Cabbage virus disease is one of the most significant diseases affecting Chinese cabbage and other cruciferous vegetables. It is commonly referred to as "Orphan" or "Cramp" due to its characteristic symptoms. The disease is particularly prevalent during the seedling stage, especially before the sixth leaf appears. Infected plants show bright veins and chlorotic streaks along the leaf veins, while the leaves may become curled or distorted. As the plant matures, the veins become twisted, and the leaves turn yellow-green with necrotic spots. The overall growth is stunted, and the root system becomes underdeveloped, often appearing brown and weak.
The main pathogens responsible for this disease include the Turnip mosaic virus (TuMV), Cucumber mosaic virus (CMV), and Tobacco mosaic virus (TMV). TuMV is transmitted by aphids and can be inactivated at temperatures between 55–60°C within 10 minutes. CMV, which has a spherical shape, is also spread by aphids and is inactivated at 60–70°C over the same time period. TMV, on the other hand, spreads through mechanical contact.
The disease cycle typically begins in wintering hosts such as Chinese cabbage, radish, and spinach. In spring, the virus spreads via aphids or direct contact with host plants, and then moves to summer and autumn cruciferous crops. Drought and high temperatures significantly favor the occurrence and spread of the virus. Early sowing, high soil temperature, and low moisture levels increase the risk of infection.
In northern and northeastern China, the virus survives in underground storage areas during the off-season and re-emerges in spring. Greenhouse and plastic greenhouse environments provide ideal conditions for continuous viral circulation. In southern regions, where the climate remains mild year-round, the virus persists without a dormant phase.
Aphids play a crucial role in the transmission of the virus. Studies have shown that intercalary necrotic spots are more common in certain directions on cabbage leaves, indicating a strong relationship between aphid activity and virus spread. Preventive measures should focus on controlling aphid populations and monitoring their flight patterns.
To manage the disease effectively, several strategies are recommended:
1. **Resistant Varieties**: Selecting resistant cabbage varieties is an effective long-term solution.
2. **Seedling Management**: Avoid planting seedlings near cruciferous crops. Soil should be treated with insecticides to control aphids before transplanting.
3. **Netting Covers**: Cover seedlings with fine mesh nets (40-45 mesh) to prevent aphid access. White nets are particularly effective as aphids avoid white colors.
4. **Timing of Sowing**: Plant early, but avoid sowing too early to reduce the risk of initial infection.
5. **Granular Insecticides**: Use granules mixed with ash or clay, containing dimethoate or chlorfenapyr, to repel aphids before and after sowing.
6. **Chemical Treatments**: Commonly used chemical agents include Virus A (20% copper hydroxide), Plant Disease Spirit (15%), and 83 Activator. These should be applied every 7 days for 3–4 times for best results.
7. **Disease-Free Seeds**: Use certified disease-free seeds to minimize the risk of introducing the virus.
A practical method for identifying infected plants involves removing the outer leaves and examining the base of the leaf for vascular damage. Healthy plants will have white, tender tissue, while diseased plants show yellow or brown discoloration.
By combining cultural, biological, and chemical control methods, farmers can significantly reduce the impact of cabbage virus disease and ensure better crop yields.
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