In 2016, an asparagus grower in southern Ontario picked up a used De Cloet Hi-Boy originally used to spray tobacco. His vision was to create a three-row herbicide sprayer for asparagus and we were invited to participate. His concept was to design shrouds that would contain the herbicide, but not snag the asparagus or drag heavily on the ground. This article follows the development of the sprayer from concept to testing to final product.
The sprayer itself was a classic three-wheel, self-propelled affair. The asparagus was planted on four foot centres, leaving a three foot alley. While the goal was to hang three shrouds off the boom, we started with one to work out the bugs.
This operation uses 2,4-D to control weeds in the alleys and while a little can hit the asparagus stem up to 12 inches (where the branching starts), we wanted to avoid contact at all costs. That led us to the TeeJet AI 95° flat fan nozzle, which produces a Very Coarse to Extremely Coarse spray quality. A single nozzle could be suspended to span the 3 foot width of the alley.
The first version of the shroud was suspended off the boom from four anchorage points. A certain amount of of play was allowed so the shroud would find plumb (i.e. hang vertically), even when the sprayer boom yawed or pitched over uneven ground.
The shroud was constructed of sheet metal, angled to reduce the potential for contact with the asparagus branches, and terminated in stiff, nylon brush-style mud flaps commonly seen on trucks. These brushes were cut to a few inches in length to span the distance between the side of the shroud and the ground. This would create a “seal” to prevent spray from escaping, maintaining some degree of contact with uneven ground.
We tested the first version by placing water sensitive paper in two positions on the ground, just inside the reach of the brushes. We had to be careful not to run them over with the centre wheel of the sprayer. We also adhered two papers to the angled inner walls to see how much, if any, spray was hitting the inside of the shroud.
Our first pass on June 16th was at 9:00 am, 19.1 ºC (66.4 ºF) with a cross wind of 5 to 7 km/h (3.1 – 4.3 mph). relative humidity was high at 85% and travel speed was slow at 3.2 km/h (2 mph). We started with the .06 AI tip at 50 psi, but we drenched all the targets with excessive coverage because we were travelling so slow. We also found the stiff brushes were creating furrows in the soil, as shown below.
For our second pass, we tried the .04 tip and raised the shroud while dropping the tip to keep it suspended 15 inches over the ground. We were still drenching the targets and noticed the shroud was hitting the asparagus spears, causing physical damage. The damage is shown below – note the dark green on the bent spear.
This led to a decision to flare the side walls more aggressively, bringing them further into the centre of the alley and away from the spears (shown later in the article). This had the added benefit of angling the brushes as well to get a maximum span for weed control in the alley. For the final coverage pass we used the AI .03 tip, which gave more than 45% coverage on the ground, with even distribution, and there was no indication of spray on the papers adhered to the inside of the shroud. This coverage is more than is likely required, and the operator should be able to spray up to 6.5 km/h (4 mph) without compromising coverage.
Since the coverage tests, the grower added additional sheet metal fenders to the the existing fenders, encasing the wheels and creating a smooth transition for the shroud to gently deflect the asparagus. The fenders were needed because the grower found the asparagus was being pushed out by the wheel fender only to bounce back in front of the shroud, which snagged the fern and damaged it. The additional fenders keep the fern spread and prevent it getting caught in front of the shrouds.
The grower was very happy with the sprayer’s performance and planed to build another. Why be satisfied with the status quo when you can tap into your creative side and be innovative? If you don’t think you’re imaginative enough to try upgrading equipment on your farm, here’s a simple test to prove that it’s in you. It’s easy to see the bird in the image below, but with a little concentration you’ll be rewarded with a ski-jumping rabbit.
Thanks to TeeJet for donating the nozzles and water-sensitive paper and to Ray and Brad Vogel of Lingwood Farms for inviting me to participate.
Cleaning, flushing, triple-rinsing… whatever you call it, sprayer sanitation is a time-consuming and distasteful task.
Methods vary, but they generally span from the classic triple rinse (30-45 minutes) to a full tear-down and decontamination (many hours and likely an overnight soak). The operator decides how much time and effort to invest depending on the chemistry they’ve just used and the crop they intend to spray next. Learn more about the power of dilution in this article and in this article.
Unfortunately, two facts are certain:
At minimum, operators should rinse the sprayer at the end of each day… and they generally don’t.
It is only after spraying a sensitive crop that the operator truly knows whether the sprayer was cleaned sufficiently.
Continuous Rinsing
We’ve promoted Continuous Rinsing as a viable alternative to Triple Rinsing in previous articles (see here and here). Executed correctly, the method:
greatly reduces the time required,
is as effective,
eliminates operator exposure, and
reduces potential environmental contamination.
Continuous rinsing requires the installation of a dedicated “rinse pump” to transfer clean water to the product tank from the rinse tank via the wash-down nozzles. This permits the main product pump to operate simultaneously, emptying the product tank and spraying the rinsate out the boom.
Imagine your sprayer empties at the end of the row. You position the sprayer at a headland or a row you sprayed earlier. A toggle switch in the cab engages the rinse pump and the wash-down nozzles start spraying clean water into the product tank. You then resume driving and spray until the rinse tank is empty. During the process, any solution in the return/bypass line is quickly diluted, and any standing volume in the system is displaced by clean water.
It takes five minutes and you never left the cab.
Remember: Rinsing can dilute residue to ~2-5% in most of the sprayer plumbing, but it is not intended to replace the more rigorous decontamination process. Closed circuits, filters and dead-end plumbing can still harbour residue >15%.
Installation
Working with GreenLea Ag Center in 2017, we installed a Continuous Rinse system on a Case IH Patriot 4440. It has a 1,200 gal. product tank, a 140 gal. rinse tank and a 120 foot boom. A parts/price list for the Patriot installation appears at the end of this article.
Additionally, we have included the parts/price list from our 2016 HJV Equipment installation on a RoGator 700, which had a 700 gal. product tank, 50 gal. rinse tank and a 90 foot boom.
Still further, we have included three homegrown solutions from operators that developed their own continuous rinse systems.
Sizing the Rinse Pump
It is very important that the rinse pump has the capacity to operate the wash-down nozzles and still supply clean water at a rate approximately equal to the rate at the boom. Basically, “in must equal out”. If the rinse pump supplies too much clean water, the volume rises in the product tank and efficiency is reduced. If it cannot supply enough, the main product pump will lose suction and not function correctly.
We installed a Hypro 9303C-HM1C centrifugal pump (max flow rate of 114 gpm at 130 psi), matching the make and model of the exiting product pump. A length of channel was installed on the chassis to mount the pump and close-coupled hydraulic rinse pump motor, and a valve block.
Really, electric pump installation is easiest. An alternate pump that has been used is this one from Pattison Liquid. For added benefit, it’s a chem transfer pump that can handle the pesticide formulations. If the pump doesn’t give enough flow, a second one can be installed parallel to double the flow.
Hydraulics
Let’s being with advising caution: If you are uncertain about your hydraulic capacity (and tightly designed systems rarely have extra) then consult with a manufacturer-certified service technician, or consider an electrical alternative.
For the Patriot, the auxiliary hydraulic circuit was used to drive the hydraulic rinse pump; we piggy-backed off of that existing system. In this case, Continuous Rinsing increased the load on the auxiliary hydraulic circuit, but only marginally, so performance was acceptable.
We drew that hydraulic flow directly from the auxiliary pump output using a ‘T’ piece to ensure full pressure was available when needed. Then we broke into a common low pressure return manifold using another ‘T’ piece to provide the return flow.
Originally, we were concerned that robbing too much hydraulic flow could compromise sprayer operations. We therefore exchanged the hydraulic motor that came with the pump for one that required less hydraulic flow. However, the pump operated at such a high speed that the rinse tank was drained in two minutes! We felt this would not give the operator enough time to make minor adjustments (see the “Avoid Airlock” section later in the article). We also felt the rinsate would not have enough time to hyrdate any residue in the tank and lines. We therefore returned to the motor that came with the pump, slowing the pump and bringing our rinse time to approximately five minutes.
We installed an on/off hydraulic control valve block and solenoid controlled by a toggle switch in the cab. When the rinse switch was engaged, 12 volt DC opened the solenoid, allowing hydraulic oil from the auxiliary pump to turn the rinse motor, which in turn powered the rinse product pump.
Avoid Airlock by Balancing Flow
While Continuous Rinsing works well with an unbroken stream of clean water, there is demonstrated benefit to allowing the pump to draw a small amount of air. The bubbles are reputed to scrub the lines more effectively than water alone. It is possible that the new Hypro 9307 series centrifugal pump, which claims to eliminate dry run, would facilitate this.
However, avoid excessive cavitation or airlock of the main product pump. This will damage the pump seals and interfere with pump suction. If the main product pump is a piston-diaphragm pump, avoid losing the prime by letting a small volume of rinse water build up in the product tank before spraying the rinsate.
Maintaining the balance between the supply from the rinse pump, and demand by the product pump, will take careful trial and error. If the sprayer employs a rate controller, speeding up or slowing down travel speed is a means for making adjustments to match the two flows. Alternately, an operator can adjust the pressure regulator manually. Remember, the nozzles won’t need to work optimally so you have the option to use fairly low pressures to match flows.
In the case of an operator applying 28-0-0 using dribble bars or fertilizer nozzles, there is likely too much flow at the boom for the rinse pump to keep up. While we have not tried it, but as long as there was sufficient volume in the clean water tank, it might be possible to rinse the boom section by section, starting with the outside sections and moving in towards the centre.
Lessons Learned
The installation was a learning process, during which we noted the following:
At first, the rinse tank slowly emptied through the rinse pump, even when it wasn’t in use. We prevented this by installing a 10 psi check valve between the pump and main tank.
The rinse pump ran dry and burned the seals when the operator forgot to turn it off after the rinse tank was empty. We considered a timer or alarms to prevent this, but chose to install a level sensor (essentially a float) which would cut the 12 Volt DC feed to the on /off solenoid, effectively turning the system off when the rinse tank was empty. Note: the sensor is not in the parts list – it was purchased for ~$10.00 CAD from Amazon.
When deciding where to draw hydraulic flow to run the rinse pump, we first tied into the main hydraulic circuit (i.e. not the auxiliary). This negatively affected both steering and boom control. Beware drawing flow from critical safety systems such as steering.
Future Development and Other Advantages
GreenLea was exploring an option to use the rinse pump to bypass the product tank, and flow directly to the boom. This can be accomplished by teeing an electrical 3-way ball valve just after the pump to allow flow directly from the rinse tank (see dashed line in the flow schematic shown earlier in the article). Imagine being rained out, or having excess mix left in the tank at the end of the day. This system would allow the dilution of any corrosive chemical from a sensitive precision application system without losing or contaminating the spray tank. It should be noted, however, that high precision spray systems (e.g. AIM Command, Pro and Flex) would still require the operator to open the boom flush valves manually to allow the boom purge.
Growers have suggested the system might also be used to get a sprayer to end of a row if it threatens to run empty before completing the pass. A small volume of clean water added to the tank would displace the 15-30 gallons of unusable volume and stretch the application. Be aware that this would also dilute the product due to the agitation/bypass and should only be considered when a minute or less of additional spray is required.
Homegrown Solutions
Tyler Patriot (Electrical)
David Kucher (@DavidKucher) from Saskatchewan installed Continuous Rinse on his Tyler Patriot (75 foot boom, 800 gal. product tank).
Here’s what he had to say:
The rinse system I was using on my sprayer previously involved a lot of time and effort. Plus, the quality of job it did was sometimes imperfect (I keep pictures on my phone of a canola crop that was damaged because of a poor rinse job from a few years ago). The old system used the main product pump to rinse, so there was a bunch of valves under the sprayer that needed to be turned, and the pump had to reprime for each rinse. It was tedious.
Uncertain about the hydraulics, David elected to use an electrical pump, but had difficulty finding one that would produce enough pressure and flow. Most electric pumps were too small and it would have taken more than one, plumbed in parallel, to achieve the volume numbers required. However, David found a high-flow 489G-95 AMT High Head Washdown Pump (1 HP, 1-1/4×1 IN/OUT, 12 VDC,Cast Iron,Buna-N) which he got from the US for about $1,200.00 CAD. Max flow was 56 gpm.
Note: In 2020 this pump model changed to the 12DC-95.
He removed the majority of plumbing, valves, and related complexity from the old rinse system. The Continuous Rinse was comparably simpler and isolated from the rest of the sprayer plumbing. It just involved a fill line from his two clean water tanks, the new rinse pump, and the existing rinse nozzle inside the product tank.
When the product tank empties, David holds down a push button dead-man switch he installed to activate the rinse pump. If he wants to do a more thorough job, he flushes the product tank and plumbing for about two minutes, then stops, gets out and opens the boom end valves. Then he climbs back in and does another one minute flush.
Approximately 30 gallons of water go through on each flush and my only issue is that I waited so long to install the system.
Author’s note: Positive displacement electrical pumps (which have zero risk of seal loss) are reasonable alternatives to centrifugal pumps. Depending on the size of the sprayer, multiple pumps plumbed in parallel can provide sufficient flow. We elected to use two Hypro electric roller pumps (model 4101 N-H) for the 2016 RoGator 700 installation. Cheaper, low amperage 12V diaphragm pumps from Delevan and FLOJET with capacities of 5-8 gpm are also available.
John Deere 4830 (Hydraulic)
Russ Enns (@EnnsFarms) from Saskatchewan installed a Delavan HD Magnum 125 hydraulic driven pump (1-1/4” suction, 1” discharge, 5-7 gpm of hydraulic flow). He mounted it on the same mounting plate as the main product pump, just on the opposite side, using the same bolt holes.
It was tied hydraulically to the main product pump, so the rinse pump could only run when the product pump was operating. The hydraulic supply from the sprayer went through an electric/hydraulic block via a solenoid resting in the closed position. A rocker switch in the cab used 12V to activate the rinse pump from the cab. Return hydraulic pressure from the rinse pump was tee’d into the main solution pump hydraulic return.
The clean water intake for the rinse pump was tee’d into the factory rinse tank. The discharge side of the rinse pump was plumbed to a check valve and tee’d into factory tank rinse system. Here’s the discharge line, check valve and tee into factory rinse (below).
Russ mounted a large pressure gauge on front right axle to monitor rinse pressure. It’s easy to see from the cab, and easy to tell from the pressure when the rinse tank is empty.
In this case, Continuous Rinse is used in tandem with an Accu-volume tank gauge so Russ could monitor the level in the main product tank from the cab. Depending on the nozzles being used, he found that the rinse pump supplied clean water faster than the rinsate could be sprayed.
So, after finishing a field (or changing chemical, etc.) Russ turned on the rinse system while spraying the rinsate out on the field. The Accu-volume alerted him if clean water was accumulating in the product tank. If it got to ~20 gallons, he would briefly suspend the rinse pump while spraying to allow the level to drop. Then, he would start the rinse pump back up. He repeated this process until the clean water tank was empty.
Russ had many of the main components on hand, but estimates replacement value at ~$1,200.00 CAD. He noted that while installation was straight-forward, he originally piggy-backed the rinse pump’s hydraulic supply off the main solution pump, and it didn’t work correctly. We did that too, Russ 🙁
“Time savings and environmental considerations are the biggest benefit of this system to me. Being able to finish spraying a field, and immediately start rinsing and spraying the diluted solution is a huge time saver. I feel it’s a far more thorough rinse and a better/quicker dilution rate compared to how I previously handled rinsing and spraying out the diluted solution. Another benefit is that even though it’s plumbed into the factory rinse, the factory rinse system can still be used normally if for some reason the continuous rinse pump quits.”
Gregson Trailed (Electrical)
Continuous Rinse isn’t only for grains and beans. Matthew Droogendyk installed two 12v pumps on his trailed vegetable sprayer that matched the flow of the main pump. They had an electrician install a box for switching the the pumps and two solenoid valves on at the same time.
They noted an issue when trying to prime the main pump after emptying the tank. If the tank was sprayed completely empty, the main pump took time to get primed again. This affected rinsing time as well as the balance between supply and demand. Through trial and error they determined that running the rinse pumps for 1 minute (~15 gal) gave enough time to rid the main pump of air. Then the flows matched at about 15 gpa. Re-priming took about 5 minutes, and then an additional 2 or 3 to rinse using about 45 gallons of clean water. They found there was no need to replace their original tank rinse nozzles.
Tank Rinse Nozzles
One of the challenges of installing continuous rinse is ensuring the tank rinse nozzles are capable of rinsing the entire solution tank interior at potentially low pressure and low flow. In 2019, Lechler released the ContiCleaner range of rinse nozzle. Four ISO colour-coded nozzles capable of operating from 2-5 bar (29-72.5 psi), with flows from 6.5-32.3 L/min. (1.7-8.5 gpm). This will enable operators to better match the rinse nozzle(s) to the clean water pump. Be aware they are very difficult to source in North America. We tried and weren’t able to get them.
Parts / Price List
The following two parts/price lists are in Canadian Dollars. They do not include tax or labour and prices change depending on where and when parts are purchased. As you have read from the operators that installed their own Continuous Rinse systems, there are many possible solutions, so these lists are provided only for reference. Click the link to download a PDF.
Before contacting them, have the following information on hand:
Sprayer tank volume (both product and rinse, if applicable)
Boom length
Nozzle spacing
Largest nozzles mounted/used on the sprayer (excluding fertilizer nozzles)
Power available on sprayer (e.g. 12V available? Max amp? Hydraulic capacity?)
Thanks to Russ Enns, David Kucher and Matthew Droogendyk for sharing their install stories. Thanks to Adam Beaumont and Ehrin Frid for the Case IH and RoGator installations, and to Mike Cowbrough (@cowbrough) of OMAFRA and the Ontario Soil and Crop Improvement Association for collaborative support.
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 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.
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
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:
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).
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.
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.
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.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 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.
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.
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 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.
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.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 (September 9).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. 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.
