The pilot had planned to fly the foreign registered aircraft to Miami, FL to visit the Venezuelan Consulate's office before continuing on to Venezuela. The aircraft was modified with an auxiliary fuel tank in the hopper. Also, authorization was obtained to carry extra weight to ferry the plane. Before takeoff, the plane was fueled to 6600 lbs, 600 lbs over the limit for agricultural operations. After takeoff, the pilot remained in the pattern and made 3 landings. On the fourth takeoff, the aircraft entered a spin and crashed. Two witnesses, who were pilots, reported that the plane seemed to be near a stall while in the traffic pattern. They reported that on the last takeoff, the plane was in a nose high attitude, began a shallow turn, then entered the spin. One estimated the spin began at 300 ft, the other witness estimated it began at 400 ft. Another pilot landed about 15 minutes after the accident. He reported wind shear and turbulence in the pattern. No preimpact discrepancies were found with the aircraft or engine.