On August 10, 2003, at 1415 central daylight time, a Weatherly 620A, N4656M, piloted by a commercial pilot, sustained substantial damage when it impacted trees while landing on runway 30 (2,528 feet by 100 feet, turf) at Hofer Private Airport (SD13), Doland, South Dakota. Visual meteorological conditions prevailed at the time of the accident. The pilot reported no injuries. The 14 CFR Part 137 aerial application flight was not operating on a flight plan. The local aerial application flight originated at 1345. The pilot reported he struck power lines while performing an aerial application to a field. The airplane remained airborne, and the pilot returned to his private airstrip about seven and a half miles south of the power lines. The pilot reported that the power line had wrapped around the landing gear and tore the brake line to the left and right main landing gears. Prior to the landing, the pilot applied pressure to the brakes and realized the brakes would not be operational during the landing. While landing the airplane veered off the runway and impacted trees.