Abnormal temperature and precaution against Rice Seedling Diseases

Seedling disease is the general name of a variety of physiological diseases and infectious diseases during the period of rice seedling cultivation, also known as seedling rot. Physiological rotten seedlings refer to the symptoms of rotten seeds, rotten buds, black roots, green wilt and yellow withered seedlings caused by adverse environmental conditions, while infectious rotten seedlings refer to the symptoms of dead seedlings caused by cotton rot and standing blight. The northern rice area is often attacked by low temperature and cold spell weather during the seedling raising period, and the annual incidence of rotten rice seedlings is 10% to 23%.

Symptom characteristics-nbsp1, physiological rotten seedlings: 1. Rotten seed means that the seed is rotten before it germinates; 2. Rotten bud means that the newly germinated bud is dysplastic and curl in the shape of a fishhook, die without rooting, or rot in the mud, or form floating seedlings. Black root, refers to the root of the seedling blackened and rotten, leaves gradually withered; 4. Green withered, refers to the seedling green not yellow suddenly withered, the base is not rotten, the seedling is not easy to pull up; 5. Yellow blight means that the seedlings slowly turn brown, wither and die, the roots rot, and the diseased seedlings are easy to pull up. Second, infectious rotten seedlings: 1. Cotton rot can occur in 5-6 days after sowing in paddy seedling field, and the seedling height is about 3 cm, which harms young roots and buds. A small amount of milky gel appeared at the crack of the seed shell or at the base of the bud, gradually growing radial white flocculent hyphae, gradually showing ferruginous, green-brown or dirty brown; seed decay could not germinate, or the base of diseased seedlings rotted and withered. The disease occurs from point to patch, and when it is serious, it dies in patches. two。 Standing blight, wet seedling, dry seedling and film seedling are common in seedling field, the symptoms are as follows: (1) bud rot, young roots of young buds turn brown, twist, rot and die before they are unearthed, and pink and white mildew layer is produced in the later stage; (2) needle rot, the heart leaf of the seedling is withered and yellow from the upright needle to the 2-leaf stage, the base turns brown, sometimes brown spots appear on the leaf sheath, the mildew layer occurs at the base of the stem, and the seedling is easy to be pulled out. (3) Yellow withered, the seedlings occurred from 1 leaf to 3 leaves, the lower leaves began to wither and wilt, the root hairs were sparse, and the base became brown and soft rot in the later stage; (4) withered, mostly occurred around the 3-leaf stage, the heart leaves or upper leaves of the seedlings were rolled into willow leaves, and the root hairs were sparse, and the base became brown and soft rot in the later stage, which was easy to cluster.

Pathogen and occurrence regularity-nbsp physiological rotten seedlings are mostly caused by poor seed quality, uneven cold and heat in the process of accelerating germination, poor sowing quality, deep water storage, hypoxia and asphyxia, and excessive sunny or temperature difference after cold seedling stage, while black root is caused by excessive fertilizer and deep water storage, resulting in a large number of reducing substances such as hydrogen sulfide and iron sulfide to poison the seedlings. The cotton rot of infectious rotten seedlings is mainly caused by fungi such as Rhizoctonia solani and Rhizoctonia solani, while the disease is mainly caused by semi-known fungi such as Fusarium and Sclerotinia solani. The pathogen can live in the soil for a long time, overwintering with mycelium, oospore and sclerotia in soil or in diseased remains, and spread by current and airflow. Rhizoctonia overwintered with mycelium and sclerotia in diseased remains and soil and spread by running water. Invaded mainly through wounds and young tissues.

In order to control rice seedling diseases, comprehensive measures should be taken to improve seedling raising methods, improve seed quality and sprouting techniques, strengthen seedling field management and supplemented with chemical control. Adopt plastic film seedling, floppy disk seedling and dry seedling according to local conditions, it is best not to use water to raise seedlings. The seedling field chooses the plot with shelter from the wind to the sun, flat terrain, medium fertility and convenient drainage and irrigation. Seed retention, seed storage, seed drying and seed selection can improve the seed germination rate. The seeds were soaked in warm water (55 ℃ for 10 minutes) or medicament (50% carbendazim 800 times solution for 3 days). During the budding period, the temperature is stable above 10 ℃, which can prevent too high or too low, ensure that the buds are uniform, neat and strong, and enhance the cold resistance of seedlings. Strengthen seedling management, fine soil preparation, ensure bed surface leveling, bed temperature and permeability; choose sowing when the temperature is stable above 10 ℃; scientific irrigation, temperature control with water to protect seedlings; rational fertilization, pay attention to the combination of nitrogen, phosphorus and potassium, increase the application of organic fertilizer, avoid partial nitrogen, and enhance the disease resistance of seedlings. Drug control, timely use of medicine at the initial stage of the disease, sprinkling 1000 times of Dexamethasone, or 1000 times of Dysenamine, 5.5% of seed Ling 3000 × 5000 times, 58% Metalaxyl manganese zinc 1500 times, 2kg per square meter. & nbsp

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