Common Diseases and Prevention Methods of Spring Lettuce

As the spring lettuce growing season enters its critical phase, farmers are facing significant challenges in disease management. This period is crucial for both production and crop health, as it's also when many common diseases tend to occur. Recently, technicians from the Dingzhou Vegetable Station in Baoding visited a lettuce farm in Ta Xuan Village and identified several key issues. Common problems included downy mildew, viral infections, and stem cracking. To help local farmers better understand and manage these issues, I'll share detailed information on the symptoms and control methods of these prevalent diseases. First, **stem collapse** is a major concern. It typically occurs during the later stages of lettuce growth when the inner stem splits longitudinally. The cracks can be deep, reaching the center of the stem, and the affected areas often turn yellow-brown and become soft. This condition is usually caused by an uneven supply of water and nutrients, or by extreme fluctuations in soil moisture—too dry or too wet. When the stems are nearly mature, the outer skin becomes lignified. If a large amount of water is applied at this point, the skin cannot expand, leading to cracking. To prevent stem collapse, it's essential to maintain proper irrigation and fertilization. Keep the field consistently moist, watering every 7–10 days depending on conditions. Increase the use of phosphorus and potassium fertilizers to strengthen the plant structure. Next, **downy mildew** is one of the most widespread diseases affecting lettuce. It primarily affects the leaves, causing them to turn yellow early in the infection stage. In adult plants, the disease starts from the lower leaves and spreads upward. Initially, small, yellowish, irregularly shaped spots appear on the leaves. As the disease progresses, a white moldy layer develops on the underside, which may spread across the leaf surface. In the late stages, the lesions turn brown and merge, causing the leaves to wither. In severe cases, the disease can also infect the stems, turning them dark and weakening the plant. For control, apply a 72% DuBang KeLu solution diluted at 600–800 times or 58% metalaxyl-manganese zinc at 500 times. Spray every 7–10 days, alternating between different products to prevent resistance. Third, **viral disease** can affect lettuce at any growth stage, causing symptoms such as mosaics, leaf deformities, yellowing, stunting, and necrotic spots. Infected plants are generally smaller, with reduced yield and quality. Leaves show mottled patterns, with bright veins and irregular spots. Some leaves may curl or shrink, and the margins may appear damaged. In advanced stages, brown spots or necrosis can appear along the veins. Prevention begins before sowing. Soak seeds in warm water or trisodium phosphate to reduce virus transmission. Additionally, using plant regulators like Virus A, Green Wind 95, or Alizarin can help improve plant resistance. Fourth, **sclerotinia rot** typically starts at the base of the stem and spreads upwards and downwards, causing the stem to rot. Affected areas develop cotton-like fungal growth, with black sclerotia inside. The upper parts of the plant may wilt and die quickly. This disease thrives in high humidity and dense planting conditions, especially after storms that allow the pathogen to enter through senescent plant parts. To manage sclerotinia, spray with a 50% boscalid solution diluted at 1500 times, or 40% sclerotin net at 1000–1500 times. Apply regularly, especially after heavy rains. Lastly, **stem elongation (convulsions)** is another issue, characterized by thin, elongated stems, small leaves, and poor flesh development. This condition is often due to insufficient fertilizer, especially a lack of base fertilizer, which limits stem enlargement. Water stress and high temperatures can also contribute to this problem. To prevent convulsions, ensure adequate base fertilizer application and maintain proper water and nutrient balance. Monitor temperature during the seedling stage to avoid excessive heat, which can trigger this disorder. By implementing these management strategies, farmers can significantly reduce the impact of these common diseases and improve the overall quality and yield of their spring lettuce crops.

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