How to prevent and control downy mildew in Welsh onions? What is the best medicine to use?

Welsh onion is one of the main crops grown in northern regions and is relatively rare in southern regions. It is understood that some diseases occur when growing Welsh onions, among which the most common disease is downy mildew, and once downy mildew occurs it will affect the growth of Welsh onions. So how to prevent and control downy mildew in Welsh onions? What is the best medicine to use?

I. Introduction to downy mildew in Welsh onions

1. In which season is downy mildew in Welsh onions prone to occur?

Downy mildew in Welsh onions generally occurs mostly during continuous rainy weather in spring and autumn.

2. What are the symptoms of downy mildew in Welsh onions?

Large yellow-white elongated oval lesions appear on the leaves and flower stalks of Welsh onions, with a white mold layer on the surface that later turns green or dark purple. In severe cases, the diseased plants wilt and turn pale yellow.

3. Where is the pathogen of downy mildew in Welsh onions?

The pathogen overwinters on leaves in the form of oospores and hyphae, and after forming conidia the following year, it becomes the primary infection source. Conidia form at night and disperse during the day. The spores invade through the stomata of the leaves, and disease occurs after a latent period of 5-10 days; many conidia form on the leaf surface, becoming the source of reinfection.

II. How to prevent and control downy mildew in Welsh onions?

1. Select disease-resistant varieties. It is understood that varieties of Welsh onion with purple-red false stems, thin leaf tubes and thick wax powder are less affected by the disease.

2. Implement crop rotation and avoid continuous cropping. Maintain field sanitation, thoroughly remove diseased residues after harvest, and carry out deep plowing in time.

3. Choose flat, well-drained fertile loam as the seedbed and planting site.

4. Drain promptly after rain; when soil moisture is high, carry out shallow intertillage to reduce soil moisture.

5. Plant at a reasonable density, strengthen fertilizer and water management, eliminate diseased seedlings when transplanting, and in the early stage pull out systemically infected diseased plants in the field, take them out of the field and burn them.

III. What specific medicine is best for downy mildew in Welsh onions?

According to experienced old farmers, Manhattan Master Hou No. 2 fungicide is one of the specific medicines for downy mildew in Welsh onions, but the medicine needs to be used according to the disease situation at different growth stages of Welsh onions, as follows:

For downy mildew in Welsh onions, spray medicine for prevention and control at the seedling stage and early stage of disease onset. Metalaxyl·mancozeb wettable powder, Sandofan wettable powder, metalaxyl wettable powder, Previcur aqueous solution, Curzate wettable powder, etc. can be used, and treatment should be based on the disease situation. If the condition is relatively severe, spray once every 10 days, and 3 consecutive sprays are enough.

IV. Occurrence pattern of downy mildew in Welsh onions

Cool and highly humid weather is conducive to the development of the pathogen and the occurrence of the disease. When the temperature is around l5°C and there is relatively more rainfall, it is conducive to disease onset. From mid-April to early May (May-June in Northeast China), when there is continuous rainy weather or frequent heavy fog or thick fog, downy mildew may become pandemic. Fields in low-lying areas, with flood irrigation, dense planting and poor growth are especially severely affected. In summer, high temperatures inhibit disease onset. The degree of disease onset in autumn is also positively correlated with rainfall, and improper irrigation also induces more severe disease. Fields with severe disease in autumn also have severe disease the following spring.

Summary: The above content is an introduction related to the prevention and control of downy mildew in Welsh onions and treatment with medicine, and it is hoped it can help grower friends in need. This article is compiled from relevant professional knowledge.