During the early rice seedling stage, temperature fluctuations are common, and cold waves frequently occur. This unstable weather is not favorable for the emergence and healthy growth of dry-seeded seedlings. In the field conditions of early rice, various seedbed diseases can develop, which differ from those affecting water-seeded rice. Therefore, it's essential to enhance the identification and management of these diseases.
Dry-seeded seedlings, when covered with mulch, experience high temperatures under the film, creating an ideal environment for rice blast. Additionally, the use of acidic soil in dry seedbeds can increase disease severity. When seedlings grow in dry soil without sufficient moisture, their ability to absorb water-soluble silicates is reduced, leading to lower accumulation of silicic acid in the epidermal cells, which weakens their resistance to pathogens. Dry-seeded seedlings that grow vigorously are also more susceptible to rice blast. To prevent this, proper seed treatment is crucial. Soaking seeds in 0.5-1% lime water or using a 300-fold dilution of strong chlorine solution for 12 hours before planting can help reduce infection risk. After seedlings emerge and leafhoppers appear, the mulch should be removed. Spraying 20% tricyclazole wettable powder at 50–75 grams per acre can effectively control the disease.
In the early stages, yellow (white) disease may occur, characterized by thin, pale leaves, soft new roots, and lighter-colored leaves. Two main causes include prolonged exposure to low temperatures after uncovering the seedlings, which damages chloroplasts and leads to yellowing, and dry, infertile soil causing chlorophyll deficiency, especially iron deficiency. When temperatures rise, seedlings may gradually recover. Applying 600–800 times diluted Dry Yuyu No. 1 can help restore green color within 2–3 days. Ferrous sulfate spray also shows some effectiveness.
Another condition, known as yellow seedling disease, occurs due to excessive drought or uneven fertility. Symptoms include yellowing of young leaves starting from the base, with a slight reddish-orange tint. New leaves may grow slowly but remain normally colored. Although the plants don’t usually die, they tend to dry out. Prevention involves careful fertilization, timely watering, and adding appropriate amounts of "enemy pine" to avoid blight.
Rhizoctonia is a fungal disease that affects young shoots and roots, causing browning, distortion, and rot. Infected seedlings may have dark white roots with yellow-brown spots, browned and softened stems, and curled, wilted heart leaves. The base of the plant may show white, pink, or gray mold. There are two types: blue-green and dry-yellow. At the two-leaf stage, checking for dew on the leaf tip is important. If no dew appears, it may indicate the onset of blight. Immediate application of 65% Dukesson WP is recommended. Mix the powder with a small amount of water to form a paste, then dilute with more water. Avoid mixing with alkaline pesticides during application.
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