Craig Cowing wrote:
Is it a good idea to treat the
tree before I put it into winter storage? I'm wondering if the mites
winter over in the tree?

Mites overwinter as eggs or as adult females in soil and leaf litter.
The mite on juniper overwinters as eggs. My references say they begin
to be a problem in May, and are worst in hot dry weather, but I don't
know how you overwinter your bonsai: if you have them in a place where
they may get unseasonably warm, the mites would hatch and become active
earlier: it takes 10 days for the life-cycle to be completed, so in a
few weeks you can have a serious outbreak.

I'd recommend an insecticidal oil in late winter. That would smother
the eggs.

Nina