Powdery mildew remain among the most important pathogenic fungi in greenhouse vegetable production, and are the cause of extensive fungicide use in European horticulture. Although the underlying mechanisms are not known, the ability of soluble silicon (Si) to reduce the impact of powdery mildew infection on several greenhouse crops has been amply described. Still, the use of Si in greenhouse production is very limited. one major reason for this is the challenge associated with the standard form of application, which is amendment to soil or nutrient solutions. In the present study, foliar applications of two commercially available silicon (Si) based products were evaluated for their effect in reducing powdery mildew development in commercial greenhouse cucumber production.