By Susifu
United Kingdom 
My Fatsia Japonica is sick too - but it is only the new leaves - they are covered in a brown dustlike substance and are curling up and going black! Never had this problem before it is always a healthy beautiful plant! What can it be?
5 May, 2014
Answers
The brown dustlike substance is indumentum isn't it? The new growth has it but it disappears gradually as the leaves expand.
I think that is separate from the blackening, which as DM said is likely wind or frost catching the tender bits before they've had a chance to toughen up.
5 May, 2014
Hi, welcome to GoY, is the plant in a windy position? it sounds as though it could be dieback,caused by cold winds, Derek.
5 May, 2014