Lilac trees are a lot like lilac bushes, except, of course, a great deal taller. A lilac tree may grow to 30 feet in height. They also have a rounded shape and great clusters of blossoms that bloom on the sides of the branches in beautiful white, violet, lavender and deep purple spikes. While lilac trees are relatively disease-resistant, they do take a long time to recover when they experience stress. They may stop blooming altogether in some cases. For this reason, you must be alert with your lilac tree so that you can target any disease-related problems before they place serious duress on your plant.
Several types of disease affect lilac trees. Lilac blight, mycoplasma and powdery mildew are common lilac disease problems. Ring spot virus can also infect lilac trees as well as lilac bushes, and in rare cases lilac wilt can also affect lilac trees, depending on where they are planted.
Symptoms of lilac tree diseases tend to be characterized by their visual effects on the tree. For example, leaves may appear scorched and brown around the edges. They may also develop a variety of dark rings and spots. Flowers also tend to wilt and die. Additionally, some diseases cause a white, black or gray substance to take over the plant, spreading along branches and onto leaves and flowers. You may also notice that parts of your plant are turning black or have developed large, lumpy growths.
Diagnosing the Problem
Once you have identified your lilac tree's symptoms, you need to diagnose the problem so that you can establish a treatment plan. Lilac blight is generally characterized by scorched-looking leaves and blackened shoots. In short, the young growth on your lilac tree will be dying. Mycoplasma (also called witches broom) creates large, lumpy masses on the branches of lilac trees, while powdery mildew, true to its name, is characterized by a grainy film of gray, black or white that spreads along leaves, branches and flowers. Ring spot virus causes yellow rings on the leaves of the plant, while lilac wilt causes sudden, abrupt wilting usually only on one side of the plant.
Treating Your Lilac Tree's Disease
Some types of lilac tree disease are untreatable, and your only option is to remove the plant before other plants around it are infected. Ring spot blight and lilac wilt are both untreatable. Powdery mildew will usually run its course without seriously damaging the tree and without too much damage to the beauty of your plant because it generally strikes after the tree is done blooming for the season. However, without a fungicide treatment, it will happen again at the end of the next season. If your tree develops mycoplasma or lilac blight, you will need to remove the affected portions of the plant. Be sure to dispose of them in garbage bags rather than dropping the pieces on the ground or in a compost pile, and sterilize your pruning shears with rubbing alcohol each time you make a new cut. This should bring these diseases under control without killing the plant.
Preventing Lilac Tree Disease
Lilac trees need plenty of sun and air circulation. This helps prevent nearly all infections. Additionally, make sure that you do not plant your lilac tree in an area where eggplant or tomatoes grew previously. These plants leave fungal organisms in the soil that lead to lilac tree wilt and can kill your lilac tree.