The pilot reported that he accomplished a high reconnaissance before maneuvering to descend for an aerial application. He recalled that his attention was split between visually acquiring the intended application area and the indications on his digital map mounted in the cockpit. He descended below a tree line into the intended application area, but "I was still attempting to compare the crop on my field to my map, and was not looking outside the aircraft as diligently as required." He diverted his attention outside the cockpit and noticed powerline wires at eye level. He asserted that he immediately lowered the collective and applied forward cyclic, but the main rotor mast struck the powerline wires. He landed the helicopter in the field, however, the main rotor blades sustained substantial damage. The pilot reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.