According to the pilot and a witness, he was spraying a field as part of the federally sponsored boll weevil eradication program. The pilot was flying south on his final pass to trim the edge of the field, when the airplane's right wing contacted unmarked power lines which are 80 feet agl. Subsequently, the airplane impacted the ground, the wings separated from the airframe, and the airplane came to rest inverted. The pilot stated that the 'trim was intended to be accomplished beneath overhead power lines.'