First, the symptoms Downy mildew usually begins with the lower leaves and begins to develop light green water-stained spots. The edges of the lesions are not obvious. Later, it develops yellow irregular lesions. When the humidity is high, the gray and white layer of the leaves grows and gradually becomes Dark gray. In the shed, the diseased leaves gradually turn yellow and dry when the drought occurs, and when the air humidity is high, the diseased leaves become rotten. Second, the law of occurrence Downy mildew is a parasite, and spinach downy mildew can only infect spinach. The germs use oospore to overwinter in the leaves of diseased plants or with mycelium on the host and seeds. The sporangia are produced in late spring, and the sporangia are matured and transmitted by airflow, rainwater or field operations. When the germination occurs, germ tubes or zoospores are generated and invaded from the stomata of the host leaves or the gap between epidermal cells. In the later stage of the disease, the downy mildew often produces oospores in the tissues, and with the diseased plant residues overwintering on the ground, it becomes the initial infestation source of the bacteria in the next growing season. The optimal temperature for sporangia germination is 7~18°C. In addition to temperature, high humidity is more important for the formation, germination, and invasion of pathogenic sporangia. In the onset temperature range, it is rainy and foggy, the air is humid or the humidity in the field is high, the planting is too dense, and the air and light transmission between the rows are poor, which are all likely to induce downy mildew. In general, the replanted plots and watersheds are too heavy and the disease is heavy. Third, prevention and control measures 1. Agricultural control. First, it takes 2-3 year rotation for serious disease fields. Apply sufficient organic fertilizer to improve the disease resistance of plants. The second is the rational close planting, scientific watering, flood prevention to prevent flooding, to prevent the spread of disease and water. Increase ventilation and reduce humidity. Third, if a diseased plant infected with Downy mildew is found, it must be removed in a timely manner and brought out of the field to be burnt or buried. At the same time, lime is used to treat the planting holes to prevent the spread of the disease. At the time of harvest, the stubble leaves are completely removed and taken out of the field to be buried or burned. 2. Chemical control. It can be sprayed with 75% chlorothalonil wettable powder 500 times in the early stage of the disease. When the disease is severe, it can be sprayed with 58% methasone zinc wettable powder 500 times or 69% zinc methacrylate zinc wettable powder 800 times. Spray once every 7 days, continuous control of 2 or 3 times, can effectively control the spread of downy mildew. At the same time, it can be combined with sprayed foliar fertilizers and plant growth regulators for better control. Conductivity Meter, Compact Conductivity Meter, Smart Conductivity Meter, Smart Portable Conductivity Meter INESA Scientific Instrument Co., Ltd , https://www.inesarex.com