Brad, you say that this resembled leaf spot in the beginning. Have you considered the possibility that this could be bacterial leaf spot? I didn't know that bacterial leaf spot could make whole fans collapse, but I recently read a description of bacterial leaf spot making the center fans brown, soft and slimy and "We were afraid we would lose all my seedlings."
You can read the whole story here yourself and see if you think it's worth considering:
http://www.rockytopgardens.com... .
As I said the idea of bacterial leaf spot causing these kind of damages are new to me, but if that is what you have, the article has a solution. This is also new to me, as I thought there was no cure for bacterial leaf spot.
