By Padrion51
County Durham,
United Kingdom 
Please can someone Tell me what this is on the underside of My Rhododendron . I have searched online but seen nothing that resembles the problem .I thought Rust/ Lace bug and soot but it is not . It is a favorite plant which I have had for many years and do not want to lose it .Any help would be truly appreciated .
20 Apr, 2017
Mould from either aphid or scale insect which produce a honeydew liquid. A systemic insecticide for the above should sort it out. Perhaps a spray of diluted washing up liquid to clear the old mould if the plant isn't too big.
20 Apr, 2017