The right spray boom from the tailwheel equipped agricultural airplane became entangled with tall wheat while landing on a narrow gravel airstrip. The 2,236-hour commercial pilot, who reported having accumulated a total of 128 hours in the same make and model of airplane, lost control of the airplane resulting in a ground-loop. The aft section of the fuselage sustained structural damage. The turbine powered airplane came to rest in an upright position and the pilot was able to exit unassisted. The wheat was displaced approximately four feet from the airstrip's left edge and was growing adjacent to the right edge. Earlier that day, the pilot reported that he had observed wheat entangled in the right spray boom following two previous landings on the same airstrip. An examination of the airplane's right wheel at the accident site revealed that it was free to rotate and that the right brake was not dragging. The wind velocity at the time of the accident was reported between 1 to 3 knots.