Can I repair speaker foam?

I got an old pair of Polk Audio speakers and a mid range speaker foam has a 3/8's tear. Can I glue it or make some kind of repair?
Better to have a professional refoam them with new foam. Not sure where glue will get you. Have both pairs done while you're at it.
Refoam them yourself. It's inexpensive ($25 for a pair) and easy. I've refoamed 2 sets of speakers myself with no problems.
Do the following 2 things.

1) do not use the speakers, as this may cause further tearing of the foam, and then has the potential of causing the voice coil to rub against the inside slot of the magnet. Once that happens you then need a full re-cone, and
that is when things get espensive.

2) remove both midranges, and call Millersound in PA, ask for Bill. Do web search, or look at Mail the pair of drivers to them. You will have speakers that perform like new.

I'm not affiliated with Millersound, but I have had numerous drivers repaired by them (different sizes, different manufacturers). I have friends that have been very happy with both the price, and the quality of the work.

It sounds like you caught this early enough.
It depends on the quality of the speaker - check with polk. I went through my manufacturer and have had drivers re-coned a couple of times (simple procedure common in high end gear - studios, for example, damage speakers regularly, transport, dropped microphone, incorrect patch panel setting etc.).

For lower end stuff it is cheaper just to replace the entire driver or speaker as the drivers are not worth much and labor is costly.

I would not recommend you go through a third party unless they are approved by Polk. Neither would I recommend you mess with this yourself....the interface between cone and rubber/foam surround is a significant source of distortion in most to get it done right or replace the driver altogether.
You can try a little tape on the back side, but I would bring it in to a shop and have them put a new surround on.