Bonide 8066 Captain Jack's Bacillus Thuringiensis BT Organic Worm & Caterpillar Control, 32 oz. Ready-to-Us - Quantity 1

Just use Captain Jacks BT. I keep this stuff in the house specifically for the Mountain Laurel caterpillars. It kills them immediately and you’ll only need to reapply in about 5 days to make sure they are gone. I’m normally a live and let live kinda guy in my native garden but these guys will DESTROY all new growth on your ML and basically set you back a whole season of growth. I learned this the hard way my first year experiencing them. I now keep this stuff around and will routinely check my mountain laurels annually for early signs of these guys just so I can immediately annihilate them.

This is what I use