On July 30, 2002, at 2050 central daylight time, a Cessna A188B, N9639G, operated by Ellinwood Flying Service, was substantially damaged during a forced landing following a loss of engine power while spraying an agricultural field. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 aerial application flight was not operating on a flight plan. The commercial pilot reported no injuries. The local flight originated from the Rice County Municipal Airport (LYO), Lyons, Kansas, at 2020. The pilot reported he was finishing spraying a field when he "encountered an unscheduled power rollback." He executed a forced landing to an alfalfa field since the available power was insufficient to sustain flight. During the landing roll the airplane impacted a berm and received substantial damage. The inspection of the airplane's fuel system revealed the fuel strainer was blocked with a black rubber like substance. The fuel truck that fueled the airplane was checked for contaminates. The same type of substance that was found in the airplane's fuel filter strainer was found in the tank of the refueling truck.