We recently upgraded plesk to v11.0.9 at work
We use an external DNS service, so dont need plesk to handle it for us.
it turns out that there isnt a way to disable dns from the plesk panel.
you can go to tools > DNS settings and turn DNS off
but that only applies to new domains.
if you need to turn off dns for all of your existing domains, try this:
assuming that your domains are all in /var/www/vhosts
ls /var/www/vhosts | while read x; do /usr/local/psa/bin/dns --off $x; done
it will itterate through all the domains listed in /var/www/vhosts and will turn their dns off.