Use of adjuvants in the application of agricultural pesticides

Although some adjuvants promise different solutions in the application of pesticides, there is a considerable distance between the promises and their real functions. 

The history of agricultural adjuvants begins in the 18th century, when pine resins, wheat flour, molasses and sugar were used to promote physical and chemical changes in spray mixtures, which at that time were based on lime, sulfur, copper and arsenate. , and thus improve pest control.

Since then, adjuvants have been part of the spraying routine. Data from the “World Agricultural Adjuvants Market” report points to North America as controlling 40% of the adjuvants market. Brazil, along with all of Latin America and Asia, is considered an “unexplored” market with enormous potential for growth.

Agricultural adjuvants are powerful tools available to farmers; these products allow them to overcome factors that hinder the application of pesticides. The application process is quite complex and several factors interfere positively or negatively.

Adjuvants are any substances or compounds without a phytosanitary function, that is, without a pest or disease control function. Therefore, they should not be applied alone. Adjuvants must be added to the spray solution in order to facilitate application, increase effectiveness or reduce the risk of human and environmental contamination due to drift.

These products can be considered as activators and aim to directly improve the activity of the pesticide, mainly by increasing the absorption rate. Activating adjuvants include surfactants, vegetable oils, methylated seed oils, mineral oils, silicone derivatives, as well as nitrogen fertilizers.

Adjuvants can also be termed as useful. These act as facilitators of the spraying process by reducing the negative effects of spraying and do not directly influence the efficiency of the pesticide. Useful adjuvants include compatibilizing agents, depositors, dispersants, drift controllers, foaming agents, water conditioners, acidifiers, buffers, humectants, ultraviolet ray protectors and dyes.

Many times, even the manufacturers themselves are not aware of the functionality of their adjuvants, and there may be mistakes in the information contained in the product leaflet or label. Knowing this, some public research and teaching institutions (IAC, Unesp Botucatu and Jaboticabal, Uenp, UFU, among others) together with the private sector (Sabri Sabedoria Agrícola, Forplant, among others) have been pioneers in the development of methods to evaluate adjuvants. Because, despite being widely used, adjuvants do not have specific legislation, and there is no particular methodology for their evaluation.

Due to the number of variables involved in field studies, it is difficult to interpret results. Therefore, several researchers have advocated laboratory studies. For example, the production of drift-prone droplets during spraying may go unnoticed in field analyses, but not under controlled laboratory conditions. These laboratory studies are of great importance, as such drops, which are susceptible to drift in the field, may not even make a difference in the control of diseases, pests or weeds, but they can be fatal to pollinating insects such as bees, in addition to also contaminating water courses. water and urban areas.

 

TESTING ADJUVANTS

That said, researchers from the Faculty of Agricultural Sciences of Botucatu (Unesp) carried out a detailed study with 18 adjuvants commonly used in mixtures with pesticides in agricultural spraying. This study's main objective was to facilitate the choice of an adjuvant, its classification and even the registration of adjuvants.

In this study, the effect that adjuvants have on the surface tension of the drops, that is, on the spreading of the drops over the target, was evaluated; the change made by the adjuvants in the size of the sprayed droplets, as well as the potential risk of drift that the adjuvants provide.

Surface tension was determined by gravimetric method, by measuring the masses of sets of drops on a precision analytical balance. For droplet size analysis, a real-time droplet analyzer was used (Spraytec – Malvern Spraytec Real Time Droplet Sizing System), based on the laser beam diffraction technique. This droplet analyzer checks the DMV (Mean Volumetric Diameter), that is, the average size of the droplets produced by a spray nozzle. Finally, to analyze the potential risk of drift of the adjuvants, a wind tunnel was used, made of wood and producing the wind necessary for the tests by a fan. The system was sized to provide a wind flow of 7km/h.

To better understand this study, the researchers chose to present the data in tables with the name of the adjuvants, their composition, the function described on the product label by the manufacturer, the type of formulation and the effects caused by the adjuvants on surface tension, on the droplet size and drift potential.

Based on this study, it can be concluded that the adjuvants evaluated reduced surface tension in relation to water, that is, all products promote the spreading of sprayed drops over the deposited surface. This means that it is possible to cover the same leaf area by applying less water per hectare, consequently increasing the application yield, treating more hectares per hour, which has a series of advantages.

It was also possible to observe in this study that some adjuvants increase the size of the droplets. Increasing the size of the droplets has the positive side of reducing the drag of droplets by the wind, which increases the chances that the applied pesticide will reach the target. On the other hand, the increase in the size of the drops can be a disadvantage, as it impairs the penetration of the pesticide into the lower parts of the plant canopy or lower part, since larger drops, when reaching the top of the plants, suffer the umbrella effect. , with drainage.

DRIFT

Regarding drift, for many adjuvants there is a considerable distance between what is promised by manufacturers and their real functions. Some adjuvants that promise to reduce drift actually increase the drift potential of the application, that is, the application of pure water produces less drift than the application of water with these adjuvants.

However, what the farmer, agronomist or commercial representative must understand is that every adjuvant has its strengths and weaknesses. This way, when the strengths of an adjuvant are known, it is possible to exploit them to its advantage. Likewise, it is essential to know the weaknesses of an adjuvant to guard against possible harmful effects that may occur at the time of application.

The economic, environmental and social sustainability of the use of pesticides in agriculture depends on research, the transfer of information and the training of individuals involved in the spraying process, as there is no 100% application if the responsible professional is not trained.

Henrique Borges Neves Campos, Sabri – Agricultural Wisdom

Article published in issue 164 of Cultivar Máquinas.