Chengde City is located in the northern part of Hebei Province, known for its extensive greenhouse agriculture. The city has a total of 76,000 acres of greenhouses, with over 20,000 acres dedicated to tomato cultivation in solar greenhouses. In recent years, a serious problem has emerged: tomato root-knot nematode disease, affecting more than 7,000 mu (about 1,167 acres) of solar greenhouses. This disease causes significant losses, with an average loss rate of 20% to 30%, and in severe cases, up to 60% to 70%. The impact has been felt across several districts, including Chengde County, Chiping County, Shuangye District, and Shuangqiao District, causing great economic hardship for many local vegetable farmers.
To address this issue, we have conducted three consecutive years of field investigations and research since 2000, leading to the development of effective prevention and control strategies.
First, the pathogen responsible is the southern root-knot nematode (*Meloidogyne incognita*). Adult males are slender, while females are pear-shaped and milky white. These nematodes primarily infect the fibrous and lateral roots of tomatoes, forming small swellings or galls. Infected roots become unable to absorb water and nutrients properly, leading to stunted growth, wilting, and even plant death.
The nematode's life cycle occurs entirely within the solar greenhouse, spreading through infested soil, diseased seedlings, and irrigation water. It affects not only tomatoes but also crops like cucumbers and celery. The nematode thrives in warm conditions, particularly when the soil temperature is between 25–30°C and the moisture content is around 40%. However, during the cold winter months, when temperatures drop below 10°C, the nematode becomes inactive. In open-field farming, where winters are much colder (-10°C to -23°C), the nematode cannot survive the winter. But in solar greenhouses, which remain covered from late September to early October, the nematode continues to develop and infect plants.
Once inside the roots, the nematode secretes substances that cause abnormal cell proliferation, resulting in root knots. After reaching the fourth stage, the nematode mates and lays eggs. The male then leaves the host and dies, while the eggs hatch and continue the infection cycle. Nematodes prefer loose, dry soil, which explains why the disease is more prevalent in such conditions. They are mainly found in the top 3–10 cm of soil, where crop roots are concentrated.
To manage this disease, several methods have been recommended:
1. **Crop Rotation**: Rotating with rice or other non-host crops like onions, leeks, peppers, and garlic can reduce nematode populations in the soil.
2. **Soil Treatment**: Applying 60–70 kg of quicklime per acre during the off-season and keeping the soil flooded for about 20 days helps control nematodes effectively.
3. **Freezing Treatment**: In heavily infested greenhouses, applying a layer of frozen water before and after November 20, without covering the greenhouse, can freeze the soil and kill the nematodes after two months.
4. **Field Management**: Strengthening field management, ensuring proper fertilization and irrigation, can improve plant resistance. Infected plants should be removed, burned, or deeply buried to prevent further spread.
5. **Chemical Control**: Using 5% Miler granules at a rate of 4 kg per mu during planting can help control nematode damage.
These measures have proven effective in reducing the impact of root-knot nematode disease, helping farmers protect their crops and maintain productivity in the challenging environment of solar greenhouses.
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