Bacterial Canker and Dieback (Xanthomonas populi)
From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.
Importance- Bacterial Canker is an extremely serious branch and stem disease of all species of Populus. It is now found only in northern France, Belgium, the Netherlands, the Federal Republic of Germany, the United Kingdom, Ireland, and Denmark. Selection and breeding programs have produced many resistant clones.
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Look For:
- On branches or small stems, blisters that become black, cracked, sunken areas of bark that may have cream to white bacterial ooze during cool, moist periods.
- Leaves on small shoots or on small stems near cankers may have blackened necrotic areas and later die.
- Small stems may break at canker area.
- Dead branches in larger trees.
- Trunk deformities looking like cankers, irregular galls, or severely roughened bark on larger trees.
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 Bacterial Ooze.
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Biology- Bacterium can spread by windblown water droplets, tools, insects and animals. Infection is through leaf scars and fresh wounds on branches and stems. The extent of bark and stem symptoms depends on the tree's susceptibility to the disease.
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Monitoring- Careful monitoring for this disease is essential in North America to detect it early and eradictate it. Examine young trees for bacterial ooze on blister-like or blackened areas on branches or main stems near shoot bases and blackened leaves on such shoots. Any stem breakage should be closely examined for such symptoms. Carefully monitor poplars from the Tacamahaca section because they may be especially susceptible. Willow is also susceptible to this bacterial disease and should be included in any monitoring program where both poplars and willows are being grown.
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 Old canker and rough bark of affected stem.
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 Young canker and blackenend bark of affected.
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Control:
- Planting highly resistant clones from selection and breeding programs--the only way to control this disease.
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