In the process of rapeseed growth and development, various leaf color changes such as red, yellow, brown, dark purple, blue-purple, and gray can occur due to improper management or nutrient deficiencies. These symptoms often indicate specific issues that need timely identification and treatment to ensure healthy plant development.
**First, Red Leaves**
Red leaves in rapeseed are commonly caused by several factors:
1. **Drought**: During the seedling stage, drought can lead to slow growth, dwarfing, and light red discoloration of the leaves. To address this, timely irrigation is essential. Ditch irrigation should be used, avoiding flooding to prevent seedling rot.
2. **Waterlogging**: Excessive moisture during the seedling stage can also cause red leaves. To manage this, deep trenches should be dug to lower the water table and improve drainage.
3. **Aphid Infestation**: Severe aphid infestations can cause leaves to shrink and turn red. A solution of 50% anti-inferiority WP (10–20g) mixed with 20–30kg of water can be sprayed to control the infestation.
4. **Frost Damage**: Sudden temperature drops below 0°C in winter can cause frost damage, resulting in red leaves. Applying about 100kg of wood ash per acre can help reduce the risk of freezing.
**Second, Yellow Leaves**
Yellow leaves in rapeseed may be caused by different nutrient deficiencies:
1. **Nitrogen Deficiency**: Lack of nitrogen leads to stunted growth, small leaves, and yellowing starting from the older leaves. Applying 15–20kg of ammonium bicarbonate per acre or using a 1%–2% urea solution for foliar spray can help.
2. **Sulfur Deficiency**: Unlike nitrogen deficiency, sulfur deficiency starts from the younger leaves. Adding 10kg of gypsum powder per acre during cultivation can aid in recovery.
3. **Acid Damage**: Acidic soil can cause yellowing of new leaves. Applying 50kg of lime and 50kg of ash per acre helps neutralize the soil and correct the issue.
**Third, Brown Leaves**
Brown leaves typically signal potassium deficiency. Symptoms include yellow spots on old leaves, which develop into brown lesions. At the seedling stage, applying 7–10kg of potassium chloride per acre or spraying 0.1%–0.2% potassium dihydrogen phosphate solution 2–3 times can be effective.
**Fourth, Dark Purple Leaves**
Dark purple leaves are a sign of phosphorus deficiency. The plants grow slowly, leaves become small and dull, and purple spots appear along the edges. During the seedling stage, mixing 25–30kg of calcium phosphate per acre into the soil can help. For later stages, spraying 1% superphosphate solution 2–3 times is recommended.
**Fifth, Blue-Purple Leaves**
Blue-purple leaves indicate boron deficiency. Leaves initially appear dark green, then become smaller, brittle, and curl inward. Spraying 50–100g of borax dissolved in 50kg of water during the seedling, flowering, or early growth stages, repeated 2–3 times, can resolve the issue.
**Sixth, Gray Leaves**
Gray leaves are a symptom of zinc deficiency. The leaf margins turn gray and white first, gradually spreading toward the center. The veins remain green while the rest turns pale. In the seedling stage, mixing 1.5kg of zinc sulfate with 30–40kg of dry soil per mu can help. Later, spraying 0.3%–0.4% zinc sulfate solution 2–3 times is effective.
By understanding these symptoms and addressing them promptly, farmers can significantly improve the health and yield of their rapeseed crops. Regular monitoring and proper nutrient management are key to preventing and treating these issues.
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