How do I know if it is Thousand Cankers Disease?

It starts with yellowing and thinning of the upper canopy, followed by branch death. You will need an arborist to confirm the presence of the beetle.

Can I use systemic pesticides?

Systemic treatments are sometimes used for high value trees, but they must be applied by a licensed professional.

Black Walnut: pests, causes and fixes

Check these first

Look for small holes or sawdust on the bark.
Check the canopy for branches that are dying back.
Inspect the leaves for signs of chewing or webbing.

Likely causes

Walnut Twig Beetle
Most likely
How to tell: Look for small entry holes in the bark and branch dieback in the upper canopy. This beetle carries the fungus that causes Thousand Cankers Disease.
What to do: Prune and destroy any branches showing signs of dieback. Consult a local arborist if you suspect a widespread infestation in your area.
Walnut Caterpillar
Possible
How to tell: Large groups of hairy caterpillars feeding on leaves. They often congregate on the trunk or branches when not feeding.
What to do: Use a high pressure water spray to knock them off the tree. For heavy infestations, apply a targeted insecticide.

Pests on other plants

Find out what's wrong with your black walnut

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

When to worry

Thousand Cankers Disease is fatal and requires immediate professional attention. Caterpillar damage is usually manageable unless the tree is very small.

Stopping it coming back

Keep the tree vigorous with proper watering and avoid wounding the bark, which can attract beetles.

Black Walnut: pests? Check yours with a photo

Every plant is a little different. Take a photo of your black walnut and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

Get the app · Or check it from a photo now, free

Questions people ask

How do I know if it is Thousand Cankers Disease?: It starts with yellowing and thinning of the upper canopy, followed by branch death. You will need an arborist to confirm the presence of the beetle.
Can I use systemic pesticides?: Systemic treatments are sometimes used for high value trees, but they must be applied by a licensed professional.

How do I deal with pests on my Black Walnut?