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Thousand Cankers Disease
Walnut Twig Beetle and Exit Holes  Thousand Cankers Disease Damage
             Kathy Keatley Garvey, UC ANR                                                                                                         Ned Tisserat, Colorado State University,

State Issues Quarantine to Stop Spread of Thousand Cankers Disease
Quarantine for Thousand Cankers Disease:

Virginia is under state quarantine to control the movement of the Walnut Twig Beetle and associated fungus Geosmithia morbida.  Under this quarantine Walnut wood and living trees (any species in the Juglans genus), Walnut Twig Beetle, and Geosmithia morbida, cannot be moved outside of Prince William County or the cities of Manassas and Manassas Park.  Several other cities and counties are included under this quarantine.  Note that branches and wood chips, (including composted wood chips) are included in this quarantine and also cannot be moved.  For detailed information on the Quarantine please visit The Virginia Department of Agriculture and Consumer Services.

To prevent the introduction of other invasive species, firewood and other untreated wood should not be moved far distances. Generally, it is recommended to move untreated wood no farther than 50 miles from its source, ideally under 10 miles is best.

Thousand Cankers disease (TCD) was originally found in New Mexico and Colorado, where the native walnut trees are naturally resistant.  Black walnut is native to the eastern US, but settlers moving out west sometimes took black walnut trees with them, to plant at their new homes.  TCD was first found to be killing black walnut trees in Colorado in 2003.  Although it was a pretty big problem for trees in Colorado, a large prairie separates the Colorado infestations from the native range of black walnut. Land managers in the eastern US hoped this would provide some protection, but TCD was found in Knoxville, TN in the summer of 2010.  This was the first confirmed infestation east of the prairie, well within the native range of black walnut.  In 2011, TCD was also confirmed in Chesterfield and Henrico Counties in Virginia.  In 2012, TCD was confirmed in Prince William County (see Infestation Update below).
TCD is a very interesting disease because it is caused by a fungus, but is carried from tree to tree by a beetle.  Without the walnut twig beetle, the fungus would have a very hard time infecting more trees. The walnut twig beetle’s life cycle includes four stages.  The adult lays eggs on a black walnut tree, and larvae hatch from the eggs.  The larvae burrow into the tree, and eat the phloem and cambium under the bark, leaving behind tunnels or “galleries” where ever they go. The larvae will eventually pupate and turn into adults, who chew their way out of the tree and fly on to lay eggs somewhere else.  The fungus, Geosmithia morbida, grows in the galleries created by the larvae.  The fungus also feeds on the tree, killing the plant tissues as it grows.  All of this happens on a really small scale, but eventually enough galleries are formed and become infected with Geosmithia morbida that they kill the entire tree.  You probably won’t see the insect itself, (the beetle is about the size of a grain of rice!), but you can see the symptoms of yellowing leaves and top down dieback in black walnut.
Infestation Update (Fall 2020): Since PWC was quarantined in 2012, the Mosquito and Forest Pest Management Branch has been investigating the  extent of the problem.  Monitoring efforts were initiated in Summer 2013 by establishing trap sites throughout the county.  Our monitoring efforts involve setting up black funnel traps with a pheromone that attracts walnut twig beetles. Technicians check them weekly and send suspect insects to Virginia Tech for official identification.  Visual surveillance is also performed to track tree health and symptoms of TCD.
Four new positive sites were found in addition to the initial infestation found in Occoquan in 2012. In 2017 Walnut Twig Beetle was confirmed at six sites on the eastern end of the county including sites along the Route 1 corridor, Old Bridge Road, and eastern Dumfries Road. Monitoring efforts will continue to track the spread of the infestation.
For more information about symptoms and what you can do, click here.

 Contact Us

14879 Dumfries Road
Manassas, VA 20112
Phone: 703-792-6279
Fax: 703-791-3092


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