THE PILOT MADE AN AERIAL APPLICATION SWATH RUN TOWARD RISING TERRAIN, INITIATED A TURN AROUND MANEUVER, DIVERTED HIS ATTENTION TO KEEPING THE SPRAYING AREA IN SIGHT AND THE ACFT LOST AIRSPEED. HE APPLIED FULL POWER AND ATTEMPTED TO DUMP THE CHEMICALS BUT WAS UNABLE TO DUMP THE LOAD BEFORE THE ACFT IMPACTED A HILL.