In the winter and spring seasons, vegetable seedlings grown in greenhouses are often vulnerable to diseases. This is mainly due to low bed temperatures, insufficient light, poor air circulation, and high humidity, all of which create ideal conditions for pathogens to thrive. These factors can lead to seedling failure, making it crucial to implement preventive measures. Here are some effective strategies:
1. **Use of Sterile Soil**
When growing vegetables, it's best to use fertile field soil that has not been used for solanaceous crops (like tomatoes or peppers), melons, or cruciferous vegetables (such as cabbage) for at least five consecutive years. Sandy soil is preferable, and you should select topsoil from a depth of 13 to 17 cm. Avoid using garden soil directly as planting medium. To prevent the spread of harmful bacteria, the soil should be disinfected. Common methods include:
- **Carbendazim Treatment**: Mix 25–30 grams of 5–30% carbendazim wettable powder per 1000 kg of soil. Dissolve the powder in water, spray it onto the soil, mix thoroughly, cover with plastic, and let it sit for 2–3 days to kill pathogens like blight.
- **Formalin Disinfection**: Use a ratio of 1 part formalin, 100 parts water, and 4000–5000 parts soil. Mix evenly, pile up, cover with plastic, and leave for 2–3 days. Afterward, remove the plastic to allow gas to dissipate, and wait 1–2 weeks before use.
- **Methane Treatment**: Stack the soil into a 30 cm mound, drill holes every 30 cm, fill each with 5 ml of pesticide, and cover with soil. Repeat this process until the entire mound is treated, then seal it with plastic for 7–10 days. Afterward, turn the mound and allow the gas to escape to avoid plant damage.
2. **Seed Treatment**
Soak seeds in warm water at 50°C for 15 minutes, then cool them in cold water and dry before sowing. This method helps reduce disease risk. Alternatively, treat seeds with 50% carbendazim or 50% thiram at a rate of 0.3% of the seed weight for additional protection.
3. **Improve Cultivation Practices**
Water the beds before sowing, and maintain proper spacing to promote strong, healthy seedlings. Avoid overwatering and ensure proper drainage to control humidity. Keep the temperature stable, especially during cold periods, and provide adequate ventilation to reduce moisture buildup. Maximize light exposure by opening covers early and closing them late, even on cloudy or snowy days. Early transplanting helps prevent root damage and promotes better growth.
4. **Chemical Control**
At the first sign of disease, remove infected seedlings immediately and apply protective sprays. Common fungicides include:
- A copper-based solution made by mixing 2 parts copper sulfate with 11 parts ammonium carbonate, left to rest for 24 hours, then diluted 400–500 times.
- 50% carbendazim diluted 600 times.
- 75% chlorothalonil or 70% trichlorfon wettable powder diluted 600–800 times.
- A 0.1–0.2% copper sulfate solution.
After spraying, reduce humidity by sprinkling grass ash or dry soil between plants.
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