Thousand Cankers Disease:
Thousand cankers disease is a newly discovered disease of walnuts including black walnut. The disease results from the walnut twig beetle (Pityophthorus juglandis) hosting a canker producing fungus in the genus Geosmithia (proposed name Geosmithia morbida). The disease was thought to be restricted to the western United States where over the past decade it has been involved in several large scale die-offs of walnut, particularly black walnut, Juglans nigra. Unfortunately, it has now been found in eastern Tennessee.
Thousand Cankers Disease Host Carrier:
The walnut twig beetle can carry spores of Geosmithia morbida as an external contaminant on its body. When the beetle tunnels into walnut limbs, the fungus colonizes the gallery walls and adjacent bark tissue. Eventually all of the inner bark is killed and the branch dies. The number of cankers that are formed on branches and the trunk is large and thus the name thousand cankers is used describe the disease.
Thousand Cankers Disease Early Symptoms:
Symptoms can be noticed as early as late June. The walnut tree can look "thin" in portions of the crown with yellowing and wilting leaves. These compound leaves may appear smaller than normal. As the disease progresses, there will be a collapse of limb foliage and cankers may be seen on branches below the wilting foliage.
Thousand Cankers Disease Late Symptoms:
Black walnut trees usually die in less than three years after first symptoms are seen. Smaller branches have numerous tiny holes and larger branches will show cankers in inner bark tissue when scraped. All symptoms occur within the bark but not found in the wood.
Thousand Cankers Disease Control:
Effective controls for thousand cankers disease have not yet been identified. If they exist, their development will require better understanding of the biology of the walnut twig beetle and the canker-producing Geosmithia fungus. The ability of insecticides (for beetle management) to help manage Thousand Cankers Disease appears to be limited and without controlling the beetle host not much can be done to control the canker.