​Walnut Twig Beetle and Thousand Cankers Disease

Thousand Cankers Disease of Walnut

Thousand cankers disease (TCD) is a disease complex native to the western United States that primarily affects black walnut, Juglans nigra. This disease is the result of the combined activity of a fungus, Geosmithia morbida, and the walnut twig beetle (WTB) Pityophthorus juglandis.

Thousand cankers disease currently threatens millions of black walnut trees in forests and urban areas. Black walnut is an important species with great economic and ecological value throughout its native range. TCD is not federally regulated. Several states have established quarantines in an attempt to prevent the disease from spreading.

Maryland Quarantine Order

On January 12, 2015, the Maryland Secretary of Agriculture issued a quarantine order to minimize the risk of moving infested material out of the limited action area in Cecil County and to provide confidence in Maryland walnut products moving into neighboring states from non-quarantined areas. The 2015quarantine order has been updated to include all of Baltimore City and part of Baltimore County. The new quarantine was signed on May 1, 2019, by the Maryland Secretary of Agriculture. The quarantine order, map, press release,  and quarantine area map links are listed on this page under Quarantine Information. 


TCD was first discovered within the native black walnut range in the U.S. in 2010 in Tennessee. In 2011, Forest Pest Management begun visually serving for TCD, and in 2012 added 28 pheromone baited traps to the survey. No visual signs of TCD were observed and on WTB were collected.
In the summer of 2013, MDA visually surveyed 248 areas and deployed 29 pheromone traps (see map). All visual surveys and traps were negative except one in Cecil County in the Fair Hill Natural Resource Management area (NRMA).  All four collections from this trap were positive for WTB. The identification was confirmed (on January 6, 2014) by Joel Floydo  Domestic Diagnostic Coordinator, USDA Animal and Plant Health Inspection Service. A total of 30 WTBs were collected. Visual evidence of TCD was not noted. Branch samples collected on December 19, 2013 were analyzed and TCD was not detected.  Several times during the winter of 2013/2014 additional branch samples were taken and TCD was not detected.

In 2014, the positive trap was reset on April 1 and checked every two weeks from spring into the late fall. This trap was taken down on December 2, 2014.  Eighteen WTB were collected. To try to determine the extent of the WTB infestation, 12 pheromone baited traps were deployed near the initial positive trap. Thirteen traps in total were deployed in Fair Hill NRMA. Statewide, 43 pheromone baited traps were deployed in 2014. Only the original positive trap was positive for WTB.  At this same site, bait logs were deployed in 2014. These logs were black walnut branches about 1.5 inches in diameter and 12 inches in length and baited with WTB pheromone. On October 6, 2014, USDA-FS and the University of Minnesota confirmed the presence of Geosmithia morbida – the pathogen that causes TCD - from one of the logs.  

A quarantine has been issued by MDA to minimize the risk of moving infested material out of the limited action area, and to provide confidence in Maryland walnut products moving into neighboring states. In addition, Fair Hill NRMA agreed to discontinue the firewood cutting program.

Current Situation

In 2018, forty-nine (49) traps were set in 18 counties across Maryland for detection. Thirteen (13) traps were set in Cecil County for delimiting. Trap CE01 was again positive for WTB in 2018. Four (4) traps were set near a positive site discovered in Baltimore City by Plant Protection in an exotic wood boring beetle survey in 2017. Traps BC01, BC02, BC03, and BC04 were also positive for WTB. Branch samples taken from the tree at BC04 were also positive for TCD. Initial identification of WTB in trap samples was made by Lawrence Barringer, PDA entomologist. Specimens were confirmed by Dr. Robert Brown APHIS PPQ Domestic Identifier at Purdue University Geosmithia morbida (TCD) was detected by Jennifer Juzwik, Pathologist USFS NRS, and confirmed by DNA analysis by her Research Associate, Anna Yang, UM. Trees at the original positive site have not shown evidence of decline as of yet.

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