While conducting spraying operations, the aircraft hit a single wire earth return (SWER) power line. The power line contacted the propeller and proceeded to wrap about the propeller hub. The power line was pulled taut by the aircraft, the pilot lost control, and the aircraft impacted the ground 1,000 metres beyond the point of wire contact. The lateness of the day combined with low overcast is believed to have contributed to the pilot's inability to detect the wire in his flightpath. During the impact sequence, the underfloor framework with the attachment points for the seat and seat belt appear to have distorted altering their geometry. This in turn may have allowed sufficient movement of the pilot against the loosened restraints for his head to contact with the instrument panel. As he was wearing a helmet at the time, the sequence resulted in severe concussion and not a more serious head trauma.