Prior to the commencement of the spraying operation, the pilot carried out an aerial survey of the area noting the position of all wires. On the first run, the aircraft was flown under both sets of wires. When the run in the opposite direction was commenced, the pilot intended flying the helicopter over the first set of lines and under the second set of lines. However, the helicopter collided with the second set of lines and impacted the ground 70 metres beyond the wires. The pilot stated that he had forgotten about the second set of wires and was flying the aircraft higher above the crop than normal. The previous night the pilot had had a disturbed sleep and was probably suffering some fatigue.