To investigate the effects of silicon on the growth characteristics and the reduction of the powdery mildew damage to Zinnia (Zinnia elegans Jacq. ʻMagellanʼ), an experiment was carried out as a factorial experiment in the form of a randomized complete block design with two factors including eight treatments and three replications. The first factor included silicon concentrations at four levels (0, 50, 100, 150 mg L-1 Si) and the second factor consisted of the Si application methods (foliar spray and medium drenching). Depending on the concentration and method of silicon supplied, several horticultural traits were improved as a result of Si supplementation. Silicon content of Si-treated plants (100 and 150 mg L-1 Si foliar spray) significantly increased as compared with untreated controls. Disease severity of powdery mildew was reduced by sodium silicate. The results of our study demonstrated that foliar spray treatments were more effective in managing disease than drenches treatments. پرونده مقاله