The pilot reported that immediately after touchdown he heard a “pop” or “snap,” at which point his left foot and the left rudder pedal moved fully forward to the firewall. Left rudder control was lost, and the airplane continued down the runway as the tail swung left. Unable to regain directional control, the airplane veered off the right side of the runway, ground looped, and sustained substantial damage to the left wing. A postaccident examination determined that the rudder bar assembly weld had failed at the attachment to the rudder pedal. The operator stated that the airplane is normally operated on wheel/skis, which require increased rudder pedal forces during ground operations. The operator also noted evidence of preexisting cracking along the weld that was not identified during the most recent maintenance inspection.