On December 3, 1998, at 0900 central standard time, a Grumman G- 164B, N6676Q, operated by a commercial pilot collided with power lines during an aerial application flight in Naponee, Nebraska. The pilot received minor injuries. The airplane was substantially damaged. The 14 CFR Part 137 flight was operating in visual meteorological conditions without a flight plan. The flight originated from a private grass airstrip in Naponee, Nebraska, approximately 20 minutes prior to the accident. The pilot stated that he made a swath run to the south over a field. He made his turn back to the north and was flying another swath run at a slightly lower altitude when the airplane collided with two of three wires which crossed the field. The pilot reported the airplane decelerated, rolled 360 degrees, and impacted the terrain in an upright position. The pilot reported the field being sprayed was at the bottom of a "canyon". The poles from which the wires were suspended were on hills on both sides of the canyon. This was the first time the pilot had sprayed this particular field and he was unaware of the wires.