Wilting Lilacs

Asked June 19, 2020, 4:02 PM EDT

We have a row of common lilacs.

A couple of years ago, one of them almost completely died. I pruned it back, but it has been very slow to put out much new growth.

This year, I have one that had a large section die off and was rotten, and two more that the leaves are starting to show signs of wilt.

I pruned them every year right after flowering to keep the size under control. The get a little bit of powdery mildew every year, but we don't treat it.

They layout is as such:

(wilting) (wilting) (healthy) (died 2 years ago) (healthy) (dead section) (healthy) (healthy) (healthy) (healthy)

Any thoughts on what this is?

UPDATE: The decline continues and there now look to be “bite” marks any many leaves. Photos attached.

Oakland County Michigan

1 Response

From the pattern of symptom development and the pictures of the bark, I suspect that you are having recurring issues with lilac borer. The borers are the larva of a moth that lays eggs in older branches of lilacs. The larvae bore into the tree damaging the sapwood. If you find round 1/4' holes in the branches that are symptomatic, this would indicate borers are the problem. They prefer older branches and your lilac may benefit from complete removal of the older branches. You might consider the renewal pruning described in the pruning article below to prevent housing more lilac borers in your plant. Wait until later in the year to do the pruning. The egg-laying adults are most active in late spring and early summer.

Borers would not cause the pictured chewing damage on the leaves. If you can catch one in the act, we have the best chance of identifying it. One possibility is leafcutter bees. They are valued as pollinators and generally do not threaten the health of an established plant.