What are the characteristics of downy mildew in Chinese cabbage? How to prevent and control it?
During the cultivation of Chinese cabbage, it is inevitable that some diseases will harm the growth of Chinese cabbage. Downy mildew is one of the important diseases of open-field Chinese cabbage in autumn and can cause damage throughout the entire growth period of Chinese cabbage. So what are the characteristics of downy mildew in Chinese cabbage? How to prevent and control it?
1. What are the characteristics of downy mildew in Chinese cabbage?
Chinese cabbage downy mildew is a common fungal disease during the cultivation of Chinese cabbage.
When the disease occurs at the cotyledon stage, a white mold layer appears on the underside of the leaves. Under high temperature conditions, nearly round dead spots often appear on the diseased parts. In severe cases, white mold also develops on the stems and leaf stalks, and the seedlings and leaves die.
At the adult plant stage, small light green to light yellow spots appear on the upper surface of the leaves, which expand into yellow-brown spots. The lesions are limited by the leaf veins and appear angular. When humid, a white mold layer develops on the lesions on the underside of the leaves. When Chinese cabbage enters the heading stage, under suitable conditions, the lesions on the leaves increase and merge, the leaves turn yellow and wither, and the diseased leaves spread from the outer leaves to the inner leaves. In severe cases, the plant cannot form a head.
When seed plants are affected, white mold can grow on the leaves, flower stalks, floral organs, and seed pods. The flower stalks and floral organs become enlarged and deformed, the petals turn green, and the seed pods become light yellow and shriveled.
The disease mainly damages the leaves, initially as light yellow or yellow-green lesions, which after expansion become yellow-brown, angular or irregular in shape.
2. How to prevent and control downy mildew in Chinese cabbage?
1. Select disease-resistant varieties
There are significant differences in disease incidence among varieties. Chinese cabbage varieties resistant to viral diseases are generally also resistant to downy mildew and can be selected according to local conditions.
2. Sow at the appropriate time
The suitable sowing time should be determined according to the crop rotation, variety, and climate. Early sowing results in severe disease, while late sowing results in milder disease but insufficient heading. However, if a year with high temperature and drought occurs, Chinese cabbage should be sown appropriately later. Hybrid varieties have stronger disease resistance than farmer varieties, so their sowing time can be scheduled earlier.
3. Sow at the appropriate time
The suitable sowing time should be determined according to the crop rotation, variety, and climate. Early sowing results in severe disease, while late sowing results in milder disease but insufficient heading. However, if a year with high temperature and drought occurs, Chinese cabbage should be sown appropriately later. Hybrid varieties have stronger disease resistance than farmer varieties, so their sowing time can be scheduled earlier.
4. Control insects to prevent viral diseases
Early virus-diseased plants are often also plants in which downy mildew occurs early and severely. Chinese cabbage viral disease is transmitted by aphids, so early aphid control should be carried out. Suitable pesticides include 5% acetamiprid emulsifiable concentrate, 2.5% beta-cyhalothrin wettable powder, and 2.5% deltamethrin emulsifiable concentrate, etc. Virus-diseased plants should be pulled out promptly.
5. Pull out central diseased plants and clean up diseased leaves
For early-onset disease, central diseased plants can be pulled out. When the disease is widespread, diseased leaves and severely diseased plants should be cleaned out of the field as soon as possible and promptly disposed of harmlessly
6. Chemical control
Corresponding control agents should be selected according to the stage of disease occurrence. When the disease has not yet occurred in the field, if adverse weather such as continuous rain, fog, or insufficient sunlight occurs, or if the field is planted too densely and ventilation is poor, sprays such as 1.6% diethyl aminoethyl hexanoate aqueous solution or 0.0016% brassinolide aqueous solution can be applied to enhance the plant's disease resistance. At the early stage of disease, sprays such as 70% propineb wettable powder or 75% chlorothalonil wettable powder can be used for protective spraying, once every 5-7 days, for 2-3 consecutive applications. During the disease period, sprays such as 687.5 g/L fluopicolide·propamocarb suspension concentrate, 45% amobam aqueous solution, or 40% fosetyl-aluminum wettable powder can be used, once every 7-10 days, for 2-3 consecutive applications.