The pilot reported that during a pull-up at the end of an east-west swath run, the airplane struck power lines that were close to the edge of the field, and oriented north-south. He further reported that after striking the power lines, the airplane lost aileron control. During the ensuing forced landing to an unimproved field, the airplane was structurally damaged. Scratch marks, corresponding to transmission wire, were found on the left wing and the left main landing gear.