The importance of the right adjuvant for greater efficiency in application technology

Increasingly present in spraying, adjuvants are important tools in the preparation of syrup for those who want to ensure maximum efficiency in the control of insects, pathogens and weeds.

By definition, an adjuvant is considered to be any product that, when mixed in the preparation of the phytosanitary mixture, is capable of modifying or improving the action of the fungicide, herbicide or insecticide. This positive effect may be due to the improvement in the stability of the spray solution inside the sprayer tank, in the formation and path of the droplet between the sprayer and the target and in the behavior of the droplet when it is deposited on the leaf surface.

There are many factors capable of compromising the quality of the application and interactions within the sprayer tank. In this initial and very important stage, the quality of the water (first factor) must be considered very carefully before preparing the solution.

Depending on the water collection source and the time of year, characteristics such as pH and hardness can vary considerably. Water is considered “Hard” when there are divalent cations expressed in calcium and magnesium carbonate equivalents greater than 321 ppm. This analysis is very important and can be done on the property through collection and sent to laboratories that commonly carry out soil analysis. This collection and shipping is important to be repeated at four times of the year, at the beginning of summer, autumn, winter and spring, as depending on the rainfall regime the concentration of cations in the water can vary. If the water used for spraying has a value well above 321 ppm (“Hard” water), the products to be mixed to make the spray, such as fungicides, insecticides and especially herbicides, may partially or completely lose their effectiveness. In this scenario, it is essential to use adjuvants to correct the quality of the water to be used in preparing the syrup. Ammonium sulfate and products composed of non-ionic surfactants are the main options for correcting water hardness, without having an effect on its pH. Acids such as phosphoric acid, in addition to reducing hardness problems, also reduce the pH range of the water.

It is very common for water with high hardness to also demonstrate pH values ​​above 7, when this hardness is due to alkaline earth metals such as Magnesium and Calcium. Almost always, if the water has a pH value above 7, there may be hardness problems. However, water hardness problems can occur even when it has a pH value below 7. In this case, the source of hardness is due to transition metals such as Iron, Copper, Zinc, Manganese, among others. The pH of the water, in turn, also plays an important role in the quality of the syrup, as if it is above 7, most of the phytosanitary products used in preparing the syrup may suffer degradation through the process called alkaline hydrolysis. For all intents and purposes, the best pH range for most products today is 5 to 7, in situations where the water is not classified as hard.

In addition to water correction, the use of adjuvants can improve mixtures of oil-based products in water, a process called “emulsion”, and the mixture of water-insoluble products, such as most fungicides, through a process called “suspension”. ” in water. For both processes, adjuvants can be added to the syrup to benefit the stability of the mixture. Such adjuvants are entirely composed of surfactants. These vary according to the type of surfactant used. A very clear example of a surfactant used in our daily lives is kitchen detergent. This contains surfactants capable of mixing tap water with the grease on dishes and cutlery. Naturally, water does not mix with oils and fats, but when we mix detergent, the water can mix and remove all the dirt. This occurs because surfactants are molecules that have an affinity for both water and oils and fats. As a result, they function as a bridge between water and oils and fats. Each adjuvant contains a specific type of surfactant that performs different functions, in addition to just reducing the surface tension of the mixture. In some cases, the use of adjuvants can prevent incompatibility problems between products used in the tank, or even facilitate the process of cleaning product residues that can accumulate in the sprayer.

Another function widely performed by adjuvants is to improve the droplet pattern formed by the nozzles and to manage drift during the transport of the drops, leaving the nozzles, until they effectively reach the target.

Starting with the effect they can have on the nozzles, some adjuvants can reduce or increase the size of the sprayed droplets. More importantly, some adjuvants can improve droplet size uniformity in certain nozzles. A clear example of this phenomenon occurs for nozzles equipped with air induction tips, where the use of surfactant adjuvants can increase and improve the uniformity of the droplets generated, by facilitating the mixing of air in the droplets produced. The use of oils in this situation can disrupt the uniformity of the drops and even increase losses due to drift.

The use of adjuvants capable of increasing the viscosity and surface tension of sprays, such as polymers, oils and gums, can increase the size of the droplets produced by the nozzles and reduce drift problems during spraying in adverse weather situations. It is very common to find this effect in oil-based adjuvants, especially mineral ones, to the detriment of vegetable ones, as they have longer chains. Additionally, the oils increase the lifespan of the droplets until they evaporate, providing more time until they can reach the target.

In addition to providing a stable effect on the mixture in the tank and in the production and transport of droplets, adjuvants can also play a fundamental role in the behavior of the droplet deposited on the target.

When the drop arrives at the target, which is a plant surface, some phenomena may occur, depending on the size of the drop. Large droplets can hit the target, ricochet and run to the ground, or they can fragment into smaller drops that, in reaction to the impact, can be thrown off the leaf. The use of surfactant adjuvants in this case reduces the binding energy of the molecules, causing the droplets to spread when they reach the target, avoiding problems of ricochet and droplet fragmentation. Furthermore, surfactants can improve the affinity of droplets with the leaf surface, reducing their contact angle and spreading. This effect is also important in the case of small droplets that are sprayed on hairy leaf surfaces. In this case, without the use of adjuvants, most of the fine drops are retained in the hair, without being able to effectively wet the leaf surface.

Some surfactant adjuvants, such as the organosilicone class, reduce surface tension so much that they can improve the absorption of certain products by the leaves, as they allow the scattered contents of the drops to enter the leaf stomata. Oil-based adjuvants, such as mineral, vegetable and methylated oils, are now essential tools for the use of fungicides, as they improve the absorption of the active ingredient by the leaf. However, when it comes to oils, the absorption process occurs through the leaf cuticle, where there are waxes and cutin, so that the oils dissolve part of these waxes, opening the way for the active ingredient to enter the leaf surface. Care must be taken when using these adjuvants, as in doses higher than recommended or in high light situations, there may be adverse effects such as phytointoxication, as the wax that protects the leaf is temporarily disrupted.

Knowing the different specificities of adjuvants, simply choose which one can contribute most to the spraying to be carried out, considering the types of product, sprayer, target and weather conditions during application.