At 1256 mountain time, a Piper PA-28-181 lost aileron control in flight and was damaged in a resulting emergency landing. The pilot was not injured. The pilot said he was practicing maneuvers for his commercial certificate and attempted to make a clearing turn when the ailerons failed to respond. He declared an emergency and landed on a dirt road, using rudder and throttle to control the airplane. After landing, the right wing struck a tree. An FAA investigator found a fastener on the floor that attaches the left control wheel to the control column. When the column was moved, the ailerons worked normally.