On July 21, 1998, at 0840 central daylight time (cdt), a Grumman G- 164, N698Y, piloted by a commercial pilot, was substantially damaged during a collision with trees, the roof of a house, and the ground while maneuvering for a forced landing. Visual meteorological conditions prevailed at the time of the accident. The 134 CR Part 137 aerial application flight was not operating on a flight plan. The pilot reported minor injuries. The flight departed Hoxie, Kansas, at 0835 cdt. According to the pilot, he felt "...that something was wrong..." during a turn a turn when the airplane was about 300-feet above the ground. He said he observed the airspeed indicator needle showing a loss of airspeed. As he maneuvered the airplane toward an area away from the town he was flying over the airplane lost altitude. As the airplane lost altitude and collided with trees next to a home that its landing gear struck. After hitting the home s roof, the airplane-nosed over as it collided with the ground. Witnesses reported hearing the engine miss as it flew past their location. The on-scene investigation revealed no mechanical anomalies with the airframe or engine that would prevent flight, except an inoperative left magneto. The Federal Aviation Administration Principal Maintenance Inspector s report is appended to this report. The pilot was splashed with encapsulated methyl parathion that was in the airplane s hopper tank during the ground collision. The trade name for this chemical compound is PENNCAP-M. A blood sample from the pilot was subjected to a toxicological examination at the Federal Aviation Administration Civil Aeromedical Institute located in Oklahoma City, Oklahoma. The examination showed the pilot had 0.006 ug/mL of Methyl parathion was detected in the sample. According to the manager of the Toxicological laboratory, this amount of chemical would not affect the pilot s performance.