The pilot reported that after conducting a pass over a field during an aerial application flight, he passed clear of a tower but did not see the tower support guy-wires and collided with them. He stated, "After the guy-wire impact there was an immediate sound of the engine starting to lose power and/or shut down." The pilot then performed an emergency landing on a gravel road without further incident. A post flight inspection revealed substantial damage to the fuselage and left wing. The pilot reported there were no pre-impact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. ADDITIONAL INFORMATION Aviation Life Support Systems The pilot reported that he was wearing a Gentex Corporation HGU-55/E helmet for the flight. He stated, "The face shield/visor protected my eyes and upper face from impact injuries of the windshield/miscellaneous debris and also from engine oil." He also stated that, "The helmet itself protected my head from physical injury." The helmet sustained no noticeable damage from the accident. The Air Tractor AT-402 airplane flight manual states the following placard must be displayed, "Occupant must attach seatbelt and shoulder harness and wear a DOT approved or mil-spec crash helmet."