Canker Diseases

Compiled by Ned Tisserat, Colorado State University:

Canker Diseases Cankers are dead areas on the stem bark and cambial area caused by fungi, bacteria, or other living agents. Cankers can kill plants especially if the plant is stressed and can not defend itself well. Drought, freeze damage, dormancy, soil conditions, other diseases and insects are common stresses that allow canker organisms to damage trees. Canker causing organisms spread from tree to tree by wind and occasionally by insect vectors. Canker causing organism usually enter the tree through wounds or branch crotches. Canker causing organisms grow in the bark and kill the tree by killing the cambium. Diagnosis Hints: Cankers may be sunken if the canker has been active for several years killing the cambium while surrounding tissue continued to expand. Rapid killing of bark and cambium of a branch or stem by an aggressive canker organism does not produce the typical sunken canker seen in many picture guides. Some cankers may be oval, elongate or round. The resulting damage of a canker is usually dieback of the portion of the tree above the canker. Determining what canker is on your tree is important because it could be caused by a slow growing organism that will not kill you tree rapidly and you can do something about it. Physical wounds/injuries differ from cankers in that canker-causing organisms expand the affected area over time killing more bark each year. Physical wounds or injuries from cankers are evidence of expansion of the canker. Old callus ridges, involving several layers of sunken wood produce a 'target' appearance of canker expansion. (Physical wounds have a smooth wood wound surface and usually have callus around the edge indicating the tree is trying to grow over the wound.) Insect borers are often found associated with cankers since both organisms are found on stressed trees. Management: Disease prevention usually involves improving the growing environment, reducing stresses and planting disease resistant species. Some cankers can be removed if the plant is healthy and can defend itself. There are limited chemical treatments for canker problems. Canker Diagnosis Guide Host Symptoms and Signs Disease Aspen Large black callus ridges around sunken canker Ceratocystis canker Aspen White flecks in black-sooty bark- long elongate canker Cryptosphaeria canker Aspen Sooty/black bark with small cup shaped fruiting bodies on bark- Black canker Aspen and many hardwoods Discolored bark with small pimples spaced about 1/4 inch apart Cytospora canker Aspen only Checker board pattern of bark cracking in canker Hypoxylon canker Many hardwoods-elms, honeylocusts, Orange/pink to black pin head sized fruiting bodies sticking out from bark or just under thin bark layer Tubercularia canker Honeylocust Irregular brown to black fruiting mass in lenticels on main stem or small pin head sized pycnidia on branches Thyronectria canker

Siberian Elm Canker Black Canker On Aspen Cryptosphaeria Canker on Aspen Dothiora Canker Sooty-Bark Canker On Aspen Endothia Canker of the Gambel Oak

Hypoxylon Canker Nectria and Tubercularia Cankers Cytospora Canker Leucostoma and Valsa (Cytospora) Cankers Rose Canker

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