On July 15, 1996, at 1015 central daylight time (cdt), a Cessna A188B, N9703J, registered to W. L. S. Flying Service, of Litchfield, Illinois, was substantially damaged following a partial loss of engine power and subsequent forced landing in a farmer's field approximately 1/4 mile north of the Saint Charles County Airport, Saint Charles, Missouri. The commercial pilot reported no injuries. The 14 CFR Part 137 aerial application flight was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The flight departed from the Saint Charles County Airport, Saint Charles, Missouri, at 1005 cdt. According to the pilot's written statement, he loaded the airplane with 1,000 pounds of millet seed and 3/4 of a tank of 100 low lead fuel (40 gallons). The takeoff and climb out were normal. The pilot conducted three to four aerial application passes when he noticed that the airplane's engine "...was running smooth but with a definite loss of power." The pilot tried to climb over the tall trees but lost a lot of airspeed. The pilot stated, "At this point, the airplane was very difficult to control. I had to push full forward just to keep from stalling. The airplane never did stall, but because the plane was loaded, the landing was very hard." Before impact with the terrain, the pilot attempted to dump the load with out success. The pilot stated, "Everything seemed to happen in just a few seconds, and my main concern was to try to keep the plane flying." A Federal Aviation Administration (FAA) Principal Maintenance Inspector (PMI), represented the NTSB on-scene. The PMI inspected the engine and accessories. No discrepancies were found.