Abstract: Powdery mildew caused by Microsphaera alphitoides Griff. et Maubl. is a majorthreat affecting the survival and growth of oak regeneration. An experiment was performed in aQuercus robur L. naturally regenerated forest in northwestern Italy in order to assess theeffectiveness of sulphur and potassium dihydrogen phosphate against powdery mildew. Bothtreatments reduced significantly disease severity on seedlings compared to controls (p < 0.05).The best result was obtained with sulphur. An additional experiment was conducted by usingpotassium phosphite. Results suggest that these treatments may be suitable to control powderymildew in natural forests.