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The Missouri Department of Agriculture is asking folks who harvest black walnuts to be on the lookout for a pest that could possibly wipe out the trees in our region.
Thousand Cankers Disease (TCD) is a pest complex that has caused mortality in walnut in many western states. It is now present in the eastern native range of black walnut, but has not yet been detected in Missouri. 
The walnut twig beetle is dark brown and smaller than a grain of rice.  It looks very similar to the broken tip of mechanical pencil lead.  This situation could become catastrophic, eliminating the black walnut species, if walnut twig beetles colonize in areas where black walnut grows as a native tree.
Recent observations in Colorado suggest adults and larvae burrow under the bark of trees during the winter. In the spring the adults emerge and begin to make new tunnels under the bark and lay eggs. A generation can be completed in about 6-7 weeks. 
Two, possibly three overlapping generations will be produced during a growing season. In Missouri, beetles may emerge a few weeks earlier, possibly as early as late March in southern Missouri. Adult beetles may also become more active on warm winter days.  Some experts say it could take a decade or longer for a tree to die once it becomes infected with TCD.
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Some warning signs that a tree has been infected are that the leaves on the upper branches of the tree will turn yellow and wilt.  Branches then could die from the upper crown downward.  New sprouts could germinate from the tree roots or trunk, giving the tree a bushy appearance. 

Cankers produced from the beetle/fungal attack are under the bark and may be hard to see. Some seepage from the bark may occur, and tiny “pinholes” mark the beetles’ exits from the bark, but are difficult to detect. Carefully removing upper layers of bark from dying limbs exposes numerous dark brown cankers with tiny beetle tunnels in the centers of the cankers.
The Missouri Department of Agriculture is as has enacted a state exterior quarantine to protect Missouri's black walnut resource from Thousand Cankers Disease. The quarantine prohibits wood products, including walnut bark and all firewood, from infected areas from coming into Missouri. States affected by Missouri’s quarantine include Arizona, California, Colorado, Idaho, Nevada, New Mexico, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Utah, Virgina and Washington. Several other states have enacted similar quarantines, including KansasMichiganNebraskaOklahomaIndianaMinnesota,WisconsinArkansasIllinois and West Virginia. The known infested states of North CarolinaOhioPennsylvaniaTennesseeVirginia and also have state quarantines.

If you think you have seen the twig beetle or TCD in Missouri, contact the Missouri Department of Agriculture, Office of the State Entomologist at (573) 751-5505.

For more information go to the following website:  http://extension.missouri.edu/emeraldashborer/pdf/thousandcankersfaq.pdf