Some sort of mold?

Hello,

I have woken up this morning to find the following ladybird size dark brown lumps of mold with white edges that are quite stringy and cotten like when rubbed off on the stems of a couple of my Acers.

Can anyone tell me what it is and whether any treatment is necsesary?

Thanks!

 

Those are scale insects - a pest - you will need to get rid of them. (You will find plenty of advice on google.)