This is a newly recognized disease (2008) of certain walnut species (Juglans sp.) caused by a fungus (Geosmithia spp.) that is carried by a bark beetle (Pityophthorus juglandis).

Over the past decade, thousand cankers disease has been attributed as the cause of widespread walnut mortality in nine western states (AZ, CA, CO, ID, NM, NV, OR, UT, and WA). Since 2010 has been confirmed within the native range of black walnut in the states of Tennessee, Pennsylvania, and Virginia.

You can learn more about TCD in your state using the “TCD in your state” dropdown menu in the left sidebar. If your state is not listed then TCD has yet to be detected.

The walnut twig beetle is believed to be native to North America. It was first described in 1928 from western New Mexico and has substantially expanded its range within the past couple of decades.

The fungus that causes the cankers was first described in 2008 and named Geosmithia morbida. The fungus is introduced to the trees by adult bark beetles causing numerous small cankers to form around the beetle galleries in the bark.

Preliminary research suggests the fungus might be native or has been present in the walnut twig beetle range a long time.

Take a look at our resources to help correctly identify walnut and TCD. If you suspect TCD, you may access reporting information specific to your state through the “TCD in your state” dropdown menu in the left sidebar.

You may also report any suspected finds of TCD in your state to your state member of the National Plant Board, your State Department of Agriculture, State Forester, or Cooperative Extension Office.

See our additional resources for more information.

Unfortunately, the cankers from TCD rarely show any of the external symptoms that are associated with most canker producing fungi that affect trees. The affected area is shallow and confined to the phloem of the tree so that it can easily be missed if inspection cuts are made too deeply into the sapwood. Minor weeping may occur at points where walnut twig beetles enter the bark but often no symptoms area associated with the beetle attacks aside from minute entry wounds or star shaped cracks.

Walnut twig beetles tunnel into the tree and introduce the fungus, which then kills an area under the bark. These dead areas are called cankers. When the walnut twig beetles are abundant, numerous cankers can form and coalesce to girdle twigs and branches, restricting movement of water and nutrients.

At this point, crown symptomns will begin to appear. Leaves in upper branches will turn yellow, wilt, and die. Branches die back gradually from the upper crown downward. Browning leaves often remain attached to twigs. New sprouts may grow from the tree roots or trunk giving the tree a bushy appearance below dead branches. Trees usually die within three years after initial symptoms are observed in the crown of the tree.

The Geosmithia fungus can consistently be recovered from the body of beetles, their galleries, and their frass. It appears that the fungus is essentially always found in association with the walnut twig beetle. Because of this the detection of the walnut twig beetle in a walnut tree can be considered equivalent to detection of TCD.

Pictures of the symptoms can be found in our photo gallery.

No, black walnut can be affected by several other diseases and insects. The USDA Forest Service published a key to identify other common black walnut issues.

Well watered and well maintained black walnut have been killed by the disease. The effects of drought on thousand cankers disease is probably minimal and indirect.

A canker is an area of dead plant tissue (lesion) on a plant stem, twig, or branch. These dead areas can block water and nutrient transport to portions of the plant and eventually cause these portions to die.

Cankers produced from the beetle and fungal attack are under the bark and may be hard to see. Some seepage from the bark may occur, and tiny “pinholes” mark the beetles’ exits from the bark. Carefully removing upper layers of bark from dying limbs exposes numerous dark brown cankers with tiny beetle tunnels in the centers of the cankers.

Pictures of the cankers can be found in our photo gallery.

The walnut twig beetle is dark brown and very tiny (1.5-2.0 mm). It is smaller than a grain of rice and similar in size to a broken tip of a mechanical pencil lead.

Pictures of the walnut twig beetle can be found in our photo gallery.

This insect has not been thoroughly studied. Recent observations suggest adult beetles overwinter in the thick bark of walnut trunks. The beetles emerge in the spring and fly to limbs where they initiate tunneling under the bark and lay eggs. A new generation can be completed in about 6-7 weeks, resulting in two or three generations during a growing season.

A more detailed description can be found in this factsheet about TCD of walnut(PDF) from Colorado State University.

Once your tree is symptomatic, it will likely not recover; however, we recommend that you contact a tree care professional immediately to determine the best option for preventing further damage to your tree.

In states where TCD is known to already be present further planting of black walnut is not currently recommended. Healthy trees do not need to be preemptively harvested to avoid the disease as the beetle and fungus do not damage the inner part of the tree. Infected trees can still be salvaged as long as the bark, phloem, and cambium are removed and disposed of properly.

No, the beetle tunneling, fungal growth, and staining are primarily limited to the tree bark and extend only slightly into sapwood, causing no injury to marketed wood. Neither of the two species associated with thousand cankers will affect the quality of the wood in any manner.

Observations in the western states indicate TCD is usually fatal; although trees that are well-sited and grow vigorously may resist, in part, the effects of thousand cankers disease. Furthermore, some Juglans species and hybrids appear to be more resistant to thousand cankers than black walnut. The course of disease may be substantially slowed in such trees.

Black walnut (Juglans nigra) is extremely susceptible to TCD and is the species of greatest concern. Evaluating other species is a major focus of ongoing research and while there is some tentative evidence suggesting resistance and susceptability to TCD varies, many other walnut species could also be affected. Hickories (Carya sp.) appear to be immune.

A more detailed description can be found in this factsheet about TCD of walnut(PDF) from Colorado State University.

The length of time it takes for a tree to die after it is first attacked by the walnut twig beetle is currently unknown; however, trees usually die within three years after initial symptoms are observed in the crown of the tree.

So far, no effective treatment has been found, but research is ongoing to try and identify treatments for the walnut twig beetle and/or the fungal canker.

A more detailed description can be found in this factsheet about TCD of walnut(PDF) from Colorado State University.

Walnut twig beetles can be trapped in traps designed for other bark beetles, however this trapping has not proven to be very efficient.

A more detailed description can be found in this factsheet about TCD of walnut(PDF) from Colorado State University.

Absolutely. TCD is presently having devastating effects on black walnut in many western states and has recently been confirmed in black walnut’s native range. If walnut twig beetles are allowed to spread, this situation could become catastrophic, resulting in the elimination of black walnut species in a manner previously demonstrated by the emerald ash borer (affecting Fraxinus spp.), Dutch elm disease (affecting American elm) and chestnut blight (affecting American chestnut).

Healthy trees do not need to be preemptively harvested to avoid the disease. Infected trees can still be salvaged for their commercial value (if so desired) as long as the bark, phloem, and cambium are removed and disposed of properly. The beetle and fungus do not damage the inner part of the tree.

Good sanitation will help protect your trees. If you have several walnut trees remove all dead/dying infected walnut trees from your property and dispose of the wood properly to reduce the chance of having your other trees attacked. Proper disposal of wood is by burning in accordance with your local air quality and burning regulations, or burying as soon as possible.

All efforts should be made to keep your walnut trees as healthy as possible. Avoid damaging the trunk or roots around your walnut tree during construction projects and lawn maintenance.If you are planning a construction project, contact a certified arborist to get advice on how to best protect your trees.

Logs and standing trees affected with TCD can support development of tremendous numbers of walnut twig beetles. As long as live beetles remain associated with this wood it remains extremely infectious and can easily allow the disease to spread. Because of this it is critically important to take every precaution against spreading walnut twig beetles and TCD through the movement of walnut.

Even moving walnut from non-quarantined areas is risky as pest infestations can take years before being discovered. Trees can be harvested and shipped after they are infected, but before being symptomatic or an official quarantine is announced. When possible, it is strongly recommended that wood be milled and used locally to prevent accidental spread of walnut twig beetles that can move the disease into new areas.

More information on the risks of moving wood can be found at Don’t Move Firewood website.

It is still reasonable to expect that spread of TCD can be contained. Effective regulations to prevent further spread of walnut twig beetle infested material are being considered and their adoption will have tremendous effect in reducing the risk of TCD spreading in the upcoming decades.

As public awareness of thousand cankers increases it is hoped that movement of infested walnut wood originating from infected and quarantined areas will largely cease. Woodworkers, lumber yards, tree removal services and firewood distributors are among the key groups that need to be provided information on this new disease.

At this point in time there is no need for walnut producers in the eastern US to alter any production practices or marketing plans. However, they should be engaged in the public relations work needed to restrict movement of walnut products that can support live walnut twig beetles and thus reduce the possibility of its spread into eastern production areas.

It is extremely important that walnut wood is never moved from areas where TCD has been detected. Due to the high value of black walnut for woodworking purposes, the movement of walnut wood is a serious concern.

Salvaged trees with bark intact will very likely contain these beetles. Walnut bark, or logs with bark intact, may be sources of infective beetles. Milled wood without bark and logs without bark that have been dried for three years or more likely will not be a source of risk.

More information on the risks of moving wood can be found at Don’t Move Firewood website.

It is very unlikely that any insect aside from the walnut twig beetle is important in the course of this disease.

Unlikely. There is no evidence the walnut twig beetle develops galleries in walnut hulls, and the Geosmithia fungus would be unable to effectively colonize the tree without the presence of the beetle.

Yes, walnut twig beetles have survived after bark has been chipped for mulch.

You can learn more about TCD in your state by choosing your state under TCD Locations.