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Mosquito and Forest Pest Management
Asian Tiger Mosquito
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Thousand Cankers Disease of Black Walnut
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State Issues Quarantine to Stop Spread of Thousand Cankers Disease
On July 21, 2011, t
he Virginia Department of Agriculture and Consumer Services established a temporary quarantine in an effort to prevent the artificial spread of this disease (
a fungus that attacks walnut trees
to uninfested areas of the Commonwealth. It is spread by walnut twig beetles, which bore under the bark of the tree, leaving pin-sized holes. Effective January 2, 2012, the Thousand Cankers Disease Quarantine was made permanent. As a result of additional TCD detections in Fairfax, King William, New Kent and Prince William counties, the TCD quarantine was expanded in 2012. Localities now included in the quarantine include Chesterfield, Fairfax, Goochland, Hanover, Henrico, King and Queen, King William, New Kent, Powhatan and Prince William counties and the cities of Colonial Heights, Fairfax, Falls Church, Manassas, Manassas Park and Richmond. The quarantine prohibits the movement of all walnut plants and walnut plant parts, including logs, stumps, firewood, roots, branches, mulch and chips out of the quarantined area.
for details about the quarantine.
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 xylem and phloem, leaving behind tunnels or
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.
, 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
that they kill the entire tree.
You won’t see the insect itself, but you will see the symptoms of yellowing leaves and top down dieback in black walnut.
Infestation Update (December 2013):
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 19
throughout the county.
Our monitoring efforts involve setting up
black funnel traps
with a pheromone that attracts male walnut twig beetles. They are installed in late June-early July, and remain up until the end of August. Technicians check them weekly and send suspect insects to Virginia Tech for official identification.
Four new positive sites were found in addition to the initial infestation found in Occoquan in 2012. The 4 new sites were in Lake Ridge along Old Bridge Road, at Veterans Park, Dale City Recreation Center, and at Rippon Landing (
). Monitoring efforts will continue to discover more infested areas and to track the spread of the infestation.
For more information about symptoms and what you can do, click
14879 Dumfries Road
Manassas, VA 20112
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