Aerial spray application technology

The most used devices for generating droplets in aerial applications are rotary atomizers, important allies in rust control.

Among the various diseases that attack soybean crops, Asian rust is still one of the main concerns for soybean producers in Brazil. Considering the degree of vegetative development of plants at the time of application, often with total closure of the lines between rows due to the large leaf area, it became a general consensus that application techniques would need to offer drops with good penetration and coverage capacity. canopy, even for the application of fungicides with systemic action characteristics.

Taking as a basis the research published on the subject in the last decade, it is observed that the majority of technical recommendations for rust control are based on the preference for preventive applications from flowering onwards (R1), opting for curative applications when rust appears in the vegetative stages. Following this principle, it is extremely important to understand and adapt the application technology so that the correct balance can be achieved between the necessary effectiveness and the desired environmental safety, within the fundamental concepts of good practices and sustainability of phytosanitary treatment.

APPLICATION TECHNOLOGY

Droplet size and application rate are basic factors that must be considered in the first step when planning an application. Other important factors, such as meteorological (climatic) conditions, product recommendations and operating conditions, must be considered together so that the entire system is adjusted, aiming for maximum performance with minimum losses, always with the least impact. environmentally possible.

For contact products or those with less systemic action, the use of smaller drops and/or a larger volume of syrup is necessary, due to the greater dependence of this technique on target coverage. In the case of products with greater systemic action, dependence on coverage tends to be slightly lower. As an example, if the application target includes the internal or lower part of the plants, as in the typical case of a fungicide application for rust, good droplet penetration is necessary and, for this purpose, smaller-sized drops and If possible, increase the volume of syrup. However, it is worth remembering that very fine droplets are more sensitive to evaporation and drift processes, which can reduce the amount of products that are deposited on the targets, reducing the effectiveness of treatments.

One of the biggest challenges when planning an application is precisely deciding on the droplet spectrum: should we use finer drops or thicker drops? From a practical point of view, the ideal is to find a balance between the coverage and penetration performance of the application (using fine drops, when possible), with an adequate potential for reducing the risk of losses, which would lead us to prefer the application of medium drops when necessary.

Another fundamental aspect of planning an application is adapting the application technology to the meteorological conditions present in the application locations. Applications with relative humidity below 50% and ambient temperatures above 30 should be avoided.^oC, as well as preference should be given to average wind speeds between 3km/h and 10km/h. The absence of wind can also be harmful, due to the chance of thermal inversions or rising heated air, phenomena that hinder the deposition of the finest droplets. Meteorological limits must be considered in all applications and, eventually, can be partially relaxed according to the application technology that will be used, as long as this action is fully surrounded by common sense. It is important that the limitations set out in the product leaflets are observed and, in any case, it is recommended that the final decision whether or not to proceed with the application always rests with the responsible agronomist.

DROPLET GENERATION IN AERIAL APPLICATIONS

The most commonly used devices for generating droplets in aerial applications for rust control are rotary atomizers. Atomizers use centrifugal energy from high rotation, which, in turn, is generated by air flow in flight. There are two types most used in Brazil: screen atomizers and disc atomizers. The liquid flow in the atomizers is adjusted by a system of variable orifices and by the spray pressure in the hydraulic spray system. Some simpler atomizers use a hydraulic connection with flow restrictors formed by perforated rings, while others use a rotary adjustment system called a Variable Restriction Unit (VRU). The intensity of droplet fragmentation depends on the rotation of the atomizer, which is defined both by the angle of attack of the propeller blades and by the aircraft's own flight speed.

As in the example of hydraulic nozzles, the combination of droplet size and flow rate should be obtained by consulting tables or applications provided by the manufacturers. However, for atomizers manufactured in Brazil this is not always easy, as there is a shortage of technical material and it is not always possible to obtain accurate information about the spectrum of drops generated.

In the case of imported atomizers, such as Micronair, the manufacturer provides an online application (http://www.micron.co.uk/droplets) that allows the precise calculation of the droplet spectrum based on research carried out at leading universities, such as the University of Queensland (Australia).

In search of more precise information about the real droplet spectrum generated by national atomizers, AgroEfetiva carried out research in the laboratories of the University of Nebraska-Lincoln (USA), in partnership with Unesp-Botucatu/SP (Brazil), aiming to collect data from droplet spectrum from national atomizers using the same droplet analysis methods.

Based on this research, it was possible to carry out a comparative analysis between the droplet spectrum data from national atomizers with the Micronair AU-5000, a model that is often used as a reference in Brazil for estimating the droplet spectrum generated by screen atomizers. An example of this analysis can be seen in Table 1, which presents data from the national Microspin atomizer compared to data generated for the Micronair AU-5000.

Based on the values ​​observed in Table 1, it is important to evaluate the possible impact of the application technology on the rust control performance potential, taking as a hypothesis the application of the same fungicides by air, using the two atomizers in the same operating conditions. According to data generated by AgroEfetiva, the Microspin atomizer offers systematically higher DMV than that generated by the Micronair AU-5000, when adjusted at the same propeller blade angles. As examples, at an adjustment of 75 degrees, the Microspin's DMV is 21% greater than that of the Micronair, while for the 60 and 45 degree angles the values ​​are 49% and 51% greater, respectively.

It is also interesting to note that for the same blade angle adjustments, the rotations obtained in the atomizers are different, and this difference is variable. As examples, at 45 degrees the Microspin spins at 4.509rpm, while the Micronair reaches 6.068rpm. As for the 75-degree rotation, the values ​​are much closer, with 1.780rpm for the Microspin and 1.784rpm for the Micronair. However, it should be noted that, regardless of the rotations being practically equal at the 75-degree angle, the DMV generated by the Microspin is 21% greater than that generated by the Micronair.

The fact that the Microspin generates larger drops than the Micronair, when at the same setting, does not mean that one is better than the other, or vice versa. It just shows that they are different. For this reason, the common practice in the field of using Micronair data to benchmark the expected performance of any national screen atomizer should be avoided. It is necessary to seek the correct droplet spectrum information for each atomizer, so that it is possible to consider the application technology for each working condition.

 

Ulisses R. Antuniassi, FCA/Unesp; Alisson AB Mota, Rodolfo G. Chechetto; Fernando K. Carvalho, AgroEfetiva

Article published in issue 165 of Cultivar Máquinas.