In nature, there are thousands of varieties of annual and perennial weeds. These ubiquitous “annoyances” are in stiff competition for cultivated plants, taking away moisture, light and nutrients from the soil. Such a common method as weeding is not always effective in controlling weeds, since perennial species quickly grow from parts of rhizomes remaining in the soil. That's when the herbicides come to the rescue for weed control.
Herbicide action
Herbicides are special chemicals designed to control
quantity or prevention of weed growth. In addition, with the help of herbicidal agents, it becomes possible to reduce or even completely eliminate mechanized or manual cultivation, thereby reducing moisture loss and preventing soil erosion. Herbicides are divided into two categories - non-selective (continuous action) and selective (selective action).
Weed control herbicides non-selective
Continuous herbicides used when not on the field
(garden) of cultivated plants, as they destroy all available vegetation, penetrating the leaf surface. Typically, non-selective agents are used before the first seedlings appear, after harvesting, or when the field settles in pairs. However, recent developments make it possible to apply certain types of herbicides of this category as selective to genetically
modified varieties and hybrids of crops (for example, to soybeans, sugar beets, potatoes, etc.), since they have a resistance gene to these agents. The action of non-selective herbicides can be carried out in two ways - contact and systemic. With contact action, drugs directly affect the treated surface. They begin to work very quickly and are not washed off by rain. With a systemic action, the active substance, moving along the plant to the points of its growth, causes them to die. Such funds are absorbed into the plant more slowly, but they very effectively destroy perennial weeds with a powerful and extensive root system.
Selective weed control herbicides
Selective action herbicides are applied to specific crops without damaging them, but only to control weeds growing with the crop on the same field. These funds belong to different chemical classes and have different mechanisms of action. To exclude the phytotoxicity of the drug by culture, in certain cases, antidotes are used. Herbicides for killing weeds have biochemical selectivity based on the ability of the plants themselves to destroy their toxic compounds to non-toxic. Morphological selectivity is based on differences in the external structure of cultivated plants, namely in the shape and arrangement of leaves, as well as in the features of their surface (pubescence, wax coating, etc.) - all this prevents the penetration of herbicides.
Topographic selectivity is characterized by the fixation of the introduced herbicide in the upper soil layer by absorption by colloidal particles (clay, humus), due to which the toxic effect of the drug does not reach the roots of the cultivated plant, and weeds growing in the upper soil layer are destroyed. Currently, selective herbicides are the most effective for killing weeds. The price of these drugs depends on their composition and mode of action.