Salicylic acid (SA) and Sil-Matrix 29% SL (SM) (potassium silicate, potassium salt of silicic acid) were used to manage white rot of onion caused by Sclerotium cepivorum Berk. at the rate of 1, 2 and 3mM of SA and 1.5, 3 and 6ml/L of SM as transplants dipping followed by foliar spray by the same concentrations at 6 and 12 weeks from transplanting under greenhouse and open field conditions. The fungicide folicure 25% EC (Tebuconazole 25%) was used as comparison. All treatments reduced white rot infection compared with non-treated plants either in greenhouse or field. SA at the rate of 3mM gave the best reduction where it gave 35.0% and 26.0% infection under greenhouse and field respectively. The best treatment of SM was 6ml/L which gave 45% and 38.2% infection under greenhouse and field respectively. Compared to non-treated plants, all treatments increased onion yield, bulb weight, and plants height. SA at the rate of 3mM gave 144.3% and 160.4% increase in yield and bulb weight respectively, while SM at the rate of 6ml/L gave 24% as best increase in plants height. Soluble protein, free amino acids, reducing sugars, phenolic compounds, peroxidase and polyphenol oxidase activity increased after dipping while it varied after spraying.