How to use herbicide safely
In some books, the selectivity of herbicides can be divided into six categories: selective dislocation, time difference selectivity, morphology selectivity, physiological selectivity, biochemical selectivity, and selectivity of protective substances or safeners. Actually, this includes both the selectivity determined by the properties of the drug itself and the different application methods and effects of crops and weeds. It should be the selective use of technology.
First of all, non-selective herbicides, also known as phytotoxic herbicides, are called "sweeping light." Glyphosate, paraquat, sodium pentachlorophenate, etc., can only be used when there is no crop in the field, and must be sown or transplanted until the agent loses its activity. It should be noted that the rate of decline of these herbicides is often high, the soil does not retain water, and the rate of decline of the drug is faster in the presence of rainfall. In fact, this is already a difference in the time when crops and weeds are used to start growing, and it is also a time difference selection technique.
If we use crop and weed seed and root system to distribute the difference in the depth of the soil, spreading the pesticide on the soil surface 1 to 2 cm, can kill or inhibit the weed seeds that can germinate in the shallow layer, and the crop (such as wheat) or fruit trees Roots are deep and unaffected. For example, soybeans before sowing use Alachlor (muscle), corn, cotton, soybeans, peanuts, wheat and other crops after sowing before the application of acetochlor. It should be noted that in soils with low sand content and low organic matter content, in the event of rainfall or the formation of stagnant water, the pesticide may infiltrate downwards and be prone to phytotoxicity. Seeds sown in shallow crop fields, such as some vegetable fields, are not suitable for the use of such agents. For the same reason, if you spray paraquat in an orchard, you must choose a wind-free weather, preferably in the afternoon when the air flow rises insignificantly, so that weeds that are sprayed directly onto the ground will not spread to the leaves of fruit trees. Or outside the orchard.
The third type utilizes differences in the morphology of crops and weeds, typically using 2,4-D-butyl ester. The drug is a selective herbicide of hormone type. The low concentration has a stimulatory effect on plant growth, and the high concentration inhibits or even kills. One of its selective herbicidal actions is to use the growth point of grass crops wrapped in layers of leaves, while the growth point of dicotyledonous weeds is always exposed. In this way, under the same spraying conditions, the growing point of the dicotyledonous weeds will be higher in the amount of drug, which will cause distortion or inhibition. When using such drugs, pay attention to the time of spraying. Before the wheat is used for 4 leaves and after jointing, it is not appropriate to use drugs. Otherwise, the wheat will form malformed spikes. It is also necessary to choose no-weather weather spray to prevent the pharmacy from floating to surrounding vegetables or melons and fruit fields. After spraying, the equipment must be carefully cleaned to avoid affecting other farmland.
The use of propanil in rice fields, for example, is due to differences in the biochemical reactions of pesticides in rice and barnyardgrass, and rice can rapidly hydrolyze propanil, which is truly selective. Similar herbicides such as rice Honda use glutinous rice, corn fields use simazine and atrazine, soybean fields use tolusulfuron, and carrot fields use trifluralin. They are safe to use in suitable fields, but the use of wrong fields or excessive residues can also cause phytotoxicity.
In terms of building materials, industrial products, daily necessities, floor leather, floor tiles, artificial leather, pipes, wires and cables, packaging films, bottles, foaming materials, sealing materials, and fibers, PVC was the world`s largest production of general-purpose plastics, and its applications are very widely. Widely used in all aspects.
PVC is a white powder with an amorphous structure. The degree of branching is relatively small. The relative density is about 1.4. The glass transition temperature is 77~90°C. It begins to decompose at about 170°C. It has poor stability to light and heat. After prolonged exposure to sunlight, it will decompose to produce hydrogen chloride, and further automatically catalyze the decomposition, causing discoloration, and the physical and mechanical properties also rapidly decline. In actual applications, stabilizers must be added to improve the stability of heat and light.
the Degree of polymerization of SG5 is 1000. usually we also call PVC Resin S1000. Its K-value is K67.
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