Sterile herbicide
That is to say, there is no selectivity for plants, and' killing at sight of green' can make all plants exposed to this medicine suffer and die. At present, there are mainly the following types in China:
(1) Paraquat is a quick-acting contact poison with moderate toxicity. After exposure to this drug, chlorophyll and photosynthesis of plant leaves will be destroyed rapidly, and will change color after 2-3 hours. This drug only acts on the green tissue of plants, without conduction and internal absorption, and can only harm the parts in contact with the drug, and cannot penetrate the bark after embolization. Once in contact with soil, it will be absorbed and passivated, and will not harm the roots and soil of plants.
(2) diquat (Linong) is a quick-acting herbicide with moderate toxicity and slight conductivity, which can be quickly absorbed by the green tissues of plants and make the infected parts yellow. Similar to paraquat, it can't penetrate the cork skin, has no destructive effect on underground rhizomes, loses vitality quickly after contacting with soil, and is harmless to seeds in soil. It is suitable for weeding broad-leaved weeds and can also be used as a desiccant for seed plants to accelerate withering treatment. When corn, rice and wheat are ripe, the moisture content in their grains is high. This medicine (20-40g active ingredient and15-20kg water per mu) is sprayed and harvested after 3-4 days. The water content of seeds is about 30% lower than that without pesticides.
(3) Glyphosate is a low toxicity, systemic and conductive herbicide, which mainly leads to plant death by inhibiting protein synthase in plants. It can not only be conducted to underground roots through stems and leaves, but also be conducted at different tillering stages of the same plant, which is especially destructive to underground tissues of long-term deep-rooted weeds. It can also be used to smear tall weeds and shrubs or inject them into non-target tree species with a tree injector as needed, and all can achieve ideal results. The absorption and conduction of drugs are greatly influenced by temperature and concentration. The conduction is slow at low temperature and low concentration, and it usually takes 10- 15 days to take effect, and it can reach 3-7 days at high temperature.
(4) sulfometuron-methyl (Sencaojing) is a pre-bud and post-bud herbicide with low toxicity and strong activity, with systemic property. After the liquid medicine is absorbed by the plant green tissue, the synthesis of amino acids in the body is blocked, the cell division at the root growth end is destroyed, the plant growth is blocked, and then the plant is obviously purplish red, greenless and necrotic. Weeding irrigation has broad spectrum and high activity, and can completely kill the roots, stems and leaves of weeds. The drug can also exert its pre-germination activity and inhibit the germination of weed seeds after infiltrating into the soil. According to the type of soil, 25-50g effective components are applied to each mu of weeds and shrubs, and the residual effect lasts for several months or even more than one year. Therefore, it is often used for weeding irrigation in forest land, opening forest fire isolation belt, clearing forest land after logging, leisure non-cultivated land and roadside wasteland. It is found that some conifers can metabolize this drug into inactive glycosides, which is selective. Therefore, it can be the best selective pesticide in some conifer nurseries and young forests, and it can also cause phytotoxicity to other plants.
selective herbicide
It refers to a herbicide that is selective to plants within a certain dosage range and only kills weeds without harming crops. There are many kinds of herbicides and their applications are complex. Weeding effect and crop safety are closely related to local soil quality, temperature, grass period and crop growth. Therefore, the use of this kind of herbicides must be combined with the actual situation of the land, and the different functional characteristics of each variety should be used for compound test. In practice, we constantly explore and summarize the best variety, the best dosage and the best use method suitable for the local farming system, so as to achieve the best effect with half the effort. According to the main action characteristics of these herbicides, they can be roughly divided into the following two categories: one is pre-bud selective herbicides; Second, selective herbicides after germination (seedling). Some varieties have the function of weeding before germination and after seedling, while others have the function of weeding before germination besides after seedling. It can only be divided according to its main functions. Because of the incomplete understanding of its product characteristics, it is not necessarily accurate and scientific, and it is for reference only.
(1) Pre-germination herbicide refers to the herbicide applied to the ground before or after sowing, so it is also called soil treatment agent, and its main control object is annual weeds that germinate with seeds. Among them, acetochlor (Hennessy), butachlor (Machete), alachlor (Lasso), metolachlor (Dor), pendimethalin (Bu, Shi Tian), naproxen, butachlor, clomazone and herbicides are the main varieties to control gramineous weeds. The main species for controlling broad-leaved weeds are: oxyfluorfen (GOR), acetochlor, atrazine, bensulfuron-methyl, heptachlor, oxadiazon and ametryn.
(2) Post-emergence selective herbicides refer to herbicides that are harmless to crops when weeds are treated with liquid medicine after they are unearthed and become seedlings. Among them, there are two herbicides, namely stem and leaf herbicides, which are mainly used to control gramineous weeds: propargyl, propargyl and fenoxaprop-p-ethyl. The main species for controlling broad-leaved weeds are: 2.4 butyl, 2- methyl -4- chloro-sodium salt, bentazone (prometryne), diclofenac (broad-leaf withered), flumazone (clofenuron), herbicide (Gaoteke), chlorimuron-methyl, sulfuron-methyl, tribenuron-methyl (Superstar), metsulfuron-methyl, and tribenuron-methyl. 4. Plant growth regulators refer to agents that can regulate plant physiological functions and promote or inhibit plant growth and development. According to the mode of action, it can be divided into two categories: one is growth promoter, and the main varieties are gibberellin indoleacetic acid, ammonium nitrophenolate, sodium nitrophenolate, brassinolide and so on; The other is growth inhibitor, the main varieties are paclobutrazol, uniconazole, chlormequat and so on. However, it should be noted that these two effects are not absolute, and the same regulator will have different effects on plants at different concentrations.