The pilot reported that, during a practice agricultural application flight with water, after overflying the field, he pulled up hard to avoid a tall tree. He leveled out for about ¾ of a mile to build airspeed and initiated a turn to overfly the field again. During the turn the airplane began to buffet, and the pilot knew it was a "pending stall." He pushed the stick forward, descended, so he pulled back on the stick again and the airplane buffeted again. He pushed the stick forward again, the main landing gear tires contacted the ground and the airplane became airborne again. The airplane approached power lines, the pilot banked left, the airplane "lost air speed" and aerodynamically stalled, and impacted the ground. The airplane sustained substantial damage to the left and right wing. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The automated weather observation station, located about 4 miles east of the accident site, reported that, about 5 minutes after the accident, the wind was from 270° at 4 knots. The pilot reported that after he exited the airplane, he realized that there was a tailwind at an estimated speed of 10 to 15 mph. The pilot was flying to the east.