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Powdery mildew is a common disease on the melon crops. It occurs on open field cultivation in the north and south of China, greenhouse cultivation, cucumber, pumpkin, summer squash, melon and other melon crops. Cucumber is the main victim, so the focus is on cucumber powdery mildew. (I) Pathogens and infestation of powdery mildew are caused by infection with powdery mildew or mono-filamentous fungi, belonging to the genus Erysiphe and monofilament of the subphylum Ascomycotina, among which monofilaments are mainly monofilaments. Shell is. Erysiphe graminis has two main characteristics. One of them is an obligate parasite, that is, it can only absorb nutrients in the living host. When the host ages, it develops into a closed-capsule shell. "It is. The other major feature is the external parasitism, that is, its mycelium does not invade the human body growth and development, but only the formation of the suction device, sucking host nutrition, growth, development, reproduction are on the surface of the host tissue. Due to the above characteristics, it is completely different from other pathogenic infections. It is not the first occurrence of the disease, but the first sighting of the pathogen, but the first sight of the pathogen, and finally the occurrence of traces on the host tissue. Its morphology is also different from that of other bacteria. It produces conidiophores on the surface of the host and produces a string of conidia on the stem. Like many common cucurbits (hawthorn bunches), many of these conidia have matured. Scattered and floating everywhere, it becomes its infecting and spreading body and falls on the surface of the host organization. Germination produces hyphae, and then a suction device is inserted into the host tissue for nutrient absorption. The hyphae grow and develop on the surface of the host tissue and produce conidial stems and conidia. At the late stage of the parasitic growth, the climate became cold and the temperature became smaller. The conidia produced closed crust shells, which were left over in winter in the fields. At the end of the second year in the late spring and early summer, when the temperature rose above 20°C, it was released from the capsular sac by capsular spores, spread by the airflow, and landed on the surface of the host. Another one-year host life began. Erysiphe graminis mainly invaded the leaves of cucumbers. On the host leaves, most of the growth and development stages of the cucumbers absorbed the nutrient of many leaves. At the same time, the host leaves also reached the later stage of development, so the yellow leaves were early. During the cycle of infection, plastic greenhouses and greenhouses become good "transit stations" and "campsites" for powdery mildew. The main factors affecting the incidence of powdery mildew are temperature and humidity. The temperature of spore germination is 10-30°C and the optimum temperature is 20-25°C. As a humidity condition, the powdery mildew is rather special and it does not require as much relative humidity as other fungi. The opposite is true. Larger humidity (for example, in the presence of water droplets) instead causes the spores to swell and rupture. Loss of life, its suitable relative humidity is 35-45%. Therefore, the requirements for temperature and humidity of powdery mildew are: neither cold nor hot nor dry or wet. In addition, the growth and development of powdery mildew requires shading scattered light or weak light and a young, leggy host. (II) Micro-pollution and pollution-free prevention and control techniques 1. Selection of disease-resistant varieties In the prevention and treatment of powdery mildew, the selection of disease-resistant varieties is consistent with the resistance to downy mildew. In other words, under normal circumstances, the resistance to downy mildew is also resistant to powdery mildew, and its main goal is to choose thicker leaves and thicker cell wall varieties. 2. Creating disease resistance conditions includes widening the row spacing, increasing ventilation and light transmission conditions, increasing phosphorus and potassium fertilizers, and controlling plant leggy. 3. The environment fumigation of spores of powdery mildew spatters and adheres to the space around the diseased plants. It is very prone to attack in greenhouses and greenhouses in autumn and winter. Powdery mildew is particularly sensitive to "sulphur", so it can be per 1000 square feet (nearly one and a half minutes). With sulfur powder 0.3-5 kg ​​plus sawdust or other combustion ignited fumigation, sealed smoked stuffy day and night, you can kill the powdery fungus, smoked stuffy again every 3 days, and then sowing or planting. During the growth of cucumber, the sulfur powder can be reduced by half, the time can be reduced to one night, and once again smoked once every 5-7 days. The effect is good. 4. Chemical control When the central diseased plant occurs in the field, it is necessary to promptly spray and control, and 50% thiophanate-methyl wettable powder 1000 times liquid or 75% chlorothalonil wettable powder 500-600 times liquid can be used, every 5 - Sprayed once every 7 days, according to the Tianjin Academy of Agricultural Sciences, the 30% 90% dipoxysteroids have good control effect and 800 times solution has therapeutic effect. Alternating use of pesticides can avoid the resistance of powdery mildew. Do not ignore spray on the ground when spraying. Japan's experience of spraying 4000 times of Bleiton is very good. Spraying 4000 times of Bayerton + 1000 times of chlorothalonil works well, and it can also treat other fungal diseases occurring in the same period.