THE PILOT STATED THAT HE NOTED FROST ON THE WINGS BEFORE TAKEOFF, BUT FELT THERE WAS NOT ENOUGH TO BE CONCERNED. HE INITIATED A TAKEOFF ON A 2500 FT AIRSTRIP WITH A LOAD OF PARAQUAT AND WATER. THERE WAS A SLIGHT TAILWIND. HE STATED THAT DURING THE TAKEOFF ROLL, THE ENGINE DID NOT APPEAR TO BE DEVELOPING FULL POWER. HE ACTUATED THE DUMP HANDLE TO LIGHTEN THE LOAD, BUT STRUCK A 5 FT BANK NEAR THE END OF THE STRIP. AN EXAMINATION OF THE AIRCRAFT AND ENGINE REVEALED NO PRE-CRASH MALFUNCTIONS OR FAILURES EXCEPT CONSIDERABLE LEAD DEPOSITS ON THE LOWER SPARK PLUGS. HOWEVER, THE ENGINE OPERATED NORMALLY DURING A RUN-UP CHECK. THE PROPELLER CONTROL WAS FOUND POSITIONED LESS THAN HALF WAY FROM THE HIGH PITCH SETTING. THE PILOT STATED THAT HE EXERCISED THE PROPELLER CONTROL SEVERAL TIMES BEFORE TAKEOFF. HE INDICATED THAT HE MAY HAVE MISTAKENLY LEFT THE PROPELLER CONTROL IN A HIGH PITCH, LOW RPM POSITION.