By chemical composition Herbicides are divided into two groups: inorganic and organic. Inorganic include: sodium nitrate (NaN03); sodium arsenite (Na3As03 - NaAsO2); sodium borate (NaB407 10H20); sulfuric acid and its compounds (H2S04 and CuS04); ammonium sulfamate (NH4S03 NH2); sodium thiocyanate (NaCNS); sodium chlorate; potassium cyanate (KCN03); calcium cyanamide (CaCN2). The organic group includes 2,4-dichlorophenoxyacetic acid (2,4-D); 2-methyl-chlorophenoxyacetic acid (2M-4X); 2-methyl-4,6-dinitrophenol (DNOC); 2,4-dinitro-6-secbutylphenol (DNBP, butafen); pentachlorophenol; isopropyl-N-(3-chlorophenyl) - carbamate (chloro-IPA), phenylisopropyl-carbamate (IPA), etc. The vast majority of herbicides that are currently used are organic compounds. Based on their effect on plants, herbicides are divided into general exterminators and selective ones. The former are capable of killing all plants (weeds and crops). They can be applied before sowing or planting, after sowing (planting), but before emergence cultivated plants, in gardens, nurseries, along roads and in the fight against unwanted shrubs. Selective herbicides are much more common. They destroy plants of some species, but do not have a negative effect on plants of other species. These properties of herbicides make it possible to combat weeds during the growing season of crops. It should be noted that the selective effect of herbicides in this group is manifested only when used in small doses. Higher doses affect all plants. Herbicides of general exterminatory and selective action are divided into contact (local action) and systemic (moving). Contact herbicides are those that destroy plant tissue in areas of direct contact. They hardly move around the plant, therefore, the death of weeds in crops will largely depend on the degree of wetting. When treating crops with contact herbicides, only the above-ground part of the weeds is destroyed. Their underground organs remain unaffected, and many perennial weeds grow back. Contact herbicides with selective action include: dinitroorthocresol (DNOC), dinitroorthobutylphenol (DNBP), pentachlorophenol (PCP), nitrafen (preparation No. 125), kerosene, etc. The systemic group includes herbicides that quickly move from the point of application throughout the plant. Entering its organs, they disrupt the metabolism and lead the plant to complete death. Systemic herbicides are very effective in controlling root shoot and rhizomatous weeds. These herbicides include: derivatives of phenoxyacetic acid (2,4-D, 2M-4X, 2,4,5T), phenoxybutyric acid (2M-4XM, etc.), urea (monuron, fenuron, diuron), triazine (simazine, atrazine, IPA, chlorIFK, etc.) and representatives of groups with different chemical structures (2,3,6-TB, TXA, dalapon, alipur, endothal, murbetol). Based on the nature of their entry into plants, herbicides are divided into leaf action (contact and systemic) and root action (soil action). The former penetrate plants better and affect them more when applied to leaves than to other organs. Root herbicides enter plants more intensively through root system. Such herbicides include simazine, monuron, avadex, chlorIFK, dalapon, endothal, 2,4-DES, HDEC, etc. Based on the speed of damage and death of weeds, herbicides are divided into two groups: fast-acting (acutely toxic) and slow-acting (chronic toxicity). ). The first group includes contact drugs. From herbicides of chronic toxicity, weeds die off gradually, their complete death sometimes occurs after a few months.
Repeated and systematic treatment of weeds with herbicides can give lasting results throughout the season. They represent chemical substances, adversely affecting the development and growth of the plant. Herbicides are used only for weeds.
In order to know which drug is best to treat weeds, you need to know the specifics of its action. Home distinctive feature Such means have their spectrum of action. All herbicides are divided into two groups: continuous action and selective.
Those substances that are part of continuous action herbicides are capable of destroying all vegetation that was present during spraying. Such radical drugs are used in areas where vegetation is contraindicated.
The action of herbicides of this type is divided into subgroups, namely:
Contact herbicides begin to act on the plant only when the drug gets on the leaves or stems. The leaves begin to turn yellow, wither and dry out. All this leads to the complete destruction of the weed.
The use of soil herbicides is appropriate in cases where the weed has managed to pour its seeds into the soil. Such preparations are applied directly to the ground. They have a detrimental effect on weed seeds and thus prevent them from germinating.
Systemic herbicides are considered one of the most popular, as they quickly and effectively affect the development of the weed. When such a herbicide hits a weed, it not only affects the outer shells, but is also absorbed into the plant itself. It spreads throughout the weed, which means that its action is also aimed at destroying the root system.
Of course, systemic preparations are incomparable with soil herbicides. Systemic herbicides can have a complex effect on the plant, while soil herbicides can only affect the seeds.
The second large group of herbicides is headed by drugs with selective action. These substances can only kill certain types of weeds. When choosing such drugs, you must carefully read the instructions for use of the herbicide. Often it indicates full list weeds that may be adversely affected by the selected drug.
When purchasing selective herbicides, you need to know:
Can herbicide harm humans? The instructions for herbicides always indicate the level of danger and toxicity for humans. All substances that are part of the selected drug have different degrees toxicity.
The price of herbicides varies depending on the system of action. average price one liter of herbicide can be 200-5000 rubles per 1 liter.
Which herbicides are considered the most popular on the market? chemicals? The action of herbicides is directed against weeds that could be permanent “residents” of any territory or site for years. Therefore, the fight against them is considered one of the most difficult.
After reading dozens of reviews about herbicides, we can come to a conclusion about the most popular drugs that can really help radically:
The herbicide Roundup is considered a non-selective systemic drug. Has a wide range of effects, especially on perennial weeds. It is considered one of the most radical drugs in the world. The final destruction of the weed occurs 14-15 days after treatment.
Herbicide Tornado is aimed at systemic effects. It is used as universal remedy from weeds. It contains an increased concentration of the main active ingredient.
Prima herbicide is considered a powerful drug containing two active ingredients. It is often used to control weeds that grow in areas with grain crops and corn.
Herbicide Gold is used against cereal monocotyledonous and dicotyledonous weeds. It is used in fields with corn, rapeseed, sunflower, soybeans, etc.
Herbicide Hurricane is a systemic preparation that can be used both in fields and private land plots. Shows itself well among vineyards, forest plantations, gardens and fields. It has a wide field of action, therefore it is considered a universal remedy.
Stomp herbicide is used to control weeds in vegetable beds. It is considered a herbicide double acting, since it can systemically influence the weed and destroy seeds through the soil.
Titus herbicide is a post-emergence preparation that is used to control weeds in areas where tomatoes, potatoes and corn will be planted. It is considered a systemic drug. It is popular due to its low application rate, high selectivity and long-lasting effectiveness.
Herbicide Zenkor is intended for systemic action on the weed. The drug has a wide spectrum of action. Features a long protection period. Fights annual dicotyledonous weeds.
Herbicide Eurolighting is a post-emergence preparation. Aimed at the destruction of cereals and dicotyledonous weeds. Acts through vascular system plants and through the soil. One treatment will be enough to keep the soil clean throughout the growing season.
Granstar herbicide is used to remove weeds from barley, wheat, sorghum, soybeans, and rapeseed. Has a wide range of effects. It perfectly destroys dicotyledonous weeds, as it has a systemic effect.
Gesagard herbicide has a fairly long period of exposure - 10-12 days. Used for potatoes, vegetable crops, corn, coriander, sunflower, grain crops. Not phytotoxic.
Today at agriculture from point of view economic feasibility It is quite beneficial to use herbicides against weeds. With their help, weeds are destroyed in crops, while the cultivated useful crops are not affected harmful effects destructive chemicals (subject to optimal application doses).
At their core, herbicides are organic and inorganic compounds. They have the ability to quickly penetrate the tissues and cells of weeds, which leads to their death. Depending on their type, these chemicals can affect different parts of plants. Some of them penetrate deep into the structure through the root, others through the surface of the leaves.
Thus, herbicides for killing weeds are one of the current agricultural chemicals to date.
However, if we talk about these chemicals in in a broad sense, then they are used not only to combat unwanted vegetation. Depending on the objects they must destroy and the goals, 3 large groups of substances are distinguished:
1) Herbicides themselves. They are precisely used in agriculture to destroy weeds.
2) Arboricides. These drugs are designed to eradicate shrubs and trees.
3) Algaecides. Products that work well against aquatic vegetation. They are often used to clean water bodies.
Some of the drugs can cope with several tasks at once and are effective in several directions.
Inorganic compounds include magnesium chlorate, ammonium sulfamanate, calcium cyanamide and several other substances.
The group of organic herbicides is much richer and more diverse. These include:
1) Benzonitriles. For example, Ioxynil.
2) Substituted phenols. Such as DNOC.
3) Carbamates. This type includes Carbin, IFC.
4) Amides. Among the most famous are Difenamide, Solan.
5) Triazines. These include Propazine, Simazine, Prometrin.
6) Urea derivatives. Here we can highlight Meturin, Kotoran, Fenuron.
7) Derivatives of uracil. The main one is Lenatsil.
One of the characteristics of all these herbicides is based on their spectrum of action. These drugs can destroy all plants or only parts of them, so they are divided into continuous or selective action.
But there are continuous action herbicides that can quickly decompose. They can also be used on cultivated plantations. For example, on busy fallows (after harvesting fallow crops) or during the stubble period. They help well in the fight against perennials.
Sometimes such preparations are used in vineyards, orchards, and also to protect against weeds those crops that are considered row crops and have row spacing of at least 70 cm.
Almost all inorganic compounds are classified as continuous herbicides. This group also includes a number of organic substances: Glyfogan, Roundal, Arsenal.
Among the most common drugs that destroy all plants are:
1) Glyphosate.
It copes well with weedy cereal annuals and perennials, as well as dicotyledons. Its action is aimed at inhibiting amino acids, as a result of which unwanted plants treated with it die. The herbicide Glyphosate is often used on tea plantations and for processing in citrus and orchards. It can be used in the spring during active growth unwanted plants or in the fall after harvest.
2) Diquat.
Used to control weeds in potato and carrot crops. For this purpose, it is applied in the spring before the emergence of useful crops. Diquat can also act as a desiccant (a substance that helps plants dry out). In this capacity, it is often used immediately before harvesting alfalfa, sunflower, and clover.
Copper sulfate is considered to be the very first selective herbicide. Laboratory research showed that this salt has an adverse effect on the development of dicotyledonous weeds.
This group also includes sulfonylureas, as well as those herbicides that prevent the accumulation of fats. Such preparations are usually applied to the leaves of weeds.
But substances based on trifluralin are usually applied to the soil. They are used to destroy dicotyledonous and cereal weeds. Often used to protect tomatoes, carrots, cabbage, and cucumbers.
All selective herbicides are divided into 2 large groups:
1) Widely selective.
Can destroy weeds different types. For example, triazine-based preparations, which work well with both dicotyledonous and monocotyledonous plants.
2) Narrowly selective.
Preparations aimed at destroying a specific type of plant. Thus, the herbicide Grodil is used to treat barley and wheat crops. It will easily destroy the tenacious bedstraw. Tristar will help get rid of millet, tuber grass, and barnyard grass on rice plantations.
1) Applied in autumn or spring before sowing crops.
2) Used together with sowing plants.
3) Applied after sowing 3-4 days before germination.
4) Applied at the very beginning of the growing season.
In this regard, two more types of herbicides are distinguished: soil and foliar.
In order for the addition of a substance to give the expected result, it is necessary to pay attention to the following aspects:
1) Soil structure. It is desirable that the soil lumps be as small as possible. Then we can talk about an even distribution of the funds used.
2) Soil moisture. If the soil is dry, herbicides lose their effectiveness.
3) Substance consumption rate. This is very important for soil preparations, and shallow embedding into the soil (up to 5 cm) also increases efficiency.
4) Soil type. Sandstones are characterized by low humus content, therefore they belong to light soils. Herbicides can be used on them in minimal quantities. Rich organic compounds lands where the humus content exceeds 6% are classified as heavy soils. Therefore, the dose of the drug should be increased. Otherwise, he may lose activity.
5) Weather conditions. At low temperatures or drought, the effectiveness of herbicide treatment is significantly reduced.
The most well-known soil preparations include Harnes for corn and Stefacil for beets.
All types of foliar herbicides are widely selective drugs. That is, they provide negative impact on most of the weeds, and not just on a certain group.
As for dosage, it is not fundamental for foliar herbicides. You can reduce the rate, but the product will still cope with the task - it will prevent the formation of seeds or reduce their germination.
Today, preparations based on glyphosate are often used - Accord, Glycel, Forsat.
1) Contact.
Such substances damage only those parts of the weeds with which they come into contact. The rest remain without visible changes. For example, when using foliar herbicides, the roots of perennials may not be harmed. Therefore, it is important to pay attention to the thoroughness of the coating with the solution and the uniformity of its application. This group includes Bazagran, Acet, Betanes.
2) Systemic herbicides.
They are able to penetrate deep into the structure, spreading, leading to damage to the plant. Particularly effective for controlling weeds with a powerful root system. Here you can highlight Glyphosate, Buran, Roundal.
1) Membrane-destroying cells (definyl ethers, bipyridyls). They act instantly, within several hours. The plant dries out.
2) Suppressing the formation of amino acids (sulfonylureas and others). There is a lack of proteins in the plant, which blocks its growth. The result can be seen in a few days.
3) Hormone replacement (benzoic, pyridine carboxylic acids). This type herbicides deplete plants. They are especially effective against dicotyledonous weeds; their movement in grain crops is difficult.
4) Fat inhibitors (benzofurans). Growth stops almost immediately, death occurs after 2 weeks.
5) Suppressing photosynthesis (triazines, nitriles). Usually used against dicotyledons, less often for cereals.
6) Pigment inhibitors (clomazone, fluoride-containing herbicides). Plant development is suspended.
7) Suppressing cell division (chloroacetamides). The growth of shoots and roots slows down, nutrition is disrupted and the weed dies.
New types of herbicides are constantly emerging. Scientists are creating new drugs, modern technologies are improving old drugs, making them effective, and hopefully safer.
V.M.ZHEREBKO,
Professor of the Department of Phytopharmacology and Zoology of the National Agrarian University (Kyiv)
Herbicides are chemical compounds that are used to kill seedlings and seedlings of weeds or other unwanted vegetation in crops, fruit trees, vineyards, pastures and other lands. Name "herbicides" comes from the Latin words “herba” - grass and “cido” - to kill, destroy.
The range of herbicides produced by industry is very wide. Based on their chemical composition, they are divided into inorganic and organic. Only a few herbicides and defoliants (means for pre-harvest removal of leaves) are inorganic - magnesium chlorate, calcium chlorate chloride, etc. Their use is decreasing from year to year.
The vast majority of herbicides belong to products of organic synthesis, derivatives various classes chemical compounds.
Aliphatic derivatives carboxylic acids:chlorinated(TXA), amides and nitriles (dual, harnes, trophy, trophy-super, frontier, butizan), quinolines (facet).
Derivatives of aromatic carboxylic acids: benzoic (banvel, kerb), hydroxybenzoic (totril, pard-ner). Aromatic amine derivatives: nitroanilines (treflan, nitran, herbitref, stomp, penitran);
diaryl ethers (blaser 20, takl, goal).
Cyclohexane-dione derivatives(poast, nabu, centurion, select). Derivatives of aryloxyal-cancarboxylic acids: phenoxyacetic acid (2,4-D, 2M-4Х), phenoxybutyric (2M-4ХМ, 2,4-DM), phenoxypropionic (2М-4ХП), aryloxyphenoxypropionic (illoxan, furore-su-per , puma-super, shogun, targa-super, fusilad-super, zellek-super).
Derivatives of carbamic and thiocarbamic acids: carbamic (betanal, betanal AM, carbine), thio-carbamic (eptam, eradican, vi-tox).
Triazine derivatives: symmetrical - sym-triazines (atrazine, gesagard, semeron); unsymmetrical-as-triazines, or triazinones (Goltix, Zencor).
Urea derivatives: aryldialkyl ureas (Dozanex, Maloran), sulfonylureas (Glin, Grodil, Titus, Milagro, Granstar, Harmony, Tell, Caribou, Lenok, Sirius).
Organophosphorus(roundup, that's it).
Imidazolinones(pivot, arsenal).
Heterocyclic compounds, derivatives: pyridine (Lontrel-300, Lontrel Grand, Reg-lon Super, Racer), furan (Nortron, Stemat), uracil (hexylur), pyridine (lentagran, Pyramin Turbo); ti-adiazine (bazagran); pyridinyl (starane). Combined preparations: based on sulfonylurea (cowboy, cross, satis, trezor, di-kuran-forte, basis); based on atra-zine (primextra, primextra gold, laddock, laddock new, lentagran-com-bi), based on phenmedipham and desme-dipham (benogol, betanal progress AM, betanal progress OF, burefen FD, regio plus, stephamate, sinbetan D forte), based on bentazone (bazagran M, galaxy top), based on 2,4-D
(buctril D, dialen C, dialen-super,
lancet, landmaster, lontrim),
Depending on the properties of herbicides and the nature of their effect on plants, they are of continuous and selective (selective) action.
Herbicides continuous actions are used to destroy all weeds and other unwanted vegetation on non-agricultural lands (roadsides, irrigation and drainage canals, power lines, sites that are being prepared for construction, etc.). On agricultural lands, continuous action herbicides can be used during the absence of cultivated plants on them (for example, in the system of main or pre-sowing tillage, in fallow fields), as well as by targeted spraying in orchards, vineyards, fruit and forest nurseries. The most notable representatives of this group are Roundup and its analogues. Other herbicides can also have a continuous effect if they are used at excessive rates.
Herbicides selective (selective) actions destroy or oppress some plants without causing serious harm to others. Their selectivity depends on the anatomical, morphological and physiological characteristics of plants and is determined by the chemical structure of the compound, the rate of application, the form of the drug (formulation), the period and method of application, the development phase of cultivated plants and weeds, as well as the conditions external environment(soil, humidity, temperature) and other factors. Drugs such as dialen, bazagran, granstar, for example, cause the death of dicotyledonous weeds in cereal crops, which characterizes them as drugs with broad selective action. Some herbicides have narrow selectivity. Thus, targa, fusi-lad, poast, furore-super destroy monocotyledonous weeds in dicotyledonous crops, and puma-super is capable of suppressing wild oats and common broom in winter wheat crops, although they belong to the same family.
The selectivity of herbicides is often due to differences in anatomical and morphological structure plants. It is called topographical. Plants with a dense cuticle and a waxy coating, as well as with dense drooping, are more resistant to herbicides, as they prevent the entry of drugs into the plant. Plants with narrow vertical leaves (onions, garlic, etc.) promote swelling of the working fluid from the surface of the leaf blade. More resistant to drugs that are retained in top layer soils, plants with a deep root system, in particular field sow thistle, creeping bitterweed, horsetail, field bindweed and other perennial weeds.
Herbicide-resistant crop plants may exhibit biochemical selectivity, that is, to promote the rapid conversion of herbicide molecules into inactive components. Some of them have the property of quickly releasing herbicides through the root system in an unchanged state, remaining intact. Sustainability cereal plants to the action of 2,4-D is a consequence of the detoxification of the herbicide by binding it to protein complexes of cellular structures, cytoplasmic membrane proteins, as well as the formation of complexes with compounds of non-protein origin. The sensitivity of weeds to the action of herbicides is explained by significant irreversible disturbances in metabolic processes, which leads to their death. The selectivity of symmetric triazine derivatives is determined by the characteristics of the movement of herbicides and their accumulation in places of phytotoxic action. In resistant plants (for example, corn), atrazine accumulates in the roots, while in sensitive species it accumulates in the leaf apparatus, that is, in places of photosynthetic activity. In addition, due to the destruction of the herbicide by redox enzymes (peroxidase), s-triazine herbicides in corn are broken down into non-toxic compounds.
Knowledge of the mechanisms of plant resistance to herbicides makes it possible to control this process. The use of antidotes - chemical means of increasing the resistance of cultivated plants to herbicides - is considered promising. Using 1,8-naphthylacetic acid anhydride by treating corn seeds, it is proposed, for example, to protect crop seedlings from the toxic effects of eptam, alachlor, metolachlor, chlorsulfuron and other active ingredients of herbicides.
The use of M,M-dialyl-2,2-di-achloroacetamide (P-25788) can protect corn from negative influence eptam, adding it to the working herbicide mixture in an amount of 0.25-0.5 l/ha. Based on the use of this antidote, the herbicide eradican is produced, to which corn is highly resistant.
With the help of antidotes and prolongers, it has become possible to enhance the activity of soil herbicides against weeds, while maintaining selectivity to cultivated plants. By adding the antidote R-29148 (S-ethyl-diapropylthiocarbamate) to cap-tama, and the prolongator R-33865 (0,0-di-ethyl-0-phenyl-phosphorothioate) to kera-dican extra, you can significantly enhance the effect of herbicides on late shoots millet weeds, gumai and others, as well as against the second “wave” (summer shoots) of weeds through high selectivity to corn.
Even greater opportunities in managing plant resistance to herbicides are revealed by using advances in biotechnology and genetic engineering. Definition genetic code Plant resistance to herbicides makes it possible to transfer resistance genes to crops and solve the problem of regulating the level of weediness in crops using continuous action herbicides to which the crop did not have resistance (glyphosate, ammonium glufosinate, etc.).
Positive results have been obtained from transferring genes for resistance to ammonium glufosinate (Basta, Liberty) and glyphosate (Roundup) in sugar beets, corn, soybeans, rapeseed and other crops. In this way, it will be possible to destroy all weeds in crops that are resistant in the post-emergence period, when they have not yet caused damage. great harm. Selectivity is a relative concept, since most herbicides in higher standards can overcome the threshold of cultural stability.
Depending on the characteristics of their action on plants, all selective herbicides are divided into two large groups: contact and systemic. To herbicides contact actions include drugs that are capable of infecting plants in places of wetting (contact) with the working mixture. Contact preparations are practically unable to move along the conducting system of plants, because of this they do not penetrate the root system of perennial weeds, and the latter grow back.
Herbicides systemic actions are able to move through the vessels, affecting the entire plant, causing the death of both its above-ground and underground organs.
In While moving through the vessels of plants, partial inactivation of herbicides occurs through their absorption by cells and destruction by enzymes with the formation of complex compounds. Herbicides move through the phloem into the root system and generative organs, and accumulate in zones of active growth, causing profound disturbances in physiological processes, which results in the death of sensitive plants.
With the soil solution, herbicides are absorbed by root hairs, move through xylem vessels and by transpiration current to the above-ground plant organs. Systemic drugs advisable to use in the fight against perennial species weeds whose root system penetrates deep into the soil.
According to the methods of penetration into plants, contact and systemic herbicides are distinguished into foliar preparations - those that penetrate through above-ground organs (leaves, stems, petioles) and that are used after the emergence of crops and weeds (betanal, roundup, po-ast, grodil, etc. .), and soil, root action, which enter plants through the root system and affect the seedlings of weed seeds (dual, zenkor, prometrin, etc.).
The selection of herbicides to protect a particular crop is carried out according to the list of pesticides and agrochemicals approved for use in agriculture, focusing on the resistance of the crop to the herbicide, taking into account the spectrum of its action on the species composition of weeds.
The proposed classification of herbicides is based on the accepted world classification of active ingredients of pesticides (A World Compendium: The Pesticide Manual, 1994) and general proposals of scientists.
In the fight against weeds, the use of more than 120 types of chemicals is currently permitted in agriculture. The range of available herbicides is constantly improving and increasing due to the creation of highly selective ones in relation to weeds and at the same time not affecting the growth and development of cultivated plants, not accumulating in agricultural products and not polluting environment. To systematize and effective use Herbicides belonging to different classes of chemical compounds are classified according to various characteristics and properties.
Based on the nature of plant damage, herbicides are conventionally divided into continuous-action (general-destructive) herbicides and selective (selective) action herbicides.
Continuous herbicides destroy all plants - both cultivated and weeds. In this regard, they are used on uncultivated heavily polluted lands - roadsides and fields, in storage areas for open air agricultural machinery, etc., and in cultivated fields free of cultivated crops: in the post-harvest period, in fallows. In some cases, general exterminator herbicides are specifically used in gardens, forest plantations, row crops with wide row spacing, and in vineyards. Continuous-action herbicides also include selective-action herbicides, which in high doses destroy those plants that they do not affect at recommended doses.
Selective herbicides constitute the largest group of those used in agricultural practice. They do not damage cultivated crops, but destroy or suppress the development of certain types of weeds.
The division of herbicides into general exterminators and selective ones is also conditional because general exterminatory herbicides, more often used in the form of additives in small doses to other compounds, are used as selective preparations. Conversely, selective herbicides used in higher doses can cause complete death of all vegetation.
Phytotoxicity of certain selective herbicides for various types plants are not the same. Therefore, herbicides with a wide and narrow spectrum of action on plants are distinguished. Herbicides wide range actions are capable of destroying many plant species, even those that are far from each other in systematic position. Narrow-spectrum herbicides are used to control individual species or groups of weeds.
Depending on the nature of their action on plants, herbicides are divided into contact and systemic. Contact herbicides damage only those plant organs or tissues on which they fall and with which they come into contact. However, their influence on weeds is limited, since in perennial weeds, when the above-ground parts of plants, leaves and stems die, the root system retains its viability and can produce new shoots. Systemic, or traveling, herbicides easily penetrate plant tissues through above-ground or underground organs and, moving along the phloem or xylem, enter into various chemical reactions, occurring in plants. This disrupts the normal metabolic process in plants, causes disruption of physiological and biochemical reactions in them, which leads to various pathological phenomena. Representatives of this group of herbicides are especially effective in the fight against perennial weeds that develop powerful vegetative reproductive organs.
Based on the nature of penetration into plants, herbicides are divided into:
1) foliar herbicides penetrating through leaves and other above-ground organs, which are used to control vegetative weeds;
2) herbicides of root or soil action penetrating through roots or seedlings, which are applied to the soil before the emergence of weeds;
3) herbicides of combined action penetrating into plants both through above-ground organs and through the root system.
In relation to the botanical class of plants, their systematic position, systemic herbicides are divided into two groups: anti-dicots and anti-monocots (anti-cereals). Dicotyledonous herbicides damage only those plants that belong to the dicotyledonous class and have no effect on monocotyledonous plants. This is mainly due to the anatomical and morphological features of the structure of plants. Herbicides 2,4-D, 2M-4X and others are used to destroy broad-leaved dicotyledonous weeds in crops of monocotyledonous crops (cereals).
When making optimal standards anti-monocot and anti-cereal herbicides destroy monocotyledonous plants without damaging dicotyledonous plants. Herbicides sodium trichloroacetate, dichloroalurea, dalapon and others are used to destroy cereal weeds in crops of broad-leaved dicotyledonous crops - sugar beets, sunflowers, cotton, etc.
Based on the method of application and treatment of plants and soil, herbicides are also divided into two groups. Herbicides that are used only by spraying vegetating weeds to suppress and destroy them, and soil herbicides that are applied to the soil in dry form or by spraying the soil surface. These herbicides are applied to the soil either without subsequent incorporation, or with their incorporation into the soil using harrows or cultivators. Some herbicides that quickly evaporate or decompose in the light require immediate application to the soil.
Based on the duration of residual action, herbicides are divided into the following.
1. Herbicides with a long residual effect. The residual effect of these herbicides, even at recommended application doses, remains in the soil for more than one year, especially on low-humus soils and in years with insufficient moisture. The aftereffect for a long time on uncultivated lands, in gardens, and tree plantations has a positive effect in the fight against weeds. At the same time, in field, fodder and vegetable crop rotations, where these herbicides are most often used, such an aftereffect is undesirable, since crops sensitive to these herbicides, sown or planted the following year after the use of herbicides, are often damaged.
2. Herbicides with short residual action. After using these herbicides in recommended doses to control weeds next year, crops can be cultivated according to their rotation in crop rotation without much risk. When using herbicides derived from 2,4-D in crops, for example, cereals, and 2M-4X in flax crops, other crops can be sown within two months.
The composition and forms of technical preparations of herbicides, timing and methods of their application. Herbicides used in agriculture are technical preparations containing from 10 to 90% of the active substance (a.i.) of the chemical compound of the herbicide itself. Used as inert fillers and ingredients various connections, giving the technical preparation good flowability, non-caking during storage and preventing the decomposition of herbicides. For improvement physical and chemical properties solutions of herbicides prepared for application to the soil, surfactants are introduced into the composition of their technical preparations. Thanks to them, the surface tension of the solution is reduced, and the surface of the plant or soil is better wetted by the herbicide solution. To increase the phytotoxicity of the herbicide in relation to weeds resistant to it, immediately before use it is often mixed with some inorganic substances, most often with mineral fertilizers.
Currently produced technical herbicide preparations have different physicochemical properties.
Depending on the physical state of the technical preparation, herbicides are produced in the following forms.
Wettable powders that form an aqueous suspension with water.
Soluble powders that form true solutions with water.
Mineral-oil suspensions that form water-oil suspensions with water.
Aqueous solutions and water-soluble concentrates. Both forms of drugs are highly soluble in water in any ratio, but they easily freeze at low temperatures and thus lose their phytotoxic properties.
Emulsion concentrates that form non-separating emulsions of varying concentrations with water.
Granular preparations (granule size is about 0.1-0.2 mm). They can be soluble or insoluble in water.
Some herbicides can be prepared in different forms.
The timing of herbicide application depends on the biological characteristics of crops and weeds, and the properties of technical preparations. With pre-sowing application, herbicides are applied to the soil before sowing or planting cultivated crops and, as a rule, with their subsequent incorporation into the surface layer of soil using harrows or cultivators. Typically, soil herbicides are used in these cases. When seeding, herbicides are applied simultaneously with sowing or planting crops. Post-sowing - immediately after sowing or planting crops. When applying pre-emergence herbicides, the soil is treated two to four days before the emergence of potatoes, corn, carrots and other crops, but when there are already massive emergence of weeds. In this case, both foliar and root herbicides are used. At the beginning of the growing season of cultivated plants and during the period of mass emergence of weeds, as well as pure pairs and on uncultivated areas of land against especially malicious weeds, post-emergence application of foliar herbicides is carried out. The effectiveness of post-emergence herbicide application largely depends on the developmental stage of both crop plants and weeds, the amount of herbicide applied, weather conditions during the period of herbicide application. To destroy harmful weeds in the post-harvest period, both foliar and root herbicides are used, which must be completely inactivated by the time of sowing or planting subsequent crops.
The introduction of herbicides into the soil and the treatment of weeds with them can be carried out in various ways. In case of an oversight, the entire surface of the field is treated with the drug. Row application of herbicides is used in row crops. In this case, the treatment of weeds with herbicides is carried out only in the rows of cultivated plants, and weed control is carried out between the rows mechanically tillage implements. Belt application of herbicides allows you to destroy weeds in the strip of rows of belt sowing (carrots, millet, etc.). With the directed method of applying herbicides, they spray the lower tier of cultivated plants (if their height is at least 30-40 cm) and the soil. At the same time, low-growing weeds and the soil surface are well moistened by the working solution of the herbicide, and dense covering tissues and old leaves of cultivated plants well protect their lower parts from penetration of the herbicide into them. To destroy malicious and quarantine weeds, a focal method of processing clumps and individual areas of uncultivated land is used.
Belt, row and targeted application of herbicides in crops is more economical than with continuous cultivation of crops, since this reduces the consumption of herbicide preparations per unit area without reducing the effectiveness of weed control and, in addition, has environmental significance, since the soil is less polluted .
