I did some looking after seeing your post and found the page below. On the right-hand side if you scroll down a little, where it says "Pests and Problems: Fungal Disease", there are four diseases listed that are linked to more information if you click on them.

I had to prune some dead limbs off of a viburnum 'Mohawk' this summer. The leaves wilted first like it was too dry (even though it wasn't) but I don't recall seeing any spots on the leaves. Hope I don't regret not cutting out the whole shrub and burning it so it wouldn't spread. There are two more viburnums planted fairly closeby.

Here is a link that might be useful: Viburnum opulus - Univ of Illinois