On July 17, 1993, at 2100 central daylight time (CDT), an Aero Commander S2R, N5635X, registered to Mid Continent Aircraft Corp., Hayti, Missouri, sustained substantial damage in a forced landing near Hoople, North Dakota. The airplane experienced a partial loss of engine power while the pilot was conducting aerial application operations under 14 CFR Part 137. Visual meteorological conditions prevailed at the time and no VFR flight plan was filed. The aircraft was substantially damaged and the commercial pilot was not injured. The flight originated at St. Thomas, ND, at 2040 CDT. The pilot stated the engine began to run rough during a spray run. He said he released the load and attempted to make a landing on a nearby road, but did not have sufficient power to make it to the road. He landed in a wheat field, and the airplane nosed-over during landing roll. The examination of the engine revealed the number 3 cylinder was cracked.