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Thousand Cankers Disease Detected in Baltimore City and County

State to expand quarantine zone to City, parts of Baltimore County

ANNAPOLIS, MD – The Maryland Department of Agriculture today enacted a quarantine, effective immediately, that makes it illegal for anyone to move any walnut material and hardwood firewood out of a 185 square mile area that covers Baltimore City and parts of Baltimore County. This action is in response to the detection of thousand cankers disease in a Baltimore industrial area. An existing quarantine remains active in Cecil County, as well.

The area quarantined includes all of Baltimore City and the southeast corner of Baltimore County (map). Non-compliance with the quarantine order could result in criminal or civil penalties.

“The department remains vigilant in preventing the spread of infectious plant disease,” said Secretary Joe Bartenfelder. “This quarantine is a necessary measure to protect our industry from thousand cankers disease and ensure neighboring states that Maryland walnut products remain safe for purchase.”

Thousand cankers disease 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, Pityophthorus juglandis.

The quarantine is designed to prevent the spread of thousand cankers disease, and restricts movement out of the quarantined area of all walnut material without a certificate of inspection for this pest. This includes nursery stock, budwood, scionwood, green lumber and firewood. It also covers other walnut material that is living, dead, cut or fallen, including stumps, roots, branches, mulch and composted and un-composted chips. Due to the difficulty in distinguishing between species of hardwood firewood, all hardwood firewood is considered quarantined.

Nuts, processed lumber and finished wood products without bark are exempt from the quarantine.

This is the second detection of the disease in Maryland since 2015. Walnut twig beetles were discovered at a trap site in 2018. Additional surveys were completed and the fungus was detected in walnut trees within 1 mile of the site. All samples were sent to the U.S. Forest Service and confirmed positive by their lab.   

Since 2011, MDA’s Forest Pest Management and Plant Protection sections have worked with the Maryland Department of Natural Resources and University of Maryland Extension to survey for walnut twig beetles and slow the spread of thousand cankers disease, for which there is no known cure.

Impact of Thousand Cankers Disease

Walnut trees become diseased when walnut twig beetles, which carry this fungus, tunnel beneath walnut bark, causing small cankers to form. The beetles, dark brown and about the size of a poppy seed, are extremely difficult to detect. As more beetles attack, cankers increase, slowly starving the tree of nutrients, killing it within 10 years of initial infestation.

Early disease symptoms include the yellowing of leaves and foliage-thinning of the tree’s upper crown. As the disease progresses, larger limbs die followed by the trunk.

Black walnut trees produce high-valued lumber used in woodworking and furniture-making. Walnuts are consumed by humans and wildlife. Black walnut trees are important in riparian forest buffers which are planted to provide better fish habitat, cleaner streams and a healthier watershed for the Chesapeake Bay.

Since many species of wood-boring insects, including walnut twig beetle and emerald ash borer, can be spread through transport of infested firewood and logs, campers and homeowners are encouraged to use only locally harvested firewood, burn all of it on-site and not carry it to new locations.

People who suspect they have seen thousand cankers disease should contact their local county extension office or MDA’s Plant Protection section at, 410-841-5920. Visit the department’s website for more details.

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Contact Information

If you have any questions, need additional information or would like to arrange an interview, please contact:
Jessica Hackett
Director of Communications
Telephone: 410-841-5888