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Thousand Cankers Disease: Frequently Asked Questions

How can I tell if my black walnut tree is affected?

The beetles and fungus girdle the twigs and trunk restricting water and food movement within the tree so symptoms often mimic that of drought stress. Symptoms include yellowing, browning and wilting foliage, usually starting at the top of the tree and progressing downward. The brown leaves often remain attached to the branch after the branch dies. Trees showing symptoms in the fall may not leaf out at all in the spring or will leaf out but quickly collapse once temperatures increase.

How long does it take this disease to kill my walnut trees?

Once a tree begins to show symptoms of dieback and wilting foliage, it takes 2-3 years for a tree to die.  However, the beetle may take as much as 8-10 years of continuous feeding before crown symptoms begin to appear.

What does the walnut twig beetle look like?

The dark brown beetles are hard to see because they are very small; most are approximately 1.5 mm in length. The exit holes are again very small and best seen with a magnifying glass when looking at smaller twigs.

Will the walnut twig beetles attack trees other than walnut?

No, walnut twig beetles attack only walnut trees. Black walnuts are at highest risk. English (Persian) walnuts are not attacked as readily as eastern black walnut.

My walnut tree still has some green leaves. Will it recover?

Any portion of your tree that is dead or has brown leaves will not recover or releaf back out again. Trees attacked by walnut twig beetles often sprout from the base of the tree. Generally, basal sprouts are not well attached to the trunk and should not be left to grow into large trees.

TCD is very aggressive. Once your tree is symptomatic, it will not recover. If your tree is not symptomatic, there is a chance you might prevent attack if you follow the guidelines below. The disease is often found in the tree long before symptoms appear, however, so we highly recommend that you contact a tree care professional immediately to determine if your tree is already infected and determine the best option for preventing further damage to your tree.

What can I do to save my walnut trees?

Good sanitation - 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 or burying all branches and smaller diameter wood as soon as possible.

Walnut wood should not be kept for firewood. If wood is kept to be milled or used in woodworking projects, it must be debarked. Waste bark from any debarking activity should be burned or buried to prevent the beetles from emerging and attacking other walnut trees.

Maintain overall tree vigor - All efforts should be made to keep your walnut trees as healthy as possible. Trees should be watered at the rate of at least 15 gallons per inch of trunk diameter every two to three weeks through the summer months (example: 10-inch diameter tree should receive 150 gallons of water every 2-3 weeks). Roots can continue to grow during winter months so supplemental watering should be continued monthly on warmer days through the winter. Avoid damaging the trunk or roots around your walnut tree during construction projects and lawn maintenance. Avoid using your walnut tree for a child's swing or other recreational use. If you are planning a construction project, contact a certified arborist to get advice on how to best protect your trees.