What is a Fungicide?
Agents that kill pathogens or inhibit their growth without interfering with the normal growth of the plant are collectively known as fungicides. With the development of fungicides, further subcategories have emerged, such as bactericides, virucides, and specific fungicides targeting fungi.
Classification by Mode of Use
√ What is a Protectant?
Protectants are applied to the plant or its surrounding environment before pathogenic microorganisms make contact with or penetrate the plant. They inhibit the germination of pathogen spores or kill them upon germination, thereby shielding the plant from harm. This mode of action—whereby pathogens are killed upon contact with the chemical residue on the plant surface—is known as a protective effect. Agents exhibiting this action are called protectants. Examples include Bordeaux mixture, zineb, copper sulfate, copper oleate (Green Copper), mancozeb, and chlorothalonil.
√ What is a Curative Agent?
These are used when pathogenic microorganisms have already invaded the plant, but symptoms have not yet fully manifested (the plant is in the incubation period). The chemical penetrates the plant epidermis into the internal tissues; through translocation, diffusion, or the production of metabolites, it kills or inhibits the pathogen, halting further damage and allowing the plant to recover. Agents with this curative function are known as curative agents. Examples include thiophanate-methyl, carbendazim, and kasugamycin.
√ What is an Eradicant?
These agents are applied after the plant has become infected and act by directly killing pathogens that have already invaded the plant. Agents with this eradicating action are called eradicants. Examples include arsenic-based fungicides (e.g., methanearsonate), sodium pentachlorophenate, and lime sulfur.
Classification by Translocation Characteristics
√ Systemic Fungicides
Systemic fungicides can be absorbed into the plant through leaves, stems, roots, or seeds. Once inside, they move via translocation through plant fluids, diffuse, persist, or produce metabolites. They can control diseases where pathogens have penetrated deep into plant tissues or seed endosperm, protecting crops from infection or treating plants that are already infected; thus, they possess both curative and protective properties. Examples include carbendazim, prochloraz, thiophanate-methyl, metalaxyl, fosetyl-aluminum, thiophanate-methyl, fenaminosulf, triadimefon, metalaxyl-copper, oxadixyl-mancozeb, and carboxin-thiram mixtures.
√ Non-systemic fungicides
Non-systemic fungicides are agents that cannot be absorbed, translocated, or retained within the plant. Most fungicide varieties fall into this category; they are relatively economical and less likely to induce pathogen resistance. However, most offer only protective action and cannot control diseases that have already penetrated the plant tissue. Examples include zinc sulfate, copper sulfate, dodine, chlorothalonil, sulfur-based mixtures, wood ash, Bordeaux mixture, mancozeb, and thiram.
Classification by mode of action
1. Interfering with the pathogen’s respiration process and inhibiting energy production.
2. Interfering with the biosynthesis of vital cellular components such as proteins, nucleic acids, and sterols.
Resistance issues and application strategies
Protective fungicides generally have a broad spectrum of activity but lower potency. Systemic fungicides typically possess higher potency but a narrower spectrum, with some varieties exhibiting specific toxicity toward certain pathogens. Because systemic fungicides often target a single site within the pathogen, resistance can easily arise through genetic mutation.
To prevent or delay the development of resistance, appropriate protective and systemic fungicides can be applied in combination, or different fungicides can be rotated; this approach leverages the strengths of each to achieve superior control.
Application methods—such as seed treatment, foliar spraying, soil treatment, or fumigation—should be selected based on the disease’s characteristics and the crop’s cultivation system. We welcome your comments!
