单词 | herbicides | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
释义 | herbicidesherbicidesHerbicidesHerbicideschemical substances that are used to destroy vegetation. Depending on the type of their action on plants, herbicides are divided into contact types, which kill all forms of plants, and selective types, which strike certain kinds of plants and do not harm others. Contact herbicides are used to destroy vegetation around industrial buildings, at felling areas, airports, railroads, and highways, under high-voltage power lines, and in drainage channels, ponds, and lakes; selective herbicides are used to protect cultivated plants from weeds (chemical weeding). The division is arbitrary, since in the majority of cases, depending on concentration, rate of distribution, and conditions of use, the same substance can be either contact or selective. For example, in doses of 1.2-1.6 kg of active substance per hectare (kg/ha), chlorphenydim and dichlorphenydim destroy annual weeds in cotton crops, whereas at higher doses they affect all plants. The selectivity of the action of a herbicide is determined by its chemical composition, the form and doses of the preparation, the method and times of crop treatment, the growth phases and the anatomical and morphological structures of the plants, and soil and climatic conditions. A distinction is made between biochemical and topographical selectivity of herbicides. In biochemical selectivity the action of the herbicide is based on its interference with plant metabolism. In most cases biochemical selectivity is manifested as the nonuniform conversion of the herbicides. In resistant plants the herbicide is blocked by the cell components and is decomposed to nontoxic compounds or to toxic compounds, with their subsequent inactivation; in sensitive plants, it either depresses the plant (inhibiting action) or under the action of cellular components is decomposed to toxic compounds that kill the plant. For example, in resistant maize, simazin and atrazin are decomposed to nontoxic compounds; in plants that are sensitive (rootstock perennial weeds), they are not decomposed. The topographical selectivity of herbicides is associated with differences in anatomical and morphological structure and in the method of application. The use of 2M-4Kh in flax sowings is based on a sensitivity of this type. Flax, unlike many dicotyledonous weeds, has low sensitivity to 2M-4Kh when given large-drop spraying of this herbicide in the arborescent phase, since the solution drops run off the narrow leaves, which are covered with a waxy deposit and are placed at a sharp angle to the stem. Plants that are thickly covered with fine hairs, which do not become impregnated, and plants with thick cuticula of low permeability and a small number of stomata, are more resistant to herbicides. For example, varying sensitivity to herbicides
even of plants of the same species is explained by topographical selectivity: plants that grow in the shade and on moist soil that is rich in nutrients, especially nitrogen, grow up more delicate and more sensitive to herbicides. Herbicides may have wide or narrow selectivity. For example, 2,4-D, which kills all dicotyledonous plants, has wide selectivity, whereas propanid, which kills Holcus mollis in rice crops, has narrow selectivity. Depending on their capacity for migration within the plant, contact and selective herbicides are divided into local and systemic categories. Local herbicides (for example, dinitro-ortho-cresol [DNOC], propanid, gramokson, and sodium pentachlorophenoxide), upon coming in contact with the plant, cause local poisoning of parts of the tissue, which rapidly wilt, turn brown, and shrivel. Systemic herbicides (for example, 2,4-D, 2M-4Kh, simazin, atrazin, and chlor-phenydim) can move through the vascular system of plants along with nutrients and metabolic products, causing general poisoning (deformation of the stem and leaves, gradual depression of growth, chloroticity, brittleness of leaves and stems, and sterility), which is particularly valuable for combating perennials and weeds with a powerful root system. Local and systemic herbicides are applied to the leaf surface of plants (leaf herbicides) and to the soil (soil or root herbicides). Many herbicides can be used both to treat underground parts of weeds and for introduction into the soil. Modern herbicides are organic compounds, which are divided into a few large groups: substituted phenols (DNOC, sodium pentachlorophenoxide), benzonitriles (ioksinil and others), quaternary ammonium compounds (region, ramok-son), chlorophenoxyalkylcarboxylic acid derivatives (2,4-D, 2,4-DM, 2,4-DP, 2M-4Kh, 2M-4KhM, 2M-4KhP, and 2,4,5-T), benzoic acids (2,3,6-TBK, Banvel-D), halogenated aliphatic acids (TKhA, propinate), carbamates (khlor-IFK, IFK, and karbin), thiocarbamates (diallat, eptam, tillam, triallat, and ialan), amides (solan, propanid, and diphena-mide), urea derivatives (dichloralurea, phenuron, meturin, and arhezine), uracil derivatives (lenatsil), triazines (simazin, atrazin, propazin, grometrin, and desmetrin), and herbicides of other groups (daktal, pikloram, and treflan). Some inorganic substances—ammonium sulfamate, potassium cyanate, sodium nitrate, and sodium, magnesium, and calcium chlorates—are also used as herbicides on a limited scale. More than 1,000 compounds with herbicidal properties are known; about 140 are used to combat weeds (see Table 1). Herbicides are mainly prepared in the form of solutions, pastes, water-moistenable powders, and emulsion concentrates. The main method of use is by spraying, from the ground and from airplanes, using aqueous solutions, emulsions, and suspensions. Granulated herbicides are used, but so far their use has been insignificant. Herbicides are applied before or after fall plowing, at various lengths of time before sowing an agricultural crop, in the period between sowing and the appearance of shoots, and at various phases of development of the shoots. The herbicide dose depends on the degree of contamination of the fields, the type of strain of the crop, the soil and climatic conditions, and the agrotechnical methods. The selective action of a herbicide is manifested more strongly at low dosages; at very high dosages it vanishes completely. At identical dosages, a decrease in temperature to below 8°-12° C (except in the case of triazines) weakens the action of the herbicides, whereas an increase in temperature enhances it. Local herbicides act better in clear weather at 18°-22° C. On light soils the herbicide doses are usually less than on heavy, humus-rich soils, which retain the herbicide more strongly. Approximate doses and times and methods of application to plantings of main agricultural crops are given in Table 2. The following herbicides are used against annual weeds of leguminous crops (doses in kg/ha are given in parentheses): prometrin (1.5-2.5), aphalone (2-3), DNOC (3-4), and sodium pentachlorophenoxide (6-8), which are applied simultaneously with planting or three to four days later; for soybeans, treflan (1-2) is applied before sowing; and for potatoes, amine salts (1-1.5) and esters (0.8-1), 2,4-D and 2M-4Kh (1-1.5), meturin (2-3), and arhezine (2-3), not later than five to six days before the shoots appear. To combat creeping couch grass, TKhA (20-30) is introduced under the spring plowing. The herbicide 2M-4KhM (2-3) is used against annual dicotyledonous weeds of clover; 2,4-DM (1.5-2.5) is used against alfalfa weeds during the development phase of its first triple leaf; to combat dodders, the stubble of perennial grasses is sprayed with DNOC (1.5), sodium pentachlorophenoxide (16-20), and region (1-1.5) one to three days after the first mowing. In gardens, vineyards, and berry patches, the most commonly used herbicides are simazin, atrazin, TKhA, propinate, and region; at mowing times and on pastures, amine salts and esters of 2,4-D are used. Chemical methods of weed control are usually used in conjunction with agrotechnical methods. The use of herbicides in agriculture aids in the improvement of agrotechnical methods. For example, chemical weeding made it possible to change over to close hole sowing of maize and cotton and ridge sowing of potatoes and to reduce the number of cultivations of the space between rows. The use of herbicides is very profitable and on the average raises grain harvests by 2.5 centners per ha (2,4-D), rice harvests by 4-7 (propanid), and harvests of maize for verdure by 50 and of corn by 7 (simazin and atrazin). In addition, the use of herbicides provides significant economization in manual labor. Most herbicides have medium or low toxicity to humans and warm-blooded animals; only a few (DNOC and sodium pentachlorophenoxide) are highly toxic. Most are preserved unchanged in the soil for a maximum of a few weeks, and only some derivatives of triazines, urea, and trichlorobenzoic acid, introduced in large doses, may be preserved for a number of years. To prevent unfavorable action of herbicides (entry into reservoirs, accumulation in plant fodders and animal products, and so on), the rules given in the instructions for their use must be strictly observed; if there are effective biological methods of controlling weeds, preference is given to them. When working with herbicides, rubber gloves, protective clothing, gas masks, and goggles are worn to prevent the preparation from coming into contact with exposed parts of the body and from entering the mouth, nose, and eyes, and the rules of personal hygiene are observed. REFERENCESMel’nikov, N. N., and Iu. A. Baskakov. Khimiia gerbitsidev i reguliatorov rosta rastenii. Moscow, 1962.Prakticheskoe rukovodstvo po primeneniiu iadokhimikatov i gerbitsidov v rastenievodstve. Moscow, 1963. Rakitin, Iu. V. “Biologicheski aktivnye veshchestva kak sredstva upravleniia zhiznennymi protsessami rastenii.” In the collection Nauchnye osnovy zashchity urozhaia. Moscow, 1963. Spravochnik po primeneniiu gerbitsidov. [Moscow] 1964. Crafts, A. S., and W. Robbins. Khimicheskaia bor’ba s sorniakami. Moscow, 1964. (Translated from English.) Weed Control Handbook. Edited by J. D. Fryer and B. A. Evans. Oxford-Edinburgh, 1968. N. N. MEL’NIKOV and L. D. STONOV |
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