Bacterial blight of poplar causes leaf spots, which begin as small, dark, water-soaked spots. Twig dieback and branch or trunk cankers may also occur. Blighted shoots often turn black and appear scorched or burned as they die back. Infected tissues are less resistant to frost damage. Also, the bacteria often infect through wounds caused by frost injury. The bacteria are easily spread by rain, insects, and pruning tools. The disease is caused by the same bacterium that causes bacterial blight of lilac, euonymus, willow, and many other woody plants.

Management Options

Non-Chemical Management

Space trees and prune to provide good air circulation. Humid conditions favor disease development.
Avoid overhead irrigation.
Avoid wounding plants.
Prune out and destroy infected plant parts during dry periods. Make pruning cuts well below infection and sterilize tools between cuts. Do not compost diseased materials.
Provide proper culture. Healthy plants are more disease-resistant and more tolerant of damage.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Apply before fall rains and again before budbreak in spring. First apply to a small section of the tree and wait a few days to determine if the spray causes any plant damage. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

Bonide Liquid Copper Fungicide Conc/Organic Gardening
Active ingredient: copper octanoate | EPA reg no: 67702-2-4
This list may not include all products registered for this use.

Images

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Caption: Poplar bacterial blight Photo by: C.R. Foss

WSU Extension

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