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Lilac Bacterial Blight


Lilac Bacterial Blight

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Caused By:-     The Bacteria Pseudomonas syringae


Lilac Bacterial Blight is caused by the bacterium Pseudomonas syringae pv. syringae. The disease is also commonly referred to as Shoot Blight and Blossom Blight. The disease starts as brown spots on stems and leaves of young shoots as they develop in early spring. A yellow halo may also be around the spot. Spots become black and grow rapidly, especially during wet and rainy periods. At first, leaves look perfectly healthy and then a short time later they look as though someone has placed an open flame near them. Further infectious development depends on the age of the part attacked. On young stems, infection spreads around the stem and the shoot which bends over wither and die. Infected leaves blacken rapidly starting near the margin and continuing in a wedge-shaped pattern down to the petiole. Eventually the entire leaf dies. On older leaves, spots enlarge slowly. Sometimes, several spots will run together, and the leaf may crinkle at the edge. On mature stems, spots usually enlarge along the stem, causing leaf death only within the infected area. Infected flower clusters rapidly blackened. Buds may fail to open or may turn black and die shortly after opening. The same organism is the source of bacterial blight on pear, blueberry, cherry, maple, and many other woody plants and the symptoms of lilac blight are similar in appearance to fire blight in fruit trees or to those of winter injury.
The disease is usually associated with plants that have been stressed or weakened by drought conditions, frost damage, soil pH, poor or improper nutrition and infection by other pathogens and/or have been wounded.
This bacteria has also been reported on Forsythia, Blueberry, and other ornamental plants.
Lilac blight bacteria over-winter on diseased twigs including old cankers, tools or on healthy wood.
The Bacteria is spread by wind, rain, insects in the spring during wet weather. Once the bacterium reaches the host plant, it needs a natural opening or wound to gain access to the internal tissues.Picture by William Jacobi, Colorado State University,


Try to keep the plant as healthy as possible by applying compost mulches and fertilisers.
Prune plants to allow good air circulation through the tree.
Infected branches should be pruned 20 to 25 cm (10-12 inches) below the visible infection. Pruning should be done during dry weather to minimize the chance of spreading the pathogen. Pruned branches should be burnt. Always sterilise pruning tools between cuts to prevent spreading the bacterium to other areas on the tree.
Where possible plant resistant varieties.
Apply disinfectants, antiseptics or a chlorine or streptomycin Bactericide or a fungicide containing copper for management of Bacterial Blight early in the spring.
Overuse of nitrogenous fertiliser causes soft growth which is more susceptible to this bacteria.

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