In 2019 we evaluated the spray coverage from nine application methods on corn silks. The results showed that a directed application from drop hoses (aka drop pipes, drop legs) suspended in between the rows gave significantly higher deposits. If you’d like some context and history, the article can be found here. The results led us to wonder… if a directed application resulted in superior coverage, did that translate to improved efficacy?
Drop Hose Design
Around this time we started considering the Beluga Drop Hose developed by Agrotop (Germany) and distributed by Greenleaf Technologies (USA). Other commercial, flexible drop hoses tend to snag in dense foliage, deflecting or swaying during an application. The Beluga was stiffer and their unique low-profile nozzle body had less potential to snag. Further, unlike homemade, inflexible drop pipes or other commercial solutions such as the Y-Drop with 360 Undercover, the Belugas were lightweight and did not need a break-away section to prevent damage.
We already had some experience with the Beluga, having previously used it in an onion fungicide study. In that study the drop hose treatment deposited approximately twice the tracer dye both at the top and the bottom of a mature onion canopy compared to a conventional overhead broadcast treatment. However, if we were to use them in corn, we would have to make changes to the design. We’d need longer drops and a wider swath to ensure coverage of the entire plant, with particular focus on the corn silks.
Construction and Installation
We ordered 150 cm (60″) drop hoses with two nozzle bodies each so we could customize them. The instructions were in German but after running them through translation software we were confident in how to proceed (download the translated copy here). We started by determining the hose length. Mounting plates (included) were temporarily fixed to the boom using quick ties and the boom was raised above the corn canopy. The Beluga quickly and easily “keys” into the plate allowing it to swing freely and find plumb. The hose had to clear the ground but still be long enough to span the target region in the canopy.
The corn was planted on 76 cm (30″) spacing. We mounted the drop hoses on the boom so they would align with the alleys, thereby moving between the planted rows. We elected to use 110° flat fan nozzles spaced 38 cm (15″) apart to ensure 100% overlap at the target. Using the jig provided, we drilled holes for the two nozzle bodies. Then we blew-out the hoses to clear them of any plastic shavings that could plug nozzles. The hoses were cut to length and the end plug was installed with a hex key. Once we found a rhythm, the assembly went quickly and easily.
The Drop Hose Experience
We felt it was important to describe the utility of drop hoses. The sprayer operator made the following observations based on their experience:
- Installing and uninstalling the drops took roughly 60 seconds apiece, including moving the ladder.
- Deflection was minimal, even when they were dragged perpendicular to the rows through headlands.
- Initially, it was a little unnerving not being able to see the spray but the operator quickly got used to it (see video below).
- There was no issue folding the boom or driving between fields with the drops installed. They did note that the lugs on the front tires did contact the drops on tight turns, but adjustments were made.
- The drop hoses rinsed as easily as any nozzle. There were initial concerns that using 015’s nozzles to maintain the target 20 gpa might cause plugging issues, but none occurred.
- The drops were resilient. The operator bent the hoses by lowering the boom and then dragged them along the ground. They returned to plumb and appeared undamaged.
- Once removed, the drops stored compactly and easily on a utility shelf, repacked in their original box.
Sprayer Settings and Plot Design
The sprayer was self-propelled with a rear-mounted 36.5 meter (120″) boom. Treatments were eight corn rows wide. The boom was nozzled from left to right per the following table. Travel speed was between 8.85 – 11.25 km/h (5.5 – 7 mph) and the application volume was 225 L/ha (20 gpa).
|Overhead Broadcast||Directed (Beluga)||Unsprayed Check||Overhead Broadcast||Directed (Beluga)||Unsprayed Check|
|TeeJet AIC11005’s on 15″ centres||4 Airmix 110015’s per drop on 30″ centres||Nozzles blocked||TeeJet AIC11005’s on 15″ centres||4 Airmix 110015’s per drop on 30″ centres||Nozzles Blockled|
The study took place in 2021 in Port Rowan, Ontario on 11.3 ha (28 acres) spanning two fields. Each treatment was a single pass covering either 0.32 or 0.43 ha (0.8 or 1.06 ac). There were two different tank mixes: The first was 405 mL/ac of Miravis NEO and 50 g/ac of Delegate. The second was 303 mL/ac of Headline AMP, 202 mL/ac of Caramba and 50 g/ac of Delegate. The specifics of each treatment and the number of replicates are captured in the table below.
|Broadcast (Overhead)||Miravis NEO||Home Field||1.06||4|
|Broadcast (Overhead)||Miravis NEO||Shop Field||0.8||2|
|Broadcast (Overhead)||Headline AMP + Caramba||Home Field||1.06||4|
|Directed (Belugas)||Miravis NEO||Home Field||1.06||4|
|Directed (Belugas)||Miravis NEO||Shop Field||0.8||2|
|Directed (Belugas)||Headline AMP + Caramba||Home Field||1.06||4|
|Unsprayed Check||n/a||Home Field||1.06||8|
|Unsprayed Check||n/a||Shop Field||1.06||2|
Preliminary and Qualitative Results
A qualitative comparison of randomly-selected ear leaves showed less evidence of disease in the fungicide treatments compared with the unsprayed check. There was also less evidence of disease in the Directed application treatments versus the Overhead broadcast application treatments. There was no obvious difference between the two fungicides used. There was very little evidence of Western Bean Cutworm in any of the treatments or unsprayed check, so the impact of Delegate will not be discussed in this article.
Cob Size / Quality
Preliminary samples showed evidence of disease and tapered-ends in both fungicide treatments and the unsprayed checks, but the size and quality of the cobs from fungicide treatments seemed better. We were encouraged, but reserved judgement until the final yield numbers were in.
Final, Quantitative Results
Each treatment yielded corn with different moisture levels, so we chose not to compare bushels per acre harvested. Instead, we calculated net revenue based on current market values in the Port Rowan area. We normalized the treatment yields by moisture level and calculated their relative drying costs. Then we accounted for the other inputs (see list below) using the following formula:
Net Revenue (CDN) = Seed Yield × Corn Sale Price − Drying Cost − Treatment Cost
- Treatment Cost- Miravis NEO: $16.66/ac
- Treatment Cost- Headline AMP: $12.73/ac
- Treatment Cost- Caramba: $3.02/ac
- Treatment Cost- Custom spray price: $12.00/ac
- Drying Cost: $0.58-0.64/bu (based on moisture levels)
- Corn Sale price: $6.00/bu
We plotted net revenue from each application method in a box and whisker plot (see below). Only the unsprayed check appeared normally distributed. ANOVA did not indicate a statistically-significant difference between application methods and the unsprayed checks at a 95% confidence level. This means we cannot say with confidence that we would see this trend again next year in these fields, or elsewhere. We will be repeating this work in the coming years. Nevertheless, in this study, the mean net revenue in CAD for each application method indicated the following differences:
- Directed vs. Unsprayed check: Profit of $27.76/ac CAD
- Directed vs. Overhead broadcast: Profit of $33.37/ac CAD
- Overhead broadcast vs. Unsprayed check: Loss of $5.61/ac CAD
When the mean net revenues for each application method are separated by fungicide, the same trend is observed: Directed applications yielded a higher mean net revenue than Unsprayed checks, which in turn yielded a higher mean net revenue than the Overhead broadcast application method (see below). There was no statistically significant difference between the two fungicides. While it appears the Headline AMP / Caramba condition yielded higher revenues, this is likely not the case. When the mean net revenues from the Unsprayed checks were used to normalize the two fungicide conditions, the results appeared very similar (data not shown).
Return on Investment
We can estimate the return on investment for this scenario. 48 Beluga drop hoses ($9,600.00 CAD) with 192 nozzles ($1,920.00 CAD) cost $11,520.00 CAD. Compare this to the cost of 72 nozzles ($720.00 CAD) in the Overhead broadcast application method. Based on the mean net revenues in this study, the Beluga drop hose method would pay for itself in 316 acres.
All the corn harvested in this study, no matter the treatment, was rated Grade Two. However, this does not account for mycotoxins. Mycotoxins are natural chemicals produced as by-products of fungal growth. At sufficiently high levels, the consumption of mycotoxins can have detrimental health effects to humans and animals. Deoxynivalenol (DON aka vomitoxin) and zearalenone are of particular concern and are found in corn with Gibberella ear rot (a common ear mould).
Years where growing conditions are especially warm and moisture is high (E.g., precipitation, fog, dew) favour ear mould growth. This is further exacerbated when conditions include prolonged dry-down times and harvest is delayed. The regional environmental conditions in this study were highly conducive to ear mould development.
The fungicides used in this study are both prophylactic products, which means they had to be in place prior to infection. Both are rated for the suppression of Gibberella ear rot, which according to the PMRA Regulatory Directive Guidelines for Plant Protection Products (2003) should give “Consistent control at a level which is not optimal but is still of commercial benefit”. By comparison, a product rated for control of a pest will give >95% efficacy.
Given the high potential for disease and the suppression rating of the fungicides used, we collected random samples from each treatment at the auger. They were homogenized into two-pound samples of corn from each treatment and submitted to A&L Canada Labs for mycotoxin analysis. The results (see graphs below) indicated high levels of DON and Zearalenone in all treatments, with no statistically-significant differences and no obvious trend. For context, DON levels of 5.1 ppm have historically resulted in the rejection of corn at grain elevators. A preliminary survey suggests that the levels detected in this study were higher than those found in other Ontario corn-growing regions. This may be because those regions did not experience such high humidity.
We know from studies in several other crops that drop hoses provide more uniform spray coverage in large canopies than overhead broadcast methods. Specifically, we know from our 2019 work that we see higher deposition levels on corn silks using drop hoses compared to overhead broadcast and aerial application methods. The rapid return on investment and ease-of-use of the Beluga drop hose system make it an excellent candidate for fungicide and insecticide applications in corn.
In comparing the mean net revenues in this study, we did not see statistically significant differences. However, we did see that Directed applications resulted in a net profit of $27.76/ac CAD versus unsprayed checks. We also see that the Broadcast application resulted in a net loss of $5.61/ac CAD. General consensus is that spray coverage is a critical factor when using suppressive pesticides. Coupled with the qualitative results, we propose that the superior coverage from the drop hoses maximized the protection provided by the fungicides. The financial loss incurred from the conventional Broadcast application method coupled with the results of the mycotoxin analysis raise important questions about the overall efficacy of fungicides for ear moulds.
Unlike other grain crops, there are no decision support models (E.g., DONcast in wheat) to optimize the timing of fungicide applications in corn. The same variety of corn was used throughout this study and all treatments were applied within a reasonably-short period of time according to environmental conditions. And so, if the best products available were applied using an application method that provided excellent coverage, why were mycotoxin levels so high?
It can only be concluded that the ear mould pathogens were not sufficiently controlled by suppressant fungicides. Those that remained unchecked thrived in the warm and humid conditions, producing high levels of mycotoxins. Unlike horticultural systems where fungicides are reapplied multiple times according to precipitation and plant growth, corn fungicides are applied only once and expected to provide protection for three or more weeks. This study demonstrates the need for more accurate forecasting, pathogen-resistant varieties and more efficacious ear mould fungicides in order to successfully and consistently reduce mycotoxin levels.
Thanks to Petker Farm Ltd. for conducting the study. Thanks to Corteva and Syngenta for contributing the pesticides used.