Walnut Twig Beetle & Thousand Cankers Disease Management

About Thousand Cankers Disease (TCD)

Thousand cankers disease (TCD) is a disease complex native to the western United States that primarily affects black walnut, Juglans nigra. TCD was first discovered within the native black walnut range in the U.S. in 2010 in Tennessee.

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 Orders

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 2015 quarantine order has been updated to include all of Baltimore City and part of Baltimore County.

A new quarantine was signed on May 1, 2019, by the Maryland Secretary of Agriculture.

Monitoring Activities

The Maryland Department of Agriculture in cooperation with the U.S. Forest Service has conducted several programs to monitor this pest/disease complex.

Visual Surveys

From 2011 through 2013 visual surveys of walnut stands were conducted throughout the state. Field staff were looking for symptoms of premature yellowing in early summer and dieback in the trees. Since the disease was not known to be wide spread these survey were discontinued.

Trapping

Since 2012 pheromone baited traps have been set throughout the state at selected walnut stands. Traps are monitored from Mid Summer through Mid Fall, with bi-weekly collections. Samples are sent out of state for inspection and pest identification. Walnut Twig beetles have been recovered from one site in Cecil County. This site has been extensively monitored with additional traps.

Disease Identification

At the Cecil Co. site wood samples were taken from the positive trap site and cultures run to identify the presence of the fungus. One tree has tested positive. Other trees at the site have not. Additional sample will be done if other sites have positive beetle collections.

Monitoring History & Findings

2011 & 2012 Findings

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 no WTB were collected.

2013 Findings

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.

2014 Findings

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.

2018 Findings

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.

​Walnut Twig Beetle & Thousand Cankers Disease Management