Nothing says spring like the fresh, lush buds of the lilac tree wafting out their unmistakably sweet scent. Hence, there is nothing worse for the spring gardener than to anticipate the first buds of this briefly blooming tree and be greeted instead with black streaking, white spots, or gray webs covering the once lush foliage. Early intervention and quick action once disease is present can prevent unnecessary loss of your beloved lilac.
Pseudomonas syringae pv. Syringae, the bacteria commonly known as lilac or bacterial blight, affects all kinds of lilacs but especially Asian varieties such as the Japanese tree lilac. The disease manifests as dark streaks on foliage and stems as well as sores or spots. Open blooms will brown, and closed buds blacken. Prevention is the best deterrent for this blight. Choose disease-resistant lilac varieties. Plant them with plenty of space between each tree or bush to discourage spread and encourage air circulation. Avoid over-fertilization, which can make the lilac susceptible to the disease.
If your heart-shaped lilac tree leaves appear to have white talcum powder sprinkled all over them, then you may have a powdery mildew infestation. Leaves will look cloth-like with a web of fine mold over the surface. Powdery mildew spreads easily from infected trees and shrubs to healthy ones through splashing rain, careless watering, crowded plants, and using dirty tools on healthy specimens. Once the disease has taken hold, little can be done except contain the infestation until winter. Cut back and destroy all the infected material, as it will overwinter on dead plant material and can spread from the compost pile.
Resembling a wasp, this black and yellow striped moth known as Podosesia syringae lays it's eggs in the branches of the lilac tree. Larvae work their way out of the branches and emerge as adults to carry on the destruction. Old, decaying branches and stems are the most attractive to the lilac borer for egg laying. Keep your lilac tree well pruned, removing the oldest and any dead or non-producing canes yearly. Set traps in the spring, and apply sprays to infected trees at varying times throughout the season depending on where you live. Contact your local university extension office for recommendations.