CROP DUSTER FLEW WRONG PATTERN AND CUT OFF AN ACFT ON FINAL APCH CAUSING NMAC.

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LNDG RBL; CA; FLT OF 2. ENTERED R BASE TO RWY 15 AS OTHER TFC WAS APCHING FROM FAR SIDE OF FIELD RPTING 5 MI S. MY FLT WAS 4 MI N. I CALLED FINAL AND SHORT FINAL FLT OF 2. I LANDED AND CLRED AND LOOKED BEHIND TO SEE A YELLOW CROP DUSTER TYPE TOUCHING DOWN BEHIND ME AND AHEAD OF MY SECOND IN FLT. #2 IN FLT HAD TO MAKE A GAR. A CROP DUSTER PLT CAME VERY CLOSE TO MY PARTNER AND CAME AROUND IN A SHARP S-TURN TO LAND BEHIND ME. I TALKED TO THIS PLT AND HE WAS VERY INDIGNANT TO ME. WE STAYED AND ATE LUNCH WHILE THE CROP DUSTER FLEW ONTO ANOTHER TOWN. BOTH I AND THE CROP DUSTER HAD 2-WAY COMS WITH RED BLUFF RADIO. I FEEL THAT THIS PLT WAS AWARE OF OUR PRESENCE AND INTENTIONALLY FLEW AROUND MY PARTNER. SUPPLEMENTAL INFO FROM ACN 267916: I WAS BELOW HIM BY 10 FT AND BEHIND HIM BY ABOUT 10 FT. I ASKED HIM IF HE SAW ME DOWN UNDER HIM. NO RESPONSE. AFTER A FEW SECONDS; HE LEFT AND FLEW WAY WIDE. I THOUGHT HE WAS LEAVING. HOWEVER; HE CAME BACK AT ME FROM THE OTHER SIDE -- KIND OF AN S-TURN AND THEN LANDED. I DID A GAR. DURING MY GAR I ASKED THE RED BLUFF FSS FOR A RADIO CHK. IT WAS LOUD AND CLR.