Black Walnut Mortality in Colorado Caused by the Walnut Twig Beetle and Thousand Cankers Disease

Fig. 3. Cankers caused by Geosmithia are visible only after the outer bark is removed: (B) coalescing cankers eventually girdle the branch resulting in dieback.



Image from Plant Health Progress article:
Black Walnut Mortality in Colorado Caused by the Walnut Twig Beetle and Thousand Cankers Disease