There are nearly 1,000 weed species in agricultural fields nationwide, with 20-30 major species causing crop damage leading to reduced yields. The principle of herbicide killing is relatively complex. After herbicides are absorbed by plants, they form a complex multitude of factors that play some kind of disturbing role in the normal physiological and chemical processes of plants. Weed absorption of herbicides, in the weeds constantly carry out the process of material exchange and energy metabolism, that is, the absorption of nutrients for assimilation and elimination of waste for the process of heterogeneity. Some important aspects of this metabolism are hindered or destroyed, life will stop or be inhibited. The use of herbicides can make weeds these important links are hindered and destroyed, physiological and biochemical imbalance, so that the life of weeds to stop or be inhibited, so as to achieve the purpose of weed control. The mechanism of herbicides can be broadly divided into the following five.

1、Hindering photosynthesis

Photosynthesis is an important process for higher green plants to obtain energy and manufacture nutrients, which is the basis for the existence of plant life. If photosynthesis is disturbed or destroyed, plants will die abnormally. Photosynthesis is the process by which chlorophyll absorbs light energy and converts carbon dioxide and water into carbohydrates, as well as the complex process of releasing oxygen.

The essence of photosynthesis is the conversion of light energy into chemical energy. Photosynthesis is divided into two steps: photosynthesis and dark reaction. Herbicides can hinder both the photosynthesis and dark reaction. Many herbicides enter the body of the plant, reach the leaves, and have a strong inhibitory effect on photosynthesis, so that the plant will be depleted of stored nutrients, but no nutrition, which will lead to starvation.

There are also herbicides that can affect the dark reaction. The dark reaction is the second step of photosynthesis, which is carried out in the absence of light conditions.

2. Destruction of absorption and energy metabolism

The energy required for plant growth and development is obtained through absorption, which is the source of energy for plant growth activities. Photosynthesis is an energy storage process, absorption is an exergy process. In the absorption process, plants form high-energy bond carbohydrates to provide the energy needed for growth and development. When certain important aspects of plant uptake are disrupted, the survival of the entire plant is affected and death results. For example, when thatch wilt is absorbed into the weed, it replaces the site of pyruvic acid, which plays an important role in the absorption process, disrupting the plant's absorption, inhibiting the synthesis of acids and enzymes, and suppressing the metabolism of fats and sugars, leading to the death of the weed. Some herbicides cause weed death by destroying energy metabolism.

3、Inhibition of protein, nucleic acid and other substances synthesis role

Many herbicides enter the body of weeds, destroy the normal physiological function, inhibit the synthesis of proteins and nucleic acids, thus causing the death of weeds.

4、Interference with the role of plant hormones

The plant body contains a variety of hormones, which are important for the coordination of plant growth and development, and are indispensable substances for the regulation of plant growth, development, flowering and fruiting. 2,4-Drop, dicamba and other hormone-type herbicides into the weed body, destroying the original balance of natural hormones, so that the plant appears to be deformed development, cell division, elongation and differentiation irregularities, which can interfere with the normal growth of sensitive plants. In the different organs of the victim weed reaction is different, stimulating effect and inhibition phenomenon coexist, breaking the regularity, so that all parts of the plant coordinated with each other, but also the relationship between each other and the constraints of abnormal changes. Therefore, after the weeds absorb the herbicide, the internal radical abnormality, so that the weeds produce physiological disorders, stalk distortion and deformity, foliage crumpling and discolouration and loss of green, resulting in death.

5、Hindering the transport of nutrients

Monocotyledonous and dicotyledonous plants have different structure of the formation layer, dicotyledonous leaves are ring bast, monocotyledonous leaves are sporadic distribution of vascular bundles. When some herbicides enter the weed body, and through the sieve tube conduction in the bast, can make the cell division of the formation layer, excessive elongation, become deformed and necrotic, so that the blockage or destruction of the bast tissue, hindering the transport of nutrients, so that the weed can not get nutrients, water and cause death.