University of Maryland Extension

Bacterial Blights of Lilac

Author: 
D. Clement & M K Malinoski, University of Maryland Extension, Home and Garden Information Center
bacterial blight on lilac

(More diseases of trees and shrubs)

The most visible symptoms of bacterial blight on lilac are the blackening of new green shoots, leaves, and flower buds during rainy, mild spring weather. Older woody stems are rarely attacked. In Maryland, spring frost damage and late fall or winter pruning seem to predispose shoots to bacterial blight infection. Early symptoms are visible as dark lesions on new shoots that quickly girdle and cause wilting of stems, leaves or flower clusters. Leaf symptoms are irregular dark spots on leaves sometimes ringed by yellow halos. Leaf spots quickly grow together and blight entire shoots. Stem lesions on green twigs start as dark streaks that quickly girdle and cause wilting and blackening of shoots.

bacterial blight lilacBacterial blight of lilac is caused by the bacterium Pseudomonas syringae pv. syringae. This bacterium is commonly found on leaf surfaces as part of the natural population of microorganisms on plants. A unique feature of this bacterium is that it can enhance frost damage and disease severity by serving as an ice nucleation agent on leaf surfaces.

Management:

This disease can usually be managed through cultural practices that reduce abundant new shoot growth. Avoid over fertilization and excessive pruning to prevent an over abundance of young susceptible shoots in the spring. Prune or thin lilacs in early summer to promote better air circulation and allow time for wounds to heal before next season. However, quickly prune out diseased shoots during dry periods, and remove the clippings from the area.

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