According to the helicopter pilot, he was completing north-south herbicide spray patterns with winds varying from the east to south at 4 to 5 mph. As the pilot positioned the helicopter for the next northern track, he "began to feel the aircraft start to lose altitude after the turn." The pilot stated that he tried to regain control by pushing forward the cyclic and lowering the collective to "get out of the settling with power." When ground contact was imminent, he raised the collective to cushion the impact. The helicopter touched down, spun, and rolled onto its left side. Post-accident examination by a Federal Aviation Administration inspector revealed substantial damage to the tail boom. The pilot stated that there were no pre-impact mechanical malfunctions.