It's baaaack...
Coming out of a tough winter (2024/25) into a cool, wet spring, it was bound to happen. Lilac blight thrives in that environment.
The University of Minnesota Extension directs people to prune them hard. That does have an effect, however, Septoria Leaf Blight (aka Pseudocercospora) can persist for several years on plant debris such as leaves, stems, dead flowers & bark. I know... bummer. IF you didn't get rid of all of the plant debris (which is quite difficult) there's a likelihood of reinfection. Mine are as you can see above. But that doesn't mean the end. You can try again.
Septoria is specific to the leaves and fortunately is more of an aesthetic issue than a severe health problem for plants. However, early disease emergence followed by leaf loss reduces photosythesis and the ability of plants to generate energy which can increase plant stress and reduce plant health.
The common lilac (Syringa vulgaris) is the most affected by the disease. Check out this article from the UofM Extension which shares information on managing the disease.
I know some of you are heartbroken over the loss, so maybe you want to give it another year before doing anything drastic like ripping them out completely. I found further intomation on the University of Oregon Extension site.
Hard pruning after discovering the disease
The photo above is from a friend of mine. Hard pruning on older shrubs and cleaning up the debris can be good on several levels including disease control as well as renewal which allows for a fuller flowering season and controlling size.
Experts recommend burning all infected parts as soon as you notice them. If you intend on burning the debris, FIRST alert your local Fire Department to be certain you are allowed to do this on your property. If you cannot, talk with your Fire Department or City Staff and ask them where you may be able to dispose of the diseased debris. A Copper Fungicide (active ingredient being copper sulfate) sprayed during the early spring each year should help prevent the problem before the buds begin to break. Lilac blight bacteria overwinter on diseased twigs and also on healthy wood. Factors that weaken or injure plants include wounds, frost damage, soil pH, poor or improper nutrition. This leaves an opening for infection by pathogens, predisposing them to the disease.
Actions to take include:
- Plant resistant species or cultivars such as Japanese Tree Lilacs and Korean varieties. Additionally, the Bloomerang series exhibits good resistance.
- Do not fertilize late in the season.
- Do not over-fertilize young plants.
- Maintain adequate spacing between plants and prune to provide good air circulation within the canopy.
- Prune out and burn all affected tissues immediately. Again, check with your local fire department and/or your City officials.
Sources of this disease can include old cankers, healthy buds, leaf surfaces and nearby weeds and grasses. Wind, rain, insects, tools and infected nursery stock spread the bacteria. I know... it sounds defeatist but hang in there if you have lilacs you love.
About 8 years ago... alas it's bigger but not prettier
Blinded by the Blight... (IYKYK) and if not, don't worry about it,
The Garden Scoop