Herbicides: classification, properties and applications
Herbicides are a broad group of chemical compounds designed to destroy or suppress undesirable, primarily weed, vegetation. In modern agriculture, they are a key tool for increasing yields, since weeds compete with crops for water, nutrients and light. By application volume, herbicides consistently rank first among all crop protection products, providing crop protection at almost all stages of cultivation.
Chemical Nature and Classification
The vast majority of modern herbicides are organic compounds synthesised by humans; inorganic compounds have not found wide application in agricultural practice. Herbicides are classified according to several key criteria that determine their behaviour in the agrocenosis and application technology.
By the nature of action on plants, herbicides of continuous and selective action are distinguished. Continuous-action herbicides suppress all plant species without exception and are used mainly on fallows, in industrial zones, along roads and when preparing a field for sowing. Selective herbicides affect only certain weed species without damaging crops; this group forms the basis of chemical weeding in crops.
By the method of penetration and distribution in the plant, contact and systemic preparations are distinguished. Contact herbicides act only at the application sites, destroying cell membranes and causing tissue death, but do not penetrate the root system of perennial weeds. Systemic herbicides are absorbed by leaves or roots and move through the vascular system of the plant, affecting the entire organism, including underground organs, which ensures the death of rhizomatous and root-suckering weeds.
By spectrum of action, herbicides are divided into narrow-spectrum and broad-spectrum preparations. Narrow-spectrum compounds affect a limited number of species or even a single weed species, while broad-spectrum ones are effective against a significant number of species. By mechanism of action, groups are distinguished that disrupt photosynthesis, inhibit cell division (mitosis), have a hormonal effect (synthetic auxins) and inhibit the synthesis of amino acids or lipids.
Active Ingredients
The modern range of herbicides includes several main chemical classes. Glyphosate derivatives (N-phosphonomethylglycine) are systemic continuous-action broad-spectrum herbicides; they inhibit the EPSPS enzyme, blocking the synthesis of aromatic amino acids, and are used to control annual and perennial weeds, as well as undesirable tree and shrub vegetation. Synthetic auxins based on 2,4-D (2,4-dichlorophenoxyacetic acid) and its analogues cause uncontrolled growth and death of dicotyledonous weeds; they are widely used in cereal rotations, often in combinations with dicamba or chlorsulfuron.
Sulfonylureas are a class of highly active systemic broad-spectrum herbicides acting at extremely low doses and inhibiting the enzyme acetolactate synthase (ALS), which leads to the cessation of cell division. This group includes metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl and their combinations. Chloroacetamides (e.g., acetochlor), dinitroanilines (trifluralin), triazines and other classes are also used, each with a specific mechanism of action and spectrum of activity.
Formulation Types
Herbicides are produced in various formulation types that ensure ease of storage, transportation and application. The most common are soluble concentrates (SL), emulsifiable concentrates (EC), suspension concentrates (SC), water-dispersible granules (WG), wettable powders (WP) and concentrated colloidal solutions. The choice of formulation is determined by the physicochemical properties of the active ingredient, the application method and safety requirements. Liquid forms are convenient for precise dosing and preparation of working solutions, while granular forms are used for soil application and reducing the risk of spray drift.
Applications
Herbicides are used in crop production to protect cereals, industrial, vegetable, fodder and fruit crops. Application technologies include pre-emergence soil treatment, post-emergence spraying of growing weeds and band application in rows. A separate area is desiccation (drying) of crops before harvest and treatment of fallow fields. The effectiveness of herbicides depends on the development stage of the crop and weed, weather conditions, soil type and compliance with application regulations.
Safety and Regulatory Framework
All pesticides, including herbicides, are subject to state registration and standardisation. General requirements for pesticides are established by GOST R 51247-99, and safety requirements for application — by GOST 12.3.041-86. According to the degree of hazard, chemical substances are divided into four classes in accordance with GOST 12.1.007-76: extremely hazardous, highly hazardous, moderately hazardous and low-hazard. When working with herbicides, personal protective equipment must be used, consumption regulations and waiting periods must be observed, and drift of preparations to neighbouring fields and water bodies must be prevented.
Market and Trends
Herbicides form the largest segment of the crop protection market. In the structure of domestic production, they account for about 68% of output, reflecting high demand for weed control products in the cultivation of major agricultural crops. The Asia-Pacific region and the countries of North and South America remain the largest consumers, while Russia and a number of CIS countries are actively developing their own production.
Key industry trends are related to the search for active ingredients with new mechanisms of action to overcome weed resistance, the development of combined preparations, reduced application rates and the transition to low-volume spraying technologies. Attention to the environmental friendliness of formulations and to biological-based products is growing. Organising supplies of herbicides, including the selection of the active ingredient and formulation type for a specific crop and phytosanitary situation, requires an individual approach.