Effect and importance of using protective fungicides

Fungicides are chemical compounds that can be classified as eradicant, protective, systemic and mesostemic. Protectors are effective when applied before the introduction of the fungus into the host's tissues, forming a barrier that prevents the penetration of fungi by inhibiting the germination of spores, while systemic ones are absorbed by the plant and moved to other parts, inhibiting the proliferation of the pathogen. .

The successful control of a protective fungicide not only depends on its fungitoxicity, but also on a series of other variables such as adhesiveness, tenacity, persistence and, fundamentally, the application technology used.

The quantity of drops (drop density) and quality (drop spectrum) of the fungicide sprayed, deposited and its adhesiveness to the plant should result in a uniform and homogeneous distribution of the recommended amount of active ingredient. Thus, the characteristics of a fungicide formulation are determining factors within a series of variables that guarantee the effectiveness of a product.

Among the factors inherent to the formulation that are extremely important for the applicability of the product are particle size, wettability and the composition of the surfactants used in the product, which can directly interfere with its tenacity.

Tenacity is the relative ability of a fungicide to remain adhered to the surface where it was applied, in other words, it is resistance to the effects of adverse weather conditions. Once applied to the plant surface, a chemical compound must be able to remain active for a certain time. To do this, it must have tenacity, which can also be defined as the ability to resist volatilization, sublimation, hydrolysis and washing by rain or irrigation.

Fungicides that have high tenacity also have longer residual power. If a chemical adheres strongly to the leaf surface (tenacity) it is possible that this effect can last for a long time (persistence).

The action of dew and rain is probably the main factor that reduces the tenacity of fungicides. In the case of protective fungicides, this characteristic becomes one of the most important, as they must persist for a long period on the treated surface without being removed or decomposed.

According to Azevedo, 2003, protective fungicides from the dithiocarbamate chemical group have a removal percentage of 78% (SC formulation) to 85% (WP formulation) after the application of simulated rain and protectors from the inorganic chemical group have 43% (SC formulation) to 53% (WP formulation) removal after simulated rain, demonstrating the importance of the formulation in the persistence of a protective fungicide.

There is a general consensus that protective fungicides are important tools for crop health, contributing greatly to disease control and being fundamental in resistance management. Over the years, several advances have been achieved in improving the characteristics of the formulations of these products, mainly the introduction of less toxic and environmentally friendly compounds onto the market.

However, despite the development time, all the efficacy and practicality tests, the regulatory requirements and all the recommendations for the correct use of fungicides, situations in the field do not occur as they should, and the problems that have arisen are not few.

Among the main problems we can mention the use of prohibited products or without due regulation, degradation products or metabolites (this fact is known worldwide and serves as an example of the precautions we must take when recommending some chemical groups), persistence in the environment environment and maximum tolerance limit (residues).

In practice, it is difficult to find all the desirable characteristics in a single product, however, the choice must be based on the fungicide that presents the greatest number of benefits. In short, the majority of products are chosen with known and proven effectiveness, without environmental problems and which economically satisfy the user's requirements.

This article was published in issue 182 of Cultivar Grandes Culturas magazine. Click here to read the edition.