How to prevent and cure onion purple spot?

How to prevent and cure onion purple spot? What harm does onion purple spot disease have? Also ask the netizens who know to help introduce that purple spot mainly harms onions and green onions, as well as garlic and leeks. Therefore, the farming network has sorted out the harm and control methods of onion purple spot, which are listed in detail below for netizens' reference. The harm of onion purple spot: purple spot mainly harms leaves, pedicels and bulbs on onions. The disease spot first occurs from the leaf tip, or forms in the wound damaged by thrips. At the initial stage, the disease spot is small, gray to light brown, purplish in the center, with black-gray mildew. The spot soon expands into an oval or spindle-shaped, sunken, dark purple, forming concentric patterns, surrounded by yellow halos. When the humidity is high, the purple spot will expand to the whole leaf, which often makes the onion leaf turn yellow, die or break from the bottom up, which seriously affects the yield and quality of fresh onion. Purple spot disease is easy to occur under warm and humid conditions, susceptible to bulb expansion, sandy soil, dry land, early seedlings, old seedlings, lack of fertilizer, weak growth of onions and thrips. Prevention and control methods of onion purple spot: method one, clean the onion plantation, remove the residual body and other sources of infection. Second, strengthen management, apply more base fertilizer and topdressing to make onion grow strong and enhance disease resistance. Irrigation should be controlled after the onset of the disease to reduce soil moisture and prevent thrips as early as possible so as not to cause wounds. Method 3. Soak the onion seeds with 40% formaldehyde 300 times solution for 3 hours before sowing, and wash them in time after soaking. Method 4. Spray 75% chlorothalonil wettable powder 600x liquid, or 64% chlorothalonil wettable powder 500x liquid, 70% mancozeb 500x liquid, 40% Dafudan 500x liquid, or 50% propofol 1500 times liquid, copper ammonium mixture 500x liquid, 2% multi-antibiotic 30ppm, 50% Sukeling 30ml 50g, onion and garlic germ net and other medicament spray, any of the above agents can be used alternately. Every 7 Mel 10 days, prevention and treatment of 3 Mel for 4 times in a row, adding 5 Mel 10 grams of neutral detergent to each 10kg solution can increase the adhesion of the solution. Planting onion topdressing method onion seedling method