Bag Worms seem to be everywhere this year!  They are typically not seen until late summer in August sometime.  While we have seen them on a variety of plants like roses and hawthorns, they really are devastating to Juniper type plants.  They are an actual worm that live inside of cocoon shaped bag.  They will come out of the bag and feed on the tree and in turn killing it.  What makes them hard to kill is getting a quality product to penetrate the bag.  For this reason, you need to use a systemic type insecticide that has a long residual.  When they come out of their bag and feed on the tree they will ingest the product and then die.  They can create a lot of damage very fast so when you see them it is important to act fast.  Hope this helps!