Disease name: Thousand cankers disease (TCD)
Pathogen name: Geosmithia morbida (fungus)
Hosts: The primary host for thousand cankers disease is black walnut (Juglans nigra). It can infect other species of Juglans.
This fatal disease is widespread in several western and southwestern states. It has also been found in localized areas of a few eastern and midwestern states.
The disease is vectored (spread) by the walnut twig beetle (Pityophthorus juglandis).
It may also be spread through the transport of infected lumber, firewood, and wood pallets.
Symptoms
Thousand cankers disease symptoms include yellowing of foliage and eventual dieback of infected branches.
Infected trees develop numerous, small, round to oval cankers beneath the bark. These cankers damage the tissues directly under the bark.
In some cases, there is no visible sign of the canker on the surface of the bark. In other cases, the bark covering the canker may crack and show dark colored staining.
Holes made by bark beetles can be seen in the bark and beetle galleries will be present in the canker itself.
Disease Cycle
The fungus that causes thousand cankers disease overwinters in infected trees.
The larvae of the walnut twig beetle tunnel into infected cambium to feed and then pupate.
When adult beetles emerge, they carry fungal spores with them to other trees. Adult beetles tunnel out galleries in which to lay their eggs. During construction of these galleries, spores of the fungus are introduced into the phloem and cambium of the tree.
The fungus kills small patches of tissue, forming cankers under the bark. Many of these small cankers develop on one tree. The small cankers coalesce into larger ones, leading to the eventual death of the host tree.
Management
Cultural Management
Several states have quarantines in place to minimize the spread of thousand cankers disease. Suspected cases should be reported to the state plant regulatory official in your state.
Chemical Management
At this time, there is no effective management of the thousand cankers disease fungus or its vector, the walnut twig beetle.
For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.