On July 17, 1995, about 0720 central daylight time, a Cessna A188B, N731NP, registered to Kimmel Aviation, Inc., collided with a ditch while moving with no one on board at Aberdeen, Mississippi, while on a 14 CFR Part 137 aerial application flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot, who was not onboard at the time, was not injured. The flight was preparing for departure at the time of the accident. The pilot stated he started the engine and taxied to the chemical loading area. While the engine was left idling he placed the loading hose in the aircraft's hopper. He got off of the aircraft to start the chemical pump. The engine suddenly began to increase in rpm and the aircraft started to move. He attempted to catch the airplane but could not. The aircraft collided with a ditch and came to rest. Postcrash examination revealed the throttle cable had broken. According to the operator the throttle arm on the carburetor is spring loaded to the full throttle position.