Picture of Healthy Black Walnut Photograph by: Leo Donovall, Pennsylvania Dept of Agriculture
The Pennsylvania Department confirmed the presence of Thousand Cankers Disease (TCD) in 2011. The disease was found on black walnut trees in Bucks County.
In 2022, the department repealed its quarantine order for TCD. TCD is now considered a public nuisance and plant pest. The same is true for the fungus Geosmithia morbida and the walnut twig beetle (WTB). Here are the criteria:
Native populations of Juglans nigra (black walnut) are largely unaffected by TCD here. This is despite detections of the beetle and/or fungus in nine states.
Surveys show the percentages of black walnut trees with TCD stayed the same in two locations for 3 years.
TCD outbreaks in Tennessee and Virginia may be a result of drought stress of the trees.
High precipitation and soil water potentials were associated with extensive new foliage. Stem growth and TCD recovery were also contributing factors.
The presence of TCD and/or the fungus in the eastern US could be part of a nationwide endemic. This could be related to the widespread presence of Geosmithia in other parts of the country.
Logs treated with certain entomopathogenic fungal pathogens provided suitable control of WTB populations. These commercially available pathogens include Beauvaria bassiana or Metarhizium brunneum. Tests of the pathogens and synthetic pyrethroid against WTB infection found similar results.
Thousand Cankers Disease is caused when Walnut Twig Beetles tunnel beneath the bark. These beetles carry a fungus (Geosmithia morbida) and their tunnelling creates small cankers. Repeated beetle attacks and cankers disrupt water and nutrient movement throughout the tree. This leads to dieback of branches but has not been shown to kill the tree.
Two early symptoms are the yellowing of leaves and foliage thinning of the upper crown. TCD can progress to kill larger limbs with droughts and other stresses. However, this danger is now considered less likely even in the trunk.
The department will continue to monitor walnut twig beetle and TCD outbreaks.
Photograph by: Whitney Cranshaw, Colorado State University, Bugwood.org
Timeline
TCD was described in the western United States in the 1990s. However, the disease was not well understood until after 2000.
Since 2010, TCD has been confirmed in Tennessee, Virginia, Ohio, and North Carolina. This shows the disease is spreading beyond the western United States.
On July 29, 2011, Penn State Plant Disease Clinic received a suspect sample from Bucks County, PA.
By Aug. 9, 2011, PDA and USDA confirmed the presence of both the walnut twig beetle and fungus from Bucks County.
Agriculture Secretary, George Greig signed a quarantine order on Aug. 10, 2011. The order stopped the movement of all walnut material and firewood from Bucks County.
On June 23, 2014, PDA and USDA confirmed the presence of both the beetle and fungus from Chester County.
Agriculture Secretary, George Greig signed a new quarantine order on July 22, 2014. This order included Bucks, Chester, Delaware, Lancaster, Montgomery and Philadelphia counties.
Survey results and research show that TCD damage is less severe than expected. Juglans sp., particularly Black Walnut, can also recover from infestation. Agriculture Secretary Russel Redding repealed the quarantine order, effective January 15, 2022.
Surveys for damage and spread will continue to ensure the health of the Juglans species.
Response
The quarantine repeal encourages businesses to continue inspecting products for walnut twig beetle. Treatment options are available for walnut twig beetle. There are also treatment options for logs for commerce that do not use methyl bromide.
Most states repealed their TCD quarantines. For changes in quarantine status, visit: www.nationalplantboard.org.