Insecticidal soap will kill them.

tj

+1 to sawfly larvae.

They can do a lot of damage very quickly. If the infestation is not too bad, put on some plastic gloves, hold a container of soapy water under the affected branch and start knocking them off. They will start dropping quickly into the container. Repeat daily for the next few days.

Thank you all. I cut all the branches and put in a bucket of water to drown.

There was no need to remove the branches. The buds on the end were still good.

tj

Blasting with a hose a few times would have done it. Cutting the branches off wasn't a great idea.