Analysis of the cause of the disease: 1. The onion disease is a fungal disease, and the pathogen is the flagellate Phytophthora infestans. This kind of fungus has strong ability to resist adverse environment and can survive in the soil for several years. It likes high temperature and high humidity. The development temperature is 15-35 °. In the early stage of the disease, there will be spots that are not obvious in the white and white areas. When the humidity is high, there will be sparse white mold; when the humidity is small, the white mold disappears. 2. The incidence is often caused by pathogens hidden in the diseased plants, in the soil, in the composting winter, and then in the spring, with the wind, rain and other conditions to spread; sometimes due to improper farming operations, causing transmission. Therefore, the onion field with unreasonable planting density, continuous wet and rainy days, low-lying terrain, and poor drainage often has serious disease.
Control measures: 1. To make a reasonable rotation, advocate the rotation of non-onion garlic crops for more than 2 years to reduce the source of the bacteria. 2. The correct field management is equally important: timely drainage, to ensure that it is not wet; timely ventilation work and the application of a new high-fat film 600 times night can automatically form a layer of physical polymer film to isolate pests and diseases. 3. Chemical control: Spraying at the beginning of the disease. The selection of the agent must be targeted. When the pesticide is configured, it must be used together with the new high-fat film. It can form a protective film on the surface of the onion to control the volatilization of the pesticide, prevent the rainwater from scouring, reduce the dosage per acre and reduce the control effect. Multiple times. Can also be added to the foliar fertilizer to increase efficiency.
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