Early prevention of onion four diseases

The main diseases of onion are downy mildew, gray mold, rust and soft rot, which should be controlled as soon as possible. Downy mildew and Botrytis cinerea downy mildew mainly damage the outer leaves and pedicels of onion. The suitable temperature for the disease is 10-20 ℃. It can occur in April-May or November-December. At the beginning of the disease, there are oblong or banded sunken disease spots on the outer leaves of the infected plants, dark yellow in the center of the disease spots, and white downy mildew on the disease spots when the air humidity increases. When the temperature is high, the growth of the diseased plant is dwarfed, and the leaves are often twisted from the diseased spot, and finally the whole plant dies. Botrytis cinerea mainly harms onion leaves. At the beginning of the disease, there are white dots on the leaves, and in severe cases, there are as many as hundreds of white spots, and finally the leaves appear gray mildew layer, and then rot. The methods of controlling onion downy mildew and gray mildew are similar. Agricultural measures: clean up the ditch system so that open water can drain and dark water can filter; apply mature organic fertilizer and increase phosphorus and potassium fertilizer. Chemical measures: spray with Doxoqing (3% polyantimycin water agent) 600 times 800 times, once every 7 to 10 days, continuously prevent and cure for 4 times; or use 30% carbendazim 1000 times 1500 times liquid to irrigate roots or spray; you can also use 25% metalaxyl wettable powder 500 times liquid or 75% chlorothalonil wettable powder 800 times liquid spray. Onions are susceptible to rust when the temperature is low or the fertility is insufficient. At the beginning of the disease, light yellow oval spots appeared on the leaves and pseudostems, and in the later stage, the epidermis of the diseased part ruptured and scattered yellowish brown rust-like powder. To control onion rust, 2000 times of 15% triadimefon wettable powder or 1000 times of 70% mancozeb wettable powder can be sprayed. At the same time, 20 ml of Pu K crop germicidal repair solution was sprayed with 40 kg of water per mu. Soft rot onion soft rot is a bacterial disease that invades from the wound. There are milky white spots in the lower part of the diseased leaf, the leaf tip turns yellow at first, and extends downward, the base of the leaf sheath softens and decays, the bulb is water-stained and rotten, some of the whole plant turns yellow and withered, and some begin to rot from the neck of onion, and then spread to the whole plant. Agricultural measures: control pests and reduce wounds; remove diseased plants and disinfect disease holes with lime or sulfur powder. Chemical measures: spray 20 ml of PK crop germicidal repair solution with 40 kg of water per mu, or spray 5000 times of 90% neostigmycin wettable powder at the initial stage of the disease.