by Ann DavenportQuaking Aspen (Populus tremuloides) has become a staple in many northern landscapes. We love its straight form, smooth gray-green bark, and the way its leaves quiver in the wind. Its strong presence is able to bring a little bit of the north woods to our urban landscapes. Sometimes despite our best efforts, pests and or disease can put a blemish on our otherwise well manicured space.The U.S. Department of Agriculture Forest Service has categorized Hypoxylon Canker, caused by the fungus Entoleuca mammata, as one of the most important diseases affecting Aspen in our area (Anderson, R., Anderson, G., & Schipper, A., 1997). The fungus enters the tree through wounds in the bark. Wounds can occur through insect damage or mechanical damage (pruning, mowers, etc…). Initial infections often occur in small branches. With age, the infection moves into the main stem of the tree. Unfortunately, the prognosis for trees infected with Hypoxylon Canker is grim. Once the cankered area reaches the main trunk it will girdle the tree. Most trees that reach this stage will die within five years.

Here are some things to look for when monitoring Aspen for signs of infection:• Leaves on the infected branch(s) appear smaller than normal, turn yellow, then brown• Cankers usually begin near wounds, branch stubs, or at the base of branches• New infections are marked by sunken bark which is initially yellowish-orange, turning black at the center with yellowish-orange margins as the infection ages• During early infection, the bark of the canker has a blistered appearance• With time, the blistered area breaks apart and falls off revealing blackened woodUnfortunately, there is no chemical treatment for Hypoxylon Canker. Trees with main trunk infections should be removed to prevent further spread to nearby Aspen. Routine monitoring of trees in the landscape can help identify early signs of the disease. Removal of infected braches before the cankered area reaches the main trunk may delay infection. This should be done during dry periods to minimize spread of the fungus. In general, pruning cuts should only be made when necessary and sterilization of equipment between cuts is recommended to minimize risk of spread. The best way to protect your Aspen from this disease is to provide an environment that encourages tree vigor; appropriate fertilization, and adequate water to prevent drought stress.Source:Anderson, R., & Anderson, G., (1997). Hypoxylon Canker of Aspen. U.S. Department of Agriculture Forest Service. Forest Insect & Disease Leaflet 6. Retrieved August 1, 2010 from http://na.fs.fed.us/spfo/pubs/fidls/hypoxylon/hypoxylon.htm

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