The pilot reported that about halfway through the first spray pass he experienced a complete loss of engine power. The pilot stated that he pulled up out of the field, dumped the load, and chose to land straight ahead in an adjoining field. The pilot reported that after touching down and holding the stick back the tail started lifting. Before it stopped, the airplane nosed over and came to rest inverted. A Federal Aviation Administration (FAA) airworthiness aviation safety inspector conducted a post accident examination of the airplane. The airplane's most recent annual inspection had been completed the day prior to the accident. The FAA inspector found the engine's Py line had not been secured properly, which would have prevented proper fuel scheduling to the engine's fuel control unit. The inspector also reported that the outboard leading edge of the left wing tip had sustained substantial damage, which would have adversely affected the flight characteristics of the airplane.