Posted: 26/02/2015 at 11:52
Lichen is a sign of clean, still; damp air and is not harmful to plants though it can indicate a lack of vigour. Some judicious pruning to take out dead, broken and weak spindly stems plus one or two of the oldest stems and a good general feed of blood, fish and bone or pelleted chicken manure which will feed beneficial soil organisms as well as the plant should help.
I have noticed a lot more lichen on my red and blackcurrant bushes this winter as they are now protected from strong westerly and northerly winds by a windbreak fabric strung along the fence. I find it rather attractive but the oldest stems will be cut out at harvesting time to enable easier collection of the fruit and thus keep the plants renewed.
Here is what the RHS says - https://www.rhs.org.uk/advice/profile?pid=411