My husband grew up in the heart of Appalachia and while there visiting over the holidays I noticed a number of old wives’ tales that are still running rampant from his parents and grandmother and aunts. These have always fascinated me to no end. I’m especially interested in the origin of some of them. Among others, I recently heard from my husband’s aunt that children who are sweating should not wash their hands because it will make them sick, and from my father-in-law that heartburn is a result of not enough acid in your tummy and in order to cure it you should swallow a spoonful of white vinegar when you feel symptoms. (It actually took a lot of energy to not express my annoyance with the ignorance of this, but I did also manage to politely refuse the vinegar they tried to force-feed me.) Now in the true spirit of fighting ignorance, where do some of these come from and how do they get to be so accepted?
Maybe from children who were sweating because they had a fever, and the handwashing thing is just a “post hoc ergo propter hoc” logical fallacy???
I grew up in Appalachia also, so I’ll contribute one – although this one borders on superstition rather than OWT. When I was a teenager, so this was mid-70s, I started to step in among the tomato plants Mom grew in the back yard to pull a weed, and Mom stopped me. When I asked why, she said, “You’re having your period! You’ll hurt the plants if you go in there.”
I was quite taken aback by that. Mom, though not college educated, was well read, and we did, after all, live in metropolitan Appalachia, not up a holler. 
You might be interested in the Foxfire Project. It started as a school teacher’s class project several decades back and grew into much more. It had it’s roots in Appalachia and covers home remedies as well as many other aspects of rustic arts and life before modern conveniencies and products. Here’s the Wiki article, w/ links to other Foxfire sites: