Thanks for contacting us about the holes that have been chewed in your lilac, and for sending the picture. It could be either leafcutter bees http://extension.colostate.edu/docs/pubs/insect/05576.pdf or a root weevil http://extension.colostate.edu/docs/pubs/insect/05551.pdf. In the picture, it appears to be root weevil feeding. The leafcutter bee cuttings are usually more circular and larger. The weevil chews notches out of the edges. Look at more of the chewing on your lilac and compare to the pictures in each of these links.

If it’s leafcutter bees, the damage is superficial and does not require treatment. And in fact, you are helping one of our native solitary bees – a pollinator – rear her young!

If it’s the root weevil, the leaf damage is also primarily superficial but the root damage by the larva can be an issue. If your lilac tree has dieback of branches, that may be the cause. If you are only seeing leaf damage, treatment is probably not needed. If you do treat (see the above fact sheet) for the weevil, be sure to read the product label thoroughly.

Now, about the lack of blooms. If your lilac is getting full (or mostly) sun, and appropriate water, that’s all it really needs. However, pruning timing is critical. Lilacs need to be pruned right after they bloom. They make the flower buds for next year very soon, and later pruning or shaping can remove those newly formed buds, causing no flowers for next spring. A late frost/freeze on emerging buds in the spring can also kill buds.

I hope next year brings more lovely, old-fashioned blooms for you!

Karin