How to prevent and cure green onion downy mildew? What is the best medicine to use?

Spring onion is one of the main crops in the north, but it is rare in the south. It is understood that some diseases will occur when planting green onions, among which the most common disease is downy mildew, which will affect the growth of green onions once downy mildew occurs. So how to prevent and cure green onion downy mildew? What is the best medicine to use?

I. introduction of downy mildew of green onion

1. In what season is it easy to have green onion downy mildew?

Green onion downy mildew usually occurs when it is overcast and rainy in spring and autumn.

two。 What are the symptoms of green onion downy mildew?

Large yellow-white oval disease spots appeared on the leaves and pedicels of Welsh onions, and there was a white mildew layer on the surface, and then turned green or dark purple. In severe cases, the diseased plant showed yellowish wilt.

3. Where is the pathogen of green onion downy mildew?

The pathogen overwintered on the leaves in the form of oospores and hyphae, and became the primary source of infection after the formation of conidia in the second year. Conidia form at night and scatter during the day. After invading from the stomata of the leaves, the disease occurred during the incubation period of 5-10 days, and many conidia were formed on the leaf surface, which became the source of re-infection.

Second, how to prevent and cure green onion downy mildew?

1. Disease-resistant varieties are selected, it is understood that the disease will be lighter in the varieties with purplish red stem, thin leaf tube and thick wax powder.

two。 Implement crop rotation to avoid continuous cropping. Maintain pastoral hygiene, thoroughly remove the sick and disabled bodies after harvest, and plough deeply in time.

3. Choose the fertile loam with flat terrain and convenient drainage as the seedbed and planting land.

4. Timely drainage after rain, when the soil moisture is high, shallow ploughing to disperse soil moisture.

5. Reasonable close planting, strengthen fertilizer and water management, eliminate diseased seedlings during planting, early pull out infected plants in the field system, and take them out of the field to burn.

Third, what specific medicine is the best for green onion downy mildew?

According to experienced farmers, Manhattan Hou Master 2 fungicide is one of the specific drugs for downy mildew of green onions, but it needs to be used according to the incidence of green onions at different growth stages, as follows:

Spraying control of green onion downy mildew at seedling stage and early stage can be treated with metalaxyl manganese zinc wettable powder, alum wettable powder, metalaxyl wettable powder, Pulike water agent, Kelu wettable powder and so on. If the disease is serious, spray once every 10 days, three times in a row.

4. Occurrence regularity of downy mildew of scallions

Cool and humid weather is beneficial to the development of pathogens and the occurrence of diseases. When the temperature is about 15 ℃ and the rainfall is more, it is beneficial to the disease. Downy mildew may be prevalent when there is continuous rain or heavy fog from mid-April to early May (May-June in Northeast China). The disease is especially serious in low-lying land, flood irrigation, close planting and poor growth. The summer temperature is high and the disease is restrained. The degree of disease in autumn is also positively correlated with rainfall, and improper irrigation also aggravates the disease. The disease was serious in autumn and also in the following spring.

Summary: the above content is about the prevention and treatment of green onion downy mildew and drug treatment, hoping to help growers in need. This paper is integrated with relevant professional knowledge.