The commercial pilot was spraying a field in his single-engine agricultural airplane when the radial engine's chip light detector illuminated followed by a rough running engine and subsequent loss of power. The pilot was unable to maintain altitude and made a forced landing to a narrow gravel road. As the plane touched down, the right wing contacted the tall rows of corn that lined the narrow road, which caused the airplane to ground loop and enter the corn field. Examination of the airplane revealed it sustained substantial damage to the fuselage, empennage, vertical stabilizer, and both wings. The loss of engine power was undetermined.