Symptoms are also called rice fever, fire violence and kowtowing violence. It is distributed in all rice areas in China, mainly damaging leaves, stems and ears. Due to the different damage periods and parts, it can be divided into seedling blast, leaf blast, node blast, ear neck blast and grain blast. Seedling blight occurs before the third leaf, which is caused by seed carrying bacteria. The diseased seedlings were gray-black at the base and brown at the upper part, and curled up and died. When the humidity is high, a large number of gray-black mold layers, namely, pathogenic bacteria conidiophore and conidia, are produced in the affected area. Leaf blast will occur throughout the growth period. The harm from tillering stage to jointing stage is more serious Due to different climatic conditions and disease resistance of varieties, the disease spots are divided into four types. Chronic disease spots begin to produce dark green spots on leaves, and gradually expand into spindle-shaped spots, often with extended brown necrosis lines. The center of the lesion is gray-white, the edge is brown, there is a pale yellow halo outside, and there is a gray mold layer on the back of the leaf. When there are many lesions, irregular large spots are formed and develop slowly. Acute disease spots form dark green, nearly round or oval spots on susceptible varieties, and brown mold layers are produced on both sides of leaves, which turn into chronic disease spots when conditions are not suitable. Young leaves with white spots are infected, producing white near-circular spots without spores, which can turn into acute spots when the climatic conditions are conducive to their expansion. Brown spot type lesions are mostly on high resistant varieties or old leaves, and the brown spot of needle tip size only occurs between leaf veins and rarely produces spores. The disease can also occur on the tongue, ears and pillows. Heat preservation often occurs after heading, which initially produces brown spots on rice nodes, and then gradually expands around the nodes, making the diseased parts black and easy to break. It happened early and formed a withered ear. It only happens on one side, causing the stem to bend. Brown spots were formed in the early stage of ear neck plague, which turned the ear neck brown after spreading, and also caused withered white ears. Late development leads to valley. The damage of branches or panicle axes leads to the failure of spikelets. Rice blast produces brown oval or irregular spots, which can make rice black. Some glumes are asymptomatic and brown, which makes the seeds carry bacteria.

The pathogen is rice blast fungus. It is called Magnaporthe grisea. It is called Magnaporthe grisea and belongs to subfamily Fungi. The sexual type is Magnaporthe grisea. It belongs to Ascomycetes subfamily. It has not been discovered under natural conditions. Conidiophore is unbranched, with 3-5 clusters, protruding from the host epidermis or stomata, with a size of 80- 160×4-6 (micron), 2-8 septa, slightly enlarged base, light brown, curved top and conidia. Conidia are colorless, pear-shaped or rod-shaped, with 1-3 septa, the size of which is 14-40×6- 14 (micron), and podocytes at the base. During germination, the cells at both ends set up a bud tube, and the top of the bud tube produces adherent cells, which are nearly spherical and dark brown and close to the host, leading to the invasion of invading silk. The strain can be divided into 7 groups, 128 physiological races.

Transmission routes and pathogenic conditions The pathogen overwinters as conidia and hyphae on rice stalks and rice. The conidia produced in the following year spread to rice plants by wind and rain, germinated and invaded the host and spread to neighboring cells, forming a central diseased plant. The conidia formed in the diseased area were reinfected by wind and rain. Sowing infected seeds will cause seedlings to wither. Appropriate temperature and high humidity, rain, fog and dew are all conducive to the onset. The temperature limit of mycelium growth is 8-37℃, and the optimum temperature is 26-28℃. The upper limit of sporulation temperature is 10-35℃, the optimum temperature is 25-28℃, and the relative humidity is above 90%. Spore germination needs water and lasts for 6-8 hours. Appropriate temperature can form adherent cells and invasive filaments, penetrate the epidermis of rice plants and diffuse nutrients between cells. Continuous rain, insufficient sunshine or sunny days, or fog or dew in the morning and evening, the disease expands rapidly. Variety resistance varies with region, season, planting years and physiological races. Indica rice varieties are generally superior to japonica rice varieties. The resistance performance of the same variety at different growth stages is also different. Seedlings are susceptible to diseases at the four-leaf stage, tillering stage and heading stage, the diseases at the round stalk stage are lighter, and the diseases of the same organ or tissue are more serious at the tender stage of the tissue. The disease resistance was weak at the beginning of ear stage. Partial application of nitrogen fertilizer is beneficial to diseases. Early irrigation or long-term deep irrigation has poor root development, weak disease resistance and serious diseases.

Control method (1) Select 2-3 local disease-resistant varieties according to local conditions, such as early rice: Zao 58, Xiangzaoxian No.3, 2 1, No.22, 86-44, 87- 156, Wandao 6 1 and Ganzaoxian. Mid-season rice varieties: Qibaozhan 1, seven show No.3, Peiza Shanqing, and late-season rice varieties include Xiushui 644, Yuan Jing No.4, Jindao 308, Jingdaoxuan 1, Ji Jing 15, Huajing 45, Liao Jing 244 and Shennong 90/kloc-0. Rice varieties resistant to ear neck blast, such as No.3, No.5, Jing 3119 and China 9 1, can be selected for dry farming. Disease-resistant varieties such as Zhengzhou Zaojing and Zhonghua 8 can be selected for dry direct seeding of rice. (2) Leave seeds in disease-free fields, treat diseased rice stalks and eliminate bacterial sources. (3) According to the law of rice fertilizer demand, the formula fertilization technology was adopted to realize the alternation of dry and wet in the later stage, which promoted the maturity of rice leaves and enhanced the disease resistance. (4) seed treatment. Soak the seeds in warm soup at 56℃ for 5 minutes. Soak the seeds with 10%40 1 antibacterial agent 1000 times or 80%402 antibacterial agent 2000 times and 70% thiophanate-methyl wettable powder 1000 times for 2 days. Seeds can also be soaked in 1% lime water, 10- 15℃ for 6 days, and 1-2 days at 20-25℃. The limewater layer is higher than the rice seed 15cm, take it out, let it stand and rinse it with clear water for 3-4 times. Soak the seeds in 2% formalin for 20-30 minutes, and then cover the seeds with film for 3 hours. (5) Seize the critical period of chemical control and use drugs in time. Catch leaf blast early and treat ear blast hard. Spraying 20% tricyclazole wettable powder 1000 times or 40% isoprothiolane (Fuji 1No.) EC 1000 times, 50% carbendazim or 50% thiophanate-methyl wettable powder 1000 times, 50% thiophanate-methyl. 40mg/kg of kasugamycin or spreading agent can also be added to the above drugs, and the effect is better. The leaf temperature should be controlled at 2-3 times, and the ear blast should be well protected at heading stage, especially at booting stage (broken belly stage) and full heading stage.