How did cucumber get powdery mildew?

Cucumber powdery mildew, commonly known as "white disease" and "powdery mildew", is one of the most common diseases in the middle and late stage of cucumber production. It has the characteristics of long damage time and difficult eradication, which brings certain difficulties to control. In general years, the yield is reduced by about 10%, and in epidemic years, it can reach 20% ~ 40%. How can we fundamentally control the harm of powdery mildew?

Harmful symptoms

Cucumber powdery mildew mainly harms leaves, followed by petioles and stems. When the leaves are infected, small and round white powder spots are produced on the front or back of the leaves in the early stage. With the development of the disease, the small powder spots gradually expand into white powder spots with inconspicuous edges, which can cover the whole leaf surface in the later stage, and the leaves are like a layer of white powder. So it's called powdery mildew. Wipe away the white powder, you can see that the affected leaves are green, and the white powdery mildew layer is old and gray in the later stage of the disease. Many dark brown spots were produced on the diseased spots, and finally the diseased leaves turned yellow-brown and died. Under the condition of high humidity, the pathogen can also infect the stems and flower organs of melon, and white powder spots will also appear on the stems and vines.

Occurrence characteristics

Powdery mildew is a fungal disease caused by ascomycete infection. In southern China, mycelium or conidia overwinter or overwinter on melon crops. In the northern region, the pathogen overwinters in the soil with diseased residues, or overwinters on protected sweet potato crops. In the second year, when the conditions are suitable, the closed capsule germinates, and the conidia produced are spread to the host leaves by airflow or rain. White mycelium-like lesions were formed after 5 days, and matured after 7 days, forming conidia to spread and reinfect. Generally, under high temperature and dry environmental conditions, cucumber is prone to disease in the middle and late growth period.

Prevention and cure method

First of all, we must choose disease-resistant varieties. At present, there are many cucumber varieties in China, and most of them are resistant to powdery mildew. We can choose suitable disease-resistant varieties according to different planting seasons and different planting areas. In the middle and late stage of cucumber growth, the lower old leaves should be removed in time to strengthen ventilation and light transmission.

At the early stage of onset, 25% azoxystrobin suspension 20-30ml/mu, 38% azoxystrobin suspension 30-40ml/mu, or 25% pyraclostrobin EC 20-40ml/mu, or 40% bendazole water dispersible granule 20-30g/mu, or 30% triflumizole wettable powder can be selected. Every 7 ~ 10 days, 1 time, 2 ~ 3 times in a row.