http://www.sallys-place.com/food/columns/gilbert/mustard.htm
Like a number of field flowers/weeds, wild mustard is a European import. The seeds either arrived as stowaways in shipments of grain or were deliberately imported by the early settlers for culinary or medicinal reasons.
By the by, commercial mustard is artificially colored yellow. "Natural" mustard is a rather drab and dowdy brown.
I'd be leery of eating wild mustard growing in commercial corn fields. I believe that wild mustard is one of those weeds with the valuable talent for pulling contaminants out of the soil in which it grows--and commercial corn fields are not friendly, organic places.
Still the temptation in the spring. Dandilion greens and wild mustard will thin your sluggish blood.