Hello fellow plant lovers, I decided to trim my Japonica today. In other years it has had an unsightly black coating which I have been able to spray off with a high powered hose. What i discovered after cutting it back is that it has a strange growth on the underside of the leaves. Here's a low rez photo that I took with my iPhone. If anyone can tell me if I should be concerned then please let me know. Many thanks in advance. Timothy
Looks like Cotton scale .....and the black coating you washed off was probably sooty mold, a result of the sugary deposits that these scales produce which encourages the growth of this mold.....
Shrub is Pieris japonica, which you should specify in future if you want to be clear - other common examples are Aucuba japonica, Fatsia japonica and Skimmia japonica. And that's just a set of popular broad-leaved evergreen shrubs that grow in shade (including the Pieris). There are also various other popular plants that have the specific epithet "japonica".
Thank you ian66 & Ron B. Sorry for being so unspecific about what kind of Japonica it is but the shrub was in our yard when we moved in several years ago so I don't have a tag telling me which kind it is nor did I know how many kinds there are. I'm better informed now. We do appreciate your prompt replies.