Onions are common vegetables in our daily life. They are delicious and nutritious, and are very popular among people. In the process of onion planting, it is inevitable that some pests and diseases will be attacked. Among them, downy mildew is a common disease, which seriously jeopardizes the normal growth of onion. This article will introduce the method of preventing and treating onion downy mildew. It is helpful to plant onions.
First, the symptoms
Onion and onion are mainly harmful leaves and pedicels. The peduncle is yellowish-white or yellowish-yellow infestation, spindle-shaped or elliptical, with white mold on it and 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. These strains 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, which in severe cases affect the upper half of the leaves. The plants are yellow or dead, and the diseased leaves are inverted "V". The peduncle is infected with the same symptoms as the leaves, and is easily broken by the diseased part. 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 surface is rough or shrunken, the plant is dwarfed, and the leaf is twisted and deformed.
Second, the disease cycle and disease factors
The oospores overwinter on the host or seed or in the soil, germination in the spring of the next year, and intrusion from the stomata of the plant. When the humidity is high, sporangia are produced on the lesions, and they are transmitted by wind, rain, insects, etc., and re-infected. Generally, the terrain is low, the drainage is poor, and the heavy stagnation is heavy, and the weather is cloudy and rainy or often foggy.
Third, prevention
(1) Choose plots with high topography and easy drainage, and implement 2-3 years of rotation with crops other than onions.
(2) Select resistant varieties. Generally, the red and yellow skin varieties are more resistant to diseases, such as the 掖 1 1 and so on.
(3) Seed dressing with 35% Ledomer with a seed weight of 0.3%, or soak for 25 minutes with warm water at 50 °C, then immerse in cold water, remove and dry, and sow.
(4) Clean up the diseased plants at the time of harvest and bring them out of the field for deep burial or burning.
(5) Spraying 90% triethylphosphinate aluminum wettable powder 400-500 times solution, or 75% chlorothalonil wettable powder 600 times liquid, 50% nail cream copper wettable powder 800-1000 times liquid, 64 at the beginning of the disease % antivirus 矾 wettable powder 500 times solution, 72.2% Plex water agent 800 times solution, 70% ethyl manganese wettable powder 500 times solution, S0% succinate, ethyl phosphine aluminum wettable powder 500 times solution, 7-10 Once a day, continuous control 2-3 times.
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