Autumn Chinese cabbage remains the most widely cultivated vegetable in the city. To ensure high and stable yields, it is essential to implement proper management practices and apply scientific plant protection techniques. The key to pest and disease control lies in prevention, combining agricultural and biological methods. If chemical intervention is necessary, avoid using highly toxic or residue-heavy pesticides to maintain the safety and quality of pesticide-free Chinese cabbage. As a result, a comprehensive guide on managing pests and diseases in autumn Chinese cabbage has been shared with numerous local farmers.
(1) **Viral Diseases**: This disease commonly occurs during the seedling stage, especially when the plants have 7–8 leaves and are exposed to prolonged high temperatures and drought conditions. A large aphid population can accelerate disease spread, leading to symptoms such as leaf distortion, mosaics, stunting, deformation, and necrotic spots. Control measures include increasing phosphorus and potassium fertilizer application to boost plant resistance, watering promptly during droughts to reduce heat stress, and avoiding conditions that promote disease development.
If the disease is already present, apply 1.5% Lingzhi Emulsion diluted at 1000 times, and spray every 7–10 days for 2–3 applications.
(2) **Downy Mildew**: This disease thrives during periods of temperature fluctuations, especially after rain. It primarily affects the leaves, causing yellowish, indistinct spots. On the underside of the leaves, a sparse white mold layer may appear, eventually leading to browning and drying of the foliage.
To manage this, alternate between 164% antivirus (diluted 500 times) and 70% mancozeb (also diluted 500 times), applying them every 7 days. Alternatively, use 25% Rhododendron (800–1000 times dilution) and 72% urea manganese zinc WP (800–1000 times) alternately once a week.
(3) **Soft Rot Disease**: This typically appears in the middle to late growth stages. The infection starts at the base of the plant, causing yellowish, watery lesions. Initially, symptoms are subtle, but over time, the leaves droop during the day and become limp, eventually lying flat on the ground or becoming dry and brittle. In severe cases, the roots rot, exuding a foul-smelling liquid.
Control strategies include: removing pests promptly to reduce plant wounds, draining water immediately after rainfall to control field humidity, cultivating the soil if needed, and promptly removing and disinfecting infected plants with quicklime powder. For chemical control, use 72% agricultural streptomycin wettable powder, neophytin at 5000 times dilution, or 77% copper oxychloride at 500 times, repeating the treatment 2–3 times.
(4) **Black Rot**: Characterized by "V"-shaped lesions on the leaf edges, which gradually expand inward. The surrounding tissue turns yellow, and the leaves become dry and brittle in severe cases. The heart of the plant may rot, and the root vascular system may turn black. This disease spreads through insects and agricultural activities, and is promoted by high humidity and excessive dew.
To prevent and control black rot: practice proper irrigation and drain water promptly after rain; control pests and minimize crop damage during field operations. At the first sign of disease, spray agricultural streptomycin or neophytin at 200 ppm, or use 401 antibacterial agent at 600 times dilution, or 50% DT fungicide at 700 times, alternating regularly.
(5) **Melasma**: Lesions appear as round, 2–6 mm diameter spots, brown or dark brown with clear concentric rings. Wet lesions develop a black moldy layer, and severe infections cause the entire leaf to die. This disease is common under cool temperatures (13–15°C), high humidity, heavy dew, early sowing, poor nutrition, and inadequate management.
Control methods include: increasing phosphorus and potassium fertilization, managing irrigation, and draining excess water after heavy rains. At the onset of the disease, spray 75% chlorothalonil or 64% antiviral at 500 times dilution. Other options include 50% acetaminophen at 1500 times or 58% metalaxyl-manganese zinc at 500 times, alternating between these products for better effectiveness.
(6) **Insect Pests**:
- **Locusts**: Remove weeds along the field edges and alternate spraying anti-influx at 2000 times with imidacloprid at 1000 times.
- **Cabbage White Butterfly (Pieris rapae)**: Apply 2.5% highly effective cypermethrin emulsifiable concentrate at 2000 times or Kungfu at 3000 times.
- **Diamondback Moth**: Due to its resistance to organophosphates and pyrethroids, it’s best to avoid those. Instead, use 5% Ruijin special suspension at 2000 times and 20% diflubenzuron at 600 times alternately.
By following these integrated pest and disease management strategies, farmers can significantly improve the yield and quality of their autumn Chinese cabbage while maintaining environmental and food safety standards.
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