Chemical methods of weed control – a set of methods aimed at destroying and preventing the spread of weeds with the use of chemicals.
Herbicides (lat. herba – grass, ceado – to kill) – chemical substances used to kill and suppress the growth of weeds. The list of herbicides approved for use in agriculture and private farms in Russia is annually updated by a special commission on the agro-industrial complex.
- Current status
- Classification of herbicides
- Timing of herbicide treatments
- Methods of herbicide treatment
- Herbicide release forms
- Herbicide consumption rates
- Conditions for using herbicides
- Characteristics of main herbicides
- Peculiarities of herbicides application for different crops
- Improvement of herbicide use technology
- Occupational health and safety when using herbicidesAll of the information in this section are legal requirements in the Russian Federation. Other countries may have different requirements.
- Harm caused by weeds
- Agrocenoses, agrobiocenoses, agrophytocenoses
- Biological and ecological characteristics of weeds
- Classification of weeds
- Accounting and mapping of weeds
- Threshold of harmfulness of weeds
- Methods of weed control
- Useful properties of weeds
- Harm caused by weeds
- Agrocenoses, agrobiocenoses, agrophytocenoses
- Biological and ecological characteristics of weeds
- Classification of weeds
- Accounting and mapping of weeds
- Threshold of harmfulness of weeds
- Methods of weed control
- Useful properties of weeds
Herbicides were first used in the late 19th century. They were mainly inorganic substances: copper nitrate (nitrous copper), seven-water ferrous sulfate (iron sulfate), ammonium sulfate, sulfuric acid, sodium nitrate, sodium arsenite, kainite, calcium cyanamide, and others.
Nevertheless, due to significant shortcomings, herbicides were not widely used until the 1940s of the XX century. Only one third of arable land and perennial plantations in Russia were treated with herbicides.
After the discovery in 1941 of 2,4-dichlorophenoxyacetic acid (2,4-D) – a synthetic growth regulator, herbicides were widely used in weed control. 2,4-D, its salts and esters at concentrations of 0.01% lead to the death of dicotyledonous plants without causing the death of monocotyledonous plants.
Subsequent studies have shown that other substances, such as derivatives of 2-methyl-4-chlorophenoxyacetic acid (2M-4X) and trichloroacetic acid (TCA), have similar properties.
Herbicides are an integral part of modern agriculture, combining the chemicalization of production with the use of energy-saving and conservation tillage technologies.
Chemical methods of weed control have a number of drawbacks:
- emergence of herbicide-resistant weeds (superweeds);
- lack of selectivity;
- long-term inactivation;
- lack of necessary preparations;
- pollution of the environment and agricultural products.
Research in the development of new herbicides is ongoing in many countries. The promising areas of these studies are the elimination or minimization of the negative effects of application.
According to the data of the All-Russia Research Institute of Plant Protection, herbicides on grain crops in Russia yields 0.2-0.25 t/ha extra, on corn – 0.5 t/ha, on silage – 5 t of green mass from 1 ha, on sugar beet – 2 t of root crops from 1 ha, on rice – 0.8-1 t/ha (propanide). Under irrigated agriculture, due to more favorable growth conditions for weeds, the use of herbicides is of great importance.
Promising herbicides include cowboy (0.15-0.20 kg/ha), dialen-super (0.8-1 kg/ha), basagran etc.
Classification of herbicides
To date, there is no unified classification of herbicides. They are classified according to a number of features: chemical composition, methods of application, nature of action, degree of danger to humans and warm-blooded animals, impact on products and the environment.
Classification of herbicides:
- By chemical composition:
- By nature of action:
- continuous (general exterminating);
- systemic (selective):
- without growth-regulating action;
- with broad selectivity;
- with narrow selectivity.
- By site of action:
- leafy, with movement through the plant;
- soil, through the root system;
- foliar and soil.
- By timing of application:
- before sowing or planting;
- simultaneously with sowing or planting;
- after sowing or planting, before sprouting;
- after sprouting of the crop;
- during the period of mass regrowth of weeds.
- By degree of toxicity:
- highly toxic toxic substances LD50 <50 mg/kg;
- highly toxic substances LD50 = 50-200 mg/kg;
- medium toxic substances LD50 = 200-1000 mg/kg;
- low-toxic LD50 >1000 mg/kg.
- By phytotoxicity:
- medium sensitive;
- By duration of action:
- with long duration;
- with short.
Continuous and systemic herbicides
Herbicides of continuous (general extermination) action are active against almost all types of plants and are used to destroy vegetation in areas without crops: on the roadsides of railroads and highways, power lines, drainage and irrigation canals, sports fields, cattle farms, around grain factories, in areas of quarantine weeds, etc.
The current level of research on selective herbicides allows their use in crops of most crops.
Selective properties of herbicides depend on a number of factors:
- anatomo-morphological (shape of leaves, their location, pubescence, waxy patches, etc.) and physiological features of plants;
- chemical composition of the herbicide;
- physicochemical properties;
- physiological activity;
- differences in cell protoplasm properties.
Selective properties depend on application rates of herbicides. For example, 2,4-D and 2M-4X are effective against many dicotyledonous weeds in grain crops. Exceeding the established doses makes them herbicides of total action, causing death of all plants.
Broadly selective herbicides affect many weeds without damaging crops. For example, atrazine kills a wide range of dicotyledonous and monocotyledonous weeds in corn crops.
Herbicides of narrow selective action affect several species or only one species of weeds. For example, Avadex is used against wild oat (Avena fatua) in wheat, barley and pea crops, affecting it for a limited time in the phase of 1-2 leaves. Propanide is used to control barnyard grass (Echinochloa crus-galli) in rice crops, while its effect on other weeds is limited.
Systemic herbicides are subdivided into:
- with typical growth-regulating action – leading to disruption of growth and cell division, deformation of stems and leaves, proliferation of tissues, and formation of aerial roots. When used in recommended doses, they are highly selective toward dicotyledonous plants and have no effect on cereals.
- Without typical growth-regulating action – affect photosynthetic and other processes of plant life. Often there is a change in coloring of leaves, plants wither and die off.
- Substances of contact action cause leaf burns in places of contact, destruction of chlorophyll and plant death (nitrafen, reglon, etc.).
The first two groups include: 2,4-D, 2M-4X, simazine, atrazine, pyramine, chlor-IFC, eptam. They are especially effective against perennial rhizomatous and root-shoot weeds.
Herbicides by site of action
Leaf-acting herbicides have an effect mainly at the points where they reach the plant or, moving through the plant, have a systemic effect on the tissues.
Soil herbicides are absorbed by the root system and transported to the aboveground organs. They have an effect in the roots or in the aboveground part of the plant.
Herbicides can also be classified by site of action into:
- contact, that is, herbicides that act directly on the parts of the plant on which they were applied;
- translocated, i.e. herbicides that get on some parts of plants, but have an effect on other parts.
The selectivity of contact herbicides in foliar applications depends in part on the differential retention of the herbicide by the crop and weeds. For example, pea leaves are covered with a large amount of epicuticular wax, which repels aerosol droplets. The leaf wax of marie white (Chenopodium album), for example, is not as water-repellent and is damaged by greater retention of contact herbicide. Other post-emergent herbicides have a contact effect on the crop, and if the amount of wax on the leaves is low or damaged by wind, hail, frost, flying sand particles or mechanical damage of some kind, the effectiveness of the waxy cuticle is reduced and serious burns can occur.
If post-emergence preparations are planned, the amount of wax on the leaves can be checked before spraying by taking a sample of the plant and dipping it in a container with a 1% solution of methyl violet dye. The plant is then taken out and the excess dye is carefully shaken off. The amount of dye retained indicates areas where the waxy cuticle is damaged or incomplete. This level is evaluated and the decision to apply herbicide is made when a satisfactory level of dye-repelling tissue is reached. In some cases, it may take several days for the wax to build up before spraying is safe, especially after a period of poor weather conditions.
Translocated herbicides are absorbed and transported in the vascular system of the plant. Selectivity depends on the resistance of the crop and the susceptibility of the weed to the herbicide. The crop may have a mechanism to break down the herbicide to a non-toxic derivative, or conversely, a susceptible weed may metabolize the toxic derivative through a biochemical process that the crop does not possess. An example is non-toxic MCPB, which is converted to toxic phenoxyacetic MCPA by b-oxidation in susceptible broadleaf weeds, whereas legumes lack this metabolic process. The selective use of bentazone may be due to differential retention and uptake as well as the ability to metabolize bentazone, and this material is widely used on legumes (Vicia) and beans (Phaseolus).
Herbicides of different application periods
Herbicides applied before sowing seeds or planting seedlings, before weeds sprout. Usually they are called pre-sowing herbicides. This group includes both soil herbicides used before sprouting and leaf herbicides used after sprouting.
Herbicides applied simultaneously with sowing are usually called with-sowing herbicides. They are applied by taping into the zone of the row and the protective zone between the rows (not cultivated), as well as by continuous spraying. They are mainly used in row crops.
Pre-sowing and with-sowing herbicides are often incorporated into the seed bed by cultivation. Cultivation required to mix them effectively in the seed bed can result in too thin a layer, which can adversely affect crop growth. On soils with a denser structure, seeding may be delayed until soil conditions are suitable for the use of incorporation methods. Pre-seeding herbicides are usually used where perennial grass populations are present.
Herbicides used after the seed is sown, before crop and weed emergence, are predominantly soil-acting. Often referred to as preemergence herbicides. Some of them act on emerged weeds by contact, others destroy weeds by absorption from the soil, others work in a combination of both, most of them disrupt photosynthesis. Materials whose action is based on absorption from the soil are classified as residual herbicides. They have low solubility and persist in surface soil layers, but to be effective, most require moisture soon after application to penetrate the soil within reach of weed seeds and roots. The selectivity of pre-emergent herbicides is achieved by planting the crop below the location and availability of the herbicide in the soil, and in some cases by the innate tolerance of the crop to the herbicide.
The effectiveness of residual herbicides is affected by the amount of clay and organic matter in the soil. Clay particles can adsorb the chemical on the surface, thereby blocking a proportion and reducing efficacy. Organic matter acts in a similar way. Residual herbicides are degraded by ultraviolet light if they remain on the surface, and bacteria complete the process in the soil. Pre-emergent contact herbicides rely solely on killing weeds that appear before seeding. Because weed control and crop emergence usually coincide, the ability to use them on some crops is limited.
Postemergence herbicides are applied by spraying the soil solidly or by tape at the base of the stem, making sure the solution does not reach the vegetative parts. They are also called post-emergent herbicides. Post-emergent herbicides act on leaves only by translocation or by contact and translocation, and in some cases they also have a residual effect. The selectivity of such preparations can be explained by the absence of contact with the leaves of the crop due to the waxy cuticle of the leaves (waxy coating, such as in peas or cabbage) or the absence of negative effect on the crop when absorbed by the leaves.
Sensitive and herbicide-resistant plants
Depending on the response to herbicide application, cultivated and weed plants are divided into:
sensitive – completely destroyed;
medium-sensitive – die off partially or are depressed;
The phase of development affects the sensitivity to the action of herbicides. Both cultivated and weed plants show the greatest sensitivity at an early age, especially during germination.
The presence of a stronger root system has a positive effect on plant resistance.For this reason, perennial weeds are more resistant than annual weeds. For example, the active root system of such weeds as Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis), creeping mustard (Rhaponticum repens), field bindweed (Convolvulus arvensis), field horsetail (Equisetum arvense) which lies more than 10 cm deep is resistant to atrazine which cannot penetrate to greater depths. This property allows using this drug in gardens and forest nurseries, destroying weeds whose root system lies in the upper layers of the soil without affecting the roots of trees and seedlings.
Short- and long-acting herbicides
Long-acting drugs that last more than one year include atrazine, propazine, simazine, diuron. Short-acting ones are 2,4-D, 2M-4X, reglon, pyramine, promethrin, tillam etc.
The effect of herbicides aftereffect should be taken into account when rotating crops in crop rotation.
Timing of herbicide treatments
Depending on the timing of treatment herbicides are distinguished:
- pre-sowing application to the soil with incorporation by harrows or cultivators;
- post-sowing application to the soil with or without simultaneous embedding;
- pre-emergence spraying of the field before the crop emerges;
- post-emergence spraying;
- post-harvest treatment during the periods of weed growth.
Pre-emergence treatment with herbicides is limited to a few days – from sowing to emergence of seedlings, and if herbicides cannot be incorporated into the soil by treatment, non-volatile preparations should be used.
Pre-sowing and pre-emergence treatments are effective because they suppress weeds in the most vulnerable early growth phases, when the susceptibility of crops to weed infestation is greatest.
Methods of herbicide treatment
Herbicide treatments are divided into:
- continuous – treatment is carried out evenly over the entire area, used in crops and unoccupied fields;
- row treatment – used more often in row crops;
- banded – used in the same way as the row method;
- focal – local suppression of weeds, more often used in the fight against
- especially harmful and quarantine weeds with the help of herbicides of continuous action.
Post-emergent treatments are carried out by spraying. Treatment timing and application rates play an important role to prevent damage to cultivated plants.
In row crops post-emergent directional spraying is used with special sprayers in the inter-row or rows.
Technologies for using granular herbicides are being developed. Application is carried out by special machines to a given depth in the row or row-spacing, or by scattering on the soil surface. Granules have a number of advantages: longer action in the soil, decomposition processes under the influence of microorganisms are slower.
In some countries herbicides are applied together with irrigation water. This method is called herbigation.
On soils subject to erosion, the use of herbicides in fallow fields allows reducing the number of treatments.
Herbicide release forms
Forms of herbicides can be:
- powdered, water-soluble and water-insoluble (suspensions), containing up to 50-80% of the active ingredient;
- aqueous solutions and water-soluble concentrates;
- emulsion concentrates;
- granules, contain up to 5-10% of the active substance;
The form of the drug affects the effectiveness of the herbicide.
The formulation may contain surfactants (sulfanol, OP-7, OP-10, etc.) to improve emulsion or suspension stability, as well as for better wettability and adhesion to the treated surfaces.
Herbicide consumption rates
Optimal rates of consumption, timing and methods of application are established for all herbicides.
The exact rate of herbicides consumption is determined taking into account the following factors:
- species composition of weeds;
- granulometric composition of soil and content of organic matter
- weather conditions at the time of processing;
- residual effect on subsequent crops.
Consumption rates are often calculated in kilograms of active substance per 1 ha D or in kilograms of preparation (technical product) per 1 ha:
where d is the rate of active ingredient consumption, kg/ha, A is the content of the active ingredient in the technical preparation, %.
It is also possible to calculate the rate of herbicide consumption, at given rates of the preparation:
The rate of herbicide consumption for strip application used, for example, in row crops, is calculated according to the formula:
where Dл is the rate of herbicide consumption at tape application, kg/ha; Dc is the rate of herbicide consumption at continuous application, kg/ha; S is the spraying belt width, cm, M is the width of row spacing, cm.
When using herbicides in liquid form, the rate of liquid consumption is calculated taking into account the used machinery and equipment. For contact preparations of soil action liquid consumption rates are higher. In case of aerial treatment rates are lower than when using mounted or trailed sprayers coupled with tractors.
Approximate rates for ground sprayers: when using contact herbicides are 300-600 l/ha, systemic – 150-300, soil action – 300-400 l/ha.
Consumption rate of the liquid in case of aerial spraying with low-volume spraying is 25 l/ha in grain crops; with the relative humidity of less than 50% – 50 l/ha. Soil herbicides and when treating rice crops liquid consumption is 50-100 l/ha, flax crops – 100-150 l/ha.
The concentration of the working solution K, % depending on the herbicide consumption rate for the active substance D, kg a.d./ha and the liquid consumption rate Q, l/ha, is calculated by the formula:
Doses of herbicides are adjusted taking into account the sensitivity of cultivated and weed plants. To control perennial weeds the application rate is increased by 15-25%.
Conditions for using herbicides
Influence of weather conditions
Wind. Wind gusts cause uneven distribution and increased evaporation of herbicide solution during spraying. At wind speeds of 3.6 m/s, droplets with a diameter of less than 100 µm are completely blown away by gusts even at a sprayer distance of 38 cm from the soil surface. Drift decreases with increasing droplet size, and at a diameter greater than 325 μm stops.
Therefore, optimal spraying conditions for ground-based boom sprayers are formed in windless weather, for aerial spray generators – wind speed should not exceed 2 m/sec. In order to protect the crops sensitive to the drug, a 5-10 m wide protective strip is left on the neighboring areas, its width is increased in windy weather, or no spraying is conducted at all. For aerosol generators protective strip is 100 m, and in the case of aerial spraying with wind direction to the adjacent field it is increased up to 2 km.
Precipitation. Spraying is carried out in the morning and evening if there are no precipitations. During the daytime, ascending air currents lift small drops of solution upwards and can carry them over long distances. Herbicide effectiveness decreases if there is precipitation during the spraying or during the first 6 hours after it.
Temperature. Optimal air temperature for the processing is 16-22 °C. Low temperatures reduce the drug effectiveness due to reduced growth activity of weeds, high temperature – increases evaporation of the solution and pose a threat to crops in neighboring fields which are sensitive to herbicide.
Influence of soil and external conditions
Soil moisture. Low soil moisture reduces the effectiveness of a number of herbicides, detoxification is slower, which leads to a prolonged effect on subsequent sensitive crops of the rotation. High moisture contributes to the penetration of herbicides deep into the soil, where they are quickly inactivated, not creating the proper effect in the upper layers.
Sunlight. Herbicides that are not resistant to sunlight (Triallat, Treflan, Tillam, etc.) should be incorporated into the upper layers of the soil.
Soil composition. Soils rich in humus or silt fractions have increased adsorption to herbicides, which reduces their effectiveness. Therefore, in such soils the consumption rates are increased. On the contrary, doses are reduced on poor sandy and sandy loam soils.
Characteristics of main herbicides
Salts and esters of 2,4-D and 2M-4X are widely used in the control of dicotyledonous weeds. The recommended rate is up to 0.5-1.6 kg/ha. In winter and spring wheat, barley, winter rye, oats, sorghum, millet, and cereal forage crops 2,4-D is used in the rates of 1,2-1,6 kg/ha in the phase of crop tillering before the beginning of emerging into the tube.
To control resistant (Tripleurospermum, Stellaria, Polygonum, Galium, Violet, Viola), cereal weeds (bristlewort (Setaria), hedgehog (Echinochloa), wild oat (Avena fatua), bluegrass (Poa)) and perennial weeds (thistles (Sonchus), creeper vine (Convolvulus), couch grass (Elytrigia), etc.) are used. ) mixtures of 2,4-D with dicamba, picloram or chlorosulfuron (grodil, grandstar, harmoni) are used. These herbicides have high efficiency at low doses: 10-70 g/ha for grain crops.
Against certain harmful weeds herbicides of narrowly targeted action or specially synthesized ones are used. For example, Avadex (2-4) and Triallat (1.6-3.2) are used against oat (Avena fatua) by preemergence or preplant spraying with immediate embedding. If necessary, the treatment is repeated after harvesting.
Glyphosate-basedThe use of glyphosate is currently restricted in some countries due to its possible carcinogenic effects on humans. Note UniversityAgro.ru. total action preparations are widely used in the agroindustrial complex and private farms. Different doses of 2-3 to 6-8 have shown their effectiveness in controlling many malevolent weeds in crops of different crops (subject to crop protection), vineyards, fruit plantations, nurseries, hayfields and pastures, and bare fallows.
Peculiarities of herbicides application for different crops
Grain legumes have high sensitivity, which limits the use of herbicides. On soybean and bean crops pre-sowing treatment with treflan with immediate embedding at rates of 4-10 kg/ha is carried out. In crops of soybeans, beans, peas, fusilad (2-4 kg/ha) is sprayed in the phase of 4-5 leaves.
Promising herbicides for treatment of legume crops include nabu (1-3 kg/ha), pivot (0.5-1 kg/ha), etc.
Cultivation of corn for grain and green fodder because of possible yield losses up to 25-30% of the weed infestation is possible only with the use of herbicides.
Against dicotyledonous weeds herbicides 2.4-D (0.85-1.4 kg/ha), Basagran (2-4 kg/ha), Dialen (1.9-3 kg/ha) are used. A mixture of bentazon with atrazine (3-4 kg/ha) and lontrel-300 (1.0 kg/ha) is used against resistant and grasses. Dual (1.6-2.1 kg/ha) or Prim-Extra (4-6 kg/ha) is used to treat soil or corn sprouts.
Promising herbicides in corn crops include titus (0.04-0.05 kg/ha) and its mixture with pressed (0.35 kg/ha).
Sugar and fodder beets
Reduction of sugar and fodder beet yields from weed infestation can reach 30-50%.
- betanal (4-6 kg/ha) in the phase of two true leaves in the crop;
- pyramine (4-8 kg/ha);
- hexilur (1-2 kg/ha);
- eptam (2.7-8.0 kg/ha) in pre-sowing, pre-emergence treatment or on crop sprouts;
- lontrel-300 (1-2 kg/ha) spraying at the appearance of 1-3 pairs of leaves.
Against cereal weeds apply – dual, nabu, targa, zelek, caribou.
Agritox (1-2 kg/ha), Stomp (5 kg/ha), Zenkor (1.4-2.1 kg/ha), Tezagard (3-4 kg/ha), Topogard (2-4 kg/ha) are used for preemergence treatment.
Fusilad (2.0 kg/ha) and targa (2-4 kg/ha) are used to treat seedlings 10-15 cm in height against cereal weeds in the phase 3-5 leaves, including against couch grass (Elytrigia repens).
Early sunflower plants are sensitive to a large number of systemic herbicides.
Promethrin (2-4 kg/ha), haptan (4.2-5.6 kg/ha), and trifluralin (3.3-8.3 kg/ha) are used for pre-sowing treatment.
Fusilade (1-2 kg/ha) treatment is carried out in the phase of 2-4 leaves in weeds.
Against dicotyledonous weeds in flax crops at the 5-12 cm height in herringbone phase use 2M-4X (0.8-1.5 kg/ha), Basagran (2.7-4 kg/ha), Lontrel-300 (0.1-0.3 kg/ha), Cross (0.01-0.015 kg/ha).
Dual (1-2.1 kg/ha), Treflan (3.2-4 kg/ha), Triallat (1.2-2 kg/ha) are used to control cereal weeds, including specialized ones, as pre-sowing soil spraying with immediate incorporation.
Tomato. For tomato planting treatment: soil spraying before sowing or seedling planting with Nitranan (3.3-5 kg/ha), Treflan (2.0-2.4 kg/ha). Against annual and perennial cereal weeds 15-20 days after planting or in the phase of 1-2 true leaves of culture – nabu (2.5-5 kg / ha) and zencor (0.7-1.4 kg / ha).
Carrots, celery, parsley, dill. Pre-emergence soil spraying – malorane (3-4 kg/ha) and nitran (2.5 kg/ha). After sprouting – Prometrin (2-4 kg / ha).
Cabbage. When no-planting method of cultivation, spraying of soil with Semeron (1-2 kg / ha) before sprouting. Nitran is used before planting of seedlings with embedding in the soil at a rate of 3.3-5 kg / ha, butisan (1.5-2 kg / ha) – 1-7 days after planting.
Table beet. Treatment is similar to sugar and fodder beets.
Cucumber, onion, garlic. Apply targa (1-2 kg/ha), treflan (4-6 kg/ha), dual (1.1-2.1 kg/ha), etc.
Fruit gardens, berry orchards, nurseries and medicinal herb plantations
Herbicides of continuous and systemic action are used in directional spraying, i.e. with protection of cultivated plants. For this purpose, glyphosate and nitossorg (4.0-8.0 kg/ha) are used in vineyards, fruit, citrus and tea plantations during mass regrowth of perennial weeds.
The same herbicides are used on unused strips, gas pipelines, airfields, power lines, and other non-agricultural land to control unwanted deciduous trees (aspen, alder, birch, etc.).
In crops of succession, oil poppy, marigold, chamomile apothecary use preplanting treatments with Dual (1.5 kg/ha).
Plantations of strawberry, lavender, peppermint, clary sage, essential rose, melissa, and other crops receive directional treatments with Zencor (2,1-2,2 kg/ha), Lontrel (1,0-1,7 kg/ha), Pyramine (2-4 kg/ha), Kerb (3-5 kg/ha) when weeds grow in mass.
Improvement of herbicide use technology
One-sided application of the chemical method of weed control leads to the actualization of a number of problems:
- insufficient data on the effect of conditions under which the phytotoxicity of herbicides is fully manifested;
- violation of agricultural techniques, leading not only to a decrease in herbicide efficacy, but also the applied farming system;
- use of one type of herbicide for a long time leads to suppression of sensitive weeds and accumulation of resistant ones.
To prevent negative effects and get the maximum effect it is necessary to take into account agroclimatic conditions, the state of weeds and cultivated plants, weed infestation of fields, to comply with the application regulations. To solve the problem of proliferation of resistant weeds, herbicides of broad selective action should be used with alternation by years.
Chemical methods of weed control should be part of a comprehensive system of extermination measures. Agrotechnical methods are the priority, while chemical methods are additional.
Introduction of energy-saving soil-protecting technologies has also aggravated the problem of controlling resistant weeds. Research is being conducted on ways to improve the effectiveness of herbicides along the lines of:
- changing the timing of treatments;
- increasing the effectiveness with the help of mixtures of herbicides, growth regulators and fungicides;
- research of new promising drugs;
- development and mastering of herbicide systems.
Herbicide system is a set of measures aimed at systemic extermination and preventive measures to control weed infestation on agricultural land and adjacent areas and is an integral part of the farming system.
The system of herbicides is inseparably connected with the system of farming, including ecological and environmental safety of systems of protection of agrophytocenoses from weeds, as well as high economic and biological efficiency.
To date, the developed systems of herbicides allow:
- more fully use the potential of the crop rotation;
- strengthen the effect of agronomic practices and fertilizers as regulators of weed infestation;
- systematically consider the effect and aftereffect of each herbicide;
- reduce consumption rates and the number of treatments due to the positive effect, combining all elements of the system;
- replace, where possible, chemical methods of weed control with non-chemical methods.
The system of herbicides in crop rotations is determined by the composition of cultivated plants, agroclimatic conditions and soil type. For example, in crop rotations on sod-podzolic soils (1 – seeded fallow, 2 – winter wheat, 3 – barley + perennial grasses, 4-5 – perennial grasses, 6 – winter wheat, 7 – potatoes, 8 – barley) herbicides were used only in crops of winter wheat, potatoes and barley. At the same time the reduction of weed infestation was 80-95%, and the productivity of the crop rotation increased from rotation to rotation.
Toxicity of herbicides
All herbicides are toxic substances. Toxicity is measured by LD50 (mg/kg of live weight), i.e. the dose that, if ingested, kills 50% of warm-blooded animals.
According to the degree of toxicity herbicides are divided into:
- strongly toxic – LD50 < 50 mg/kg,
- highly toxic – LD50 = 50- 200 mg/kg,
- moderately toxic – LD50 = 200-1000 mg/kg,
- low-toxic – LD50 > 1000 mg/kg.
Most herbicides approved for use are low-toxic. Compliance with safety regulations ensures harmlessness to humans and animals.
In Russia, the legal framework for the use of agrochemicals, including herbicides, is defined by Federal Law of the Russian Federation No. 109-FZ of June 24, 1997 “On the safe handling of pesticides and agrochemicals”.
A number of technical regulations (standards, sanitary rules and instructions, occupational safety instructions) establish requirements and norms for work with agrochemicals, their storage and transportation. These rules are mandatory for familiarization and execution by persons engaged in work with agrochemical means of plant protection and weed control.
Occupational safety requirements for working with herbicides
Persons who are familiar with safety regulations on the use of herbicides are allowed to work with herbicides. The rules should include information about the properties of the used drugs, its effect on people, precautions during work, first aid in case of poisoning.
Persons under 18 years of age, pregnant and lactating women are not allowed to work with herbicides.
Persons allowed to work with herbicides must undergo periodic medical examinations (for occupational hazards), establishing professional suitability and the possibility of developing occupational diseases. According to the requirements of the law, medical examinations are subject to the condition if the workplace according to the results of the Special Assessment of Working Conditions (SAWC) has a class of harm 3.1 or higher. Also, when a class 3.1 chemical factor is set workers are given milk.
According to the Standard norms of issuing special clothing, workers are provided with special clothing. When working with solutions filters of respirators should be changed 2-3 times a day. At the end of work, protective clothing and personal protective equipment (PPE) are washed with warm water and soap and dried. Respirators are washed and treated with 0.5% solution of potassium permanganate or alcohol, washed with clean water and dried. Store protective clothing and PPE in a specially designated place.
Persons guilty of violating the rules of safe handling of agrochemicals shall be held liable in accordance with the legislation of the Russian Federation.
Rules for storage and transportation of herbicides
Containers intended for transportation and storage of herbicides should be sealed, easily cleaned and decontaminated. It is not allowed to transport and store preparations with food, fodder and agricultural products.
Special warehouses are used to store herbicides, separated from farm and residential buildings by at least 200 m. They should be equipped with ventilation and lighting, with no access to unauthorized persons. They are designed sloping floors without slots and basement, shower and washbasin, provide room for storage of protective clothing and a first aid kit. Release of agrochemicals from the warehouse is carried out by written order of the head of the enterprise or the chief agronomist. Storage of herbicides without packaging is not allowed.
Vehicles, containers and equipment are decontaminated after use: metal objects are treated with kerosene or 3-5% soda ash, wooden ones – with calcium chlorate; containers from agrochemicals are burned, the remains of the solution are disposed according to instructions.
Safety precautions when working with herbicides
Work with herbicides is carried out under the supervision of a specialist. Prior to treatment, the inhabitants of nearby settlements are notified. This measure is necessary to prevent accidental poisoning of animals and bees from chemicals during treatment and after it. Beehives should be closed for the period of treatment. Treated plants for animals are not suitable for fodder for two weeks. Cattle driving routes shall be at least 200 m away from the place of preparation and pouring of solutions.
Treatment of fields and areas located at a distance of 300 m from water bodies, household and residential areas is allowed to treat with low-toxic herbicides by ground boom sprayers with the permission of the plant protection station.
Filling stations are located at a distance of at least 200 m from residential and farm buildings. Solution preparation and filling operations must be mechanized. At the end of the works the filling station site is treated with bleach and plowed over.
It is forbidden to eat, drink or smoke during the work. At the end of the work carefully wash hands and face with soap and water or take a shower.
First aid in case of poisoning
Common signs of poisoning are dizziness, cramps, chills, nausea, sore throat, coughing, etc.
At the first signs of poisoning, the worker shall immediately be taken away from the place of work to clean air and a doctor shall be called. Give the doctor the name of the active ingredient of the agrochemical and the label or instructions to the drug, which indicates the first aid measures for poisoning.
If the chemical agent enters the stomach, cause the victim to vomit by giving a few glasses of warm water and several tablets of activated charcoal beforehand.
If the chemical comes into contact with exposed parts of the body, rinse immediately with plenty of water, then wash with soap. In case of contact with eyes, rinse with plenty of water, then treat with a 2% soda solution.
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