The pilot explained that he flew a perimeter reconnaissance of the fields designated for fungicide application with the helicopter. He identified hazards to flight (wires, houses, terrain features, wind direction, etc.) and then completed applications over three of the assigned areas before beginning a fourth. As the pilot aligned the helicopter for an application pass and descended to “spray height” he detected a “loosely strung” powerline across his path that sagged to about “4-5 feet above the height of the corn.” The pilot attempted to climb the helicopter over the wire but was unsuccessful. Immediately after contact with the wire, the pilot experienced a “very rough” vertical vibration and decaying rotor rpm, so he initiated a power-on autorotation for landing. At touchdown on upsloping terrain, the helicopter pitched forward, the pilot corrected with an aft cyclic input, the helicopter entered a “dynamic rollover” to its right and came to rest on its right side substantially damaged. The pilot reported that he was uninjured in the accident, and that there were no preimpact mechanical anomalies with the helicopter preventing normal operation.