Nearing the completion of the task the aircraft struck a single power line. The aircraft remained airborne but the pilot decided to land in a paddock and assess the damage. He found that the top 30 centimetres of the rudder had been torn off. Prior to spraying the paddock, the pilot had physically checked the position of the powerline. During the application he had flown under it at least 12 times but whilst considering the best method to complete the clean-up runs, he forgot about its presence. The front mounting of the wire deflector had been attached to the top of the fibreglass cockpit and not mounted onto the solid roll-cage framing. When the powerline contacted the wire deflector, the fibreglass failed and allowed the deflector wire to sag under the imposed load. This allowed the powerline to run a lower path and sever the rudder substantially below the rear deflector attach point.