On September 15, 2005, about 1830 central daylight time, a Bell 206B, N2995W, piloted by a commercial pilot, sustained substantial damage during a forced landing following an uncommanded right rotation near Elk Point, South Dakota. The 14 CFR Part 137 aerial application flight was operating in visual meteorological conditions without a flight plan. The pilot was not injured. The local flight was originating at the time of the accident. According to the pilot's written statement, he had departed from the shoreline of the Mississippi river into a 2 to 3 mile per hour wind. He stated that when the helicopter was about 100 feet in altitude, 100 yards from the shore, and indicating over 50 miles per hour, a slight right turn was initiated. He stated that full left pedal input would not stop the right turn. The pilot elected to return to the shore. He stated that as he approached a flat area, he felt that he would not be able to reach the intended landing area and attempted to turn back toward the river. He said that the left rear skid contacted the sloping ground and the helicopter slid down the slope and cam to rest on its left side. Examination of the helicopter subsequent to the accident failed to reveal any anomalies. Continuity of the tail rotor drive and control systems were confirmed. A maintenance record entry dated September 14, 2005 indicated that the tailboom had been replaced. Determination of proper rigging of the tail rotor could not be determined due to bending of the tail rotor control push-pull tubes from impact forces. The pilot reported unlimited visibility, a temperature of 70 degrees Fahrenheit, and south winds at 2 to 3 miles per hour.