Posted: 14/08/2013 at 06:40
There's no point in spraying unless you know what you're spraying against - and there are very few bugs that will affect syringia (lilac).
There is a blight condition which is spread by a bacterium - it usually affects lilacs that are stressed due to difficult growing conditions (under/over watering - too much nitrogenous fertiliser etc).
But also some lilacs are prone to browning and dropping their leaves early, and we are heading for autumn now (sorry folks )
If I were you, if the browning leaves are just on one shoot, I'd remove and burn it to be on the safe side. Then I'd make sure that there's a clear area of soil around the base of the shrub, and mulch it well with good garden compost, and then cross my fingers. It'll probably be fine