On August 6, 2008, approximately 0700 mountain daylight time, a Grumman G-164A, N7487, registered to and operated by Doyles Ag Services, and piloted by a commercial pilot, was substantially damaged when it nosed over on soft terrain following a loss of power while maneuvering near Walsh, Colorado. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 137 without a flight plan. The pilot was not injured. The local flight originated from Springfields (8V7), Colorado, approximately 0630. The pilot said he was spraying a corn field southeast of Walsh. As he was making an aerial application pass, a cylinder on the engine cracked --- "blew a cylinder" --- and the engine lost power. The pilot made a forced landing in a nearby field. The airplane crossed a road at a speed of approximately 25 mph and the tail bounced up in the air. After crossing the road, the main tires settled into soft earth and the airplane nosed over. In addition to a bent propeller and "minor top wing damage," the vertical stabilizer was crushed.