In this installment, Dr. Tom Wolf, intrepid reporter, braves the unforgiving wilds of Saskatoon as he investigates claims of mysterious devices popping up all over the city. Colloquially referred to as “nozzles” these items are imprinted with obscure codes that scientists are struggling to decipher. Be the first to learn how to read a nozzle and nozzle table in our newest installment.
We’ve heard it often: calibrate your nozzles to be sure your boom output is uniform across its entire width. The downside of poor uniformity is obvious: strips of over- or under-application causing problems with pest control or crop tolerance. A graduated cylinder held for 30 s under each nozzle is the approach of choice. Several electronic versions exist to make the job easier, for example the Spot On.
But there’s more to the story. Nozzle calibration only ensures volumetric uniformity from nozzle to nozzle. It serves to identify worn, plugged, or damaged nozzles, and little else.
After release, the spray is atomized and distributed across a wider area with a properly developed pattern. An operator adjusts boom height or spray pressure to generate proper overlap for a given fan angle at the target height. Unfortunately, the uniformity of this pattern can’t be measured with a graduated cylinder, so we’ve traditionally used a “patternator”, a flat collector placed under a few nozzles that uses a series of channels to show the peaks and valleys of the volumetric distribution. Both calibration and patternation are done with a stationary spray boom. Nozzle manufacturers employ both methods to ensure their products meet international uniformity standards before marketing.
A spray patternator determines the uniformity of a stationary boom’s spray distribution (Photo: TeeJet)
Burt even that isn’t enough. We can have good volumetric distribution but still have inconsistent coverage in places. To identify those regions, we need a way to measure small amounts of spray deposit under a moving boom, ideally in the canopy we intend to treat. Here we have a few options. We can place a tracer (dye, salt, etc.) in the tank, and collect spray on small collectors placed throughout the area to be treated. We collect the samples, wash them, and analyze the solvent for the tracer. This requires special equipment and takes time. It’s useful, but only measures dose, not droplet size or density.
Plastic straws can act as collectors of sprays under field conditions.
Monofilament strings can be used to collect spray over long distances.
A faster way is to use water-sensitive paper, about which we’ve written here and here. Using WSP is fast and easy, and it can provide additional information such as the number of droplets per unit area, or the total percent of the area covered, or even the size of the deposits, with the right equipment. We call this “coverage”, and believe this to be one of the two components of good pest control (the other being “dose”, the total amount of material deposited). Because the world isn’t fair, WSP isn’t great at quantifying dose.
Water-Sensitive paper provides a quick visual indication of the deposit, not just amount but also qualitative aspects such as droplet size and distribution.
The industry has done a good job of identifying the dose required for good control, and this is reflected in the rate recommendations on a label. But there are a few gaps. They don’t tell us, for example, what “good coverage” is, despite often telling us to “ensure” it.
Back to Deposit Uniformity
We quantify deposit uniformity by calculating the Coefficient of Variation (CV) of a series of measurements. The CV is defined as the standard deviation of these measurements, expressed as a percent of the mean value.
Because it’s hard to measure, it’s easy to ignore. But here are a few basics our research has told us: (In the first three examples, deposits were measured under a spray boom using petri plate or drinking straw samplers. There was no interference from a canopy. The last example was taken from within a canopy.)
When measuring the deposited dose, the CV under a boom tended to rise with increased wind speed. This is no surprise, as it reflects that more wind has a greater chance to displace spray from its intended destination.
Spray deposit uniformity, observed during various spray drift studies, tended to decrease with higher wind speeds.
Higher booms and increased travel speed also tended to increase deposit CV.
Faster travel speeds during spray drift studies tended to decrease uniformity.
Finer sprays tended to increase deposit CV. This makes sense, as the finer droplets are more easily displaced by air movement.
Coarser sprays created more uniform deposits possibly because they were more resistant to turbulent displacement.
Deposits were reduced and became more variable deeper in a broadleaf canopy. Again this makes sense, as there are a lot of obstacles to clear and canopies themselves are by no means uniform.
Deposit amount was lower in the canopy, as expected. But the lower deposit was also more variable.
Also note that the CV in the canopy was quite a bit higher (40 – 60%) than for the exposed targets (10 – 20%). That’s another challenge.
To recap, the best uniformity was achieved with low booms (as long as patterns overlap sufficiently), slow speeds, low winds, and coarser sprays. It’s easy to see that current spray practice isn’t always conducive to uniform deposits.
Deposit variability as captured by a 2 mm diameter string with two sprayer configurations.
So What?
Why does uniformity matter? It matters because more variable deposits are less efficient. They require higher doses for the same effect as uniform deposits. Here’s why:
The figure below shows a typical dose response curve for a herbicide. On the y-axis, we see weed biomass, on the x-axis herbicide dose. At low pesticide doses, not much happens. (In fact, we often see a slight increase in biomass with very low herbicide doses.) As we increase dose, biomass begins to decline, and as dose increases further, the effect begins to taper off. At a certain dose, no further biological response is possible.
A typical dose response curve for a herbicide.
In the next figure, we see that application of a uniform dose “a” results in biomass “y”, about 20% of untreated.
A dose response curve represents the weed biomass that resulted from any applied dose.
Next, we apply the same average dose, but we do it non-uniformly. At some locations under the boom, the deposit may be 40% higher or lower than average. The result is response “z”. Weed control is worse, as bad as it would have been at a lower uniformly applied dose (effective dose “b”).
A variable dose across a field results in many individual weed biomasses because of deposit variation. The net result is lower control.
This effect only happens when the effective dose is near the lower inflection point of the dose response curve. Perhaps we’re shaving rates. Perhaps the weather is challenging the herbicide’s performance. Or perhaps the weed is difficult to control. Under those conditions, any gain in performance with a higher dose is less than the penalty from a lower dose.
There are two ways to correct this performance loss. One is to apply a higher herbicide rate. It’s commonly done, as insurance against – you guessed it – variability, and it’s one reason why label rates have some flexibility. The second way is to improve deposit uniformity. In effect, better uniformity allows for rate reductions.
Label rates are typically in the flat region of the dose response curve to allow for variable conditions in weed susceptibility, weed growth stage, growing conditions, and deposit variability.
Take Home Message
Uniform spray deposition improves overall control. Our examples used herbicides, but the same is true for fungicides and insecticides. It’s true for field crops as well as fruit and vegetable sprays.
Uniformity is especially important when the application is done under adverse conditions in which the pesticide performance is challenged. It’s a fundamental part of good application practice.
It’s not always easy to improve uniformity. But at least it should be measured. Without measuring it, an applicator may never know how much product is being wasted. Have a look at the Crop Adapted Spraying approach Jason is using, it’s a template for all sorts of applications.
What can you do? The easiest task is to record the flow from each nozzle. The results might be surprising. Ensuring proper and consistent boom height is also important. Using water-sensitive paper to visualize the quality of the job would be icing on the cake. And adjusting application method, with uniformity as a goal…that gets you a gold star.
When we consult a nozzle catalogue we are interested in the flow and droplet sizes produced at a given pressure. Perhaps we should also consider the effect of pressure on spray angle. We have several articles discussing the collective impact of spray overlap, nozzle spacing and boom height on coverage uniformity (Check here and here for example). However, we don’t really address the fact that fan angle is not a constant. This may be more relevant with the growing adoption of spot sprayers.
To illustrate the potential for fan angle variation, we assembled a collection of red, flat fan nozzles (‘04s) from several manufacturers. We plugged each nozzle into a spray pattern table, set the regulator at a given pressure, and photographed the spray angle and flow distribution. This process was repeated for each nozzle at seven different pressures within the manufacturer’s approved range of 20-80 psi. After digitizing the photos, we measured the spray angle using a digital protractor.
We anticipated a concomitant increase in spray angle as the pressure increased. This is not news. Anyone who has operated a sprayer has seen the spray pattern open up as the boom fills and pressurizes. Bear in mind this was only performed once (i.e. n=1), so while it illustrates trends it shouldn’t be mistaken for a rigorous scientific comparison. Further, this demonstrates a static situation and not a dynamic one where travel speed, wind conditions and the vortices from the sprayer it self will influence matters.
We saw similar trends with nozzles other than 110˚ fans, but let’s focus on 110˚s due to their current popularity.
Fan angles for five common 110 degree AI flat fans over their manufacturer-recommended pressure range
The spray angle for 110˚ nozzles ranged from 75˚ at 20 psi to approximately 143˚ at 80 psi. One nozzle failed to reach 110˚ at any pressure. Conversely, there was another that was over 110˚ at nearly all pressures. Ideally, spray nozzles should be operated around the middle of their manufacturer-recommended operating range. Three of the nozzles tested came close to 110˚ at that median pressure, but only the TeeJet AIC110-04 measured 110˚ at the middle of its recommended range (~50 psi).
Using that nozzle as an example, let’s look at the pressure, spray angle and subsequent distribution of flow along the swath at three different pressures. At 20 psi, the spray angle was 85˚. The yellow balls are floats that reflect flow as a series of cross sections of the swath. We see that aside from the tapered edges (which illustrate the need for 100% overlap between neighbouring nozzles) the distribution was fairly even. One of the priorities in nozzle design is to ensure a low coefficient of variability over the operating pressure range. In other words, the length of the swath may change, but the spray quality and uniformity in that swath is still within spec. At 50 psi the nozzle produced the expected 110˚ fan, and the spray distribution remained even. At 80 psi, the angle spread out to 125˚, spanning a greater distance, but it started to produce a less-even distribution.
Photographs of spray angle and distribution for the TeeJet AIC110-04 at the extreme low, middle and highest pressures of its recommended pressure range.
When fan angle changes with pressure, it can have significant implications. Nozzle spacing on a boom varies from sprayer to sprayer. Generally 50 cm (20 inch) centres are the standard in North America, but we’ve seen 15″ and even 10″. Nozzle spacing and boom height collectively determine the degree of spray overlap. Excessive overlap isn’t a problem, although additional nozzles do mean added expense, cleaning time and potential for plugging. Conversely, gaps in the pattern could lead to sub-lethal applications or flat-out misses. For example, in this soybean demo plot (below) we sprayed a contact herbicide at low pressure to collapse the spray pattern. You can see the alternating stripes of hits and misses that resulted from an incomplete overlap of spray.
Soybean demo plot sprayed with a contact herbicide using 110˚ air induction flat fans at 20 psi. The collapsed spray pattern did not overlap sufficiently to burn the entire crop down, leaving a striped pattern and demonstrating the poor coverage.
Nozzle manufacturers generally recommend a 100% spray overlap for flat fans. This creates sufficient overlap when the boom sways low to the ground. It also increases the degree of droplet size homogeneity under the boom as coarser and fewer droplets are generally found at the “horns” or edges of the pattern compared to the centre. In order to ensure this degree of overlap, sprayer operators should observe and consider changes in fan angle over their typical pressure range. Otherwise, the cost of poor deposit uniformity under the boom could be high.
Operate nozzles around the middle of the manufacturer-recommended pressure range. However, just because a nozzle is rated over a range of pressures does not mean the angle is constant.
Lower pressures are a greater concern than higher pressures. 30 psi is the absolute lowest pressure for operating a 110˚ air induction flat fan; the ideal operating range for these nozzles is 50-70 psi.
If nozzles are not maintaining the recommended 100% overlap at your preferred pressure range, then consider switching nozzle rates, and adjusting pressure and boom height.
This work was performed with Victoria Radaukas, 2015 OMAFRA application technology summer student.
If you’re a sprayer operator with some experience behind you, you may have applied mercury arsenate, nicotine, Paris green, or perhaps even DDT. All of these historical pesticides were effective, but they were also toxic to both the applicators and the environment. Fortunately, today’s agrochemical manufacturers produce pesticides that are effective while being far less hazardous.
One important aspect of modern synthetic pesticides that enhances their efficacy is their ability to redistribute. Pesticide redistribution is the movement of a pesticide from its initial point of deposition to a different spot on or in the plant. Pesticides that can redistribute can improve pest control compared to those that must contact the target pest but cannot innately redistribute. This is especially true when spraying hard-to-wet plant tissues, such as flower clusters or fruit. Even when the immediate coverage of these tissues is insufficient, the subsequent relocation beyond the initial spray deposit can result in a more effective protective barrier. When plants are rapidly growing, many of these products can translocate through the plant tissues to protect newly emerged tissue that did not receive a direct deposit.
Some of the most difficult and persistent pests are more effectively controlled by redistributing pesticides. Materials that move within the plant after application provide improved control of piercing-sucking insects such as aphids and psyllids, as well as pests that feed in difficult-to-spray areas such as under leaves. These products can absorb into plant tissue, increasing their resistance to wash-off by rain or irrigation.
Five Types of Pesticide Redistribution
There are five significant types of pesticide redistribution: translaminar, vapor, xylem, phloem and redistribution via precipitation
Translaminar Redistribution
Translaminar redistribution (Figure 1) in its most literal sense is a compound moving from the side of the leaf that received spray, to the unsprayed opposite side. This results in protection on both sides. However, translaminar redistribution also involves limited radial movement providing a “halo” of protection around the initial deposition. The extent of this area of influence is product-dependent.
Figure 1. Schematic of translaminar redistribution, with small round dots indicating deposition of pesticide, arrows indicating the direction of redistribution, and the shading indicating the area of the plant protected by the pesticide.
Vapor Redistribution
Vapor redistribution (Figure 2A) occurs when surface depositions volatilize and move laterally along a plant surface, re-adsorbing to the plant surface in new locations as they move. Again, the extent of vapor activity is product specific, but also condition specific requiring an optimal combination of temperature, relative humidity, wind, and solar radiation to facilitate volatilization. When pesticides are referred to as “locally systemic,” it often implies that they exhibit translaminar and/or vapor redistribution properties.
Figure 2. Pesticide redistribution type schematics (A) vapor, (B) xylem, (C) phloem. The small colored groups of dots indicate deposition of pesticide, while arrows indicate the direction of redistribution, with shading representing the area of the plant protected by the pesticide.
Xylem and Phloem Redistribution
Xylem redistribution (Figure 2B), also called xylem systemic, refers to the absorption of a pesticide and subsequent systemic movement of the pesticide through the xylem vessels of a plant. Xylem vessels move water and minerals in an upward and outward direction in plants. There is very little movement of water and nutrients downwards or backwards along branches or leaves in xylem vessels. Xylem redistribution can help protect growing tissues from damage by pests or diseases when the pesticide redistributes from the point of application to the newly developing tissues. Most systemic fungicides and insecticides redistribute via the xylem.
Phloem redistribution (Figure 2C), also called phloem systemic, is the bi-directional movement of pesticides in the phloem vessels of a plant. Phloem vessels transport sugars and other nutrients both to the roots of plants and upwards and outwards to shoots and fruits/seeds. Phloem systemic pesticides are sometimes called “true systemic,” because they can translocate throughout the entire plant.
Some pesticides that redistribute via the xylem or phloem can be applied to the soil substrate to be absorbed by the roots and redistributed throughout the plant. The process of plant nutrients or pesticides being transported from one place to another within the plant is called translocation.
Soil-Applied Systemics
Several factors affect a pesticide’s ability to redistribute. These factors affect the speed of uptake, the duration and extent of translocation, and the amount of accumulation in plant tissue relative to the initial dose. For pesticides labeled for soil application, their uptake by plant roots and redistribution via xylem or phloem can lead to long residual efficacy of the product; Up to eight weeks or more depending on the product, plant, and soil. This is in contrast to foliar-applied products, where good residual efficacy could be expected to last two to three weeks depending on the product. However, foliar-applied products tend to provide a more rapid kill of target pests and a more rapid absorption and translocation of active ingredients.
For soil-applied systemic pesticides, the composition of the soil substrate can affect the uptake of the pesticide by the plant. Growing media high in organic matter (>30% bark or peat moss) can bind pesticides, making it difficult for plants to absorb them through roots and subsequently translocate via the plants vascular system. Soil applications of systemic materials should take place one to six weeks prior to the onset of the insect pest or pathogen. This allows sufficient time for the pesticide to translocate to, and accumulate in, target tissues. The more water-soluble pesticides (e.g. Thiamethoxam) are taken up more rapidly than the less water-soluble pesticides (e.g. Imidacloprid).
Redistribution via Precipitation
In contrast to systemic pesticides, contact pesticides cannot redistribute on their own. However, rain or irrigation can spread the deposit to some degree, increasing coverage area. This effect should not be relied upon, as it depends on the product formulation, the intensity of the precipitation, and the interval following application. In the case of prolonged precipitation, the residual activity of contact products can be greatly reduced as they are diluted and washed off plant tissues.
Plant Morphology
The status of the plant to which they are being applied is a significant consideration when applying redistributing pesticides. Both soil-applied and foliar-applied pesticides are more rapidly absorbed and redistributed when applied to young plants or juvenile plant tissue. In general, when plants are actively growing, have a strong root system, or are actively transpiring, they tend to absorb and translocate pesticides more rapidly than when plants are growing slowly. In addition, plants with difficult to wet leaves or surfaces due to thick cuticles or waxy layers tend to not absorb pesticides as readily. Penetration into plants with difficult to wet surfaces can be improved by adding adjuvants such as surfactants to tank mixes.
Multiple Modes of Redistribution
The extent to which each product can redistribute can be thought of as a continuum. Generally, when a product exhibits some form of redistribution, it can also redistribute via a different method. A good example of this is xylem and translaminar redistribution. When a product can redistribute via the xylem it generally can move through the leaf via the translaminar pathway as well. Some products can redistribute via the xylem, translaminar, and vapor pathways all at the same time. Others, while technically able to redistribute via more than one mechanism, are only biologically effective via one mechanism.
Consult the Pesticide Label and Other Reputable Sources
The best way to determine how a pesticide product redistributes is to consult the manufacturer’s label, as well as technical information from reputable sources such as government or academia. If a manufacturer provides a technical information bulletin it is generally available on their website on the pesticide product page along with the label. However, because there are no standardized metrics to rate pesticide redistribution, there can be significant disparity between products. Some products that are advertised as being xylem systemic for example, are actually less systemic than products that are not even advertised as being systemic. Additional information on the efficacy and redistributing characteristics of specific products can be obtained from extension agents or crop consultants.
Conclusion
In summary, when selecting a pesticide remember to consider the four different pathways of redistribution (xylem, phloem, translaminar, and vapor) and how these methods may improve the efficacy of your application, allowing you to get more out of every drop.
Spot spraying promises to dramatically cut herbicide use. Data from Green-on-Brown (GoB) sprays suggest at least 50% and possibly 90% savings are possible, depending on weed density and the system employed. These savings are significant. But system performance depends on the nozzle selection even more than for broadcast sprays. What are the issues?
Pattern Width
Spot sprays represent a unique mix of single nozzle banding and multiple nozzle broadcasting on the same boom at different times and locations, depending on what the weedy spots require. Both need to be optimized to get the best performance and savings out of such a system.
Even (Banding) Nozzles
Let’s say the spot spray boom has a spacing of 10” (25 cm) and is carried by wheels to ensure consistent height. An operator would want the spray pattern to have a very similar width as the nozzle spacing. A 30 degree even fan angle would create a band of about 10” wide at a boom height of 19” (48 cm, download a worksheet that solves this for any fan angle and boom height here). Assuming a travel speed of 12 mph (20 km/h) and a pressure of 40 psi (2.75 bar), an 03 sized nozzle would apply 14.9 US gpa (139 L/ha) in these 10” wide bands.
But most applicators would be uncomfortable with zero overlap, and would prefer to raise the boom to allow, say, 20% overlap. This would ensure targetting of taller weeds that appear exactly between two sprays, for example. At 22” (56 cm) boom height, the pattern would be about 12” (30 cm) wide and affording 1” overlap on either edge.
Spot spray booms activate any number of nozzles depending on the weed locations.
Because the application is diluted by the extra pattern width, the applied volume is now 12.4 US gpa (116 L/ha), about 20% less than before. This change is easily accommodated by mixing the product more concentrated in the tank. The downside is that the overlap in banded sprays receives twice the dose, and this is less than ideal.
Tapered (Overlapping) Nozzles
A possible solution is to employ tapered flat fans that are the standard type on broadcast booms. These produce more of their volume in the centre, diminishing at the edges, to allow for overlapped patterns and thus functioning better when more than one nozzle is activated. In addition, the extra coverage from a wider pattern is not as wasteful as it is from an even pattern type since it comprises less volume. A single nozzle spray, however, would have a higher dose in the centre than at the edges, since a single pattern has a bell-shaped volume distribution. (note: a single nozzle moving through air loses some of its volume from the centre and places it at the edges, due to aerodynamics of the fan shape. That levels out the bell shape somewhat.)
Broadcasting
When more than one nozzle is triggered by the sensor, the spot spray of that region is just a small section of a broadcast boom. The average dose is now related to the nozzle spacing, not the actual band width as it was for a single nozzle. The wider the section of nozzles that are activated simultaneously, the less inefficiency a wider individual pattern creates because it’s only wasted on the outside edges of the outside nozzles.
Clearly, a sprayer that sometimes functions as a single nozzle spot spray, and at other times as a broadcast boom requires some compromises. Monitoring the activation of nozzles and learning from the relative frequency of single vs multiple nozzle activations will be useful to optimize the configuration. But when boom height is constant, a good compromise solution is possible.
Suspended Booms
A more challenging situation arises from suspended booms that do not hold a consistent height. Let’s assume a boom height variance of 10” (5” in either direction), and a wish to retain 20% overlap at the lowest height to avoid misses from a 30 degree nozzle. The lowest height would have about a 12” pattern width, achieved at 22”. The boom would be set 5” higher, 27” (69 cm). At this height, a 30 degree fan would produce a band width of 14.5” (37 cm), producing a 45% overlap. If the boom sways up to 32” (81 cm), the pattern width would be 17.1” (43 cm).
For multiple adjacent nozzles, boom height determines overlap, and a minimum overlap must be achieved even when the boom sways low.For single nozzles, boom height determines band width and therefore dose.
This is where it gets tricky. At suboptimal heights, the difference between a single band and a section of overlapping patterns increases. Do we calculate the tank mix for the rate a single nozzle delivers within its band, or for a set of nozzles activated simultaneously? If we knew that the majority of activations are for a set of two or more nozzles, we could opt to assume an application rate of a boom section with 10” spacing. An 03 nozzle at 40 psi and 10” spacing would apply 14.9 gpa (139 L/ha). But when a single nozzle is activated, the application volume in the 14.5” band is just 10.2 US gpa (95 L/ha), and the plants that triggered just a single nozzle would be under-dosed.
At the top of the sway (32”), a single nozzle’s wider pattern would deliver about 8.7 gpa (81 L/ha) , another 16% less spray volume than at 27”. At the low end of its sway, the band is 12” wide, applying about 12.4 gpa (116 L/ha) , 23% higher than the 10.2 gpa rate at the 27” boom height.
It’s clear that to take advantage of the potential savings of spot spraying, and to ensure good success with single nozzle activation, consistent and accurate boom heights are essential. I’m not sure how much more obvious a development priority can be.
Band Length
Spot sprays allow the user to select the length of band that the spray is activated for. Shorter band lengths require more targetting certainty. If booms and travel speeds are both low, an individual detected weed can be targetted accurately with relatively short band lengths because relatively little can happen to displace the spray during its short journey. But as booms and travel speeds are higher, the time that the spray arrives at the target is more difficult to predict and longer band lengths need to be programmed. For example, wind can push the spray off its target. Or the faster speeds impart more of a horizontal vector to the spray, causing it to land further away from the point of release.
The variances in where the spray lands along the direction of travel depend on droplet speed and boom height. A conventional flat fan nozzle produces an initial droplet velocity of about 20 m/s. These droplets slow at a rate dependent on their size and whether they’re entrained in the spray plume. At 45 cm below the nozzle, larger droplets are still moving at 10 m/s. Smaller droplets are only moving at 1 to 2 m/s.
Droplets take time to reach their target, and the spray band length must accommodate variance in this time arising from different from boom heights or droplet speeds.
Let’s assume an average droplet speed of 10 m/s for the journey. At that speed, the spray takes about 0.05 s to travel the 0.7 m (27”) from nozzle to target. During that time, the sprayer going 12 mph (5.6 m/s) moves about 0.25 m forward, as do the larger droplets from the released spray. If the boom sways down to 22” or up to 32”, the distance travelled by the sprayer is 0.2 and 0.3 m, respectively. In other words, the band length would need a buffer of 10 cm to accommodate the variability of the beginning and end of the band.
Overall Efficiency
Are these numbers such a big deal? You might say that we’re already cashing in on some big savings here, so why sweat the details?
It’s the principle and the resources. If we’re talking about individual nozzle band width and its change with boom height, accommodating boom sway means applying more than necessary on average to avoid under-dosing when booms sway high. The examples used here show a potential dose variance of 40% with a boom sway of 10”, a modest assumption. That’s a big number to leave on the table. If we had a constant boom height, we could decide what overlap we wanted and minimize these losses.
One of the features on most spot sprayers is to turn on all nozzles of a section that exceed a certain boom height. While this prevents under-dosing and ensures an area is treated even when the sensor is outside of its optimal range, it is possibly an unnecessary use of product.
If we’re talking band length, adding 10 cm to a band length of 50 cm is 20% over-application. That can also add up.
The key to being efficient with spot sprays is accurate and consistent boom height. We know we can do that with a wheeled boom. But show me a suspended boom that can deliver on this, and I see an instant industry leader in spot spray application.
