The pilot reported that while on takeoff roll with the wind calm, he noticed that the airplane had failed to gain enough speed to lift off. He then added throttle and attempted to dump the load, but the dump-stop prevented him from jettisoning the load. The pilot stated that at the very end of the runway the airplane lifted off, followed by the tailwheel impacting a small ridge, which slowed the airplane. The aircraft subsequently cleared a ditch and then started impacting young trees, with large trees directly in front of him. The pilot added that he then pulled the power off and landed in a field of young trees. The upper and lower wing panels were substantially damaged. The pilot stated that the accident could have been prevented had he made sure that the dump stop was flipped over prior to takeoff, which would have allowed the load to be dumped faster. The pilot also stated that due to the temperature having increased from what it was earlier that morning, he should have reduced his chemical load. The density altitude at the time of the accident was calculated to be about 2,042 feet mean sea level (msl); the elevation of the airstrip was about 90 feet msl. The pilot reported no mechanical malfunctions or failures with the airplane that would have precluded normal operation.