On June 13, 1999, at 1000 central daylight time, a Bell 47G-3B-1, N64292, sustained substantial damage during a forced landing following loss of engine power. The accident occurred in a crop field, near Austin, Minnesota. The commercial pilot reported no injuries. The aerial application 14 CFR Part 137 flight was operating in visual meteorological conditions. No flight plan was on file. The local flight departed about 0945. The pilot said that the engine "overspeeded" and then quit completely. He said that he was conducting a swath run at the time and the helicopter was flying about 40 MPH at an altitude of 5 to 10 feet above the ground. He said he attempted to make a run-on landing; however, the skids dug into the soft terrain and the helicopter nosed down. He said then the main rotor blades cut through the tail boom. He could not account for the power loss. The owner had recovered the helicopter to his facility prior to notifying the NTSB of the accident. A post accident examination of the engine, transmission, clutch, and airframe failed to reveal any pre-accident anomalies. There was fuel present in the tank. Fuel filters and strainers were checked and found to be clean. The engine was started and ran. Oil pressure, fuel pressure, and manifold pressure showed indications. A magneto check was conducte4d and both magnetos functioned. The clutch was engaged and found to function. Control continuity was intact except for impact damage and functioned when activated.