? Pathogens overwinter on rice straw and rice with conidia and hyphae, among which diseased grass is the main source of infection of early rice. The conidia produced in the second year spread to rice plants through wind and rain, causing diseases and forming central diseased plants. After that, conidia were continuously produced on the infected rice plants and reinfected many times through wind and rain. After rice harvest, the pathogen overwinters on diseased grass and diseases.
? The occurrence and development of rice blast are restricted by varieties, water and fertilizer management and climate, in which the disease resistance of varieties is the internal cause, the quality of water and fertilizer management is an important factor affecting the disease resistance of rice, and climate is the necessary condition for the occurrence and epidemic of diseases. The main factor leading to the different severity of the disease from year to year is climatic conditions; The main factors causing the different severity of field diseases are cultivation management measures and disease resistance of varieties.
(1) climate. The temperature is 20- 30C and the relative humidity is above 90%, which is beneficial to the occurrence of rice blast: the heading stage of early rice in Jianghuai area is often in the rainy season, which often leads to the epidemic of ear neck blast. During the booting and heading stages of late rice, if it is cold, rainy or foggy, the disease resistance of rice will be weakened, which will easily lead to the epidemic of ear neck plague.
(2) Water and fertilizer management. Excessive application of nitrogen fertilizer, especially in the later stage, will induce the serious occurrence of ear blast. Long-term flooding or cold water series irrigation and flood irrigation will hinder the growth of rice roots, reduce the disease resistance of rice plants and cause serious diseases.
(3) Disease resistance of seed crystal. The resistance of rice to rice blast varies from variety to variety. Generally, indica rice is more disease-resistant than japonica rice, and glutinous rice is more disease-resistant than glutinous rice. The resistance of the same variety is different at different growth stages. -Generally, the disease is most likely to occur at the seedling four-leaf stage, tillering stage in the field, and the end of booting stage to the beginning of booting stage.
Prevention and control methods:
Comprehensive measures must be taken to control rice blast: on the basis of breeding high-yield and disease-resistant varieties, on the premise of eliminating pathogenic bacteria, improving cultivation techniques to enhance rice disease-resistant ability, and focusing on pesticide control according to weather, seedling situation and illness.
(1) Select high-yield and disease-resistant varieties. Selecting high-yield and disease-resistant varieties is an economical and effective measure. Under the guidance of local agricultural technology departments, varieties with strong disease resistance can be selected according to local conditions.
(2) eliminate pathogens. Weeding in case of disease should be handled in time, and it is not allowed to return directly to the field or pile up near the seedling field. No need to build a shed, no need to accelerate germination, no need to tie seedlings with diseased straw, and no need to bring germs into rice fields. Seed collection should be strictly disinfected. The main methods are as follows: soaking seeds with 25% fresh-keeping EC 3,000 times (that is, 2 ml of one seed mixed with 6 kg of water can soak seeds for 3 kg), soaking seeds in conventional rice for 48 hours, soaking seeds in hybrid rice for 8~ 10 hours, and taking out seeds to germinate directly after soaking; Soak the seeds 12-24 hours with 500 times of strong chlorine semen (once every 3-4 hours), then rinse the liquid with clear water to accelerate germination; Early rice and middle rice were soaked in 10% quicklime for 2-3 days, and late rice was soaked in 1-2 days.
(3) Strengthen water and fertilizer management. Rational fertilization, increased application of organic fertilizer, popularization of N, P and K formula fertilization, scientific use of water at the same time, prevention of long-term deep irrigation at booting stage, frequent irrigation of shallow water, timely and moderate drying of fields.
(4) chemical control. The prevention and treatment of seedling blast and leaf blast should be controlled in the early stage of the disease, especially when acute spots appear, and the medicine should be sprayed immediately, and the disease should be treated several times continuously. The prevention and treatment of ear and neck plague should be controlled from the onset to the full heading stage, and the drug should be used 2-3 times. Optional chemicals: 40% Fuji 1 EC 75- 100 g per mu, 20% tricyclazole wettable powder 100g, or 40% mirex suspension 200 g.