On July 22, 1993, at approximately 1200 central daylight time, an Air Tractor AT 301, N3650U, was substantially damaged when it struck trees during a forced landing near Garner, Arkansas. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the aerial application flight. During an interview conducted by a Federal Aviation Inspector and in a written statement, the pilot reported that he heard a loud bang, followed by severe engine vibrations. He further reported that he just completed an aerial application pass over a cultivated field. During the subsequent forced landing, the pilot attempted to shut down the engine but it continued to run. He related that he was unable to slow down enough to land and flew into the trees at about 20 feet above ground level, prior to ground impact. Examination of the airplane by the FAA inspector revealed that a 20 inch section of one of the propeller blades had separated in flight for undetermined reasons. A review of the airplane's maintenance records revealed that the engine received a major overhaul on January 31, 1990. The engine and Hamilton Standard propeller (s/n 2176) was installed on N3650U on February 23. The records did not indicate the overhaul date or total time on the propeller.