On August 25, 2000, at 2000 central daylight time (cdt), an Air Tractor AT-401, N91842, operated by a commercial pilot, was destroyed when it struck a tree and the terrain, during an attempted forced landing on an alfalfa field. Prior to the forced landing, the airplane's engine lost power, while the airplane was maneuvering. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was being conducted under 14 CFR Part 137. There was no flight plan on file. The pilot sustained no injuries. The local flight originated at Superior, Nebraska, at 1930 cdt. In his written statement, the pilot said he was spraying a milo field, 3 miles southeast of Superior, Nebraska. While in a turn to south, "the engine started to sputter and miss. Smoke started coming out of the left hand side of the engine ... a substantial power loss followed." The pilot turned the airplane to the north and attempted to put down in an alfalfa field. During the landing attempt, the airplane struck some hay bales and a tree. A Federal Aviation Administration inspector, examined the airplane at the accident site. The airplane's wings were broken aft from the fuselage. The engine and hopper were broken off the front of the airplane. The main landing gear were broken aft. The fuselage was twisted and buckled. The empennage was intact. Flight control continuity was confirmed. An examination of the engine revealed a cracked exhaust valve on the number 7 cylinder. No other anomalies were found.