Posted: 17/05/2012 at 22:01
Lilacs are generally left alone - prune them after flowering if you have to.
S Harrison, it does sound worrying. There is detailed information here, but it does sound as though that is your problem.
When you plant up your lilac suckers, plant them in pots to avoid spreading it.
You may also like to have a look at this site, particularly point vii.