Onions are a common vegetable and a vegetable that many people like. Onion downy mildew is a common disease in the growth process. This disease may lead to the reduction of onion production. Let us introduce the symptoms and prevention methods of onion downy mildew.
　　
Onion downy mildew symptoms
Onion downy mildew mainly harms onion leaves, especially onions. The disease begins with the outer leaves and develops from the bottom to the inner leaves. The lesions with mild pathology are pale green, long elliptic or long strips. After enlargement, the lesions are large, and the leaves are withered. In severe cases, the onion leaves are dry or yellow and dead except for the heart leaves. Early in the morning, the diseased leaves withered; when wet, the diseased leaves rot. When the humidity is high, the disease minister produces a white to purple gray mold layer, that is, the cysts and sporangia of the bacteria. Seedlings are often perishable and die.
Incidence condition of onion downy mildew pathogen
The pathogen is a fungus. The bacterium is attached to the diseased body or seed by oospores or overwintered in the soil. It germinates in the spring of the next year and invades from the stomata of the plant. When the humidity is high, sporangia are produced on the lesion. After the sporangia is heated, it is spread by airflow, wind and rain, insects, etc., and reinfected. The relative humidity of the air is above 95%, and the temperature is around 15 °C. There are two main incidence peaks in a year, with the highest incidence from April to May. The disease is aggravated by low temperature and heavy rain and heavy fog. The terrain is low, the drainage is poor, the over-close planting, the heavy land, the poor plant growth and the flooding of the flood are also serious.
Onion downy mildew prevention and treatment method
1. Select disease-free seeds and use the new high-fat membrane seed dressing introduced by the agricultural resources Taobao guide before sowing. It can keep warm, moisturize and swell, improve the germination rate of seeds and make the seedlings strong. Repel underground pests and isolate viral infections. It can also be mixed with a seed coating.
2. Strengthen the management of the field: choose the land with high terrain, good drainage and ventilation. 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 the new high-fat membrane anti-bacteria was spread and sprayed in time. After harvesting, the diseased bodies are completely removed, concentrated, and deep-plowed to reduce the source of bacteria.
3, chemical control: spraying in the early stage of the disease, spray once every 7-10 days, even spray 3-4 times, often 70% ethylphosphorus aluminum manganese zinc wettable powder 600-800 times, 25% Metalaxyl creamy mildew WP 1500-1000 times, 50% Anke WP 2500 times, new high-fat film 500 times.
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