Oh my gosh! You have a bad bagworm infestation. The create a protective 'bag' around them with the leaf material. Commonly seen on arborvitae. Pick off by hand or spray! They've been on there for a while.

Here's more info. Get them off, make sure the plant is watered. Give it time, to see if it recovers.

Here is a link that might be useful: treating bagworms

Just a note from experience, when you handpick them be sure to kill them. I had them on a shrub years ago and spent a good bit of time picking them off one by one into a bucket. I left the bucket on the porch overnight and the next day they had crawled out of the bucket and into my foundation shrubs! I still get the willies thinking about it.

They are all over three of the bushes. Is there an insecticide that will kill them?

BT - Bacillus thuringiensis

Here is a link that might be useful: see attached

Bt won't help at this stage of the caterpillars' life cycle. It needs to be applied when they are very young and small.

Truly, I know you don't want to hear this, but handpicking is your best option at this time. It won't take all that long, and you can do a little bit every day.