How to control rice sheath blight by reducing 1000-grain weight of rice

Sheath blight is one of the three major diseases of rice in the world, which causes early withering of rice leaves and poor growth, thus reducing 1000-grain weight and increasing the rate of blighted grain, which has a great impact on rice yield. Generally, the production will be reduced by 5%, 10%, and the heavy one can be up to 50%.

Rice sheath blight

(1) the source and symptoms of the disease

The pathogen is fungus, and the pathogen is Rhizoctonia solani, which mainly harms the leaf sheath and leaves of rice. In the early stage, the disease spot occurred in the lower leaf sheath, first appeared oval dark green water-stained spot, then gradually expanded into moire, the edge was brown, the middle was gray-white, the disease spot seemed to have blue light, turned gray-green when wet, and in the later stage of rice, it gradually spread to the upper part, and the whole plant died in severe cases. Flat brown sclerotia were produced in the lower leaf sheath, and the sclerotia was easy to fall off.

Different from the symptoms of saline-alkali damage: the symptoms of rice sheath blight at seedling stage are similar to those of saline-alkali injury. the difference is that sheath blight generally occurs from the edges and corners of the rice field, the disease spot is mostly out of the water, there is blue light on the surface of the diseased tissue, and salt-alkali damage occurs evenly in the whole field. A layer of white nitrate can be seen on the surface of the necrotic leaf sheath, and the disease spot is mostly near the surface of the water, without blue light.

(2) occurrence regularity

The overwintering sclerotia in the field soil is the main source of primary infection, which usually occurs first from the corner of the field. After transplanting rice seedlings, the sclerotia attached to the leaf sheath at the base of the rice plant, germinated and infected the leaf sheath at the base of the rice plant. The development of the pathogen requires high temperature and humidity, the optimum temperature is 2832 ℃ (2-4 ℃ higher than that of rice blast), and the most suitable relative humidity is more than 96%. From the peak tillering stage to the early booting stage, the disease spread horizontally among rice plants or clumps, and then vertically from the lower part of the rice plant to the upper part. Partial application of nitrogen fertilizer, long-term soaking in deep water and excessive density of rice caused serious disease.

The varieties planted in the past, such as Yanfeng series, 10 you 18 and reclaimed rice 2015, were highly susceptible to rice false smut.

(3) Prevention and control methods

When raking the ground in spring, remove the sclerotia and other sundries floating on the water surface at the corner of the ground, and take them to the field to burn or bury deeply, so as to reduce the source of bacteria. In the disease level expansion stage, when the disease point rate reaches 20%, the medicine is sprayed for treatment. The key to prevention and treatment is to catch early (spray medicine at least once before jointing) and spray well (enough water and accurate dosage).

(1) use 5% Jinggangmycin water agent 100ml / mu.

(2) 10% uniconazole (Yansheng) 40g/ mu.

(3) 12.5% hexazolol (trimethopril) 20g/ mu. Spray 15-25 kg of water and apply it again every 10 days or so, usually 3 times in a row.

(4) 50% propiconazole 8-10ml/ mu.

(5) Aimiao (difenoconazole / propiconazole) can also treat rice sheath blight for two times.