Looking through the Google results, the term seems to appear in the late 80s.
Joe E. Barnhart, Stephen Winzenburg **1988 **“Jim and Tammy: charismatic intrigue inside PTL”
Terry Cole-Whittaker 1987 “*Inner Path from Where You Are to Where You Want to Be: A Spiritual Odyssey” *
Hillel Schwartz **1990 **"Century’s end: a cultural history of the fin-de-siècle–from the 990s to the 1990s"
Laura Coltelli 1990 “Winged words: American Indian writers speak”
*The ecologist: Volumes 20-21 * 1990
Marjorie Gersh **1990 ** “California and Hawaii publishing market place: a comprehensive directory of markets, resources, and opportunities for writers” In a list of things not to submit for publication
Rik Scarce 1990 “Eco-warriors: understanding the radical environmental movement”
From an etymological point of view, these references indicate that the term became popularised in certain groups in the late 70s/ early 80s sometime. By the late 80s the term was still unusual enough that it required quotes when used alone.
The fact that “woo woo land” is used multiple times in the late 80s and doesn’t receive quotes suggests that either this is the real origin of the expression, or else it is self-evident enough not to require them.
I did find one *possible *reference from 1976
“Spiritus mundi: essays on literature, myth, and society” Northrop Frye. Referring to the work of German author Oswald Spengler:
The relevance of this is debatable IMO. The reference is to woo-woo noises. not to woo woo beliefs, and as Nametag points out, there are endless examples of onomatopoeic usage of “woo” prior to the late 80s. However it is interesting for two reasons.
Firstly it is the earliest use of the term in reference to pseudoscientific writings.
Secondly it supports the “ghost/scary noises” origin of the term. It is clear from context that it is meant to refer to scary noises, and that he knew that his audience would understand that without it being explained.
So while I’m undecided that this is the earliest example of woo-woo being used to mean garbage, it is an interesting date point.
Me too. In fact that’s where I always assumed it originated.
And of course it was used by the Three Stooges as well, in a similar context.
So there seem to be two equally plausible explanations: the “spooky ghost noise” explanation and the Daffy Duck style madness “woo woo” sound.
The Frye reference given above suggests the ghost story origin. The “Woo Woo Land” usages popular in the 80s suggests the Daffy Duck origin.