What are the best practices for dealing with an under-productive team member?

Have an open conversation and communication with that employee. Is something else going on in their personal live, do they need help? Offer help of ways for them to improve? Do they need more training, guidance, coaching? There is not much info in the question, were they long term employee, how was their performance in the past etc. I will start by understanding them and offering help/guidance. As a last resort you can use warnings and performance improvement plan but I would strongly suggest you find a solution before PIP as when you are at the point there is hight chance that you’ve already lost the employee

I normally say, nobody wakes up in the morning trying to make their fellow employee’s life miserable. When IT fails at delivering on its promise, I try to work with people to help them understand that nobody woke up trying to make you have a bad day. We may not have considered all of your needs when setting a policy or we've had to scale some things. 

I'm always telling my employees to think about what they're delivering to people not as a checklist of requirements to fill—because that's easy for engineers and IT people to do—but think about what it would be like if you were sitting in their chair, living that thing you delivered every day. If you were doing that, would you be happy? You're trying to get them to think about what they deliver in a different way, from the point of view of having to sit in a chair every day for what is now way more than eight hours a day. It goes back to the golden rule but it's so fundamental.

Nobody comes into work thinking that they'll do a terrible job. If they are not being productive there is some reason behind it or it might just be an off day. Digging in deeper, trying to help and empathize with them helps elevate that conversation and also makes them much closer to the organization. And their productivity definitely will improve.