Thousand Cankers Disease
Geosmithia morbida (vectored by Pityophthorus juglandis)
7 host plants
Last updated
In walnut trees, you may notice the telltale signs of thousand cankers disease: numerous small cankers appearing on trunks and branches, often with amber-colored ooze at their centers. These cankers start as tiny lesions but accumulate over time, giving the disease its name. The small bark beetles that vector the disease work year-round, though activity peaks during warmer months. An infected tree might look deceptively healthy at first, with full foliage despite the cankers forming beneath the bark.
If you spot these symptoms on a walnut, the disease is already progressing and will eventually kill your tree; there is no cure once infection takes hold. What matters most is preventing spread to other walnuts in your area. Do not move firewood, chips, or branches from infected trees to other locations, and if you must remove an infected tree, chip the material promptly as the beetles cannot survive in properly dried chips. The key to managing this disease is prevention: avoid planting susceptible walnut species in areas where thousand cankers disease is already established.
Quick Reference
Management
Cultural Controls
- Do not plant susceptible species in areas where TCD is known to occur.
- Maintaining excellent tree health by providing adequate water and good nutrition may help slow progress of the disease, but will not prevent infection or eventual death of infected trees.
- In known TCD areas, do not move live plant material or raw wood (branches, chips, logs, firewood, stumps, etc.) from susceptible trees.
- Beetles are able to complete their lifecycle in cut wood and can also reinfest cut logs that retain any bark.
- Beetles have been observed to survive in large-diameter, freshly cut chips.
- However, chips will dry and become unsuitable host material for both beetles and fungus in a relatively short time, so chipping is considered one of the better ways to deal with infested materials.