Walnut tree disease spreads to northeastern Colorado

Thousand cankers disease, a relatively new disease to Colorado that is lethal to infested black walnut trees, has now arrived in the northeast plains. The disease was confirmed in Fort Morgan through cooperative efforts of the Colorado State Forest Service, Colorado State University Extension, City of Fort Morgan and the CSU Plant Diagnostics Clinic, and likely arrived in the community through the movement of infested wood.

After being introduced to Colorado in recent years, thousand cankers disease has caused significant tree mortality in many of the state’s urban forests, primarily along the Front Range from Fort Collins to Pueblo. Converse to emerald ash borer, another recently arrived Colorado tree pest that spread westward across the Great Plains via the transport of infested wood, thousand cankers disease has the potential to spread in the opposite direction, to the Eastern U.S. – potentially impacting large numbers of commercially valuable walnut trees.

“In the Midwestern states, black walnut trees have significant economic value,” said Boyd Lebeda, acting district forester for the CSFS Fort Morgan District. “So the spread of this disease could be damaging not only here, but to tree resources and related markets in other states.”

Thousand cankers disease is caused by a fungus carried by the walnut twig beetle. Once the fungus is introduced to a tree, it causes small dead areas in the bark called cankers. Trees are eventually killed by overwhelming attacks of walnut twig beetles and subsequent cankers that girdle branches. Currently, there are no effective methods for saving trees with the disease, and many states east of Colorado already have quarantines prohibiting the movement of walnut material.

The CSFS, CSU Extension and partner agencies have been in the process of monitoring the state’s black walnut trees for the past few years, travelling through communities in eastern Colorado to record tree locations and current conditions.

Landowners with black walnut trees in Morgan County and elsewhere in Colorado should inspect them regularly for symptoms including sparse foliage, leaf yellowing or wilting, branch dieback and excessive staining of the bark surface. Any suspect trees should be reported to the nearest CSFS or CSU Extension office.

Anyone who has a black walnut tree removed within the City of Fort Morgan can contact the city at 970-542-6311 to determine the best way to dispose of the tree.

Everyone can help minimize the spread of this and other tree diseases, including emerald ash borer, by not transporting raw wood – including logs, firewood, lumber and wood chips – to new locations.

For more information about thousand cankers disease, go to csfs.colostate.edu(PDF).