The fungal agent Microsphaera alphitoides is one of the main agents responsible for degradation of oak ecosystems in Moldova. The development and spread of the oak powdery mildew in the researched areas occurred during two stages of leaves infestation (primary infestation, in spring, through ascospori and secondary infestation, in summer, through conidia), directly depended on meteorological parameters and the presence of the source of infestation. The meteorological conditions in 2018 allowed the spread of the disease in oak stands, especially during the secondary infestation, when leaf infestation with the fungus mycelium was at medium level (inside the experimental surfaces) and reached a medium to strong level of infestation on trees at the forest edge. The high susceptibility of oak trees to this disease requires development of strategies to reduce the risk of "powdery mildew".