Thousand cankers disease is a fungal disease of walnuts that is carried from tree to tree by a small bark beetle called the walnut twig beetle. It has killed countless ornamental black walnut trees in the western U.S. and was found for the first time in the eastern U.S. in 2010.
The association of the walnut twig beetle with the fungus that causes thousand cankers disease is a recent discovery. While researchers have known of the beetle's existence for some time, the fungus was only recently discovered. It has since been identified as a new species, fittingly named Geosmithia morbida.
When an adult walnut twig beetle bores into the bark of a walnut tree to lay its eggs it also infects the tree with the pathogen that causes thousand cankers disease. At the sites of infection, small lesions, or cankers, form just under the outer bark. The beetles within the tree also emit pheromones, chemical signals that summon other walnut twig beetles to the tree.
For each beetle that bores into the bark, another small canker is formed, eventually covering the branches and trunk of the walnut. As more cankers are formed, they merge and limit the ability of the tree to transport and store nutrients, slowly resulting in tree death.
The best estimate is that a tree will die 2 to 3 years after the first symptoms occur. It is likely that at that point the tree has already been infested for several years. In the West, it may take a decade or more to kill a tree.
Once a tree begins to decline from thousand cankers disease it will not recover. Advances in research may change this, but for now there is no therapeutic cure.
At first, one may notice a thinning tree top, discolored or smaller than usual leaves, and/or individual branches dying. On close inspection, small holes where the beetles have entered and exited the bark may be seen and if a very thin layer of the bark is removed or scraped, small oval or round cankers may be seen. Cankers are dark brown and less than an inch across (about the size of a quarter).
Currently, the tree care community does not know how to protect or save trees from thousand cankers disease. Keeping trees as healthy as possible through good forest and ornamental tree management practices might delay infestation and/or disease development. The best thing to do is to quickly detect its presence in new areas and destroy affected tree materials. If you have several walnut trees, remove all dead and dying infected walnut trees from your property and dispose of the wood properly to reduce the chance of having other trees attacked. Properly dispose of material from affected trees by burning or burying branches and smaller diameter wood as soon as possible.
The primary focus right now is to prevent further spread of this disease, especially spread facilitated by humans. Transporting woody materials from dead or green affected trees to a new location can spread the insect and fungus to new areas. Don't move firewood or other unprocessed walnut wood products out of areas where thousand cankers disease has been detected or is suspected to be present. Use locally grown firewood or wood that has been heat treated and inspected.
If you think you walnut trees may be suffering from Thousand Cankers Disease, contact Cutting Edge Tree Care Specialists today.
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