Walnut Twig Beetle and Thousand Cankers Disease of Black Walnut

Thousand cankers disease is caused by the fungus Geosmithia morbida, and this pathogen is transmitted by the walnut twig beetle, Pityophthorus juglandis.  This disease impacts black walnut and, until 2010, was only found west of the Mississippi River.  The disease gets its name from the many tiny black cankers caused by the fungus growing in the phloem.  This fungus is brought in by walnut twig beetles, which bore into the tree and create galleries.  In addition to the cankers and tiny beetle entrance holes, infected trees also exhibit yellow foliage, wilting, and eventual branch mortality.  One beetle and canker will not kill the tree, but mass attacks by beetles can result in thousands of little cankers that eventually coalesce and girdle the tree.  There are no known control or management options for thousand cankers disease.  Care should be taken to prevent the spread of the disease by buying local firewood, or wood from which you know the source, and watching for symptoms in existing trees.