Downy mildew is one of the common diseases of onions and onions. Scallion and onion downy mildew are obligate parasites that only harm onion vegetables. The following small series of Huinong.com will focus on the prevention and control measures of onion downy mildew. 1. Symptoms of onion downy mildew Onion downy mildew mainly damages leaves and pedicels, and bulbs can also be affected. Infected with leaves and pedicels, primary yellow-white oval lesions, easy to produce gray-white mildew layer when the humidity is high, the later mildew layer turns purple gray or light yellow, that is, the cysts and sporangia of the bacteria. Downy mildew also causes systemic infections, resulting in a dwarfing of plant growth retardation. When the disease conditions are appropriate, the mildew layer grows directly from the leaves or pedicels, and then the leaves and pedicels gradually turn from green to yellow. Infected plants can cause dryness in the diseased department and above. The onion bulbs became soft after infection, the leaf deformities were distorted, the outer scales were rough and shrunken, and the infected plants were generally dwarfed. 2. The pathogen of onion downy mildew : fungus Peronospora schleidenii Ung. [Synonym: Peronospora destraotor (Berk.) Casp.] is a genus of the genus Flagellate, known as the genus Onion. 3. Transmission route and disease conditions of onion downy mildew The pathogen is lurking in the bulb with hyphae or overwintering with the oospores in the diseased leaves, pedicels or bulbs of the host, and on the seeds or in the soil. When the plants buried in the soil in the spring of the next year grow new leaves, the bacteria that overwinter in the bulbs are likely to cause infection of the plant system, and the diseased plants appear to be dwarfed. The overwintering pathogen oospore in the soil disease residue can be splashed on the leaves by rainwater, etc., sprouting the tube, invading the leaves from the leaf stomata, completing the initial infection of the field, and then forming lesions. The sporangia on the lesions spread by wind, rain and insects for a second infection. In a cool, rainy, foggy weather, the disease is prone to epidemics. The low-lying terrain, poor drainage, and heavy sputum are prone to morbidity and the incidence is heavier. 4. Onion downy mildew prevention and treatment method 1 seed and onion disinfection Seed dressing with 0.3% 35% metalaxyl seed dressing, or soak in warm water at 50 °C for 25 minutes, then immerse in cold water to cool, dry and then sow. Before planting the scallions, the diseased sputum and weak sputum are eliminated, and the scallions are soaked in 25% of the 25% metalaxyl WP 500 times solution for 10 to 20 minutes. 2 rounds The plot with heavy onset of downy mildew should be rotated with non-onion crops for 2 to 3 years. 3 Strengthening management Choose green onions and onions with high-lying terrain, fertile soil and easy-to-drainage plots, and drain and drain after heavy rain. Apply sufficient organic fertilizer and increase phosphorus and potassium fertilizer. Onions generally apply 4000-5000 kilograms of fermented manure per acre, as the base fertilizer, and then apply 25 to 30 kilograms of nitrogen, phosphorus and potassium compound fertilizer after sputum, and then planted after shallow sputum, the onion cultivation should not be too dense, and timely Topdressing to enhance the disease resistance of onions. Pay attention to the development of the disease in the field, and the initial disease leaves should be removed in time. The pasture must be cleaned in time after harvest. 4 chemical control If the diseased plant is found in the field, the diseased leaves should be removed. Use 50% Anke-Mn-Zn wettable powder 500 times solution, or 72% gram dew (Cream cyanide) wettable powder 800 times solution, or 72.2% Plex water agent. 500 to 800 times solution, or 25% metalaxyl WP 500 times solution, or 58% metalaxyl-manganese zinc wettable powder 500 times solution, or 40% ethyl phosphine aluminum wettable powder 200 to 250 times solution , or 30% DT suspension agent 400 ~ 500 times solution, or 75% chlorothalonil WP 600 times solution or 50% methyl thiophanate WP 800 times solution. Spray once every 7 to 10 days, and spray continuously for 2 to 3 times. The above is how to prevent onion downy mildew, and hope to help the growers to control onion downy mildew. Bluetooth TWS hearing earphones for impairment Shenzhen Sunshine Technology Co.,Ltd , https://www.shenzhenyatwin.com
