I didn't think that the etymological link from 'fields' to 'rustic' or 'unpolished' was immediately evident but looking up the adjective 'agrestal' which pertains to uncultivated plants (i.e. weeds and other wild-growing things like brambles) made the connection a bit firmer in my mind.
My ideal vacation would not be to Paris or the Bahamas, but rather a small cabin by a lake; something quiet and agrestic and away from civilized society.
"Samuel!" shouted the governess, "You will use a knife and fork properly or you will not eat! I will not abide such agrestic behaviour at the dinner table."