At present, it is the stage of early spring watermelon seedlings, due to unfavorable environmental conditions coupled with poor management, often lead to a variety of physiological diseases of watermelon seedlings. Some common physiological diseases and prevention methods are introduced as follows so that everyone can take timely measures to prevent it.
1. Stable seedlings. The seedlings showed less growth, slower leaf development, new leaf color, grayish-green leaf, thicker leaves, shrinkage, and stiff tissue; yellow cotyledon and true leaves, yellowish roots in roots, and even browning, with few new white roots. 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.
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 nursery bed has a heavy soil mass, high soil moisture content, poor root absorption capacity, continuous rain after planting, and severe seedling emergence. 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.
Control methods: 1 Select a loose, well-ventilated pastoral soil as a nutrient soil, and try not to use the soil-heavy river mud. 2 To improve the nursery environment, use geothermal lines or mulch to cover seedlings, raise the temperature, cultivate and grow normally, develop well roots, and moderate seedling age (30 to 35 days for self-rooted seedlings and 40 to 45 days for 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 the seedbed temperature, is not conducive to root growth. 5 When planting, the sorghum deep groove is used for cultivation, drainage is enhanced, and decomposed organic fertilizer or chemical fertilizer is appropriately added 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. When planting, care should be taken to protect the root system and prevent root damage.
2. Lengthy 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.
Causes: Water shortage in watermelon seedbeds, excessive temperature, and prolonged emergence of seedlings when soil and air humidity are high. 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, increase the temperature difference between day and night, and appropriately lower the temperature and humidity under conditions of insufficient light.
3. Thin and weak 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 and superphosphate 250 grams 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. 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.
Cause: The temperature is too low, coupled with excessive humidity, it is easy to cause roots.
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 °C ~ 30 °C, ground temperature to maintain above 16 °C, and do seedbed insulation to prevent cold wind blowing. Pay attention to ventilation, implement a small water pouring, to prevent the seedbed humidity is too large.
5. Blade 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. Capping. The growth points of watermelon seedlings are degraded, and new leaves cannot be normally drawn. There are only two cotyledons, some of which can form 1 to 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 the moisture management of seedbeds, timely ventilation, reduce humidity, and pay attention to insulation.
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