Care for diseased Lilac - Ask Extension
I have a 25 year old lilac that appears to have several problems. I used to give it lime every spring and forgot this year. But I don't think that i...
Knowledgebase
Care for diseased Lilac #812565
Asked September 28, 2022, 10:24 PM EDT
I have a 25 year old lilac that appears to have several problems. I used to give it lime every spring and forgot this year. But I don't think that is the problem! The leaves are turning brown in large patches (not little insect dots). They are curling up and falling off. The tree is almost bare. However, there are numerous limbs that are green (that is they bend and don't break off). There are buds on those limbs. Other limbs have some sort of white fungus. The tree is due for a cutting out of old limbs. Do I need to cut the entire tree down?
Montgomery County Maryland
Expert Response
We think the scorched-looking leaves are essentially due to drought and heat. It has been pretty hot, dry, and windy lately as well and that takes a toll on late-season leaves, which tend to look pretty tired by the end of the growing season anyway.
If the plant is healthy we'd expect new healthy leaves to flush out in spring. Are they blooming for you? Often as our landscapes mature, plants that were once in full sun (which they need to bloom well) aren't any longer.
Lilacs are acid lovers so we wouldn't put lime on them as that is not what they prefer.
Old-fashioned lilacs are not particularly heat resistant, and most are prone to powdery mildew in our climate. Sometimes it's best to replace them with different cultivars, those bred with some resistance to disease, or perhaps a whole new type of plant better suited to the situation.
Here is our page that will tell you more, including about heat, pruning and replacement suggestions:
https://extension.umd.edu/resource/lilac-identify-and-manage-problems
The white you are seeing is a type of sucking insect called scale, in this case we think it's an armored scale White Prunicola Scale:
https://extension.umd.edu/resource/white-prunicola-scale
Armored scales can be hard to control. Given that you can get to the branch easily, you could try taking a stiff brush and a container of soapy water and scrub/dislodge most of them.
The shrub looks sparse though and it may be a good time to start thinking about a replacement.
Christine
If the plant is healthy we'd expect new healthy leaves to flush out in spring. Are they blooming for you? Often as our landscapes mature, plants that were once in full sun (which they need to bloom well) aren't any longer.
Lilacs are acid lovers so we wouldn't put lime on them as that is not what they prefer.
Old-fashioned lilacs are not particularly heat resistant, and most are prone to powdery mildew in our climate. Sometimes it's best to replace them with different cultivars, those bred with some resistance to disease, or perhaps a whole new type of plant better suited to the situation.
Here is our page that will tell you more, including about heat, pruning and replacement suggestions:
https://extension.umd.edu/resource/lilac-identify-and-manage-problems
The white you are seeing is a type of sucking insect called scale, in this case we think it's an armored scale White Prunicola Scale:
https://extension.umd.edu/resource/white-prunicola-scale
Armored scales can be hard to control. Given that you can get to the branch easily, you could try taking a stiff brush and a container of soapy water and scrub/dislodge most of them.
The shrub looks sparse though and it may be a good time to start thinking about a replacement.
Christine
