Your Japanese tree lilac does well in residential areas. If you are fortunate to have one planted in full sun, the tree will reward you with beautiful prolific blooms. Suitable for urban settings and tolerant of less than ideal soil, your Japanese tree lilac is susceptible to a few pests and diseases.
Lilac Borer and Leaf Miner
If not kept watered during dry spells and fertilized, your Japanese tree lilac is a target for lilac borer. These larvae will infect the branches by tunneling inside of them, causing them to weaken and break off.
In early summer if the leaves of your tree lilac are unhealthy looking, a closer inspection might reveal the presence of the lilac leaf miner. The caterpillar that emerges from the leaf will devour many of the tree's leaves.
A serious disease than can affect your Japanese tree lilac is bacterial blight. This disease will appear on your tree as black stripes on the leaves, or one side of each leaf will turn black. Once turning black the leaves will die and fall from the tree.
If your tree lilac has leaves with brown spots that eventually fall out of the leaf, your tree may be dealing with leaf blotch. Leaf spots can be caused by many different fungi, and only a horticulturist can determine if it is leaf blotch.
When your weather is wet for a long period of time, your tree lilac is susceptible to powdery mildew. The leaves on your tree lilac will be covered with a powdery white substance. If your tree is shaded by other trees or structures, it can suffer a very heavy covering of powdery mildew.
Long before the fall season the leaves of your tree lilac wilt and fall off the tree. You are looking at a case of verticillium wilt. Soon some or all of the branches will die.
Bacterial Crown Gall
A glance at your tree lilac shows growths along the soil line. Round and warty, these galls will necessitate the removal of the infected plant and prevent you from planting in this area again as the bacteria is in the soil.
You can reduce the chance of any of the pests or diseases affecting your Japanese tree lilac by following a few steps. Plant your tree lilac in the right area. While tolerant of poor soil conditions it does need full sunlight. Because soil conditions may be less than ideal, be sure to fertilize at regular intervals. If your climate is on the wet or damp side, thin your tree lilac for better air circulation. Follow these steps and then sit back and enjoy your beautiful Japanese tree lilac.