After completing the first swath run the pilot climbed the aircraft over a single set of power lines. At the end of the second run the aircraft was flown under these wires. When the pilot then commenced a climb he observed a second set of wires, he attempted to fly the aircraft under them but the canopy of the aircraft struck the wires. The aircraft remained airborne, however, by using the rear vision mirror, the pilot saw that the fin and rudder were extensively damaged. Rather than risk a loss of control situation he landed the aircraft in a field of tall sugar cane. Prior to commencing the task the pilot was given a map of the area by the property owner. The map was marked with the area to be sprayed and also had indicated, by the use of crosses, a power line at the end of the spray run. The pilot assumed that these crosses indicated only one set of wires. Being anxious to complete the task he did not carry out a reconnaissance before commencing to spray.