The pilot was conducting spray runs parallel to an electrical power transmission line. During one run the aircraft collided with a feeder line at 900 to its track. The collision damaged the rudder and vertical stabiliser and although the aircraft remained airborne the pilot had difficulty with directional control. He did not attempt to jettison the load. The pilot continued to fly the aircraft straight ahead until it approach a field that was suitable for a forced landing. During the attempted landing the aircraft was affected by a strong crosswind and the pilot was unable to prevent it from weathercocking into wind and colliding with some trees. The pilot had been made aware of the main but not the feeder line. He had not noted the feeder line during his pre-application inspection, probably because the line was not visible against the dark background created by the crop. The pilot later indicated that, after the collision, he was reluctant to jettison the load as he was uncertain what effect the sudden loss of weight would have on aircraft stability. When the aircraft weathercocked into wind the damage to the rudder prevented him from being able to exercise sufficient directional control.