By Olrac
United Kingdom 
i have had two pierius trees for many years with beautiful results, however this year they are covered with black deposit. it is not loose like soot and wonder if you can help
jw lpool.
20 Mar, 2016
Previous question
« Just opened a pack of Richard Jackson's root booster & noticed a strong...
Inspect the backs of leaves, stems and woody parts for scale insects - some look like little shield shaped objects with white fluff around them, others look a little different - you may see tubular white 'deposits' on the backs of leaves, or small, yellow nymphs. Spray/treat for scale and the sooty mould should disappear on its own over time; the sooty mould arises because of the sticky deposits left by scale infestation. See link below for more info
https://www.rhs.org.uk/advice/profile?PID=483
21 Mar, 2016