On May 31, 2018, about 1115 central daylight time, a Thrush Aircraft S2R-H80, N6215P, received substantial damage during a runway excursion during takeoff on runway 18 from a private airstrip near Parkin, Arkansas. The pilot was not injured. The aircraft was registered to Mid Continent Aircraft Corp and operated by Air Aids, Inc., under the provisions of Title 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which was operated without a flight plan. The local flight was originating at the time of the accident. The pilot reported that during the takeoff roll the right rudder pedal went all the way forward. Since the airplane was equipped with toe-brakes, once the pedal was all the way forward against the material hopper, he had no way to maintain directional control of the airplane. The pilot attempted to stop the airplane using reverse pitch on the propeller, but the airplane went off the east side of the runway and struck a ditch. Examination of the airplane after the accident revealed that the rudder pedal adjustment mechanism consisted of a track that allowed the rudder pedal shaft to move fore and aft, with a detent pin that engaged holes in the track. The track was equipped with a safety stop bolt to prevent the rudder pedal shaft from travelling too far forward and exiting the end of the track. The track assembly for both the left and right rudder pedal showed wear on the track and the stop bolt installed forward of the most forward detent position. The right adjustment track had a semi-circular section worn completely through that matched the shape of the rudder shaft. This was consistent with the rudder shaft being stopped by the stop bolt rather than being locked in the forward detent position. Determination of how long the rudder system had been used in this manner could not be determined. The "Before Starting Engines" checklist current at the time of the accident contained the instruction "Rudder Pedals – ADJUST and LOCK". Review of the airplane maintenance records showed that the airplane had accumulated 991 hours time in service as of its most recent annual inspection dated December 29, 2017. The airplane manufacturer released a Service Letter, SL-AG-126, on June 11, 2018, entitled "Rudder Pedal Mechanism Inspection", detailing proper use, rigging, and maintenance of the rudder system, including the rudder pedal adjustment mechanism.