The browning of the leaves sounds like Bacterial Blight and can be treated with a copper based fungicide spray.  In future years, treat before it show up to prevent it.     The tiny worms a can be killer with a spray of an insecticide like EIGHT but is likely a minor pest and not causing the brown patches.  Here are a couple of links you should find helpful:

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/common-lilac-problems.htm

http://www.bonide.com/trusted-brands/eight/