How I Disable Posting New Threads on 1st Forum Level
 

1st level forum: Music
2nd/sub-forums: Rock, Pop, Rap, Country, New Age etc...

I want members the ability to post in 2nd/sub-forums level ONLY, no one has the ability to post/make new threads in 1st level Music.

I've seen this done on another site and I'd like to know how to do with mine.