Tree problems · Disease

Thousand Cankers Disease: signs and what to do

Thousand Cankers Disease is a tree disease, often seen on black walnut. Look for: yellowing and wilting of leaves in the upper crown, then dieback of branches.

General information, not a diagnosis. A certified arborist or your county extension office can confirm.

Disease
Black walnut

Signs to look for

Tick what you see. More ticks make it more likely, but only an on-site look can confirm.

Yellowing and wilting of leaves in the upper crown, then dieback of branches
Many small dark cankers under the bark of branches, often found only after peeling the bark
Tiny round exit holes made by the walnut twig beetle
Fine, sawdust-like material or tiny galleries just under the bark
Twigs and small branches dying and the crown thinning over a few years
Sprouts forming along the trunk as the tree declines

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Season

Crown dieback is easiest to see in summer when leaves should be full. The beetle can be active across the warm months.

How it spreads

A tiny bark beetle (the walnut twig beetle) carries a fungus (Geosmithia morbida) into the bark. The beetle makes wounds and the fungus makes many small cankers that cut off the flow of water and food. Moving walnut wood, logs and firewood can carry it to new places.

Where it is found

It was first noticed in the western United States and has since been found in some eastern states, where black walnut grows naturally. Check your state official map; ranges change.

Official sources

What to do

1
Take photos of the crown, the branch tips and any small holes in the bark.
2
Do not move walnut logs, branches or firewood out of the area.
3
Call your extension office or state agriculture department to ask about testing and local rules.
4
Have a certified arborist look at the tree. Other problems, such as drought and root damage, can look similar.
5
Follow your state's advice on how to dispose of a confirmed tree, such as chipping or burning on site where allowed.

Safety first: do not climb, do not cut near power lines and do not use a chainsaw on storm-loaded wood. Call the utility for downed lines and 911 if anyone is in danger.

Prevention

Keep walnut trees healthy with deep watering in dry spells and no root damage. Buy firewood near where you burn it, and do not move walnut wood between regions.

When to call a pro

Call a certified arborist if a black walnut has crown dieback, many dead twigs, or shows beetle holes, or if it stands near a house or driveway.

Not sure who to call? Read how to hire a tree service or check is my tree dangerous?

Trees it affects

Usually seen on: Black walnut.

Black walnut

See all species in our tree library, or pick a tougher tree with the tree picker.

For tree companies

How to explain thousand cankers disease to a customer

Tell the homeowner that walnut dieback can have several causes, and that you will check before saying it is this disease. If you suspect it, explain that reporting it and following local wood-moving rules protect other walnut trees. Do not use fear to sell a removal.

Send this page to the customer after your visit so they can read the signs in plain words. See also selling plant health care and the job photo checklist.

Questions

What is thousand cankers disease?

It is a disease of walnut trees, mainly black walnut. A tiny beetle carries a fungus into the bark and causes many small cankers.

Why is it called thousand cankers?

A sick tree can have a very large number of small dead patches under the bark, mostly around the beetle tunnels.

Can I cure an infected walnut?

There is no known cure for a tree that is badly infected. Healthy trees in good care are better able to cope with stress.

Can I use the wood from an infected tree?

Rules differ. Ask your state agriculture office before moving or selling any walnut wood from a suspect tree.

Does it harm people or pets?

No. The risk is to the tree itself, and to a weak tree dropping limbs.

How do I know it is not drought?

Drought and root damage can look similar. A lab or expert check of the bark and the beetle is needed, so ask an arborist or extension office.

Can Lirevon diagnose thousand cankers disease on my tree?

No. Lirevon is a remote marketing team for tree service companies and does not do tree work. This page is general information, not a diagnosis. A certified arborist or your county extension office can confirm what is wrong with your tree.

How do I find a good local pro for this?

Search Google Maps for certified arborists or tree services near you, read their reviews and ask for proof of insurance. Get two or three written quotes. Our guide on how to hire a tree service lists the questions to ask.

When customers spot thousand cankers disease, they call

Make sure someone answers. Missed-call text-back, lead follow-up, booking and review requests, set up for you. See our services and pricing.

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