The role of raw cow's milk and whey (40 and 50% dilution in water) and number of sprays against cucumber powdery mildew caused by Sphaerotheca fuliginea was studied in greenhouse experiments during 2017/18 and 2018/19. As a result of number of sprays, the disease severity percentage and area under the disease progress curve (AUDPC) were affected by the number of sprays with raw milk and whey. The number of sprays played an important role in controlling powdery mildew, and significant differences have occurred among all applied sprays. Four sprays with intervals of one week was the effective treatment in reducing disease severity, AUDPC values, compared to other treatments, i.e., two and three sprays in comparison to the fungicide as well as a control treatment. Additionally, treated plants showed a significant increase in plant growth and yield parameters in case of spraying four times. Also, the activity of defense-related enzymes (catalase, peroxidase, and polyphenoloxidase) and amino acid proline was high in response to increasing the number of sprays at four times compared with untreated plants. Light and scanning electron microscopic observations showed a clear change in the morphology of S. fuliginea spores, in addition to hyphae degradation and loss the vitality of conidia as well as rupturing the content of conidia. The results obtained also indicated that cow's milk and whey dilution effectively reduced the powdery mildew signs and symptoms on infected cucumber plants at 50% with the four sprays treatment being the most effective treatment.