How to prevent and control rice leaf spot

The symptoms are also known as rice flax leaf blight. It occurs evenly in all the rice areas of the country. The disease can occur from seedling stage to harvest stage, and the aboveground parts of rice plants can be damaged, especially leaves. The seed sprouts are damaged, the coleoptiles turn brown, the buds are not pulled out, and the cotyledons die. The disease of leaf and leaf sheath at seedling stage is mostly elliptical disease spot, such as flax grain size, dark brown, sometimes the disease spot expands into a strip, and the seedlings die when there are many disease spots. Adult leaves infected with the initial brown spots, gradually expanded into oval spots, such as sesame grain size, the center of the spot brown to gray, the edge of brown, there are different shades of yellow halo around, serious even into irregular large spots. The diseased leaves withered inward from the leaf tip, damp brown, and black mildew (conidiophores and conidia) were produced on the dead seedlings. The disease spot on the leaf sheath was oval at first, dark brown, the edge of the disease was light brown, water-stained, and then turned into a gray-brown irregular spot in the center. The injured part of the neck and branches is dark brown, causing the ear to wither. The grayish black of the grain affected in the early stage of the disease expanded to the whole grain, resulting in blighted grain. In the later stage, the lesion was small and the edge was not obvious. Seriously ill grains are brittle and brittle. When the climate is humid, the above diseases grow black villous mold layer, that is, pathogen conidiophores and conidia.

Pathogen Bipolarisoryzae (BredadeHann) Shoem. It is called Daoping umbilical helminthosporium, which belongs to the subphylum fungus. Different HelminthosporiumoryzaeBredadeHaan. Conidiophores 2-5 fascicles protruding from stomata, unbranched, slightly curved, septate. Conidia terminal, oblong stick-shaped or cylindrical, slightly curved, brown, with 3-11 diaphragms, size 24-122 × 11-23 (μ m), sexual Cochliobolusmiyabeanus (Itoetkuribayashi) DrechslerexDastur called uterine spiralis, a subphylum of ascomycetes, only found on the culture medium, not produced under natural conditions.

The pathogen of transmission and disease condition overwintered by mycelium in the diseased residue or attached to the seed, and became the source of infection at the beginning of the next year. The conidia on the disease spot can survive under dry conditions for 2-3 years, the latent hyphae can survive for 3-4 years, and the hyphae lose their vitality after turning into the soil for a winter. After sowing the diseased seeds, the latent mycelium can directly invade the seedlings, the conidia can be blown to the seedling field or Honda by the wind, and the germinating hyphae can penetrate directly or invade from the stomata. When the conditions are suitable, the disease will appear quickly and form conidia. Re-infection by wind and rain transmission. The disease is serious when there is high temperature, high humidity and fog dew. Acid soil, sandy soil, deficiency of phosphorus and potassium. The dry seedling field is seriously ill. The temperature limit of mycelial growth is 5-35 ℃, the optimum temperature is 24-30 ℃, the temperature limit of conidia formation is 8-33 ℃, and the optimum temperature is 30 ℃. The temperature limit of germination was 2-40 ℃ and 24-30 ℃ was the most suitable. There must be water droplets in spore germination, and the relative humidity is more than 925. It can invade the host in 4 hours at 25-28 ℃ at saturated humidity.

Prevention and control methods (1) deep ploughing to eliminate recommendation and reduce the source of bacteria. Diseased straw should be disposed of and destroyed in time. (2) leave seeds or disinfect seeds in disease-free fields. (3) increasing the application of rotten compost as base fertilizer, topdressing in time, and increasing phosphorus and potassium fertilizer, especially the application of potassium fertilizer can improve the disease resistance of plant plants. Acid soil should pay attention to drainage and proper application of lime. Shallow irrigation should be done frequently to avoid poor ventilation caused by long-term flooding. (4) Pesticide control see rice blast.