Corrosion from salt water and/or fatigue can cause wing failure. I know of a case where an Aero Commander wing failure happened while turning final for landing at Love Field. The aircraft was a company shuttle on which the procedure was to shut down the left engine for passenger boarding at each stop, which happened a dozen or so times a day. A crack in a wing spar, aggravated by the vibration from engine starting cycle, got longer each time, until finally the little bit of added stress from banking for the final turn was too much.
"Fate is the Hunter." (Ernest Gann)