Characteristics of the 8424 watermelon variety and efficient, high-yield cultivation methods
I. Origin of the Name "8424" Watermelon
1984 was a memorable year in the history of watermelon cultivation in Nanhui, Pudong. That year, Professor Wu Mingzhu, a researcher at the Hami Melon Research Center of the Xinjiang Academy of Agricultural Sciences, in Xinjiang, known as the land of snow lotus and melons at the foot of the Tianshan Mountains, bred a superior variety coded No. 24. It was an early-maturing variety, hence the name "Zaijia 8424" watermelon.
China is the world's largest producer of watermelons, but watermelons did not originate in China. The watermelon's place of origin is Africa, where it was originally a wild plant of the Cucurbitaceae family that was later cultivated by humans into an edible watermelon. As early as four thousand years ago, the Egyptians were already growing watermelons. They gradually spread northward, first from the Mediterranean coast to Northern Europe, then southward into the Middle East, India and other places. In the 4th and 5th centuries, they were introduced into China from the Western Regions, which is why they are called "xigua" (western melon).
II. Variety Characteristics of the 8424 Watermelon
Zaijia 8424 is an early-maturing watermelon variety. It takes about 28 to 45 days from flowering to fruit ripening. It has moderate growth vigor and good fruit-setting ability. The fruit is round, with a green rind covered in narrow dark-green stripes, giving it an attractive appearance. The flesh is red, crisp in texture and excellent in taste, with a center sugar content of 11-12 degrees. The average single fruit weighs 3-4 kg, and it is tolerant of storage and transport. With reasonable close planting, the number of seedlings set per mu is 600-700 plants. It is suitable for two-vine or three-vine training, prefers fertile soil and moderate irrigation. It is suitable for early-maturing plastic film mulching and open-field cultivation. If it rains during the flowering period, artificial supplementary pollination should be carried out, and harvesting at nine-tenths ripe is preferable. Do not water in the 3 days before harvesting to prevent fruit cracking and reduced sugar content, and please refer to local cultivation practices. It is suitable for early-maturing cultivation or long-season cultivation under protected conditions. Sow at the end of March and beginning of April, with a row spacing of 2.4 × 0.8 m, planting about 250-300 plants per mu, with three-vine training, and take care to harvest at the right time.
III. Common Types and Characteristics of 8424 Watermelon
Black Beauty: oval shape, small fruit, pure black rind.
Seedless watermelon: round shape, striped rind.
Striped-rind watermelon: oval shape, large fruit, rind with alternating light green and dark green.
Te Xiaofeng: round shape, striped rind, yellow flesh.
IV. Efficient, High-Yield Cultivation Techniques for 8424 Watermelon
1. Site Selection
For watermelon fields, avoid continuous cropping on the same land, and do not rotate with cucurbit crops such as cucumber, melon and zucchini, in order to prevent Fusarium wilt. Generally, dryland rotation is 7-8 years or more, paddy-upland rotation is 5-6 years, and paddy field rotation is 3-4 years. It is best to choose a watermelon field with high, dry terrain, facing the sun and sheltered from the wind, with deep soil, loose texture, good drainage and preferably irrigation available. In arranging the preceding crop, adapt to local conditions and raise the multiple cropping index. In the suburban counties of our city, corn, sweet potato, millet, soybean and others can all serve as preceding crops. Peanut fields should be used with caution due to rodent damage. When using intercropping and relay intercropping, match crops reasonably; for example, spinach, small radish, rapeseed and potato are all suitable. Intercropping in cotton fields and wheat fields, as well as summer sowing after wheat stubble, are also being developed; summer sowing in Wuqing County reached more than a thousand mu. In villages with many people and little land, wide-row sparse planting with multiple crops for multiple harvests can be adopted to make full use of land, light and heat, and improve economic returns.
2. Land Preparation, Fertilization and Bed Making
(1) Land preparation
For spring-sown watermelon fields, deep plowing by machine should be done to 20-30 cm before winter, plowing only without harrowing, so the clods freeze and dry out, which helps weather the soil, freeze pests to death, accumulate snow and store moisture. In early spring, as appropriate, harrow finely and level while taking advantage of soil moisture. Then, according to the cultivation method planned, dig watermelon trenches (also called high-yield trenches). Digging watermelon trenches can thicken the active soil layer, promote root extension, and make it convenient to apply base fertilizer in a concentrated way. The trenches are mostly oriented east-west and arranged north-south. At a row spacing of 1.6-1.8 m, dig trenches 50-60 cm wide and 40 cm deep, placing the 20 cm of topsoil on the south side of the trench and the subsoil on the north side.
(2) Applying base fertilizer
Watermelon has luxuriant stems and leaves, a short growth period, high yield and a large fertilizer requirement. Base fertilizer must be applied adequately to provide basic nutrients for the entire growth period of the watermelon. This is especially true for film-mulched cultivation, where topdressing is inconvenient; if the base fertilizer is insufficient, it easily causes premature aging of the plants and affects fruit development. The base fertilizer is mainly long-acting organic fertilizer, with an appropriate amount of chemical fertilizer added.
1. The amount of fertilizer applied depends on soil fertility. For medium- and lower-grade land, 3000-5000 kg of high-quality barnyard manure per mu, or 150-200 kg of cake fertilizer, may be applied. For land with high fertility, 2000-2500 kg of barnyard manure or 100 kg of cake fertilizer may be applied. The soils of the suburban counties of our city are generally deficient in phosphorus, and sandy soils are deficient in potassium, so the proportion of phosphorus and potassium fertilizer should be increased; for example, 50-70 kg of superphosphate and 10-15 kg of potassium sulfate per mu may be added.
2. Method of applying base fertilizer. When the amount of coarse manure is large, most of it can be broadcast before winter plowing, leaving a small portion of high-quality coarse manure mixed with all the cake fertilizer to ferment and decompose, then applied in a concentrated way in the watermelon trenches. Use part of the topsoil from the south side of the trench to mix with the fertilizer and apply it into the trench, then return the remaining topsoil and level it.
3. Seed Selection and Seed Treatment
(1) Seed selection. Choosing excellent varieties is the prerequisite for high yield and good quality. At present, the excellent varieties suitable for production and application in our city include:
Early-maturing and early-to-mid-maturing types: Zhengza No. 5 and No. 7, Shuangxing No. 11, Jingxin No. 1, etc.;
Mid-maturing and mid-to-late-maturing types: Zhongyu No. 6, Fengshou No. 3, Jinhuabao (Pz), and among the Guanlong series, Jinzhong Guanlong, Xinyou No. 2;
Late-maturing types: Xin Hongbao and the Xin Hongbao series, including Jubao No. 1, Huaxia Xin Hongbao, etc.
They may be purchased according to the variety descriptions from the sales unit and local cultivation conditions. The purchased varieties must also be strictly rogued of off-types and inferior seeds, and shriveled, mixed and moldy seeds removed, so as to help the sprouts emerge uniformly and strongly.
(2) Disinfection. In the past, melon growers often used hot-water seed scalding, but because the temperature and time are hard to control, it is not advisable to use. Suitable methods include:
1. Warm-water seed soaking. Use warm water at 55°C (two parts boiling water to one part cold water), with a water volume 5-6 times the seed volume, soak the seeds for 30 minutes, stirring while soaking, and let cool naturally. Do not use an aluminum basin, so that the water temperature does not drop too quickly and fail to achieve the disinfection purpose. After 30 minutes, change to cool water at 20°C and continue soaking.
2. Chemical disinfection. For warm-water-treated seeds, after soaking in cold water for 2 hours, or for dry seeds after soaking in cold water for 4 hours, carry out chemical disinfection. (1) Soak in 100-fold formalin solution for 10 minutes, then rinse the solution off thoroughly with repeated washes. This can kill Fusarium wilt and anthracnose pathogens on the seed coat. (2) Soak in 10% sodium phosphate solution for 20 minutes; this can kill viruses. (3) Soak in 2%-4% bleaching powder solution for 30 minutes; this can kill pathogens.
(3) Seed soaking and germination. Soak the disinfected seeds in water at 20°C for 6-12 hours (depending on seed coat thickness), then remove them, rub off the mucilage with a towel, wrap them in a damp cloth, and place them at 25-30°C to germinate. Generally after 1-2 days the seeds "show white" (radicles emerge). During this period, check temperature and humidity frequently. When rinsing with water, the water temperature should be 30°C; heat sources for germination can be an electric heating pad, soil warming box or heated brick bed. Using body warmth by carrying them close to the body is safer and more reliable. The standard is that the "white" should not exceed 3 mm; if too long, it affects sowing. For some seeds that first "show white" to 2-3 mm, pick them out in time and place them at room temperature of 15°C, which can inhibit elongation and make them sturdy. Once 80%-90% of the seeds have sprouted, they can be sown.
4. Sowing
(1) Sowing time. The standard for open-field sowing time is when the 10 cm soil temperature is stable above 15°C and the final frost has passed at emergence; this is the safe sowing period. In the suburban counties of our city, this is generally April 15-20. If using single-film flat covering, sowing can be delayed by 2-3 days. If using plastic film with trench-style covering, with sprouts and seedlings up to 2 true leaves growing under the film, the sowing time can be half a month earlier than in the open field. If using plastic film plus small arched shed double covering, sowing should be in mid- to late March. For cold-frame seedling raising, sowing can be in early March, with transplanting and setting out in early April, plus small arched shed covering. Wheat intercropping should be May 20-25. Summer sowing after wheat stubble should be July 15-30 so that the early stage avoids the rainy season.
(2) Planting density. Watermelon planting density varies with variety, cultivation method, management level, soil fertility and other conditions. Sparse planting may be only 300-400 plants per mu, while dense planting may reach 2000 plants. Determining density can be considered from the following aspects:
1. According to variety: weak-growing early-maturing varieties, 1000 plants per mu. Strong-growing mid-maturing varieties, about 800 plants per mu. Large-fruited late-maturing varieties may be planted at 500-600 plants per mu.
2. According to cultivation method: open-field cultivation should be relatively sparse. Protected cultivation should be relatively dense. The aim is to make full use of land, space and growing time, and improve economic returns.
3. According to soil fertility and management level: poor land should be dense, fertile land should be sparse. If the management level is high and labor is sufficient, planting may be appropriately dense; otherwise, it should be appropriately sparse.
4. At present, foreign countries adopt low density to give play to the advantages of individual plants, produce large fruits and set more fruits, thereby improving yield and quality. For example, Japan plants only 110 plants per mu, and at most only 300; greenhouse cultivation uses 370-400 plants per mu; open-field cultivation in the United States uses 144 plants per mu. These situations are for reference only.
(3) Sowing method. Trench-hole dibbling is generally used, requiring fine land preparation and sufficient bottom moisture. For open-field sowing and through-film sowing, it is advisable to open shallow trenches and cover with deep soil. That is, the trench hole is 2-3 cm deep, 3-4 cm wide and 12 cm long. If moisture is insufficient, water must be spotted in. Put 4 seeds per hole, with a seed spacing of 3 cm. Place the seeds flat on the bottom of the trench, with the sprout tip pointing downward. Do not place the seeds upright, to avoid emerging with the shell. After sowing, first cover level with wet soil and press lightly. Then cover with a small mound of soil (length, width and thickness of 13 × 5 × 5 cm), and pat the surface firm. After 4-6 days, when the young sprout bends its neck, remove the soil mound, and the seedlings can emerge. If sowing first and then covering with film, do not cover with a soil mound, and the sowing depth should not exceed 2 cm. Germinated seeds should be sown in grades according to sprout length, so that emergence is neat and uniform.
5. Field Management
(1) Seedling-stage management. With the focus on preserving full stands and cultivating strong seedlings, the management priorities differ according to cultivation method.
1. Spring-sown open-field cultivation. Focus on preserving soil moisture and raising soil temperature. Before the growing point breaks, carry out fine intertillage and loosening of the soil to promote root development. When the first true leaf unfolds, thin the seedlings and keep the strong ones. When the second true leaf unfolds (forming a cross), apply a seedling-promoting fertilizer in the trench. Apply 2-3 g each of urea and diammonium per plant, taking care to apply extra to weak seedlings, 8-10 cm away from the seedlings, and not too concentrated, to avoid fertilizer burning the seedlings. Water lightly as appropriate. At 4-6 true leaves, observe seedling condition, skillfully apply a vine-establishing fertilizer and water appropriately. In the field generally carry out deep intertillage and weeding once or twice. Do not earth up around the plants too early, and do not injure roots when loosening the soil by intertillage.
2. Ordinary mulching cultivation. Focus on releasing seedlings from the film in time, thinning and setting seedlings in time, and controlling underground pests early. Pay attention to weather forecasts; when releasing seedlings, prevent cold damage; generally no topdressing or watering during the seedling stage.
3. Improved-type, cold-frame-type and small arched shed mulching cultivation. Focus on ventilation hardening, pest control and weeding; generally do not water during the seedling stage, to prevent excessive stem growth. Ventilation hardening can begin after emergence when the air temperature inside the film exceeds 35°C. For improved-type and cold-frame-type, it is advisable to open vents above the seedlings, which later serve as the passages for releasing seedlings from the film. Make the openings go from small to large, gradually strengthening hardening. If sudden cooling occurs, add straw mat covering. When the outside air temperature is stable above 20°C or the seedling leaf tips touch the film, the seedlings can be released from the film. But if low temperature occurs, release should be postponed, and soil clods should be used under the film to prop it up to prevent scorching the seedlings. For small arched shed double covering, keep the air temperature inside the shed at 22-25°C. On sunny mornings when it exceeds 25°C (often reaching above 35°C at noon), ventilation can begin. Open a slit on the leeward side for ventilation and gradually enlarge it; after sufficient hardening, when the outside daily average temperature is above 20°C, the shed can be opened.
(2) Topdressing
1. Topdressing amount. It should be determined according to the absorption pattern of watermelon. Watermelon's fertilizer absorption can be roughly divided into three stages:
Seedling stage (before the plant forms a cluster): a slow absorption stage, absorbing 0.5% of the total of the three major elements over the whole life;
Vine-extending stage: an accelerated absorption stage, accounting for 14.5%-30% of the total;
Fruiting stage: a high-speed absorption stage, accounting for 70%-85% of the total.
During the growth process of watermelon, nitrogen is absorbed relatively early, increases rapidly during the vine-extending stage, and peaks during the fruit-swelling stage. Phosphorus is absorbed relatively more at the seedling stage, and its absorption peak appears earlier, gradually decreasing during the fruit-swelling stage. Potassium is absorbed very little at the seedling stage, increases slowly from vine extension to fruit setting, and rises sharply during the fruit-swelling stage. Therefore, the amount of topdressing should follow this principle: apply seedling-promoting fertilizer lightly, apply vine-extending fertilizer skillfully, apply fruit-swelling fertilizer heavily, and quickly apply a rejuvenating fertilizer after harvesting the first crop of melons.
2. Types of topdressing. Mostly quick-acting chemical fertilizers, or fermented and decomposed cake fertilizer and dried manure. Some people believe that a large amount of chemical fertilizer will make watermelon quality poor and not sweet. Experiments have proved otherwise: as long as the three major elements are properly matched, it can completely replace organic fertilizer and further improve yield and quality. Only applying nitrogen fertilizer alone or using too much nitrogen fertilizer will lower quality.
3. Timing and methods of topdressing
(1) Seedling-promoting fertilizer: apply according to seedling condition. Generally applied when the second true leaf unfolds. It must be applied in open-field cultivation; under plastic film mulching it is generally not applied, or applied only to weak seedlings. Use 4-5 g of urea per plant, or 4-5 g of diammonium phosphate, or 2-3 g of each mixed together, applied in a trench 8-10 cm from the seedlings, then cover the trench level.
(2) Vine-extending fertilizer: in open-field cultivation it should be applied when the plant forms a cluster (4-6 leaves); under film mulching it should be applied when the vine tip begins to extend. Use fully decomposed cake fertilizer, dried manure, etc., with a small amount of chemical fertilizer added. Nitrogen, phosphorus and potassium must be matched. Generally, 25-50 kg of cake fertilizer per mu plus 10-15 kg of superphosphate and 5-7 kg of urea is called vine-promoting fertilizer. Method: on one side of the extending vine, open a trench 20 cm from the seedlings, 10 cm deep and 10 cm wide, apply the fertilizer, and cover it well with soil.
(3) Fruit-swelling fertilizer: generally, when the second and third female flowers have set fruit and the young fruit is the size of an egg, apply quick-acting chemical fertilizer heavily. With phosphorus and potassium as the main components and nitrogen fertilizer in combination, generally use 15-20 kg of potassium nitrate phosphate fertilizer per mu, plus 10 kg of urea and 10 kg of potassium sulfate. Or 15 kg of diammonium phosphate, plus 10 kg of potassium sulfate, 5 kg of urea and 5 kg of calcium magnesium phosphate fertilizer. Broadcast on the opposite side of the melon vines; the soil surface may be scratched, but do not open trenches to avoid injuring roots. During the powdery bloom stage, generally no more topdressing (especially nitrogen fertilizer), to avoid causing "belted fruit" or "white-belted fruit" (yellow or white appearing in the center of the flesh, from the flower end to the stem end). However, when vines and leaves show aging and yellowing, a 0.3% solution made by mixing monopotassium phosphate and urea at 1:1 can be used for foliar spraying.
(3) Watering. Watering at the right time according to the water requirements of watermelon at different growth stages is the guarantee of a high yield. Water demand is relatively low at the seedling stage, so generally no watering is done, to avoid lowering soil temperature. The main approach is to conserve water and harden the seedlings, promoting deep rooting. In open-field cultivation, supplementary watering should be done at the right time (that is, to supplement insufficient soil moisture) to prevent drought-stunted seedlings. Method: together with applying the seedling-promoting fertilizer, water lightly in the fertilizer trench, and after the water seeps down, cover with soil (called hidden watering). It is best done on a sunny morning, which will not cause the soil temperature to drop. When the plant forms a cluster, together with applying the vine-extending fertilizer, water hiddenly to promote vine growth; water slowly and lightly to moisten the soil, deciding according to weather, soil and seedlings. Watering is essential during the fruit-swelling stage; this is the key water for ensuring a high yield. After broadcasting the fruit-swelling fertilizer, water slowly until thoroughly soaked. Water once every 5-7 days, using surface irrigation on the beds to keep the ground moist. If under mulching cultivation, surface irrigation can be carried out in the trench between the two rows where the vines climb on the back side. Never use flood irrigation; water until thoroughly soaked.
(4) Pruning and vine pressing
1. Pruning. The axillary buds of watermelon have strong sprouting ability and easily form many branches, consuming much nutrition; if fertility is insufficient, this will inevitably cause small fruit and poor quality. Therefore, appropriate pruning is needed to form a reasonable vegetative body, facilitate ventilation and light penetration, improve photosynthetic efficiency, and promote fruit setting and fruit growth. (1) Pruning methods: they vary with variety, fertility and density. Generally applicable methods include single-vine, double-vine and three-vine pruning. Single-vine means keeping only the main vine; it is suitable for high-density seed propagation and greenhouse or glasshouse cultivation. Double-vine pruning is selecting one strong side vine at the base of the main vine and letting it climb parallel to or opposite the main vine. It is suitable for early-maturing varieties at medium density. Three-vine pruning is selecting and keeping two strong side vines at the base to advance together with the main vine, commonly called "one horse, three arrows." It is suitable for low density, high fertilizer and water, and large-fruited varieties with a relatively developed vegetative body. At present, some only carry out fertilizer and water management without pruning, letting them grow freely and saving labor. For varieties with weak branching ability, this can also achieve a fairly good harvest, but it consumes much fertilizer and soil fertility, the fruits are small, quality is poor, and output value is low, so it is not advisable. Especially for varieties with strong branching ability, not pruning will reduce yield by more than 30%.
(2) Timing of pruning: open-field cultivation should prune early, beginning when the vine tip starts to extend. Mulching cultivation should prune later, when the main vine reaches 40-50 cm and the basal side branches are 15 cm long; too early is not good for root growth. Too late consumes more nutrients. After fruit setting, except for the side branches 2-3 nodes before and after the fruit, which should be removed early, generally no further pruning is done.
2. Vine pressing. First press the base (also called earthing up or stabilizing the seedling). After the plant forms a cluster, it is top-heavy and easily has its hypocotyl broken by wind in open-field cultivation. The base of the seedling must be stabilized. First gently scrape away the dry soil at the base, press the seedling down in the direction of vine extension with wet soil, and build a small soil mound. In small arched sheds, generally no mound is built; when the main vine is 60-80 cm long, coil the vine to prevent the vine tip from touching the film and being scorched.
Functions of vine pressing:
First, it fixes the vines and prevents wind from rolling them and causing damage to vines and young fruit.
Second, it distributes the main and side vines evenly between rows, improving photosynthetic efficiency.
Third, it can regulate the relationship between vegetative growth and reproductive growth, enabling vines and leaves to accumulate more nutrients and become thick and plump, which is beneficial for fruit setting and fruit growth.
Fourth, vine pressing can promote adventitious roots at vine nodes and expand the absorption area. Vine pressing methods are divided into open pressing and hidden pressing. Open pressing is pressing soil clods on the internodes of the vine. First scrape the ground surface under the vine level, then use a melon spade to cut out a firm wet soil clod and press the vine tightly. Hidden pressing is burying a section of the melon vine in the soil. Use a melon spade to first scrape the ground level, insert it into the soil 6-8 cm deep, swing the melon spade to press out a groove, or make a small trench 3-4 cm wide and 8-10 cm long, place the vine into the groove, and gently press and bury it with soil, so that the vine and leaf stalks are not injured and the leaves lie flat without touching the ground. Open pressing is suitable for areas with heavy, sticky, moist soil and a high groundwater table. Hidden pressing is suitable for sandy soil, drought-prone, low-rainfall areas with low groundwater. Vine pressing should be done in the afternoon; in the morning the vines are brittle and easily broken. The severity of vine pressing can regulate the growth of vines and leaves. For vigorous growth, use heavy pressing, that is, press close to the vine tip, leaving only a small part at the top, which can control vine-tip growth and promote thick, plump vines and leaves in the middle and lower parts, benefiting fruit setting. For weak growth, press lightly to promote faster vine and leaf growth. For overly vigorous plants, use reverse pressing, that is, pressing the vine back, then returning it, or even topping the main vine and pinching out the growing point, using a side vine to replace the main vine. Generally, vine pressing is done three times, called three cuts, with each cut about 50 cm apart. The first cut should be firm, the second cut severe, and the third cut should press steadily when keeping the fruit; once the fruit is set, no further pressing is done.
(5) Fruit-setting management
1. Fruit-setting node position. The ideal fruit-setting position is the second and third female flowers on the main vine. The first female flower is mostly poorly developed and forms a small fruit, deformed, with thick rind and prone to hollow heart, because the temperature is relatively low at flowering and fruit setting, the vegetative body is small, the leaves produce less nutrition, and the fruit grows slowly; it should be removed early. To ensure fruit setting of the second and third female flowers, carry out artificial pollination. Pollination time: on sunny days 7-10 o'clock, on cloudy days 8-11 o'clock, but the fruit-setting rate is highest when pollinated within 2 hours after flowering; after 10 o'clock the stigma secretes mucus, affecting pollination and seed set. Rainfall is the greatest obstacle to pollination and fertilization; female flowers that cannot be pollinated and fertilized will certainly drop. If it rains 3 hours after pollination, the pollen tubes have already entered the stigma, so generally there is little effect on fruit setting. Pay attention to weather forecasts, and prepare small paper caps to cover pollinated female flowers against rain, removing them after two days.
2. Number of fruits retained. Generally one fruit is retained per plant; for robust plants, when the main-vine fruit is from the end of the powdery bloom stage to fixed size, select and retain one fruit on a side vine. With three-vine pruning, if the main vine does not set fruit, the two side vines may each retain one, called "two dragons playing with a pearl." At the same time, top the main vine and remove the branches. For sister fruits (one on each of two consecutive nodes) and twin fruits (two born at one node), remove the weak and keep the strong, to reduce nutrient consumption. 3. Protecting the fruit and making a fruit platform: use moist soil to build a sloped soil platform, place the young fruit smoothly on the platform to prevent soaking by rainwater. Take care to shade the fruit from strong sun, and gradually turn the fruit along the direction of the stripes to prevent rotting from overcast and rainy weather and to make the rind color evenly.
6. Pest and Disease Control
Damping-off, Fusarium wilt and anthracnose are the three main diseases of watermelon. To control damping-off at the seedling stage, ensure good ventilation in the seedbed and control watering. Control methods for Fusarium wilt and anthracnose: avoid continuous cropping, generally with an interval of 4-5 years; do a good job of clearing ditches and draining water; promptly pull out diseased plants when found. Chemical control: spraying with 75% chlorothalonil wettable powder, or 70% dexon, or 20% Shibaoling, or Bordeaux mixture all give very good control effects. The main watermelon insect pests include: yellow squash beetle, cutworm, aphids and red spider mites at the seedling stage. Chemical control methods are: use dichlorvos, dimethoate, trichlorfon and carbofuran for control respectively; the effects are all fairly good.
7. Ripening and Harvesting
(1) Identifying ripe watermelon. The signs of a ripe watermelon are that the seeds and flesh show the color specific to the variety and the seed shell hardens. Fruit maturity is the main aspect in measuring the commercial quality of watermelon. Poorly matured melons have a thick rind, pale color and low sweetness. Over-mature melons have disintegrated flesh cells, soft tissues, and phenomena such as inverted flesh, spongy heart and hollow heart. Identification methods include calculating, looking, listening and testing: Calculating: from flowering to maturity, early-maturing varieties need 28-30 days; mid-to-late-maturing varieties need 31-35 days; late-maturing varieties need 36-40 days. Mark in batches at flowering or during artificial pollination, so as to harvest in stages. For the same variety, if the temperature is high and light is sufficient during fruit growth, it ripens early; under cloudy, rainy and low-temperature conditions it ripens late. But the accumulated temperature value for physiological maturity is the same. Early-maturing is 700-800°C, mid-maturing about 900°C, and late-maturing about 1000°C.
Looking: A ripe melon shows an aged rind with luster (oily skin), and the powdery bloom largely disappears. The shaded side turns yellow. Most of the pattern on the rind extends from the stem end to the flower end, called the pattern reaching even; the top of the melon is sunken, and the bristles on the stalk are sparse.
Listening: Tap with the hand and listen to the sound; a ripe melon gives a muffled "peng peng" sound, an unripe melon gives a clear "deng'er deng'er" sound, an over-mature one gives a low "du du" sound, and a hollow or bad melon gives a "bu bu" sound. However, thick-rind, mealy-fleshed varieties may have a low, muffled sound while the melon is not yet ripe. Crisp-fleshed, thin-rind varieties may have a clear sound while the melon is already ripe; the fluctuation test should be used. Testing: Hold the melon in the left hand and tap gently with the right hand; if the left hand feels an obvious vibration, it is a ripe melon; little or no vibration means not very ripe or unripe. The reason is that in a ripe melon the flesh cell cavities enlarge, the middle lamellae of the cells dissociate, the gaps increase and are filled with gas, so the vibration wave is transmitted quickly.
(2) Harvesting. The appropriate harvest maturity should be considered from aspects such as variety, marketing destination and fresh-keeping period. For thin-rind, easily cracked varieties such as Jingxin No. 1, for local supply harvest melons at 9-tenths ripe, and for more distant supply harvest melons at 8-tenths ripe. For varieties with strict maturity requirements such as the Xin Hongbao series and Guanlong series, for long-distance transport and sale harvest melons at nine-tenths ripe, and for local supply harvest melons at 10-tenths ripe. For one week of fresh-keeping, harvest melons at 8-9 tenths ripe. Points to note when harvesting:
First, cut with a knife and leave the melon stalk, which is good for fresh-keeping and for judging freshness.
Second, harvest on sunny early mornings; do not harvest on rainy days, and delay harvesting after rain. After harvesting, do not expose to strong sun or rain.
Third, handle gently during harvesting and transport.