On July 21, 2008, approximately 1430 central daylight time (CDT), a Piper PA-36-285, N57601, was substantially damaged upon impact with terrain during a forced landing due to a partial loss of engine power on initial takeoff. The commercial pilot, the sole occupant, was not injured. The airplane was registered and operated by Bertrand Spraying LLC. Visual meteorological conditions prevailed and a flight plan had not been filed for the 14 CFR Part 137 aerial application flight. The local flight, which was originated at the time of the accident, departed an unregistered airport three miles east of Petersburg, Texas. The pilot reported he never got full power during takeoff roll and that he experienced an additional partial loss of power shortly after takeoff before crashing less than one mile southeast of the airport. The Part 137 Chief Supervisor was at the departure airport and observed the airplane stall just before it impacted on its nose and then came to rest upright. The operator reported that, at the time of the accident, the airplane had accumulated 3,415 hours total time, with an engine total time of 2,097 hours. The most recent annual inspection had been performed on May 15, 2008; the airplane had flown 103 hours since that inspection. The engine was removed from the airplane and examined on October 15, 2008. The throttle body "butterfly" valve had sooting consistent with back firing of the engine and was contaminated with an accumulation of impacted dirt. The top mounting lug on the left magneto was worn excessively and a non-standard piece of metal had been inserted as a spacer under the mounting lug. The left magneto had evidence of oil seepage within the magneto and there was evidence of oil in the area around the points in the right magneto. Several of the spark plug electrodes were "excessively worn" in accordance with industry guidelines. The engine driven fuel pump had a ruptured seal and oil contamination was found in the area between the accessory case and the fuel pump. Corrosion, contaminants, and evidence of previous water contamination were observed in the airframe fuel filter, fuel pump, fuel screen and flow divider. The wreckage was released to the owner.