How to control rice panicle blast? When is the best time to apply? How to judge?

According to the recent field monitoring results of rice blast in rural surveillance networks in Heilongjiang Province, combined with the comprehensive analysis of rice varieties, resistance, field growth, cultivation management and meteorological conditions, it is estimated that there is a risk of recurrence of rice panicle neck blast in Heilongjiang Province this year. So how to control rice panicle neck blast? When is the best time to apply the medicine? How to judge?

Rice neck blast is a common and airflow disease in rice. Rice neck blast is easy to occur during flowering and filling stage if the climatic conditions are suitable. After infection, with the reproduction and harm of the pathogen, the neck node of the ear is necrotic, and the nutrient channel transported to the ear is blocked, thus forming a white ear or shrunken grain of rice. In the year in which panicle neck blast occurred, the yield was generally reduced by 10% to 20%, serious fields by more than 30%, or even no harvest. Once the panicle neck is infected with rice blast, it has a great impact on the yield and quality of rice.

1. Harmful symptoms

Panicle neck rice blast mainly occurs on panicle neck or rachis and branches. Ear neck disease, the disease spot brown or gray-black, spread up and down from the ear neck, can be as long as 3-4 years. Early onset, serious disease, resulting in white ear; late onset, mild disease, resulting in a decrease in 1000-grain weight or blighted grain. Panicle neck blast often causes spike stem breakage, and the symptoms on rachis branches, branches and regenerated branches are similar to those in panicle neck, but only some spikelets above the disease spot are damaged, resulting in unfruitful spikelets.

two。 Route of transmission and law of occurrence

The pathogen overwintered with conidia and mycelium on rice straw and rice, and the following year produced conidia and spread to rice plants by wind and rain, germinated and invaded the host and spread to neighboring cells, forming central diseased plants. The conidia formed in the disease department are re-infected by wind and rain. Sowing infected seeds can cause seedling plague. The suitable temperature, high humidity, rain, fog and dew were favorable for the disease. The mycelium growth temperature was 8: 37 ℃, and the optimum temperature was 26-28 ℃. The temperature of spore formation is 10: 35 ℃, the optimum temperature is 25: 28 ℃, and the relative humidity is more than 90%. Spore germination needs water and lasts for 6 hours and 8 hours. Suitable temperature and humidity can form attachment spores and invade filaments, penetrate the epidermis of rice plants and spread among cells to absorb nutrients. Under the conditions of continuous rain, lack of sunshine, sometimes sunny and sometimes rain, clouds and dew in the morning and evening, the disease spreads rapidly.

3. Disease condition

3.1 Resistance of varieties: there are obvious differences in resistance among different varieties. at present, most of the resistant varieties used in production are vertical resistant varieties, and their resistance can only maintain resistance for a certain period of time because of the composition of physiological races. Once the inferior race becomes the dominant race, some varieties will lose their disease resistance and cause diseases to occur. The resistance of indica varieties was better than that of japonica varieties.

3.2 the number of bacteria sources: for example, there are many bacteria in the seeds, and there is no seed soaking disinfection, especially the diseased rice straw and blighted grain have not been destroyed or not thoroughly treated, and there are many overwintering bacteria sources, once they encounter suitable temperature and humidity conditions, they will spread quickly and the disease will be serious.

3.3 the meteorological conditions are bad: if the continuous overcast and rain at the tillering stage, with more rain days and times, forming the environmental conditions of high humidity, low temperature and low sunshine (less sunshine hours), the disease resistance of rice will be reduced, which is beneficial to the occurrence of the disease. If the continuous rainy weather occurs before and after the heading stage, more rainfall days and more rainfall times, resulting in the conditions of high humidity, low temperature and low light, it is not conducive to the growth of rice, but it is beneficial to the production of spores and spore germination and invasion, among them, high humidity is beneficial to spore germination and invasion, while low temperature and low light conditions make neck blast, node blast and grain blast more serious.

3.4 weak field management: if the application of nitrogen fertilizer is too much, too late, often cold water irrigation, deep water irrigation, etc., will reduce the disease resistance of rice and aggravate the disease. At panicle stage, the disease resistance was the weakest at the beginning of panicle. Partial application and excessive application of nitrogen fertilizer are beneficial to the disease. The root system of long-term deep irrigation is poor, the disease resistance is weak, and the disease is serious.

4. Prevention and treatment of misunderstanding

Neck blast is a kind of rice blast that occurs on the neck of panicle (where the spike axis connects with rice). The neck of the panicle is the only way to transport the photosynthates from rice leaves to the panicle, and it is also the part where rice plants are most likely to be infected with rice blast. In recent years, the reason why the incidence of rice panicle neck blast is serious, mainly due to poor control, there are misunderstandings.

4.1 Pesticide was applied only at the time of white ear: when the blast pathogen had just invaded, it generally showed no symptoms and was not obvious at the initial stage of the disease. It is too late to wait until the white ear appears due to disease and necrosis of the ear neck. The control of rice neck blast generally requires the use of drugs at the breaking and early heading stage, blast-susceptible varieties or non-blast-resistant varieties or fields that are overgrown, and again at the full heading stage (when heading reaches about 80%). The occurrence of rice blast is greatly affected by the environment, the disease conditions at the tillering stage are not suitable, and the occurrence of seedling blast may not be serious; if the conditions at the panicle stage are suitable, it may show susceptibility. For varieties susceptible to blast or non-resistant, overcast and rainy weather occurred at the panicle stage, regardless of the severity of seedling blast, it may lead to the panicle neck blast epidemic. Therefore, even if the seedling blast is not serious, the control of neck blast should be strengthened in the fields with susceptible or non-resistant varieties, or in the fields with serious rice blast over the years, and the pesticides should be used once at the initial heading stage and full heading stage.

4.2 varieties with strong blast resistance ignore the use of pesticides: there are no varieties with absolute resistance to rice blast, and the resistance is relative. Although the incidence of blast-resistant varieties is significantly lower than that of susceptible varieties, it is also possible to grow in fields with serious disease all the year round (the nest of rice blast), or to apply nitrogen fertilizer, to grow too vigorously, and to encounter overcast and rainy weather at heading stage. For perennially diseased fields, even for resistant varieties, we should pay attention to timely control of panicle neck blast; for fields with partial application of nitrogen fertilizer and vegetative growth, whether resistant or susceptible varieties, the control of panicle neck blast should not be ignored.

4.3 No medication in case of rain at heading stage: overcast and rainy weather at heading stage may cause serious disease, such as the large planting area of susceptible varieties, it may also cause panicle neck blast panicle epidemic. Therefore, the control of panicle neck blast should be applied once at the initial heading stage and full heading stage of rice, and should be supplemented in case of rain within 8 hours after application. Even if it is cloudy and rainy, you should use the medicine between the rain. High-quality rice, varieties or combinations planted for many years, fields with serious seedling blast, rice fields with overgrowth of plants, cold-soaked fields and fields with rainfall at heading stage should be used once at the initial heading stage and full heading stage.

5. Prevention and cure measures

According to the occurrence characteristics of rice panicle neck blast, the control method of "prevention first and comprehensive control" should be adopted.

5.1 selection of good varieties: high-quality and high-yield varieties (combinations) with good resistance should be selected and the resistant varieties should be replaced in time after continuous planting for several years.

5.2 completely eliminate the source of bacteria: for the fields where rice blast has occurred, the diseased straw in the field should be cleared or burned in time to reduce the number of overwintering bacteria; seed soaking and disinfection with prochloraz and strong chlorine can kill the germs carried by rice seeds and prevent evil seedling disease at the same time.

5.3 Scientific operation of fertilizer and water: on the basis of dry cultivation and strong seedling, popularize the wide row spacing cultivation of 30 years. In fertilizer operation, increase the application of base fertilizer, heavy application of leaf fertilizer, skillful application of panicle fertilizer. In general, the fields with a yield of 550 to 650 tons per mu applied 12.5 to 13.5 tons of pure nitrogen, in which bottom fertilizer and leaf fertilizer accounted for 3540%, panicle fertilizer accounted for 20,30%, and the last leaf fertilizer and panicle fertilizer were 30 to 40 days apart. On the basis of nitrogen control in the middle stage, panicle fertilizer should be fertilized with yellow fertilizer, early yellow fertilizer, late yellow fertilizer, thin soil and less fertilizer. After planting in the water layer management to the effective tillering stage, maintain the shallow water layer, and pay attention to the proper drying for new water; timely roast the field at the ineffective tillering stage; maintain the shallow water layer at the young panicle differentiation stage, and keep the water layer at 4 to 6 times at the heading and flowering stage; after entering the filling stage, adopt the management method of dry, wet and shallow water irrigation.

5.4 timely chemical control: fields with seedling plague and leaf plague, susceptible varieties, low-lying old disease areas soaked by flood, sprayed once 2 days before the break and at the early stage of full heading, 20% tricyclazole 75 100 g per 667 tons, or 40% Fuji 1 100 g, 50: 75 tons of water will be sprayed through the plants, and alternate use of corresponding pesticides can improve the control effect.

5.5 precautions for prevention and control: first, the prevention and control of rice blast should adhere to the strategy of "prevention first" and strictly control the time of prevention and control. pesticide application at the break stage is the key to harvest or not, and pesticide application at full heading stage is a measure to harvest more and harvest less. Second, avoid spraying at flowering stage, and try to choose before 10:00 and after 4pm, because spraying at flowering stage, the liquid can easily enter the flower organ, hurt or kill pollen, anther, ovary, etc., at the same time, the liquid will wash down pollen, seriously affect pollination, resulting in an increase in the sterile rate of rice; third, use enough medicine, mix enough water, spray evenly and thoughtfully on the ear layer, and spray the plant through. Fourth, the varieties of pesticides used for more than two times should be used in rotation to avoid drug resistance. Fifth, take shelter from the rain and apply the pesticide. If there is rain within 8 hours after the application, you should catch the gap between the rain. Avoid