Emerging Threat, To Iowa's Forests, Communities, Wood Industry & Economy, Thousands Cankers Disease, 2022

(2022) Emerging Threat, To Iowa's Forests, Communities, Wood Industry & Economy, Thousands Cankers Disease, 2022. Natural Resources, Department of

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Abstract

Since the 1990’s black walnut has been dying in Western U.S. (CO, NM, AZ, UT, ID, CA and OR). The deaths are caused by a walnut twig beetle (Pityophthorus juglandis) that carries a fungus (the proposed scientific name is Geosmithia morbida) which is spread as the beetle tunnels through tree tissue. Beetles can reach very high populations and numerous cankers can develop. Instead of one large girdling canker, tree decline and death appears to result from the high number of cankers (causing the creation of the name Thousand Cankers Disease, TCD). Initial symptoms involve yellowing and thinning of the upper crown, which progresses to include death of progressively larger branches. During the final stages large areas of foliage may rapidly wilt.