Powdery mildew (Erysiphe alphitodides Griffon & Maubl.) infection has become a big problem. Especially amongst young pedunculate oak and sessile oak trees in Slovenia and around the world. In an attempt to prevent powdery mildew growth, we have experimented with two different sprays (Vitisan and Plantonic) to protect oak trees. We set 20 experimental plots in the Krakovski gozd forest. Five of them were control plots and hence no spray was used. Five were sprayed with Vitisan, five sprayed with Plantonic and five sprayed with both Vitisan and Plantonic. Forty seedlings were randomly selected for evaluation of damage from powdery mildew and the seedlings height was recorded. Evaluating our results showed that there were statistically significant differences in the level of infection on the leaf surface and in the relative height increment of sprayed and unsprayed seedlings. Sprayed seedilings were less infected and relatively higher than control. The use of both Vitisan and Planonic preparations together proved to be a successful combination.
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