The pilot reported that he was spraying a potato crop and had 150 litres of chemical on board. Weather conditions were fine with a south easterly wind of three to five knots. He commenced his first run which was in a westerly direction and uphill. At the end of the run he switched off the spray and commenced a left climbing turn to avoid a nine metre high hedge with a house behind. The aircraft did not respond to control inputs and started to head for the hedge. The pilot managed to avoid the hedge but said the aircraft felt "mushy" and started to go down. The aircraft hit the ground and rolled over. The pilot did not claim there was any fault with the engine. He had been flying a more powerful turbine powered helicopter until recently when he was endorsed on the Hughes 300. He had limited experience on the aircraft type at the time of the accident.