I don't know much, but I'll try. Hope you're still reading, geebee.

Nothing fancy here, I have a few Stella D'ors, in their 7th season this year. Over the past two years I've had more yellowing/browning out at ground level - still good blossoms, but waning. I meant to lift & divide them last fall and again early this spring - but, I failed to do so. They got really sad looking this summer and I did the divisions mid-July and hoped for the best.

I divided two in half and another in thirds. The little pieces I put back in my ground are looking very perky and the pieces I gave away are holding their own too.

So, maybe you don't have a fungus, but just a need to lift and divide?