By Davidz
United Kingdom 
Our rhododendrum leaves have a dirty sticky substance on them. What is it and how do we clean them and stop it spreading?
25 Mar, 2012
Answers
Thank you. I think we've got a big problem now. The dirty mold is everywhere. We've just noticed it on our camellia bush, and we have a big garden! I think we will need to apply a spray. There's too much to just wash.
25 Mar, 2012
Sorry 'wash' meant spray! Also DAvid do a Google search on aphid residue to see if it really matches. Where are you in the UK?
25 Mar, 2012
Yes, I've googled photos of dirty mold from aphids, and it's the same. We're in Halebarns, Cheshire
25 Mar, 2012
On with the spray!
25 Mar, 2012
Alternatively, check out www.greengardener.co.uk for a biological control
25 Mar, 2012
Previous question
Possibly aphids on your rhododendron leaves, wash with agricultural soap and look for evidence of aphids.
25 Mar, 2012