An Introduction to Common Types of Fungicides and Their Modes of Action

Fungicides, also known as biocides, bactericidal and algicidal agents, microbicides, etc., generally refer to chemical preparations that can effectively control or kill microorganisms in water systems - bacteria, fungi and algae. Internationally, they are usually the general term for agents used to control various pathogenic microorganisms. So what are the common fungicides? What are their modes of action?

I. Zineb

1. Mode of action: The technical material is a grayish-white or pale yellow powder with a rotten egg odor. It is a protective fungicide with strong contact-killing action against various pathogens such as downy mildew, late blight and anthracnose fungi.

Its active ingredient is easily oxidized in water into an isothiocyanate compound, which strongly inhibits enzymes containing -SH groups in the pathogen's body, and directly kills pathogen spores, preventing pathogen invasion, and is safe for crops. Application should be timed at the early stage of disease onset, and its residual period is relatively short. It is low in toxicity to higher animals and irritates the skin and mucous membranes.

2. Targets of control and application techniques: At the early stage of disease onset, spray with an 80% wettable powder at 500 times dilution to control various diseases of cucurbits such as damping-off, seedling blight, angular leaf spot, fusarium wilt, anthracnose and downy mildew. Spray again after 7-10 days.

II. Mancozeb

1. Mode of action: Mancozeb is a broad-spectrum protective fungicide, and its mechanism of action is to inhibit the oxidation of pyruvic acid in the fungal body. The technical material is a grayish-yellow powder, and it also easily decomposes when exposed to moisture at high temperatures. It is low in toxicity to higher animals, and has a certain irritating effect on human skin and mucous membranes. It is toxic to fish; at the tested doses, no "three-cause" phenomena (carcinogenicity, teratogenicity, mutagenicity) were found.

2. Targets of control and application techniques: To control anthracnose, phytophthora blight, downy mildew, leaf spot and black spot of cucurbits, spray mancozeb at the early stage of disease onset, then spray once more after 7-10 days, for a total of 2-3 sprays.

III. Thiophanate-methyl (Topsin-M)

1. Mode of action: Thiophanate-methyl is a highly effective, low-toxicity, low-residue, broad-spectrum, systemic fungicide with both protective and curative action. Its mechanism of action is that when the agent is sprayed on the plant surface and absorbed by the plant, it is decomposed within the plant through a series of biochemical reactions into methyl benzimidazole-2-yl carbamate (i.e. carbendazim).

It interferes with the formation of the spindle in the mitosis of the fungus, causing the germ tube grown from germinating pathogen spores to become twisted and abnormal, and the germ tube cell wall to become distorted, etc., thereby preventing the pathogen from growing normally and achieving a fungicidal effect. The pure product is colorless crystals, difficult to dissolve in water, and stable to acids and bases. It is low in toxicity to higher animals, low in irritation to skin and mucous membranes, low in toxicity to fish, and safe for plants.

2. Targets of control and application techniques: Use a 70% wettable powder at 500-700 times dilution. It has good preventive and curative effects against gray mold, powdery mildew, anthracnose, brown spot, leaf mold, etc.; spray once every 7-10 days, for a total of 2-3 sprays. It can also be used for seed treatment at 0.3%-0.4% of the seed weight; or a 70% wettable powder at 500 times dilution can be used for root drenching, which also gives good results against fusarium wilt.

IV. Chlorothalonil

1. Mode of action: Chlorothalonil is a broad-spectrum fungicide that can replace organic sulfur and copper preparations. It has a preventive action and no systemic translocation action. Its mechanism of action is to act on the 3-glyceraldehyde phosphate dehydrogenase in fungal cells, binding with the cysteine-containing protein in the enzyme, destroying the vitality of the fungus, so that the metabolism of the fungal cell is disrupted and it loses its vital force.

Chlorothalonil has good adhesion on the plant surface, is not easily washed off by rain, has a stable efficacy and a long residual period. The pure product is white crystals with no odor; the technical grade product is yellow crystals with a slightly pungent odor, insoluble in water, slightly soluble in organic solvents such as acetone, stable at room temperature, stable to general acids, bases and ultraviolet light, but not resistant to strong acids, resistant to rain erosion, and non-corrosive. It is low in toxicity to higher animals and highly toxic to fish.

2. Targets of control and application techniques: To control downy mildew, anthracnose and phytophthora blight of cucurbits, at the early stage of disease onset, spray with a 75% wettable powder at 500-800 times dilution, with a spray volume of 1,000 kg per hectare, and spray once more after 7-10 days; a 500-600 times dilution can control diseases such as damping-off and seedling blight at the seedling stage.

V. Ridomil (metalaxyl, Apron, metalaxyl-M)

1. Mode of action: Ridomil is a systemic fungicide with upward and downward translocation, with protective and curative action. When the agent is sprayed on plants, it can be absorbed by the plant's seeds, roots, stems and leaves and translocated to all parts, so it has a dual protective and curative action.

The pure product is white crystals, easily soluble in water and various organic solvents, stable under neutral and acidic conditions, easily decomposes and loses efficacy when encountering alkali, and has a residual period of 10-14 days. It is low in toxicity to higher animals; under test conditions no "three-cause" phenomena were seen in animals; it is low in toxicity to bees, but irritates the eyes and skin.

2. Targets of control and application techniques: To control diseases caused by downy mildew, phytophthora and pythium fungi of cucurbits. When the disease first appears in the field, spray with a 25% metalaxyl wettable powder at 600-800 times dilution, then spray once more after 10-15 days, for a total of 2-3 sprays; if rainy weather persists for a long time, the number of applications should be increased accordingly. Use a 35% seed dressing agent for seed disinfection, dressing at 0.2%-0.5% of the seed weight.

VI. Tolclofos-methyl

1. Mode of action: This agent is a broad-spectrum systemic fungicide suitable for controlling soil-borne diseases, mainly exerting a protective action; it has strong adsorption, is not easily lost, and has a relatively long residual period.

The pure product is white crystals, and the technical material is a colorless to light brown solid, almost insoluble in water, non-flammable, non-explosive, and easily soluble in various organic solvents. It is relatively stable to light, heat and moisture, and has good storage stability. It is low in toxicity to higher animals and safe for bees and fish.

2. Targets of control and application techniques: It has strong killing activity against various pathogens such as Deuteromycetes, Basidiomycetes and Ascomycetes, and is used to control soil-borne diseases such as Rhizoctonia and Sclerotium. To control seedling blight of cucurbits, soak seeds in a 20% emulsifiable concentrate at 250 times dilution for 30 minutes; after sowing, spray the soil surface again with the same concentration of the solution.

VII. Copper hydroxide

1. Mode of action: The active ingredient is a blue gelatinous or amorphous blue powder, composed of spherical needle-shaped particles of hexacarbon copper ions, which can quickly adhere to the crop surface and has a lasting efficacy. It is low in toxicity to higher animals. It is a broad-spectrum fungicide that works by releasing copper ions to evenly cover the plant surface, preventing fungal spores from invading and thus providing protection; when the cells of the pathogen contact the copper ions, they are killed, while the plant is unaffected, so it is a residue-free, pollution-free pesticide.

2. Targets of control and application techniques: Copper hydroxide can control fungal and bacterial diseases on many crops, and is suitable for various diseases of cucurbits such as leaf spot, anthracnose, early (late) blight, seedling blight and downy mildew.

At the early stage of disease onset, spray with a 53.8% dry suspension at 1,000 times dilution, or a 77% formulation at 500-1,000 times dilution. Because of its excellent solubility, diffusibility and suspension, applying it once more after about 10 days can control the spread of the disease; under unfavorable climatic conditions, multiple applications should be considered. To control fusarium wilt, drench the roots with a 77% formulation at 500-600 times dilution.

VIII. Copper-ammonia complex (tetraamminecopper sulfate)

1. Mode of action: The pure product is a dark blue liquid. It is a highly effective, low-toxicity, low-residue, broad-spectrum fungicide with relatively strong systemic action, mainly exerting a protective action.

2. Targets of control and application techniques: To control fusarium wilt of cucurbits, drench the roots with a 23% aqueous solution at 250-300 times dilution; to control gummy stem blight, phytophthora blight and bacterial angular leaf spot, spray with a 14% aqueous solution at 250-300 times dilution. Apply once every 7-10 days, for 2-3 consecutive applications.

IX. Kangku Ning (Kangku Ling, copper-ammonia complex with zinc)

1. Mode of action: Kangku Ning has a protective action and a certain permeability, but its systemic curative effect is not ideal; applied to crops it can supplement some trace elements and enhance disease resistance, while also acting directly on the pathogen, giving good control of fusarium wilt of cucurbits. This agent appears as a dark blue concentrated solution, generally stable, and tends to form a precipitate under alkaline conditions. It is low in toxicity to mammals.

2. Targets of control and application techniques: At the early stage of fusarium wilt occurrence, use a 25.9% aqueous solution at 500-600 times dilution, drenching 250 ml per plant, or use 1,500 ml of the 25.9% aqueous solution per hectare plus 750 kg of water for spraying. Depending on the disease condition, apply at intervals of 7-10 days for 3-4 consecutive sprays; alternatively, use a 20% aqueous solution at 400-600 times dilution, drenching 250 ml per plant, and depending on the disease development, drench once more after 7-10 days, for 3-4 consecutive drenches.

X. Carbendazim

1. Mode of action: Carbendazim is a broad-spectrum, low-toxicity, systemic fungicide with protective and curative action. Its mechanism of action is to interfere with the formation of the spindle in the mitosis of the fungus, thereby affecting cell division. The pure product is white crystals, soluble in dilute hydrochloric acid and acetic acid, and forms the corresponding salt, which is Fungicide Bao or Rongjun Ling. It is low in toxicity to higher animals, very low in toxicity to fish and bees, and safe for plants.

2. Targets of control and application techniques: It is effective against many Ascomycetes and Deuteromycetes. To control various diseases of cucurbits such as fusarium wilt, gummy stem blight, anthracnose, powdery mildew, downy mildew and leaf spot, spray with a 50% wettable powder at 600-800 times dilution at the early stage of disease onset, spraying once every 7-10 days, for a total of 2-3 sprays. Alternatively, dress seeds at 0.1%-0.3% of the seed weight, or drench roots with a 500 times dilution, pouring 250 ml per plant, or disinfect the soil with 6-8 grams per square meter of seedbed.

The above is an introduction to the types of common fungicides and their modes of action. Generally, when using fungicides, the instructions provide a recommended concentration, and you can use them according to the instructions, but it is best to apply them at the concentration proposed by the local plant protection technical department on the basis of efficacy trials. In dry or hot summers, the concentration used should be reduced to avoid phytotoxicity.

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