WHILE PRACTICING THE PICKUP PHASE OF A BANNER TOWING OPERATION, ON A PRIVATE STRIP, IN CONWAY, SOUTH CAROLINA, THE PILOT LOST CONTROL OF THE AIRCRAFT AND COLLIDED WITH A DITCH. THE PILOT STATED THAT HE HEARD A 'POP'. THE AIRCRAFT THEN ENTERED A STEEP NOSE DIVE. THE PILOT ALSO STATED THAT HE HAD LOST ELEVATOR EFFECTIVENESS. THE DIVE SHALLOWED OUT BEFORE THE AIRCRAFT COLLIDED WITH A DITCH AND NOSED OVER. THERE WERE NO MECHANICAL PROBLEMS FOUND WITH THE AIRCRAFT.