My apple plants started to wilt

I have two apple plants which are a few months old, and a couple days ago their leaves started to wilt the branches are getting thinner and can't hold them anymore.
There has been construction work near me lately and they got a lot of white dust on them, I washed it of with a water sprayer and moved them inside, but it doesn't seem to help.
Does anyone know what might be happening to them? I'd really appreciate anyone who helped me.