In the nature there are thousands of varietiesannual and perennial weeds. These ubiquitous "bothers" make up a tough competition for cultural plants, taking away their moisture, light and nutrients from the soil. Such a common method as weeding is not always effective in combating weed vegetation, since perennial species quickly germinate from the remaining parts of the roots of rhizomes. That's when the herbicides come to the rescue to kill the weeds.
Action of herbicides
Herbicides are special chemicals intended for control
quantity or prevention of weed growth.In addition, with the help of herbicidal agents, it is possible to reduce or even completely exclude mechanized or manual cultivation, thereby reducing the loss of moisture and preventing soil erosion. Herbicides are divided into two categories - non-selective (continuous action) and selective (selective action).
Herbicides for the destruction of weeds non-selective
Herbicidal preparations of continuous action are used in the absence on the field
(garden) of cultivated plants, since theyDestroy all available vegetation, penetrating into the leaf surface. Typically, non-selective agents are used before the emergence of the first shoots, after harvesting or when the field settles on steam. However, recent developments make it possible to use some types of herbicides of this category as genetically selective
modified varieties and hybrids of crops(for example, to soybeans, sugar beets, potatoes, etc.), since they have a gene of resistance to these agents. The action of non-selective herbicides can be carried out in two ways - contact and systemic. With the contact action, the preparations influence directly on the treated surface. They start working very quickly and are not washed away by rain. With systemic action, the active substance, moving along the plant to the points of its growth, causes their death. Such drugs are absorbed into the plant more slowly, however, perennial weeds that have a powerful and extensive root system are very effective.
Herbicides for the destruction of weeds, selective
Herbicidal preparations of selective actionapply to specific crops without damaging them, but only to suppress weeds growing with the crop in the same field. These means belong to different chemical classes and have different mechanisms of action. To eliminate the phytotoxicity of the preparation by culture, antidotes are used in certain cases. Herbicides for the destruction of weeds possess biochemical selectivity, based on the ability of plants themselves to destroy their toxic compounds to non-toxic ones. Morphological selectivity is based on differences in the external structure of cultivated plants, namely in the form 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 byfixation of the introduced herbicide in the upper soil layer by absorbing it with colloidal particles (clay, humus), so that the toxic effect of the preparation does not reach the roots of the cultivated plant, and the weeds growing in the upper soil layer are destroyed. The most effective at present is selective herbicides for the destruction of weeds. The price of these drugs depends on their composition and mode of action.
