What are Cankers?
By Mitch Hoy, ISA Board Certified Master Arborist #MN-4814BT
Fungal cankers are caused by various fungi that enter through wounds or natural openings on trees. These fungal infections cause sunken or raised dead areas of bark that enlarge over time, eventually girdling and killing branches or the entire tree. Signs of fungal cankers include discolored bark, lesions and oozing sap on stems, and gradual canopy die-back.
Fungal cankers are common on maple, elm, spruce, locust, poplar and fruit trees. Some fungal canker species produce fruiting bodies that appear as small, raised bumps on infected bark called pycnidia. Cankers can become infection sites for wood-decay fungi and slime-flux cultures.
Temperature and moisture conditions favoring fungal growth also promote canker development. Cankers are opportunistic pests- they develop on trees that are stressed by environmental conditions, such as soil compaction and water deficit. Cankers are very common on poorly planted trees in compacted urban soils.
If you notice fungal cankers forming on your trees, take action right away. Prune out infected branches well below visible canker margins and hire a qualified arborist for any large or aerial work. Adress the growing area of your tree- eliminate competition from turf grass and install a mulched area out to the edge of the canopy for better moisture retention, nutrient recycling, and respiration for roots. Irrigate your tree deeply and infrequently (once a week) during drought to encourage a healthy root system and support tree defenses. Arborists can decompact soil without damaging roots with an air knife. Chemical control methods are largely ineffective.
Sources:
Dreistadt, Steve. Pests of Landscape Trees and Shrubs, An Integrated Pest Management Guide, Third Edition. Davis, California: The Regents of the University of California, 2019.
Sinclair, Wayne and Lyon, Howard. Diseases of Trees and Shrubs, Second Edition. Ithaca, New York: Cornell University Press, 2005.
Images:
Coral Spot Nectria Canker on Honey Locust (Gleditsia tricanthos), UMass Amherst
