Pesticide applications using the low volume technique

Applications of pesticides using the low volume technique will only have excellent results if there is synergism between all the factors involved in the application, which ends up becoming a major challenge for operators.

In the context of contemporary agriculture, reducing operational costs has become increasingly important within the grain production process. One of the most important operations within cultural practices is the spraying of phytosanitary products. In soybean cultivation, this operation represents 25% to 30% of the production cost and it is precisely in this crop where efforts are concentrated to improve spraying techniques with the aim of reaching the target correctly and reducing operational costs.

In Brazil, the low volume terrestrial technique has been adopted on a large scale over the last five years, while countries such as Argentina, Bolivia and Paraguay have adopted the low volume technique earlier using conventional boom sprayers and hydraulic power spray tips. (conventional).

The terminology of “low volume” in terrestrial application is very relative and it is not yet possible to specifically find application rates that fall into this category in the literature. For some people, low volume means application rates lower than 80L/ha, for others, rates lower than 50L/ha and in the reality of some countries rates lower than 20L/ha, in this case some authors even use the terminology “ultralow volume". Whatever the volume applied, when using the term low volume, it indicates that there has been a reduction in the application rate. This reduction in the application rate certainly brings operational advantages that are reflected in reduced costs, however, the technique of reducing application volume must be taken very seriously and with great discretion and professionalism, as in addition to advantages, it also presents risks. Therefore, the application volume that should be sought is the “optimal volume”, the one that, together with the right droplet size, suitability of spray and application of knowledge, will provide adequate coverage to control the desired target.

There are many cases where the applicator seeks an “x” volume of application, whether due to the influence of professional colleagues, lectures focused on spraying, etc. In these cases there is a very high risk of applying low volumes because an “x” application volume cannot be considered “optimal” without first evaluating the arrival of the drops at the target and knowing the effect of weather conditions on the drops along the route. exit from the spray tip until deposition and total absorption by the plant or insect pest. To do this, it is essential to use water-sensitive papers that will show whether or not there was necessary coverage. Regardless of the application, the use of water-sensitive paper is very important, as it is the tool that helps to define the “optimal volume” when making decisions.

OPERATIONAL FACTORS

The low volume technique involves several factors that can be decisive for the success or otherwise of the application. When working with lower volumes of syrup the risks increase, but, on the other hand, low volumes can result in better applications, as long as they are carried out with great professionalism. The factors that must be taken into consideration are the quality of the mixture and the application.

SYRUP

The spray and its preparation are important factors that must be taken into consideration, as spraying low application volumes means less water per hectare. The positive point of using less water is the reduction in the risk of losing the active ingredient molecule due to the cations present in water considered hard, that is, with a high Ca content.²⁺ in G²⁺. Furthermore, when using smaller volumes of water, the concentration of the active ingredient in the syrup increases. This is a beneficial point and in some cases provides faster target control. The negative point is the risk of incompatibility between phytosanitary products. When using higher concentrations the risk increases, which is why it is very important to know in detail the effect of the mixture that will be made. To avoid problems with incompatibilities, it is recommended to make pre-mixes to study compatibility at the concentration that will be used due to the low application volume.

APLICAÇÃO

There are many factors in the application process that can lead to the success or failure of a phytosanitary treatment. One of these factors is target coverage, which is directly related to spreading factors, recovery rate, plant surface per hectare, application volume and droplet size. The volume of application is decisive in increasing or reducing coverage, however, it is not the main factor in obtaining the desired coverage even in different conditions of plant surface in the hectare. At low volume, due to the fact that the amount of mixture that will be applied per hectare is reduced, there is a reduction in the percentage of coverage. In the low volume technique, to maintain adequate coverage or necessary for successful target control, it is necessary to use adequate droplet sizes, that is, with a classification between fine and medium. However, the droplet size classification is not enough, it is necessary to use spray tips that, in addition to producing this droplet size, are capable of producing uniform drops. There are some spray nozzle options with these characteristics in the formation of droplets, including an empty cone (TXA), a flat deflector jet (TT), and even a common flat jet (XR). Each model with its particular characteristics (Figure 1).

The choice of which cutting-edge model to use for a given application within the context of low volume will depend on the technique that will be used and the lowest capacity in liters per minute available in each cutting-edge model, however, it is important to take into account that, when using low volumes (less than 20L/ha) the spray tip flow needs to be very low, even at high application speeds. In a hypothetical example, to apply 20L/ha at 25km/h with a nozzle spacing of 50cm, a nozzle with a flow rate of 0,42L/min is required. This means that the available options would be the TXA8001, TT11001 or XR11001 tips at a pressure of approximately 3,4bar. In a practical analysis, within the three models mentioned, we must take into account which one presents the greatest risk of clogging and discard this option, as clogging causes failures and operational delays. Because they are low-flow tips, the orifice is smaller and the risk of clogging increases. Therefore, considering their construction model, the tip with the greatest risk of clogging would be the XR11001. For this reason, we could only choose between TT11001, which has a tubular shape inside, which facilitates the passage of fluid with less risk of clogging, and/or TXA8001, which is the tip with less risk of clogging, as it is an empty cone and have an internal construction that facilitates the passage of fluid even with particles that can lead to partial or total clogging. Even so, the appropriate use of filters is always recommended, including the main filter, line filter and nozzle filter, in order to minimize clogging.

After this analysis it is necessary to take into account the size of the droplet. If the application is herbicides, the most appropriate option is to use a tip with a transition in droplet classification between medium and fine, in this case the Turbo Teejet tip is a great option.

In the following example, the result of a desiccation application (glyphosate + adjuvant) with the Turbo TeeJet TT11001 tip can be seen at an application rate of 22L/ha with a travel speed of 15km/h and nozzle spacing of 70cm. The working pressure was approximately 3bar, which generated drops classified as “fine” (Figure 2), which generated excellent coverage of concentrated drops.

Another great example of successful applications with low volume in desiccation is using an application rate of 8L/ha. In this situation, the active ingredients glyphosate, fluroxypyr and an adjuvant were used. Of the 8L/ha, 4L were of product and 4L of water, this shows the high concentration of the syrup, which resulted in rapid action and control. Those responsible for these applications only use this application rate, as they have trained operators, use sprayers with appropriate onboard electronics, respect and monitor climatic limits, in addition to using excellent quality spray tips, in this case the TX-VS2 tips were used. . The coverage result is shown in Figure 3, in which very fine and concentrated drops can be observed. 

Some professionals question the use of the conical jet tip in applications with boom sprayers and even more so for the application of herbicides. The main reason for the question, in addition to the risk of drift, is that the theory shows the volumetric distribution of the conical jet tip to be uneven, which would not cause adequate application along the bar. What leads to this conclusion is the analysis of volumetric distribution on collection tables suitable for this purpose, however, the analysis of volumetric distribution in this case is carried out with the sprayer stopped or statically in a laboratory. In practice, no sprayer works stationary, and it is for this reason that the result observed on the volumetric distribution table in static conditions does not apply in practice, as in field applications vector factors come into play due to the displacement of the machine and the energy droplet kinetics, causing the spray bar to form an application curtain, as long as the appropriate boom height is used. In this context, conical jet nozzles can be used in boom sprayers, preferably with low volumes, as with conventional application volumes there are other options with less risk. At low volume, greater care must be taken in relation to drift and overlap, as conical jet tips have an angle of 80°, this requires greater attention from the operator in relation to the bar height used.

For applications where there is a greater leaf mass of the crop, such as insecticide and fungicide applications in soybean crops at the end of the cycle, the best indication would be the TXA tip (empty conical jet), as it produces fine to very fine drops. . In these cases, greater penetration of drops into the canopy is necessary and overcome the umbrella effect created by the plant surface. In this type of application, it is very important to adopt the “optimal volume” technique and check what is the appropriate application volume to reach the lowest level.

Figure 4 shows the excellent results of an application of fungicide with adjuvant in the soybean crop at stage R3 with an application volume of 30L/ha under favorable climatic conditions. The machine's travel speed was 15km/h with a nozzle spacing of 50cm and a TXA8001 spray tip at approximately 3bar.

It is important to remember that just arriving at the target is not enough, it is necessary to know the droplet's lifetime after its deposition, as these are fine drops and are more susceptible to evaporation. In many cases the droplet settles, but evaporates before penetrating the plant tissue and this directly affects the control. 

SCRATCHS

In applications of phytosanitary products there are many risks of losses and contamination, and in applications with low volume these risks are even greater, as these are applications with drops that are more susceptible to losses. These losses can be due to drift (endodrift and exodrift), thermal inversion and evaporation. In this case, exodrift, thermal inversion and evaporation are the loss processes that deserve greater attention, as low volume applications are made with droplets that can be lost by drift or evaporate both in the process of reaching the target and in the absorption process. . For this reason, it is very important to take into account the use of adjuvants, such as syrup conditioners and especially those that protect the drops from evaporation and provide the appropriate life time to complete the process.

In conventional applications, the droplet size change technique can be used in cases of unfavorable weather conditions. For example, in a fungicide application where fine drops are used to obtain good penetration and coverage, when there are adverse conditions it is possible to change to a tip with medium or maximum thick drops, in this case it is necessary to increase the application rate so as not to compromise coverage. . In low volume applications, if there is a change in droplet size, coverage is greatly compromised, which is why, in most situations, applicators choose to apply only in ideal conditions and not exceeding the maximum temperature limits (30°C) and wind (10km/h), as well as the minimum limits of relative humidity (50%) and wind (3km/h). In many cases, nighttime application becomes a great option, as long as the sprayer is equipped with suitable onboard electronics and an operator capable of performing nighttime operation, in addition to having adequate crop conditions. For example, a nighttime fungicide application may not be as effective as a daytime application, as the drops have greater difficulty reaching the lower third of the crop due to the positioning of the leaves. Various applications of herbicides, as well as insecticides in corn crops, are favored by nighttime conditions.

Another very high risk in the low volume technique is the sprayer operator. There are many cases where the technician responsible for the application has knowledge of the technique, properly calibrates the machine, stipulates the “optimal volume” for the application and failures still occur. In most of these cases, the only factor causing the failures is the machine operator, who, simply by deviating from the recommendations made by the person responsible, causes major losses in efficiency in the application process.

This shows that the low volume technique will only have excellent results if there is synergism between all the factors involved in the application.

FINAL CONSIDERATIONS 

 The low volume technique, considering applications below 40L/ha, as well as any type of application involving phytosanitary products, requires a lot of responsibility and professionalism. When reducing the application volume, the risks increase and this is why low volume is not a technique that can be adopted simply. It is necessary to have trained professionals, sprayers in excellent condition and with a phytosanitary product circuit prepared for low flows, high-quality spray tips, monitoring the arrival of drops at the target, monitoring weather conditions, knowledge of the interaction between the products in the spray solution and above all, know in detail the risks that this technique presents. On the other hand, once the technique and the factors surrounding it are mastered, safer and more effective applications can be achieved.

Rodrigo Alandia Roman, TeeJet Technologies

Article published in issue 147 of Cultivar Máquinas.