The pilot of the aerial application airplane stated that he was about 200 feet above ground level and was lined up about one-half mile from the field he was going to spray. He set a descent angle to clear powerlines. Approximately 30 feet above the crop he began to level off and engaged the spray handle. He said, "I felt the aircraft start to load the wings and then just give-way." The airplane descended into the crops and sustained substantial damage. The pilot reported no mechanical malfunctions with the airplane reference the flight. His safety recommendation stated that if a shallower approach angle was used or if the level off maneuver was started higher, the accident may have been prevented.