The pilot was engaged in spraying a small crop of tomatoes. This was the first time he had sprayed this paddock. The farmer provided him with a map of the area to be sprayed, but the powerlines were not marked on the map, so a briefing was conducted on the location of the powerlines. There was a set to the north of the paddock and two sets to the south. Before he commenced spraying, the pilot conducted an aerial inspection of the area. During the aerial inspection he was in radio contact with the farmer and believed he had located all the powerlines. Shortly after commencing the job, the pilot manoeuvred the aircraft for a run in the northerly direction. His intention on this run was to fly below a powerline that on previous runs, because of the disposition of that particular line, he had flown over. When manoeuvring to fly below this line, the aircraft hit another line 80 metres to the south. The pilot was not aware of the presence of the line the aircraft struck. The aircraft hit the ground and was destroyed by the impact and the resulting fire. The briefing received by the pilot was inadequate.