How to Manage Pests
Pests in Gardens and Landscapes
Shallow bark canker—Erwinia
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.
round spots on trunk