Onion downy mildew mainly refers to important diseases on green onions and onions. When conditions are appropriate, the spread of diseases is rapid, resulting in serious losses. In addition to scallions and onions, downy mildew also harms other plants such as garlic and leeks. Therefore, timely pesticide control is the key. FHM fence factory provides a variety of GBW Hexagonal Wire Netting to support your selling.You could have a multiple choice here.Gbw Hexagonal Wire Netting is always made of hot dipped galvanized wire.The hot dipped galvanized wire run though the mould of hexagonal mesh machine and then the wire is weaved to mesh. The various mesh holes are decided by all kinds of moulds. Gbw Hexagonal Wire Netting,Galvanized Wire Chicken Wire Mesh,Weaving Gbw Hexagonal Wire Netting,Hexagonal Wire Netting DINGZHOU FEIHONG METAL MESH LIMITED , http://www.fhmfencing.com
The genus onion is mainly caused by harmful leaves and pedicels. The peduncle is yellow-white or yellow-yellow infestation on the peduncle, spindle-shaped or elliptical, with white mold on it, and later turned pale yellow or dark purple. The middle and lower leaves are infected, and the diseased part is gradually drooping. False stem disease is more ruptured and curved. Infected by bulbs, it can cause systemic infection. The diseased plants are dwarfed, the leaves are deformed or distorted, and when the humidity is high, a large amount of white mold grows on the surface.
Onion downy mildew is mainly harmful to leaves. The diseased lesions are pale green and long oval, and when it is severe, it affects the upper half of the leaves. The plants are yellow or dead, and the lesions are inverted "V" shape. The peduncle is infected with the same symptoms as the leaves, and it is easy to be broken by the disease. When the humidity is high, the disease minister has a white to purple gray mold layer, that is, a cystic stalk and a sporangia of the pathogen. The bulb becomes soft after infection and the outer scale is rough or shrunken. The plants are dwarfed and the leaves are twisted and deformed.
Pathogen and pathogenesis: The disease is caused by fungal infection of the genus Gunigerin. According to the pesticide network , the pathogens mainly use oospores to survive the soil in the soil with the diseased residues , and the mycelium can also lurk in the bulbs for wintering. In the second year, it was splashed by rainwater and transmitted to the leaves for initial infection. When wet, the diseased part produced a large number of sporangia, which mainly spread with the airflow, causing reinfection. Rainwater and insects can also spread, and whether seeds can be transmitted remains to be studied. It is cool and wet at night, warm during the day, and heavy fog is exposed. The soil moisture condition is conducive to the occurrence and prevalence of the disease.
The specific prevention methods are as follows:
Use disease-free seeds and seed treatment: choose the disease-free plot to keep the seeds, the newly purchased seeds are soaked in warm water at 50 °C for 25 minutes, and then sown after cooling.
Strengthen the management of the field: choose high-rise, well-drained, ventilated plots for planting. Apply fertilizer to the fertilizer and increase the application of phosphorus and potassium fertilizer. Rational irrigation, do not make the onion too wet. The diseased plants were found and removed in time. After harvesting, the diseased bodies are completely removed, concentrated, and deep-plowed to reduce the source of bacteria.
Pesticide prevention and control points: China's pesticide network recommends that the initial stage of the disease should be sprayed once every 7-10 days, even spray 3-4 times. The usual agent has 70% Ethium Phosphate, Mn, Mn, WP, 600-800 times. 25% of the metalaxyl cream can be 500-1000 times, 50% Anke wettable powder 2500 times, 70% dry moisturizing agent 500-700 times, 72.2% mildew 700-1000 times liquid.