Why do Chinese cabbages get viral disease? How is it treated?
Cabbage viral disease, also known as “guding disease” and “choufeng disease”, together with downy mildew and soft rot is known as one of the three major diseases of Chinese cabbage. In ordinary epidemic years it can cause about 10% yield loss, in some severe outbreak years it can reduce yield by more than 30%, and in seriously affected areas it can even cause total crop failure, severely affecting the yield and quality of Chinese cabbage. So why do Chinese cabbages get viral disease? How is it treated?
1. Why do Chinese cabbages get viral disease?
Chinese cabbage viral disease is caused by a virus and is transmitted in the field by aphids. Chinese cabbage is most susceptible during the seedling stage before it has 6-7 leaves, which is called the susceptible period, and it is also the dangerous period for aphid transmission, that is, the effective transmission period. During this period, the earlier the plant is infected, the more severe the disease and the greater the loss; infection after this period results in milder disease. When Chinese cabbage encounters high temperature and drought after sowing, or when soil temperature is high or lasts for a long time, aphid reproduction and activity are favored, root growth and development of the Chinese cabbage are inhibited, and resistance declines, making the plant prone to disease at this time. In addition, early sowing, large numbers of aphids, plus extensive field management, low-lying land with poor ventilation or dry soil, and lack of water and fertilizer all lead to more severe disease.
When cabbage encounters high temperature and drought after sowing, or when soil temperature is high or lasts for a long time, root growth and development are inhibited, the above-ground part remains stunted and does not grow, the host's disease resistance declines, and the virus incubation period is shortened. The spring and autumn peaks of aphid occurrence coincide with the susceptible period of cabbage, and disease is likely when temperatures are 15-20°C and relative humidity is below 75%. Generally, the earlier the sowing date, the earlier the infection, the more severe the disease, and the greater the damage; seedlings before the 7-leaf stage are most susceptible when soil and air temperatures are high and conditions are dry, while infection at later stages causes milder disease. Plots adjacent to cruciferous vegetables can transmit the virus to each other, which can also lead to severe disease. In addition, different cabbage varieties differ significantly in their resistance to viral disease.
2. How is Chinese cabbage viral disease treated?
1. Choose disease-resistant varieties, such as Zao Shu No. 5, Lu Bai No. 1, 2 and 4, Xiafeng Chinese cabbage, Xiaoza 56, Aikangqing, Sanyueman green cabbage, Siyueman green cabbage, etc.
2. Sow at the appropriate time, slightly later, so that the seedling stage avoids the high-temperature period. In Zhejiang and the middle and lower reaches of the Yangtze River, autumn Chinese cabbage is generally best sown from late August to early September; in the Beijing area, sowing at the start of autumn is best.
3. Apply sufficient base fertilizer, increase phosphorus and potassium fertilizer, and control nitrogen fertilizer by applying less. If the seedling stage encounters a high-temperature, dry season, water frequently to lower temperature and retain moisture, promote root growth of the cabbage plants, and improve disease resistance.
4. Pay attention to timely control of aphids. During the seedling stage before the 7-leaf stage, control aphids once every 7-10 days. Seedlings can also be raised under silver-gray shade netting or 22-mesh insect-proof netting to avoid aphids and prevent disease.
5. Chemical control: at the early stage of disease, apply viral inhibitors together with growth promoters. For growth promoters, options include Yelüzhuang concentrated foliar fertilizer at 3000-4000 times dilution, etc. For viral inhibitors, options include 2% Junke Duke aqueous solution at 200-250 times dilution, or 20% Virus A wettable powder at 500 times dilution, or 1.5% Bingduling emulsifiable concentrate at 1000 times dilution, or 1.5% Zhibingling II emulsion at 1000 times dilution, or 40% Bingdubike wettable powder at 500 times dilution, once every 7-10 days, for 3-4 consecutive applications.