When warm air is cooled, it loses some of its moisture-holding capabilities. This change often occurs at night, when plants (and other objects) cool. Once the temperature of the surface of the leaves, for example, drops below the dewpoint, it causes water to condense, forming the shiny dew that causes so many to question early morning spray applications.
The question is often: will the spray run off the plant or will it get so diluted that it doesn’t work anymore?
In a dew chamber, work has shown that large spray droplets are more likely to run off a plant saturated with dew than their smaller counterparts. However, similar work showed that spray efficacy was not altered by droplet size.
Wolf discusses this work and the potential answer to the seemingly conflicting findings. Wolf also explains how grassy weeds compare to broadleaves, the role of surfactants, and what to consider when making the decision to spray through dew or not.
One of the pleasures of working in agricultural extension is when you’re able to help a grower solve a problem. This was one of those happy occasions. An orchardist purchased a Lipco multi-row recycling sprayer and wanted help evaluating their spray coverage.
We worked in 3.7 m (12 foot), mature, high-density Royal Gala trees. The sprayer was driving at 5.0 km/h (3.1 mph), operating at 11 bar (160 psi) using orange Albuz 80 degree air-induction flat fans. This resulted in about 350 L/ha (~37 gpa).
This grower wisely invested in the air-assist option, which produces a vertical plane of somewhat laminar air to entrain the spray and carry it into the centre of the target canopy. Whatever spray blows through the tree should impact the opposing shroud and get recycled back to the tank. All in all, how could you miss?
…we managed to.
Water sensitive papers were placed back-to-back facing each alley (in other words, facing the spray booms). Despite our best efforts, each pass resulted in inconsistent coverage. Papers were replaced in the same location and orientation for each pass and no settings were changed. Nevertheless, sometimes a paper got spray and sometimes it didn’t. What was going on? It was as if the two air streams were interfering with one another – almost cancelling each other out.
Air from tangential (cross-flow) fans oriented perpendicular to the canopy in direct opposition will cancel out. This reduces canopy penetration.
Where possible, do not position laminar air outlets in direct opposition. The convergence creates a high-pressure zone that reduces spray penetration. Some sprayers are designed to avoid this by staggering air outlets one ahead of the other. Laminar flows will deflect unpredictably around this pressurized area and carry droplets back out of the canopy. Unless the canopy is particularly narrow and sparse, turbulent air handling systems do not typically create this problem. In both cases, canopy penetration is improved when fans are staggered and/or are angled slightly forward or backward.
Grey arrows indicate direction of travel. The air outlets of wrap-around sprayers should be symmetrical when viewed from behind. A. Tangential fans in direct opposition: Poor coverage. B. Tangential fans angled forward/backward: Possible vortices and good coverage. C. Tangential fans angled backward: Good coverage, but if the angle is too steep, air will not penetrate the canopy. D. Straight-through axial fans in direct opposition: Good coverage in denser canopies. E. Straight-through axial fans angled slightly backward: Good coverage but limit the angle to prevent the trailing edge of the air wash from missing the canopy entirely. F. Straight-through axial fans angled forward: Slight angles are acceptable, but too much in this image. Wind created by travel speed subtracts from air energy. This creates a risk of reduced coverage and increased operator exposure.
We decided to turn the outer boom/shroud/fan assemblies 10˚ backward by loosening the four bolts at the top of the gantry (see below). This minor change in configuration improved spray coverage significantly. Increasing the angle beyond 10° might have caused the air wash to trail along the canopy face and would have made sprayer turns difficult at the row ends.
We loosened the four clamping screws to adjust the fan angle on the outer boom of this Lipco Recycling Tunnel sprayer.
We replaced the water sensitive papers and ran another pass. The operator later told me he could see the leaves and branches rustling in the row where we made the adjustment, but not in the unadjusted row. The result on water-sensitive paper was dramatic.
Since experiencing this in 2013, I have been told that the Lipco instruction manual advises against air in direct opposition. It was a poorly translated and somewhat obscure sentence buried in the manual, but I concede that it was there. Determine whether your sprayer produces more laminar or more turbulent air, and explore how their relative orientation impacts canopy penetration.
The John Deere ExactApply system has a pulsing feature, more commonly known as “Pulse Width Modulation” (PWM). From the operator’s perspective, it’s important to know the Duty Cycle that the system is operating at. The Duty Cycle (DC) is the percentage of time that the pulsing solenoids are “on”, or flowing. At the average travel speed, the pulsing system should operate at 60 to 80% DC for optimum performance. For in-depth explanation of ExactApply, read here.
Unlike its PWM counterparts (Raven Hawkeye, Capstan Pinpoint), the new John Deere 4600 monitor does not display the DC by default. Fortunately, it offers a module for insertion to its run pages.
The module isn’t perfect, and inserting it into an active run page is torture.
Here is how to bring this module onto a 4600 screen:
1. On 4600 Monitor, click on “menu” (bottom right).
2. Select “Applications” tab.
3. Choose “Layout Manager”.
4. Edit Run Page Set.
5. It’s easiest to copy an existing Run Page, rename it, and then customize its modules.
6. Make room on new Run page for new module. On my copy of the “Spraying” run page, I’ve deleted a module on the bottom left that I have elsewhere. Now “Add Module”.
7. Select “Machine Settings” tab, then “Boom & Nozzles”.
8. Scroll down to “Section Flow %” (four windows) and “Add Module”.
9. Module is placed in available open area. There is a warning if not enough screen space is available.
10. Save new Run page. Make sure it’s part of the “Active Run Page Set” in Layout Manager so it’s available to scroll to while spraying.
The module is a bar graph that gives you relative DCs along boom. In the first example, we’re driving straight and everything is fine. After a couple of shoulder checks, we pull out the smartphone and take a picture.
The bar graph format is useful during turn (left in this example, forcing higher DC to outside of boom, the right).
If it plateaus on outside (as in tight right turn, below), you are under-applying on the outside since the DC can’t go higher than 100%. Slow down and that improves it because it lowers the duty cycle of the entire machine.
Slowing down may cause too low a DC, resulting in over-application on inside of boom because the DC can’t be reduced below 15%.
Remember, for Turn Compensation to work, make sure the box is checked (Menu|Boom & Nozzles|ExactApply Config/Spray Mode|Manual Setup|i|<down four screens>|Turn Compensation Check box). While you’re there, make sure the “Limit Minimum Flow %” is unchecked. This lets DC go down to 15%, from 25%.
Capstan Ag brought Pulse Width Modulation (PWM) to spraying in the mid 1990s. Over the past 20 years, it has become commonplace on Case sprayers as AIM Command and AIM Command Pro, and as an aftermarket product, called Sharpshooter or PinPoint, on any brand sprayer. If you’re new to the concept, read about it here and here.
A sprayer turn, without turn compensation. Note the darker dye on the innermost nozzles and lighter deposits on the outer wing.
The latest versions (AIM Command Pro and PinPoint) offer turn compensation and individual nozzle sectional control. But there remains a large base of older AIM Command units that lack turn compensation. And of course, sprayers that lack PWM alltogether, possibly because of cost.
The Capstan EVO addresses both issues. Introduced in January of 2019, it gives older AIM Command units affordable turn compensation. As a bonus, a complete new EVO install on non-PWM sprayers is available at a significant discount compared to most other PWM products.
EVO features many of the same basic PWM capabilities as its bigger cousins, but with a shortcut, explain Capstan representatives.
As always, a change in travel speed changes the duty cycle of the pulsing solenoid, adjusting flow rate of the nozzle without a change in pressure. This provides the consistency in performance that we love about PWM. Drift or coverage are controlled by the operator who makes changes to spray pressure from the cab, with a commensurate background adjustment in duty cycle so that travel speed is unaffected.
With the EVO, the shortcut is that sectional control is by plumbed section. Technically it’s possible to add sections, but the rate controller and the sprayer wiring would have to allow it.
Spray dosage for sectional turn compensation for six sections of equal size, with the centre of each section applying the target dose. As always, some lateral movement of spray from adjacent nozzles will occur.
Turn compensation is part of EVO, and this is an important benefit that was previously only available in more expensive versions of a PWM product. Each section will have a fixed turn compensation based on the speed of the centre of the section. Its performance will depend on the size of the sections.
For a 100′ boom with six 10-nozzle sections turning around an object with a 60′ diameter, our modelling shows that the deviation from perfect turn compensation is least on the outer wings (where it’s most important) and grows towards the inside of the turn. In this example, the outer section’s end nozzle under-applies by 6% relative to the ideal, and the innermost nozzle on this section over-applies by 7%.
On the next section, these deviations are 7% under and 8% over, then 8% under and 9% over.
Moving from the centre of the sprayer to the inner wing, deviations are 9% under and 12% over, then 12% under and 16% over, and finally 16% under and 24% over.
Spray deposition on an un-compensated turn.
On an uncompensated boom with the same dimensions, the outermost nozzle would be under-dosing 38% and the innermost nozzle would be over-dosing by 267%.
Recall that it’s more important to be accurate on the outer wing than on the inner, for the purpose of delivering the full spray dose in a turn.
Repeated year-after-year under-dosing at the periphery of a turn such as field corners, or around permanent features such as sloughs, trees, or stone piles results in weed problems.
EVO is intended for users with an original SharpShooter or AIM Command who would like turn compensation but don’t want to a whole new PWM system. EVO provides new modules and a new screen, but users save money because they can keep their existing solenoids, says Capstan.
Capstan says that EVO is for every brand of sprayer ordered without pwm control from new to 15 years old. It’s an easy upgrade for owners of AIM Command & SharpShooter systems because these already have most of the components, and install times are therefore lower for these machines. Existing solenoids and wiring harnesses can be retained.
Owners of high clearance pull type sprayers will also see the advantage of turn compensation and pressure control at an attractive price point.
EVO modules and tools needed for installation
I was present during an installation of these new modules on an existing Case 3330 sprayer with AIM Command. It took one person, with occasional assistance from a second, less than 1 h to do the conversion.
Removal of AIM Command modulesInstallation of EVO board containing all modules and replacement plugins
A new installation would require an additional several hours to install wiring harnesses and solenoids. Times will vary with sprayer model and technical experience of the installers.
The EVO electronics run in parallel to the existing sprayer monitor. It allows the existing monitor to control sections and determine the flow requirements. It does not control pump speed, it simply reads the flow, pressure, and gps signal from the sprayer’s systems and uses them to determine the duty cycle (DC) that ensures the spray pressure remains constant. On AIM Command units, the pressure control module remains installed and pressure adjustment remains possible through AIM Command in cab controls.
Entering system settings into new EVO monitor
It’s possible to set the pulsing frequency between 3 and 30 Hz in EVO, an industry first. The lower the frequency, the wider the dynamic flow rate. Capstan advises to maintain a frequency above 10 Hz for spray operations. Lower frequencies may be used for fertilizer applications, where prescription maps require a higher rate range and where uniformity requirements are more relaxed.
EVO Monitor contains an option in which to select pulsing frequency
Testing of completed EVO Installation
The monitor has an intuitive readout of average DC and a bar graph showing the DC across sections in a turn. If this bar maxes out on the outer sections during a turn, simply slow down to lower average DC and provide extra capacity to those sections.
EVO monitor during operation. Readout includes current spray pressure, duty cycle, and turn compensation status.
Lowering the cost of PWM makes it attractive to a new group of users. It also offers a more affordable upgrade path for owners of AIM Command or SharpShooter systems that currently do not have turn compensation.
Spray application by drone is here. It’s common practice in South East Asia, with a very significant proportion of ag areas now treated that way. Estimates from South Korea, for example, suggest about 30% of their ag area being sprayed by drone. It’s in the US, too. The Yamaha RMax and Fazer helicopters, which pioneered drone spraying in Japan dating back to the mid 1990s, have been approved for use in California since 2015. DJI, the world’s largest drone manufacturer, introduced their ag model, the Agras MG-1, to North America in 2016. Many other spray drones are available or in development.
As William Gibson, the author of Johnny Mnemonic, once said,
“The future’s here, it’s just not widely distributed yet.”
DJI Agras MG-1 spray drone (Source: DJI.com)
Proponents of drone spraying cite a drone’s ability to access areas where topography is a problem, such as steep slopes, where productivity of manual application is much lower, or low areas where soil moisture prevents ground vehicles. Operator exposure is reduced compared to handheld application.
Opponents talk about productivity and cost factors compared
to manned aerial application, spray drift, and rogue use.
Before drone spraying becomes commonplace, two important
things need to happen.
Federal laws need to be updated to accommodate the unique features of remotely piloted aircraft systems (RPAS), as they’re now called. Current laws make many assumptions unique to manned ships, and the process to correct that will require some patience. A thorough review for US laws, and their shortcomings, can be found here.
Federal pesticide labels need to permit the use of drones for application. As of August, 2021, Canadian labels have no such registered use.
There is no doubt that we need to prepare for a future that includes spraying by drones. Features such as topography adjustment for height consistency and autonomous swath control are already essentially standard, and the capabilities that improve control and safety will continue to develop.
And yet I’ve been nervous about the prospect of pesticide application with drones. My primary concern is around – you guessed it – spray drift. Because a drone payload is relatively small (about 5 to 25 L, depending on the model), application volumes will need to be low to have any sort of productivity. How low? For manned aircraft with a 200 to 600 gallon hopper, 2 to 4 US gpa (18 to 36 L/ha) are the lowest commonplace volumes. The lower volumes require a Medium spray quality (among the finer sprays in modern boom spray practice) to achieve the required coverage.
It’s a simple concept: the less water is used, the smaller the droplets need to be to provide the necessary droplet density on the target. Drift control with coarser sprays requires higher volumes, and true droplet-size-based low-drift spraying can’t really happen at volumes less then, say 5 to 7 US gpa.
At 2 to 4 US gpa, a drone would be able to do perhaps 1 acre per load. While OK for spot spraying, it represents a serious productivity constraint for anything larger. There will be a push toward lower volumes, perhaps 0.5 to 1 gpa (5 to 10 L/ha). The only way these will provide sufficient coverage is with finer sprays, ASABE Fine to Very Fine, with expected problematic effects on off-target movement and evaporation. These fine droplets are also more prone to the aerodynamic eccentricities of aircraft.
Vortices from the rotor can create unpredictable droplet movement (Source: kasetforward.com)
The current regulatory models for aerial drift assessment in North America, AgDISP and AgDRIFT, are not yet able to simulate drone application. But by entering finer sprays into these models for their conventional manned rotary wing aircraft, we can see that buffer zones will be higher. Much higher. And that outcome will give pause to regulators. Failure to control the movement of a spray is, and should be, a problem.
Estimated Buffer Zones (calculated by AgDISP) for a reference rotary wing spray aircraft, using three pesticide toxicologies and two spray qualities.
Furthermore, ultra-low volume (ULV) sprays can change the efficacy of some products, and these will require new performance studies. At this time, regulators are seeking information not just on spray drift, but on product efficacy, operator and bystander exposure, and crop residues.
Regulators are currently collecting spray drift and efficacy data from drones. Since the drones available in today’s market do not conform to a common design standard like fixed or rotary winged manned aircraft, each model may have its own characteristics and need its own study. Some will have rotary atomizers, others will use hollow cone hydraulic sprays. Some will have electrostatic charging, others may propose special adjuvants.
Once data are assessed, there will likely be restrictions in flight height, flight speed, wind speed, spray quality, water volume, perhaps air temperature and relative humidity (or Delta T). This is not new to spraying, as current labels already constrain use for both ground and aerial spray application, more so for aerial.
The obvious question is how these proper application practices can possibly be assured. Operators will need more than just regulatory approval to use a drone, they will require proper training, similar to what a commercial aerial applicator now receives prior to operating a business.
Recall that our aerial applicators are governed by national organizations, the NAAA in the US and the CAAA in Canada. These organizations are in regular contact with federal regulators to assure compliance. They also help fund research into application efficacy and safety. They organize conferences in the off-season and calibration clinics in the growing season. At these, flow rates are confirmed and deposited droplet size is measured. Spray pattern uniformity is assessed and corrected as necessary.
Should drone applications be exempt from these controls? I don’t think that would be wise. Are we ready to implement them? Absolutely not.
These requirements would change the drones’ economic model. And despite these precautions, a drone may still leave the control of a pilot due to unforeseen technical or human events.
In the US, Yamaha does not sell their drone helicopters. Instead, they deploy their own teams to make the applications. This way, they have assurance that only trained and experienced pilots use the technology.
As the industry gears up for the first registrations, we see drone service companies take a leading role in testing. Much is being learned via legal applications of liquid micronutrients, for example, or limited use of pesticides under approved research permits. And I’m pleased to see the recognition of drift management in these efforts through the use of low-drift nozzles. We are off to a promising start.
Requests for drone use are in progress at our regulatory agencies. The outcomes of their risk assessments will provide important initial guidance, and food for thought and discussion. In the meantime, the drone development continues at a rapid pace, with new features and greater capacity at each iteration.
