Rice blast disease is one of the major diseases of rice. The city has an incidence of varying degrees each year. In recent years, due to factors such as variety resistance, fertilization level, and climatic conditions, local areas have become heavier, and serious fields have almost lost their crops. The occurrence of early rice was lighter, and the occurrence of late rice was heavier. I. Symptom identification Rice blast occurs throughout the growing season of rice. According to the different stages and damage, it can be divided into seedlings, leafhoppers, knots, panicles, and grain pods. most influential. Seedlings are caused by seed bacteria and occur before the three-leaf stage. At first, water-stained spots appeared on shoots and buds, and then the base of the diseased plants became black-brown at the base and yellowish-brown or red-brown on the upper part and then died. When wet, the diseased area can grow a layer of gray green mold. Drought and semi-arid fields in the drylands are more common when they are grown on plastic film. Leafhoppers occur on the leaves of the seedlings and adults. Usually occurs in the midst of childbirth, and when severely developed, the far-infarction field is like a fire, and the plants are dwarfed to form a “collapse pondâ€. There are four types of lesions: 1, acute type: lesions were dark green, both ends of the sharp, elliptic, positive and negative dense gray green mold layer. In the humid climate, rainy and rainy, excessive nitrogen fertilizer, plant growth and green, covered with leaves, varieties susceptible to conditions easily occur. The appearance of acute lesions indicates that the varieties have low disease resistance and suitable climatic conditions. They are a sign of the epidemic of rice blast and must be immediately controlled by drugs. 2. Chronic type: Acute type lesions can be converted to chronic type when the weather is dry or controlled by drugs. This lesion is the most common, it is generally spindle-shaped, with two ends pointed, the center is a gray-white collapsed part, the edge is a brown necrotic part, and the periphery is a yellow poisonous part; the brown necrotic thread runs through the lesion and Both ends extend, which is an important feature of rice blast. When the weather is wet, a gray green mold layer can also develop on the back of the lesion. 3, brown spots: lesions were brown dots, limited to veins. Occurred in the disease-resistant varieties or rice plants in the lower part of the old leaves. 4, white point type: This type of lesions is rare, more often appear in the young leaves of susceptible varieties near the white round dots, when the climate is appropriate, the white point type will turn into acute type lesions. Frugality generally occurs on the first and second sections of the flag leaf, and the first dark brown spots appear on the section, and then the ring expands to the entire section. When wet, a layer of gray green mold layer is produced on the joints, and the diseased section in the later period shrinks and sinks, resulting in the bending of the stem section or easily broken. Panicles occur on the neck, cob, and branches. The lesions were water-stained light brown dots at the beginning of the lesion and gradually developed around the panicle neck, cob, branch stalk extension and up and down development. After the color became deep brown or dark green, resulting in the valley or even white spike. Grain pods occur on the husks and shields. The early onset lesions were elliptical and gray in the middle. Afterwards, the entire grain turned into a dark gray valley. Late onset of the formation of oval or irregular brown spots. Second, the occurrence of rice blast disease is caused by a fungus-like disease. The pathogens used wintering for mycelium and conidia on sick grass and diseased valleys. Therefore, sick grass and diseased valley are the main source of the first infection of the following year. In addition, the uncooked bar and the sick rice straw and rice scattered on the ground are also the source of the first infection. The occurrence and development of rice blast are restricted by the variety, fertilizer and water management and climate conditions. The resistance of the variety is the internal cause, and the management of fertilizer and water is the main factor affecting the disease resistance of rice. Climate is the epidemic of disease. Necessary conditions. The main factor that causes the severity of the disease during the year is the climatic conditions; the main factor that contributes to the severity of disease among the plots is the disease resistance of the cultivated management measures. 1. Climate: When the temperature is in the range of 20-30 degrees Celsius and the relative humidity is above 90%, it is favorable for the occurrence of rice blast. In late booting and heading stage of late rice, the resistance of rice is weakened in case of low temperature, cloudy rain or dew, and it is easy to cause the epidemic of panicle blast. 2, fertilizer and water management: the application of excessive nitrogen fertilizer, especially if used too late, will induce severe panicle blast. Long-term water flooding or cold water strung irrigation, flood irrigation, impede the growth of rice roots, reduce the resistance of rice plants. 3. Disease resistance of varieties: Rice resistance to rice blast differs depending on the variety. General japonica rice than japonica disease resistance. In the same variety, resistance is also different at different stages of growth. Generally susceptible to disease in the 4 leaf stage, tillering stage, end of panicle to heading. 3. Prevention and Control Methods Prevention and control of rice blast must adopt comprehensive measures: The selection of high-yield and disease-resistant varieties should be used as a basis to eliminate the source of disease, improve the cultivation techniques to enhance the disease resistance of rice, and focus on pesticide application based on the weather, seedlings, and disease conditions. Prevention. 1. Selection of high-yield and disease-resistant varieties: At present, the varieties of early and late rice planted in our city are not yet significantly resistant to rice blast. In the old ward of rice blast disease, we need to further screen resistant varieties. 2. Sterilization source: The diseased straw should be processed in time and cannot be returned to the field or stacked near the field. No sick straw is used for scaffolding, germination and barbelling so as not to bring germs into rice fields. Seed disinfection method: Use 25% of fresh-keeping grams of emulsifiable concentrate 3000 times (that is, 2 ml of a pair of water 6 kg, can be soaked in 3 kg) soaking, conventional rice leaching 48 hours, hybrid rice soaking 8-10 hours. Fresh chicken soaked can be removed directly after germination. 3, improve the cultivation techniques: do a reasonable fertilization, increase the application of organic fertilizer, phosphorus and potassium fertilizers, while scientific water, prevent flooding. 4. Chemical control: The prevention and treatment of seedling mites and leaf mites must be mastered at the early stage of disease. In particular, when acute types of mumps occur, they should be sprayed and prevented immediately. For the prevention and treatment of panicle blast, the drug should be applied 2 to 3 days before the break, and the drug should be used once every 7-10 days depending on the weather conditions. The agent may use 40% Fuji No. 1 EC 75-100 ml/mu, or 20% tricyclazole 100g/Mu wettable powder. Mu water 50-75 kg, fine spray.