Help

I go to the haunted houses every year, especially The House of Shock in New Orleans. They play movies on a big screen before it opens. They played a movie on there that i would love to watch but nobody can tell me the name. It is an older movie (if i had to guess i would say from the 60's or 70's). It is set at an old farmhouse. Really gives you a creepy feeling the whole time i watched it. There is one scene where there is a person in a bathtub and it looks like something is growing out of them. They are covered in what looks like some kind of disgusting mushrooms or something like that. People are getting slaughtered. I believe somebody jumps out of the barn window. If anyone has any idea about what this movie is, it would be greatly appreciated.