Spraying operations were planned to be conducted on two paddocks. A briefing on the operation was passed to the pilot by telephone by one of the owners of the property the previous evening. The briefing indicated that a particular power line was strung outside the boundary of the smaller of the paddocks, clear of the likely swath run approach path. Based on the information supplied, the pilot drew a map of the area. In fact, the line cut across the corner of the paddock. Before commencing operations, the pilot carried out an aerial inspection of the area. However, he failed to detect the actual position of the power line. While descending for the first run over the paddock, the aircraft struck the line. The impact partially severed the left wing, and a fire broke out behind the engine firewall. The pilot was able to complete a semi-controlled landing in the adjacent paddock, and the fire was extinguished by the ground party.