Apple tree got white mold like coating

Apple tree got white mold like coating all over the base of the tree and the trunk. Got a birds nest on top of it, so could be bird droppings but wanted to double check that it isn't a bug or infection.

 

Woolly aphids

https://www.rhs.org.uk/advice/profile?PID=724

 

Could be either woolly aphids or more likely Oyster scale aka American Blight. Either way you need to remove it asap, it does harm the tree eventually. Scrub the bark with a Horticultural soft soap. You need a soap based insecticide as the white covering is a wax which is impervious to water. The soap dissolves the wax and allows the insecticide to get at the insect.
You could also use Methylated spirits which has the same effect.