On August 6, 2005, at 1900 central daylight time, a Grumman G-164, N636U, was destroyed by impact with the terrain and post impact fire during a forced landing after a loss of power during takeoff from runway 30 at the Marshalltown Municipal Airport (MIW), Marshalltown, Iowa. The pilot received minor injuries. The 14 Code of Federal Regulations Part 137 aerial application flight was departing MIW on a local flight. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed. The pilot reported that he completed the sixth spray load of the day and he landed at MIW to refuel and take on chemicals. He reported that he topped off the fuel tanks and loaded about 115 gallons of pesticide water mix. He reported that he taxied to the end of runway 30 and performed an engine run-up and control check. He reported that the airplane was functioning normally when he departed. He reported that at approximately 100 feet above ground level (agl) at the departure end of the runway, the engine began to lose power. He reported that he did not have enough power or altitude to perform a 180-degree turn back to the airport, nor was he in a position to make it to a road for an emergency landing. He reported, "I dumped the load and landed in a corn field just west of the airport. After the airplane came to a rest, it caught fire. I exited the left side door and walked to the road." The airplane was consumed by fire. A witness reported that he observed the airplane during the takeoff. The witness reported that he heard the airplane's engine sputtering and backfiring as it banked to the west. He observed the airplane go down and he heard the impact. A Federal Aviation Administration airworthiness inspector examined the airplane. He reported that the fire damage to the engine precluded an inspection of the engine's ignition and fuel system.