By Goringfolly
West Sussex,
United Kingdom 
Is this some sort of scale insect? For the last 4 years it has appeared on the trunk of my dwarf Acer. A 'soft' scale type insect with wooly fluff underneath it.
It gradually spreads upwards into the branches. In previous years I have wiped it off with meths but this year I used Malathion. It does not harm the tree but is unsightly and returns annually.
5 Jul, 2010
Answers
Yes, its Cushion Scale.
5 Jul, 2010
Thank you. Yes I have just checked and cushion scale it is.
5 Jul, 2010
Previous question
Does look like scale insect - unfortunately, there's nothing to stop it from returning year after year.
5 Jul, 2010