Tree Notes is about trees -- especially native trees, trees for wildlife, and trees in history.

Sunday, February 25, 2007

Wooly Hemlock Adelgids Invading Kentucky

Native hemlocks face a grave danger.

Wooly adelgid infestation, photographed by Flikr user Nicholas_T
The native hemlock trees of eastern Kentucky's mountain regions are threatened by a tiny sap-sucking insect -- the wooly hemlock adelgid, an insect brought from China in the 1920's. The wooly hemlock adelgid is widespread in the eastern United States, but it has only recently been spotted in Kentucky.

The following description of the wooly adelgid problem in the southeastern U.S. was provided by the National Forest Service. (At the time this was written, Kentucky had not yet been invaded)
Hemlock woolly adelgid (HWA) is a non-native invasive pest that impacts eastern hemlock and Carolina hemlock. HWA has spread to the Southern Appalachian region of northern Georgia, western North Carolina, eastern Tennessee, and southern Virginia. Without control, hemlocks typically die within five to seven years after infestation.

Hemlock trees serve important ecological roles in the southern Appalachians. They are a keystone species in near-stream areas, providing critical habitat for birds and other animals, and shading streams to maintain cool water temperatures required by trout and other aquatic organisms. Hemlocks are also prized for their visual beauty in both forest and urban settings, and are a contributor to residential property values.

Source " Emerging Issues in the South: Hemlock Wooly Adelgid" a website of the USDA Forest Service, Southern Research Station Headquarters in Ashville, North Carolina. Viewed 2/25/07 at No longer available.

You should suspect adelgid infection of any hemlock trees that have white, wooly deposits on the undersides of the branches. The wool-like appearance of the insect's secretions is the reason it is called the "wooly hemlock adelgid." 

According to a document published by the University of Kentucky, Meeting the Threat of the Hemlock Wooly Adelgid by entymologists Lee Townsend and Lynne Rieske-Kinney, the insect is susceptible to the insecticidal soaps and dormant oils that one can purchase in any garden chemical department. Several treatments are required, and they must be timed to the life cycle of the adelgid. Local county extension agents can advise the best times in spring or fall to spray.

Alternatively, the ground around the tree can be soaked with an insecticide containing imidacloprid so that the tree's roots carry it into the tree. Another method is to inject the insecticide into the tree's trunk. Either way, the adelgid will be killed as it sucks the insecticide-laden sap.

Townsend and Rieske-Kinney caution that the insect can be carried from perch to perch on the feet of birds, so bird feeders should never be placed near hemlock trees.

It seems that this threat is possible to manage in the backyard, but more difficult to control in woodlands. The infestation can be spread by felling an infected tree or by dragging around infected branches. Get advice about treatment, and proceed with care.

A healthy hemlock, white pine and hardwood forest in northeast
Pennsylvania. Photographed by Flikr user Nicholas A. Tonelli

Updated July 28, 2013.

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Enrich your life with the study of trees.

"The power to recognize trees at a glance without examining their leaves or flowers or fruit as they are seen, for example, from the car-window during a railroad journey, can only be acquired by studying them as they grow under all possible conditions over wide areas of territory. Such an attainment may not have much practical value, but once acquired it gives to the possessor a good deal of pleasure which is denied to less fortunate travelers."

Charles Sprague Sargent (1841-1927)

Print references I frequently consult

Benvie, Sam. Encyclopedia of North American Trees. Buffalo, NY: Firefly, 2000.

Brockman, C. Frank. Trees of North America: A Guide to Field Identification. Ed. Herbert S. Zim. New York: Golden, 1986.

Cliburn, Jerry, and Ginny Clomps. A Key to Missouri Trees in Winter: An Identification Guide. Conservation Commission of the State of Missouri, 1980.

Collingwood, G. H., Warren David Brush, and Devereux Butcher. Knowing Your Trees. Washington: American Forestry Association, 1978.

Dirr, Michael. Dirr's Hardy Trees and Shrubs: an Illustrated Encyclopedia. Portland, Or.: Timber, 1997.

Elias, Thomas S. The Complete Trees of North America; Field Guide and Natural History. New York: Book Division, Times Mirror Magazines, 1980.

Grimm, William Carey. The Book of Trees;. Harrisburg, PA: Stackpole, 1962.

Hightshoe, Gary L. Native Trees, Shrubs, and Vines for Urban and Rural America: a Planting Design Manual for Environmental Designers. New York: Van Nostrand Reinhold, 1988.

Little, Elbert L. National Audubon Society Field Guide to North American Trees. New York: Chanticleer, 1996.

Martin, Alexander C., Herbert S. Zim, and Arnold L. Nelson. American Wildlife and Plants. New York: McGraw Hill, 1951.

Mitchell, Alan F., and David More. The Trees of North America. New York, NY: Facts On File Publications, 1987.

Randall, Charles E. Enjoying Our Trees. Washington: American Forestry Association, 1969.

Settergren, Carl D., and R. E. McDermott. Trees of Missouri. Columbia: University Extension, 1995.

Sternberg, Guy, and James W. Wilson. Native Trees for North American Landscapes: from the Atlantic to the Rockies. Portland: Timber, 2004.

Wharton, Mary E., and Roger W. Barbour. Trees and Shrubs of Kentucky. Lexington: University of Kentucky, 1973.

Wyman, Donald. Trees for American Gardens. New York: Macmillan, 1965.

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