Detailed Explanation of Key Points on Mulberry Cultivation and Silkworm Rearing Techniques
Planting mulberries and rearing silkworms already emerged in ancient times in our country. Our country can be called a major silk nation. Our country's silk is not only produced and sold domestically, but even exported far abroad. For so many years, silk has remained in a state of supply falling short of demand, so the market for silkworm rearing is very good.
The Environment for Mulberry Growth and Development
1. Temperature: Mulberry trees need to be within a certain suitable temperature range to grow normally. When the air temperature is above 5°C, mulberry roots begin respiration. When the air temperature is above 12°C and moisture is sufficient, winter buds sprout, and branches and leaves accelerate their growth as the temperature increases from 25°C—30°C.
2. Light: Mulberry is a sun-loving plant. It needs sufficient sunlight to carry out photosynthesis better and to grow normally.
3. Water: The whole mulberry plant has a water content of 60%. Insufficient water will hinder the growth of mulberry roots and new shoots; the leaves will wilt and droop, and in severe cases turn yellow and fall off. Too much water leads to poor soil permeability, lack of oxygen, poor leaf quality, and poor mulberry growth. Prolonged flooding can also cause mulberry trees to die. Mulberry leaves with excessive water are not good for rearing silkworms. Mulberry is a deep-rooted plant, drought-tolerant but not waterlogging-tolerant, so when choosing a mulberry orchard, the groundwater level should preferably be lower than 3 chi below the ground surface, because most of the mulberry root system is distributed in the upper layer 20—30 cm below the surface.
4. Air: Air is also an indispensable element for the physiological activities of mulberry trees. At night, mulberry trees need to take in oxygen, and during the day they need to take in CO2 for photosynthesis to produce nutrients.
5. Mulberry growth requires various nutrient elements, here mainly referring to N, P, K. N: the main component for synthesizing protein in mulberry leaves. P: can promote cell division, growth of roots and stems, formation of chlorophyll, and enhance the stress resistance of the tree body. K: helps the transport of nutrients, strengthens roots and stems, and promotes maturity. In addition to the above main elements, trace elements such as calcium, magnesium, sulfur, boron, zinc, iron, copper, and manganese are also needed.
6. Soil: Soil is the foundation for mulberry growth. Its growth is closely related to soil layer structure, pH value, moisture, and nutrients. Mulberry has strong adaptability and can grow within a pH range of 4.5—9, that is, in acidic or alkaline soil. Sandy soil and red loam soil can both be used, but it grows best in neutral sandy loam.
Methods of Propagating Mulberry Seedlings
I. Selection and preparation of nursery land: The nursery land should be selected as sandy loam with sufficient sunlight, good ventilation, flat terrain, close to a water source, and free from bacterial wilt damage. Before sowing, the land should be turned and prepared, and 40—80 loads of decomposed organic fertilizer per mu should be applied as base fertilizer. The seedbed should be 4—5 cun high, 4 chi wide, with a 1-chi working row, and turtle-back shaped to prevent water accumulation.
II. Sowing period and methods
1. Period: In our province there are spring sowing and autumn sowing. Spring sowing is around Qingming (that is, late March—early April). Early sowing is better, and at the latest it should not exceed the end of April, because if it is late it may suffer from rain erosion, and high temperatures may kill the tender seedlings by scorching. Autumn sowing is around Qiufen (that is, late September). This should also be done early, but not too early. Autumn sowing has high temperatures and drought, so fertilizer and water management should be strengthened.
2. Methods. Broadcast sowing: about 2 jin of mulberry seed per mu. Drill sowing: 1.2—1.4 jin of mulberry seed per mu, with ditch depth and width of 1 cm×1 cm, and ditch spacing of 17—20 cm. To spread the seeds evenly, mix in 4—5 times fine sand or fine soil. After spreading, lightly scatter a layer of plant ash, then cover with grass sections, and spray water. After two leaves appear, remove the grass. Shade nets can also be used.
Precautions for Planting Mulberries
1. Preparation of mulberry seedlings. For self-propagated mulberry seedlings, it is best to do this during the winter dormant period of mulberry trees. If buying seedlings, buy seedlings without disease (especially bacterial wilt), do not damage roots and branches, keep as many seedling roots as possible, and do not let the seedlings be exposed to wind, sun, or piled up and heated.
2. Planting period: They can be planted in all four seasons. By custom, winter and spring planting are more common, and there are also those planted after summer and autumn. Winter planting is mostly during Xiaohan—Dahan (early January in the Gregorian calendar).
3. Planting density: Generally, hybrid mulberries are 5000—7000 plants per mu, with single-row and wide-narrow row planting. Single-row planting is conducive to weeding, intertillage, and fertilizing. The row direction is best east-west, which is good for light. Specifications for single-row planting: row spacing 1.8-2 chi, plant spacing 0.3-0.4 chi.
Precautions on the Timing of Fertilization
1. Winter base fertilizer: Combined with winter plowing and sun-whitening, begin opening trenches and applying organic fertilizer in early to mid-December.
2. Heavy application of spring bud fertilizer: In spring, when mulberry buds have grown to 2-3 cun, promptly apply quick-acting fertilizer, 50-70 jin of ammonium sulfate per mu, or 20-30 jin of human and livestock manure, ammonium bicarbonate, or urea.
3. Summer topdressing: Temperatures are high, rain is plentiful, and mulberry trees grow quickly.
4. Autumn supplementary fertilization: The general requirement for fertilization is to fertilize for each batch of mulberry, and prevent excessive partial application of N fertilizer. N, P, K should be applied in combination, mainly organic fertilizer, with inorganic fertilizer as a supplement, and the two should be applied together. After fertilization, 15 days must pass before picking leaves to rear silkworms; otherwise, the absorbed fertilizer has not yet transformed and will be harmful to the silkworms.
Requirements for the Silkworm Rearing Environment and Feed
1. Temperature: Silkworms do not have a fixed body temperature. They are governed by the external temperature and regulate themselves by the heat energy produced by internal metabolism and the evaporation of water. The level of temperature directly affects the physiological activities and growth and development of silkworms. The temperature at which silkworms can grow and develop normally is 20-28°C. Too high or too low will cause physiological disorders, leading to poor development and the occurrence of diseased and dead silkworms. Young silkworms have stronger resistance to high temperatures, while grown silkworms have weaker resistance to high temperatures. Therefore, the temperature should be adjusted according to changes in the silkworm instar. Generally, the temperature requirements for rearing bivoltine varieties are: 1st-2nd instar, 26-28°C. 3rd instar, 25-27°C. 4th-5th instar, 23-25°C.
2. Humidity: The humidity requirements are: 1st-2nd instar, 80-85%. 3rd instar, 75-80%. 4th-5th instar, 70-75%.
3. Air (airflow): Pay attention to fresh air and ventilation, with a certain airflow.
4. Light: Light affects hatching. Young silkworms are phototactic, while large silkworms are photophobic. Under light conditions, silkworms increase their food intake, the instar period is prolonged, and the total cocoon amount and yield increase. Rearing young silkworms in light reduces sand-burrowing silkworms, which is beneficial for preserving the number of silkworms. When mounting on cocooning frames, if the light is even, double cocoons will be reduced and the rate of good cocoons will be increased.
5. Feed: For the first instar, feed light green leaves (the 4th leaf from top to bottom). For the second instar, feed dark green leaves (the 5th-6th leaves from top to bottom). For the third instar, feed three-eye leaves and blind-selected leaves (the 7th-8th leaves from top to bottom). For the fourth-fifth instars, all leaves except tender leaves, muddy leaves, yellow leaves, and insect-damaged leaves can be used. In order to improve spring silkworm rearing and increase the rearing amount of the first batch, because the temperature of the first spring batch is low, in the winter mulberry pruning style, more large tree-tail mulberries can be retained for use as mulberry for young silkworms.
Silkworm Rearing Techniques
1. Incubation and collection of newly hatched silkworms
① Incubation: So-called incubation is the protection process of keeping silkworm eggs taken out of storage under reasonable environmental conditions so that they develop smoothly until hatching on the scheduled date. The spring period is generally 10—11 days, and the autumn period 9—10 days, after which the newly hatched silkworms can be collected. If they are immediately acid-treated eggs, silkworms will emerge one day earlier. Methods and technical requirements for incubation. (omitted) When receiving silkworm eggs, special attention must be paid to safety, sun protection, heat prevention, and prevention of contact with harmful gases.
② Collection of newly hatched silkworms: On the morning of the day of collection, expose the silkworm eggs to light. After the newly hatched silkworms emerge, collect them at 8—9 a.m. The collection movements should be gentle, and do not injure the newly hatched silkworms.
2. Methods for collecting newly hatched silkworms:
① For loose eggs, there are the net collection method and the cotton paper collection method;
② For flat-attached eggs, there are the mulberry lure method, the knocking-down method, and the inverted mulberry lure method. After collection, set the seat according to the prescribed area. When one sheet of silkworm eggs hatches relatively uniformly, the initial seat area is 0.1 m2.
3. Rearing techniques:
① Rear young silkworms well: A dedicated young silkworm room is required.
② Rear large silkworms (grown silkworms) well: The twenty-character policy “young silkworms raised with nylon, large silkworms raised in pits, thorough disinfection and disease prevention, full feeding and heat prevention.”
Types of Silkworm Disease Prevention and Control
I. Infectious silkworm diseases: pebrine disease (parent stock disease), bacterial diseases (gastrointestinal disease, septicemia, poisoning disease), viral diseases (polyhedrosis, nuclear polyhedrosis, viral softening disease), fungal diseases (white, Aspergillus, green, paste, brown, gray and other muscardine diseases). In recent years, viral diseases have appeared in rural areas, such as more polyhedrosis, with symptoms including empty head, high segments, fat male, and dry white abdomen. These are all midgut-type and body-cavity-type polyhedrosis, mostly infected and developing in the middle and late stages of the fifth instar. Some cannot cocoon after mounting, and some cannot pupate, bringing great losses to production.
II. Non-infectious silkworm diseases: parasitic diseases (polyvoltine maggot disease, acariasis), poisoning (pesticides, toxic gases), stinging injuries (mulberry tussock moth, stinging caterpillar), trauma, and diseases caused by physiological factors. In Guangdong silkworm areas, polyvoltine maggot disease occurs most frequently.
III. Comprehensive prevention and control of silkworm diseases. There are many types of silkworm diseases, and prevention and treatment methods differ. At present, once silkworm diseases occur, the possibility of cure is not great, and the effect is not ideal. Therefore, for silkworm diseases, the policy is still prevention first, combined with prevention and treatment.
① Thorough disinfection, elimination of pathogens, and cutting off transmission routes. Treatment of the environment, dead silkworms, rotten silkworms, silkworm litter, etc., disinfection of silkworm rearing tools and the environment, as well as disinfection of the silkworm body and silkworm seat, and strengthening the prevention and control of mulberry diseases and insect pests, implementing disease prevention measures.
② Strengthen management, enhance the constitution of silkworms, and improve their disease resistance.
③ Promptly confirm the type of disease, identify the cause, and control its spread.
In the process of rearing silkworms, the most important things are the methods of disease prevention and the treatment of diseases. It is hoped that the above introduction by the editor can help beginners in silkworm rearing. However, in actual breeding practice, the editor still suggests communicating more with successful people and learning from their successful experience.