I have a Japanese lilac tree that is about 15 years old. It has done really well until this year. We have had an unusually dry summer and in the last couple of weeks I have noticed there are brown leaves on the tree, and 2 days ago I noticed the remaining leaves were looking wilted. I have watered the tree over the last 2 days and it has perked up some but I am worried that I might lose it. Is there anything more I can do to revive this tree and get it through the coming winter?
It sounds like your tree is showing stress from the lack of water, though over watering can also cause similar signs on the tree.
During warm and dry conditions you should water your tree once a week. To check the soil moisture level you will need to dig down to about 8 to 10 inches in the soil around the tree and canopy. The soil should be moist but never soggy. You should be able to make a ball of soil that holds but opens up when placed back in the ground. It shouldn't drip water when squeezed.
The amount of water will depend on your soil type.
In the spring following blooming you can prune any branches that may have some die back.