Lilac in Distress
We inherited a lilac tree with our new house. It was a little scraggly, with some dead branches and no central trunk. It bloomed fine this spring (though it seemed like it was maybe a little earlier than normal). Over the past two months the tree has really deteriorated. The leaves curled and some turned yellow, and now they are dropping. There is also a green moss-type thing growing on the trunks. We tried more water and less water - neither seemed to have any effect. It is on the south side of our house so really bakes some days.
The lilac looks mature and stressed. It has lived a long life and will not return to its former glory. We recommend that you replace the lilac or plant another type of shrub. Match the new plant to the site conditions and mature height and width.
In general, lilacs grow best in full sun in a well drained soil. For best growth lilacs require renewal pruning.
Here i s some information on why they may decline. They can become stressed due to poor site conditions, poor drainage, drought, etc. When subject to this they can be susceptible to a fungal disease called powdery mildew, a bacterial disease, and possible borers. For borers all you can do is prune out damaged wood.
The old fashioned lilacs can be susceptible to powdery mildew which can be common when we have rainy wet weather in the spring and warm days followed by cool humid nights. Here is more information on on our website,
Control begins by selecting powdery mildew resistant varieties. There are different species of lilacs and the reblooming lilacs (Bloomerang series) that are resistant. Make sure the plants are in full sun with adequate air circulation to reduce humidity levels. Fungicides are not curative for powdery mildew. Pruning for better air circulation may help.
Lilacs are susceptible to a bacterial disease, Pseudomonas syringae, which can cause leaf spotting and scorch on the leaf edges. Disease-resistant cultivars of lilac are the best defense against this problem. On susceptible plants, there is no spray treatment that is effective for this. The best thing you can do is try to manage it through cultural practices such as pruning in early summer (after flowering) to promote better air circulation and minimize leaf wetness. Avoid overfertilization. See more information on our website. https://extension.umd.edu/hgic/topics/bacterial-blights-lilac