Spraying operations were being conducted in generally calm weather conditions. One load had been sprayed successfully, but the pilot later advised that, as he manoeuvred at the end of the second run with the next load, sink was encountered. Although he dumped the remainder of the load, he reported that he had insufficient time to increase power. The aircraft collided with a tree, then struck the edge of a road and groundlooped into an adjacent crop. Weather conditions at the time were unlikely to have produced any sink. It was probable that while turning towards rising ground the pilot misjudged the slope of the terrain. The aircraft had stalled, with insufficient height available in which to effect a recovery.