By Jesse Lee
What does it look like?
Thousand Canker disease is a fairly new development, and is actually an insect-disease complex. The complex is formed by the walnut twig beetle (Pityophthorus juglandis) and the cankers caused by the beetle in conjunction with the fungus Fusarium solani. The overwhelming amount of cankers that form on the trunk and branches has led to the name, Thousand Canker.
The walnut twig beetle is a small, brownish-yellow bark beetle, and the associated fungal cankers are usually brownish-black, though some bark shows amber staining.
Host material and range
Native to North America, the walnut twig beetle can be found throughout the Western United States, including Arizona, California, Colorado, Idaho, New Mexico, Utah and Washington.
The pest feeds on black walnut, with the first reported black walnut mortality associated with the pest-disease complex originating out of New Mexico in 2001. Thousand Canker also affects Arizona walnut and little walnut trees, though not to the same degree as the black walnut.
Prior to the 2001 report, walnut beetle was not readily associated with significant black walnut die-off. However, since the 2001 report, widespread black walnut mortality has been found, most recently in Oregon and Washington.
The walnut twig beetle damages the tree in the larval stage through branch tunneling and feeding, but the long-term damage comes from the cankers developed from the fungal pathogen carried by the beetle.
Although proper prevention and treatment controls for Thousand Canker have not yet been fully identified, ensuring that trees are healthy, with plenty of nutrition and water for increased vigor, remains one of the best options.
Because the threat is fairly recent and is still undergoing testing, effective treatment methods have not been completely identified. In fact, the best treatment method currently entails rapid detection and removal of infested trees before the pest-disease complex can spread.
Discussions at the recent Entomology meetings suggested systemic treatments with neonicotinoid insecticides for twig feeding and possibly lower trunk applications in early fall with contact insecticides for the over-wintering stage. While no fungicide has been found to effectively treat the resulting canker, microinjections of phosphite have been suggested, and research is currently ongoing.
What can you do?
Keep an eye out for beetle damage and canker formation, understanding that bark removal may be necessary to gauge the full extent of fungal damage.
Jesse Lee is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit<ITAL] www.Mauget.com to learn more about Thousand Canker disease, steps taken to prevent and control it, and proper pesticide application and use.