During a Christmas tree harvest the pilot was repositioning the trees from the harvest field and placing them into the bed of the load truck using an 18-foot tag line. He had completed at least five loads prior to the accident load. On the accident load the pilot had just released the load into the truck when he felt the helicopter was encountering a settling with power condition. The pilot attempted to maneuver the helicopter to land on the road in front of the load truck. The pilot thought he was clear of the truck when the main rotor blades hit the truck just above the cab. The helicopter impacted the ground and the main rotor blades separated the tail boom. The pilot reported no preimpact mechanical malfunctions or failures with the helicopter or engine, which would have precluded normal operations.