Sycamore Tree - is it dying?

[nature]

The tree is at the bottom of our garden- its looking rather un-healthy, there is a rusty colour on the the bark of the trunk and it is travelling upwards. The branches are covered with a silver powdery stuff and green clumps of, what looks like moss, but it isn't- the leaves on the tree used to be quite dense, but this year, although it came into bud, when it finally bloomed the leaves on it are not as dense. Can anyone help - this would be much appreciated.

[aeshna5]

Any chance of photos showing these things. The orange on the trunk may be a harmless alga + the whitish/silver things may well be scale insects, Pulvinaria sp.