First, yellow dragon disease causes symptoms such as whole plant or partial shoot yellowing. Young trees may show overall yellowing or mottled discoloration on certain branches, with a lack of uniform yellow coloration.
Countermeasures include purchasing disease-free seedlings and isolating them during planting. Timely removal of infected shoots is essential. Once diseased plants are identified, they should be cut and burned immediately to prevent the spread of the disease.
Second, fertilizer damage can also lead to yellowing of the entire plant or parts of the shoots. Symptoms include yellowing in both young and mature trees.
To address this, affected roots should be excavated and trimmed back to healthy tissue. Fungicides should be applied at the right time to restore root vitality. Organic fertilizers should be applied in appropriate amounts based on tree age, vigor, fruit load, and soil conditions. Over-fertilization should be avoided. Animal manure must be properly composted at high temperatures before application, and foliar fertilizers should be used when needed. Fertilization should be done in trenches, and the soil should be covered after application to maintain moisture and prevent root damage.
Third, waterlogging can cause yellow shoots. The symptoms and identification methods are similar to those of fertilizer damage.
Root rot treatment follows the same steps as for fertilizer damage. However, it is important to ensure proper drainage by digging ditches around the orchard. This helps manage water accumulation after rain and prevents drought stress. Maintaining a strong root system is crucial for tree health.
Fourth, poor soil quality with low organic matter (less than 2%) can lead to nutrient deficiencies, causing yellowing. Symptoms include yellow pigmentation, magnesium deficiency, and zinc deficiency in both young and mature trees.
To improve this, expand planting holes, turn over the soil, and apply organic fertilizers to increase organic matter content to at least 2.5%. Foliar sprays containing nitrogen, phosphorus, potassium, calcium, magnesium, and zinc can help enhance growth and overall tree health.
Fifth, other external factors can also cause shoot yellowing:
1. Excessive use of herbicides can harm beneficial bacteria, contaminate the soil, and lead to yellow shoots. Accumulated harmful substances can degrade soil structure, reduce oxygen levels, and hinder root development, resulting in poor nutrient uptake and yellowing.
2. Nematode infestation can damage roots, causing root nodules and poor nutrient absorption. To control nematodes, all animal manure must be composted at high temperatures. Applying 3% Miller or 10% Kedan at 12 kg/mu or 10 kg/mu respectively can help manage the issue.
3. Heavy ring cuts or pest damage from longhorn beetles can cause yellowing. Adjust ring cutting based on tree age, vigor, and fruit load. From May to June, remove egg blocks and monitor pests regularly to avoid shoot yellowing.
4. On grafted rootstocks, excessive fruiting can weaken the tree, leading to yellowing. Proper fruit thinning, balanced fertilization, and efficient water management are essential to maintain tree health and prevent early aging.
Sixth, comprehensive measures are necessary to prevent yellowing. The main principle is to use disease-free seedlings and avoid introducing materials from infected areas. Implementing standardized citrus cultivation practices and focusing on key measures is essential.
1. Full implementation of balanced fertilization is crucial. Formulating fertilizers for "cold fertilizer," "strong bud fertilizer," "strong fruit fertilizer," and "autumn shoot fertilizer" is key. The recommended ratio of nitrogen, phosphorus, potassium, calcium, and magnesium is 1: (0.3-0.4): (1-1.2): (0.4-0.5): (0.14-0.15).
2. Reform orchard cultivation and management practices. Expand soil, improve soil structure, and apply organic fertilizers. For young trees, focus on deep soil improvement and root development. For mature trees, timely harvesting and root pruning help maintain soil fertility. During cold seasons, adjust environmental conditions by applying lime and using root-reinforcing agents. Prune trees to improve light penetration and air circulation.
3. Ensure effective irrigation and drainage systems for scientific and rational water use.
4. Carry out winter clearing of the orchard and implement frost protection measures. Apply organic fertilizers in deep trenches before cold weather. Prune diseased branches, clear fallen fruits, and burn or bury them. Use high-quality pesticides for cleaning. Apply trunk whitening, cover the soil, and spray phosphorus foliar fertilizer during dry weather. A typical whitening agent formula includes 10 kg of water, 4 kg of quicklime, 1 kg of sulfur, and 0.1 kg of salt.
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