The pilot was involved in spraying operations and this was his first takeoff for the day. The strip was 700 m long, covered with 30 cm long grass and ran downhill to the east. There was no wind at ground level so takeoff was to the east.. After lift off, at an altitude of about 10 ft, the pilot experienced tail buffet and then sink. The aircraft then hit a fence and gate at the end of the strip which tore off a spray boom, tailwheel and main wheel. The pilot dumped the load and landed straight ahead. After the accident the pilot and the company chief pilot made a closer assessment of the strip and surrounding terrain. That assessment indicated that the point from where the take-off run was commenced was probably shielded from a light westerly breeze (ie a tailwinid) but once the aircraft got airborne closer to the eastern end of the strip, the westerly breeze was encountered. Although the strip was covered in long grass, it was evident from wheel marks that the aircraft had become airborne after a ground roll of between 450 and 500 m.