I must warn you that today’s post is a bit depressing. If you enjoy the beauty of walnut trees (Juglans nigra) and the delicious nuts that they produce, you may be a little sad after learning of the latest disease that is infecting these beautiful native trees.
Thousand Cankers Disease is caused by a fungus, Geosmithia morbida, that is brought into the phloem of the tree by the walnut twig beetle. Essentially, the fungus catches a ride on the beetle and is thereby introduced to the tree. The subsequent individual canker that is produced by the tree isn’t especially large, but there can be 35 cankers in a square inch of wood. These smaller cankers coalesce and turn into larger cankers that ultimately kill the tree. The trees essentially die of starvation as the phloem tissue is prevented from delivering the carbohydrates that are produced through photosynthesis to other areas of the tree where they are needed.
The walnut twig beetles like to feed on young, tender new stems and it is virtually impossible for the average homeowner to scale a large walnut tree to have a look. The beetles move south in the tree to the lower trunk tissue during the winter; it may be possible to observe some of the cankers and/or entry points at that time.
WHAT ARE THE SYMPTOMS OF THOUSAND CANKERS DISEASE?
The first clue that your walnut tree may be infected with Thousand Cankers Disease is branch dieback. As the leaves and branches are starved of nutrients, the tree’s self-preservation mechanism is to eliminate the area that isn’t receiving the “food” that is needed. The individual beetle entry points are small so they can easily go unnoticed. The cankers sometime weep sap and this is a dead giveaway that your trees are infected.
How does the old saying go: “the best defense is a strong offense”? If you currently have black walnuts on your property, make sure that they are not stressed by competition with turf and other plants. Mulch them well and supplement their water during times of drought. As with most insects, the walnut twig beetle will seek out the weakest trees first so anything that you can do to keep your trees thriving instead of just surviving is a plus.
WHAT CAN BE DONE IF YOUR TREES ARE INFECTED?
Unfortunately, not much can be done to save the trees once they are infected. In theory, systemic insecticides can be applied to the tree to lessen the activity of the beetles. If you suspect that your trees may be infected with Thousand Cankers Disease, I would seek the council of your local Extension Agent or an ISA Certified Arborist. If there is any saving grace to this disease, it is that the fungus is not translocated in the vascular tissue like Dutch Elm Disease.
It’s an unfortunate reality that Thousand Cankers Disease has already been identified in Virginia and Pennsylvania. I’m sure that as time goes on, this disease will continue to spread in the Mid-Atlantic gardening states. Let me know if you have any experience with Thousand Cankers Disease by leaving me a comment below or e-mailing me at email@example.com. Happy gardening!