THE ACFT WAS DAMAGED IN A FORCED LANDING AFTER ITS ENG LOST POWER DURING PULL-UP FROM THE LAST (CLEANUP) SWATH RUN. APRX25 MIN BEFORE THE ACDNT FLT, THE PLT LANDED TO RELOAD WITH CHEMICALS. THE OWNER STATED THAT WHEN THE PLT WAS ASKED IF HEWANTED FUEL, HE SAID 'NO' BECAUSE HE HAD 10 TO 12 GAL WHICH HE CONSIDERED TO BE ENOUGH TO FINISH THE SPRAYING OPERATION FOR THE DAY. THE PLT STATED THAT HE MADE SVRL LANDINGS DURING THE DAY TO REFILL THE HOPPER. THEN WHEN HE WOULD TAKEOFF, THE ENG PROVIDED FULL POWER (2775 RPM); HOWEVER AFTER MAKING SVRL SWATH RUNS, HE NOTED THAT THE ENG WOULD ONLY PROVIDE 2500 RPM DURING PULL-UPS. DURING PULL-UP ON THE LAST CLEANUP RUN, THE ENG DID NOT RESPOND WHEN FULL THROTTLE WAS APPLIED. POWER WAS NOT RESTORED & THE ACFT STALLED & FELL TO THE GROUND. APRX 31 MI NE AT WATERTOWN, SD, THE TEMP & DEW POINT AT 1951 CDT WERE 77 & 64 DEG, RESPECTIVELY. ACCORDING TO ICING PROBABILITY CHARTS, CONDITIONS WERE CONDUCIVE TO CARBURETOR ICING.