Fungicides: classification, properties and applications

Fungicides are a group of chemical preparations designed to destroy or prevent the development of pathogenic fungi — the causative agents of diseases in agricultural plants. Fungal infections can destroy a significant part of the harvest, deteriorate product quality and cause economic damage, so fungicides are a critically important element of the plant protection system. Their range is constantly expanding, and classification is becoming more complex as new active ingredients and mechanisms of action appear.

Classification by Nature of Action

By the nature of action on pathogens, fungicides are divided into two main groups: protective (prophylactic) and curative (therapeutic, eradicant).

Protective fungicides prevent plant infection by acting on the pathogen before it penetrates the tissues. They suppress mainly the reproductive organs of the fungus and are applied in periods preceding the mass spread of infection. Protective contact preparations do not penetrate the plant in quantities capable of suppressing the pathogen and act upon direct contact with it; their duration of action depends on meteorological conditions and requires regular repeated treatments.

Curative fungicides act on the vegetative and reproductive organs of the pathogen that has already penetrated the plant tissues and can stop the development of the disease. This group includes many systemic preparations that penetrate the plant and move through its vascular system.

Classification by Mobility in the Plant

Modern classification takes into account the ability of the active ingredient to penetrate plant tissues and move through them. Contact fungicides remain on the plant surface and act upon direct contact with the pathogen; they have a broad spectrum of action (multi-site activity), affecting several biochemical reactions in fungal cells simultaneously. Penetrating (local) fungicides overcome the cuticle and are absorbed into underlying tissues but remain in the application zone; these include translaminar compounds capable of moving to the opposite side of the leaf.

Acropetal (xylem-mobile) fungicides move upward through the plant along the water potential gradient. Systemic (phloem-mobile) compounds move both acropetally and basipetally, i.e., possess truly systemic properties. It is systemic preparations that provide protection for new growth and organs remote from the application site.

Active Ingredients and Chemical Classes

The modern range of fungicides includes several main chemical classes. Triazoles (DMI fungicides) inhibit ergosterol biosynthesis by blocking C-14 demethylation; they have systemic action and are widely used on cereals. Strobilurins (QoI fungicides) inhibit respiration by blocking complex III in mitochondria and are characterised by a broad spectrum of activity. Carboxamides (SDHI fungicides) also disrupt respiration by acting on complex II; they are effective against a wide range of pathogens and are often used in mixtures with triazoles and strobilurins.

Other important classes include phenylamides (metalaxyl, mefenoxam), active against oomycete pathogens, benzimidazoles (carbendazim), dithiocarbamates, morpholines and anilinopyrimidines. Combined preparations containing active ingredients from different classes allow the spectrum of activity to be expanded and the risk of resistance to be reduced.

Formulation Types

Fungicides are produced as emulsifiable concentrates (EC), suspension concentrates (SC), water-dispersible granules (WG), wettable powders (WP), soluble concentrates (SL) and other forms. Specialised forms — flowable concentrates for seed treatment (FS) — are used for seed treatment, ensuring uniform coating and retention of the active ingredient on the seed surface. The choice of formulation is determined by the properties of the active ingredient, the application method (spraying growing plants, seed treatment, soil treatment) and safety requirements.

Applications

Fungicides are used to protect cereals, industrial, vegetable, fruit and berry crops, grapes, potatoes and other plants. The main application methods include seed treatment (pre-sowing treatment), spraying growing plants during the growing season and soil treatment. Protective preparations are applied before symptoms of the disease appear, curative ones — at the first signs of infection. The effectiveness of fungicides depends on the correct choice of active ingredient, timing of treatment, application rate and quality of application.

Safety and Regulatory Framework

Fungicides, like other pesticides, are subject to state registration and standardisation. General requirements are established by GOST R 51247-99, safety requirements for application — by GOST 12.3.041-86. According to the degree of hazard, substances are classified according to GOST 12.1.007-76 into four classes. When working with fungicides, personal protective equipment must be used, application regulations, waiting periods and environmental protection measures must be observed.

Market and Trends

Fungicides occupy the second most important segment of the crop protection market after herbicides. In the structure of domestic production, they account for about 16–17% of output, while the range is constantly updated through the emergence of new active ingredients and combined preparations. Key trends are related to the problem of pathogen resistance, which stimulates the development of molecules with new mechanisms of action and the rotation of chemical classes. Interest in biological fungicides and low-environmental-impact preparations is growing. Organising supplies of fungicides, including the selection of the active ingredient and formulation type for a specific crop and pathogen spectrum, requires an individual approach.