Black Soot

Hi ,can anyone tell me what is causing the black sootlike stuff on my rhododendrons,azaleas and pieris please and what can I do about it,they look a right mess ,never seen it on them before

I wonder if this is sooty mould, although I've never seen it on my rhodo, azalea or pieris before, but have had it on my camellia.

Sooty mould develops on the surface of leaves when sap, or honeydew, drips down onto the surface from sap-sucking insects above. Scale insect is the usual culprit. 

Sheddy, take a look at the underside of the leaves above the sooty ones and see if you can find scale insects feeding. If you have then you'll need to try and get rid of these pests in some way (not easy), but if not we'll have to think again. Let us know what you find.

It can also be caused by honeydew dripping from overhanging trees. If this is the case, all you can really do is wait for fresh leaves on the bushes. Although it's ugly, it won't do your plants permanent harm.

Oh yes, and you can wash it off – although not sure you'll be able to use a hose pipe for teh job! I can't in my area. If the rain has softened the black coating try sponging it off, or fill a pressure washer with water and try getting spraying it away.

On my camellia I just went over teh bush with a bucket of water and a sponge, and this did the trick.

I have the same problem with my pieris and it is so bad that the 'black soot' was all over the plant pot and stems.  I was told to spray the plant with water and bicarbonate of soda.  It has has one blast so far and the black is starting to wash away? watch this space