The occurrence and control of rice blast

Rice blast is one of the three most important diseases of rice. In the end of the year, rice production is generally reduced by 10-20%, and in serious cases it is 40-50%. Sick seeds, diseased rice straw and unrefined straw-containing fertilizers are the primary sources of infection for each year of disease. After seedlings or adult plants are invaded, conidia produced by the diseased part are reinfected by airflow.
First, the onset of symptoms due to the time and location of the damage is different, can be divided into seedlings, leafhoppers, knots, panicles, and grain pods. In general, leafhoppers and panicles are more harmful.
1. Ye Zimiao can occur from the three leaf stage to the panicle stage. It usually occurs from the tillering period to the jointing period. The most common typical symptom in susceptible varieties is spindle-shaped lesions with brown necrotic lines extending toward the veins at both ends. The lesions are grayish-white in the centre, brown on the edges, and a light yellow halo on the periphery, with a gray moldy layer on the back. The lesions spread slowly. In sensitive disease climate, leaves often produce dark green near-round to elliptical lesions, and there are a large number of gray mold layers on both sides. The appearance of this type of acute lesions is a sign of the disease's prevalence. In the old leaves of highly disease-resistant varieties, only needle-sized brown spots are produced and no spores are produced.
2. The ear-neck pheasant initially produces brown dots on the neck of the panicle. After expansion, the panicle and neck become brown or dark brown. Cobs and twigs become brown or gray after damage.
Second, the occurrence of related factors with the epidemic
1, varieties of disease-resistant varieties of silicified more brittle, strong resistance; japonica rice is more resistant to expansion, stem rice more resistant to invasion. Rice is most susceptible to disease during the tillering stage and early heading stage. It is the most susceptible on the day of emergence, and the disease resistance is enhanced after 5 days.
2. The cultivation and management of nitrogen fertilizer is too late, causing the rice plant to grow mad; the leaf is soft and drape, and is vulnerable to pathogens; in the condition of excessive nitrogen fertilizer, applying phosphorus and potassium fertilizers, especially potassium fertilizer, will aggravate the occurrence of diseases; Sandy soil is prone to disease; in case of over-drought in fertilizer field, rainfall or irrigation occurs after excessive drought, and it is easy to induce the epidemic of rice blast; the application of inorganic fertilizer is heavier than that of organic fertilizer; long-term deep-irrigated rice fields, cold-sweeping fields, and water-leakage fields are liable to induce rice blast.
3, climatic factors When the temperature is 20-30 °C, the humidity in the field is above 90%, the rice plant surface to maintain a layer of water film for 6-10 hours, the rice blast disease is prone to occur. If the average temperature in the ten days is 24-28°C, and there is a saturated humidity above day and night, rice blast disease becomes popular. Rainy, foggy, dew, and low light weather are prone to rice blast.
Third, prevention and control measures
1, selection of disease-resistant varieties
2. Strengthen the cultivation and management of shallow-water ground irrigation, timely field drying, and late-stage wet and dry cultivation and management methods can make rice plants grow robustly, increase resistance to diseases, and inhibit the reproduction and infection of pathogens, so that diseases do not occur or occur less frequently. .
3. Appropriate application of fertilizers Nitrogen, phosphorus and potassium should be used in conjunction with organic fertilizers and inorganic fertilizers. Appropriate use of siliceous acid fertilizers such as grass and wood ash. Do base fertilizer, early application of fertilizer, see the seedlings in the middle and late days to see Tian Qiao fertilizer. Cold paddy fields pay attention to increase phosphate fertilizer.
4. Chemicals prevention and treatment Pay attention to the protection of susceptible varieties and susceptible rice fields, timely control of rice blast, and prevention of panicle blast. When rice leaf blast occurred, it was sprayed in time to control the disease. Later, depending on the development of the disease and the weather, spraying once every 6-7 days. Prevention of panicle cervix should be applied for the first time when rice cracked 70% to heading 5%, and the second drug should be applied at the heading stage. In general, 100 grams of 20% tricyclazole or 100% of rice bran is used to spray 40-50 kilograms of water, and the two drugs can be applied alternately.

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