Shortly after initial takeoff for an aerial application flight, the airplane's canopy opened. At an altitude of approximately 300 feet above the ground the commercial pilot pulled the throttle back while attempting to close the canopy. After unsuccessfully trying to close the canopy, the pilot pushed the throttle back up but the engine did not respond fast enough to prevent the airplane from impacting the ground. The pilot was not injured. Examination of the airplane revealed a bent firewall and both main landing gear were torn from the airplane. A post-accident engine and airframe examination was conducted by a Federal Aviation Administration investigator. No engine, fuel or airframe problems where discovered which would have contributed to a loss of airplane performance. The canopy latch did show excessive wear and lacked any lubrication. Additionally, the aft frame of the canopy that makes up the hinge portion was completely rusted through in three places. An annual inspection was completed on the airplane February 8, 2008.