Originally Posted by Prism99

I would probably try soaking overnight in water and vinegar and/or OxyClean. If there is still an odor in the fabric that you can detect, chances are it is mold. I would set aside that fabric for making rag rugs and not use it in a quilt.

Edit: Here are a couple of websites with methods to try.
http://www.wikihow.com/Remove-Musty-Smell-from-Clothes
http://blackmold.awardspace.com/black-mold-clothes.html

You could also try soaking/washing the fabric in Nok-Out, but that starts getting pricey:
https://www.nokout.com/home.php