1, stiff seedlings. Seedling growth is small, leaf development is slow, new leaf color is grayish green, leaf blade thickens, shrinks, and tissue is stiff; cotyledons and true leaves turn yellow, underground roots yellow, and even brown, fresh white roots are less. The stiff seedlings are different from the growth points produced by improper use of foliar fertilizers and pesticides to stop growing, the leaf shape becomes smaller, the leaf margins rewind, the leaves become thicker, and the symptoms of shrinkage and twisting are greater. Once the seedlings of the watermelon seedlings have been sterilized, the recovery will be very slow, which will delay the favorable growth season and seriously affect the yield and benefits. Stiff seedlings are the main physiological obstacles for watermelon seedlings. Causes: 1 The temperature of seedbed is low, especially the soil temperature is low, which can not meet the basic temperature requirement of watermelon root system. 2 The seedling bed has a heavy soil mass and a high soil moisture content. It is difficult to root in humid and poorly ventilated root zone conditions, and the roots have poor absorption capacity. Continuous raining after planting and severe seedlings are particularly serious. 3 Nutrition soil is not properly prepared. Application of seedlings or planting holes without organic decomposition or organic fertilizer do not cause excessive burning of roots or application of chemical fertilizers, or chemical fertilizers applied to the roots closer to the soil solution concentration and damage the root. 4 poor seedling development. When planting, the seedling age is too long. In the process of planting, there is too much root damage, or the soil preparation and planting operation are rough. The roots are overhead, the roots are not in close contact with the soil, and the hair roots are affected. 5 Underground pests damage the roots. Prevention measures: 1 Select a loose, well-ventilated pastoral soil or paddy field soil as a nutrient soil, do not try to use the soil muddy heavy river mud. 2 To improve the nursery environment, use geothermal lines or mulch to cover seedlings, raise the ground temperature, cultivate and grow normally, develop well roots, and have moderate seedling age (40-45 days for self-rooted 30-35 grafted seedlings). 3 Apply rotten organic fertilizer to the seedbed, lightly apply compound fertilizer away from the root, or spray foliar fertilizer to prevent root damage. 4 timely watering, so as not to reduce seedbed temperature and ground temperature, adverse root growth. 5 When planting, the sorghum deep groove should be used to strengthen the drainage, and the hole fertilizer (decay organic fertilizer or chemical fertilizer) should be added appropriately to promote root growth. 6 pay attention to hardening seedlings before transplanting. 7 timely colonization, to prevent the impact of low temperature after planting, select the cold tail warm sunny day colonization.
2, long seedlings. Watermelon seedlings grew too vigorously and appeared leggy, showing internode elongation, petiole and leaf body lengthening, light green leaves, thin leafy leaves, and tender tissue. Reasons for the occurrence: lack of light in the watermelon seedbed, high temperature, high soil and air humidity, grafted watermelon breeding process, rootstock, scion in the temperature, light, gas control is not the case, prone to seedlings seedlings. The leggy seedlings have poor adaptability to low temperature and are prone to frost damage. Prevention methods: Reasonable adjustment of light, temperature and humidity. The seedbed is divided into sections for timely ventilation, dehumidification, increased light, and avoidance of excessive temperatures. Lower the night temperature and increase the temperature difference between day and night. Under the condition of insufficient light, lower the temperature and humidity appropriately.
3, thin seedlings. The seedlings of watermelon seedlings are small, light in color, small in true leaves, shrunken, and thin in stems. Causes: 1 Poor nursery conditions, poor root development. 2 lack of fat. Prevention measures: 1 Improve the conditions of nursery, use nutrition and temperature measures to raise seedlings. 2 Mix suitable amount of quick-acting fertilizer on seedbed soil or nutrient soil, and add ternary compound fertilizer 250 g and superphosphate 250 g per cubic meter of soil. 3 Add foliar fertilizer in time and spray foliar with 0.2%-0.3% potassium dihydrogen phosphate or 0.2% urea.
4, roots. Occur mainly in the nursery, live watermelon seedling roots or stems, watermelon seedlings are a common physiological disease. When roots occur, the roots do not grow new roots or adventitious roots. The roots turn brown and rot. The cotyledons and new leaves become thin, yellowish-brown or milky yellow, the leaf margins scorch, and the shoots wilting. When the scorch is severe, the dry film becomes dry and lacking in symptoms. The diseased seedlings are easy to pull up, there is no root hair, and the main roots and fibrous roots turn brown and rot. Prevention measures: 1 Take quick seedlings, such as the use of geothermal lines, nutrition and other facilities nursery. 2 seedbed should be selected in the terrain Gaozao, leeward, sunny, drainage convenient place, seedbed bed should be fully before the sun, Shizu base fertilizer. 3 Treatment of bed soil or nutrient soil with medicaments. 4 Seeds were soaked with warm water at 55°C for 15 minutes before sowing and germination after soaking. 5 to strengthen the seedbed management, seedbed temperature should be controlled at 20-30 °C, ground temperature maintained above 16 °C, and seedbed insulation to prevent cold wind. Pay attention to ventilation, implement a small water pouring, to prevent the seedbed humidity is too large.
5, leaves whitening. When the first true leaf appeared, the edges of cotyledons and young leaves became chlorogenic and white, resulting in stagnant seedling growth. The light can restore growth, and the cotyledons and true leaves are dry and only the growth points are retained, resulting in long seedlings or even stiff seedlings. In severe cases, cotyledons, true leaves, and growing points are all frozen to death. Causes: Frozen seedlings, improper ventilation during seedling period, and drastically reduced bed temperature. Prevention measures: timely sowing, improve the insulation measures of the seedbed to ensure that the bed temperature is above 20°C during the day and not lower than 15°C during the night. In the morning of emergence, there is no premature ventilation, and the amount of ventilation should be gradually increased to avoid sudden changes in seedbed temperature and injury to the seedlings.
6, capped. The growth point of watermelon seedlings is degraded, and new leaves cannot be normally ascended. There are only two cotyledons, some of which can form 1-2 true leaves but the leaves are atrophic and there are no growing points. Causes: 1 Chen seeds have low vitality. 2 Low temperature, seedling growth point is attached to water droplets. Control measures: 1 Use seeds with strong germination potential. 2 Strengthen seed bed temperature management, timely ventilation and reduce temperature.
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