Hello: Our four lilac trees were doing beautifully till this year. They are about 10 years old so well established.
This year there is too little bloom and many upper branches are black and look dry and dead.
Should i prune them out or is this a one year problem and they will bounce back next year.
Thank you for contacting the Toronto Master Gardeners.
Your description of the symptoms reflect lilac bacterial blight is most likely caused by a bacterium Pseudomonas syringae pv. Syringae.
Recommended course of action is to prune and burn all infected parts as soon as you notice them. Make sure to disinfest the pruning shears between cuts. A spray of copper sulfate during the early spring each year should help prevent the problem before the buds begin to break. Apply a bactericide to protect healthy shoots.
Lilac blight bacteria over-winter on diseased twigs or on healthy wood. Factors that weaken or injure plants – wounds, frost damage, soil pH, poor or improper nutrition and infection by other pathogens – predispose them to the disease.
Sources of this disease can include old cankers, healthy buds, leaf surfaces and nearby weeds and grasses. Wind, rain, insects, tools and infected nursery stock spread the bacteria.
It can be helpful to prune your lilacs to allow better air can circulation Minimize fertilization . Do not fertilize because high nitrogen favors disease development.
Lilac blight is difficult to control and it is recommended that you buy blight-resistant varieties whenever you plant new lilacs.