To reach or pick s.t. with a pole or stick; to get or remove s.t. with an instrument that can't be reached with one's hand (as ear wax or s.t. dropped in a hard to reach place).
The -un imp. focuses on an obj. that has use for the person. The -an imp. focuses on the benficiary or an obj. that is being removed and has no use.
Who picked my mangoes (with a pole)?