How to comprehensively prevent and control infectious silkworm diseases? Detailed explanation of key technical points
During the @#@250@#@ process, the occurrence of infectious silkworm diseases often leads to poor cocoon harvests and reduced cocoon quality. Therefore, disinfection and disease prevention must run through the entire sericulture process. On the basis of focusing on disinfection before sericulture, doing a good job of disease prevention during the rearing period and disinfection after sericulture is completed, and carrying out comprehensive prevention and control, can pathogens be thoroughly eliminated and the occurrence of infectious silkworm diseases be prevented.
1. Promptly cull diseased silkworms. Many infectious silkworm diseases, such as midgut-type nuclear polyhedrosis, viral flacherie, pebrine, and bacterial gastroenteritis, etc. In the early stage of infection with the above diseases, silkworms often show symptoms such as slow growth, a thin and small body, and uneven development. At this time, large numbers of highly virulent pathogenic microorganisms have already been discharged from the body through the feces and digestive fluids of diseased silkworms, contaminating mulberry leaves and the rearing bed. This causes reinfection and is one of the important reasons for outbreaks of silkworm disease transmission.
Practice has shown that rearing large and small silkworms in the same room often causes severe silkworm disease in the later batch. If diseased silkworms are discovered as early as possible and small silkworms are reared in separate rooms, with dedicated use of personnel, rearing rooms, and rearing tools, it can not only improve the rearing level, but is also an important measure for preventing silkworm diseases.
2. Disinfection of the silkworm body and rearing bed. The pathogenic microorganisms contaminating the silkworm body and rearing bed mainly come from the excrement, digestive fluids, or body fluids of diseased silkworms in the rearing bed. In addition, outdoor pathogenic microorganisms can be brought into the room with mulberry leaves, rearing tools, or by the rearers, and can also settle onto the rearing bed with airflow and dust. Therefore, regular disinfection of the silkworm body and rearing bed can promptly kill pathogenic microorganisms and is an important measure for preventing the occurrence of silkworm diseases.
At present, three types are commonly used in production: silkworm body and rearing bed disinfectants, fumigants, and liquid preparations. Powder preparations mainly include lime powder, bleaching powder, fungicide powder for flacherie prevention, Disease Prevention No. 1, and Canzuojing; liquid preparations include Flacherie Prevention Ling No. 2; fumigants include Youlüjing, etc. These agents are generally used once daily starting from the first feeding of newly hatched silkworms at each molting. In areas and seasons where flacherie occurs frequently, one additional application is made during the peak feeding period of each instar. When flacherie has already occurred, use once daily for several consecutive days until flacherie no longer occurs.
Fresh lime powder is the most widely used, economical, and effective disinfectant in sericulture production. Generally, it is used once daily starting from the third instar. When silkworm disease has already occurred, first strictly pick out diseased small silkworms and appropriately increase the number of applications.
Disease Prevention No. 1 is divided into two types: for small silkworms and for large silkworms. Generally, it is used once for newly hatched silkworms and once at the start of each instar, and when silkworm disease occurs it can be used once daily. Wrap it in gauze and evenly sprinkle it on the rearing bed, preferably covering the rearing bed and the surface of the silkworm body with a thin layer like frost. The amount used increases as the silkworm instar increases. Keep the rearing bed dry during use, and do not feed wet mulberry leaves.
The method of using Canzuojing is the same as that of Disease Prevention No. 1.
Bleaching powder can also be mixed with lime powder to prepare a flacherie-prevention powder containing 2% available chlorine (for small silkworms) or 3% (for large silkworms). The method of use is the same as that of Disease Prevention No. 1, but note that it should be prepared and used immediately, and the bed should be cleaned immediately after use.
3. Disease prevention measures in sericulture operations. Disease prevention measures during sericulture operations include: (1) Undisinfected rearing tools are prohibited from being brought into the rearing room for use. (2) Tools for transporting silkworm excrement must be strictly separated from tools for transporting mulberry leaves. (3) Silkworm nets after bed cleaning should be frequently sun-dried for disinfection. (4) When entering the rearing room and the leaf storage room, insist on changing shoes, and wash hands before feeding and adjusting mulberry leaves and after bed cleaning. (5) Set up a dedicated leaf storage room, and disinfect the leaf storage room and mulberry-picking tools once per instar with 0.5% available chlorine bleaching powder solution. (6) After bed cleaning, disinfect the floor of the rearing room with 0.5% available chlorine bleaching powder or lime slurry. (7) Diseased silkworms must not be discarded randomly or fed to poultry; they should be placed in lime slurry for immersion disinfection and then deeply buried in the soil. (8) Silkworm excrement used as fertilizer must be composted and fully fermented and decomposed before use. It is prohibited to spread and dry silkworm excrement near rearing rooms or mulberry fields.
4. Disinfection after sericulture is completed. Disinfection after sericulture is completed is commonly called "huishan disinfection." After sericulture and cocoon harvesting are completed, the pathogenic microorganisms carried by leftover diseased silkworm corpses, silkworm feces, and dead-cage rotten cocoons easily spread to the rearing room, rearing tools, and surrounding environment, becoming a source of infection for the next silkworm season. To this end, the following points must be achieved: (1) Rearing tools and other items used for sericulture and mounting should first be sprayed and disinfected with 0.5% available chlorine bleaching powder or 1-2% lime slurry, then cleaned, sun-dried, and stored. (2) Used old mounting materials and waste should be burned, or gathered together with silkworm excrement for composting. If some mounting tools still need to continue to be used, they must be disinfected and properly stored together. (3) The rearing room, leaf storage room, and mounting room should be cleaned and disinfected, thoroughly removing residual materials such as diseased silkworm corpses, rotten cocoons, and silkworm excrement. (4) The surrounding environment of the rearing room should be cleaned thoroughly.
5. Select and rear robust varieties and strengthen rearing management. There are obvious differences in the disease resistance of silkworms. Therefore, selecting and rearing robust silkworm varieties and enhancing the constitution of silkworms is an important part of silkworm disease prevention and control.
Large silkworms have stronger disease resistance than small silkworms, but at this stage they have weak adaptability to high-temperature and high-humidity environments. During the large silkworm stage, special attention should be paid to preventing high temperature and stuffiness, strengthening ventilation and air exchange, spreading the rearing bed thinly, and providing good mulberry leaves for full feeding.
6. Prevent and control mulberry field pests to avoid mutual infection. Mulberry field pests can also develop diseases such as flacherie, viral diseases, bacterial diseases, and pebrine, and many of these pathogenic microorganisms can mutually infect silkworms, becoming a source of silkworm disease infection. When applying pesticides in mulberry fields, close coordination with sericulture is required to avoid mulberry leaf contamination, and according to the residual effective period of the pesticide, apply pesticides and pick leaves in divided sections and zones.
7. Promptly diagnose silkworm diseases and control the spread of the disease. Different types of silkworm diseases have different symptoms. For the same case, symptoms are not entirely the same due to different onset periods. Diseased silkworms are mostly first discovered among late-molting silkworms and weak small silkworms with delayed development. When carrying out diagnostic examination of silkworm diseases, late-molting silkworms and weak small silkworms should be taken as key targets for inspection, ultimately achieving the goal of timely diagnosis and comprehensive prevention and control of silkworm diseases.