Author: Jason Deveau

RPAS Swathing in Broad Acre Crop Canopies

This work was performed with contributions from Adrian Rivard (Drone Spray Canada) and Adam Pfeffer (Bayer Crop Science – funding partner). Dr. Tom Wolf is gratefully acknowledged for his editorial support and assistance interpreting the results.

Introduction

This research is part of a continuing effort to identify best practices for broad acre crop protection using remote piloted aerial systems (RPAS). Previous work in wheat, corn and soybean has provided insight into how RPAS operational settings and environmental factors affect drift potential, effective swath width and spray coverage. This information, paired with advancements in RPAS design, has helped operators to improve spray deposit accuracy.

However, RPAS still produce what has traditionally been considered poor (or at least sporadic) broad acre coverage. Many studies have illustrated these shortcomings using herbicides or fluorescent tracers. Contributing factors include inappropriate operational settings, low application volumes (20-50 L/ha) paired with coarser spray qualities, and inaccurate swath widths. In light of these issues, we struggle to reconcile claims of acceptable disease control, which is arguably the greatest challenge in a spray-based crop protection paradigm.

Tar Spot

One real-world example of intermittent disease control from aerial applications (not just RPAS) is the case of tar spot in corn. Tar spot is a fungal disease caused by Phyllachora maydis and it is becoming a significant economic concern in Ontario. Left unchecked the disease causes rapid, premature leaf senescence. This reduces photosynthetic capacity, and ultimately, yield. Depending on spray timing, crop variety, environmental stressors, and the product applied, protection should last for up to three weeks.

In the last few years there have been several reports (both in Ontario and in corn-producing US states) of tar spot “striping” following aerial sprays. Crops seem well protected directly beneath the flight path (green and healthy), but efficacy tapers to failure towards the edges of the swath (brown and desiccated). Fundamentally, this is likely due to inadequate spray coverage caused by an overestimation of the effective swath width.

Figure 1 Tar spot striping in Western Illinois following two applications from a fixed wing sprayer (2023).

Figure 2 Tar spot striping from RPAS volume trials. A brown strip can be seen between two passes in each RPAS treatment of 30 and 50 L/ha. The top is an application by a 100 foot horizontal boom. Each treatment is separated by an unsprayed check. (2023).

Figure 3 – Tar spot striping in Ontario corn following fungicide application by helicopter (2024).

Effective Swath Width (ESW)

The measured swath width presents the lowest variability (as indicated by the coefficient of variability, CV) while minimizing the degree of over- and under-dosing. As a matter of operational productivity, wider swaths mean wider route spacing, which is attractive because it means fewer passes and faster applications. Once the agronomics are considered, the effective swath width is that portion of the swath that gives the desired biological result. It may equal, or only be a fraction of, the measured swath width. It is plausible that inappropriate effective swath widths from aerial applications are common, but have not always been detected, because:

Generally, fungicides are weakly systemic and give modest yield increases from disease suppression and their “stay green” properties. Until tar spot, a sub lethal dose of fungicide did not lead to rapid and acute crop failure.
Most growers do not intentionally leave unsprayed checks, or the check locations do not coincide with disease presence.
The applied product rate is sufficiently high to cover regions of under-application.
Taken together, deficiencies are often too subtle for passive detection.

This is not to suggest that pilots intentionally inflate swath widths. Swaths are evaluated during fly-in calibration sessions using established protocols (e.g., Operation S.A.F.E.), and RPAS swath evaluation has emulated these practices. Calibrations take place on bare ground or stubble/grass using two-dimensional samplers (i.e., continuous samplers like string or bond paper, or discreet samplers like water sensitive paper). However, this protocol does not account for any physical interference from the crop canopy itself. This may have negative implications, particularly given the unique nature of the RPAS swath.

RPAS tend to produce swaths with a very narrow span and a steep profile. To a certain extent, their swath widths share a direct relationship with altitude and headwind speed, and coarser sprays result in narrower swaths (with Dr. Michael Reinke, MSU). The outer edges of the RPAS swath represent the least amount of spray volume along the width, and this coincides with the turbulent dispersion zone of the downwash. Therefore, those extremes should contain a higher proportion of low-energy droplets moving in multiple directions relative the centre of the swath.

While crop morphology and planting architecture are contributing factors (i.e. part of the agronomic use case), it is generally accepted that the degree of spray penetration falls off exponentially with canopy depth. It follows that this should also be the case for any lateral movement, resulting in a significantly shorter swath in-canopy versus on bare ground.

Materials and Methods

Spray Sampling

Spray deposition was sampled using a 15.8 m (52 ft) Speed Track (Application Insight LLC) loaded with 3-inch bond paper (Staples Canada). The spray mix was 0.3% v/v FD&C Blue #1 Liquid. Bond papers were analyzed using a Swath Gobbler (2nd gen software – Application Insight LLC) at 100 mm sampling rate (i.e., ~150 discreet images per sample). Hue: 32-180. Saturation 17-60. Value: 156-255.

The Swath Gobbler produces a complete, correlated and ordered record of the cross-section of a swath. For each discreet image, it reports the number of individual droplet stains on the sampler per area. It also reports percent area covered by measuring the total number of pixels with dye divided the total number of pixels in the image.

The device deliberately does not calculate a Droplet Size Distribution (DSD) of the stains. This is because any DSD calculated from paper collectors relies on assumptions that cannot be validated, such as the fact that all droplets are captured and detected, spread factors are known for that application condition and similar for all stain sizes, there are no multiple hits, etc.

RPAS

The sprayer was a DJI T40, calibrated according to the pilot’s standard operating procedure (Drone Spray Canada). Certain operational settings varied with treatment and will be detailed later in this section.

The flight path was perpendicular to the sampler, aligned with the centre using pin flags as references for the pilot. Spraying began approximately 20 m prior to the sampler to ensure the RPAS was at target speed and continued some 20 m past the sampler.

Figure 4. DJI T40 approaching sampler on bare ground. Sampler was later moved into the adjacent wheat field (left).

Defining Coverage

Swath width will be calculated from two different coverage metrics.

Percent Area Covered describes the amount of surface area covered by deposit. Given the variable degree of stain diameter (a function of sampler material, spray mix, and droplet velocity) this value can only be used as a relative index (i.e., can only be compared to itself). No conclusions can be drawn about how spray interacts with plant tissue, but generally more coverage correlates to improved crop protection.

Deposit Density describes the number of individual droplet stains on the sampler per area. Higher densities can imply more uniform distribution over the plant surface, which is particularly important for contact materials.

Previous studies (with Dr. Tom Wolf, Agrimetrix Research and Training, data not shown) indicate a higher correlation between deposit density and swath width at lower versus higher spray volumes. Lower volumes are typically comprised of finer droplets, which are more accurately resolved using deposit counts. Swath widths determined by deposit density also tend to be longer than those determined using percent coverage, better aligning with real-world observations of efficacy.

Wheat

R40 wheat was planted on October 9th, 2023, at 808,000 seeds/ha (2 million seeds/ac). Wheat height at the time of the trial was 60 cm (25 in). The location was 45180 Fruit Ridge Line, St. Thomas, Ontario. Deposition trials took place on May 23rd. Wheat stubble swath testing also took place at this location on May 15th.

The RPAS was programmed to apply 50 L/ha using a 260 µm droplet diameter according to the DJI software. Air speed was 5 m/s and the flow rate was 11-12 L/min as it passed over the sampler. Swath was programmed at 8 m.

Coverage was evaluated for water (control) and for a spray mix containing 0.15% v/v Interlock (a drift mitigating adjuvant – Winfield United) and 0.15% v/v Interlock + 0.125% v/v Activate Plus (a spreader adjuvant – Winfield United). For bare ground, each treatment had three passes (n=3) except for water, which had four (n=4).

The wheat canopy was only sprayed with water three times (n=3). Limited passes were made because it served as a proof of principle. Any indication of relevant differences in the swath width would justify later trials in corn and soybean. These first passes revealed issues with the experimental design that were later corrected:

The RPAS spray tank level was not held constant. The RPAS weight affects the intensity of the downwash. The volume dropped from 30 L to ~20 L over the course of the experiment. In future trials, a tank volume of 20 L was maintained from a premixed source.
The wind direction occasionally shifted from a direct headwind to a partial cross wind from the RPAS’s right. In future experiments, we waited for an optimal wind direction before starting each pass.
The RPAS altitude was set to 3 m above bare ground. We assumed it would climb to account for the height of the wheat, but the canopy did not register with the RPAS sensors. As a result, spray was released ~60 cm closer to the wheat heads than to the ground in bare ground swathing. In future experiments, we confirmed that the RPAS was 3 m from the top of the crop canopy.
Despite best efforts, moving the sampler into the wheat parted and distorted the canopy. As a result, the sampler was not as obscured as it should have been. We developed strategies to minimize canopy distortion in corn and soybean that will be described later.

Figure 5. Top-down view of sampler in wheat canopy. Note that the canopy did not close over the sampler as intended.

Corn

Corn was planted on May 15th, 2024, at 13,300 seeds/ha (33,000 seeds/ac). The sampler was erected in the field on July 3 to allow the canopy to grow up and around it. Deposition trials took place on July 26 and every effort was made to leave the canopy undisturbed around the sampler. Corn measured 2.4 m (9 ft) at the tassel and 1.2 m (4 ft) at the silks. The sampler height corresponded to the ears. The location was 42°40’52.1″N 81°04’45.9″W near 5277 Quaker Road, Sparta, Ontario.

Figure 6 Sampler erected to 4 ft. Crop grew around the sampler to minimize any canopy disturbance.

Figure 7 Sampler position relative to ears during sampling.

Figure 8 Installing Speed Track for swath testing in wheat stubble.

Soybean

Soybean was planted on June 30^th, 2024, at 80,800 seeds/ha (200,000 seeds/ac) on 38 cm (15 in) centres. Deposition trials took place the morning of August 14. While the densest area was selected for the trials, the field was patchy with crop height spanning 20-25 cm (8-14 in). Each section of the Speed Track was inserted under the canopy separately to avoid disturbing or damaging the plants. The track was elevated ~10 cm off the ground. The location was at 42°46’50.4″N 81°08’20.8″W near 43900 Talbot Line, Central Elgin, Ontario.

Corn and Soybean Treatments

The following treatments were repeated three times in-canopy (n=3) (Table 1). The actual flow rate (recorded as the RPAS passed over the sampler) was always ~1.5 L/min less than programmed.

Treatment #	Droplet Diameter (µm)	Programmed Swath (m)	Volume (L/ha)	Rate (L/min)	Flight Speed (m/s)	Spray Mix
1	320	10	20	10.5	10	water
2	320	8	30	10.5	8.3	water
3	320	8	50	10.5	5	water
4	320	8	30	5.7	5	water
5	500	8	50	10.5	5	water
6	320	8	50	5.7	5	0.5% Masterlock
7	320	8	30	10.5	8.3	0.5% Masterlock

Table 1 RPAS operational settings for corn and soybean treatments

The following treatments were repeated three times on wheat stubble (n=3) (Table 2). Once again, the actual flow rate (recorded as the RPAS passed over the sampler) was always ~1.5 L/min less than programmed.

Treatment #	Droplet Diameter (µm)	Programmed Swath (m)	Volume (L/ha)	Rate (L/min)	Flight Speed (m/s)	Spray Mix
1	320	10	20	10.5	10	water
2	320	8	30	10.5	8.3	water
3	320	8	50	10.5	5	water
4	320	8	30	5.7	5	water

Table 2 RPAS operational settings for wheat stubble treatments

Weather Data

The RPAS flight path was into the prevailing wind, but minor variations occurred throughout sampling. Weather was recorded as the RPAS passed over the sampler using a Kestrel 3550AG weather meter in a vane mount positioned on a tripod 2 m above ground (Table 3).

Terrain	Wind Speed (km/h)	Direction Relative to Flight Path	Temperature (°C)	Cloud Cover (%)	RH (%)
Bare Ground	3-5	Headwind +/- 25° from starboard	20-21	0	60
Wheat Canopy	5-7	Headwind +/- 25° from starboard	21-22	0	60
Corn Canopy	2-4	Headwind +/- 15° from starboard	23-26	<10	75
Wheat Stubble	4-7	Headwind +/- 15° from starboard	26-28	<10	65
Soybean	3-4	Headwind +/- 15° from starboard	22	0	55

Table 3 Average weather conditions during trials.

Results

Raw Coverage Expressed as Percent Coverage or Deposit Density

Coverage can be presented as raw data plotted by swath position. This is a qualitative means for assessing the swath. The bare ground data has been presented (using both coverage metrics) as an example (Figures 10 and 11).

Figure 10 Swath coverage data for water on bare ground expressed as percent area covered. All four passes are plotted.

Figure 11 Swath coverage data for water on bare ground expressed as deposit density. All four passes are plotted.

Repetitions were similar enough to imply that environmental conditions were consistent during sampling. By averaging the repetitions, coverage in-canopy can be more easily compared to that on bare ground Figures 12 and 13).

Figure 12 Average swath coverage data expressed as percent area covered. Bare ground (n=10). Wheat canopy (n=3).

Figure 13 Average swath coverage data expressed as deposit density. Bare ground (n=10). Wheat canopy (n=3).

The magnitude of coverage on bare ground exceeded that in-canopy, tapering to similitude and near-zero at the edges of the pattern. It can therefore be concluded that the entire swath was captured, and that spray was filtered by the canopy before reaching the sampler within.

The difference between bare ground and the wheat canopy was greater when the data were presented as percent area versus deposit density. Differences in the number of deposits from finer sprays were more accurately resolved using deposit density than percent coverage. Since it can be expected that smaller droplets penetrate a canopy better than coarser droplets, it may be more appropriate to use deposit density to document their presence. We also saw indications of wider swaths when data were presented as deposit density, as well as a bimodal distribution that reflected the positions of the two rotary atomizers.

While informative, this raw coverage format did not allow empirical comparisons. Each pass must be converted to a swath width.

Converting to Swath Width

Each pass was transformed by averaging Swath Gobbler data to a single value every 0.5 m. Data were then entered into the www.sprayers101.com swath width calculator and the SW was manually determined for each pass. Criteria was the lowest overdose, lowest underdose and lowest CV for an idealized threshold coverage of 90% that of the highest value in the swath. In the following histogram, the SW from all treatments have been averaged for ground and canopy terrains (Figure 14).

There was a significant reduction in swath width in a wheat canopy compared to stubble or bare ground. There was a 41.2% reduction in swath width in a canopy when measured as percent area covered and a 26.6% reduction when expressed as deposit density. As previously stated, deposit density better reflects the contribution of finer deposits, which tend to penetrate deepest into crop canopies.

Figure 14 Average effective swath width for all treatments on all terrains. Swaths expressed from both percent coverage and deposit density metrics. Standard error bars presented. Canopy (n=45). Ground (n=22).

When the data is considered by terrain and by crop, we see that swathing on bare ground or in wheat stubble doesn’t have a significant impact. This justifies combining those data as “Ground” in subsequent analyses.

Another observation that supports the use of deposit densities is the difference between the intended (i.e., programmed) swath width and the detected swath width on ground (Figure 15). The SW on ground was closer to the intended 8 or 10 m swath width when expressed as deposit density. It was approximately half the desired width when expressed as percent coverage, which is considerably less than common practice.

Figure 15 Average effective swath width for each crop and terrain. Swaths expressed from both percent coverage and deposit density metrics. Standard error bars presented. Ground 8 m swath (n=19). Ground 10 m swath (n=3). Canopy 8 m swath (n=39). Canopy 10 m swath (n=6).

Canopy Effect

By percent area, corn had the biggest reduction in swath width compared to bare ground, then soybean, then wheat (Table 4 and Figure 16). This suggests the SW shares an inverse relationship with the canopy depth. However, the relationship reversed when SW was expressed as deposit density. The relationship between droplet size, crop physiology, planting architecture and canopy penetration is complicated, and no conclusions can be drawn beyond a reduction in SW in-canopy.

Crop	% Reduction in SW (% area)	% Reduction in SW (deposits/cm²)
Corn	44.0	20.6
Soybean	32.2	28.3
Wheat	21.7	31.5

Table 4 Reduction in average effective swath width in-canopy by crop compared to on ground. Swaths expressed from both percent coverage and deposit density metrics.

Figure 16 Average effective swath width for each terrain. Swaths expressed from both percent coverage and deposit density metrics. Standard error bars presented. Bare ground (n=10). Wheat Stubble (n=12). Corn Canopy (n=21). Soybean Canopy (n=21). Wheat Canopy (n=3).

Effect of Volume on SW

The effect of spray volume on swath width is not immediately clear. When the data were expressed as deposit density, volume shared an inverse relationship with SW in canopy (Figure 17). There appeared to be no effect when expressed as percent coverage. The inverse relationship is weakly expressed, if at all, for both metrics on bare ground.

Figure 17 Average effective swath width by volume and terrain. Swaths expressed from both percent coverage and deposit density metrics. Standard error bars presented. Canopy 20 L/ha (n=6). Canopy 30 L/ha (n=18). Canopy 50 L/ha (n=21). Ground 20 L/ha (n=6). Ground 30 L/ha (n=3). Ground 50 L/ha (n=13).

Effect of Speed on SW

For most RPAS designs, lower volumes are applied at higher flight speed (Table 5). Previous work demonstrated that higher flight speeds tended to result in wider swaths and an increase in drift. Do higher speeds cause wider swaths in-canopy, despite lower volumes?

Volume Applied (L/ha)	5 m/s Flight Speed	8.3 m/s Flight Speed	10 m/s Flight Speed
20	–	3 treatments	9 treatments
30	9 treatments	12 treatments
50	34 treatments	–	–

Table 5 – Number of treatments for each flight speed by volume applied.

Flight speed had a clearer impact on swath width than spray volume did (Figure 18). There was a positive relationship between flight speed and swath width as measured by deposit density in canopy and on bare ground.

Figure 18 Average effective swath width by speed and terrain. Swaths expressed from both percent coverage and deposit density metrics. Standard error bars presented. Canopy 5 m/s (n=27). Canopy 8.3 m/s (n=12). Canopy 10 m/s (n=6). Ground 5 m/s (n=16). Ground 8.3 m/s (n=3). Ground 10 m/s (n=3).

Just as with volume, there appeared to be no significant effect on swath width in either canopy when expressed using percent coverage. This was likely because finer sprays were better able to penetrate a canopy and deposit density is better able to resolve their presence.

Conclusions

There was no difference in SW between stubble and bare ground. The SW on-ground was far closer to the programmed 8 or 10 m swath width when expressed as deposit density.

There appears to be a significant reduction of SW in-canopy versus on-ground. A crop canopy created a 26.6% reduction when expressed as deposit density. Specifically, corn was -20.6%, soybean was -28.3%, and wheat was -31.5%. Previous work has demonstrated diminishing coverage with canopy depth in corn, but it is difficult to make comparisons between agronomic use cases (e.g. different planting architectures and plant physiologies).

When the data were expressed as deposit density, spray volume shared an inverse relationship with SW in-canopy, but the effect on SW on-ground was less clear. However, RPAS speed had a clear inverse relationship with SW in-canopy and strong trend on-ground.

It is understood that finer spray is better able to penetrate canopies. One reason is because finer droplets are able to become entrained the downwash. Another is simply mathematical advantage, given that finer sprays are comprised of exponentially higher numbers of droplets than coarser sprays, increasing the odds of deposition. Conversely, coarser droplets (which have the greatest influence on percent area covered), are more likely to impinge on the canopy structure before reaching the sampler. Deposit density appears to be the more accurate metric for calculating SW both on-ground and in-canopy.

The reduced SW in-canopy versus on-ground explains, in part, why striping is occurring in aerial corn fungicide applications. The route spacing reflects on-ground swath width, where it should reflect the shorter, ESW.

November 18, 2024

Establishing an Optimal Airblast Carrier Volume

North American product labels may or may not include carrier volume recommendations. When they do, it could be based on a two-dimensional value like the planted area, or perhaps on row length which is more appropriate for trellised crops that form contiguous hedge-like canopy walls. Volume may be tied to product concentration, which sets minimum and maximum volumes based on product rates. Or, more commonly, volume recommendations take the form of vague guidelines such as “Spray to drip” or “Use enough volume to achieve good coverage”.

In all cases, spray efficacy and efficiency can be greatly improved by dialing-in the carrier volume to optimize coverage uniformity and reduce off-target spraying. This is easier said than done because the optimal spray volume is case-specific. It depends on a complicated relationship between:

Weather conditions (E.g. temperature, humidity, wind speed and direction)
Sprayer design (E.g. air handling, droplet size and flow distribution over the boom)
Traffic pattern (E.g. every row or alternate row)
Product chemistry (E.g. mode of action and formulation).
Target (E.g. Crop morphology, planting architecture)

It is the final variable, the nature of the target, which is the focus of this article. To learn more about the other variables, grab a copy of Airblast101.

The plant canopy and planting architecture dictate volume

Quite often, the target in airblast applications is the plant canopy. The plant canopy is the collective structure containing all plant surfaces. This could be the foliar portion of a single pecan tree, a panel of grapes, or a bay of container crops. The planting architecture describes how those canopies are arranged on the planted area. If we consider the canopy and architecture geometrically, we can make relative statements about the volume required when all other variables are equal.

Six geometric characteristics of the plant canopy and planting architecture.

Geometric Characteristic	Relationship to Carrier Volume (per unit planted area)
Row Spacing	The greater the row spacing, the less volume needed.
Plant Spacing	The greater the plant spacing, the less volume needed. This assumes gaps between the canopies (I.e. not a contiguous hedgerow).
*Canopy Depth	The greater the canopy depth, the more volume needed.
*Canopy Width	The greater the canopy width, the more volume needed.
*Canopy Height	The higher the canopy, the more volume needed.
Canopy Density	The denser the canopy, the more volume needed.

*The product of average canopy depth, width and height is the canopy volume. This value forms the basis for many dose expression models and historic carrier volume calculators such as Tree Row Volume.

Canopy density

Let’s focus on a single plant canopy. Research has demonstrated that with the possible exception of canopy height, canopy density has the greatest influence on optimal sprayer settings. Density describes the amount of matter inside a canopy relative to the volume of space it occupies. The denser the canopy, the more surface area there is to cover and the more difficult it is for spray to penetrate. While air handling plays a significant role in improving coverage, a denser canopy will almost always require a greater carrier volume.

When two physiologically diverse blocks share an alley, use the sprayer settings suitable for the larger of the two. It’s more important to ensure good coverage on the big block than to save on the smaller. — When two morphologically-diverse blocks share an alley, a two-sided, every-row sprayer should employ settings suitable for the larger of the two. It’s more important to ensure good coverage on the big block than to save on the smaller. Once the hybrid row is sprayed, settings should be modified to suit the block.

For most perennial crops, canopy density changes over the growing season. The influence of age and staging on canopy size and density will depend on the crop variety, plant health and canopy management practices. The practical implication is that as the canopy grows and fills it typically warrants an increase in spray volume. As illustrated in the figure below, the volume used should reflect the current stage of canopy development. If a volume suitable for the densest and largest stage of development is used all season, it will create a great deal of waste early in the season. However, if volume is increased incrementally to reflect canopy growth, a better fit between coverage and volume will minimize waste. In the image below, volume is increased around petal fall, but the fit could be improved with more increments. Caution is advised to ensure the volume is raised (if required) prior to immediate need, particularly during key developmental stages like bud break or bloom where fungicide coverage is critical.

The curved line represents the leaf area in a canopy (Y-axis, right) increasing over the growing season (X-axis). The volume of the spray (Y-axis, left) providing effective coverage is indicated in green. Spraying the same volume throughout the season means a lot of over-spray (red) early in the season. The target simply isn’t there yet. Using less volume early season and changing about midway through the season, or as required by canopy development, has the potential to save a lot of spray (blue) without compromising spray coverage. Note that the first volume should give sufficient coverage to reach mid-season, and the second volume should be sufficient to reach the end of the spraying season. Always err on the side of excessive coverage to buffer against the impact of unanticipated variables.

There are exceptions to this rule. Many nursery crops and mature evergreens often do not require changes to volume. High density apple orchards may or may not require an increase in volume. Early in the season, sparse canopies have low profiles that result in very low catch efficiencies. In other words, a great deal of spray misses the target. The amount of waste is a function of the application equipment design and the weather conditions. Most low-profile axial airblast systems envelop the target in spray with limited means of reducing air energy sufficiently, or to turn off the spray between trees. Further, sparse canopies do not restrict wind, which means ambient wind speed tends to be higher early in the season compared to when the trees become wind breaks. This creates a drift-prone situation and higher volumes are often used to compensate for the loss. The collective result is that excess spray volume is inevitable early season. As the canopies fill, the wind is reduced and catch efficiency increases, so trees intercept more spray without having to raise volumes. This balance eventually tips, however, and an increase in volume may be advisable.

Watch the following video to see the impact of using excessive spray volume (and poor air adjustment settings) in a young cherry orchard. The waste becomes particularly apparent at ~43 seconds when the sprayer passes in front of the woods and the plume can be seen with higher contrast. While some loss is inevitable in such a sparse canopy wall, this situation could be improved by using less carrier volume, larger droplets, the correct air settings, canopy-sensing optics and/or a tower or wrap-around sprayer design.

Adjusting spray volume sprayer settings to reflect the canopy can save money and reduce environmental impact during early-season applications and in young plantings. Mix the tank as you normally would to maintain the pesticide concentration on the label, but adjust the sprayer output to match the plant size. Performed correctly, you will be able to go further on a tank without compromising efficacy. This crop-adapted spraying method and the relationship between spray volume, concentration and dose are described further in this article and this article.

Estimating volume from canopy geometry

It is challenging to decide on an appropriate spray volume. Many operators resort to historical or regional practices and do not make adjustments to reflect their specific situation. Others refer to models such as Tree Row Volume (a.k.a. Canopy Row Volume) which relates canopy volume per planted area to spray volume. In this case, catch efficacy is expressed as a coverage factor, which is determined through experimentation specific to the crop, environment and sprayer.

Tree Row Volume = (Avg. Canopy Height × Avg. Canopy Spread × Planted Area) ÷ Row Spacing

Spray Volume = Tree Row Volume × Coverage Factor

In New Zealand, coverage factors for dilute applications to deciduous canopies range from 0.007 to 0.1 L/m³ (0.00052 to 0.00075 US gal/ft³). The range captures variation in canopy density and any product-specific coverage requirements. Oil sprays, for example, require more surface coverage than most products. While closer to “the truth”, the Tree Row Volume method is still only an estimate.

If the operator has no prior experience with the crop or the sprayer and wants a sanity-check on their estimated spray volume, we propose the following guidelines for full canopy dilute application to mature crops using every-row traffic patterns. The volumes may seem high, but recognize we have selected a very challenging scenario.

Small canopies (E.g. bush, vine, cane, high-density fruiting wall): 500 L/ha (55 US gal./ac.) to 1,000 L/ha (110 US gal./ac.).
Medium canopies (E.g. tender fruit, pome): 750 L/ha (80 US gal./ac.) to 1,250 L/ha (135 US gal./ac.).
Large canopies (E.g. tree nut, citrus): >2,000 L/ha (214 gal./ac.) and up tp 7,000 L/ha (748 US gal./ac.).
For sprayer operators that think in 100 m row lengths, consider 20 L volume per 100 m row length per 1 m canopy height.

Further Resources

No matter the approach to determining spray volume, it is imperative that coverage is assessed. It is amazing what we ask of airblast sprayers. Read this short article for some perspective on the coverage we hope to achieve from a given spray volume. We propose the use of water-sensitive paper to assess spray coverage. We describe its use and evaluation in detail in this article, this article and in this article. Dialing-in an optimal spray volume is an iterative process that requires careful observation and keeping records on what works and what doesn’t for your specific operation.

Jon Clements (University of Massachusetts) wrote a great blog post on the subject of TRV. He warns about special considerations when it comes to establishing effective volumes for plant growth regulators and links to a factsheet called Spray Mixing Instructions – Considering Tree Row Volume. The factsheet was written in 2021 by Terence Robinson and Poliana Francescatto (Cornell University) and Win Cowgill (Professor Emeritus, Rutgers University).

Finally, if you really want to get lost the weeds, check out this video recorded in 2021. I had an opportunity to learn from pros like Dr. Terence Bradshaw (University of Vermont) and participants from the Great Lakes region. They’ll tell you all you ever wanted to know about Tree Row Volume. Settle in!

Thanks to Mark Ledebuhr of Application Insight LLC for his contributions to this article.

November 1, 2024

Fungicides with a Custom Applicator: Drive-Along Diaries #4
In this fourth installment of the Drive-Along Diaries, we’ll shift our focus a little. I’ll continue to share observations about real world spraying practices, but we’ll also dip a toe into the business side of custom application. Every contractor’s situation is different, but perhaps you’ll be able to relate to some of these experiences.
4:30 am
Once again, I found myself driving through Ontario in the wee hours, sipping life-giving coffee and marveling at the total absence of traffic. I was headed to Grande Pointe near Chatham to meet with Paul Delanghe, who’d invited me to tag along with him. I was looking forward, but I was also experiencing a little dread as I imagined subjecting my posterior to another day in the buddy seat. When I arrived at 7:00, I found Paul and his staff in the office. Handshakes were shared all around. Then I dove right in by asking how he got started and how his business worked.
Hello darkness my old friend. I’ve come to sit on you again.
An evolving business model – fertilizer and/or fungicide?
Paul’s family has farmed cash crops, including field tomatoes and sugar beets, for four generations. When he left the aviation industry in 2015, he invested in a high clearance sprayer and a set of Y-drops to apply fertilizer on the family farm. It wasn’t long before he was doing neighbouring farms as well. By 2017 he was saw potential in custom fertilizer work and started Acres Unlimited (AU), which incorporated in 2019.
The original business proposition was straightforward. A split fertilizer application with optimal timing can increase yield while saving fertilizer dollars. For example, perhaps a customer would lay down 150-175 lbs of fertilizer early season, and then call on Paul for another 25-50 lbs using his Y-drops. They might request a single rate, or a variable rate depending on soil type and yield potential (or none if hail or drought wreaked havoc).
This worked well for a few years, so Paul expanded into fungicides. He observed that many corn growers didn’t want to invest in their own high clearance sprayers and preferred to let a contractor worry about minimizing the trample (~4% of the yield). In the case of wheat, many growers were too busy planting to thoroughly clean their sprayers after herbicide applications and were happy to make that the contractor’s problem.
Paul found that fertilizer applications weren’t as lucrative as fungicide applications. High volume fertilizer applications meant spraying 300 ac/day instead of the 5-700 typical of herbicide or fungicide applications. That loss in productivity bit deeper when he had to rely on the client to load UAN because it meant chasing refills and waiting on small-capacity pumps.
Those delays created scheduling conflicts. Typically, as June slips into July, the window for fertilizers closes as the window for fungicides opens. But when there’s a wet spring (like we had this year) it stretches the planting window. Paul would get calls for fertilizer applications in late July, overlapping the fungicide sprays that extended into early August.
So, was offering custom fertilizer still worth it? Fungicides represent the biggest opportunity for profit and are relatively low risk. UAN is hard on equipment and machine prices and depreciation costs have increased significantly (Paul figures $200.00 CAD/engine hour). He calculated that he would have raise his prices to $25/ac for custom fertilizer applications, and that just wasn’t feasible. So, for all these reasons, he decided to leave custom fertilizer applications behind.
Staff roles and coordination
Today, Acres Unlimited consists of Paul, two full time employees (one sprayer operator and one tender truck operator) and one part timer. In addition to working for AU, employees have personal endeavours, such as running their own farms or hauling tomatoes. That means work assignments must be flexible because availability isn’t always a given. Paul sprays from April to November and when he works on his own, he can handle 3 to 500 acres a day. As long as everyone is on board for the peak spraying season in late July / early August it all seems to work.
Staff coordinate their activities through their phones. They drop pins in Google Maps, use a group chat and call regularly to stay in touch. Each employee is trusted to operate semi independently, using their own judgement to establish the safest, most effective, and most efficient means to get the job done. I was left with the impression that the business functioned almost as a cooperative under the Acres Unlimited banner.
7:45 am – The yard
This was great office conversation, and I was so engrossed that I didn’t notice when the staff left for the yard to get ready for the day. We followed behind and Paul showed me their spraying equipment.
The Sprayers
Paul has experience with several asset tracking packages (e.g., AgLeader, Raven), but he likes John Deere’s Op Centre the most. When he started spraying, Deere was the most expensive North American option, so he went with Miller and Hagie. However, the cost of sprayers has increased in recent years and closed the price gap sufficiently for him to justify buying a 412R in 2023. AU also runs a 2022 Miller Nitro 7310, and that’s used by their second operator.
According to Paul, Deere really isn’t interested in producing a high clearance machine for corn (he was encouraged to go buy a Hagie) so he had to add tall tires and a lift kit to climb from the 1.53 m (60”) stock clearance under the frame to 1.82 m (72”). He also protected the hydraulics behind the tires by covering them with canvas bags. Other growers use 5 gallon pails or even car mats to accomplish the same thing.
Tendering equipment
AU recently upgraded to a Phiber DASH 4.4 on their 15,900 L (4,200 gallon) tender truck. It caused a little sticker shock but paid for itself very quickly. The sprayer was no longer idling while the operator filled the bowls, saving on engine hours. Plus, the less than eight-minute fill time added to their overall productivity.
The tender truck itself was designed for the operator to forklift totes onto an overhead platform and gravity feed chemistry into the inductor bowls. Paul likes the bulk format over the jugs and uses it whenever it’s feasible. However, he installed transfer pumps because they’re faster than gravity feed and do a better job emptying the totes completely. Paul prefers to trust the embossed sight gauge on the side of the bowls over a flow meter; Variability in product viscosity makes the flow meter inaccurate, and that adds up over several loads. In fact, when using totes, they’ve seen discrepancies as high as 50 L (13 gallons) at the end of a day.
There was also a humble 1994 cube truck to service the other sprayers with diesel and chemistry, and a 27,250 L (7,200 gallon) water truck. AU gets their water from municipal stations, and one was conveniently located across the street from the yard. It’s a fast fill, and while there’s rarely a line up, they still make sure to fill each night to ensure an efficient start the next morning.
Float trailer
Chatham-Kent and Essex are big counties. When Paul ran the numbers on engine hour depreciation, the operator’s time, fuel, maintenance, and tire wear, floating the sprayer between jobs made sense. So, he uses a 12,100 L (3,200 gallon) float trailer to transport his Deere 412R.
He chose the two-bowl Phiber DASH 2.4 because they use a lot of jug formats with this sprayer. The left bowl (J) is a push-to-rinse system and on the right (R), a knife. This is handy for co-packs. For example, Veltyma DLX is a co-pack with one larger and one smaller jug. The smaller jug gets upended on the rinser and the larger jug gets spiked on the knife. Spiking is faster, but there’s always a chance of stabbing yourself, so better to spike the larger jugs.
8:05 – Heading out
While I waited, Paul circle-checked the float trailer. Then he flipped open the tractor trailer hood and climbed inside to get it to start! He explained that he had to manually operate the fuel pump because the electrical was cranking too slowly. This truck had almost 1,000,000 km on it and fixing the pump was going to be ~$7,000.00, so this little work-around was fine with Paul. Plus, it’s great anti-theft security.
We drove on narrow county roads which required us to lean on the gravel curbs. Paul noted that it typically kicks up a lot of dust and aggravates the people driving behind him. It can spur them to passing unsafely. But since we’d had so much regular rain this season, there was no dust and people seemed more patient.
This isn’t actually Paul, but only a few weeks after spending the day with him I ended up driving behind a sprayer. The photo op was too good to miss. and yes, I passed him.
8:18 am – Loading
Now at our destination, Paul found a safe and accessible place to park and began untethering the sprayer. That consisted of removing the four chains with turnbuckles that secured the sprayer to the trailer. He always does this first, so he doesn’t forget before backing it off… ask him how he knows. This took about two minutes to complete. Then he hit a switch under the sprayer to send up the airbags and grabbed some gloves to start filling the inductor bowls.
As Paul was pouring chemistry into the inductor bowls his phone started ringing. He said he never answers when he’s focused on loading. It takes time and attention to ensure it’s done right, and he didn’t want any distractions. Paying a little extra time and attention now means avoiding costly issues later.
This was a 54 ac job, but Paul was adding enough for 60 acres because he didn’t want to run short. A little leftover fungicide on the next job (soybeans) would be a nice bonus for the client. Each jug was emptied, rinsed immediately, had the cap replaced and was dropped back in its cardboard box. The water truck operator would grab them later when he came with our refill. Removing caps and labels for recycling is a rainy-day job.
Prepping jugs and cardboard for recycling is rainy day work.
The loading process
Perhaps I should have explained sooner, but here’s a short and generic description of the chemical loading system. Product gets added to a conical inductor bowl. This can be via jug (poured or knifed), or from bulk containers via gravity or transfer pump, or dry products get blended with a recirculating agitator. One of several bowls might be filled, each with their own product, or one bowl can be filled and emptied serially. Then the operator starts the carrier pump and begins pushing carrier (usually water) into the sprayer tank. Once enough is loaded, a valve at the bottom of the bowl is opened and the Venturi effect creates suction to draw the chemistry into the carrier stream. Then a second valve is opened to activate a rinse head in the bowl, or this is done manually using a hand-held hose. This process can then be repeated to separate products and control mixing order. Finally, it’s followed up by more carrier to rinse the lines and finish filling.

Alternately, the suction pump on the sprayer itself can draw in carrier and the induction bowl on the side of the sprayer can be used to add chemistry. In a similar fashion, onboard water is used to rinse the jug and the bowl.
Paul used a hybrid of these two methods by engaging the pump on the tender system and the pump on the sprayer simultaneously to speed up the process. There are some caveats to doing this. The concern is that some formulations may cause damage to the sprayer pump, but Paul feels there’s so much carrier water following behind the chemistry that it flushes the pump and the entire line. Here’s how he did it.
Paul backed the sprayer off the trailer and hooked up to the front-fill. He started the pump on the DASH to add about 750 L (200 gallons) of water to the 4,540 L (1,200 gallon) sprayer tank. This was not the ideal “half full”, but unless he’s anticipating a mixing issue, that’s all he uses. In situations when he’s pushing multiple products into the sprayer, he’s found that the tank can fill before he’s done. Ironically, that’s when it’s so important to start with more water, but I’ll get off my high horse now.
He had already poured or knifed products into the bowls, so he opened the valve under the first, drawing the contents into the water stream before rinsing the bowl down. Then he did the second. Then he walked over to the sprayer and started the sprayer pump to add a “pull” to the “push” and speed up the fill before returning to the DASH to wait.
Paul said he’d installed an Accu-Volume on his Miller sprayer (and loves it) but saw no need for it on the Deere. He said the float in the tank quickly and accurately responds to the level in the tank. At that point the sprayer registered as “full”, the sprayer pump automatically shut off and the valve closed. You could hear it happen. But the DASH was still pushing and would quickly stretch and damage the hose, and even cause leaks.
That sound was Paul’s cue to quickly shut off the DASH pump. Then he closed the Banjo quarter turn valves on either side of the connection and disconnected the feed. He said he never pushes UAN through this system. Ag retailers don’t use flow meters with UAN because they can be inaccurate – instead they use weigh scales. However, it was too hard to navigate an oversized tender truck onto a scale, so UAN got loaded directly.
At 8:32 we were filled and ready to go. That was 14 minutes from the time Paul started untethering to when he started backing the sprayer off the tender truck. And it would have been a lot faster if he hadn’t taken time to explain it to me.
8:35 am – Job 1
At the edge of the first corn field, Paul unfolded the boom and set up the monitor. We would be applying 20 gpa at 60 psi and travelling about 12 mph. When spraying corn, Paul tends to travel between 10 and 14 mph. He double checked that the pneumatics he’d switched on earlier had lifted the sprayer high enough to clear the corn.
One of the chemical companies had given him a set of Low-Drift Air 11005 flat fans (PSLDAQ1005) to try, and this was his first time using them. We immediately saw that they were not all pointing in the same direction (or even alternating). They were just on willy-nilly. We figured it wouldn’t matter since we were only just clearing the tassels, but it tweaked both of our latent OCD personalities and we decided to fix them next chance we got.
Nozzles tilting at windmills – just not all in the same direction.
We finished at 8:59 am and found we’d covered 51 of the estimated 55 acres, due in part to a few missed strips and rounded-off corners. Why did we miss them? Read on.
Fungicides versus herbicides and fertilizers
I’d tagged along during fertilizer and herbicide applications, so I began to notice that overhead fungicides in corn seemed to follow different rules. Here are some observations I made throughout the day:
1. It’s not ideal to have to stretch a tank of herbicide, but you can if it’s not too dilute. And you can always go top up if you really must. However, for fungicides, you absolutely do not want to run short because that means increased trample. You can stretch the tank a little, but if it means running over corn, then leaving a few “test strips” and unsprayed corners is the profitable choice. Quote from Paul: “The most important part of fungicide in corn? Don’t run over the corn.”
2. Paul felt sectional control was more than enough resolution for fungicide applications in small/medium sized fields. The uniformity and product-savings associated with nozzle-level resolution (e.g. PWM with turn compensation) pays with herbicides and expensive fertilizer, but not fungicide.
3. A low and steady boom is ideal, but not critical for corn fungicides. Increased drift potential and a loss of coverage uniformity are still bad practice, but rather than slow down and drop the boom, we leaned into maintaining our speed and raised the boom ends until they were clear of the tassels. Even then, the centre rack was still deep in the canopy. C’est la vie.
9:00 am – Job 2
Job two was the for the same customer, so all we had to do was cross the street to a 60 acre soybean field waiting for an application of Delaro Complete. This time we were full in seven minutes (because I didn’t ask silly questions) and we were starting to run short of water. We called for more.
I haven’t mentioned it, but the Deere was equipped with Precision Planting’s ReClaim recirculating booms. He was actually one of the prototype testers, having installed it on his old Patriot a few years back and his Miller as well. I’ll discuss the system in more detail later on. So, at 9:10 am we started recirculating the boom to dilute the residual Veltyma DMX and prime the Delaro Complete. Veltyma DMX has some “greening effect” on soybean, so while a full dose wouldn’t hurt anything, it would leave a conspicuous green triangle at the edge of the field that no one wants to see.
We drove the perimeter manually. The ruts left from such a wet year kept tugging the sprayer, so Paul steered with a light touch, correcting when the wheels pulled. Once we got to the interior, we were applying 20 gpa at 13 mph. Paul relied more on autosteer (although he still fought the ruts a bit) and took the opportunity to text customers and get in touch with staff. Just as when he’s focused while loading, never taking a call, he doesn’t take them when spraying field boundaries. At 9:39 we were empty and done.
Acquiring and scheduling customers
I asked how AU found and scheduled customers. Paul said that roughly 40% of their business came from contracts with ag retailers and the remainder was direct. AU works with a few ag retailers, and they don’t all operate the same way. Here’s how it was explained to me.
Ag retailer 1 acquires a customer and sells them any number of agronomic services, including crop inputs. Then they use their own sprayer, or subcontract someone like AU to spray those crop inputs. AU has the option to decline a job (perhaps it’s too small, too distant, or generally undesirable), but they can’t do that too often. If they accept, they pick up the chemistry and apply it within 24 hours to avoid long-term storage.
Ag retailer 2 has a different arrangement. In this case Paul refers to a project management app called “Monday.com” which allows him to review and select open jobs. Once again, they pick up the chemistry and apply it within 24 hours.
AU also takes on customers directly. Weather events and breakdowns are problems for farmers but represent opportunities for contractors. AU is often hired by large farming operations (e.g. >1,000 ac) when they can’t keep up, and this is far better than chasing 10-15 ac fields.
Juggling all these customers can be challenging. In the winter, the core, repeat customers are penciled into the schedule. However, in the chaos of fungicide season, the ag retail customers get priority because of contractual obligations. And, of course, AU is always open to opportunities and slots in new jobs as best they can. They take advantage of social media while operating because Paul believes it’s important to stay involved in the community, but also because it’s a means of free advertising. People see when they’re in the area and it’s resulted in lots of jobs.
Duck hunting
I debated including this in an already epic article, but it was too interesting to leave on the cutting room floor. Paul also described a long-standing niche job working as a land manager for a few private “duck-farm” operations. Nearby Mitchel’s Bay is some of the best duck hunting in the world because of strategically placed duck-farms next to marshes or lakes. They grow corn to attract the ducks, then mow parts down to make pathways for boats, and then flood the fields using dikes and pumps.
These clubs aren’t necessarily big revenue generators. They’re perks for businesses to offer employees, or locales for casual business meetings, or maybe just status symbols for the wealthy elite. Given that they spend a lot of the year flooded, the ground is tough to spray because it’s always soft. Sprayers can’t go in full, and that tends towards premium fees for crop management.
Paul sprays for a few of these operations because he finds the whole practice fascinating. And, as a duck hunter himself, he’s permitted access to places most never see. There’s no such thing as free corn, Daffy.
9:43 am – Water fill
The water truck arrived and six minutes later we were topped up. Then it left to go support the Miller about 30 minutes away, promising to come back to us right after. Paul appreciated not having to go back to the yard for water – how can you ever be satisfied with coach after you’ve flown first class? We headed off to the next job.

Paul made this look easy.
9:51 am – Job 3
This 50 acre soybean field abutted a tomato field, and after seeing this sort of thing all season I wondered aloud if buffer zones were just a white lie that we tell ourselves. Paul chuckled and said there’s generally no stress when spraying fungicide this close to a sensitive crop, but herbicide would be tense. He changed fields on the monitor, verified that he was applying the right amount and started spraying. He noted there was a soft area in the field where the owner replanted soybeans. We avoided it.
This was one of the direct customers and not an ag retail client. The customer was a tradesman that left the crop protection choices to Paul. Custom operators can have a lot of influence on their client’s product choices because they spray so many acres with so many chemistries. In order to better guide his clients, Paul makes an effort to get involved in product testing and performance trials. But, as a sprayer operator, he’s not only interested in efficacy and price, but also ease-of-use.
Running a product comparison trial
For example, powdered manganese plugs a sprayer horribly while liquid formulations are far more forgiving. Another example, perhaps one product is 1 L/ac while another is 2 L/ac. Handling less is always easier. Or perhaps all this is trumped when a customer is swayed by loyalty points, which are issued by some registrants to reward a customer for using their suite of products.
We were done at 10:11 and found we’d covered 47.5 of the 50 acres because we skipped that wet, replanted area. That left about five acres worth of spray mix in the tank that we’d have to consider on the next job.
Recirculating booms
Paul secured the sprayer to the trailer, and we hit the road. While we drove, he talked about why he felt a recirculation system was necessary. Beyond the savings in chemistry and water, he said it was tricky charging the boom on some of the farms in the county. Severed lots meant more homes and private gardens, and that limits where it’s safe to prime.
Precision Planting released their aftermarket ReClaim recirculating boom a few years ago. We’ve written about it. Basically, it relies on dropping the pressure below the ~10 psi required to open the check valves in the nozzle bodies. So, no shut-off valves required. However, some Deere pumps won’t operate under 20 psi, which requires a work-around. Despite having that fix in place, we still saw nozzles dribbling while we were recirculating. Obviously not ideal, but Paul said it cost about a seventh of what the factory option would have cost, so he could live with it.
But there are other points to consider. For example, the sprayer doesn’t know the feature is there. So, when recirculation is engaged the sprayer “thinks” it’s spraying, and as liquid passes the flowmeter, the display shows the volume dropping… but it isn’t. As a result, the operator must know how much liquid circulated and manually adjust the volume prior to spraying.
And this system isn’t plumbed to flush the lines from the clean water tank. And it increases the length of hose that needs to be rinsed. And while you can recirculate glyphosate and UAN, many operators won’t do it with sticky products like atrazine or dicamba, preferring to just prime normally and keep them out of the recirculation lines.
While Paul and I were discussing all of this, and you can’t make this stuff up, the second operator called to say they broke an elbow on their recirculation line. To their credit, Precision was out there like a shot and had it mended in an hour (amazing service). But the delay meant we had to redistribute some of the remaining jobs. It was decided that Paul would take on some extra work and then both operators would meet up at the end of the day and split the last job.
10:50 am – Job 4
We parked, dismounted from the trailer, loaded and taxied to the headland. Paul said it was another 50 acres of corn, but I saw something was different. He treaded out the tires to a 138″ spacing to align with what I was told was a 23” corn spacing. Until now, we were on a typical 30” planting architecture. I soon learned that I didn’t like 23” corn. Tracking between such tight rows without trampling everything was a nightmare.
Here are two videos. We’re driving 30″ corn in the first and 23″ in the second.

I asked if Paul had tried row feelers, but he said they didn’t work on such tight spacing. In any case they got in the way when he used his float trailer. So, I watched as Paul studied the row ahead and referred to the feed from the cameras, micro-adjusting the steering for the entire 47.8 acre field as he fought to stay between the rows. It felt like forever, but we were done at 11:24 and back on the road for tendering a few minutes later.
11:38 am – Job 5
As we drove alongside this 45 ac field to get to the entry, we saw rows of sweet corn planted on the perimeter (surprise). Paul said there was a variety trial planted in the centre of the field somewhere as well and that we weren’t supposed to spray it. And it was another 23” row spacing.
Once again, we found it hard to stay on course. Just for added fun we got pulled by the planter draft and the occasional guess row. We finished at 12:10 pm and planned to meet the water truck. As we left, Paul reset the treads to 120” from 138”. Never good to forget that bit – again, ask Paul how he knows.
1:07 pm – Job 6
After a short and uneventful drive to the next client, we parked, loaded, and unfolded at the headland of a 45 ac cornfield. As we sprayed, Paul was on the lookout for a bridge that would give us access to another, smaller field. It turned out to be a substantial land bridge, which disappointed Paul because he was hoping to take me over a rickety little wooden bridge. The buddy seat was rough enough without testing its absorptive qualities as well, so I was good with it.
There were plenty of obstacles in this field. Paul was well acquainted with “the tree”. They’d had dealings in the past. I asked about wind turbines, which were all over the county, and I was surprised that he liked them. All turbines in the area have associated hard-packed lanes leading through the field. Paul took advantage by parking on them and filling there if needed. Plus, he watched them to monitor wind speed and inversion situations.
Still on the subject of obstacles, we found a field of peppers hidden in the corn. We left the test strip there. As we made these on the fly decisions, Paul wondered how an autonomous sprayer would handle all these little surprises. A good question.
I was finding the rows a little hypnotic and said so. Paul said corn was hard to spray day after day. In windy conditions, the tassels sway and it can make an operator dizzy. Some operators slow down to 10 mph or use row feelers to stay on track. We finished at 1:37 and when we got back to the trailer, two new jobs came in over the phone. Paul decided that his other operator could absorb those. We got ready for what might be our last job – rain was forecast
1:58 pm – Job 7
Full again, this 74 acre corn field would also get a test strip. Paul reiterated that it’s better to trample a field once, and not go in and out to get more spray mix. So, we filled for 70 acres spraying at 17 gal/ac and 9.6 mph to empty a single tankful as accurately as we could.
I watched as the pollen and anthers broke in waves over the hood and onto the steps. The radiator fan periodically reversed to blow it all out, but not as frequently as we needed. Paul occasionally did it manually. The sound of corn scraping and hitting the sprayer was loud. Paul said corn can beat the paint off a sprayer and damage the side induction bowl – wow. Carbon filtered cab or not, my pollen allergy was driving me crazy, and I was glad this was our last job. We were done at 2:37 and back on trailer five minutes later.

3:30 pm – Back at the yard
As we pulled into the yard it looked like rain was indeed coming. We weren’t worried about the fungicides we’d applied because they were rainfast in an hour. But it did put a premature end to the spray day. We’d covered more than 365 acres in the Deere, which was a light fungicide day for Paul. Combined with what the Miller did, AU covered 735 acres.
As I was packing to leave Paul asked if I was interested in seeing his new battery-powered backpack sprayer. I was, but I didn’t realize he’d put me to work spot spraying weeds. So, I suppose we actually covered 736 acres that day: 735 in sprayers, and one manual. Worth it.
September 9, 2024

Determining Airblast Travel Speed – The “Air Displacements” Method

The concept of Air Displacements was developed by Dr. David Manktelow, Applied Research and Technologies Ltd.

What is the “right” speed to drive when spraying?

Airblast sprayer operators must know their average travel speed to calculate how much pesticide and time is required to complete a spray job. Note that it’s an average, not a constant, because travel speed is significantly affected by ground surface conditions (e.g. slippage), grade (e.g. hills) and the weight of the rig (e.g. as spray mix is depleted).

The pursuit of productivity and the unchallenged status quo of traditional spray volumes, blinds many operators to the fact that travel speed is a critical factor in focusing air energy on the target canopy. As long as droplets are small enough to be entrained and directed by the air, we believe that optimizing the fit between air energy and the target canopy leads to the most frugal and effective use of spray mix and should therefore dictate travel speed. If that speed proves to be painfully slow, or terrifyingly fast, then a mismatch is revealed between the sprayer design and the operational conditions and the overall spraying strategy should be reconsidered.

This article describes a method for modelling an ideal travel speed. It can be used as a sanity check for existing operations or for those seeking to evaluate the fit of a new airblast sprayer. However, this method can only approximate travel speed. A true optimization of sprayer settings will require fine tuning using the ribbon method and, ultimately, coverage feedback from water sensitive paper (see here and an older article here). We’ll begin with how to measure average travel speed.

How to measure average travel speed

Beware the tractor speedometer or rate controller that monitors wheel rotations; both can be fooled by changes in wheel size, tire wear or slippage. GPS or radar-based speed sensors are the most accurate method.

Those that prefer a manual method can follow this classic protocol for determining average travel speed:

Go to a row that is representative of the terrain in your planting. Measure out a distance of 50 m (150 ft) and mark the start and finish positions with wire marker flags.
Fill the sprayer tank half full of water.
Select the gear and engine speed in which you intend to spray. If using a pull-behind sprayer, ensure the PTO is running or you could introduce errors.
Bring the sprayer up to speed for a running start and begin timing as the front wheel passes the first flag. This is far easier when there are two people.
Stop the timer as the front wheel passes the second flag.
Stay out of any ruts and run the course two more times.
Determine the average drive time for the three runs (i.e. the sum of all three times in seconds divided by three).
Finally, calculate travel speed using one of the following formulae, depending on preferred units:

Ground Speed (km/h) = Average drive time for 50 m (s) ÷ 13.9 (a constant)

Those that prefer a less accurate but convenient hack can download any smartphone speedometer app that can calculate an average (similar to a runner’s GPS wristwatch). Fill the sprayer tank half full and drive a representative section of your operation with the fan on and the spray off. Consult the phone for your average speed for each pass. Take a screen shot and email it to yourself as a time-stamped component of your spray records.

The “Air Displacements” method

Dwell time

Airblast sprayers use fans to move a volume of air at a certain speed, often measured in m³/hr or ft³/min. Imagine that volume of air as a three dimensional shape extending from the air outlet over a distance. Likewise, imagine the void between the sprayer outlet and the target canopy as a three dimensional shape penetrating roughly halfway into that canopy (assuming we intend to spray every row).

How long must the sprayer dwell in one spot before it pushes all the intervening air out of the way and replaces it with spray-laden air? If the sprayer drives too slowly, it will wastefully push spray through and beyond the target (i.e. blow-through). If the sprayer moves too quickly, the spray will not have an opportunity to penetrate the target canopy and most certainly not reach the highest point. This concept of focusing air energy using travel speed is called Dwell Time.

We want to calculate the volume of air the sprayer generates, compare that to the volume we want displaced, and then determine how fast we must drive to optimize the fit. We can do all this with a tape measure, an anemometer, and a partner to record the data and do a little math.

1. Measure air outlet area

With the sprayer safely off, measure the area of the air outlet(s) on one side of the sprayer. We’ll use a Turbomist 30P Low Drift Tower (below) as an example. There are two air outlets that are 5 cm wide by 150 cm high for a total area of 0.075 m² on each side. Be sure to look inside the outlet for any irregularities like baffles or obstructions intended to block air. Subtract those areas from the total. Don’t worry about small things like nozzle bodies.

For rectilinear outlets: Height (m) x width (m) = Area (m²)

For circular outlets: 3.14 x radius² (m) = Area (m²)

The air outlet on this Turbomist 30P Low Drift tower sprayer is 5 cm wide by 150 cm tall for a total area of 0.075 m².

2. Measure air speed

First, a few safety warnings: High speed air is loud and can carry debris, so always wear ear and eye protection and respect the hazards inherent to working with air-assist sprayers. Only use an anemometer rated for at least 160 km/h (100 mph) (e.g. here). Do not use a handheld weather meter such as a Kestrel because the impellor could be destroyed and become dangerous shrapnel.

Use an anemometer rated for at least 160 km/h (100 mph) (e.g. here). Do not use a handheld weather meter such as a Kestrel because the impellor could be destroyed and become dangerous shrapnel.

Bring the fan up to speed and holding the meter about 25 cm (10 in.) from the outlet, measure the air speed at several locations along the air outlet both vertically and horizontally. We calculate an average speed because many air outlets do not produce uniform air speed or volume along their outlets. For this example, we measured four locations along the air outlet on both sides of the sprayer and saw significant differences. We did this both in low and high gear (see table below).

	High Gear	High Gear	Low Gear	Low Gear
*Location Along Outlet*	*Left Side (m/s)*	*Right Side (m/s)*	*Left Side (m/s)*	*Right Side (m/s)*
Top 1/4	41.1	80.3	42.9	24.6
Upper	34.9	32.2	26.4	30.8
Lower	30.8	30.0	24.0	26.4
Bottom 1/4	33.5	40.2	26.8	31.3
Average	35.1	45.7	30.0	28.3

Anemometer readings from the low drift tower sprayer outlets, on left and right side, in high and low fan gear. Four readings from bottom to top to determine the average. Readings taken 25 cm from edge of outlet and PTO set to 540 rpm.

Multiple air outlets

Before we continue with the method, let’s change sprayers to this Turbomist 30P Grape Tower (below). The design is intended to spray adjacent rows from the vertical outlets (5 cm x 150 cm = 0.075 m²) along the tower. The upper, inverted outlets (10 cm x 63.5 cm = 0.0635m²) throw spray over the adjacent rows and cover the outside rows. The intention is to improve productivity by covering four rows of grape (or possibly three) per pass.

The Turbomist 30P Grape Tower Sprayer is a multirow system intended to drive every third or fourth row.

Lower, vertical ducts are 5 cm x 150 cm = 0.075 m²

Upper, inverted ducts are 10 cm x 63.5 cm = 0.0635m²

However, when we consider this design through the Air Displacement lens, it’s almost like having two sprayers performing two jobs simultaneously. The vertical outlets and the upper, inverted outlets are different shapes. Further, their position (distance and angle, as the top outlets are angled back more aggressively) relative to their respective target canopies are significantly different. How fast must this sprayer drive to optimize the fit? Do we have to compromise coverage and incur drift and waste from one set of outlets to accommodate the other set? The manufacturer has worked to address this potential issue by partitioning the majority of the air energy to the top outlets, but let’s see how that affects travel speed.

3. Total volumetric flow

Having already measured the outlet area, we then measured average air speed (see table below).

	High Gear	High Gear	Low Gear	Low Gear
*Location Along Outlet*	*Left Side (m/s)*	*Right Side (m/s)*	*Left Side (m/s)*	*Right Side (m/s)*
Top Outlet	27.0	26.5	27.0	26.0
Bottom Outlet	12.0	13.0	10.5	12.5

Average anemometer readings (n=4) for top and bottom outlets, on left and right side, in high and low fan gear. Readings taken 25 cm from edge of outlet and PTO set to 540 rpm.

Now we can use these two values to determine how much air the sprayer generates by calculating total volumetric flow. We first have to convert air speed from m/s to m/h to make the units work, so just multiply it by 3,600. Then we multiply that by the outlet area and we get the table below.

Average air speed (m/s) x 3,600 (a constant) = Average air speed (m/h)

Average air speed (m/h) x Outlet area (m²) = Total volumetric flow (m³/h)

	High Gear	High Gear	Low Gear	Low Gear
*Location Along Outlet*	*Left Side (m³/h)*	*Right Side (m³/h)*	*Left Side (m³/h)*	*Right Side (m³/h)*
Top Outlet	6,172.0	6,058.0	6,172.0	5,944.0
Bottom Outlet	3,240.0	3,510.0	2,835.0	3,375.0

Total volumetric flow for top and bottom outlets, on left and right side, in high and low fan gear, with PTO at 540 rpm.

4. Target volume to displace

Now that we know the volume of air the sprayer generates, let’s determine the volume of air we need to replace with that spray laden air. This is really the only tricky bit because you have to picture a cross section and then measure the shape. See the illustration below.

For the bottom outlet, it’s simple. The outlet is 81 cm from the grape panel and the grape panel is 112 cm high. We calculate the area of a rectangle by multiplying length by width, so:

Length (cm) x Width (cm) = Area (cm²)

However, the sprayer design makes the top outlet’s job trickier to figure out. This isn’t a rectangle, it’s a “quadrilateral”. We get this odd shape when either the sprayer outlet or the target canopy are significantly taller than the other. Fortunately this one has a right angle so we don’t have to brush off our high school trigonometry textbooks. Instead, we can lean on the internet using this link and plug in the values. As we can see below, the cross sectional areas spanning from the outlets and the middle of the target canopies are 0.9 m² for the bottom outlet, and 2.35 m² for the upper outlets.

This gives us a cross sectional area, but we need to convert that to a volume so we can compare the air generated to the air needed. To do that, we multiply the cross sectional area by 100 m, representing how much air would be needed over 100 m of row length. The formula and the results are presented below.

Cross sectional area (m²) x 100 m of row length = Target displacement volume (m³)

*Outlet*	*Target Displacement Volume (m³)*
Top Outlet	235.0
Bottom Outlet	90.0

Target displacement volume for each outlet over 100 m of canopy row.

5. Displacement rate

We see the target displacement volumes for each outlet are significantly different. Assuming the air from the upper outlet maintains its integrity and reaches its target canopy without being blown off course, it must produce enough air energy to fill more than twice the displacement volume of the lower outlet. We can see from the earlier calculations that it does produce almost twice the total volumetric flow. But is it enough? To know we must calculate the Displacement Rate for each outlet. Let’s just focus on the left side of the sprayer in high gear.

Total volumetric flow (m³/h) ÷ Target Volume (m³) = Displacement Rate ( displacements/h)

*Outlet*	*Displacement Rate (displacements/h) for left side of sprayer* *in high gear*
Top Outlet	26.25
Bottom Outlet	36.0

Displacement rates for the outlets on the left side of the sprayer in high gear.

So we see that the outlets at the top of the sprayer, if stationary, could displace the target volume of air 26.25 times an hour. However, the lower outlet would displace its target volume 36 times in that same hour. We see that we might have a problem. But this is for a stationary sprayer and not a sprayer in motion. The last step gives us what we came here for.

6. Ideal travel speed

We can now determine the ideal travel speed for this sprayer using that same 100 m row length.

[Displacement rate (displacements/h) x 100 m of row length] ÷ 1,000 (a constant) = Ideal travel speed (km/h)

*Outlet*	*Ideal travel speed (km/h) based on left side of sprayer*
Top Outlet	2.6
Bottom Outlet	3.6

Ideal travel speed for each outlet on the left side of the sprayer in high gear.

As we stated at the beginning of this article, this is only a model. It doesn’t account for canopy density and assumes the spray laden volume of air produced by the sprayer can reach the target intact over a given distance. However it does indicate that there is a potential issue that will lead to either over spraying the adjacent row (slower travel speed) or under spraying the distant rows (faster travel speed) which could lead to waste, drift and poor coverage.

In the image below, we chose to drive close to 2.6 km/h in high gear. No effort was made to adjust the liquid flow (i.e. change the nozzles) so there was too much spray volume here, but we can see the losses on the left (upwind) side, and the blow-through three rows over on the right (downwind) side. Leaving aside the excessive liquid volume, we could drive faster or reduce the fan gear to reduce the blow-through on the adjacent rows, but we may go too fast (or reduce the rate of air displacement) for the upper outlets to reach the target. We can already see the integrity of the upper-left outlet breaking down as it sprays into the wind.

Testing a travel speed. No effort was made to adjust liquid flow, which is excessive here. Cross wind was from the left to the right in the image. Photo by Corey Parker (Instagram: _parkerproductions)

Take home

An ideal travel speed for an airblast sprayer is more than just being productive. The spray must reach and penetrate the target. If this requires dangerously high speeds, or if you simply can’t move slowly enough, it suggests a problem with the spraying strategy. Changes will have to be made to the sprayer, the target canopy, or even the weather conditions you’re willing to spray in. Getting the job done quickly should not compromise the quality of the job. Use this method to re-evaluate your practices, or to assess the capabilities of candidate sprayers if you’re considering a new purchase. Be sure to confirm what this model is telling you using some coverage indicator, such as water sensitive paper.

Happy spraying.

August 20, 2024

Pre Emerge Spraying with a Custom Applicator: Drive-Along Diaries #3
It was May 16th, and I was standing at the front counter of Clean Field Services (CFS) in Drayton, Ontario, looking forward to an interesting day in the buddy seat. While I was waiting on the sprayer operator to check and fill the sprayer, I asked Todd Frey, Customer Service Rep, to give me some background into the company.
Clean Field Services
Todd’s father, Dennis, started spraying for a neighbour in the 1990s using a truck-mounted skid sprayer. In 2003 he began offering custom application services from their Drayton location, and in 2009 incorporated as CFS. Primarily offering contract application services to small fields (<20 acres), they also offered scouting and agronomy services, sold seed, and created nutrient management plans.
A big part of the business is liquid fertilizer. Many local retailers are set up to apply dry fertilizers, but here they pre-blend liquid fertilizer and can fill a sprayer in three minutes thanks to their new John Blue, 20 hp pump with it’s 4” inlet. More on tendering, later.
Scheduling
Todd explained that today would be all about pre-plant herbicides in soybean and corn. The farmer tills, then CFS sprays, then the farmer tills again to incorporate the herbicide before planting.
Much of the scheduling is arranged over the previous winter, but plans had to be flexible to accommodate changeable weather. Case in point, there were originally six jobs scheduled for today, but two were added at 6 am when clients called to ask for last-minute service. The wet spring was keeping farmers off their fields, so planting pressure was mounting, and sprayer scheduling had been particularly tough. Todd tells people “We’re not 911 dispatch!”, but ultimately does his best to accommodate the short notice.
That’s when Brendan Bishop came in to collect me. This was Brendan’s second year as an operator having started in 2023 as a tender truck driver and “graduating” mid-season to spraying. As I followed him out, I wondered how he’d stack up compared to the older, more experienced operators I’d worked with. Spoiler: Brendan had skills.
The Sprayers
CFS owns a John Deere 410R and a 4038. They also have an operator on retainer who owns his own 4030. CFS used Rogator in the past and Apache before that. The Rogators featured a lot of flow capacity, making them great for spraying 28%. CFS switched to Deere for the service and to take advantage of a few technologies I’ll describe shortly, and now they can stream liquid fertilizer at rates as high as 46 gpa at 14 mph.
Today, we’d be in the 410R, which featured pulse width modulation (PWM) and boom recirculation. I was told that customers appreciated the optics of not wasting up to 40 gallons on priming. But the sprayer also featured direct injection from four, 50 gallon tanks, and that puzzled me. Why would a sprayer have two seemingly incompatible features? No one would inject product just prior to the manifold and then circulate it right back to contaminate the tank.
Brendan agreed that they were mutually exclusive, but both had roles in minimizing waste and downtime from priming, rinsing, and custom spray mixes. For example, an early pass over corn might have Marksman and Armezon PRO in the tank, and then Roundup could be direct injected at rates specific to the weed pressure. On the other hand, if he didn’t need direct inject for custom mixes, he could utilize recirculation to avoid priming.
The sprayer automatically disengaged recirculation when direct injection was operating. That restriction could be over-ridden, but you couldn’t run them both by accident. Nevertheless, his policy was to always take a breath before engaging either system because a mistake might be irreversible and require a purge and refill.
8:30
We left the yard and cruised down country roads at 40 mph until we hit the more populated regions. This part of Ontario had a lot of Mennonite residents, and their horse-drawn carriages required a wide berth. That got particularly tricky on narrow roads and single-lane bridges, but Brendan was patient and obviously practiced.
We arrived at our first field at 8:50. We parked at the edge and started unfolding the boom as Brendan called dispatch on the cab radio. The field was 15 acres of Roundup ready corn, and we’d be spraying a pre emerge herbicide in 28% UAN at a rate of 20 gpa. We knew all this before we ever left the yard thanks to CFS’s operations management system.
The AgLogic Operations Management System electronically assigns work orders (e.g. chemistry, field location, field boundaries) to the equipment, allowing dispatch to track, schedule and route their assets. It also pushes weather information and any special notes to the operator. The AgLogic tablet and the John Deere monitor are supposed to be compatible with one another, and it was generally slick, but there were a few glitches.
AgLogic and the Job Centre monitors showing how the boundaries were different for the same field. The operator has to make a commonsense call.
Dennis was on dispatch, and Brendan asked if he should send for Simon, their tender truck operator. He was going to need water for the next job and had planned this job to end as empty as possible. Dennis agreed to send him as Brendan noticed aloud how rough the ground was – this field had only just been plowed. Dennis said they’d had to wait for the farmer to plow and warned Brendan of a particularly bad patch that he was familiar with. Brendan signed off and smiled as he warned me to hold on tight. Then he hit start on the AgLogic work order, and we were off.
He wasn’t joking – this ride would have qualified as a theme park roller coaster. I’m sure I left hand and face prints all over his windshield. He had to turn off boom track and go manual and had to cut a second headland. It was hard to hold the rate steady because our 4 mph speed dropped the PWM to the minimum 25 PSI and the duty cycle was maxed out.
Eventually we got up to a roaring 7.7 mph and by 9:25 we were done with less than two gallons left in the tank. While I searched for my kidneys, Brendan entered the summary into AgLogic: 19.65 gpa. He added a few choice comments to the file and in less than a minute he was done. CFS now had the information for billing with no hardcover book for the operator to mess up and no bad penmanship to decipher. As I said, slick. Have a look at a field ticket, here.
9:30
We waited in the client’s yards for Simon. Brendan said he’d fill wherever he needed to; on the shoulder of the road or slinging the hose across a ditch into the field. But a client’s yard was always safer and therefore preferred. It was worth waiting.
According to the work order, the next job was 15 acres of Roundup burndown at 12.5 gpa, so Brendan was doing the math on how much water he’d need (plus one acre’s worth for buffer). Simon showed up at 9:42 and we were loaded by 9:45. Just before we hit the road Brendan called dispatch to ask where to send Simon next. Efficiency takes planning.
9:54
We parked at the field entry and Brendan engaged the recirculation to push the remaining UAN and pre-emerge in the lines back to the tank to dilute them. Then he turned it off, engaged the direct injection of Roundup, and started priming the boom. This sprayer featured Auto Boom Prime: The operator set a target displacement volume (in this case, 40 gallons) and when the flow meter reached that value, you were primed.
As we waited Brendan explained that we weren’t doing anything today that couldn’t handle a little Roundup, so even if it somehow did circulate back to the tank, it was no big deal. He started the work order log at 10:02 checked for any warnings associated with the field before we were off again.
This was a narrow field. So narrow that we would likely overlap in the middle just from spraying the boundary. Brendan drove that first side manually, cleaning up the corners and margins while skillfully dodging fenceposts as best he could. Nevertheless, we tested the breakaway section a few times. He was nonplussed and said that any operator claiming they’ve never nicked a tree or a fencepost is either too far away or lying.
I asked why he didn’t use fencerow nozzles with Roundup and he gave two good reasons: 1. If you succeed in burning out all the grasses, broadleaf weeds like burdock move in and cause new problems. 2. Overspray was too risky when the target field abuts another crop.
Regarding his second point, I saw what he meant as we turned to spray the rest of the boundary, right next to winter wheat. On the back of the joystick are the secondary controls, which Brendan used to nudge the boom a few inches left or right along A-B line, constantly adjusting for the wheat.
At 10:17 he closed the work order, which digitally winged its way back to CFS for accounting. We folded up and followed behind as we headed back to the yard for a refill. Going back made more sense than tendering since the yard was en route to the next job.
Tendering
CFS fills their 20,000 gallon holding tanks from their own well, which is 300 feet deep and rated at 4,000 gallons per hour. Instead of installing more holding tanks, they doubled the floats to half the refill time. In addition, they have a tractor-with-wagon tender system with a 4,000 gallon capacity (and four serial induction bowls). Their transport truck is strictly for carrier and has two, 4,000 gallon tanks. In total, they can have 32,000 gallons of water on hand.
They recently improved their transfer pumps to keep up with so many small acreage jobs. It used to take up to 25 minutes to fill a 4,000 gallon trailer. Now they can pump up to 480 gpm through 4” lines and fill that same trailer in less than 10 minutes. And they have two such fill systems so no one has to wait their turn.
Their efficiencies are now found in the logistics of planning jobs that avoid rinses and minimize sprayer travel time where possible. The company isn’t afraid of road miles, preferring to drive further between jobs to avoid having to clean out the sprayer. Floating the sprayer to save engine hours didn’t made economic sense for them since you needed a wide-load permit, time to un/load the sprayer and you couldn’t transport at night.

It wasn’t “Gone in 60 Seconds” but we weren’t there much longer than that.
10:57
The next job was an L-shaped field. Brendan noted that weird field shapes were par for the course. As we drove, he said that some fields were so tight that he had to fold the booms almost completely to fit while spraying. He said he’d sprayed fields that no 120’ boom had any business being in. He’d had sideview mirrors pushed against the cab and was happy the Deere plumbing wasn’t on the outside of the folded booms, because he’d been snagged by branches in other sprayers.
Speaking of the boom, he was using LDM 08 nozzles, and the height was set to 30”. He would have liked a lower boom, but it wasn’t realistic on these rough and rolling fields. This field was short and sweet, and we were soon headed out.
11:10
This field was 19 acres and once again I saw it was narrow, meaning a lot of manual spraying on the boundary and very little autosteer in the middle. Brendan scanned back and forth between the boom end, the monitor, and ahead of the sprayer as we drove along at 7.5 mph.

When I mentioned the lack of autosteer he said he didn’t get to use it as often as I might think. Many of the corn fields he sprayed were planted by farmers with no GPS, so while he did use the A-B lines, they were mainly to alert him to turns. The actual steering was manual as he followed the planting lines.
I should mention that Brendan established a new boundary for every field, even through AgLogic provided one. He elected to establish this new boundary because once he sprayed the perimeter the monitor could tell him exactly how much area was left to spray. So, he would spray the boundary, check the area remining, and use his cell phone to calculate the differential between the volume in the sprayer and the target rate. He did this now to ensure he had enough water for the last four acres. He wanted to end empty because he would be switching back to 28% UAN next. Based on his math, he pushed the rate to 20.5 gpa to use up the water.
These rate changes would be difficult (perhaps impossible) to achieve without PWM because it would be based on pressure changes, and not duty cycle. It might even require switching nozzles. This is also when direct inject shines as it could maintain the Roundup rate independent of the carrier rate. Brendan said that fields were somehow always bigger than expected, so he was a big fan of the flexibility these features afforded him.
11:28
Now we’re back in the yard to fill with 28% UAN. Brendan was planning on a six acre corn field in the Township of Southgate, which was about a 45 minute drive, so we had to fill precisely.
We arrived at 12:27 and had to ask the client where the field was on the property. Surprise! The client wanted us to do eight acres, or 25% more than we’d anticipated. There was no way we could stretch the load that far, so Brendan told him we’d drive all eight at a reduced rate and make up the remaining nitrogen later when he came back with drops. We adjusted the rate from 28.75 gpa UAN to 22.6 gpa and at 12:46 we were done spraying, and the job submitted.
12:51
Simon is back with water and Integrity for our next job in pre-emerge corn, which is why Brendan wanted to be empty of 28% UAN. By 1:02 we were full and headed to a 32 acre job spread over two fields. Brendan chose to do the smaller, four acre field first so if he had to make any rate changes in the second field, he could spread a smaller difference over more area. Clever.
But where was this little field? Turned out, it required us to drive through a swamp, flushing two ducks and a deer in the process. As if that wasn’t bad enough, we both started to laugh when we saw the field. The ground must have been plowed 10 minutes before we arrived because it looked like an earthquake had hit it.

There’s a good reason you don’t spray freshly plowed fields. Once again, I did my pinball impression and idly wondered if Deere didn’t install seat belts in the buddy seat because they were trying to dissuade people from using it. Even Brendan bounced around despite the air ride driver’s seat.
We were relieved that the larger of the two fields was a breeze. Brendan did his math trick and elected to nudge the 16.1 gpa up to 16.7 in order to end empty. By 1:45 we were off for our last tender of the day.
1:50
The last three jobs totaled 70 acres and required a single fill. We were moving into Roundup-ready soybean, so we’d be spraying Roundup Transorb HC (glyphosate) + Tavium (S-metolachlor and dicamba). Brendan said they’d clean the sprayer thoroughly afterwards if they had to, but it was preferable to schedule a series of corn fields for tomorrow because they wouldn’t be bothered by dicamba residue.
We met the tender wagon and Brendan and Simon started loading Tavium into the inductor bowls for transfer to the sprayer. Then Brendan hosed down each bowl to rinse them and transfer that rinsate into the sprayer as well. Afterwards Brendan used the inductor bowl on the side of the sprayer to rinse the jugs because he felt the water pressure was higher on the sprayer and did a better job of cleaning them out.
2:35
This was a 11.75 acre field, and it should have been simple… but it seemed nothing was. The work order map showed the digital boundary, but the actual plowed field was much larger. So, it was one continuous field and we were supposed to spray only part of it. Where exactly was the boundary?
Eventually Brendan spotted some unsprayed grass that hinted at where other equipment had driven in the past. That subtle visual cue would have been impossible for an operator to see in the dark.
As we positioned ourselves to start spraying we saw the note on the work order to “mind the garden”. Garden? What garden!?
Eventually “Eagle-eye” Brendan spotted a couple rusty, foot-long lengths of rebar hammered into the soil along the edge of the field. They were perfectly camouflaged to match the colour of the tilled earth, hungry to puncture the tires of the unsuspecting, and doing a very poor job of indicating a “garden”. Once finished, we primed the boom (40 gallons) on the field margin to have it ready for the next job.
3:05
According to the work order, this 37 acre job warned us of yet another small garden. This garden was emerged, making it easier to find, but also making it a nerve-wracking off-target risk. So, we literally steered clear of it, leaving a wide berth.
That didn’t stop the woman who was tending the garden from marching purposely out to sprayer to get Brendan’s attention. He stopped and braced himself as he climbed down to speak to her. We both expected he’d get an earful for spraying around those vegetables. After a brief exchange he climbed back into the cab and smiled. She didn’t chew him out – she chastised him for not getting close enough! You can’t win.
4:05
The last field was 20.5 acres. It was flat, square and promised to be a straight-forward end to a complicated day. We drove 9.6 mph on the headland and just as we were finishing the circuit, we saw tilled earth outside the boundary indicated on the monitor. Wait – is that bit planted, too? Are we supposed to spray that as well?
Brendan guessed it was an additional three acres. He’d asked Simon to load an extra acre’s worth of spray mix when we loaded, and I now understood why. He did some quick math and said we’d have enough if we dropped the rate a bit.
We coasted back and forth over the field, watching the remaining volume drop on the monitor, hoping we’d make it. We considered adding rinse water to the tank to thin the concentration. That would give us enough volume, but we’d be diluting the chemistry too much. Then we figured if we had to we could empty the tank just to the point of starving the pump, add water from the rinse tank and push the ~40 gallons left in the lines from behind.
The tiny, unsprayed strip caused the PWM to flutter between one and three nozzles on that last pass. Neither of us realized we were holding our breath as we watched the spray volume drain away on the monitor.
And then we were done! It was a photo finish and we both let out an explosive gasp as we started breathing again. It was such a narrow victory that we climbed out to look in the tank, and I’m here to tell you, it simply does not get any closer than this. We bragged like successful hunters all the way back to the yard and told anyone that would listen when we arrived at 5:00.
As I packed to leave, Brendan asked Dennis if he had to go clean out the sprayer. Dennis said a little dicamba would help tomorrow morning’s pre-emerge applications, so no. But he smiled as he warned “Although, betcha someone will call in at 6 am to ask for IP beans first.” Driving home, thankful for my comfortable car seat, I wondered if they would.
Take Homes
- Planning ahead is always good advice. However for a custom applicator, it’s absolutely critical. The goal is to be efficient and effective with as little risk as possible, and you can’t accomplish that unless you know where you’re going, when you’re going there and what to expect when you arrive; and not just the immediate job but minimum three jobs ahead. When time, manpower and consumables equal money lost, the stakes are high to have a solid strategy before you leave the yard.
- Then again, rigid planning can be A BIG MISTAKE… unless it includes planning for the unexpected. Almost without exception, these fields were not as advertised. Most were larger than anticipated, so knowing how to stretch a load (e.g. dilution, changing rates, carrying a little extra, using clean water to push spray mix from behind) meant we could roll with the punches without leftovers or deficits. One strategy was to spray smaller fields first, so larger remaining fields could absorb a smaller, distributed differential. Another was to spray the headlands, calculate the remaining area, then determine a rate that fits the remaining volume in the sprayer. This all assumes you performed some solid sprayer math when you loaded, of course.
- Autosteer, while awesome, was not used near as much as I expected. Small, irregularly-shaped fields that were recently ploughed, abutting sensitive crops and land-mined with “no spray” gardens meant manual headlands (maybe two) and slow speeds. And when the client doesn’t use GPS to plant, you don’t use it to spray except to alert you to turns. Anyone that thinks the operator can be replaced by automation should ride along in these conditions. There are lots of situations where we still need grey-matter and experience behind the wheel.
June 12, 2024