The pilot was conducting a clean-up run on a crop of tomatoes, which involved flying under a main set of power lines and a branch line. He was aware of the positions of both lines. The pilot flew under the branch line and started to pull up, when he suddenly saw the main line. He then attempted to go under that line but made contact with the rudder, part of which was torn off by the impact. The pilot advised that he applied full power and full forward stick to try and counter the nose high/slow speed situation. The aircraft was vibrating badly with associated noise coming from the rear. This was later determined to be from the detached portion of rudder attached to the wire deflector cable, flailing in the slipstream and striking the rear fuselage and elevators. Because of this the pilot decided to land straight ahead immediately, however, the landing area subsequently proved to be unsuitable resulting in further damage to the aircraft.