We have a very old lilac which for the last 12 years has been smothered in purple flowers every May/June. This year the pigeons have completely eaten every leaf and flower leaving us with just a massive twig tree. This tree is probably 50-90 years old and I'm worried that it won't recover. Do I give it a hard prune back now (October 17) or wait till February? I know I won't see any flowers next year but would appreciate some advice on what to do.