Classification of herbicides according to the active substance. Types and uses of herbicides

According to the chemical composition, herbicides are divided into two groups: inorganic and organic. The inorganic ones include: sodium nitrate (NaN03); sodium arsenite (Na3As03 - NaAsO2); sodium borate (NaB407 10H20); sulfuric acid and its compounds (H2SO4 and CuSO4); 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-sec-butylphenol (DNBF, butafen); pentachlorophenol; isopropyl-N-(3-chlorophenyl) - carbamate (chloroIFK) phenylisopropylcarbamate (IFK), etc.

The vast majority of herbicides currently in use are organic compounds.

According to the effect on plants, herbicides are divided into general and selective. The former are able to kill all plants (weeds and cultivated). They can be applied before sowing or planting, after sowing (planting) but before crops emerge, in gardens, nurseries, along roadsides and in the control of 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 control weeds during the growing season of crops.

It should be noted that the selective effect of herbicides of this group is manifested only when they are used in small doses. Higher doses affect all plants. Herbicides of general extermination and selective action are divided into contact (local action) and systemic (moving). Contact herbicides are those that destroy plant tissues in places of direct contact. They almost do not move around the plant, therefore, the death of weeds in crops will largely depend on the degree of wetting. When crops are treated with contact herbicides, only the aerial part of weeds is destroyed. Their underground organs remain unaffected, and many perennial weeds grow back.

Contact herbicides of selective action include: dinitroorthocresol (DNOC), dinitroorthotorbutylphenol (DNBF), pentachlorophenol (PCP), nitrafen (preparation No. 125), kerosene, etc.

The group of systemic herbicides includes herbicides that quickly move from the place 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 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 structure (2,3,6-TB, THA, dalapon, alipur, endothal, murbetol).

According to the nature of their entry into plants, herbicides are divided into leaf action (contact and systemic) and root action (soil). The former penetrate plants better and affect them more when applied to leaves than to other organs. Root action herbicides enter plants more intensively through the root system. Such herbicides include simazine, monouron, avadex, chlorIFK, dalapon, endothal, 2,4-DES, HDEC, etc.

According to the rate 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 preparations.

From herbicides of chronic toxicity, weeds die off gradually, their complete death sometimes occurs after a few months.

There are hundreds of thousands of weeds on the earth. Most of these plants are annuals. They grow from seeds during the season, then die. But, there are other perennial species that sprout from year to year in the same area. The fight against such plants is quite difficult, as they actively adapt to any climate change.

The main problem of farmers, with the appearance of any type of weeds, is the damage to cultivated crops. Weeds struggle to survive by stealing water and nutrients from other plants. Therefore, there is a need to combat them in the territories allocated for the cultivation of industrial crops. Herbicides do the job. Ukraine and its farmers use them very actively.

Herbicides and their types.

Herbicides and their types.

Herbicides are chemicals designed specifically to kill weeds. They, like other types of drugs, have their own classification.

Herbicides of continuous action are chemical compounds that act on all plants. They are used for complete cleaning of a site of any area after harvesting, before planting crops, during deforestation, etc. You can also buy a continuous herbicide for processing heavily neglected lands.

The principle of action of this type of herbicide.

The high concentration of chemical compounds in the preparation allows you to get rid of vegetation by spraying the leaf surface. Cultures die off along with the root system after 2-3 weeks.

Selective herbicides are chemicals that target specific types of plants. This group includes the largest number of preparators. The main purpose of use is the effective control of weeds without damage to industrial crops. They are actively used by both large farms and agricultural companies, and summer residents.

Where to buy herbicides? The price of drugs.

A wide range of selective herbicides is presented in the catalog of our company. Each product is supplemented with a detailed description of the properties and actions.

Classification of herbicides according to their effect on plants.

According to the effect on weeds, herbicides are divided into several types: contact and systemic.

Contact herbicides work only at the points of contact with plants. They are not transferred through the culture vessels and do not destroy the root system.

Systemic herbicides differ in activity. They fall on the leaves, and then penetrate the internal vessels of the plants into the root, which subsequently dies off, like the whole weed. This type of preparation is most often used to control perennials and protect sunflower imi.

Classification of herbicides by penetration into plants.

The catalog of our company presents such types of preparations as soil and ground. Soil herbicides are applied after the emergence of seedlings of beetroot, soybean and cereal crops. They penetrate weeds through leaves, stems and petioles. Soil agents act on seedlings, penetrating into the plant through the root system.

How to choose herbicides?

When choosing drugs, you should always clearly focus on their focus and spectrum of action. For example, to combat beet diseases and protect soybeans, herbicides are used similar in action, but different in constituent substances. The same applies to problems with weeds and diseases of cereal crops.

Separately, it is necessary to consider herbicides for hybrid crops. To protect sunflowers, imi uses special preparations developed according to the latest technologies. The main components of the substance are aimed at combating weeds and broomrape, which cause the main damage to crops. This type of product cannot be used on other crops.

herbicide for corn.

Corn growers know that maize crops are subject to high levels of infestation. Especially at the initial stage of cultivation. This leads to a significant decrease in the yield of this agricultural crop. Therefore, the primary task of the agronomist is getting rid of weeds and expanding corn crops. To successfully solve the problem, herbicides for corn are called upon.

The most common crop weed control preparations are based on 2,4-D amine salt. Their use is recommended in conditions of good humidity. Using drugs during a drought, instead of benefit, you can get significant damage, since the drug will not be able to have a normal effect on weeds, and will cause burns to the corn itself.

Processing of crops is carried out exclusively during the formation of 3-5 sheets.

Feature of drugs.

When spraying corn crops, weed plants do not die immediately. Substances act on them gradually, slowing down growth and gradually destroying them.

Herbicide for beetroot

Weeds can be called one of the main problems in growing beets. It is with them that the root crop competes in the struggle for nutrients and elements obtained from the soil. Therefore, even with minimal contamination of crops, the yield can decrease by 20-25%.

Herbicide preparations developed for beets solve the problem of weeds and competition. Almost all of them can be used in any phase of the plant's vegetation. Rapid splitting and deactivation of substances exclude the possibility of infection of the root crop.

The effectiveness of drugs and method of application.

For the effective use of herbicides for beetroot, you must strictly follow the instructions that come with the package. It describes in detail the weather conditions and temperature regimes, the proportions of the solutions and the weeds that the active substances fight.

In our company, you can buy such types of herbicides for cultivated plants and sunflower protection imi

	Condor, VDG
	Fenizan, w.b.
	Octopus Extra, VR
	Ovsugen Express, KE
	Mitron, KS
	Lornet, VR
	Cassius, GRP
	Zontran®, KKR
	Dart, KKR
	Pomegranate, VDG

In the fight against weeds, the use of more than 120 types of chemical preparations is currently allowed in agriculture. The range of available herbicides is constantly improving and increasing due to the creation of highly selective in relation to weeds and at the same time does not affect the growth and development of cultivated plants, does not accumulate in agricultural products and does not pollute the environment. For the systematization and effective use of herbicides belonging to different classes of chemical compounds, they are classified according to various characteristics and properties.

According to the nature of plant damage, herbicides are conditionally divided into herbicides of continuous action (general extermination) and herbicides of selective (selective) action.

Herbicides of continuous action destroy all plants - both cultivated and weeds. In this regard, they are used on uncultivated heavily weeded lands - roadsides and fields, in open-air storage areas for agricultural machinery, etc., and on cultivated fields free from cultivated crops: in the post-harvest period, on fallows. In some cases, general exterminating herbicides are specifically used in orchards, forest plantations, row crops with wide row spacing, and vineyards. Herbicides of continuous action also include herbicides of selective action, which destroy in high doses those plants that they do not affect at recommended doses.

Herbicides of selective action make up the largest group of those used in the practice of agriculture. They do not damage cultivated crops, but destroy or suppress the development of certain types of weeds.

The division of herbicides into general exterminating and selective ones is also conditional because general exterminating 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 high doses can cause the complete death of all vegetation.

The phytotoxicity of individual herbicides of selective action for different plant species is not the same. Therefore, herbicides with a wide and narrow spectrum of action on plants are distinguished. Broad-spectrum herbicides are capable of destroying many plant species, even those that are far from each other in their systematic position. Narrow-spectrum herbicides are used to control individual species or groups of weeds.

Depending on the nature of the action on plants, herbicides are divided into contact and systemic. Herbicides of contact action damage only those organs or tissues of plants on which they fall and with which they come into contact. However, their influence on weeds is limited, since in perennial weeds, when the aerial parts of plants, leaves and stems die off, the root system retains its viability and can give new shoots. Systemic, or moving, herbicides easily penetrate into plant tissues through aboveground or underground organs and, moving along the phloem or xylem, enter into various chemical reactions that occur in plants. This disrupts the normal metabolic process in plants, causes a violation of their physiological and biochemical reactions, 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.

According to the nature of penetration into plants, herbicides are divided into:

1) leaf-penetrating and other aboveground organs, foliar herbicides that are used to control vegetative weeds;

2) penetrating through roots or seedlings, herbicides of root or soil action, which are applied to the soil before 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, herbicides of systemic action are divided into two groups: anti-dicotyledonous and anti-monocotyledon (anti-cereal). Antidicotyledonous herbicides damage only those plants that belong to the dicotyledonous class and have no effect on monocotyledons. 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 for the destruction of broad-leaved dicotyledonous weeds in crops of monocotyledonous crops (cereals).

When making optimal norms of anti-monocotyledonous, anticereal herbicides, monocotyledonous plants are destroyed and dicotyledonous plants are not damaged. The herbicides sodium trichloroacetate, dichloralurea, dalapon and others are used for the destruction of cereal weeds in crops of broad-leaved dicotyledonous crops - sugar beet, sunflower, cotton, etc.

According to the method of application and treatment of plants and soil, herbicides are also divided into two groups. Herbicides, which are used only by spraying vegetative weeds to suppress and destroy them, and soil herbicides, which are applied to the soil in a dry form or by spraying the soil surface. These herbicides are applied to the soil either without subsequent incorporation or with incorporation into the soil by harrows or cultivators. Some herbicides that evaporate quickly or decompose in the light require immediate incorporation into the soil.

According to the duration of the residual action, herbicides are divided into the following.

1. Herbicides with a long residual effect. The residual effect of these herbicides, even at the recommended application rates, 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, tree plantations has a positive value 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 that are sown or planted the next year after the application of herbicides are often damaged.

2. Herbicides with a short residual effect. After applying these herbicides at the recommended doses for weed control, crops can be grown in the next year without much risk according to their rotation in the crop rotation. When using herbicides 2,4-D derivatives in crops, for example, cereals, and 2M-4X in flax crops, other crops can be sown after two months.

Composition and forms of technical preparations of herbicides, terms 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. Various compounds are used as inert fillers, ingredients, which give the technical preparation good flowability, non-caking during storage and prevent the decomposition of herbicides. To improve the physicochemical properties of herbicide solutions 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 decreases, the surface of the plant or soil is better wetted by the herbicide solution. To increase the phytotoxicity of a herbicide against resistant weeds, it is often mixed with some inorganic substances, most often with mineral fertilizers, immediately before use.

Currently produced technical preparations of herbicides have different physical and chemical properties.

According to the physical state of the technical preparation, herbicides are produced in the following forms.

Wettable powders which 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 dissolve well in water in any ratio, but they easily freeze at low temperatures and lose their phytotoxic properties.

Emulsion concentrates that form non-separable emulsions of various concentrations with water.

Granular preparations (granule size of the order of 0.1-0.2 mm). They can be soluble or insoluble in water.

Some herbicides can be prepared in various forms.

The timing of herbicide application depends on the biological characteristics of cultivated and weed plants, the properties of technical preparations. In 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 soil layer by harrows or cultivators. Typically, soil herbicides are used in these cases. When sowing, the application of herbicides is carried out simultaneously with sowing or planting crops. Post-sowing - immediately after sowing or planting crops. With pre-emergence application of herbicides, the soil is treated two to four days before the emergence of seedlings of potatoes, corn, carrots and other crops, but when there are already mass shoots 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 on clean fallows and on uncultivated plots of land against especially malicious weeds, post-emergence application of leaf herbicides is carried out. The effectiveness of post-emergence application of herbicides largely depends on the phase of development of both cultivated plants and weeds, the amount of herbicide used, and weather conditions during the period of herbicide application. For the destruction of malicious weeds in the post-harvest period, both leaf and root herbicides are used, which should 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. With the wrong method, the entire surface of the field is treated with the drug. Row application of herbicides is used in tilled crops. In this case, the treatment of weeds with herbicides is carried out only in the rows of cultivated plants, and weed control in the aisles is carried out mechanically with tillage implements. Tape introduction of herbicides allows to destroy weeds in a strip of rows of tape crops (carrots, millet, etc.). With a directed method of applying herbicides, they are sprayed with the lower tier of cultivated plants (with their height of at least 30-40 cm) and the soil. At the same time, low-growing weeds and the soil surface are well wetted with the working solution of the herbicide, and dense integumentary tissues and old leaves of cultivated plants well protect their lower parts from the penetration of the herbicide into them. For the destruction of malicious and quarantine weeds, a focal method of processing curtains and individual plots of uncultivated land is used.

Tape, row and directional application of herbicides in crops is more economical than continuous treatment of crops, as this reduces the consumption of herbicide preparations per unit area without reducing the efficiency of weed control and, in addition, is of ecological importance, since the soil is less polluted .

The development of large farms has determined the need to find an easier solution for getting rid of weeds. Chemists, studying the properties of various substances, came across the ability of copper sulfate (when studying the properties of Bordeaux mixture) to inhibit dicotyledonous weeds. Later, the same property was discovered in the action of ferrous sulfate, copper nitrate, sodium chloride, sodium arsenite, sulfuric acid and other compounds.

The successful development of a new direction in chemical production began - the production of substances capable of destroying green plants. They were called herbicides (1944), from herb - plants, cide - to destroy. Herbicides have been separated into a separate group of chemicals.

Types of herbicides

The development of the herbicide industry was initially limited to a continuous action on green plants. Later, by changing the concentration, the selective effect of the herbicide on uncultivated plants was made possible. Their scanty doses at high dilution contributed to the acceleration of plant growth, that is, they no longer oppressed the plants, but acted as a stimulant. Having identified a number of necessary properties, for the selective destruction of weeds, herbicides were divided into 2 groups:

• full action,
• selective (selective) action.

Today, the first group of herbicides is used in the construction of roads, stadiums, airfields, high-voltage lines, etc. Selective herbicides have found their niche in the cultivation of crops.

Methods of herbicide action on weeds

Herbicides of continuous action destroy all vegetation, even cultivated plants. They are practically not used today in agriculture.

Selective herbicides are divided according to the spectrum of action into:

• widely selective. Destroy mono- and dicotyledonous weeds;
• narrowly selective. They affect a certain class of weeds, up to individual species. Can be used in crops of cultivated plants.

According to the method of influencing weeds, herbicides are also divided into:

• contact,
• systemic.

The group of contact herbicides needs contact with the plant. When spraying, the area of ​​contact of the pesticide with the surface of the weed is significant, which has a depressing effect on the entire plant.

Systemic herbicides, when in contact with a plant, penetrate inside and spread with a fluid flow to all its organs. This property is especially important for the destruction of perennial weeds with a powerful root system.

In agricultural production, widely selective systemic herbicides are most often used, especially for multi-species contamination.

Herbicides are available as:

• emulsion concentrates,
• wettable powders in various colours,
• suspensions.

How to use herbicides

To choose the right herbicide, you need to carry out some preparatory work before buying it:

• approximately estimate the degree of contamination of the field;
• determine the species composition of weeds.

Accounting for weediness of the field is a very important indicator. If the dose of herbicide is insufficient (desire not to poison the soil too much), not all weeds will disappear. Some will survive under these conditions, and it will be necessary to apply the pesticide again. If too high a dose is applied, cultivated plants will suffer.

In special reference books, norms and combinations of herbicides are given according to: the species diversity of weeds, the degree of contamination of plantings, the type of soil and its properties.

Methods and terms of introduction

The timing and methods of processing by pesticides depend on the type of herbicides. If a continuous non-selective herbicide is used, then it is necessary to protect the cultivated plants before applying it. When using a targeted herbicide, the age of the weeds must be taken into account. Some weeds increase the degree of herbicide resistance with age, intensively clog the crop, which reduces its yield (sometimes up to 30-40%).

According to the terms of application, they are divided into pre-emergence and post-emergence.

Pre-emergence application is carried out before sowing seeds, during sowing and for some time after sowing.

Post-emergence preparations are applied from the phase of weed germination, tillering and reaching a height of 5-10 cm. Most of the weeds die when introduced into the germination phase, with age their resistance to the herbicide increases.

For pre-emergence application, soil herbicides are usually used. They are usually applied to moist soil, which makes it easier for the drug to spread in the applied layer. Special root herbicides are applied in the form of granules and embedded in the calculated soil layer. Leaf herbicides are applied to green plants by spraying vegetative organs (leaves, stems).

Duration of action of the herbicide and its harmfulness

To increase the effectiveness of the herbicide, it is necessary to create certain conditions in the environment. So, soil and root herbicides are applied to moist soil. In the dry, they are inactive and only accumulate, and then, when watered or rainfall, their increased amounts destroy all types of vegetation (weeds and cultivated species).

After herbicide treatment of the aerial parts of weeds, dry sunny weather is necessary for 2-4-6 hours. Washing off the drug from plants requires re-treatment. Once in the soil, the drug has no effect on weeds, but accumulates in the soil.

Undecomposed herbicides with large amounts of water are washed out of the soil and enter various water bodies (ponds, lakes, rivers, seas), where they enter plants, organisms of river and marine animals and, as a result, into the human body.

Of course, timing plays a role. Some herbicides are destroyed over time under the influence of biological degradation, physico-chemical absorption, enzymatic destruction. But all of them, incl. and part of the herbicides decomposed into chemical components, have a negative impact on the soil biota involved in the formation of humus. As a result, humus formation decreases, and hence soil fertility. Some of the systemic toxins end up in the crop and on the dinner table. In general, the effect of the drug and its toxins lasts a very long time.

The duration of herbicide action is clearly demonstrated by Agent Orange, which was used by the United States in Vietnam. The drug, a mixture of defoliants and herbicides, was intended to destroy forest vegetation, but at the same time it was dangerous for people. Upon returning home, American soldiers were ill for a long time and died from oncological diseases of the gastrointestinal tract, respiration, and damage to the nervous system. After the war and up to the present, children are born in Vietnam with various disabilities. Therefore, even if your home area is heavily infested with weeds, think before using pesticides.

The use of herbicides in summer cottages

If it is impossible to do without the use of pesticides, check out the catalog of drugs approved for use in agriculture. Choose herbicides that have a short decomposition time and do not accumulate in the soil.

Today, in small packaging, Lintur, Hurricane, Tornado, Agrokiller, Fizilad are offered for processing plants and soil. The most effective technique is to prepare the solution according to the accompanying recommendation and spray the green weeds. The exposure period is from 8 to 12 days. Within a month, the above preparations decompose and do not accumulate in the soil. The effect and duration of preservation of the components of the decomposed preparation are in the special literature.

Health protection during herbicide treatment

Herbicides are poisons with a high degree of harm to health. Therefore, when using herbicides in the work, it is necessary to take measures of personal protection.

• Work only in calm weather.
• Work in clothing that completely covers exposed areas of the body (headgear covering the neck, glasses, respirator, long-sleeved gown, gloves, trousers, boots).
• after work, completely change clothes, take a shower, drink milk.

Drinking alcohol can be fatal.

• Worldwide production and use of herbicides is estimated at 4.5 million tons of drugs annually.
• Natural living herbicide. In the Amazon, ants (n / s formycins) live in symbiosis with trees of the genus Duroya. By injecting formic acid into any kind of undergrowth, except for Duroya, they clear the forest of weeds and other trees.
• According to No-Till technology, weed control without herbicides is possible if, without allowing flowering, weeds are destroyed, leaving their remains between plants. Leave all crop residues on the field. Due to the layer of mulch, weeds cannot sprout and germinate freely. A few years later, the field is cleared.
• The use of siderates. Green manure crops sown before leaving for the winter, releasing allopathic substances, act as herbicides.
• In large fields, the soil is kept in the form of green fallow. Under green fallow, dense sowing of perennial fodder crops is used. For two years under green fallow, the number of weeds is reduced by 3 times.

In the general system of destructive weed control measures, chemical methods for the destruction of weeds are now widespread.

Under the chemical methods of weed control refers to the use of various chemical compounds (pesticides) by applying them to the soil or growing weeds in crops. Such chemicals are called herbicides.

Herbicides are classified according to three criteria: chemical composition, nature of action and method of penetration into the plant.

Classification of herbicides by chemical composition

a) inorganic - sulfuric acid, sodium nitrate, calcium cyanamide, sodium cyanamide, potassium cyanamide, sodium chlorate, sodium arsenite, borates;

b) organic - dichlorophenoxyacetic acid;

c) mineral oils - volatile oils, white spirit, "activated" oils with the addition of DNOC (dinitro-o-cresol) or PCP, coal oils.

When using herbicides, you must read the instructions for use very carefully and follow the safety rules when working with them.

According to the nature of the action, herbicides are divided into two groups:

a) continuous action, i.e. destroy plants of all classes;

b) selective (selective) action - toxic for some classes and harmless to others.

Classification of herbicides according to the method of penetration into plants

a) contact - affect those parts of the plant on which the herbicide is applied;

b) systemic - able to move through the vascular-conducting system and affect all organs of plants.

Classification of systemic herbicides according to the nature of penetration into plants

a) penetrating through the leaves and other aboveground organs;

b) penetrating through the roots; they are called root-acting herbicides and are applied only to the soil before the emergence of weeds;

c) penetrating through the leaves and roots of plants.

Currently, selective herbicides are most widely used for weed control. The selectivity of action necessarily implies an unequal response either of different plants to a particular herbicide, or of one species or class of plants to different herbicides.

The selectivity of herbicides by different plants is determined by the action of a number of mechanisms that are different in nature.

The anatomical and morphological mechanism consists in the fundamental difference between plants of the classes of monocots and dicots in their anatomical and morphological structure.

The class of monocots (bluegrass) is characterized by the fact that the leaves are located at an acute angle to the stem, linear in shape, their surface is longitudinally finely furrowed, with a small number of stomata, covered with a dense waxy cuticle layer, and often they are also pubescent. An aqueous solution of the herbicide is almost not retained on the surface of such a leaf, since the leaves are poorly wetted. The growing point in monocotyledonous plants is securely covered with sheaths of numerous leaves.

In contrast, in dicotyledonous plants, the leaf blade is usually wide and often almost horizontal. Such leaves are better wetted by the herbicide solution, which spreads into a thin film and is well retained on the surface of the leaf blade. In addition, in dicotyledonous plants, the growing points are located in the axils of the leaves or at the top of the stems, are open and are easily exposed to the herbicide.

In certain plants, there is also a biochemical mechanism of selectivity for herbicides. Compounds that have penetrated into plant tissues are modified in the course of their vital activity. If such transformations occur and lead to detoxification, then the herbicide resistance of plants increases, for example, in grain breads when treated with the 2,4-D herbicide or in corn when its crops are treated with simazine. If, as a result of biochemical processes, compounds with a higher herbicidal activity are formed, then the sensitivity of plants to such a preparation increases.

The physiological mechanism of selectivity consists in changing the sensitivity of plants with their age state (young, old plants). Young plants are more sensitive and die faster.

The physical mechanism is determined by the form of the drug, its behavior in the soil, the method of application of the herbicide, the nature of the interaction of the solution with the integumentary tissues of the plant, and a number of other conditions. Some granular preparations of herbicides are characterized by high selectivity. Thus, a gradually dissolving herbicide in granules is absorbed from the top layer of soil along with moisture by the roots of weeds. This phenomenon is the basis for the use of 2,4-D granulated butyl ether in winter rye and wheat crops to control overwintering weeds.

The selectivity of some herbicides is determined by the nature of their interaction with the soil. Such herbicides as simazine, DCM, Monuron, Eptam are not able to move into the deeper layers of the soil even with an abundance of precipitation. Therefore, weed shoots appearing from the uppermost soil layer die due to the absorption of the herbicide by the roots, and cultivated plants, the seeds of which are embedded deeper than the herbicide and their root system is also located deeper than the herbicide, grow normally.