I vote with
@TomB and
@sorce.
Looks like alkali deposits to me. Very common around my area, and I see it on my trees routinely.
How long have you noticed it happening?
Do you see it on the soil also?
What type of juniper is it? It may be harmless, possibly even a bit beneficial to it.
Many times an alkali build up like that isn't too harmful and you can just brush it off with a tooth brush or the like, but after a while it can really raise the pH of the soil if it gets out of control.
Make sure you're watering all the way through the soil to prevent that. Maybe a good solid flushing of the soil once in a while.
To completely prevent it, you could water with collected rain water, filtered water, or dilute your tap water with distilled water to minimize the alkalinity of it.
