Autumn Chinese cabbage remains the most widely cultivated vegetable in the city. To ensure high and stable yields, it is essential not only to implement proper agricultural practices but also to apply scientific and effective plant protection measures. The prevention and control of pests and diseases should focus on proactive strategies, combining agricultural and biological methods. Chemical control should be used only when necessary and must avoid high-toxicity or high-residue pesticides to maintain the safety and quality of the produce. These practices have been widely introduced to local vegetable farmers to help them manage their crops more effectively.
(1) **Viral Diseases**: This disease commonly affects seedlings, especially during periods of high temperature and drought when the plants have 7–8 leaves. A large aphid population can accelerate the spread of the disease, causing symptoms such as leaf distortion, mottling, stunting, and necrotic spots. Control measures include increasing phosphorus and potassium fertilizer application to enhance plant resistance, timely irrigation to reduce heat stress, and avoiding conditions that promote disease development. If infection occurs, apply 1.5% Lingzhi Emulsion diluted at 1000 times, spraying every 7–10 days for 2–3 applications.
(2) **Downy Mildew**: This disease is common during periods of fluctuating temperatures or after rainy weather. It primarily affects the leaves, causing yellowish, irregular chlorotic spots. On the underside of the leaves, a sparse white mold layer appears, and the leaves eventually turn brown and dry. For control, alternate between 164% antivirus (500 times dilution) and 70% mancozeb (500 times), applying every 7 days. Another option is to use 25% Rhododendron (800–1000 times) and 72% urea manganese zinc WP (800–1000 times), alternating weekly.
(3) **Soft Rot Disease**: This disease typically occurs in the middle to late stages of growth. It starts from the base of the plant, with yellow, water-soaked lesions. Initially, symptoms are subtle, but as the disease progresses, leaves droop during the day and become limp. In severe cases, the roots rot, exuding a foul smell. Control involves removing pests to prevent wounds, draining excess water after rain, and promptly removing infected plants. Disinfect with quicklime powder. Chemical control options include 72% agricultural streptomycin wettable powder, neophytin at 5000 times, or 77% copper oxychloride at 500 times, applied 2–3 times consecutively.
(4) **Black Rot**: Characterized by "V"-shaped lesions on the leaf margins, this disease spreads through insects and agricultural activities. High humidity and excessive dew contribute to its development. Symptoms include yellowing around lesions, leaf drying, and black vascular tissue in the roots. Prevention includes proper irrigation, timely drainage, and minimizing crop damage. At the early stage, spray with agricultural streptomycin or neophytin at 200ppm, or use 401 antibacterial agent at 600 times, or 50% DT fungicide at 700 times, alternating between these treatments.
(5) **Melasma**: Lesions appear as round, 2–6 mm diameter spots with concentric rings and a dark moldy layer on wet surfaces. Severe infections cause the entire leaf to die. Conditions like low temperatures (13–15°C), high humidity, heavy dew, early sowing, and poor management increase the risk. Control includes increasing phosphorus and potassium fertilization, proper irrigation, and timely drainage. Early treatment involves spraying 75% chlorothalonil or 64% antiviral at 500 times. Alternatives include 50% acetaminophen at 1500 times or 58% metalaxyl-manganese zinc at 500 times.
(6) **Insect Pests**:
- **Locusts**: Remove weeds around fields and alternate between anti-influx (2000 times) and imidacloprid (1000 times).
- **Cabbage White Butterfly (Pieris rapae)**: Use 2.5% highly effective cypermethrin (2000 times) or Kungfu at 3000 times.
- **Diamondback Moth**: Due to resistance, avoid organophosphorus and pyrethroid insecticides. Instead, alternate between 5% Ruijin special suspension (2000 times) and 20% diflubenzuron (600 times).
By following these integrated pest and disease management strategies, farmers can significantly improve the health and yield of their autumn Chinese cabbage crops while ensuring environmental and consumer safety.
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