The research was carried out during a three years experimental period, 2012 – 2014, within an experimental plot populated by oak trees of different ages, located in the Forestry Direction Reghin, County of Hunedoara. The evolution of the climatic factors, and attack degrees of Forestry Direction Reghin, County of Hunedoara and powdery mildew was monitored. In the end of the experimental period, one may find that while the mean values of the climatic factors exhibit discontinuous evolutions, the attack degrees of the progressively increased from the year 2012 to 2014, from 39.67% to 44.43% for the European oak leaf roller, while for the powdery mildew it increased from 20.23% to 26.93%.