Problems With the Japanese Tree Lilac
The Japanese tree lilac is large enough to be considered a flowering tree (20 to 30 feet at maturity) rather than a lilac bush. It produces huge cream-colored flower clusters in the early part of summer. It provides shade, while also being ornamental. It grows in almost any soil conditions. However, the Japanese tree lilac can have some problems.
Plant your Japanese tree lilac in full sun in soil with good drainage. If an existing tree is in a shaded (or partially shaded) area it may develop an infection of powdery mildew. This can cause the leaves to fall off. Remove all infected leaves and consider transplanting the tree to a sunny location.
The Japanese tree lilac is less bothered by insects than other lilac plants. However, infestations can occur, especially when the tree is not planted in full sun. Borer larvae tunnel into the branches, causing wilting and broken branches. Cut off the infested part of the tree as soon as you notice the problem and destroy the cut branches. Borer larvae seem to prey on trees stressed from drought. Although the Japanese tree lilac is moderately drought-tolerant, you should water it during hot summer months.
Scales can be another insect problem. This infestation can be difficult to notice, as the scales blend in with the bark on the trunk. Spray horticulture oil on the tree to prevent a recurrence of scales.
Bacterial blight is a problem for the Japanese tree lilac and other white-flowered lilac bushes. Symptoms of this disease include black leaf spots, black stripes on shoots and new leaves turning completely black, dying very quickly. This disease comes on during the rainy season. Remove the infected areas of the tree and destroy them immediately. It also helps to thin the crown, which increases air circulation. If you are using a fertilizer that is high in nitrogen, stop. These trees only need fertilizer every few years.
Leaf blotch is another disease to which these trees are prone. The leaves develop a brown spot that falls out, leaving holes in the leaves. Again, cut and destroy the infected area as soon as you notice them.
Bacterial crown gall makes warty balls on the trunk and shoots at ground level. Unfortunately, you must remove and destroy the plant immediately. Do not plant another Japanese lilac tree, or any plant that is susceptible to this disease, in the area.