Forest Insect and Disease Newsletter

Thousand cankers disease of black walnut

photo: thounsand cankers disease from Forestry imagesThousand cankers disease of black walnut Dieback and mortality of eastern black walnut (Juglans nigra) in several western states have become more common and severe during the last decade. The first confirmation of the beetle and fungus within the native range of black walnut was in Tennessee (July 2010).

A tiny bark beetle is creating numerous galleries beneath the bark of affected branches, resulting in fungal infection and canker formation. The image:Walnut twig beetle from Forestry Imageslarge numbers of cankers associated with dead branches suggest the disease's name—thousand cankers disease. The principal agents involved in this disease are a newly identified fungus (Geosmithia sp. with a proposed name of Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis). Both the fungus and the beetle only occur on walnut species. An infested tree usually dies within 3 years of initial symptoms.

The potential damage of this disease to eastern forests could be great because of the widespread distribution of eastern black walnut, the susceptibility of this tree species to the disease, and the capacity of the fungus and beetle to invade new areas and survive under a wide range of climatic conditions in the west.

A formal state exterior quarantine restricting the import of walnut trees and certain related products into Minnesota from areas known to be infested with thousand cankers disease (TCD) was signed into effect on August 8, 2011, by the Minnesota Department of Agriculture's (MDA) Commissioner Dave Frederickson. The formal quarantine is similar to the state emergency exterior quarantine that was issued in February, with a few minor revisions based on stakeholder comments. One of these revisions is to regulate "all hardwood firewood" rather than just firewood from Juglans species, making this order consistent with the firewood regulations in other states TCD quarantines and Minnesota's emerald ash borer quarantine. More information pdf


More information about TCD and the quarantine can be found on these websites:

If you do find walnut trees with unexplained dieback or decline, please call the Arrest the Pest Hotline (1-888-545-6684) and/or fill out the 2012 Walnut Decline/Dieback reporting form This link leads to an Word document. and send it to USFS-Northern Research Station.