It does appear to be some sort of lichen. They're not parasites but usually
saprophytes meaning than they most frequently grow on dead wood, bark, etc.
The branch may have been winter-killed and the lichen is being an
opportunist. If it's a fungus, it's not one I'm familiar with, which
wouldn't be a tremendous surprise. On one small, expendable twig, scratch
through the gray bark with your fingernail (or knife). If there's some green
even just around the edges, you're ok. If all there is is brown, that twig's
gone. You can repeat this back to where you see green and prune early, or
just wait until things leaf out and then prune out the dead stuff. Here in
southern South Carolina, the new leaves on the Japanese maples are in their
prime for spring color.
Gary

"Tom Lucht" wrote in message
om...
Can anybody look at this picture and tell me if my japanese maple is
in trouble, and if so, what I can do to help it?

See picture he
http://www.tomlucht.com/public/pics/...ellow-moss.jpg

It was doing well last summer, our first summer in this house. This
spring I noticed the leaves are very slow coming back, and others in
the neighborhood are much further along. A closer inspection revealed
that many of the branches have a yellow moss or fungus, in clumps at
the ends and at the joints. On some branches, leaves are coming out
(but sickly), but no leaves at all on the branches with the yellow
stuff.

Is this something I should be worried about? What should I do?

Thanks,
Tom