Cucumber is a scientific name (Cucumis sativus) of the Cucurbitaceae family.The origin of this plant is related to south and east of Asia i.e, India and China . Cucumber cultivation has usually been around 5,000 years ago. The origin of this plant is not well known , But it is likely to be native to the tropical regions of Asia and Africa ,Because it has been cultivated for more than 3000 years as food in these areas .According to Murty and his partners, Cucumber spreads from India to the east (China) and to the west (to Asia Minor).According to data from the FAO (World Food Organization), Iran ranked 2nd in the world cucumber production after China.(Faostat, 2014). Powdery Mildew has been common in Iran since long ago,But for the first time in Iran, the written report on Esfandiari was in 1326.Powdery mildew is one of the most important diseases in the temperate and fairly dry areas.It is a common disease in all greenhouse crops. Surface contamination is caused by different species of mushrooms. Any one attacks one or two particular herbs and sometimes more. The pathogen is Sphaerotheca fuliginea.The disease is prevalent in most parts of the country and each year it causes significant damage to the product. Although the application of agronomic methods and the production of relatively resistant varieties can reduce the amount of powdery mildew , But the prevalence of the disease requires the use of chemical compounds to control it.