Yes, you can use SQL if you have Phpadmin rights.
The link is here:
http://www.moodlerific.org/2009/02/18/turning-off-autosubscribe-default-in-forums/
If you can't do that, then just be sure that when you create a new forum, you edit the settings
- SUBSCRIPTION MODE: Subscription Disabled
- READ TRACKING: Off
That way, none of your students will be subscribed to it.
If they reply to a post, they shouldn't receive notifications either.