WHILE EXECUTING AN AERIAL APPLICATION TURN-AROUND MANEUVER, THE PLT SAID THAT THE POWERPLANT SEEMED TO LOSE POWER. THE ACFT STALLED, COLLIDED WITH THE TERRAIN, SLID TO A STOP, THEN BURST INTO FLAMES. METEOROLOGICAL CONDITIONS WERE CONDUCIVE FOR CARBURETOR ICING AT THE TIME, AND POST ACCIDENT ENGINE INSPECTION FAILED TO REVEAL ANY MECHANICAL MALFUNCTIONS.