Why are the leaves on my lilac wilting?


My usually healthy lilac has been wilting. It flowered as usual, but the wilting is getting worse. Do you have any ideas what would cause this and how to treat it?


Jonathan Foster, Home Horticulture Outreach Professional

I’m sorry to hear your lilac is under the weather.

Unfortunately, there are a number of thing that might cause the lilac to wilt, both biotic (pests or pathogens) and abiotic (environmental, like water or lack of pruning), and it’s difficult to diagnose from the photo without any other clues. They like moist but well-drained soil, so check to make sure they aren’t underwatered (not likely this week, depending on where you are in Maine!) or that the soil hasn’t become compacted and wet–in the latter case, the lilac can start to experience root rot, which will cause the aboveground portions to decline. Lilacs also don’t like extreme heat, so if there has been any change in its light conditions (e.g., nearby tree removed) they can experience some wilting.

Bacterial blight and verticilium wilt are other diseases of lilac that can cause a wilting appearance–your photo doesn’t look quite like the standard presentation of either, but I do want to mention them, as you have closer access to the specimen. It’s worth also scouting the base of the lilac for holes in the stem (indicating borers) or “sawdust” on the ground or groundcover plants–these insects can cause problems for a stem if they go to work at the base.

You’ll find information, including signs to look for, on the Univ of MD Extension “Lilac: Identify and Manage Problems” page. NB: there are numerous tabs in the various panels, so look for those. Also, properly pruning lilacs can head off or remedy many problems with the shrub–I can’t be sure from your picture, but I do see a lot of stem material behind the wilting, so it’s possible your shrub needs some thinning out.

If none of the options presented above seems to resonate with what you’re seeing, or if you find no further clues to pests or pathogens, your next option is to submit more photos (including affected leaves, stems, buds, as well as a whole plant picture to evaluate the extent of the problem) or physical samples to the UMaine Plant Disease Diagnostic Lab for testing. There is a small fee for their service, but you’ll have confirmation if anything is going on, as well as recommendations for treatment.

Happy gardening.