Causes of onion disease 1 Large onion plague is a fungal disease, and the pathogen is Phytophthora nicotiana. 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, by means of wind, rain and other conditions; 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. Welsh onion disease prevention and treatment method 1 After harvest, remove the sick body in time; and concentrate on destroying the onion field. This is done to reduce the source of germs in the field and the source of germs in organic fertilizers. 2 It is necessary to make a reasonable rotation and advocate the rotation of non-onion garlic crops for more than 2 years to reduce the source of the bacteria. 3 The correct field management is equally important: timely drainage, to ensure that it is not humid; timely ventilation. Planting density should be reasonable. 4 chemical control: spraying at the beginning of the disease. The medicine can be used with 47% spring Leiwang copper. The recommended dosage is 15-20 grams of water to 30 kg (the specific dosage varies according to the situation). Chunleiwang Copper is a compound low-toxic fungicide which is compounded with Chunleimycin and Wangtong. It has double bactericidal effect. The mixture has good permeability and strong adhesion. It can form a protective film on the surface of the onion and release copper ions under certain humidity conditions to play the role of sterilization and disease prevention. This article URL: Symptom map of disease and disease prevention methods Shaanxi Hongbaiyi Biotech Co., Ltd. , https://www.sxhongbaiyi.com