On July 13, 2001, at 2000 central daylight time, a Grumman G-164A, N14AG, sustained substantial damage to the right wing when it hit a powerline during aerial application. The airplane remained airborne and returned to the Mandan Municipal Airport (Y19), Mandan, North Dakota. The commercial pilot was not injured. The 14 CFR Part 137 aerial application flight departed Y19 at 1900 on a local aerial application flight. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported the weather was hot and humid, and clouds were starting to build into thunderheads. He reported, "The air had moderate turbulence along the ground and visibility was good." He reported he had been flying a racetrack pattern during the aerial application flight, passing under a set of powerlines many times. He reported, "As I approached the line, the top wing blocked out the line as I approached. I used the base of the tower as a reference point. The end of the field was about 400 feet to the front of the airplane. As I passed I felt the sensation of a rapid rise. I pushed the stick forward[.] There was no change. I pushed the stick hard to the stop I was still going up. Then I hit, I stood hard left rudder and still had the stick forward. After bouncing around the plane was nose down. I straightened out to level flight and flew a straight line to look at the structure of the plane. There was no vibration and nothing was missing." The pilot reported he returned to Y19 and landed uneventfully. The pilot reported the airplane did not have a mechanical malfunction prior to the impact with the powerline.