Answer: Bacterial blight of lilac is caused by the bacterium Pseudomonas syringae pv. syringae. The disease is also commonly referred to as Shoot Blight and Blossom Blight. The pathogen has also been reported on Forsythia, Blueberry, and other ornamental plants. New infections are initiated in the spring during wet weather. The bacterium may have overwintered in disease cankers on the plants, on healthy plant material, in plant debris, in perennial weeds, and/or in the soil around the area. The bacterium is spread to new growth of a susceptible plant in the spring by insect vectors, on pruning tools, blowing wind and splashing rain. Once the bacterium reaches the host plant, it needs a natural opening or wound to gain access to the internal tissues.
Fungicides containing copper can be used for management of Bacterial Blight. Some products containing the active ingredient Bacillus subtilis may also be used. An application needs to be made early in the spring before the pathogen infects the host plant. Be certain to follow label instructions.
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