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Thousand Cankers Disease

Picture of Healthy Black Walnut
Photograph by: Leo Donovall, Pennsylvania Dept of Agriculture

The Pennsylvania Department of Agriculture is responsible for the identification of plants/weeds, insects and mites, nematodes, fungi, bacteria and viruses that impact Pennsylvania's natural resources, abundant flora and economy.  On Aug. 9, 2011, the department in cooperation with the U.S. Department of Agriculture and Penn State Cooperative Extension confirmed the presence of Thousand Cankers Disease in black walnut trees in Bucks County.

Thousand Cankers Disease is caused when Walnut Twig Beetles, which carry a fungus (Geosmithia morbida), tunnel beneath the bark of walnut trees, causing small cankers to form.  Over time, repeated beetle attacks and the resulting cankers cause disruption of the movement of water and nutrients throughout the tree, which leads to dieback of branches and kills the tree, usually within 10 years.  There is no known cure for Thousand Cankers Disease.

Early symptoms of the disease are yellowing of leaves and foliage thinning of the upper crown of the tree.   As the disease progresses, larger limbs are killed followed by the trunk.

The disease poses a significant threat to the state's $7 billion hardwoods industry. Black walnut trees, which make up less than half of one percent of hardwood trees in Pennsylvania, produce high-valued lumber used in woodworking and furniture-making.  The nuts of the trees are consumed by humans and wildlife.

DiseasedlimbDiseased limb
Photograph by: Whitney Cranshaw, Colorado State University,


  • Thousand Cankers Disease (TCD) was described in the western United States in the 1990s, but was not well understood until after 2000.
  • Since 2010 TCD has been confirmed in Tennessee, Virginia, Ohio, and North Carolina, showing 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 had confirmation of 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, stopping the movement of all walnut material and all firewood from Bucks County outward.
  • June 23, 2014 PDA and USDA confirmed the presence of both the walnut twig beetle and fungus from Chester County.
  • Agriculture Secretary George Greig signed a new quarantine order on July 22, 2014, to include Bucks, Chester, Delaware, Montgomery and Philadelphia counties.  Walnut material, wood chips/mulch and firewood may move unrestricted within this area, but may not move outward from the five counties.
  • Lancaster County was added to the existing quarantine in November of 2014.


  • Since this pest complex cannot be eradicated in Pennsylvania, and since black walnut is of high value to the forest products industry and to forest and urban ecologies, the Pennsylvania Department of Agriculture is joining with state and federal agencies and Penn State Cooperative Extension to slow the spread of TCD in the state through monitoring and quarantine.
  • A revised quarantine order signed July 22, 2014 increased the number of counties included in the quarantine area.  The quarantine restricts the movement of all walnut material including nursery stock, budwood, scionwood, green lumber and firewood.  It also covers other walnut material living, dead, cut or fallen including stumps, roots, branches, mulch and composted and uncomposted chips.  Due to the difficulty in distinguishing between species of hardwood firewood, all hardwood firewood is considered quarantined.
  • The quarantine also restricts the movement of walnut material and hardwood firewood from states known to have Thousand Cankers Disease including Arizona, California, Colorado, Idaho, Indiana, Maryland, Nevada, New Mexico, North Carolina, Ohio, Oregon, Tennessee, Utah, Virginia and Washington.
  • Non-compliance with the quarantine order could result in criminal penalties of up to 90 days imprisonment and a fine of up to $300 per violation, or a civil penalty of up to $20,000 per violation.
  • Survey will determine if TCD is present in other parts of the commonwealth.

Who is affected by the quarantine order?

Industries that buy or sell walnut products in the commonwealth will be affected by the quarantine order, including:

  • Lumber and wood sales
  • Artisan community that works with walnut
  • Distributors of hardwood firewood
  • Distributors of wood chips and mulch
  • Nurseries and plant merchants who sell Juglans spp. (including native plant nurseries)
  • Arborists who trim trees (will need to follow strict sanitation guidelines for disposal of any walnut debris)
  • Townships/collection businesses who remove discarded yard waste
  • Lawn maintenance/landscapers who provide clean up services.

In addition to restrictions on all hardwood firewood under the Thousand Cankers Disease Quarantine, the Pennsylvania Department of Agriculture also issued an Order of Quarantine in 2007 prohibiting the movement of firewood of all types and species into the Commonwealth of Pennsylvania unless it is labeled as "kiln dried" and/or is USDA certified.  This quarantine is designed to help slow the spread of this and other nonnative invasive forest pests and diseases that are often moved long distances hidden in firewood.  You can help protect Pennsylvania's urban, suburban, and forested areas from nonnative invasive forest pests and diseases by doing the following:

  • Buy/burn locally cut firewood
  • If you have already brought firewood from another area, BURN IT.  Do not leave it.  Do not take it with you.
  • Encourage your friends and neighbors not to move firewood distances greater than 50 miles.

For more information or to report a possible case of Thousand Cankers Disease on walnut please contact your local county cooperative extension office, or contact the Invasive Species Hotline at 1-866-253-7189 or