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fungicide (fŭnˈjəsīdˌ, fŭngˈgə–), any substance used to destroy fungi. Some fungi are extremely damaging to crops (see diseases of plants), and others cause diseases in humans and other animals (see fungal infection).
Surface fungicides, which keep harmful fungi from penetrating the tissues of a plant, include inorganic and organic compounds. Sulfur compounds, long used on plants, have been supplemented for some time by other chemicals, especially by compounds of copper, such as Bordeaux mixture. After 1945, organic salts of iron, zinc, and mercury were synthesized as fungicides. Most post-1965 fungicides are systemic, acting directly on fungal cells. Antifungal drugs, such as miconazole and terbinafine, are used for human fungal infections.
Plant fungicides are usually applied by spraying or dusting, but some types are applied to seeds and soil for the destruction of vegetative spores. Fungicides used on wood, including creosote, prevent dry rot, and certain compounds are used to make fabrics resistant to mildews. Most agricultural fungicides are preventive; those applied after infection are called eradicant, or contact, fungicides.
In the United States, fungicides are governed by the 1972 federal Environmental Protection and Control Act. They must be registered with the Environmental Protection Agency and must conform to specifications. They must control the disease without injuring the plant and must leave no poisonous residue on edible crops. Antifungal drugs are approved by the Food and Drug Administration.
See also pesticide.
in agriculture, any one of several chemical substances capable of completely (fungicides proper) or partially (fungistats) suppressing the development of disease-causing fungi in crops; one of the groups of pesticides.
Fungicides may be classified as inorganic or organic, depending on their chemical composition. Inorganic fungicides include compounds of sulfur (lime-sulfur solution, sulfur powder, sulfur colloid), copper (copper sulfate, copper oxychloride), and mercury
|Table 1. Principal organic fungicides used in the USSR|
|Preparation||Chemical name||LD50 (mg per kg body weight)||Form||Purpose|
|Vitavax ...............||5,6-dihidro-2-methyl-1,4-oxathiin-3-carboxanilide||3,200||75% wetting powder||To combat smut and Rhizoctonia disease in grain crops|
|Granozan ...............||Ethylmercuric chloride||26.4||1.8–2.3% powder||To treat seeds of grain crops, flax, sugar beets, against smut, fusarium wilt, anthracnoses|
|4,6-dinitro-o-cresol (DNOC) ...............||Sodium or ammonium salt of 2-methyl-4,6-dinitrophenol||50||40% water-soluble powder||To combat a complex of diseases affecting fruit and berry crops|
|Captan ...............||N-trichlorome-thylthio-3a,4,7,7a-tetrahydrophthalimide||9,000–15,000||0.25–0.6% suspension||To treat apple and pear trees against scab|
|Karathane ...............||2,4-dinitro-6-(2-octyl)-phenyl crotonate||980||25% wetting powder||Effective against powdery mildew on fruit and berry crops and cucumbers|
|Zineb ...............||Zinc ethylenebis (dithiocarbamate)||5,200||Slightly watersoluble powder||Effective against downy mildew of grapes, late blight of potato, southern blight of tomato|
(mercuric chloride, or corrosive sublimate). Organic fungicides (see Table 1) constitute a larger group; they include carbamic acid derivatives (zineb, kuprosin-1, poiimartsin, polikarbatsin), phthalimides (captan, ftalan), quiñones (Phygon), dinitroalkal-phenol esters (Karathane), organomercury compounds (granozan, Mercurohexane), oxathiin compounds (Vitavax), and benzimidazole-based preparations (benomyl). Depending on their effect on the causative agent, fungicides may be classified as protectants or eradicants. Protectants prevent contamination of the plant or stop the development and spread of the causative agent at the site of infection before contamination can occur, primarily by acting on the fungus’s reproductive organs; the majority of fungicides are of this type. Eradicants act on the mycelium, reproductive organs, and wintering forms of the causative agent, which is destroyed after contamination of the plant.
Fungicides are used in various ways: as seed-treating materials to combat diseases in which the causative agents are propagated with seeds or are found in the soil; as soil-treatment preparations that destroy soil-borne causative agents (particularly effective in hotbeds and greenhouses); as preparations for the treatment of plants during dormancy, when they destroy the wintering forms of the causative agent (used in early spring before blossoming, in late autumn, and in winter); as preparations for treatment during the vegetation period (mainly preparations with a protective effect, applied in summer); and as preparations for spraying and fumigating storehouses, especially granaries and vegetable cellars.
Fungicides may be either contact (local) or systemic, depending on their distribution within the plant tissue. During treatment, contact fungicides remain on the surface and destroy the causative agent upon contact. Some have a local, subsurface effect; for example, they may penetrate the hull of the seed. The effectiveness of contact fungicides depends on the length of action, the rate of application of fungicide, surface contactness, photochemical and chemical stability, and weather conditions. Contact fungicides have been used in agriculture since the late 19th century. Systemic fungicides (therapeutants) penetrate the plant tissues, circulate through the vascular system, and suppress development of the causative agent by direct action or by means of metabolism in the plant. Their effectiveness is primarily determined by how rapidly they penetrate and, to a lesser degree, by meteorological conditions. Systemic fungicides came into use in the 1960’s, much later than contact fungicides. The division of fungicides into groups is arbitrary. For example, large doses or higher concentrations of preventive preparations may have a curative effect; thus, seed-treating materials may also destroy causative agents of disease in the soil.
There are various mechanisms involved in the action of fungicides on causative agents. For example, in the treatment of diseased plants with copper sulfate, the copper penetrates the mycelium or spores of the fungus and causes the coagulation of protoplasm; 4,6-dinitro-o-cresol dissociates the processes of respiratory phosphorylation, and zineb blocks enzyme activity. The spectrum of fungicidal activity also varies and depends mainly on the ability of the causative agent to absorb one or another preparation. Some fungicides, such as organomercury preparations and carbamic acid derivatives, suppress the causative agents of many plant diseases; others have a limited spectrum of activity (for example, Vitavax is toxic principally to Basidiomycetes, which cause smut and Rhizoctonia disease), and still others exhibit exclusive specificity (hexachlorobenzene, used against covered wheat smut, and copper preparations, used against downy mildew).
Application methods for fungicides include spraying and dusting of plants and soil, seed treatment, and fumigation of seeds and storehouses. The fungicides may be prepared as dusts, emulsions, suspensions, wetting powders, or aerosols. Systematic use may reduce the effectiveness of some fungicides, owing to the formation of resistant strains of fungi. This can be prevented by strictly observing the proper rates of application and by alternating fungicides. Fungicide production is constantly increasing as a result of the great importance of fungicides to agriculture.
The toxicity of fungicides for plant organisms depends on the chemical nature and concentration or dose of the preparation, the age of the plants, the anatomy and morphology of the plant tissues, the plant’s metabolic characteristics, weather conditions, and other factors. The treatment of vegetating plants with 4,6-dinitro-o-cresol or a nitrafenol, application of which is permitted only during dormancy, substantially lowers yield. Doses or concentrations of such fungicides as butyric solutions of Meta-fos or ftalan in excess of recommended amounts may induce burns and tissue necrosis. Some fungicides, such as hexachlorane derivatives, can contaminate plants and their products and impart a specific unpleasant odor and taste. Small doses of certain fungicides stimulate plant development.
Most fungicides are slightly toxic to warm-blooded animals and man; the lethal dose 50 ranges from 500 to 11,000 mg per kg of body weight. Work with fungicides is governed by safety rules, and the use of individual safety devices, such as protective clothing, protective footwear, and respirators, is mandatory. Most fungicides are not hazardous or only slightly hazardous to insects, such as bees. Certain fungicides, for example, organochlorine compounds, have a high stability in biological media and decompose slowly, which creates a danger of their accumulation, including in plants and plant products; permissible residual quantités are usually 0.05–2 mg per kg of product. Some fungicides affect all living organism they contact and may prove harmful to useful microorganisms, insects, birds, and fish; systematic application may lead to the disturbance of biological equilibrium in biocenoses.
In order to avoid the adverse effect of fungicides on the environment, strict observance of the instructions for fungicide use is essential, especially with respect to doses and periods of treatment. In many countries, including the USSR, the use of fungicides is controlled by law.
REFERENCESKhimicheskaia zashchita rastenii. Edited by G. S. Gruzdev. Moscow, 1974.
Sistemnye fungitsidy. Moscow, 1975. (Translated from English.)
E. I. ANDREEVA