Thousand Cankers Disease
Geosmithia morbida (vectored by Pityophthorus juglandis)
Overview
An emerging disease of walnut trees caused by a fungus vectored by the walnut twig beetle. Produces numerous small cankers around beetle galleries that coalesce and girdle branches.
Symptoms
Yellowing and thinning of the crown. Branch dieback starting in upper canopy. Numerous small, dark cankers around tiny beetle entry holes under bark. Cankers coalesce and girdle branches. Tree death over 2-3 years.
Environmental Conditions
Variable
Prevention
Do not move walnut wood from infested areas. Monitor for walnut twig beetle. Maintain tree vigor. Plant resistant species where available. Quarantine regulations in many states.
Management
No effective treatment. Remove and destroy infected trees. Do not transport walnut wood. Systemic insecticides may reduce beetle populations. Report suspected cases to state forestry agencies.