How can we save a lilac that has fungus growing on it?

June 28, 2023 Ask the Expert, Garden Design and Maintenance, Managing Insect, Diseases, and Animal Pests

Question:

We have a dark purple lilac that had this fungus show up this spring on it, or at least that’s when we noticed it. It is well blossoming, plenty of leaves, etc. I am afraid this may be a death sentence for it but have learned not to necessarily rely on the internet. If there is something we can “paint” on these to stop it or even selectively prune it to stop it? 

Answer:

Liz Stanley, Horticulture Community Education Assistant

The lilac has some typical issues resulting from neglect. The shelf fungus looks like it’s on old dying wood. This is common (and the fungus is harmless). The trunks are also terribly crowded and shaded out by each other.

Although I can’t see the entire shrub, if it flowered, it’s probably going to be OK next year if it’s given a good pruning. This will open it up to more air circulation and sunlight for making next year’s flower buds. After flowering is a good time to prune. Here are the basics.

1. Remove big old dead and dying trunks as close to the base as possible with thinning cuts. A reciprocating saw is great for this.
2. Stand back and look at the overall shape and balance as you go.
3. Remove dead, damaged and crossing trunks. (At any time of year.)
4. Thin out crowded parallel growth and spindly suckers.
5. Remove spent flowers (optional).
6. Don’t attempt to shorten the shrub with heading cuts. This will look awful all season long. If it needs a bit of shortening, cut at the juncture of a young branch so the cut is hidden. Some varieties are naturally taller than others.

Here’s our fact sheet on pruning woody landscape plants which includes a video on pruning lilacs.

Lilacs like well drained soil, good fertility and a pretty high pH. (Around 6.5 – 7.0) If you want to bring it back to life, it might be worthwhile to do a soil test. Here’s how. Be sure you don’t fertilize any woody shrubs after mid-summer or they may not harden off before winter.

 

Jonathan Foster, Special Projects Assistant
What you’re seeing on your lilac is turkey tail (Trametes versicolor), a fungus that thrives on rotting wood–so while it isn’t a threat in and of itself to you lilac, it’s an indication that you’ve got some rot going in the plant due to other causes. I recommend checking carefully along the bases and lower parts of all the stems to see if you can locate holes that would indicate a boring pest. I also see that several of the stems are growing against each other, which can often lead to damaged spots from the bark being worn off by the stems pressing past each other. If you find any evidence, we can try to help identify the pest and offer guidance.

Regardless, I think the shrub could use some pruning. This would allow you to remove some of the damaged (and possibly rotting) stems, eliminate the friction spots where two stems rub together, improve the air and light to the base of the plant, and help rejuvenate the overall shrub. You will almost certainly need to remove the portions sporting the turkey tail, as you’ll probably discover dead wood underneath it. Unfortunately, there isn’t a topical sealant that would work–what you’re seeing are the reproductive structures of the fungus and sealing anything over effectively seals rot in, which won’t go well.

UMaine Cooperative Extension Video, “How to Prune a Lilac Bush”

UMaine Cooperative Extension Bulletin #2169, Pruning Woody Landscape Plants

The good news is that this probably isn’t a death sentence for the shrub. Pruning it will help remove the dead tissue and possibly reveal the cause (likely injury) of the rot, so that we can address it directly. Worst case scenario: lilacs can withstand pretty serious cutting back without long term problems, though it might take a couple of years before the shrub regains its size and beauty.