You must have done a wonderful job planting and caring for them last (droughty) summer to only lose a few leaves.
The bed I have my last three (of 8) gets fertilizer for the roses but not extra for the viburnum. 10-10-10 is fairly mild as fertilizers go. If you don't see any browning of the leaves or other stresses, I suppose a light application of this fertilizer wouldn't hurt.

Well, it cost me running that drip hose all summer, but that's another story. They are looking pretty nice with lots of growth sprouting now, so I thought I'd help with a sprinkle of fert around the base for a nice kick.

I usually sprinkle my fertilizers starting just beyond where I think the rootlets are.

Even evergreens don't retain their leaves forever...I'm thinking it's just normal getting rid of old leaves. :)

Thanks alot folks.