HANGAR CONVERSATIONS — Are Aerial Applications and Ground Applications the Same?

Dr. Diego Martin Oliva | diegomartinoliva@gmail.com Agronomist

After a long technical day in Laguna Larga, Cordoba Argentina the question of aerial vs ground applications was discussed. I was working with Salvucci Aviation making calibration and spray system adjustments. We asked ourselves, “What was the reason agricultural producers often decided to make their chemical applications with ground equipment?”

Was it exclusively due to costs? Is a ground application as efficient as aerial applications? Do growers know the benefits of aerial application?

To answer these questions, we must approach them from several prospectives. As a first step, we agreed that we should show our customers the benefits of aerial applications as compared to ground applications. Primarily, this is because of the penetration created by inertia of droplets (as long as the boom is adequately positioned) due to an aerodynamic benefit, downwash. In general terms, this makes the control of a pathogen, or pest, much more efficient.

This asset is only available with the aircraft. The desirable sum of effects of aerial application, downwash created while in ground effect, also enhances the finest drops to contact the backside of leaves, allowing droplets to reach areas where ground applications cannot.

Many pests exist on the underside of leaves? Do growers know this? In terms of biological effectiveness, there are many scientific publications that reveal this. So, is this issue just a cost issue?

On the other hand, the operational capacity of an ag-plane is absolutely better than any ground equipment by practically 10:1, with its superior applications and average swath widths addressing the pest problem much faster.

In terms of application contact with the target, a volumetric calculation graphically can demonstrate to growers the better results with a very fine droplet influenced the factors aforementioned. Maintaining a constant volume, a 500-micron droplet from a ground machine has little or no possibility of contact with the pest. But, it contains the same amount of liquid as eight drops of half its diameter (250 microns) and in turn the same amount of liquid as 64 drops of 125 microns, the typical diameter of an aerial application. The 125-micron droplets have a much better possibility of contact with the pest as there are many times more of them than the same amount of liquid made up of 500-micron droplets.

A principle of control and rate of absorption from Fick’s law details the rate of absorption of a chemical through a semi-permeable membrane (crop leaf) is directly related to the concentration gradient of the droplet. Therefore, a chemical applied by air is absorbed much faster (with less risk of loss) and controls the pest faster, since it has a much more concentrated droplet.

How then can the efficiency of both air and ground applications be analyzed objectively? To do this, we will take the following agronomic criteria:

• Mechanical damage caused by ground machines

• Severity and incidence of diseases in crops treated with aerial application, e.g. timing

• Results of the quality of the crop.

In order to analyze losses caused by mechanical damage of a ground machine with a 35 cm wide track, a crop planted in rows equivalent to 21 cm was analyzed. To analyze it, a drone flew at 100 meters was used, achieving a 2 cm pixel definition.

After analyzing and measuring all the passes of the ground machine, it was established that the minimum mechanical damage caused by tracking over the crop is of the order of 2.94%, as can be seen in the attached figure. This means for a total treated area of 100 hectares, the ground machine, as a result of its track, causes at least the loss of production of three hectares.

Regarding the severity and incidence of the diseases in treated crops, we will refer to the wheat crop that suffers from the infection of Roya (Puccinia), a polycyclic disease.

When the airplane application is used, it is possible to notice a lower effect - severity as explained earlier with more concentrated dropletsbeing absorbed quicker). There is an added benefit of a lower incidenceof the spread of the disease, since aircraft do not enter into the fielddispersing spores, avoiding a subsequent application.

In photo with three leaves, the severity of the impact due to ground equipment treatment is shown, since the pathogen’s progress was notstopped in time at the first detection and a second treatment wasneeded. In other words, the control effect of a polycyclic disease ismuch greater if it is performed by air.

Regarding the commercial quality of the trodden upon crop (treated with ground equipment) you should not forget the crop suffers a delay in itsphenological development causing green grains to appear at harvest time.This causes the grower to receive considerable discounts on the priceof his product.

Analyzing each of the concepts detailed above, it is clearly much more beneficial to apply post-emergent treatments with aerial equipment.

In summary:

• An aerial application mixture is 10 times more concentrated, which means greater, better and faster absorption.

• The mesostemic effect of current fungicides (low mobility), causes a greater need for contact. A better penetration to the middle third of the canopy is due to the downwash effect of the aircraft.

• Lower severity and incidence of polycyclic diseases when not entering the field. Thus, a lower reinfection rate, saving subsequent applications in the future.

• Greater application opportunity/ timeliness.

• Better volumetric / coverage ratio. A ground machine to achieve the same coverage would need to spray 140 liters/ha (14 gpa).

• Greater economic performance for the producer. Consider biotic, abiotic and commercial factors.

So ultimately, it remains the duty of the aerial applicator to educate his customers about the obvious benefits of aerial applications. It is not simply a false cost savings of a ground application, but a combination of several factors often unknown to the customer that prove aerial application, in the end, is most cost-effective.

Dr. Diego Martín Oliva—Curriculum vitae—Agronomist specialist in extensive agricultural spraying, MBA Specialist in Sustainable Agricultural Production (Harvard University), Technical Advisor of FeArCa (Argentine Federation of AgroChamber), Bayer - Monsanto External Technical Application Consultant, Syngenta External Technical Advisor on Aerial Application Technology, Technical Advisor to Aerial Spray Companies in Argentina and Uruguay. Member of the technical committee of the National Network of Good Practices, Member of the IRAM Technical Committee, under 14.130 Postgraduate professor at the National University of Lomas de Zamora with a degree in plant protection. Speaker in aerial application technologies.