Rapeseed plants suffering from nitrogen deficiency show symptoms such as yellowing leaves and stunted growth. New leaves develop slowly, and the foliage is small and pale. The leaf margins often turn red while the center remains yellow, resulting in a mix of yellow and red leaves. To address this issue, apply 8–10 kg of urea or 20–30 kg of ammonium bicarbonate per 667 square meters. You can also use 7.5 kg of human waste mixed with water, or spray a 1–2% urea solution (50 kg per acre) two to three times.
When rapeseed lacks phosphorus, the plants grow slowly, with small and thick leaves. The number of leaves decreases, and the leaf edges and petioles take on a purple-red color, leading to purple-red foliage. To correct this, apply 20–30 kg of superphosphate or 6–8 kg of diammonium phosphate per 667 square meters. Foliar application of a 0.2% potassium dihydrogen phosphate solution (50 kg per acre) can be sprayed two to three times for better results.
Potassium-deficient rapeseed initially shows yellow spots on the leaves, which later develop into brown spots along the edges. The leaves become thick, hard, and brittle, resembling burn damage. To treat this, apply 8–18 kg of potassium chloride per 667 square meters, or spray a 0.2% potassium dihydrogen phosphate solution (50 kg per acre) two to three times.
Boron-deficient rapeseed exhibits blue-purple spots on the leaves, with curled leaf margins and swollen rhizomes. To remedy this, spray 80–100 grams of borax dissolved in 60–70 kg of water per 667 square meters, repeating the process two to three times. This can also be combined with top-dressing applications of 500–1000 grams of boron fertilizer per acre.
During the seedling stage, drought-stressed rapeseed struggles to absorb water and nutrients due to dry soil, leading to slow growth, dwarfed plants, and pale red leaves. Timely irrigation is essential, using furrow irrigation rather than flooding to avoid further stress.
Excessive rainfall before winter or poor drainage in paddy fields can cause waterlogging, resulting in dark red leaves and root rot. To prevent this, ensure proper drainage by digging ditches, lowering the groundwater level, and loosening the soil to improve aeration and root health.
Frost damage during winter causes rapeseed leaves to turn red after sudden temperature drops below 0°C. To reduce frost damage, combine field cultivation with ditch digging, remove damaged roots, and add organic fertilizers to strengthen plant resilience.
Aphid infestations can severely damage rapeseed, causing leaf discoloration, curling, and stiffness. To control aphids, use 15g of 50% anti-insect WP or 30ml of 2.5% emulsifiable concentrate per 667 square meters, mixed with 50kg of water for effective spraying.
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