While returning to the airport after completing an aerial application, the pilot noticed a reduction in engine rpm and a rise in oil temperature. The pilot was unable to maintain altitude and he elected to execute a forced landing on a road. During the forced landing, the left wing contacted a tree and pivoted the airplane into trees. Postaccident examination of the airplane showed both wing spars and the right elevator were bent. Based on his observations during the engine failure and his past engine failure experience, the pilot suspected the main bearing failed within the engine. The engine was not disassembled for further examination and the cause of the engine failure was not determined.