km/h (3.1 mph) that’s 923 L/ha (98.7 g/ac).

    Setup 2:

    Banded application on a horizontal boom equipped with a row kits suspending three TeeJet XR 8002’s at 8.3 bar (120 psi). We angled the two side nozzles so the fans were not perpendicular or parallel with ground. This kept more spray on the raised row and out of the alleys. The swath covered 50 cm (18 in) and we calculated a nozzle rate of 1.29 L/min (0.34 gpm), so at 5.0 km/h (3.1 mph) that’s 1,016 L/ha (108.6 g/ac).

    Setup 3:

    Banded application on a horizontal boom equipped with a row kits suspending three TeeJet XR 8002’s at 6.2 bar (90 psi). We angled the two side nozzles so the fans were not perpendicular or parallel with ground. This kept more spray on the raised row and out of the alleys. The swath covered 50 cm (18 in) and we calculated a nozzle rate of 1.14 L/min (0.3 gpm), so at 5.0 km/h (3.1 mph) that’s 896 L/ha (95.8 g/ac).

    Setup 4:

    Broadcast application using a horizontal boom with TeeJet Twinjet 8004’s at 6.2 bar (90 psi) on 38 cm (15 in) centres. We calculated a nozzle rate of 2.27 L/min (0.6 gpm) so at 5.0 km/h (3.1 mph) that’s 717 L/ha (76.5 g/ac).

    Set up 5:

    Broadcast application using a horizontal boom with TeeJet Twinjet 8006’s at 6.2 bar (90 psi) on 38 cm (15 in) centres. We calculated a nozzle rate of 3.4 L/min (0.9 gpm) so at 5.0 km/h (3.1 mph) that’s 1,076 L/ha (115 g/ac).

    Protocol and Conditions

    It was late September, so the weather was a cool 8 °C, humidity was low and winds averaged 5 to 15 km/h. We timed our passes to correspond with lighter wind wherever possible. Three sets of water-sensitive paper were placed in a single row, but only one pass was made per sprayer setup. One paper was placed at the top of the canopy which is always very easy to hit, so we oriented it sensitive-face-down. The second paper was placed midway down the canopy, oriented facing up. The final paper was also oriented facing up, but placed at the very bottom of the canopy, more or less on the ground. Collectively, we spanned the depth of the canopy.

    Following each application, papers were collected for digital analysis using “DepositScan” which determines the percent of the paper covered with spray, and the droplet density. Both of these factors contribute to overall coverage. This wasn’t intended to be a rigorous experiment, so the means are presented here with standard error for the sake of comparison. There was no statistical analysis. In the case of papers located face-down, when only trace amounts of spray were discernible they were assigned a percent coverage of 1% and droplet density of 25 droplets/cm2.

    Results

    A few observations before we get to the results. Research has demonstrated that row kits and higher volumes improve spray coverage, and that’s why we tried banding the applications using row kits in Setups 2 and 3. However, this grower didn’t use GPS to plant his rows, and while they weren’t too crooked, they made it challenging to apply in a band. Further, there is some concern that a banded application would miss any inoculum in the alleys. These are important points to factor in when considering methods to control disease.

    The keen reader might notice we sprayed using pressures that exceed the manufacturer’s recommendations. In fact, none of these tips were rated over 60 psi and I used a formula to calculate their output at our high pressures. I have been heard to say (many times) never to exceed the manufacturer’s rates because it makes a mess out of the spray quality: droplets get much finer and pressure does not cause finer drops to penetrate a dense canopy. Better to switch to larger nozzles and stay within the pressures indicated on the manufacturer’s rate tables. I maintain that assertion. However, the grower was assured by fellow growers and custom applicators that this was the way to go and he wanted to try it. So, that’s where Setups 1, 4 and 5 came from.

    Be aware that a small sprayer like the one in this study needs considerable pump capacity to support such high pressure and flow to the boom and maintain effective agitation. For more information on pumps, check out this article.

    The following table expresses the coverage obtained by setup:

    Set upPaper PositionMean % Coverage (±SE)Mean Deposits/cm2 (±SE)
    Setup 1 – Broadcast XR 8006’s on 20” centres at 120 psi for 98.7 gpaTop1.0 ± 025.0 ± 0
    Middle23.6 ± 4.5253.5 ± 72.9
    Bottom15.2 ± 2.1423.2 ± 35.3
    Setup 2 – Three banded XR 8002’s at 120 psi for 108.6 gpaTop2.1 ± 1.178.9 ± 53.9
    Middle54.8 ± 12.1275.2 ± 145.3
    Bottom29.1 ± 2.7544.5 ± 70.4
    Setup 3 – Three banded XR 8002’s at 90 psi for 95.8 gpaTop7.4 ± 5.9134.4 ± 52.2
    Middle31.6 ± 15.9203.6 ± 108.5
    Bottom8.1 ± 3.9224.4 ± 102.3
    Setup 4 – Broadcast Twinjet 8004’s on 15” centres at 90 psi for 76.5 gpaTop1.0 ± 025.0 ± 0
    Middle33.3 ± 5.0240.7 ± 70.9
    Bottom12.9 ± 6.0263.9 ± 95.2
    Setup 5 – Broadcast Twinjet 8006’s on 15” centres at 90 psi for 115 gpaTop2.3 ± 1.3105.6 ± 80.6
    Middle48.9 ± 5.5194.3 ± 25.6
    Bottom19.5 ± 10.3246.8 ± 40.4

    The results may be easier to compare and contrast in the following graph.

    Strawberry coverage results for all five setups.
    Strawberry coverage results for all five setups.

    Observations

    According to the results, Setup 2 appeared to provide the best overall coverage. This is no surprise given that it was the second highest volume and employed a row kit. This corresponds with findings that have been published elsewhere. However, the excessively high pressure did create a lot of drift and the row kit didn’t always line up with the planted row. Further still, there’s the potential for missing anything that might harbour inoculum in the alleys, like runners. This setup wasn’t appropriate for this particular situation.

    The second-best overall coverage was obtained from Setup 5. This represented the highest volume, and a preferably lower pressure on twinjets, which may have allowed the spray to penetrate the canopy from multiple angles. This broadcast application is more reliable for hitting meandering rows and covers the alleys as well. So, the grower plans to employ this setup for the 2016 season, spraying at shorter intervals and confirming his coverage with water-sensitive paper. Let’s hope it works out.

    End-of-Season Update

    The grower that volunteered his time to this study has reported that his strawberries at the end of the 2016 season were absolutely beautiful. Granted, it is always difficult to draw a direct correlation between sprayer calibration and control. For example, 2016 was a very dry growing season and disease pressure was lower than in 2015. Nevertheless, spray coverage plays an important role in crop protection and our work to improve sprayer performance definitely played it’s part. His success is great news!