Isolation trials from infected sage seedlings and plants, growing in Ismailia, North Sinai and Qalubyia governorates, showing symptoms of damping –off and root rot diseases yielded Fusarium oxysporum, F. solani, Macrophomina phaseolina, Pythium ultimum and Rhizoctonia solani. However, R. solani recorded the highest frequency in isolation (52.6%), followed by Fusarium solani (24.6%), while M. phaseolina was the least (3.5%). These fungi were found to be pathogenic to sage seedlings. Rhizoctonia solani followed by F. solani were the most virulent fungi, causing the highest damping – off incidence. Three silicon (si) sources, i.e. calcium silicate, potassium silicate and sodium silicate with four concentrations (25, 50, 100 and 200 ppm) significantly inhibited the in vitro growths of R. solani in different degrees. Potassium silicate was more effective than the other silicon sources tested, and completely inhibited mycelial growth at 200 ppm. Soaking seeds (30 min.) and /or dipping treatment for seedlings (30 min.) in each of these silicon sources (400 ppm) or the fungicide Vitavax /Thiram (3 g/l water) gave sufficient control to R. solani diseases, i.e. damping –off in greenhouse and nursery as well as root rot in the field .Also, they recorded significant increases in growth parameters of seedlings (height & root length) and mature plants (height & no. of branches /plant). Potassium silicate, however, was significantly the most effective treatment among other silicon sources. Using calcium silicate and potassium silicate as dipping treatment for seedlings, gave significant increases in yields of fresh herb and essential oil content. Vitavax /Thiram treatment in the nursery and field experiments was more effective than silicon treatments, except with potassium silicate in the field, which increased fresh herb weight per plant and essential oil content than the fungicide.