Randolph's "Ozark Folksongs" has a perfect transitional form, from "bugaboo" to "foggy, foggy dew," collected in Missouri in 1938:

"I wooed her in the summer time
And part of the winter too.
Tumble into bed, pretty maid, I said,
And I'll keep you from the Boogy Boogy Boo."

As I mentioned on another thread, "foggy dew" was defined literally in 1616, without regard to the song (which didn't yet exist), as "rime."