Why are the watermelon seedlings turning yellow?

In summer, watermelon is one of the most popular fruits. In recent years, the watermelon planting area in China has been very large, and the annual output has been very high, so the price of watermelon has become very cheap. Watermelon is a cold fruit. Eating it in summer can relieve heat and thirst, eliminate inner irritability, etc. However, those who grow watermelons often encounter the problem of watermelon seedlings turning yellow. What causes this?

Why are the watermelon seedlings turning yellow?

1. Dead seedlings. The seedlings grow slowly and their leaves unfold slowly. The new leaves are gray-green in color, thickened, wrinkled, and have stiff tissues. The cotyledons and true leaves turn yellow, the underground roots turn yellow or even brown, and there are few new white roots. Stiff seedlings are different from the symptoms caused by improper use of foliar fertilizers and pesticides, which include growth points that stop growing, smaller leaves, curled leaf edges, and thickening, shrinking and twisting of leaves. Once the watermelon seedlings become stiff, they will recover very slowly, which will delay the favorable growing season and seriously affect yield and benefits. Seedling stunting is the main physiological obstacle in the watermelon seedling stage. Causes: ① The temperature in the seedbed is low, especially the soil temperature is low, which cannot meet the basic temperature requirements of the watermelon root system. ② The soil of the nursery bed is heavy and has a high water content. It is difficult for roots to grow under the root zone conditions of high humidity and poor ventilation. The root absorption capacity is poor. If it rains continuously after planting, the occurrence of seedling stunting is particularly serious. ③Improper preparation of nutrient soil. Applying uncomposted or insufficiently mixed organic fertilizer to the seedbed or planting hole may cause root burn, or too much chemical fertilizer may be applied, or chemical fertilizer may be applied too close to the roots, resulting in a high concentration of soil solution and damaging the roots. ④Poor development of seedlings. The seedlings are too old when transplanted, the root system is too damaged during the transplanting process, or the land preparation and transplanting operations are rough, the roots are suspended in the air, and there is no close contact between the roots and the soil, which affects root development. ⑤Underground pests damage the roots. Prevention and control measures: ① Choose loose, well-ventilated garden soil or rice field soil as nutrient soil, and try not to use heavy river mud. ② Improve the seedling raising environment, use geothermal lines or mulch to cover the seedlings, increase the ground temperature, cultivate normal growth, good root development, and moderate seedling age (30-35 days for self-rooted seedlings and 40-45 days for grafted seedlings). ③ Apply well-rotted organic fertilizer to the seedbed, apply compound fertilizer lightly away from the roots, or spray foliar fertilizer to prevent root damage. ④ Water at the right time and in the right amount to avoid lowering the temperature of the seedbed and the ground temperature, which will be detrimental to root growth. ⑤ When planting, use high ridges and deep trenches to improve drainage, and apply appropriate amount of hole fertilizer (rotted organic fertilizer or chemical fertilizer) to promote root growth. ⑥ Pay attention to hardening the seedlings before transplanting. ⑦ Planting at the right time to prevent the plants from being affected by low temperatures after planting. Choose a sunny day at the end of the cold season and the beginning of the warm season for planting.

2. Leggy seedlings. The watermelon seedlings grow too vigorously and become too tall, which is manifested by elongated internodes, longer petioles and leaf bodies, light green leaves, thin leaves, and tender tissue. Causes: The watermelon seedling bed does not receive enough light, the temperature is too high, and the soil and air humidity are high. During the grafted watermelon seedling raising process, if the temperature, light, and air of the rootstock and scion are not properly controlled, leggy seedlings are likely to appear. Leggy seedlings have poor adaptability to low temperatures and are prone to frost damage. Prevention and control measures: Reasonably adjust light, temperature and humidity. The seedbed is managed in sections, with timely ventilation and dehumidification, increased light and avoidance of excessive temperatures. Lower the night temperature and increase the temperature difference between day and night. Under conditions of insufficient light, appropriately lower the temperature and humidity.

3. Thin and weak seedlings. The cotyledons of watermelon seedlings are small and light in color, the true leaves are small and wrinkled, and the stems are thin. Causes of occurrence: ① Poor seedling conditions and poor root system development. ②Lack of fertilizer. Prevention and control measures: ① Improve seedling conditions and use nutrient pot heating measures to grow seedlings. ②Mix appropriate amount of quick-acting fertilizer into the seedbed soil or nutrient soil. Add 250g of triple compound fertilizer and 250g of superphosphate per cubic meter of soil. ③ Apply foliar fertilizer in time and spray the leaves with 0.2%-0.3% potassium dihydrogen phosphate or 0.2% urea.