Comprehensive Prevention and Control Techniques of Sweet Potato Stem Nematodiasis
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Sweet potato stem nematode disease is a serious threat to sweet potato cultivation. It spreads quickly and can affect the plants at various stages, including seedbeds, fields, and storage. However, it primarily targets the tubers, causing significant damage. Infected tubers often have brown or greenish spots on the skin, which may be cracked and thin. While some potatoes appear normal on the outside, the internal tissues are usually affected. This disease not only reduces the quality of the sweet potatoes but also leads to a major decrease in yield.
The disease is caused by a parasitic nematode known as the sweet potato stem nematode. These tiny worms are slender, with a slightly pointed end, measuring between 0.9 to 1.45 mm in length. They can survive the winter as adults, larvae, or eggs within the tubers, and also overwinter in the soil and manure. The nematodes are sensitive to high temperatures, and soaking them in water at 50°C for 10 minutes can kill up to 98% of them. However, they are highly resistant to cold, surviving at -15°C without dying, and can also withstand dry conditions, living for up to a year under extreme drought. This makes eradication extremely challenging.
To manage this disease effectively, several integrated measures can be taken:
1. **Planting Resistant Varieties**: Choose local varieties that are known for their resistance to nematodes. Examples include Jinshu No. 10, Yushu No. 13, Sushu No. 8, and Beijing 553, which are well-suited for the Central Plains region.
2. **Cultivating Disease-Free Seedlings**: Apply 60 grams of 3% carbofuran microgranules per square meter in the seedbed before covering the soil. Soak the seed potatoes in warm water (52–53°C) for 10 minutes before planting to eliminate nematodes. When transplanting, use aldicarb or methyl isothiazole solution. High-cutting seedlings can also help reduce nematode infestation.
3. **Establishing Disease-Free Fields**: Use certified disease-free plots for planting and strictly select healthy seed potatoes and seedlings. Summer potatoes should be grown from nurseries or cuttings from spring potatoes, planted in clean, disease-free areas.
4. **Chemical Control**: In heavily infected areas, apply methyl isofluorophate or phoxim diluted 2000–2500 times. Pour 0.5 kg per hole when planting. Alternatively, use olivine granules or stemline granules, applying 1–1.5 kg per hole and watering afterward. For less severe cases, soak the seedling bases in 150–200 times diluted solutions for 30 minutes.
5. **Removing Infected Materials**: Always remove diseased tubers and plant residues after harvesting. Burn or boil them, and avoid using infected peels, washing water, or soil as fertilizer. Ensure all fertilizers are properly composted at high temperatures above 50°C.
6. **Crop Rotation**: Rotate sweet potatoes with crops like wheat, corn, millet, cotton, or tobacco. Avoid growing sweet potatoes in the same field for more than three consecutive years to break the nematode life cycle.
7. **Adjust Planting and Harvesting Times**: In severe cases, delay planting until mid-May and harvest before the end of September or early October to avoid peak nematode activity. Dry the tubers promptly for use in brewing or as animal feed.
8. **Strengthen Quarantine Measures**: Enforce strict quarantine protocols to prevent the movement of infected tubers or seedlings across regions. This helps limit the spread of the disease.
By implementing these strategies, farmers can significantly reduce the impact of sweet potato stem nematode disease and ensure better yields and quality.