How to prevent and cure onion downy mildew?

What harm does onion downy mildew have? How to prevent and cure? Also ask experienced netizens to help introduce the harm and control methods of onion downy mildew in the field network, which are listed below for netizens' reference. The harm of onion downy mildew: onion downy mildew is mainly harmful to leaves and pedicels. Pedicel on the primary yellow-white or milky yellow larger infection spots, fusiform or oval, on which white mold is produced, and later becomes yellowish or dark purple. The middle and lower leaves were infected, and the above part of the disease gradually withered and sagged. The pseudostem is often broken and bent when infected. Bulb infection can cause systemic infection. These diseased plants are dwarfed, the leaves are deformed or twisted, and when the humidity is high, a large amount of white mold grows on the surface. The light disease spot of onion leaf is pale green and long oval, seriously affects the upper half of the leaf, the plant is yellow or withered, and the diseased leaf is inverted "V" shape. Pedicel infection has the same leaf symptoms and is easy to be broken and withered by the disease. When the humidity is high, the disease grows from white to purple-gray mildew layer, that is, the sporangium and sporangium of the pathogen. The bulb becomes soft after infection, the outer scale surface is rough or wrinkled, the plant is dwarfed, and the leaf is twisted. In general, low-lying terrain, poor drainage, serious disease in continuous cropping land, cool, rainy or often foggy weather is easy to be popular. The prevention and control methods of onion downy mildew are as follows: 1. Select the land with high terrain and easy drainage, and rotate with crops other than onions for 2-3 years. 2. Select disease-resistant varieties. In general, red skin and yellow skin varieties are more resistant, such as Yefu No. 1 and so on. 3. Mix the seeds with 35% of 0.3% of the seed weight, or soak the seeds in 50 ℃ warm water for 25 minutes, then soak them in cold water, remove them to dry and sow them. 4. clean up the diseased and residual plants during harvest and take them out of the field for deep burial or burning. 5. Spray 90% triethylphosphonate aluminum wettable powder 400 times 500 times liquid, or 75% chlorothalonil wettable powder 600 times liquid, 50% nail cream copper wettable powder 800 times liquid, 64% alum wettable powder 500 times liquid, 72.2% Pulike water agent 800 times liquid, 70% ethyl manganese wettable powder 500 times liquid, S0% ethyl phosphine aluminum wettable powder 500 times liquid, once every 7-10 days. Continuous prevention and treatment for 2 or 3 times. Click to get more onion planting techniques click to get more vegetable planting techniques