We focus on the problem of controlling pointsource induced perturbations on an infinite swept wing using linear control theory. Based on wall measurements in a spatial simulation of localized disturbances in Falkner-Skan-Cooke boundary layers, an extended Kalman filter is used to estimate the full three-dimensional wave packet. The estimated field is in turn used to calculate a feedback control which changes the growth of the disturbance into decay. This is the first time that optimal control and estimation concepts are successfully applied to construct a dynamic output feedback compensator which is used to control disturbances in spatially developing boundary layers.