Tag: asparagus

Herbicides in Asparagus – A creative solution
In 2016, an asparagus grower in southern Ontario picked up a used De Cloet Hi-Boy originally used to spray tobacco. His vision was to create a three-row herbicide sprayer for asparagus and we were invited to participate. His concept was to design shrouds that would contain the herbicide, but not snag the asparagus or drag heavily on the ground. This article follows the development of the sprayer from concept to testing to final product.
The sprayer itself was a classic three-wheel, self-propelled affair. The asparagus was planted on four foot centres, leaving a three foot alley. While the goal was to hang three shrouds off the boom, we started with one to work out the bugs.
This operation uses 2,4-D to control weeds in the alleys and while a little can hit the asparagus stem up to 12 inches (where the branching starts), we wanted to avoid contact at all costs. That led us to the TeeJet AI 95° flat fan nozzle, which produces a Very Coarse to Extremely Coarse spray quality. A single nozzle could be suspended to span the 3 foot width of the alley.
The first version of the shroud was suspended off the boom from four anchorage points. A certain amount of of play was allowed so the shroud would find plumb (i.e. hang vertically), even when the sprayer boom yawed or pitched over uneven ground.
The shroud was constructed of sheet metal, angled to reduce the potential for contact with the asparagus branches, and terminated in stiff, nylon brush-style mud flaps commonly seen on trucks. These brushes were cut to a few inches in length to span the distance between the side of the shroud and the ground. This would create a “seal” to prevent spray from escaping, maintaining some degree of contact with uneven ground.
We tested the first version by placing water sensitive paper in two positions on the ground, just inside the reach of the brushes. We had to be careful not to run them over with the centre wheel of the sprayer. We also adhered two papers to the angled inner walls to see how much, if any, spray was hitting the inside of the shroud.
Our first pass on June 16th was at 9:00 am, 19.1 ºC (66.4 ºF) with a cross wind of 5 to 7 km/h (3.1 – 4.3 mph). relative humidity was high at 85% and travel speed was slow at 3.2 km/h (2 mph). We started with the .06 AI tip at 50 psi, but we drenched all the targets with excessive coverage because we were travelling so slow. We also found the stiff brushes were creating furrows in the soil, as shown below.
For our second pass, we tried the .04 tip and raised the shroud while dropping the tip to keep it suspended 15 inches over the ground. We were still drenching the targets and noticed the shroud was hitting the asparagus spears, causing physical damage. The damage is shown below – note the dark green on the bent spear.
This led to a decision to flare the side walls more aggressively, bringing them further into the centre of the alley and away from the spears (shown later in the article). This had the added benefit of angling the brushes as well to get a maximum span for weed control in the alley. For the final coverage pass we used the AI .03 tip, which gave more than 45% coverage on the ground, with even distribution, and there was no indication of spray on the papers adhered to the inside of the shroud. This coverage is more than is likely required, and the operator should be able to spray up to 6.5 km/h (4 mph) without compromising coverage.
Since the coverage tests, the grower added additional sheet metal fenders to the the existing fenders, encasing the wheels and creating a smooth transition for the shroud to gently deflect the asparagus. The fenders were needed because the grower found the asparagus was being pushed out by the wheel fender only to bounce back in front of the shroud, which snagged the fern and damaged it. The additional fenders keep the fern spread and prevent it getting caught in front of the shrouds.
The grower was very happy with the sprayer’s performance and planed to build another. Why be satisfied with the status quo when you can tap into your creative side and be innovative? If you don’t think you’re imaginative enough to try upgrading equipment on your farm, here’s a simple test to prove that it’s in you. It’s easy to see the bird in the image below, but with a little concentration you’ll be rewarded with a ski-jumping rabbit.
Thanks to TeeJet for donating the nozzles and water-sensitive paper and to Ray and Brad Vogel of Lingwood Farms for inviting me to participate.
Learn more about spraying asparagus here.
June 6, 2022
Spraying Asparagus in Fern
This research was performed in 2012 and since then there have been considerable advances in application technology for asparagus in fern that should be considered. Be sure to read the epilogue at the end of this article.
Introduction
Diseases such as purple spot can have major economic impacts for asparagus growers, and the best line of defence is spraying the appropriate control products. The good news is that asparagus growers know this. The bad news is that there are few things harder to spray than asparagus in fern.
Asparagus infected with purple spot.
Asparagus in fern can stand 1.5 m (5 ft) high by 1.0 m (3 ft) diameter and is typically planted on 1.2 m (4 ft) centres. Asparagus in fern has a very dense canopy full of needle-shaped leaves. This dense canopy slows air movement, making conditions still, humid and very difficult for a spray droplet to penetrate.
Spraying asparagus in fern.
Spray coverage is a combination of two factors: the area of the target contacted by spray droplets, and the distribution of spray droplets over that target. For most insecticide and fungicide applications, reasonable coverage is reflected by 10-15% surface area covered paired with an even distribution of approximately 85 medium sized droplets per square centimeter. This is not a rule, but a guideline.
In order to determine the best way to spray, we have to be able to compare the coverage achieved. To do this, we used water sensitive paper, which is yellow until contact with spray turns it blue. Three sets of three targets were placed in approximately the same location for each pass.
Water sensitive paper arranged on stands, ready to be placed in the fern.
Water sensitive paper orientation and location in asparagus canopy relative to sprayer direction.
We tested five popular nozzle types, at two ground speeds using three carrier volumes to answer three questions:
1. Does spray volume impact spray coverage?
2. Which nozzle style gives the best coverage?
3. Does travel speed impact spray coverage?
Does spray volume impact spray coverage?
Five different nozzle types were used to spray three volumes onto the targets at 16 kmh (10 mph). This was repeated three times and target coverage was determined both as droplet deposits per cm² (see Figure 1) and total % covered (see Figure 2).
Figure 1. Average deposits per cm^2 for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).
Figure 2. Combined average percent coverage for five different nozzle types at 187 L/ha (20 US gpa), 234 L/ha (25 US gpa) and 280 L/ha (30 US gpa) at a ground speed of 16 kmh (10 mph).
Cards in each position consistently received a significantly higher average deposit per cm² and significantly higher average percent coverage at higher spray volumes. The relatively low coverage in the middle position was anticipated given the orientation of the targets to the sprayer.
Therefore, it would appear higher volumes result in better coverage, at least up to 280 L/ha (30 gpa). Generally, there is a threshold where exceeding a given carrier volume results in a diminishing return.
Which nozzle gives the best coverage?
Coverage from five different nozzles was compared: the Hollow cone, Flat fan, Dual flat fan, Guardian Air and Air-induced hollow cone. Given that 280 L/ha (30 gpa) resulted in the best coverage, the following figures illustrate droplet deposits per cm² (see Figure 3) and total % covered (see Figure 4) at 280 L/ha (30 gpa).
Figure 3. Average deposits per cm^2 for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).
Figure 4. Average percent coverage for five different nozzle types at 280 L/ha (30 US gpa) and 16 kmh (10 mph).
The graphs show that each nozzle followed a similar trend, with more droplets at the top of the canopy, less or par at the bottom of the canopy, and considerably less in the middle of the canopy (which is not surprising given the orientation of the target around the stem).
The trend in droplet density from highest to least coverage is:
1. Hollow Cone
2. XR flat Fan
3. Guardian Air
4. Dual Flat Fan
5. Air Induced Hollow Cone
The percent coverage data was less clear. The top two nozzles for each position were:
Top Target:
1. Guardian Air
2. All other nozzles approximately the same
Middle Target (around the stem):
1. XR flat Fan
2. Hollow Cone
Bottom Target:
1. XR flat Fan
2. Hollow Cone
It can be argued that the target at the top of the canopy is easiest to spray, and therefore does not have as much importance as the middle and bottom targets. As such, it would appear that the XR flat fan and Hollow cone nozzles give the best overall coverage. It is debatable whether the higher droplet count from the Hollow cone is more important than the higher percent coverage of the XR flat fan.
Does travel speed impact spray coverage?
Hollow cone nozzles and XR flat fan nozzles were used to spray targets at two travel speeds and three volumes. Target coverage was determined both as droplet deposits per cm² (see Figure 5) and total % covered (see Figure 6).
Figure 5. Average deposits per cm^2 for Hollow cone and XR flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).
Figure 6. Average percent coverage for Hollow cone and XR Flat fan nozzles at 280 L/ha (30 US gpa) and either 8 kmh (5 mph) or 16 kmh (10 mph).
The variability in deposit density and percent coverage from medium/fine droplets created by the hollow cone nozzles make it difficult to determine statistical significance, but the trend suggests that higher ground speeds improve coverage in the middle and bottom of the canopy. This is likely due to the wake of the sprayer and the vortices created by its passage stirring fine droplets into the canopy.
Overall recommendations
The data suggest that coverage was improved when the sprayer travels at 16 kmh (10 mph) rather than 8 kmh (5 mph). Coverage was also improved at higher spray volumes, where 280 L/ha (30 US g/ac) provided the best overall coverage for all nozzles. As for the best nozzle, this depends on the application; the hollow cone created higher droplet densities than the XR flat fan, but the XR Flat fan created higher percent coverage. Higher droplet densities may be preferred when controlling disease with contact products, but spray drift becomes a significant concern. Higher percent coverage might be preferred with locally systemic products where complete coverage is less of a concern and preventing spray drift is a priority.
Epilogue
This work was performed in 2012. Since then there have been significant advances in sprayer design for spraying asparagus in fern. Dr. Torsten Balz (Bayer Application Technology Manager) kindly provided an example of such a sprayer (see below) and a video link to watch it in action. Drop arms that bring the nozzles closer to the target at all canopy depths are an ideal solution as long as the row spacing allows clearance without snagging the drops. Further, there have been developments regarding the use of hollow cones in an overhead broadcast application. Over- and under-laps in the hollow cone swath lead to double-dosing and gaps respectively that are referred to as “Technical Strip Disease”. Combined with considerable drift potential, hollow cones are not recommended.
Air-assisted drop arms greatly improve coverage uniformity in asparagus in fern. Photo kindly provided by Dr. Torsten Balz.
Special thanks to Max Underhill Farm Supply (Vienna, Ontario) for use of their sprayer and their assistance both spraying and placing water sensitive papers in the field. Thanks to Mr. Ken Wall of Sandy Shore Farms Ltd. (Port Burwell, Ontario) for providing the site and hosting the associated workshop, and thanks to TeeJet Technologies for their donation of parts and supplies.
June 3, 2021