The weather was fine with a light breeze and occasional slight turbulence. The pilot, who held a first-class agricultural rating, made preliminary inspections of the area both from the ground and from the air, but did not accurately establish the position of overhead wires and other features. He decided on a broad spraying plan which he intended to develop as the operation progressed. The main section of the undulating terrain was treated by making runs in a single direction during which the aircraft passed beneath a primary power line approximately 40 feet above ground level. The pilot then commenced a run in the opposite direction to cover a small section which remained. While on the approach to this final run the pilot selected a fence as the point at which he could begin his climb away. He believed he would then have passed safely below both the primary power line and a spur line which ran to a nearby house. The spur line was in fact some 90 feet beyond the fence and as the aircraft climbed away it struck the wire and became inverted. After continuing out of control for a short distance the aircraft struck a group of telephone wires then continued on its descending path and made violent contact with a road. There was no outbreak of fire and the pilot was able to release himself from the wreckage.