What are the functions of fungicides and what is their principle?

What are the functions of fungicides and how to use them? Please introduce that there are two ways of action of fungicides: one is protective fungicides, the other is internal fungicides. Protective fungicides come into direct contact with pathogens in vitro or on the body surface of plants, killing or inhibiting pathogens, making them unable to enter plants, so as to protect plants from pathogens. This kind of fungicide is called protective fungicide, and its function has two aspects: one is to directly kill the pathogen in contact with the pathogen after spraying, that is, "contact germicidal effect"; the other is to spray the fungicide on the surface of the plant, when the pathogenic bacteria are poisoned when they come into contact with the fungicide on the plant, it is called "residual germicidal effect". There are mainly the following categories of protective fungicides: sulfur and inorganic sulfur compounds, such as sulfur suspending agents, solid stone sulfur mixtures, etc.; copper preparations, mainly Bordeaux solution, cupric ammonia mixture, etc.; organic sulfur compounds, such as thiram, mancozeb, mancozeb, phthalimide, such as carbendan, dicarbendan and bacteridan, antibiotics, such as Jinggangmycin, germicidal, polyoxymycin, etc. Other kinds, such as Ye Ku Ling, Ye Ku Jing, Chlorothalonil, he Sui Ning and so on. Internal absorbent fungicides can be absorbed by crops and transported to other parts of the body after they are applied to a certain part of the body. There are two transmission modes of endogenic insecticides, one is apical transmission, that is, after the drug is absorbed into the plant, it is transmitted to the apical leaf, terminal bud, leaf and leaf margin along with the transpiration flow to the top of the plant. At present, most of the internal absorption fungicides belong to this category. The other is the basal conduction, that is, the drug is absorbed by the plant and conducts downward along the transport of photosynthetic products in the phloem. Few of the internal absorption fungicides belong to this category. There are also some fungicides, such as ethylphosphine aluminum, which can be transmitted up and down. There are mainly the following categories of internal absorption fungicides: benzimidazoles, such as carbendazim, carbendazim, thiabendazole, thiophanate, carbendazim, carbendazim, thiophanate, carbendazim, carbendaz Sterol biosynthesis inhibitors, such fungicides include trimethoprim, azinoline, butyl, methylmycin and ethidium, imidazole and imidamide, triazole and triadimefon, etc. they belong to morpholine, pyridine, pyridine, imidazole, 1, 2, 4-triazole, respectively. Sterol synthesis inhibitor fungicides have both protective and therapeutic effects and have a wide germicidal spectrum. The principle of fungicides in the control of plant diseases: to put it simply, fungicides are compounds that have toxic effects on pathogenic microorganisms. However, the meaning of the word "sterilization" is not limited to "killing" the growth of pathogenic microorganisms or spore germination. Fungicides that can kill pathogenic microorganisms play a bactericidal effect, and fungicides that can inhibit the germination or growth of pathogenic spores have bacteriostatic effects, both of which can achieve the purpose of disease prevention and treatment in agricultural production. Fungicides act in different ways and are used in different ways, but fundamentally speaking, there are no more than three principles for fungicides to control diseases, namely, chemical protection, chemotherapy and chemical immunity. Chemical protection is to spray fungicides before plants get sick to prevent the occurrence of plant diseases. It means "scatter an eagle before you see a rabbit". Among the common fungicides, there are only two kinds of protective measures: one is to apply the fungicide at the source of the pathogen to remove the source of infection, and the main source of the pathogen is the place where the pathogen overwinters, the intermediate host and the soil. The purpose of eliminating or reducing infection sources through the application of fungicides is to reduce the possibility of pathogens infecting crops. For example, the removal of weeds in orchards in winter, the elimination of overwintering pathogens, seed bacteria disinfection and soil disinfection and other specific means are such chemical protection measures. The second is to spray fungicides on the crops growing in the field which are not diseased but may be infected by pathogens to prevent the infection of pathogens. After spraying fungicides on the surface of crops, they can kill the pathogenic cells or spores that come to infect the crops. In order to prevent and control the infection of soil-borne pathogens to crops, treating crop seeds with fungicides before sowing or treating seedling roots with fungicides before transplanting belong to this kind of measures. Chemotherapy is to "see the rabbit and scatter the eagle". That is, after the disease or susceptibility of plants, fungicides are applied to protect crops or pathogens, and change the pathogenic process of pathogens, so as to achieve the purpose of reducing or eliminating the disease. Prevention is more important than treatment, and the effect of prevention is also better than that of treatment. Therefore, the plant protection policy of "prevention first, comprehensive control" put forward by Chinese plant protection workers is of great guiding significance. According to the degree of infection of pathogens to plants and the way of drug use, chemotherapy can be divided into three types: one is surface chemotherapy. Some germs, such as powdery mildew, are mainly attached to the surface of plants, which can be killed by stone-sulfur mixture and play a surface therapeutic role. Non-endospermic fungicides can prevent and cure these diseases. One is internal chemotherapy, in which fungicides are introduced into crops to treat germs that have invaded the plant. Only internal inhalation insecticides, such as methyl topiramate and carbendazim, have the effect of internal chemotherapy. The effect of internal treatment of internal inhalation fungicides has two aspects: on the one hand, it is directly toxic to bacteria; on the other hand, it is to change plant metabolism, change its response to bacteria or the pathogenic process of bacteria. However, most internal inhalation fungicides have only one of these effects, and some fungicides have both. One is external chemotherapy, which is often used in the prevention and treatment of fruit tree or forest diseases. That is, scrape off the disease spots on the outside of the tree trunk or branches after being infected by germs, and then disinfect the wound with fungicides and apply protective agents or waterproofing agents to prevent the further expansion of infection. Chemical immunity is the use of chemicals to protect crops against pathogens. At present, there are three kinds of chemical immune compounds with chemical immune function, such as 2-dichloro-3-dimethyl cyclopropanecarboxylic acid, ethyl phosphine aluminum and thiaprazole. Among them, thiazolyl is the most typical chemical immune agent, which can be used to treat rice plants to induce the production of several antibacterial substances to make rice gain the ability to resist rice blast. There are many ways to use fungicides, each of which is designed according to the law of disease occurrence. The common use methods are: spraying crops in the field, soil disinfection and seed fungus disinfection. For crop spraying in the field, the factors affecting the disease control effect of fungicides in the field are no more than pesticides, environment and crops, but the technical requirements of fungicides are higher than those of pesticides and herbicides. In particular, it is necessary to fully understand the law of the occurrence and development of diseases, because the occurrence and development of diseases are not as clear as pests and weeds. Two points should be paid attention to when spraying crops in the field: the first is the type and concentration of the pesticide. The choice of the type of medicine depends on the type of disease, so it is necessary to make a correct diagnosis of the type of disease before we can prescribe the right medicine. For example, rice blast can choose rice blast, rice blast, tricyclazole and so on, wheat powdery mildew and rust should choose triazole and triadimefon, peanut leaf spot should choose methyl topiramate and so on. But it should also be noted that if the same disease occurs on different crops, sometimes the same medicine can not be used, such as Bordeaux liquid can control downy mildew, but it is easy to cause drug damage to cabbage, so it is not suitable to control downy mildew of Chinese cabbage. After the type of medicament is selected, the appropriate application concentration should be selected according to the crop type and growth period, the type and dosage form of fungicide, environmental conditions and so on. General instructions for the use of pesticides have the recommended concentration, which can be used according to the instructions, but it is best to apply according to the concentration put forward by the local plant protection technical department on the basis of efficacy tests. In dry or hot summer, the concentration should be reduced to avoid drug damage. Secondly, when using fungicides, we should also pay attention to the period and times of use. The key to mastering the law of disease occurrence and development, doing a good job in predicting and forecasting the occurrence of diseases, or making preparations for spraying fungicides according to the prediction and forecast of crop diseases by local plant protection departments. In general, fungicide spraying is carried out in the early stage of the disease, such as rice blast, especially in high temperature weather, rice blast develops rapidly, so it should be sprayed immediately. However, the development of peanut leaf spot disease is relatively slow, do not spray easily at the beginning of the disease, let alone spray before the disease, but start spraying when a certain development trend is formed after the disease. Spraying should be started immediately when climatic conditions are conducive to the rapid development of the disease, and sometimes it has to be sprayed when it drizzles in order to control the disease. The spraying period is not only determined by the law of disease development, but also consider the growth period of crops, the occurrence of many diseases are related to a certain growth stage of crops. In addition, we should also pay attention to the tolerance of crops to fungicides in each growth period to prevent drug damage. The occurrence and development of plant diseases often take a period of time, spraying fungicides is also difficult to solve the problem, often need to spray many times. The number of spraying times mainly depends on the re-infection of bacteria, the residual period of fungicides, climatic conditions, light, temperature, rainfall and so on. Disinfect the seedlings. Seed soaking should use emulsion and solution, not suspension, that is, wettable powder can not be used to soak seeds. The key to seed soaking is the concentration and time of seed soaking. Improper operation will cause poor sterilization effect or drug damage. Other factors such as temperature, seed type and location of pathogen also affect the effect of seed soaking. In general, after the seed type, air temperature and chemical type are determined, the medicament concentration and seed soaking time can be coordinated, and the seed soaking time can be appropriately prolonged with high concentration. The deep part of the pathogen or the hard seed coat can appropriately prolong the seed soaking time, and the high temperature can shorten the seed soaking time. Seed dressing requires that the seeds and powder must be dry, otherwise it will cause uneven seed dressing, cause drug damage and affect the germination rate of seeds. The amount of powder generally accounts for 0.2%-0.5% of the seed weight. When mixing seeds, the medicament and seeds should be divided into 3-4 batches, and then rotate the seed mixing container to mix evenly. After the emergence of internal absorbent fungicides, a new seed dressing method-wet mixing method has appeared in recent years. That is, wet the powder with a small amount of water, then mix the seeds, or mix the dried powder on the wet seeds to make the powder stick to the surface of the seeds. After sowing, the medicine is slowly dissolved and absorbed into the plant to conduct upward. Soil-borne diseases such as cotton Fusarium wilt and cucumber Fusarium wilt can be controlled not only by soaking or mixing seeds, but also by soil disinfection. Soil disinfection should first select appropriate fungicides according to the types of diseases, and then choose appropriate soil treatment methods according to the physical and chemical properties of the agents and soil structure and properties. The watering method is suitable for water-soluble fungicides. After adjusting the medicament to a proper concentration, the chemical solution of about 5: 10 kg per square meter can be irrigated on the ground. The lower concentration solution can be used when the soil is dry, and the irrigation volume can be increased appropriately. When the soil is moist, high concentration and small volume irrigation can be used. Fungicides with high vapor pressure can be applied at the bottom of the plough or furrow, that is, the powder or liquid is evenly sprinkled into the bottom of the first plough and covered with the soil turned over by the second plough. this method is not suitable for the soil that is too sticky, and the powder or solution can be applied on the surface of the soil, and then the powder or solution can be turned over and buried in the soil. Click to get more fungicide use technology click to get more pesticide use technology