
The research evaluated the Fertigation with silicon in the severity of the powdery mildeo (Sphaerotheca pannosa var. Rosae) in three varieties of rose under greenhouse. The experiment was a split-split plot design with silicon doses (DS) as the main-plot factor: (DS1 = 3mgL-1), (DS2 = 6mgL-1) and (DS3 = 9mgL- 1); Fertigation (L) as the sub-plot factor: (L1 = 3 mm day-1), (L2 = 5 mm day-1) and rose varieties (V) as the sub-sub-plot factor: (V1 = Vendela), (V2 = Reed Unique) and (V3 = Miracle). There were differences (p≤0.01) due to the effect of SD (silicon dose), L (fertigation) and V (varieties); As well as the DS * L interaction (p≤0.01). DS3 applications reduced fungus severity (20%) while DS1 was less efficient (230%). Lower percentages of fungal severity were obtained with Fertigation L1 (130%) and while L2 had the higher (280%). Varieties V2 and V3 were less affected by fungus (170 and 160%) while V1 was more susceptible to it (320%). The DS3 dose and the L1 fertigation interaction reduced fungal severity (75%) (p≤0.05). The behavior of the Miracle and Reed Unique rose varieties with a 3-mm.day-1 fertigation and a silicon dose of 9mgL-1 could be key to decreasing the severity of Sphaerotheca pannosa var. Rosae in flower growing areas of Colombia.