Thousand Cankers Disease
HIGHGeosmithia morbida (vectored by Pityophthorus juglandis)
Overview
A disease complex involving the walnut twig beetle and an associated fungus that has caused significant mortality of black walnut, particularly in western states. Thousands of small cankers coalesce to girdle branches and the trunk.
- Type
- Disease
- Severity
- HIGH
- Source
- USFS
Symptoms
Yellowing and thinning of upper canopy, branch dieback progressing downward, tiny bark beetle entrance holes, numerous small dark cankers under bark that merge together, staining of sapwood
Affected Species
Geographic Spread
Treatments
Quarantine and Firewood Restrictions
State quarantines restricting movement of walnut wood products and firewood from infested areas. The primary regulatory tool to slow disease spread to new regions.
Maintain Tree Health
Proper watering, mulching, and fertilization to maintain vigor of walnut trees, as stressed trees are more susceptible. Avoid wounding bark. No chemical treatments have proven effective.
Recommended Products & Tools
Helpful supplies for managing Thousand Cankers Disease. Always read and follow label directions, and confirm a diagnosis before treating.
Protectant spray for many bacterial and fungal diseases.
For the rare case sealing is advised (e.g., oaks in oak-wilt season).
Sharp, clean cuts to remove affected wood — a tree-care essential.
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Frequently Asked Questions
What is Thousand Cankers Disease?
A disease complex involving the walnut twig beetle and an associated fungus that has caused significant mortality of black walnut, particularly in western states. Thousands of small cankers coalesce to girdle branches and the trunk.
What are the symptoms of Thousand Cankers Disease?
Yellowing and thinning of upper canopy, branch dieback progressing downward, tiny bark beetle entrance holes, numerous small dark cankers under bark that merge together, staining of sapwood
Where is Thousand Cankers Disease currently found?
Thousand Cankers Disease is currently active in Arizona, California, Colorado, Idaho, Indiana, Maryland, North Carolina, New Mexico, Ohio, Oregon, Pennsylvania, Tennessee, Utah, Virginia, Washington. It has been reported in 15 total states across the United States.
What plants are affected by Thousand Cankers Disease?
Thousand Cankers Disease affects Black Walnut. Susceptibility varies by species.
How do I treat Thousand Cankers Disease?
Treatment options for Thousand Cankers Disease include: Quarantine and Firewood Restrictions, Maintain Tree Health. Treatment approaches may include chemical, biological, cultural, and mechanical methods depending on the severity and context.