Category: Speciality Sprayers

Main category for all sprayers that are not horizontal booms

Spray Coverage in Potato
In June, 2014, 30 growers attended a spray coverage demonstration in a potato field in Alliston, Ontario. Our goal was to explore three questions:
1. What is the effect of droplet size on coverage?
2. What is the effect of volume on coverage?
3. What is the effect of spray angle on coverage?
This certainly wasn’t a scientific experiment. Spray demos are a great foil for discussing droplet behaviour and teaching operators how to diagnose spray coverage. Take the “results” with a grain of salt.
Discussing spray coverage in Alliston, Ontario (2014).
In order to see spray coverage, we placed water sensitive paper in the potato canopy (see below). Water sensitive paper turns from yellow to blue when it is contacted by water. Normally, we use a digital scanner to quantify spray coverage. However, it was a very humid day and this made it difficult for the scanner to discern spray from background. We decided to assign a qualitative value to the papers based on coverage. Low (or no) coverage got a score of zero. Moderate coverage (enough to offer good control) received a score of one. Papers with excessive coverage (anything more than moderate) received a score of two. Did I mention this wasn’t a scientific experiment?
The location of water-sensitive papers in the potato plant canopy. Two plants were papered for each nozzle.
Droplet Size
To answer the first question, we compared coverage from two hollow cone nozzles. The TeeJet TXR80028, which creates a fine/medium droplet size, and the TeeJet AITX8002VK, which is air-induced and creates a Coarse/Very Coarse droplet size. In both cases the boom was approximately 50 cm (20 in) above the top of the crop, travelling at 10 km/h (6.2 mph) and spraying about 110 L/ha (~11.5 gpa).
Generally, Coarse droplets tend to move in a straight line, and are not as easily deflected by moderate wind or travel speed. Conversely, Fine droplets slow very quickly and move erratically depending on the forces acting on them.
Graph 1 – Droplet size comparison. Cumulative spray coverage achieved in four positions, on two plants per nozzle. Low-to-no coverage = 0. Moderate coverage = 1. High-to-excessive coverage = 2.
Graph 1 shows the coverage results in each position. We see that finer droplets appear to penetrate the canopy more than the coarser droplets. We also see that under-leaf coverage was difficult to achieve overall. It’s possible the small amount of coverage achieved on the under-side of the top scaffold of leaves is the result of Coarse droplets bouncing… but if that’s the case, why wasn’t there any coverage on the upward-facing leaves inside the canopy? Write me – I’m open to ideas. In any case, redistribution is erratic and should not be relied on.
This graph may appear to favour smaller droplets, but be aware that Fine droplets are prone to drift and evaporation and should not be used without making every effort to prevent off-target movement. Shrouds, low ambient wind, and slower ground speed can help. To my mind, the best drift-mitigating option that still allows the use of finer droplets is an air-assist option on the boom, which would also improve under-leaf coverage. I’ve seen it in field tomato, soybean and even field corn. It’s disappointing that there aren’t more self-propelled sprayers in Ontario that offer this feature.
Volume
To answer this question, we compared coverage from Syngenta’s potato nozzles. They aren’t generally available in North America, but we got a few for the sake of the demo. The VP04 (gold) was operated at 1.5 bar (22 psi) and sprayed 135 L/ha (~14.4 gpa). The VP05 (Orange) sprayed 180 L/ha (~19.2 gpa) at the same pressure. The boom travelled at 10 km/h (6.2 mph) at approximately 50 cm (20 in) above the top of the crop.
Generally, raising the volume-per-hectare translates to improves coverage, but at some point there is a diminishing return. Imagine comparing coverage between 1 L/ha and 100 L/ha – there would be a big difference. Now imagine comparing 500 L/ha to 1,000 L/ha – probably not much difference, because drenched is drenched.
Graph 2 – Spray volume comparison. Cumulative spray coverage achieved in four positions, on two plants per nozzle. Low-to-no coverage = 0. Moderate coverage = 1. High-to-excessive coverage = 2.
According to Graph 2, the higher volume did not improve coverage. In fact, the lower volume appears to have superior coverage, but it’s likely not significant. Remember, there are no error bars here because there’s no statistical analysis – it’s not a scientific study. It’s possible that at this stage of growth, our 150 L/ha was close to the threshold of diminishing return.
Once again, note the absence of under-leaf coverage. Truly, the more I spray vegetable and row crops with conventional nozzles on a horizontal boom, the more I think under-leaf coverage can only be achieved by Bigfoot riding the Loch Ness Monster while wielding Harry’s wand. Without directed sprays from drops (aka pendant nozzles, drop hoses, etc.) or some means of redistribution (e.g. air assist or even maybe electrostatics) droplets will not reliably change direction.
Spray Angle
To answer this question, we used Hypro’s Guardian Air nozzle (GA11003), which is a 110° wedge-shaped flat fan that we alternated between 15° forward and 15° backward on the boom. We compared it to Greenleaf’s TADF nozzle (a blue and yellow 02), which is an asymmetrical, 110° twin-fan tip, where one fan is at 50° and has a higher flow compared to the second fan at 10°. We also alternated these nozzles on the boom to take advantage of what became four different angles of attack. Both tips sprayed 100 L/ha (10.9 g/ac) from a boom travelling 10 km/h (6.2 mph) and about 35 cm (~14 in) from the top of the canopy.
Graph 3 – Spray angle comparison. Cumulative spray coverage achieved in four positions on two plants per nozzle. Low-to-no coverage = 0. Moderate coverage = 1. High-to-excessive coverage = 2.
Graph 3 shows a lot of spray impacting on the surface of the canopy, with moderate penetration to the upward-facing leaves in the inner canopy. The angled spray may have helped a little, but no more than the finer droplets from hollow cones. While others like it, my personal experience in soybean, field tomato and ginseng has shown that the spray angle does not have much bearing on crop penetration in a broadleaf canopy. Perhaps if the canopy is sparse… but not in dense canopies. This shouldn’t be a surprise because angled sprays are best suited to vertical targets, such as wheat heads. Graph 3 seems to bear this out.
Now, since I ran this last demo, I’ve learned that I really didn’t use the twin fan nozzles optimally. In order to keep the outputs comparable, the rate controller operated the TADF’s at about 30 psi. That pressure is fine for something like glyphosate, but for contact products 60 psi to 120 psi is preferable to put the droplets in the medium range and keep them moving at the right angle.
A lot of people like the asymmetrical nozzles in broad leaf crops, so if they’re working for you that’s great. Carry on! As for me, I’m hoping to run a more stringent experiment in the future to satisfy myself.
Take Home
So, as I’ve pointed out a few times, this comparison of nozzles and spray variables isn’t definitive. It was only a subjective demonstration. Further, coverage doesn’t necessarily imply efficacy: Just because you have more coverage doesn’t mean you didn’t already have enough to do the job.
Caveats aside, however, there are a few points to be made:
- Smaller droplets penetrate dense canopies better than larger droplets, as long as they survive to arrive.
- Under-leaf coverage is difficult to achieve without some form of mechanical assistance – e.g. directed application from drops, air-assist, electrostatics, etc.
- Higher volumes result in improved coverage, but only to a certain point. Volume should reflect the stage of growth.
- At the moment, I’m unconvinced that spray angles impact (dense) broad leaf canopy penetration. There are, of course, many other learned and experienced opinions for spraying vegetables.
June 8, 2015
50 Ways to Get Good Coverage – Parody
50 Ways To Get Good Coverage
Sung to the tune of “50 Ways to Leave Your Lover” by Paul Simon.
The problem is all inside your barley canopy
The answer’s easy if you find it empirically
I’d like to help in your quest for efficacy
There must be fifty ways to get good coverage
She said it’s really not my habit to intrude
Furthermore, I hope my application won’t be lost or misconstrued
But I’ll repeat myself at the risk of being crude
There must be fifty ways to get good coverage
Fifty ways to get good coverage
Lower the boom, June
Get a new fan, Stan
You don’t need to drive slow, Bo
Just get yourself drops
Jack up the press, Bess
You don’t need to discuss much
Just get a new tip, Skip
And get yourself drops
She said it grieves me so to see you in such pain
I wish there was something I could do to give you pest control again
I said I appreciate that and would you please explain
About the fifty ways
She said why don’t we both just spray a bit tonight
And watch inversion drift in the morning light
And then she kissed me and I realized she probably was right
There must be fifty ways to get good coverage
Fifty ways to get good coverage
Buy Agrifac, Jack
Get a good gauge, Paige
You might need to drive slow, Joe
Just get yourself drops
Do calibrate, Nate
You don’t need to discuss much
Just do a good job, Bob
And get yourself drops
June 7, 2015
Novel Ginseng Boom Design
In 2013 we ran a sprayer coverage demonstration in a ginseng garden in Norfolk County, Ontario. The goal was to encourage growers to reconsider their spray operation with an eye to coverage. We performed a down-and-dirty comparison between simple disc-core nozzles and the considerably more expensive Arag Microjets. Opinions were mixed, but we were confident the humble disc-core could do the job.
One grower took the day to heart.
Having experienced Alternaria infection (likely due to frost damage) in the outer rows, he decided to buy a few packages of water sensitive paper and put his spray boom to the test. Multiple ground speeds, nozzle choices, pressures, spray volumes and even nozzle orientations were tested. This led him to what we will call “ideal coverage” from what may be the perfect ginseng boom.
Possibly the “perfect” ginseng spray boom. 25 hollow cones and four drop arms sporting 2 full cones apiece.
On June 15th, the temperature was about 22 °C, winds were light and humidity was about 40%. The nozzle arrangement was 24 D4-45’s (hollow cones) on the horizontal booms, spaced every 50 cm (20 inches). The grower built four drop arms, hung over each alley (not just behind the wheels) with twin bodies that each held two D5-35’s (full cones), for a total of eight dropped nozzles.
His output was ~1,000 L/ha (115 US gallons per acre) and he sprayed at ~14 bars (200 psi) and he was travelling at ~7.2 kilometers per hour (4.5 miles per hour).
Compared to traditional methods, that’s low pressure and low volume for ginseng. The ground speed was reasonable given the art of negotiating a sprayer under a shade structure. Collectively, this is a savings in fuel, water and pesticide.
Positions for water sensitive papers.
Water sensitive papers were placed in seven positions (see image below) in a three-year old garden. In each position, the papers were folded so the paper wrapped around the stems and could show coverage facing each alley. They were placed on the stems just above the ground and just below the canopy on three plants. The seventh card was folded over the uppermost leaf, to show coverage on the adaxial (top), and abaxial (underside) of the leaf.
Water sensitive papers corresponding to the numbered positions in the earlier illustration. Cards were folded around the stems to face each alley (Cards 1-6) and around the top leaf for surface and under-leaf coverage (Card 7). There are some drenches, but no misses.
The coverage was excellent. A completely blue card represents a drench, which isn’t necessary but can be difficult to avoid when trying to spray all surfaces in a dense canopy. The rest of the papers show a high droplet density which tends to lead to an effective application. Ideally, hope to see 10-15% coverage and >85 droplets per cm². This is a difficult or even impossible prospect for abaxial coverage, but we achieved it (note the lower half of card 7).
The trick, you ask? The full cones on the drop arms are aimed so the bottom of the cone is parallel with the ground (essentially, aimed up about 30°). That creates a cloud of spray moving under the canopy, improving the odds of contact on all surfaces. It is important to not spray the cone into the ground or the raised mound, and to spray in from both sides.
The improved drop arm
The drops themselves have been modified so they are flexible enough to move through an overgrown 3rd or 4th year garden (yes, there will be some leaf damage), but are also stiff enough not to sway. This was accomplished by sliding a sheath of electrical conduit over the drop arm and using a metal stabilizing arm that terminates in a ring around the conduit.
With the right timing and product choice this method of spraying will be hard to beat. And it’s cheap! It’s going to save fuel and wear because of lower pressures, and save spray mix because he can go a lot farther on a tank spraying only 1,000 L/ha.
For more information, check out the OMAFA research article describing the original research that set us on the path of drop leg technology.
Special thanks to Richard Klosler of Michael Klosler Farms Ltd. for sharing his great boom design.
June 4, 2015
Measuring Pressure Drop
All sprayers experience a drop in pressure as the solution moves further away from the pump. Here’s why that’s important, and how to measure it.
Optimal nozzle operation in terms of spray quality and fan angle is closely tied to spray pressure. As we try to maximize travel speed range with a modern sprayer, we often push spray pressure to its limits on the low and high side. For many air-induced nozzles, spray quality and fan angle become critical at about 30 psi. We need to be sure about the exact nozzle spray pressure to prevent problems.
Pressure drop is caused by the friction that the spray solution experiences as it moves from the pump to the spray nozzles. It’s caused by a number of factors, including length of tubing, elbows, valves, screens, and other flow obstructions.
Plumbing components add friction to liquid flow. If the pressure gauge is installed before these components, the nozzle pressure is unknown but will be lower than the gauge reading.
The pressure transducer that reports pressure to the cab is usually located between the pump and the manifold that divides the spray into the various boom sections. At this point, the spray liquid hasn’t experienced any significant flow restrictions. The transducer basically reports pump pressure.
Once the spray mixture starts moving through boom sections towards the nozzles, it encounters those restrictions, and pressure at the nozzle will therefore be lower than the cab reading indicates. The higher the liquid flow, the greater the friction, and therefore, pressure loss.
Even older sprayers with only two boom sections (left and right) and few elbows and reducers, will see pressure losses due to the narrow and long boom pipe that feeds up to 60′ on each side.
The nozzle pressure can be measured with a gauge placed on a nozzle body. Simply purchase a quality gauge and a threaded nozzle cap, combine the two and install in place of a nozzle.
A pressure gauge threaded into a nozzle cap can measure boom pressure.
Operate the sprayer at your expected spray pressure (say, 60 psi) with all boom sections on. Install the portable pressure gauge on an open turret position and turn into place, noting its reading. If both gauges are accurate, the boom pressure will likely be below 60 psi.
The difference between the cab gauge pressure and the boom gauge pressure two is the pressure drop. Repeat the measurement for each boom section. Also repeat at your lowest, as well as your highest expected flow rates. Higher flow rates cause greater pressure drops.
Now, use this information to adjust your interpretation of the cab pressure reading. For example, if you want to spray at 60 psi and your pressure drop is 10 psi, then the cab pressure should read 70 psi.
If your boom pressure is higher than your cab pressure, and you’ve checked the accuracy of your new boom gauge, then don’t be too mystified. Your pressure transducer is malfunctioning.
This exercise is important if you’re trying to compare your nozzle flow to the expected nominal flow of the nozzle – perhaps you’re trying to determine nozzle wear. The nominal flow of agricultural nozzles is determined at 40 psi, so it will be important to measure the flow at exactly that pressure.
By measuring pressure drop on all your boom sections, you also get a good sense of the variability in pressure across your boom. Your measurements might reveal an obstruction or a hose kink somewhere along the line.
To see how low pressures can affect coverage, watch this video.
Note that the pulse-width modulated systems offered by Capstan, Case, and Raven use a solenoid at each valve. This solenoid adds a known, and significant, pressure drop to the spray system as can be seen here.
Pulse-Width-Modulation (PWM) solenoids typically have internal flow restrictions that can contribute to pressure drop.
Here’s a fun video filmed by the Ontario Pest Education Program during a break at Ontario’s Southwest Crop Diagnostic Days:
June 1, 2015
Off-Label Spraying: A Lose-Lose Situation
Submitted while Dustin was the Commercial Horticulture Specialist with Alberta Agriculture and Forestry.
Horticultural chemicals and pesticides often have the dubious distinction of being more expensive than their field crop cousins. In order to reduce costs, growers may sometimes buy and use chemicals which have the same active ingredient, but are not registered for the crop they’re being used on. This practice of “off-label” spraying is not only illegal and can result in severe fines, but can also be incredibly dangerous for your clients, your livelihood, and the environment.
Health Canada’s Pest Management Regulatory Agency (PMRA) is the sector of the federal government that is responsible for overseeing the registration and regulation of pesticides in Canada. This includes products that producers are more familiar with such as herbicides and fungicides, as well as less thought about products such as animal repellents, rodenticides, and disinfectants. These products are all rigorously tested to compile data on residue, efficacy and long term effects, all of which is reviewed by Health Canada prior to registration. Furthermore, the PMRA is the body in charge of monitoring and enforcing appropriate use of these chemicals to ensure public safety.
When reviewed by Health Canada, all chemicals have specified rates, target pests, and the crops on which they can be applied. ‘Off-label’ spraying can include spraying above the appropriate rate, or spraying the chemical for a pest that it is not registered for or on a crop not on the chemical’s label.
Throughout the year, the PMRA randomly selects growers for pesticide use inspections in order to ensure compliance. These inspections could be random ones, arising from increased incorrect spraying because of a label change, the need to update information or a neighbour’s complaint. The purpose of inspections is twofold in that they serve as a deterrent to off-label spraying but also as an educational tool to encourage growers to follow labels.
In an inspection, samples of vegetative material or soil are collected and sent away for testing. Should these come back showing incorrect use of chemicals, growers may be subject to increased monitoring, financial penalty or even prosecution under the Pest Control Products Act. If somebody producing food is found to be non-compliant, it could even result in the Canadian Food Inspection Agency (CFIA) becoming involved and product being recalled or destroyed.
No grower wants to purposefully put themselves, their clients or the environment at risk, so how to avoid the temptation of spraying off-label? When possible, avoid the need to altogether! Good scouting and appropriate record keeping allows growers to track outbreaks over time and better plan for them in their operating cycle. Furthermore, a good chemical inventory will give producers a better idea of how much they have of needed chemicals and whether they have enough to deal with problems when they come up. Adopting biological controls in their operation may also allow growers to nip some problems in the bud before they become full blown issues.
As with all chemicals, proper storage, labelling and disposal are all part and parcel in running a safe, effective operation. By being aware of the process and how best to handle these chemicals, growers can ensure they grow a safe healthy crop without running afoul of the law.
June 1, 2015