If it's scale, take your time and pick each one off. Use an exacto knife, or a pointy tool of some sort. Squash the little devils, and pull them off the trunk. If you do this every couple of days, you can get them under control. I wouldn't apply a systemic to a sick tree unless I had to. And it takes time for the tree to "uptake" the poison and feed it to the scale.
Nothing survives squashing.
If you want to put your tree outside, and you're sure that it is scale and aphid free, but you want to make sure not to get ants (which, after all, do carry scale and aphids and put them onto the tree) then set it into a bowl of water, with your tree's pot sitting above the water line. Like a moat around a castle. The ants can't get over the water. Simple, and poison free.
Just make sure that the tree pot is above the water, because sitting in water will rot the roots. An additional benefit is that the humidity coming off the water will benefit your tree.
Also, don't move the tree in and out if you can help it. If the day is nice, and the night is not too cold, leave it where it is. Trees don't naturally move around, and they don't like adapting to changes very quickly.
Joanie