I'm also new to manager role, but I think the first thing is you need to talk with him. Try to understanding what's going on about him, maybe it's just he had some bad time for whatever reason now. You can talk with him based on the fact of his performance and tell him your expectations. Just try to find out what's going on first before making any judgement.
I am specialized in backend web development, and have experiences in building infrastructure on cloud. I enjoy automating tasks and introducing new tools for better work performance and software quality. I mainly use PHP now, but I am familiar with Java. I would transfer to Go or Python if necessary.