This grafted Korean Lilac tree was transplanted about 15 years ago from one west-GTA zone 6b location to another 8km away. It was a few years old & 4-5 ft tall when it was moved, is now around 7 ft tall. It gets full sun from mid-morning to end of day. It was originally in very sandy soil (bare roots when it was dug up) but adapted fine to more clay-based soil and thrived for years.
Over that time it has been pruned to try to contain the sideways spread, but not professionally. 3 years ago it was very full when in bloom. The last few years there have been interior branches dying and it has a sideways lean as well. This year there are even more dead branches, and what looks like silver powder on the branches and yellow splotches on the branches – there are blossoms on the way and leaves appear to be healthy however they are more on exterior branches. Is there anything that can be done to save this, is it dying? Thank you!
It’s a little difficult to see the bark of your lilac clearly in the photo. Is the “white powder” to which you refer rough textured? Lilacs are subject to attacks by scale insects, which, in large numbers, can look like a coating on the bark. Scales are sucking insects that damage trees and shrubs by sucking plant juices, thus causing a loss of plant vigor and die-back.
Or is the white material more sawdust-like? In which case, it may be a symptom of lilac borers, Lilac borers, which burrow into the wood, usually the older branches. They are creamy-white caterpillars about ¾-inch long. They are especially damaging to grafted plants, such as yours.
The yellow-ish material may be lichen, which in itself is harmless, but may indicate an underlying issue with the tree. Usually, this relates to a root problem. You state that the soil the tree is now growing in is fine clay. Is it possible that the soil around the tree remains wet or damp?
Lilacs do not like wet feet … and this one, having “grown up” in sand may have been invisibly struggling with the clay soil conditions for some time. The “sideways lean” suggests that it may have sunk into the wet soil on one side.
Even a healthy lilac needs to have regular pruning to thin out the interior and get light and sunlight travelling through the tree. I suspect that’s why you are seeing leaves and flower buds only on the exterior branches.
As you have said, it has not been professionally pruned, with these factors in mind, just to manage the width.
If this 20 year old tree is valuable to you, it is worth investing in a professional service to do a full diagnosis, recommend solutions and prune the tree properly. To find a certified professional arborist visit the Ontario branch of the International Society of Arboriculture here.