Download Bacterial Blight of Lilac

Bacterial Blight of Lilac
(June 2, 2017)
Bacterial blight of lilac, caused by the bacterium Pseudomonas syringae pv. syringae is a common disease in
Montana during the late spring and early summer. It can occur on all types of lilac, and is most commonly
associated with stressed or wounded plants.
Symptoms
The disease first appears as brown spots on leaves and stems. Spots can then enlarge and cause contorting of
leaves (Figure 1a). Blackening and wilting of shoots can occur if the disease spreads into shoot tissue, and if
stems are girdled, distal shoots and blossoms are killed (Figure 1b).
Life Cycle
The bacterium can overwinter in cankers on the plant, in dead plant debris, on neighboring plants, or in the soil
surrounding the plant. In the spring, the bacterium can then be spread to susceptible plants by insect vectors,
pruning tools, wind, and splashing water. Infection takes place through open wounds in the plant. Freezing
temperatures in the presence of the bacterium can intensify frost damage, due the bacterium’s ability to act as
an ice nucleus.
Disease Management
Proper plant management techniques should be employed to reduce the chance of infection. Plants should
receive proper amounts of fertilizer and water to lessen stress, and when watering, care should be taken not to
allow water to splash on the leaves, which can facilitate bacterial spread. Pruning infected branches 6 to 8
inches below the point where symptoms start, and carefully disposing of branches can reduce infection. Pruning
tools should always be sterilized between cuts to prevent spreading the bacterium to other areas of the plant or
to other plants.
Figure 1. Bacterial blight of lilac. A. leaf spotting and contortion. B. leaf and stem blackening and wilting.
References
http://plantclinic.cornell.edu/factsheets/lilacbacterialblight.pdf
Cranshaw W, Leatherman D, Jacobi W, Tisserat N, Leatherman D. 2014. Insects and Diseases of Woody Plants in Colorado.
Colorado State University Extension. 322 p.
Please call if you have questions or concerns! Eva Grimme, 406-994-5150; [email protected]