Corporate News

First, stevia basic overview

    Stevia, also known as stevia, sweet grass and sweet tea, is a perennial stevia family herb, native to the Amanbai Mountains bordering Brazil in south latitude 22~24 and west longitude 55~56. The local Native Indians have used sweet grass as a sweetener for hundreds of years. It was introduced to China from Japan in 1977, and it was planted and popularized throughout the country. Stevia, commonly known as stevia, is made from stevia leaves as a pure natural, high sweetness and low high-calorie sweetener extracted and refined by modern bioengineering technology. The sweetness is 250-350 times that of sucrose, and the calories is only 1 / 300 that of sucrose. Stevia products are widely used in beverage, food, medicine, wine, tobacco and daily chemicals in the field of sugar, and diabetes, obesity, cardiovascular disease, hypertension and dental caries avoid sugar, and the pursuit of green, healthy, beautiful people the most ideal generation of sugar products, known as "the" best natural sweetener "," the third sugar source ", etc. China is currently the world's largest producer and supplier of stevia glycoproducts, accounting for about 90% of the global total output, with an annual output of about 2,000 tons.

Two, Stevia botanical characteristics

    (1) Root

    The stevia roots are composed of fine, strips of adventitious, lateral, and whisker roots. Stevia roots are mainly distributed in the upper soil, which is small. The main root group range is within a 30 cm soil layer. Stevia root functions as absorbing, transferring water and nutrients, and storing and fixing the synthesized nutrients.

    (2) Stem

    Stevia stem is relatively soft, upright or semi-upright, plant height 90-150 cm high, in the stem of the raw leaves called the section, each with two leaves opposite. The axillary buds on each segment grow opposite lateral branches, where a pair of lateral branches can also regenerate, usually in a stevia plant with about 12-24 knots. Between section between sections. The length of the internode gradually increases from the stem base to the tip, while the internode thickness is gradually weak. The stevia stem cannot continue to thicken until the tissue is differentiated and matured. Stem vascular bundles are a transport pipeline between plant roots and leaves, flowers and seeds.

    (3) Leaves

    Stevia leaves are arranged in a segment with two opposite leaves, but the leaves are different from other plants. The living position of the stevia leaves, with the increase of each section, you can see the semi-rotating position, with the so-called alternate leaves living. Stevia leaves in the early stage, and each other in the late period.

    The leaves are lanceolate wide, generally 4.5 to 9.5 cm long and 2 to 5 cm wide. The leaf margin has paler grain teeth. The leaf back, the front has short hair, different types, the number of hairs is also different. Stevia is a single leaf, with a petiole, the base of the original leaf, which develops into the young bud, which is connected to the petiole. The center of the blade runs through a main vein (or middle vein), with many small lateral veins distributed on the middle side.

    Leaf color to green type is the most, a few have light yellow, light green type. The number of leaves on the main stem, due to the difference of variety types and cultivation environment, has a great impact on the number of leaves, the annual single plant has 400-700 leaves, up to 1200 leaves. Stevia leaves have the same function as other plant leaves. It can play photosynthesis, transpiration, absorption, respiration.

    The economic utilization part of stevia is mainly of the leaves. The amount of stevia glycosides contained in each part of stevia leaves is distributed according to a certain level. The amount of stevia in different leaves of the same variety, even the same plant. Stevia leaves are the most in the middle part, and the highest content of glycosides. The content of the unfolded top leaf and the lower old leaves is low. There is no obvious difference in the amount of steviside in the main stem leaves and glycosides in the lateral leaves.

    (4) Flowers

    Stevia flowers are complete flowers, but have low self-pollination rates and the flowers are white. In the stem or upper branch, 3-6 small flowers attached to the head, flowering for 15-20 days.

    (5) Seeds

    Stevia seeds are small and slender in shape, generally 2 to 3 mm. The ripe peel is brown or black-brown. The seeds are angular in appearance and have light gray lines. At the top of the seed, the embryo is surrounded by crown hairs, showing gray. The seeds weighs 0.3-0.4 grams. From the cross section of the seed, there are seed skin, inner membrane and embryo. Stevia seeds have no obvious endosperm, and their storage part mainly depends on cotyledons. The embryo is located at the tip of the seed, and the embryo consists of the germ, cotyl, and germ root.

Third，Environmental conditions required for the growth and development of stevia

    (1) Temperature

    The appropriate temperature is necessary for the growth and development of stevia. Stevia has different temperature requirements during different reproductive periods. Stevia is native to subtropical areas and likes high temperature. Northern cultivation should especially consider the influence of low temperature. Between 20 and 25℃ is a suitable temperature for stevia germination, and both below 15℃ or higher than 30℃ are unfavorable for seed germination. If the low temperature of 8 to 12℃ lasts for 1 month in the seedling stage, the dry material weight of the leaves and the ground will be significantly reduced. The suitable temperature for stevia growth is 25~29℃. If the daily average air temperature is below 24℃, stevia will grow slowly; above 25℃, stevia will grow very fast; if the autumn daily average air temperature drops to 15℃, stevia will stop growing.

     (2) Light

    Stevia is a short-sunshine crop. The critical sunshine is 12 hours, the light time is less than 12 hours, the flowering is in advance, and the vegetative growth period is shortened. Planting stevia in our north, because it belongs to the long sunshine area, the flowering time is significantly delayed or not flowering, can not be harvested normally, can only harvest leaves.

    (3) Water

    Water is one of the most important factors for stevia growth. Stevia requires enough water to germinate, holding water of no less than 80% in the field, and the near-surface air humidity is high. When the near-surface air moisture is too low and they evaporate too fast, the seeds are difficult to germinate and take root, even if the soil humidity is very high. Soil humidity is small, near the surface air humidity is small, will make the seed germination rate is significantly reduced, after the germination of seedlings will also cause a serious phenomenon of dead seedlings. However, when the water held in the field is more than 85%, the germination rate of stevia seeds will also decline, and the rootless seedlings will increase, making serious rotten seeds. The total water consumption of stevia during the reproductive period is quite different due to the variety characteristics, group size, climate conditions, soil properties, cultivation techniques and yield levels. The total water consumption varies from 4500 to 9000 m 3 / ha over a 1-year growth cycle.

    (4) Soil

    Stevia on soil species, fertility requirements are not very strict, a wide range of adaptation. But more suitable for convenient drainage and irrigation, fertile soil of sandy loam or loam planting. Soil organic matter is required to be greater than 1.2%, quick nitrogen greater than 90PPM, quick phosphorus greater than 23PPM, quick potassium greater than 150PPM, and PH value between 5.5 and 7.5. Stevia before the crops avoid melon, vegetables, sunflower and other crops.

    (5) The nutritional characteristics and fertilizer requirements of stevia

    Stevia absorbs nitrogen, phosphorus, potassium, and trace elements throughout its life to meet the needs of growth and development. Stevia needs the most fertilizer for potassium fertilizer, nitrogen fertilizer and the least phosphorus fertilizer.

    a. Nitrogen

    Stevia nitrogen is extremely sensitive to nitrogen response, and the nitrogen supply must be appropriate. Stevia can absorb 78% of the nitrogen during the bud-forming period, which gradually drops later. When nitrogen is too much, it will lead to long stem and leaf growth, elongated internodes, weak growth, thin leaves, easy lodging and serious infection disease, lower leaves premature mildew, resulting in leaf yield, air drying rate and leaf and stem branch ratio decline, and reduced quality. When stevia is short of nitrogen, the plant growth is inhibited, the plant is weak, the stem and leaves grow slowly, the number of leaves, leaf area is reduced, the leaves are yellow-green, light and no light, the lower leaves first yellow yellow from the tip of the leaf.

    b.Phosphate

    The demand of phosphorus in stevia is secondary to that of nitrogen and potassium, accounting for 0.3% to 0.5% of the dry material weight in the plant. Phosphorus can promote seed germination and root development, enhance seedling metabolism and stress resistance, and promote flowering, seed and seed maturation. Appropriate phosphorus fertilizer was applied in the early stage of stevia, and both shoot and root development can be improved. When phosphorus is too much, it will increase the accumulation of inorganic phosphate in the plant, resulting in a dysregulation of stevia metabolism and a decreased leaf yield. When stevia lacks phosphorus, the seedling roots are weak and slow, with purplish red leaves. In severe phosphorus deficiency, the leaves turn yellow, and the symptoms are similar to the yellowing symptoms in nitrogen deficiency. It must be determined whether nitrogen deficiency or phosphorus deficiency is determined by measuring the plant.

    c.Potassium 

   Potassium is the most abundant nutrient element in stevia, accounting for about 1.5%~4.0% of the dry material weight. Potassium promotes stevia carbohydrate synthesis and transfer, improving the ability of leaves to continue photosynthesis. In high nitrogen, increasing potassium fertilizer is more effective than increasing phosphorus fertilizer. When potassium is too much, the plant will affect the absorption of molybdenum and magnesium, and adverse reactions will also occur, such as the low air-drying rate of each part of the plant, and the flowering rate and seed yield will decline. When stevia is short of potassium, seedlings grow slowly, leaves are yellow or yellow, leaf edges and tips dry. Plant potassium deficiency and seedling potassium deficiency is similar, the lower old leaves are yellow, and gradually develop to the middle. When severe potassium deficiency, the plant is weak, root dysplasia, easy to lodging.

Four, stevia seedling technology

    (1) Characteristics of stevia seed

    a.Stevia seed false rate is high, stevia self-flower infertility, mainly rely on wind and insect pollination fertilization. Seed false rate is 15~30%, such as pollination in the cloudy rain and low temperature and other adverse conditions, seed false rate can reach more than 60%, plus the seed is small, the top with a crown hair, easy to touch each other, false seed is more difficult to separate, so the seed clarity is low.

    b.Seeds are small, easy to lose germination force, stevia seed 1,000 seeds weight is only 0.3~0.4 grams, very little storage and storage, coupled with loose skin tissue, easy to penetrate into the water and air, so that the respiration is enhanced and lose germination force. The harvested seeds are stored in the room, to the next spring sowing, the germination rate is mostly between 23 and 78%, put in August, that is, all the germination power is lost. However, the germination power of closed storage is more than 90%, so the dry storage of seeds is an effective measure to maintain the germination rate.

    c.Germination varies greatly between morning and evening, and the seedlings grow slowly

    Under appropriate conditions, sowing can be produced seedlings for 4~5 days, can continue for 15~25 days to end, 40~60 days to grow to 6~9 pairs of true leaves, to reach the transplanting standard, early seedlings tender, in high temperature, drought or fertilizer concentration slightly higher, will lead to the death of seedlings.

    (2) Environmental conditions that affect seed germination and seedling emergence

    a.Thickness of seed cover soil. Stevia seeds are small, with weak cotyl elongation, poor young bud and topsoil capacity, and slightly deeper planting will seriously affect the emergence rate. According to the test of Shandong Zibo Agricultural Science Institute, the seedling yield is 62.7%, 1~2mm is 29%, and 2 m m is 22.3%.

    b.Soil water. Since stevia seeds are sown on the soil surface, the topsoil humidity is an important condition affecting seed germination and seedling survival. The soil water content remains 60% (saturated) when the soil moisture drops, the seed germination rate decreases accordingly.

    c.nursery bed temperature. Stevia seeds were in the range of 10 to 28℃, and germination period advancing with increasing temperature, optimal from 20 to 25℃.

    d.The effect of sowing period. Using medium and shed seedlings, in the adapted temperature range, the earlier the sowing, the higher the emergence rate and the number of seedlings, too late sowing, the seedling bed temperature is too high, water evaporation is fast, make the soil surface dry, hardening, that is, affect the seed germination, will also make the seedlings dead.

    (3) Technical key points of stevia planting and seedling raising

    a. Selection of seedling bed site and seedling bed setting

    Seedling should choose the sunny flat or gentle slope, close to water, convenient transportation, fertile soil, fertilizer and water strength, convenient drainage and irrigation, neutral or slightly acidic loam, sandy loam land is suitable, sand, saline-alkali land, melon, vegetables and heavy stubble stevia can not be the seedling land, when conditions should be sandwiched before sowing.

    Seedling bed system:

    ①, make the bed time. Generally, 7~10 days before sowing, specifications to wide 1.2~1.8m, 10~15m long is appropriate, too wide and too long is not conducive to management, too short and too narrow to reduce the utilization rate of the seedling bed.

     ②, Make a bed. The soil in the determined seedling bed is 10cm deep, put the bed straw (straw, straw, straw, fallen leaves, etc.) or horse dung 10cm thick, add water soaked, soil 12~14cm, smooth rake fine, soil around the bed of the steadfast, full water before sowing, bed with 2~4cm thick nutritious soil, nutritional soil is the key to the success or failure of stevia seedling.

    ③, nutrient soil preparation. Generally is mixed with fertile loamy soil and rotten organic fertilizer, nutritional soil to be fine. Preparation method: humus 30%, fine sand 5%, rotten composting 35%, rotten stable fertilizer 30% into. Different preparation methods can be adopted according to the conditions and local conditions.

    ④, make the seedling shed. Seedling shed can be used greenhouse and small arch shed, small arch shed barren 60~100cm high, after finishing the bed, timely cover the shed film, increase the bed temperature.

    ⑤, soil disinfection, and insecticidal insects. In order to prevent the harm of diseases and insects in stevia seedling stage and ensure the robust growth of seedlings, the seedling bed soil should be treated with agents before sowing.

    Soil disinfection: disinfect with * * * * * * before sowing, and spray the bed surface with 800~1000 times.

    Control of underground pests: in areas with mole cricket, grub and earthworm harm, use 1 gram of 50%% sulfur and phosphorus emulsion oil per square meter of seedling bed, mix 100 grams of fine soil, and sprinkle the bed surface into the topsoil.

    2. Sow at the right time

    a.seedtime. The suitable sowing period of stevia has obvious seasonality. Our city in early April sowing is appropriate. The basic principle is that the minimum temperature of the surface soil in the seedling bed is stable to above 1~3℃, which can be sown. Within the temperature conditions, the earlier the sowing period, the higher the seedling emergence rate and seedling formation rate.

    b.seed quantity. Suitable sowing amount is an important condition for cultivating strong seedlings. Too much seedlings are weak and susceptible to disease, and too little increases the cost of seedling raising. Generally, with 800~1500 seedlings as the standard, planting 1 hectare of land needs a seedling bed area of 100~150 square meters. Seed quality is the main factor to determine the amount of stevia seed is 50-50% -1000-1800. It is appropriate to sow 1500~2500 seeds per square meter of bed surface. The seedling formation rate is directly related to the level of seedling technology and environmental conditions.

    3. Seed treatment

    Seed treatment before sowing can improve the seedling emergence rate, seedling emergence, prevent seedling disease, and achieve the purpose of cultivating strong seedlings.

    a.Sun the seeds and remove the crown hair. By enhancing the seed germination rate, kill some of the seed surface eggs and bacteria, is conducive to the removal of crown hair. Seed with crown hair after sowing bad contact with the soil, affect water absorption germination, must be combined with drying seeds with the hand light rub, remove the crown hair.

    b.seed cleaning. Wind selection and water selection method are generally adopted. Wind selection method: with natural breeze or electric fan to blow out the empty seeds; water selection method: combined with the seeds before the sowing, soaked in water, stir for about 10~15 minutes, then stand for 1~2 hours, remove false seeds and other debris, collect full sinking seeds for bud treatment before sowing.

    c.seed disinfection. Stevia seeds are attached to a variety of bacteria, before sowing, can prevent the spread of disease. Drugs and concentration for disinfection, can choose one of the following: 50% polybacterial spirit 250 times solution, potassium permanganate 5000 times solution; 50% more than 500 times solution; 1% copper sulfate solution; 1% formalin solution. Disinfection method: put the seed in the gauze bag, first wet with water, pour to float water, and then put into the good medicine liquid, soak for 10~15 minutes, take out with water will be clean, can be directly sown, or then soak the bud.

    d.Baptist seed, prompt bud. The sterilized seeds can be sown directly or then soaked to urge buds.

    Impping: soak the seeds in cold water or 25℃ warm water for 12~18 hours, remove, pour off floating water, can sow or then sprout. 

    Bud urging: put the soaked seeds at a temperature of 20~25℃, keep moist, turn over once in the morning and evening every day, to make the temperature and humidity uniform, after 2~3 days, when half of the seeds start to dew white.

    4. Sowing methods

    ⑴. First fill the seedling bed with the bottom water. After the water seeps down, then fill the water with fine soil and water at the sink place to keep the bed surface flat and the humidity consistent.

    ⑵. Add the treated seeds to the fine soil and sawdust, mix well, and sprinkle evenly on the seedling bed multiple times.

    ⑶.sprinkle the seeds, and then with fine sieve fine sand soil, evenly screening soil, to the seeds half exposed half buried is appropriate, and then use the light press board, so that the seeds and soil close contact, and then spray fine water, so that the soil wet.

5. Seedling management

Stevia seedlings are weak, slow growth and long seedling stage. Strengthening the management of seedling stage is the key to cultivating strong seedlings.

    ⑴, Water management at seedling stage

    From sowing to seedlings 2~3 to true leaves, is the worst stage of drought resistance, must be checked every morning and evening, a little dry should be timely watering, so that the topsoil always keep wet state (with fingers pinch a little bed soil to not stick, not dripping water for watering appropriate). Water with a fine hole pot to avoid washing out the seeds or seedlings. After growing three pairs of true leaves, the root system has been lowered, which can appropriately reduce the number of watering, and still keep the root soil moist. In the middle and late stage of seedling, such as seedling growth phenomenon should control watering, strengthen ventilation and cooling and other measures, refining seedlings to promote strong. Five to 7 days before transplanting, control watering, exposing the film and refining the seedlings, so that the seedlings adapt to the field conditions and improve the survival rate after planting. The day before transplanting, pour small water to moisten the root layer to facilitate seedling initiation.

    After growing three pairs of true leaves, the root system has been lowered, which can appropriately reduce the number of watering, and still keep the root layer soil moist.

   In the middle and late stage of seedling, such as seedling growth phenomenon should control watering, strengthen ventilation and cooling and other measures, refining seedlings to promote strong. Five to 7 days before transplanting, control watering, exposing the film and refining the seedlings, so that the seedlings adapt to the field conditions and improve the survival rate after planting. The day before transplanting, pour small water to moisten the root layer to facilitate seedling initiation.

    ⑵, seedling stage temperature management

    During stevia planting, it is appropriate to maintain the surface temperature of 20~28℃, during seedling growth, 18~25℃ during the day and 12~16℃ at night, the growth below 10℃ tends to stop, but it can withstand 2~3℃ low temperature; more than 30℃ is not conducive to seedling growth：

    Seedling early the temperature is low, using the small arch shed seedling bed, night should be covered on the film curtain insulation cold, uncovered during the day, conducive to receive sunshine warming, seedling, in the warm day, should pay attention to check the bed temperature, when the bed temperature is more than 28℃, you should take cooling measures such as shading ventilation, vent gradually increased by small. When the seedlings grow to 2~3 pairs of true leaves, and the average temperature is stable at more than 12℃, the film can be gradually removed, and the film begins to uncover early and late. By 7 to 10 days before transplanting, the film is no longer covered at night.

    ⑶, apply fertilizer rationally

    Stevia seedlings grow to 2 to 3 pairs of true leaves began to be topdressing, the first topdressing after 7 to 10 days can chase again, only long seedlings do not chase or less topdressing, 7 to 15 days before transplanting stop topdressing. Use urea, nitrogen, phosphorus, potassium compound fertilizer, diammonium phosphate for topdressing fertilizer, generally every 10m2 seedling bed with fertilizer 30~50 g, 15~25 kg of water after dissolving evenly sprayed, after chasing with water washed again. Do not undertake topdressing in the hot sun.

    ⑷, interseedlings, weeding, false planting

    In order to ensure the number of stevia seedlings, often to increase the planting coefficient, and the seedling density is too large, if not timely thin seedlings, easy to grow into thin high aging seedlings or long seedlings, affect transplanting survival and leaf yield, between the first time in 1 pair of true leaf time, combined with weeding; the second seedlings, in 2~3 seedlings, weak seedlings, seedlings, seedling density from 2~2.5cm, the second seedlings can be planted.

    The root system of false planting seedlings is developed and the survival rate after transplanting is high. Using false planting, the false planting bed should be made in advance, with the running distance of 3~5cm, keep the bed soil wet at the initial stage of false planting, and water and fertilize as appropriate later.

    ⑸, insect disease prevention

    blight prevention and control, found that the strain immediately pulled out and burned, can use more than 50% bacterial wet powder 1000 times liquid, all spray seedlings, every 7 days, consecutive 2~3 times. Underground pests were found to be watered with 50% 1000 times liquid in the hazard.

Five, Stevia transplanting

    Transplanting time

    Transplanting is the beginning of stevia field production, and also one of the important links in the cultivation process of stevia. Stevia is a warm crop. If the transplanting temperature is not enough, the soil temperature is low, stevia root grows slow, the absorption capacity is weak, and the slow seedling date is extended. When the temperature of the soil deep in 10 cm reaches more than 10℃, the daily average air temperature is stable at 12~15℃. When there is no harm of late frost, it should be timely planted and early, which can increase the growth period of crops. It is conducive to preserving soil moisture, increasing yield and improving quality. The transplanting time in our city from late May to early June is appropriate.

    (2) Land selection and land preparation

    1. Choose the ground. Stevia is not very strict with soil type and fertility, and has a wide range of adaptation. Stevia is a wild plant, the origin is mainly sandy loam, the soil fertility is low. After artificial cultivation, the general conditions are better than the soil fertility in its wild places. But from the dry leaf yield and root growth, they still grow well in fertile, loose soil. The soil is fertile, loose, rich in organic matter, with strong water preservation and fertilizer preservation capacity, and good ventilation, which is conducive to the root system, plant growth and the accumulation of organic substances. Soil pH value is better than neutral, pH value less than 5.5 or greater than 7.9 are not appropriate. Should not choose low-lying waterlogged land and continuous land parcel. Avoid melon, vegetables, sunflower and excessive use of long-acting herbicide plots.

    2. Land preparation and film mulching. A week before transplanting, prepare the land from the ridge. Before starting the ridge, we should apply sufficient base fertilizer, and it is best to apply 30-50 cubic meters of high-quality farm fertilizer, 250kg of diammonium phosphate and 100kg of potassium fertilizer per hectare. After the land preparation, in order to effectively prevent weeds and reduce the middle tillage weeding, 400-500 kg of 72%1500 ml of water per hectare. Conditions can take mulch cover (mulch is best black), before mulching should be first watering, after spraying herbicide. Membrane side with soil compaction compaction, membrane surface scattered some thin soil to be planted.

Advantages of stevia mulch covering:

  ⑴, improve the ground temperature, reduce the growth of weeds, and promote the early growth. 

  ⑵. Improve the utilization rate of fertilizer, and significantly reduce the leakage, loss and evaporation of fertilizer due to rainwater.

  ⑶. Improve the soil structure and the rhizosphere environment of stevia, and avoid the soil hardening caused by rain water. 

  ⑷. Avoid the rain directly splashing the ridge surface, splashing the soil on the back of the lower leaves and causing yellow leaves. 

  ⑸, can effectively prevent plant lodging. ⑹, has an obvious yield increase effect, the yield increase range is generally more than 20%.

 Transplanting method

1. Seedling. Generally using digging and pulling seedling two methods.

    Dig and stacking seedling method: it is generally in the day before the transplanting of the seedling bed poured a permeable, easy to vertical digging and stacking, digging and stacking seedling is to use a flat shovel to dig the seedling root with soil, the root stack is a cube, this is called digging and stacking seedling method. Dig stacked seedlings because of more root belt soil, less root hair damage, seedlings do not pinch injury, roots with a considerable amount of nutritious soil, can increase the field fertility, so the survival rate is high, slow seedlings fast, growth is also vigorous.

    Pull out seedling method: before pull out seedling, seedling bed must be fully watered, not only make seedling full absorb enough water, and can make topsoil loose run, pull out when the injury is very little, take soil more. Its practice is: pinch leaf with the hand, do not pinch or very light pinch stem, avoid hurting seedlings.

    Seedling should be combined with seedling selection, to choose neat growth, root strong strong seedlings. Strictly eliminate the sick seedlings and weak seedlings. Too small, too tender planted together, too large planted together, so as not to affect the uniformity of field production.

    Transport seedlings to do a good job of moisturizing and shade work, do not let the hot sun or accumulation is too thick, so as not to rub the seedlings injured or make the seedlings slow due to water loss, slow seedlings, reduce the survival rate.

     2. Transplanting density. The ridge distance was 60cm, and the plant distance was 8- -10cm. There are 160,000 to 180,000 seedlings per hectare.

     3. Transplanting method. No mulch plot, in the first to open a ditch on the ridge, according to a certain density requirements, set the seedlings, because the stevia leaves are small, planting seedlings do not bury the bottom leaves in the soil, let alone put the growth point buried under the soil. Generally covering soil to the root neck is appropriate, the soil compaction, and then poured enough root water. Can also be in the ditch after the rapid filter seedlings, after the water infiltration soil. The land covered with plastic film is planted with sharp bamboo sticks or cut small wooden columns and holes, and is strictly covered with wet soil to facilitate heat preservation. When planting seedlings to make the seedlings vertical ground, the planting depth should be 1 / 2 of the seedling height, no heart pressure, do not hurt the bottom leaves, no nest roots. Planting time should choose morning or evening or cloudy, avoid clear noon, can also choose to transplant in light rain.

    After transplanting to timely check the slow seedlings, such as found dead seedlings to immediately planted. Supplementary planting to choose strong seedlings in the afternoon transplanting, it is best in cloudy days or rain after easy to slow seedlings, and can improve the survival rate. When the soil is relatively dry, before moving some seedlings, some water can be poured in the rhizosphere of the prepared seedlings, so that the root soil does not fall off when moving the seedlings, and the survival rate of transplanting is high.

 Vi. Field management

      (1) Pick the heart. Remove the top growth point, the effect of stevia is to increase the number of branches and leaves, improve the yield, prevent lodging prevention, etc. Heart picking method: using artificial heart picking, field heart picking is in the colonization after survival, plant height within 15~30cm, poor growth can not pick the heart.

     (2) Fertilization Stevia colonization after all slow seedlings, and then topdressing. Should be mastered flexibly, according to soil fertility, weather conditions and seedling situation. Generally topdressing 2 times, the first time in the 15-20 days after planting, apply 200-250kg of urea per hectare, and spray 0.2% potassium dihydrogen phosphate. Before the second closure, the side fertilization was combined with medium tillage, applying 500kg urea, potassium * * or potassium sulfate 200kg per hectare, and the fertilization was 5~8cm from the root, to prevent root burning. Comdressing can be used eye-catching or ditch chase, with plastic bags, under the bag hot eyes will leak the fertilizer into the ditch, soil cover strict, to prevent volatilization. Leaf fertilizer can be sprayed 3 to 4 times from early July to mid-August, once every 10 days, and boron-molybdenum microfertilizer once in late August, to achieve the effect of increasing production.

     (3) Weeding and soil loosening Weeds and stevia glory, affect the yield, and during harvest, weeds mixed with stevia leaves, affect the quality. Generally, after half a month of transplanting, the weeds will grow in large numbers, so they need to be completely removed. As long as the clean, to the closure, weeds are not easy to grow. Make sure to pull out the weeds before you harvest. Each time the soil, topdressing should be combined with weeding, the soil should not be too close to the plant, too deep, will hurt the root system, affect the growth and development. Middle weeding 2-3 times a year. If chemical weeding is used, 10.8% efficient grass covering emulsion, 400-500 ml per hectare; 15% stable emulsion, 500-750 ml per hectare. Herbicides for preventing and controlling broad-leaved weeds are harmful to stevia and should be banned. 

 Seven, Stevia pest control

     Stevia is a wild plant with a short artificial cultivation history and strong disease resistance to insects. Compared with other cash crops, the detected diseases found include head blight, stem rot, leaf spot, black spot, white sericosis, acute anthrax and mosaic virus disease. Infestations are ground tiger, aphids, oblique night moth, and the disease is more serious than pests.

     Stevia pest control must implement the plant protection policy of "prevention first, comprehensive prevention", adopt agricultural prevention and control first, with chemical control as the auxiliary, advocate the alternate use of different types of low toxicity, low residue and efficient biological pesticides, strictly implement pesticide use guidelines and control indicators, to ensure the production of green stevia products.

(1) Main diseases of stevia

Cultivation of stevia should try to avoid heavy stubble, reduce the soil hidden bacteria in the field. Do a good job of cleaning ditches and drainage in the rainy season to reduce the field humidity. At the same time, more farm fertilizer to improve soil structure, increase potassium fertilizer, promote plant growth, and enhance disease resistance.

    drooping disease

    Symptoms: mostly occur in the seedling stage, bacteria from the stem base immersed, began to appear light yellow disease spots, after gradually expanded, the victim part of the brown water stain shape decay and death. The diseased strain was immediately removed and burned down.

    Prevention and control method: sprinkle lime or Yin and Yang ash (3:1 plant ash and lime) around the strain, or with 70% 800 times liquid, 50% more wet powder 800 times liquid, 50% sterilized wet powder 1000-1500 times liquid spray.

    nigrities artis 

     Symptoms: generally occur in the peak growth period of high temperature, high humidity season, first, the middle and lower leaves appear black and brown angular spots, and quickly expanded to the whole leaf, the late onset of deciduous leaves, the yield loss can reach more than 50%. Prevention method: at the beginning of the disease occurrence, 65% substitute zinc, 500-600 times liquid or 5% well gonomycin water agent, 500 times liquid can be used for prevention. If in the harvest period, should be clear or in cloudy weather, take between cutting, artificial picking leaves to dry, to minimize the loss of disease.

    stem rot 

    Symptoms: originated in mid-late May, repeated in the first and middle of June, scattered in the field. The main symptoms are: at the beginning of the disease, at the base of the stem (about 3 cm from the ground) or at the root neck appeared brown side hanging spots, after the expansion of the ring stem obvious hanging spots, the plant gradually wilting. The stem tissue generally does not lodging after lignification, but the phloem is destroyed, the roots are black decay, causing yellowing leaves, and the plant dies. Prevention method: ① remove the plant and disinfect with lime; ② spray 96% green heng 12500 times liquid or 20% methyl 800-1000 times liquid.

    acute anthrax 

    Symptoms: It originated in late May to the middle of June, with an irregular or massive distribution in the field. The main symptoms are: mainly occur in the young leaves, young branches or top branches, initially in the leaf tip or leaf edge of the water stain, after expanding into dark brown irregular disease spots, often multiple disease spots combined into large spots, disease spots on the dense black spots, around the yellow halo. Or in the young branch stem appeared light brown oval or nearly round small spots, after expanding into a dark brown spindle or long oval depression spots, and quickly spread in the upper stem, resulting in leaf death, plant shrinkage, the top stop growth.      Prevention and control method: ① with 10% world high (phenyl ether methocyclazole) 1000-2000 times liquid; ② 25% carbon TAL 500 x; ③ 80% anthrax 600 x; ④ 75% 500 x. Continuous prevention and treatment for 2-3 times.

    Huanghua virus disease

    Symptoms: prone to high temperature and high humidity in the middle to late May to June, the disease began to turn yellow from the parietal leaves, and gradually spread to the middle and lower parts, the leaves crisp and atrophy, stop growing. Prevention and control method: once found, timely spray virus K or dongwang poison elimination or holy hand poison zun (20% hydrochloric acid), the occurrence of this disease can only play a controlling role in medication, can not cure, the best way is to take drugs before the first prevention.

   southern blight

    Symptoms: more sporadic occurrence in the middle and late growth period. After suffering, dark brown to black water stain spots appeared on the base epidermis of the stem near the ground. After about a week, the disease spot appeared gray mildew, the disease tissue was trapped, and the whole seedling withered due to lack of water. Prevention and control method: found the strain, immediately remove, disinfect with lime around the strain, or with 70% methyl Topzin powder 800 times liquid spray.

     Stevia is main pests

     The prevention and control of stevia pest control should be strictly controlled. The unit area does not meet the prevention and control index, and the number of drugs to be used before the prevention and control index should be strictly controlled. Drug use should be strictly prohibited within 15 days before the harvest.

    aphid:Symptoms: aphids harm the new buds and young leaves, causing leaf curl, wrinkle, deformity, short plants, induce mosaic virus disease, seriously affect the yield of stevia, especially drought without rain weather, more serious harm. Methods: Use 10% imidacloprid wet powder 1000 times liquid or 5% sharp strength special suspension agent 800 times liquid control.

     cutworm :Symptoms: the ground tiger larvae cut off the stevia seedling root part, resulting in the lack of seedlings in the field, broken ridge, to spend more manpower, material resources to fill the seedlings, for many years of dry land should pay more attention to prevention and control. Prevention and control method: can use 50% xin sulfur phosphorus emulsion oil 1000 times liquid or use 20% quick kill butyemulsion 40ml with water 50 kg ground spray.

    Night moth pests:Symptoms: the insect wide food, large food, with larvae bite plant leaves, 1-2nd instar larvae bite the epidermis and mesophyll, only the epidermis and leaf veins, after the 4th instar, bite the leaves, only the main pulse, the larvae density, may eat the whole field into a light rod, so that no harvest. Prevention method: can choose 2.5% enemy kill 1000-1500 times liquid, 20% quick kill 1500 times liquid, 5% inhibition big bao 1000-2000 times liquid, 1.8% avermectin emulsion 1000-1500 times liquid, should be selected in the morning, evening of two agents mixed two continuous injection times, prevention period should be selected before 3 age.

Stevia harvest and processing

    (1) Harvest time

    The harvest date of stevia leaves in our city is around September 15, generally stevia in-3- -4℃ is not frozen, after light frost twice, with branches and leaves, otherwise the leaves are easy to black or mildew deterioration.

    (2) Air method

    The method of scaffolding and drying is generally adopted. Planting one mu (1000m2) of stevia build a 6O m2 arbor, 5~6 layers, roof can be used asbestos tile, linoleum paper or stalk instead, rain to cover a layer of plastic proof, if there is empty house better, but to ventilated light, accumulation is not too tight too tight, it is forbidden to bind to prevent mildew deterioration, pay attention to pull not car and car, home immediately on drying, cannot pile up piles, so as not to heat deterioration. It can also be dried in the field, cut down the yard on the ridge, scattered the opposition without bundle, with corn straw or straw curtain covered against rain and dew, shade after the leaves.

    (3) Dry leaf storage. Harvested dry leaves should be placed in the dry place in time to avoid moisture absorption and mildew. In case of long-term rainy weather should check whether the dry leaves absorb moisture, such as moisture absorption should be overturned in time.

    (4) Quality standards of dry leaves: most of them are green, without sediment, weeds, branches, buds and other foreign bodies, without mildew and pesticide pollution, and the moisture shall not exceed 11%.

     

    

    

     

    

---

Previous：

Next：Stevia specification standard