FOLLOWING COMPLETION OF THE LAST SPRAYING PASS, THE PILOT TURNED WEST TO RETURN TO THE AIRPORT. AS HE TURNED INTO THE SETTING SUN, THE GLARE AND CHEMICALS ON THE WINDSHIELD PREVENTED HIS VISUAL CONTACT WITH SOME ELECTRICAL POWER LINES. THE AIRPLANE IMPACTED THE POWER LINES AND DESCENDED UNCONTROLLABLY TO THE GROUND. THE PILOT WAS AWARE OF THE EXISTENCE OF THE POWER LINES IN THE AREA.