Author: Jason Deveau

Spraying in Vegetable Greenhouses
Back in 2011 we toured a few vegetable greenhouses in Southern Ontario. I wanted to learn more about how greenhouses used hydraulic sprayers (i.e. not misting or fogging systems) to apply pesticides to tomatoes, cucumbers and peppers. It was an eye-opening experience for me, because like every commodity group I’ve encountered, they had their own unique way of doing things.
Manually-towed sprayers
The first operation employed a system that I’ve come to learn is fairly common in greenhouses. There is a centralized tank and pump, located outside the growing area. Products are mixed and pumped from there.
Mixing area
The pressure is set at the source so the spray mix is pumped to the rest of the greenhouse where the sprayer can be quick-connected to one of a number of outlets along a central line. I’ve been surprised in the past to see airblast sprayers set as high as 300 psi, so it really surprised me to see the pressure set to 500 psi! I was told this was necessary to counter the pressure-drop experienced at the far reaches of the greenhouse (see below).
Pressure regulator on a clearly-labeled tank.
The sprayer itself was a manually-towed vertical boom and a coil of hose. The operator would wear appropriate personal-protective equipment and tow the sprayer between the rows at a constant speed. They may or may not have the ability to control the pressure with a regulator on the boom – the nozzle selection and travel speed dictate the rate.
Manually-towed vertical boom.
Demonstrating how an operator spays greenhouse tomatoes with a towed vertical boom. This was just water, so no PPE required.
In this demo, the operator was using yellow TeeJet VisiFlo hollow cones (TX-VK3) which, despite the pressure-drop, were still operating at >300 psi and therefore beyond what the manufacturer lists in their rate charts. The resultant spray quality was Very Fine. We’ve said before that increasing the pressure does not increase the speed of tiny droplets appreciably, but that’s when we’re talking about going from, say, 60 to 90 psi. At pressures as high as 300 psi the droplets are moving fast enough to generate some air movement (i.e. making their own light wind) and there was a visible distortion of the outer potion of the crop canopy. The resultant coverage, even on the underside of a leaf (see below), was hard to fault.
Under-leaf coverage
However, as one would expect with Very Fine spray, a lot of the mist didn’t go anywhere. So while the coverage was very good, it was not terribly efficient. I was left thinking there might be an opportunity to find a savings in spray mix and reduce the potential for operator exposure by lowering the pressure. Unfortunately the regulator would not allow us to reduce the source pressure appreciably, so we weren’t able to experiment.
Automated sprayers
The next greenhouse we toured used a far more sophisticated method for applying pesticides. While they still used a centralized tank and pump, the sprayers were not hand-pulled trolleys; They were robots! Well, they were automated vertical booms that rode along the hot water pipes in the alleys between the crops. The operator would stand in the corridor and send one sprayer hurdling down the left-hand alley. The sprayer sprayed from only one side of the boom as it went. When it reached the end of the alley, the boom would rotate 180°. Just as it began the return trip, spraying the other side of the alley, the operator would send a second sprayer down the right-hand alley. As the second sprayer reached the end of it’s run, the operator would retrieve the first sprayer, and set it rocketing down the next left-hand alley. In that fashion, alternating back and forth, the greenhouse got sprayed.
Automated vertical boom sprayer
The automated sprayer was set to operate at ~350 psi, traveling at a rate of 75 meters per minute, spraying from a vertical boom equipped with five flat fan nozzles oriented vertically. Water sensitive paper (which has one face that goes from yellow to blue when water contacts it) was placed in three locations in the tomato canopy.
- One was placed directly behind the fruit with the sensitive face square to the sprayer.
- One was placed with the sensitive face facing the ground (this upside-down orientation exposed only the edge of the card to the sprayer).
- The last was oriented with the sensitive face aimed into the direction of the sprayer’s travel, again only exposing the thin edge of the card to the sprayer.
Water-sensitive paper shielded by a fruit. Sprayed with flat fan nozzles.
Flat fan nozzles
The sprayer was released to spray the 125 metre row using the flat fans. To the observer, it produced a cloud of spray that appeared to completely envelop the target row. Very little was seen to escape through the tomato canopy into the next row. When the cards were retrieved, however, the coverage was disappointing. See the right-hand column of papers entitled “Flat fan” in the image below. This goes to show that a spray cloud can fool you – always use water-sensitive paper to confirm spray coverage.
Coverage from three sets of nozzles. Papers oriented in three different ways in a tomato vine.
Hollow cone nozzles
Now, don’t look at the centre column of papers just yet (you just did, didn’t you?).
We chose to switch from the vertically-aligned flat fans to hollow cones. The concept was that the spray would be emitted from so many new angles that it would penetrate the canopy more effectively and hopefully cover more of the targets. I’ll note that we had to use extra gaskets to hold the nozzles firmly in place. The sprayer was re-nozzled, the paper targets replaced, and the sprayer sent back down the alley. Once again, the spray swath looked good to us, but when we retrieved the papers, there was almost no coverage; It was far worse than the flat fans.
Multiple gaskets were required to hold hollow cone nozzle tightly in place.
Finer droplets have very little inertia, so perhaps the high pressure made the droplets too fine for them to move very far. To test this, we reduced the pressure to 100 psi and re-sprayed the same cards, which were simply left in place. The resultant coverage was not improved.
We left the papers in place for a third pass. This time we thought perhaps the spray was still too fine because of the nozzle itself. We replaced the hollow cones with a different set of hollow cones that produced coarser droplets and the same cards were re-sprayed. Still no practicable improvement.
We were getting desperate, now. Cards were left for a fourth pass. It has been demonstrated that a slower travel speed can improve canopy penetration in orchards, berry crops and and grapes, so perhaps the sprayer was moving too quickly? The sprayer was slowed to 50 metres per minute and the cards sprayed for a fourth time. Now look at the centre column entitled “Hollow Cone (x4)” in the figure below. This coverage is the result of four passes with hollow cones. It was disappointing.
Note: a greenhouse is a very hot and humid place. Water-sensitive paper begins to discolour quickly, so don’t leave them out for longer than you have to. That’s why the top paper is cloudy-looking.
Coverage from three sets of nozzles. Papers oriented in three different ways in a tomato vine.
Twin-fan nozzles
Finally, and only because I had them with me, we decided to try dual flat fans (in this case, TeeJet DG TwinJets). Symmetrical and asymmetrical dual fans are often used to spray vertical targets in field crops (e.g. to control fusarium in wheat heads). We oriented the nozzles so they alternated 45° left, then 45° right. We also turned off every second nozzle. The idea was to prevent the fans from physically intersecting, but still create an overlapping swath. The paper targets were replaced and the sprayer was returned to its original settings (i.e. 350 psi and 75 m/sec). We managed to twist them into that orientation by using a cap with a circular opening and additional gaskets to hold the nozzle snugly. Plus, at 350 psi, we had to get the nozzles extra tight to prevent leaks.
Nozzling a vertical boom.
The result was spectacular. Here are the results once more (below). See the left-hand column entitled “Dual Flat Fan”. The cards received so much coverage that two became drenched and curled. Even the card with the worst coverage received more than enough. I will point out that this was achieved with about 2/3 the spray volume the operator typically used to spray with flat fans.
Coverage from three sets of nozzles. Papers oriented in three different ways in a tomato vine.
And, this is where the tour and our trials ended. The operator was happy with the improved coverage and so was I. I was sure to tell them that now that more spray was hitting the target, they should explore reducing the spray volume (either via reduced pressure or lower-rate nozzles) until all the papers looked more like the one in the bottom-left. I suggested a goal of about 85 drops per square centimetre (a benchmark for good coverage) rather than the drench/run-off we were currently getting. The spray mix would continue to be the same ratio of formulated product-to-carrier, but a judicious reduction in overall volume would result in reduced pesticide costs and reduced wastage as long as coverage was never compromised.
And now, a warning…
Unfortunately, as I heard two years later from a miffed agrichemical dealer, the operator did not follow through with the volume reduction. I was told the tomatoes began to exhibit symptoms that looked like blossom end-rot but he suspected it might be chemical burn. His hypothesis was that so much spray was getting to the tomatoes that it was accumulating at the bottom of the fruit during run-off, concentrating as the spray dried, and damaging the area. We may never know what really happened.
And so, it’s important to remember that whenever you adjust or calibrate your sprayer to improve spray coverage, you should reconsider how much spray you need to accomplish your goals. If you were getting poor control before the adjustment, improved coverage might help. If your level of control was already satisfactory, and your adjustments were intended to reduce wastage, consider reducing how much spray volume you use. This is called crop-adapted spraying.
Note: If you are concerned that changes to your spray practices might cause unwanted side effects, always perform trials on small test-plots and monitor the crop closely to ensure there are no negative impacts.
Take home
Greenhouse vegetable producers should consider using water-sensitive paper to test nozzle arrangement on their high volume sprayers. From our preliminary work here, dual flat fans at alternating angles might be worth exploring in hanging tomatoes. And, because it cannot be overstated, consider making changes in small test plots first and monitor the results closely.
August 24, 2016
Sprayer Top Tips – The Twitterverse has Spoken
In June, 2016 (back when Twitter was fun), someone tweeted a clever tip for sprayer operators. It got the usual round of likes and retweets, but it also inspired an idea. We decided to have a two week-long competition for the best North American tip under the hashtag #SprayerTopTips. The winner would receive a WeatherFlow windmeter. Shortly thereafter, Graham Smith (@retrofitparts) of RetroFit Parts generously volunteered a weather meter for the best UK submission.
After two weeks, we received 43 Sprayer Top Tips. Some of the submissions were best practices, some were equipment tweaks and some were downright funny. Thanks to everyone that shared their ideas, practices and sense of humour. Since Twitter limits a tweet to 140 characters, we took the liberty of interpreting a few of the tweets to ensure everyone understands the content.
Let’s be clear – we’re not endorsing any of the brands or practices here. There are some great ideas, but give it some thought if you’re thinking of adopting any of them. And so, in no particular order, here are the submissions for the 2016 #SprayerTopTips competition:
‏@a4nick – Any smartphone with apps weather, windspeed, calculator, camera, set up guides and Twitter <to access the> global knowledge of operators.
@Camcar_Ent – Put the dirt bike on the trailer to allow it to be moved where the sprayer will need a fill.
@Paulvdb2016 – Finally found the water cooler in the John Deere R series cab!
@Paulvdb2016 – Everybody breaks a few nozzle bodies each year! Save the turret part to organize your extra nozzles (WIND METER WINNER)
@LeightonBlashko – If your water/handler pump runs out of gas while spiking jugs, backflow will likely contaminate water tank. Keep fueled up!
@fortkampnathan – Add <an> electric valve to <the> mix system to keep solution agitated when spraying, and shut off when tank is near empty. Total cleanout.
@fortkampnathan – Valves on boom <section> ends to flush residue and prevent buildup in caps. Split <the> inductor and fill line to add <conditioner> with <the water>.
@twistedironfarm – Flush booms with water at night when shutting down to prevent residue buildup. Even if using same product the next day.
@landon707 – Don’t forget to feel the hubs to make sure you don’t have <one> hot one (HONOURABLE MENTION)
This got a reply from @1TonyHarding – One of these <see temperature gun image> is even better. Only ~10°C between a good and bad wheel motor on a Nitro <sprayer>.
‏@apple_grain – Talk to landlords before spraying. Some don’t understand what you are doing and why. A short chat can relieve a lot of anxiety.
@rmmathesonfarms – Stay out of the muck, it really is a buzzkill on productivity!
@T77HAM – Always organize a family day out when you want to go spraying to guarantee perfect spraying conditions.
‏‏@T77HAM – Make sure everything it greased well… putting it on its side <is> easier than scrambling underneath.
@GlenHanks – Air reel mounted on water trailer. #no blowback
@cfsdennis – Check <that> all wheels are on! <Editor’s note – This wasn’t just a photo lifted from the internet – this was his experience!>
@FreyTodd – It never hurts to double check that the field you are spraying is, in fact, all <RoundUp Ready> <More info here>
@EnnsFarmsRuss – Small blow gun tied into sprayer air system makes cleaning nozzles a breeze (WIND METER WINNER)
@EnnsFarmsRuss – A tackle box is great for keeping spare nozzles and parts and tools organized.
This got a reply from @thecropdoctor – Neater than my plastic ice cream tubs!
@thecropdoctor – Record headland sizes as well as landwork areas so if <you are> patch spraying, data is available.
‏@konopelskifarms – I spray #ReglonIon @ 20USgal/ac 6MPH 50PSI in evenings – awesome results!
@konopelskifarms – I spray Liberty at 20 US gal/ac. Great results including less bronzing. Lots of fills, but oh well.
This got two replies from ‏@skellerfarms – We upped our water volume for Liberty from 10 to 13gpa, have fewer escapes now. More water is always the answer. <and> More water (10-13gpa) and slower speeds (<13mph) means better coverage and less drift.
@skellerfarms – Getting “too windy” but need to spray? Up <the> water volume by 3-5gpa and slow to a speed near your minimum effective pressure.
@landon707 – Eye/hand wash stations on sprayer and tender. We have a garden hose on tender for cleaning filters. <More info here>
@LegueeFarms – Pattison Totalizer – loads our R4045 in 7-8 min without hot loading.
‏@ONspraysafety – If you can see the maple leaf in the <Canadian> flag, it is too windy to spray!
@ONspraysafety – If you hear sounds from far away on a calm morning, beware of a temperature inversion. <More info here>.
@WheatlanderJay – Use a 1,000 L tote with <the> top cut off for used jugs. We recycle all boxes so they never leave the shed.
@WheatlanderJay – The four R’s of spraying stewardship: Right Product, Right Rate, Right Staging, Right Application. #dontsprayandpray
@RonKrahn – 1,000L tote cages <with> nets for <storage> boxes <left image>. Use a spray record sheet to keep track of fills and <environment> <right image>.
@redwoodacres – Plumb line directly into tank for pumping in bulk chemicals. <This> keeps big hoses chemical free.
@redwoodacres – Install fresh water connection for eductor/handler rinse water <with anti-backflow>. Cleaner jugs = less exposure.
@KeatingSeed -Keep a good custom operator on speed dial.
@GavinHowley – <Install a> float valve in tender tank, hook up hose, go home for <image of a few frosty beers>.
‏@DarylTuck – When spraying at 15 MPH and spray drift starts to pass the sprayer, it’s nap time!
@ehrinf – Reload, reload, reload? Cut that time to a minute and concentrate on spraying. <More info here>.
@BlackwellBrad – Re-purpose your old Davis weather station. Know wind speed and direction.
@a4nick – Mobile phone weather apps – very handy.
Thanks to everyone that shared. Maybe we’ll do it again in 2017!
July 26, 2016

Disease Control in Berry Crops

In the spring of 2016, the Ontario Berry Growers Association (OBGA) conducted a survey of its membership to poll how fungicides were being applied. The results were very interesting.

Fungicide basics

Generally, fungicides registered for berry crops are contact products, so coverage and timing are very important. The fungicide has to be distributed evenly on the target before disease has a chance to infect the crop. That means the sprayer operator must be aware of the susceptibility of the crop to the level of disease pressure to ensure timing is appropriate. While kickback and post-application distribution of pesticide residue is sometimes possible, sprayer operators should not rely on it. The following table outlines application recommendations for a fungicide commonly used in Ontario. It combines labelled information and provincial recommendations and is representative of most fungicides.

	Summer-fruiting and Fall-bearing Raspberry / Blackberry	Highbush Blueberry	Day-neutral and June-bearing Strawberry
Labelled rate	2.5 kg/ha	2.25 kg in 1,000 L/ha	2.75-4.25 kg in 1,000 L/ha
Diseases (Labelled and Ontario provincial recommendations)	Anthracnose fruit rot, Spur blight, Leaf spot, Botrytis grey mould	Anthracnose fruit rot, Shoot blight (Mummy berry), Botrytis twig and/or blossom blight	Common leaf spot, Botrytis grey mold
Crop staging	Bloom, Pre-harvest, Harvest	First bloom, Fruit ripening	Flower bud, First bloom, 7-10 days after bloom, Pre-harvest, Through to fall

As of 2016

The spray target

The applicator reading the recommendations should be considering the best way to get the fungicide to the target. But, what is the target, and what is the best way to apply it? It seems the recommendations raise as many questions as they answer:

With the possible exception of blueberry, this fungicide can be applied through much of the growing season (especially when it’s been a wet season). That means the crop staging is highly variable.
The primary target is blossoms, but depending on the disease, leaves and stems are also important.
The label states a volume of carrier (i.e. 1,000 L/ha) for strawberry and blueberry, but not the cane fruit. It does not specify highbush blueberry versus the sessile, ground cover variety.

So, this means is the sprayer operator has to spray crops with highly variable physiology (e.g. bush, cane or sessile row crops), onto very different targets (e.g. leaves, canes, stems, flowers) throughout much of the season as the crop canopies grow and fill. This is a very challenging spray application. It would be wrong to suggest a single spray quality, water volume or sprayer set-up to efficiently accomplish all these goals (more on that later). The first consideration is the application equipment itself.

The application equipment

Berry growers employ a variety of sprayers to protect berries. Without considering models or optional features, there are three fundamentally different styles: Airblast, backpack and boom. According to the survey, the following table shows which sprayers are used in which berry crop in Ontario. Approximately 60 growers responded, and many grow more than one variety of berry and use more than one style of sprayer.

	Airblast Sprayer	Backpack or Wand Sprayer	Vert. or Hor. Boom Sprayer	Total
Highbush blueberry	8	1	0	9
Day-neutral Strawberry	3	0	21	24
June-bearing Strawberry	5	0	32	37
Raspberries & Blackberries	21	1	7	29
Total	37	2	60

So, generally, cane and bush berries are sprayed using airblast sprayers and strawberries using horizontal booms. The survey didn’t specify features such as air-assist on booms, or whether or not those booms are trailed or self-propelled. The type of, and features on, any given sprayer dictate the limits of what an operator can adjust to improve coverage.

Water volume

Respondents also reported on how much carrier (i.e. water) they used to spray fungicide on their crops. Given Canada’s propensity to report volumes in many different forms, I have converted all values into the most common units: L/ha, US g/ac and the dreaded L/ac:

	n	L/ha ± std (max./min.)	US g/ac ± std (max./min.)	L/ac ± std (max./min.)
Highbush Blueberries	7	534.2 ± 340.1 (1,000/150)	57.1 ± 36.4 (106.9/16)	216.2 ± 138 (404.7/60.7)
Day-neutral Strawberries	22	418.5 ± 192.2 (1,000/224.5)	44.7 ± 20.6 (106.9/24)	169.4 ± 77.8 (404.7/90.8)
June-bearing Strawberries	33	403.1 ± 235.1 (1,000/50)	43.1 ± 25.1 (106.9/5.3)	163.1 ± 95.1 (404.7/20.2)
Raspberries & Blackberries	27	450.1 ± 279.4 (1,200/50)	48.1 ± 29.9 (128.3/5.3)	182.1 ± 113.1 (485.6/20.2)

There appears to be a lot of variability in the volumes applied, but on the whole, very few are using the 1,000 l/ha indicated in the fungicide recommendations. The ~430 l/ha overall average is no surprise; labelled volumes are quite often higher than what sprayer operators use. In some cases, high label volumes are warranted because the product requires a “drench” application to totally saturate the target, or to penetrate very dense canopies. Conversely, a high label volume might reflect outdated practices if that label hasn’t kept up with current cropping methods or application technology. Sometimes label volumes are suspiciously large, round numbers that suggest they are intended to encompass a worst-case scenario (e.g. a large, unmanaged crop with high disease pressure and a less-than-accurate spray application). In the particular case of crops sprayed with an airblast sprayer, it is very difficult for a label to accurately predict an appropriate volume due to the variability in crop size, density and plant spacing. This has led to methods to interpret labels, such as crop-adapted spraying.

The disparity between label language and grower practices is not entirely the fault of the label. Most sprayer operators don’t want to carry a lot of water because more refills prolong the spray day. In situations where the crop has reached a critical disease threshold, or bad weather has compressed the spray window, sprayer operators sometimes reduce the volumes in the belief that “getting something on” trumps “good coverage”. Perhaps that’s true, but insufficient volumes greatly reduce coverage. This can be further exacerbated when operators do not account for the increase in crop size and density over the season, or the impact of hot dry weather on droplet evaporation.

Improving coverage

So, is there an ideal sprayer set up and volume? As previously alluded, the variability in crop staging, crop morphology, target location and spray equipment make a single recommendation impossible. But that doesn’t mean there aren’t diagnostic tools and a few simple rules to help a sprayer operator determine a volume to suit their particular needs. Much can be accomplished with these three things:

Water-sensitive paper
A modest selection of nozzles and a nozzle catalogue
An open-minded sprayer operator willing to spend a little time and reconsider traditional practices

Rule-of-thumb fungicide coverage on water-sensitive paper.

Water-sensitive paper is placed in the canopy, oriented to represent the target (e.g. leaf, bloom, etc.). It is important to put multiple papers in at least three plants to ensure the coverage reflects a typical application. The paper changes colour when it’s sprayed and this provides valuable and immediate feedback. Did the spray go where it was supposed to go and did it distribute throughout the target? If so, then the operator now knows that they can safely focus on timing rather than targeting. If not, a little diagnosis is required:

1. Were targets completely drenched? If so, there is too much coverage. Operators can drive faster (if possible, and as long as it doesn’t create drift), reduce operating pressure (if possible, and as long as the nozzle is still operating in the middle of its registered range), or change nozzles to lower rates (as long as spray quality is constant).

2 .Were targets only partially covered, as if a leaf obstructed part of the target and created a shadow? This mutual-shading is the bane of spraying dense canopies. One possible solution lies in understanding droplet behaviour: Coarser sprays generally mean fewer droplets and they move in straight lines. Therefore, when they hit a target, they might splatter or run-off, but typically their journey is over. If the spray is too Coarse, a slightly Finer spray quality increases droplet counts and may help droplets navigate around obstacles and adhere to more surfaces. Sprays that are too Fine will not penetrate dense canopies without some form of air assist. They slow very quickly and tend to drift and evaporate before they get deep enough into a canopy to do any good. A Medium droplet size is a good compromise because it produces some Fines and some Coarser drops – the best of both worlds.

Increasing volumes and reconsidering spray quality often helps, but there might be other options. If using air assist, there are tests that can confirm the air volume and direction are appropriate. Another solution might lie in canopy management (where pruning bushes and canes can help spray penetration immensely). Still another might lie in the use of adjuvants to improve droplet spread on the target.

3. Were targets missed entirely, or coverage is consistent but sparse? The operator is likely not using enough water, and/or the spray quality is too fine. It has been demonstrated time and again that higher volumes improve coverage, but operators can try any of the options listed previously for partially-obstructed coverage. All the reasoning is the same.

Conclusion

Spraying fungicides effectively requires an attentive sprayer operator. Timing and product choice are very important, but when it is time to spray the sprayer operator should diagnose coverage with water-sensitive paper, and be willing to make changes to the sprayer set-up to reflect changing conditions. Thanks to the OBGA for sharing the survey data.

June 27, 2016

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.
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.
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.
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.
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.
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.
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
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
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
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
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)
Percent coverage ranged from 37.5 to 27.0 for paraquat and 28 to 21.3 for glyphostate (Graph 6).
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.
April 20, 2016
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.
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.
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.
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).
April 18, 2016