How to Manage Pests

Pests in Gardens and Landscapes

Shallow bark canker—Erwinia nigrifluens

The most characteristic symptoms of shallow bark canker are brownish to black round spots or areas, usually several in a group, on the trunk or lower scaffolds. Newly infected areas have a margin of water-soaked bark and a central spot of black ooze that later dries, leaving a tarlike black spot. Just under the surface, dark brown areas of dying tissue are formed in the outer bark. These superficial cankers can be extensive, but they seem to cause little damage to the tree. Shallow bark canker rarely extends into the inner bark, as does deep bark canker.


Because damage is superficial, shallow bark canker is not considered a major disease of walnuts. Shallow bark canker can often be severe in stressed trees. Improving tree vigor with good fertilization and irrigation practices may help contain the disease. Cankers can be cut away, but this practice is not recommended because the disease is not serious enough to risk possible wound damage and other infections.

Brownish round spots on trunk
Brownish round spots on trunk

Large superficial canker
Large superficial cankers

Statewide IPM Program, Agriculture and Natural Resources, University of California
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