Tag: canopy penetration

Pro Tips for Pre-Harvest and Desiccation Sprays
A version of this article was originally written by @nozzle_guy as a guest blog for Farm At Hand, and is reproduced with permission.
One of the smartest decisions a grower could make is to consider a late-season harvest-aid application. Particularly in years with thinner stands, weeds can maintain a foothold. Late season moisture can give new life to late emerging plants or branches. When the crop is ready to cut, this could mean all sorts of cutterbar, pickup reel, feederchain, and sieve headaches.
A desiccant or pre-harvest herbicide application can help avoid those problems. The challenge is to get the spray into, or through, a mature crop canopy. Here are some pointers to do it right.
1. Evaluate where within the canopy the spray needs to go to do its job. If you’re considering a pre-harvest herbicide, are you looking to control dandelions or buckwheat near the bottom of the canopy, or are you trying to get thistles or quackgrass, whose leaves are near the top? If you’re mostly trying to accelerate drydown with a contact product, where in the canopy are the green stems and leaves that you need to contact?
2. Take a bird’s eye view of your canopy. That’s how the spray sees it. If you can clearly see your target, the spray application is pretty straightforward because most droplets will make their way there easily. But if the target is obscured by a lot of foliage, or if it’s vertical, the job is much more challenging and will require some combination of more water, slower speeds, angled tips or finer sprays.
3. To hit plant parts that you can’t see, one of the main tools is finer sprays. The smaller droplets have an easier time changing direction to get around obstacles like leaves, and they are also much more likely to be intercepted by petioles and stems, and to stick to them. This can be both an advantage and disadvantage – for example, the awns in bearded cereals are notoriously effective at capturing the smallest droplets before they can do any good further down. If you don’t want to install a different nozzle to get a finer spray, simply increase the spray pressure of your low-drift nozzle to 80, 90, even 100 psi. This will create enough fine droplets. But don’t expect the higher pressure to push the spray into the canopy. Only air-assist can do that.
4. To get more spray deeper into the canopy, slow down, add water, and point nozzles backward. The backward orientation helps offset the forward travel speed, giving the droplets a slower net forward velocity that helps their downward movement.
5. If you’re using contact products like diquat, paraquat, saflufenacil or carfentrazone, use generous amounts of water, and slightly finer sprays. Make sure that spray drift control remains a priority and pay attention to water quality.
6. Test your water and make sure your water doesn’t have turbidity (suspended clay or other organic matter), for glyphosate and diquat or paraquat, and hardness, for glyphosate. Aluminum sulphate can help get rid of turbidity in a pond, but it takes time (treat turbid water at least 24 to 48 h before you need it). If treating a storage vessel, expect a layer of sediment. Ammonium sulphate (AMS) and other water conditioners can remove antagonizing hard water ions like magnesium and calcium. This is especially important as we increase water volumes with glyphosate to get better coverage. The higher water volumes give a concentration advantage to the hardness minerals.
7. Diquat and paraquat’s mode of action benefits from being applied in the evening. The absence of the sun allows it to be taken up and slightly moved (by diffusion, not true translocation) within the leaf before morning sunlight activates it. Once activated by the sun, these products exert their activity and movement stops. If you’re not careful, the tighter window of evening-only applications could get you behind. And of course, be aware of the signs of inversions and know when to quit.
8. Plan ahead and make sure you give yourself enough time, because to do the job right you’ll be using more water and driving a bit slower. Focus on productivity tools like a fast, efficient fill to make up the lost time.
A good job with a pre-harvest herbicide or a harvest-aid can save many harvesting headaches, and can help dry down during less than ideal conditions. It’s another reason why the sprayer may be the most important implement on the farm.
August 30, 2022
The Ideal Sprayer (an open letter to sprayer manufacturers)
Today’s sprayer has to excel at a lot of things. It has to have capacity and low weight. It has to go fast but be comfortable. It needs wide booms that stay level over complex terrain. It has to deliver the right spray volume at the right spray quality for the job. It has to be easy to fill and easy to clean. And of course, it has to be reliable, affordable, and come with dealer support.
We’ve definitely made progress in many of these areas. But the overall package still leaves lots of room for improvement and doesn’t address some issues that are of importance to applicators. Is it time for a reset?
Let’s say cost is no object. Here’s where I think the industry could go.
Focus on spray delivery
Spraying is done to protect crops. We need to do it without harming the environment while being economical with the inputs. These three tenets make up the Application Triangle, sometimes known as the 3 Es of spraying: Efficacy, Environment, Efficiency. The triangle represents the need for balance. A gain in one or two areas often requires a loss in another. That’s why there has never been a so-called “silver bullet” in spraying.
Priority 1: Only spray when and where required. Site specific treatments and IPM have been slow to make their way to the spraying world partly because of the low cost of inputs, but also because of difficulties defining and mapping areas that require different rates or products. The machine learning revolution is changing that. Green on Brown or Green on Green sensing can do more than save inputs. They can generate maps that document the change of weed patches over time, identifying priority areas and threshold densities and flagging problems early.
Priority 2: Integrate air assist. Air carries small droplets towards the target, protecting them from displacement by travel-induced or ambient winds. Once there, air can improve target interception and retention. It has to be done right, though, as improper adjustment can result in the opposite outcome. The reason it’s high on this list is because it improves efficacy and environmental protection at a modest cost.
Priority 3: Improve droplet size control. Nozzle design has improved, but the overall range of spray qualities that is achievable for any specific nozzle remains narrow. Sprays can be made finer or coarser with spray pressure, but this has implications for pattern uniformity. Twin Fluid nozzles currently offer the widest range of spray qualities, allowing one nozzle to do it all. We simply need greater droplet size flexibility on the spray boom.
Priority 4: Use nozzle-specific rate control. At minimum, a sprayer needs a system that allows for individual nozzle rate control within a wide window, say 4:1. This allows consistent dosing over a wide speed range, turn compensation, or local adjustments to dose for specific (sensed) canopy conditions. By layering direct injection at the nozzle on top of this, the sprayer can change rate and volume independently. Being able to spray the right amount in the right spray quality at the right volume, where needed completes the opportunity created by pest and canopy sensing.
Create better infrastructure
The backbone of the sprayer, the frame, drivetrain, boom, tank, pump, and plumbing, are responsible for carrying and delivering the spray liquid. Poor management of these variables results in an unproductive, heavy machine.
Priority 1: Prepare booms for future. A limiting factor in sprayer performance is boom width and stability. Consistent and low boom heights are the cornerstone of good application, ensuring uniform distribution, reducing drift potential, and improving targeting within the canopy. But perhaps as importantly, stable booms are essential for accurate optical spot spraying and any other sensing tasks that will rise in importance. Set a standard for sway, say target height plus or minus 10 cm along the width of the boom, 90% of the time. Do the same for yaw. Accommodate brackets for sensors and wiring harnesses when designing the boom fold.
Priority 2: Improve plumbing. Poorly executed sprayer plumbing causes waste and decontamination headaches. Although rubber hoses attached to plastic fittings provide a very versatile and generic building block, they generate and hide countless niches in which pesticide mixtures or active ingredient residue can accumulate. A simplified design that incorporates more engineered stainless steel tubing, smooth directional and dimensional transitions, interior surfaces that don’t accumulate residues and generate more efficient flows – all these would improve many aspects of the spray operation. It needs to be goal oriented – i.e., zero waste in priming and cleaning, guaranteed decontaminated after a rinse cycle. Draining on the ground should not be necessary.
Priority 3: Save weight. Weight causes compaction and eats fuel. Advanced materials or techniques can save weight while preserving strength. Savings can be applied to capacity. We need to explore advanced materials and trussed or exoskeletal designs (see “Aerodynamics”).
Priority 4: Consider aerodynamics in chassis and boom design. Wind blowing past a tractor, tank or boom, or counter-rotating air from wheels creates turbulence that displaces small droplets within it, reducing uniformity. Cleaner air makes it easier to use smaller droplets, easier to implement air assist or any other drift-reducing technology. This is no small task, as air can come from any direction. But as units become larger and travel faster, this effect can’t be ignored. Monocoque designs that use aerodynamic exteriors to carry machine weight may provide an answer.
Provide quality control
Spraying can be a guessing game, hence the terms “Spray and Pray”. We don’t know the outcome for days or weeks, depending on the mode of action, and by the time the result is known, it is too late to do anything if it’s unsatisfactory. But we can do better in assuring some sort of standard.
Priority 1: Confirm pressure, flow, and patterns at nozzles. The average sprayer has one flow- and one pressure-sensor. It can confirm the flow of the entire spray boom but cannot do that at the nozzle level. PWM has helped, by inferring flow from duty cycle. But actual liquid flow, and its pressure, remain unverified at the spray tip. A visual inspection of the pattern is necessary, and this is not only impractical but also wasteful and potentially hazardous.
Priority 2: Characterize canopy. If we knew the crop canopy was dense or sparse, we could adjust the water volume or rate of the product accordingly. LiDAR (Light Detection and Ranging) can characterize the physical structure of an object that would indicate density or porosity for which a dose (or droplet size, or air) adjustment may be necessary. This is not some future technology. The iPhone 12 Pro has it. Even RGB image processing could do something very similar.
Priority 3: Confirm coverage and drift. Say we’ve characterized the canopy and adjusted the atomization to suit. Is it having the intended impact? We will need a way to verify that the settings of the sprayer result in the required canopy penetration and coverage, even drift, on-the-go. We would need sprayer-mounted sensors that see spray deposits or an airborne spray cloud. The verification must be fast enough to make corrections during the spray operation. This kind of quality control provides the feedback loop to the first priority, spray delivery. It creates a perfect environment for machine learning and continuous improvement.
Priority 4: Improve user interface. The complexity of modern equipment monitors is great if you’re familiar with their features. But if you’re a new user or less comfortable with layers of screens and buttons and warning beepers, navigating the monitor can be a game stopper. Can we have beginner modes? Or a system where the monitor more actively engages with the user, asking questions or reminding a novice of key settings? The friendliness of the interface is a sleeper issue, it seems less important at first look but can over-ride many equipment features because of the power of a positive user experience.
I challenge sprayer manufacturers to conceptualize and show us the ideal sprayer they’re working towards. The perfect unit may never reach us, as this proposal is rife with technological and cost barriers. But it is nonetheless important to identify priorities and identify possible ways to meet them. As we creep towards the solution with incremental improvements, recall that its not the size of the step that matters, it’s the direction.
October 8, 2021
Fungicide Application in Cereal, Pulse, and Oilseed Crops
Get ready for a busy fungicide season. If your growing conditions have been good, your crop is dense and vigorous, and soil moisture is adequate, you have yield potential to protect. A bit of moisture and warm temperatures at a critical time, and disease is likely to develop.
Before we delve into how to apply fungicides, let’s review the basics.
1. There is no substitute for an informed decision about whether to spray or not. Seek the advice of a professional to make sure you understand your crop’s genetic susceptibility to disease, the conditions conducive to its development, and the parts of the plant canopy that are affected and therefore need protection. How much yield or seed quality is actually at risk? What do the disease forecasts say for your area?
2. Identify the best fungicide product for your disease situation. Consider inherent efficacy, but also the longevity of the protection and the fungicide’s off-target toxicity (less toxic products can be sprayed in windier conditions without harming susceptible ecosystems). Remember that most fungicides are not curative and must be present on the plant foliage before infection takes place. Also remember that most fungicides are not easily translocated and are at best “locally systemic”. This means that fungicide deposit must cover the plant part that requires protection with an adequate droplet density. If the fungicide is systemic, these deposits must be absorbed through the plant cuticle and will only migrate a small distance within the plant tissue, usually in the transpiration stream, from the point of application.
3. Make proper timing the priority. Disease control is usually only effective if the fungicide is applied in a narrow time frame in which the crop or disease is at a certain developmental stage. A great application at the wrong time is less valuable than mediocre application at the right time. The use of low-drift nozzles should be considered an agronomic tool that permits the correct staging even under marginal wind conditions.
Let’s now review the major highlights of fungicide application in the major cereal and oilseed crops.
Wheat
In wheat, the early growth stagings for foliar fungicides are usually done to protect from leaf spot diseases such as tanspot, septoria nodorum blotch and septoria tritici blotch. Because these diseases are trash-borne, they tend to migrate up from the bottom to the top and good canopy penetration of the spray is important.
Better canopy penetration can be achieved the following ways:
- Higher water volumes. This is probably the most powerful tool in an applicator’s arsenal. More water usually delivers higher doses of active ingredient deeper into the canopy, and whatever dose does get deposited will be present in higher droplet densities. So in short, for any given spray quality (droplet size), more water provides better coverage. We all intuitively know this.
- Slower travel speeds. Moving slower imparts less of a forward velocity on the spray cloud, particularly in the larger droplets. As a result, these droplets move more vertically. In the case of a cereal canopy, more of the spray will reach the lower leaves. The finer droplets in the cloud tend to deposit with the wind direction regardless of travel speed.
- Backward pointed nozzles. If a droplet moves backwards at the same speed as the spray boom moves forwards, then it is basically standing still relative to the crop. It will have a greater chance of moving down towards the lower canopy than a droplet that’s moving forwards. The latter droplet will likely be intercepted by something vertical, like a wheat head or stem.
A single nozzle oriented back, applying a water volume that is at least 10 to 15 US gpa, will be sufficient to get good canopy coverage for leaf spot and rust protection.
Fusarium Headblight (FHB), caused by Fusarium graminearum, is a special case. It infects the wheat head at anthesis, and fungicide must be present on the head, at the glumes where the anthers emerge, at the time of infection. So we have a relatively large vertical target that is at the very top of the canopy. Initial work at North Dakota State University, followed up by work at AAFC in Saskatoon and the University of Guleph at Ridgetown, found the following:
- Angled sprays are essential. Field and lab studies showed that angled sprays were much more effective at depositing the fungicide on heads than vertical sprays. Backward pointed angled sprays provided additional help at targetting the other side of the wheat head. Twin nozzles are available from most manufacturers.
- Use Coarse sprays when angling. Angled and twin sprays have their challenges. The angle at which the spray is released dissipates quickly, particularly for smaller droplets. As a result, more aggressive angles and coarser droplets were found to be more effective. Larger droplets were able to maintain their initial trajectory for a longer distance, increasing the chance that the droplet hit the head from the side rather than passing it by vertically.
- Maintain low boom heights. Even coarse sprays are deflected by air resistance and will eventually stop moving in the direction they were first emitted. In fact, this happens within a short distance. Low booms, less than 25″ if possible, help.
- Watch wind speed and direction. Field observations show that even a moderate wind can over-ride the application practices described above, resulting in most of the spray deposited on the windward side of a target regardless of its initial release.
- Awns intercept small droplets. Many of our modern wheat cultivars are awned, and these fine structures are excellent collectors of small droplets. In early studies with durum, we found a large proportion of the spray volume on awns, where it served no useful purpose. The best way to minimize this awn interception is to ensure coarse sprays and sufficient water, no less than 10 gpa.
It’s important to maintain realistic expectations with FHB. Fungicide chemistry is improving but still offers only suppression. Crop staging is variable. Excellent application practices place the odds more in favour of disease control, but can’t change these facts.
Pulse Crops
Lentils and peas are increasingly important crops. They appear spindly in their early stages of development and are poor weed competitors. But under the right conditions, lentils soon form an impressive set of leaflets that creates one of the most impenetrable barriers in our cropping systems.
Here are some pointers for fungicide application in pulse crops:
- Understand the disease in your crop. Do you need to protect stems (anthracnose), leaves and stems (ascochyta complex, mycosphaerella), or senescing leaves or flowers (sclerotinia)? This is where the spray needs to go.
- Understand the time of disease development.
  - Trash-borne diseases like anthracnose and ascochyta will start at the bottom of a lentil canopy, and early treatment before canopy closure will be important to arrest or at least delay disease development as long as possible.
  - Late season diseases like sclerotinia and botrytis push the application timing towards a closing or closed canopy. Success of such sprays is more elusive because of the rapid development of new biomass.
- Take a bird’s eye view of the canopy.
  - If you can see the target you need to spray, the job is pretty straightforward and conventional water volumes and nozzles will work.
  - If the targets are hidden from view, it will take more water and slower travel speeds to get the required coverage. Consider the higher end of the recommended water volumes (15 gpa in most cases), slower travel speeds (10 mph).
- - When a canopy has many layers of cascading leaves, it is very difficult for a spray to get past these “umbrellas”. We’ve observed many times that a leaf is a very effective shield for anything below it. Large droplets have a hard time changing direction because of their mass and resulting momentum. But small droplets, especially those below 100 microns, can move with slight changes in air movement and get around these obstacles. Use higher pressures (to generate the finer sprays) or select finer nozzles to improve canopy penetration.
- Look at the size of the plant part you need to target. Large targets like leaves can capture almost any droplet size, but small targets like petioles or vertical targets such as stems may benefit from finer sprays, especially if they’re hidden in the canopy.
Generally speaking, dense pulse canopies will require higher water volumes and finer sprays than their cereal counterparts. Although twin fan nozzles have not been shown to provide an advantage in our studies on chickpeas, higher water volumes proved very effective at improving deposition and disease control.
Canola
Canola has two main diseases for which foliar sprays are used. A small number of producers choose herbicide timing for control of blackleg. Because the crop canopy is small and the spray targets are exposed, general herbicide application guidelines (Coarse sprays from a venturi nozzle, 7 – 10 US gpa) will provide good targeting and adequate coverage.
Sclerotinia control requires that the spray reaches buds and petals of canola that is between 20 and 50% flowering. Work at AAFC in Melfort compared conventional and low-drift sprays at two pressures, and showed that droplet size had no effect on disease control. In fact, the Fine spray produced by hollow cone nozzles at high pressure did not significantly improve sclerotinia control compared to a venturi nozzle at its recommended pressure of about 60 psi.
Subsequent lab work showed that the proportion of the applied spray that was retained by petals and buds was statistically identical for all tested sprays.
Water volumes may need to be increased for modern canola hybrids that have significant biomass at flowering. Such cultivars may grow over 1.5 m tall and present a large range of canopy positions in which buds and petals appear. As with the other crops, when a spray needs to cover more area, and especially when this area presents itself in layers, more water volume is appropriate.
Fine Sprays for Coverage
Conventional wisdom says that fungicides require finer sprays for coverage and best effect. This is certainly true in some cases, particularly where the leaf area index is high and leaves are arranged in cascading layers. But it’s time to retire this notion as general advice and adhere to research results for guidance. For FHB, the recommended angled sprays benefit from being applied in coarser, not finer sprays. And in pulses and canola, research showed that there was no benefit from finer sprays. In fact, finer sprays can impair proper timing because of their propensity for drift and rapid evaporation under dry conditions.
Modern coarse sprays produced by air-induced nozzles are less susceptible to these environmental conditions and therefore offer an important advantage: they allow for better timing accuracy. For this reason, I view them not so much as drift control tools, but rather as agronomic tools.
There is a downside to the coarser sprays – they do require more water. Volumes should always be above 10 US gpa, and many recommendations go to 15 gpa if the canopy is dense. In some cases, 20 gpa may be beneficial. These higher volumes are a reasonable price to pay to protect a valuable crop, and we certainly have the equipment to make this price bearable.
Aerial Application
Aerial application is an important way to apply fungicides. An aircraft’s chief advantage is to cover large areas with no crop trampling, and can do so even in wet conditions. As a result, they offer the timing advantage we so often mentioned in this article.
A producer hiring an aircraft for spraying ought to have a conversation with the pilot and discuss water volume and droplet size. Aircraft, out of practical necessity, apply less water and distribute it in finer sprays to offer the required coverage. Although this has been shown to be effective, it creates drift and evaporation potential. It is worthwhile to ask for higher water volumes if it means that the spray can be applied somewhat coarser, creating less drift.
The rotary atomizers on many aircraft produce fairly uniform droplet sizes and do a good job of eliminating the larger droplets. This makes even more droplets available for coverage. However, even with this technology spray drift still matters and all steps to prevent it should be taken. This means using larger average droplet sizes and increasing water volumes accordingly to their label recommendations.
June 24, 2016