AgEBB-MU CAFNR Extension

Green Horizons

Volume 20, Number 1
January 2016

While Thousand Cankers Disease (TCD) has not yet been found in Missouri black walnut, it remains our worst nightmare. Missouri has 20% (two or more times any other state) of the walnut trees in the entire native range of the species that has been nationally valued at $539 Billion. That is the "standing value" of the walnut trees and does not include the derivative values of this uniquely beautiful wood in the domestic and international market chain.

Black walnut is the most valuable timber species landowners in Missouri can grow, so the loss to individual landowners could be tens to hundreds of thousands of dollars depending upon the size of acreage with walnut. Third and fourth generation families whose businesses are exclusively dependent on black walnut nut processing or walnut wood milling could eventually have to "close up shop!" Urban parks and residential areas would face significant expense in removal of dead and dying walnut trees. It would not be a pretty sight!

TCD is spread by a tiny (1/16") walnut twig beetle thatcarries the spores of the fungal organism that causes the cankers (TCD) under the bark. Thousands of these small cankers disrupt the movement of nutrients in the tree and overwhelm the tree's defenses leading to decline and death. While the insect vector is believed to advance the infestation only a mile or two per year, it is humans that can inadvertently spread the disease hundreds of miles by moving infested firewood, logs or pieces of walnut logs with bark attached that have not been kiln dried or sanitized. Look, for example, at the rapid spread of the Emerald Ash Borer throughout the Midwest, which is in large part due to movement of infested wood, especially firewood, and not the dispersal of adults seeking new trees to infect.

Landowners can help guard against TCD becoming established in Missouri. To learn more about this disease visit http://mdc.mo.gov/your-property/your-trees-and-woods/tree-diseases-and-pests/thousand-cankers-disease or view a TCD brochure at: http://mdc.mo.gov/sites/default/files/resources/2011/01/tcdupdate4_13.pdf

There are several references with photos of symptoms to look for and who to contact for assistance. If you see declining walnut trees, especially a stand of trees with wide variation in amount of decline, take some photos of the stand, individual trees and declining areas of the tree crown, and submit them. We have pathologists and entomologists that are more than willing to look at the photos and decide if an arborist should be sent to examine the trees.

A Missouri Invasive Forest Pest Plan and a TCD Action Plan have also been prepared to provide a coordinated response to invasive pests in Missouri forests and to TCD in particular. Please note that these plans are two separate documents that are available on the MU Extension "Tree Pests" home page at: http://extension.missouri.edu/treepests/home.aspx

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