Key points for the selection of cornfield herbicides
First, the main weed species
The main weeds in corn fields are: broad-leaved weeds, sorghum, scorpion, snail, sylvestris, leeks, ramie, shovel, purslane, etc.; grass weeds, foxtail, crabgrass, tendon Grass, etc.; sedge weeds have fragrant aconite and so on.
Second, the characteristics and application of the main herbicide
1 Sulfonylurea herbicide. There are mainly sulfimsulfuron, nicosulfuron, thifensulfuron and the like.
This type of herbicide has a wide range of weeding, and the weeding spectrum of each variety is quite different. The selectivity is strong. Each variety has corresponding applicable crops and weeding spectrum. It is highly safe for crops and highly efficient for weeds. It has extremely high activity per hectare. It is a kind of ultra-efficient herbicide in grams. It is easy to use and can be used for soil treatment as well as stem and leaf treatment. It is a special herbicide for cell cycle, which does not affect cell elongation or seed. Germination and emergence, its highly specialized effect can inhibit plant cell division and inhibit plant growth. After the plant is damaged, there is a partial growth, the young tissue is chlorotic, sometimes it shows purple or anthocyanin color, the growth point is necrotic, the veins are chlorotic, the plant growth is severely inhibited, dwarf, and finally the whole plant is dead. This type of herbicide acts rapidly, and the growth stops rapidly after the weeds are damaged, and the whole plant takes a long time to die completely.
2 Triazine herbicides. There are mainly chlorpyrifos, atrazine (atrazine), cyanazine and the like.
These herbicides are all soil treatment agents, mainly absorbed by roots, and individual varieties can also be absorbed by stems and leaves; inhibiting various physiological and biochemical functions in plants, but mainly inhibiting photosynthesis of plants; mainly used for controlling Annual weeds, the control effect on broadleaf weeds is better than the control on grass weeds; biochemical selectivity is the most important characteristic of this herbicide, and it is also the reason for resistant crops such as corn; Displacement selectivity is important for many deep root crops.
3 phenoxycarboxylic acid herbicides. There are mainly 2,4-D butyl ester, 2 methyl 4-chloro sodium salt and the like.
This herbicide can be rapidly absorbed by the roots and stems of broadleaf weeds, can be transmitted together with the transpiration stream through the xylem conduit, or combined with the photosynthesis product in the phloem screen, and in the plant meristem Accumulation in (growth point); when the salt or ester of the herbicide is sprayed on the plant, the plant turns it into a corresponding acid and becomes toxic; belonging to the hormone herbicide, which can affect almost every plant Physiological processes and biological activities lead to changes in plant morphology: the leaves are curled up or down, the petiole, stems, leaves, stalks are twisted and bent, the base of the stem is swollen, short and thick secondary roots are produced, and stems and leaves are discolored. It turns yellow, dry, and the base of the stem rots, and finally the whole plant dies. In particular, the meristems of plants such as heart leaves and tender stems are most vulnerable.
4 amide herbicides. The main varieties of amide herbicides are acetochlor, metolachlor, propisochlor, alachlor, butachlor and the like.
Almost all varieties of this herbicide are special herbicides for controlling annual grass weeds, and have poor control effect on broadleaf weeds; most of them are soil treatment agents, mainly applied before seeding of crops; It is mainly used to control annual weed shoots; the herbicides used for soil treatment have a short residual effect in soil, generally 1 to 3 months, which is easily degraded in plants; water solubility is medium to high, and volatility is small. , not ionized; mainly used for soil treatment, so its herbicidal effect is subject to environmental conditions, the important factors are soil colloid adsorption and soil water content.
5 organophosphorus herbicides. There are mainly glyphosate and so on.
Some of these herbicides have poor selectivity and are often used as herbicides in forest belts, orchards, non-farm and no-till fields. Some varieties have good selectivity; glyphosate can not only prevent annual weeds, It can also prevent some perennial weeds. Some soil treatment agents can prevent a variety of annual weeds; glyphosate can be absorbed by plant stems and leaves, and can be quickly transmitted in plants, both along the xylem and down the phloem. Conduction; plant meristem is the main site of action of some species of this herbicide. Glyphosate can rapidly transmit to plant meristem and rapidly accumulate to lethal concentration, affecting the metabolic process of the entire plant meristem. Inhibition of chlorophyll synthesis is one of its main points of action. Chlorosis is the first symptom of phytotoxicity produced by plants. With chlorosis, the plants gradually turn yellow and wither, and all the aboveground parts are browned and underground parts are necrotic. At the same time, glyphosate also affects the transpiration of plants.
6 bipyridyl herbicides. There are mainly enemy grass fast, paraquat and so on.
This herbicide has a wide herbicidal spectrum, and the diquat can effectively prevent most dicotyledonous weeds, while paraquat can prevent dicotyledon weeds and grasses weeds; it is a contact herbicide, which is particularly effective. Mainly killing the green part of the plant, after treatment with the stems and leaves, under the light conditions for 1~2h, the plants will have obvious symptoms of damage; mainly acting on the photosynthetic system I, causing the electron flow to break away from the electron transport chain, thereby preventing the iron redox protein The reduction and subsequent reaction, resulting in the ultimate death of the plant; non-selective herbicides, usually used before or before emergence of the crops and after emergence, after they are exposed to the soil, they can be quickly and completely soil colloid Adsorption, so there is no residue in the soil; no metabolic degradation in plants, but photochemical decomposition on the surface of plants.
Third, the control of different types of corn weeds
1 pre-emergence weeding
Pre-emergence application can effectively control weeds before germination and cause damage. Due to early weed control, the number of ploughing can be delayed or reduced. At the same time, the corn seedlings have not been unearthed, the application is convenient, and the mechanized operation is also convenient. There are more herbicides available, and the corn is safer and the price is lower. Application of mixed soil can improve the control effect of annual large-leaf broadleaf weeds and some difficult grasses weeds that are unearthed in the soil. Disadvantages of pre-emergence application: the dosage and efficacy are limited by soil texture, organic matter content and pH. Used in sandy soil fields, in the case of heavy rain, some herbicides (Seckin, Ligulong) may be leached onto corn seeds to cause phytotoxicity. After sowing, the soil must be applied before the seedlings, and the soil must be kept moist to make the agent work. For example, under drought conditions, the herbicidal effect is poor or even invalid.
(1) Normal cultivation conditions and sensation. Generally, the agricultural production conditions are better, the water conditions are better, the sensation is better, and the past few herbicides or herbicides have been used. The main weeds in the field are crabgrass, foxtail, alfalfa and alfalfa. Etc., the herbicide can be compounded with acetaminophen, butyl hydrazine, and mepyridamidine before the seeding of the corn. This type of herbicide is mainly absorbed by buds, which can effectively prevent annual grass weeds and broadleaf weeds. The effect of closed weeding is outstanding, and should be applied before weed emergence. Although this type of herbicide has higher requirements for lyrics and poor germination and weeding effect, this type of herbicide is more resistant to rain erosion and has a strong weeding effect in rainy years.
(2) Drought conditions. If the moisture is poor during the sowing period of corn, when the herbicide is selected before the seeding of the corn, the herbicide which can absorb the roots, stems and leaves and kill the larger weeds should be used as much as possible. The large amount of water allows the agent to spray onto the soil surface. It is also possible to use a compound herbicide such as acetamidine, isopropyl hydrazine, mepyridamole or acetophenone which is commonly used in the market. The herbicides are mainly absorbed by buds, roots and stems and leaves, which can effectively prevent annual grass weeds and broadleaf weeds, not only have better closed weeding effect, but also have better anti-weed seedling effect.
2 weeding in growing period
(1) 3 to 5 leaf stage. The 3~5 leaf stage of maize is an important period for weed control in corn fields. If weeds are not timely prevented, it will directly affect the growth and yield of corn. For the soil moisture is better, the field is flat, the herbicide has not been applied before or the herbicide has been applied for a short period of time. The main weeds in the field are crabgrass, foxtail, alfalfa, and twigs, etc., and the seedlings can be applied in the 3~5 leaf stage of corn. After the stem and leaf treatment agent (free time). Pay attention to corn 5 when applying
Application in the leaf stage, the application of the drug after the 5 leaf stage of the corn is prone to phytotoxicity, and it is easy to cause phytotoxicity if it is treated with high temperature. For corn fields with long-term application of closed herbicides such as B• ,, in the 3~5 leaf stage of corn, when a large number of scented aconite and glutinous rice fields occur, nicosulfuron or sulfimsulfuron can be used. The post-emergence stem and leaf treatment agent is evenly sprayed. When the application is uneven or the dosage is large, the corn leaves have a small amount of yellow spots, which can be recovered in a short time, and generally does not affect the growth and yield of the corn. After the application of the 5 leaf stage of corn, the liquid should not be allowed to flow into the corn bell mouth, otherwise it is prone to phytotoxicity.
(2) 6 to 8 leaf stage. For fields that have not been chemically weeded, have poor moisture and have few weeds in the field, they can be sprayed with herbicides that have both herbicidal and blocking effects after corn 6-8 leaf stage and corn plant height 50 cm. Weeds that have emerged in the field can be closed without grass. For example, nicosulfuron-methyl hydrazine can be used to spray water on the water. When applying the medicine, choose windless weather. When the spray is applied, be careful not to spray the liquid into the corn bell mouth. Otherwise, it may cause phytotoxicity. For the field that failed to carry out chemical weeding in the early stage, in the case of rainy days or irrigation, the field where a large number of weeds in the field may occur, it is also possible to spray the water with nicosulfuron-methyl sulphide (cleaning). For the field where the application of the closed herbicide in the early stage failed to prevent the fragrant aconite, the scented aconite was basically all emerged, and the fragrant aconite was in the seedling stage, which was a favorable period for control. Can use 2 A 4
The sodium chloride salt sprays water on the stems and leaves. When applying the medicine, it should be sprayed on the stems and leaves of the fragrant aconite, and try to avoid spraying on the corn. During the application period, the corn 5~6 leaf stage is better, not too early and too late, otherwise it is prone to phytotoxicity. The application temperature is too high (35 ° C), and it is also susceptible to phytotoxicity to corn.
(3) After 8 leaf stage (plant height 50 cm). In the middle stage of corn growth, for the field where the previous stage of chemical weeding or the application of the drug is not good enough to control the weed damage, the corn plant height can be exceeded after the corn 8 leaf stage.
After 60 cm and the base of the corn stalks were purple, the water was sprayed with paraquat. When applying the medicine, choose windless weather. When spraying, pay attention to the spraying of the liquid to the corn stems and leaves. Otherwise, it is prone to phytotoxicity.
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