Hemlock Wooly Adelgid — An impending threat
by Louise Estabrook
December 28, 2012 12:00 AM | 1435 views | 0 0 comments | 6 6 recommendations | email to a friend | print
In north Georgia’s mountains, a tiny exotic insect known as the hemlock wooly adelgid is destroying magnificent Eastern hemlock trees, Tsuga canadensis, in record numbers. Tens of thousands of hemlocks already have been lost in Rabun, Habersham, White, Towns and Union counties, and the threat is spreading south and west, according to the Georgia Forestry Commission. If the pest is not controlled, scientists predict that Georgia and neighboring states could lose 90 percent of their hemlocks within the next decade.

Ultimately, Georgia could be faced with losing the hemlock as a forest species — an ecological catastrophe that would equal the loss of the American chestnut tree during the last century. The long-lived, shade tolerant hemlock provides food and shelter for many species — including the red breasted nuthatch and Blackburnian, Swainson’s and black-throated green warblers.

Georgia’s hemlocks often grow to stately heights along streams, where their deep shade helps keep water temperatures cool enough for trout. The roots and canopy help prevent soil erosion. Hemlock stands are also preferred habitats of rare amphibians, including the green salamander.

The hemlock wooly adelgid, a native of Asia, was first identified in the Eastern United States in the early 1950s in Virginia, where it was brought in by a plant collector. As an introduced species, it came without the natural enemies that keep it in check in its native setting. The adelgid has moved steadily into the southern Appalachian forests. In 2002, it was discovered in Georgia in Rabun County.

The adelgid lays its wooly egg sacs, about the size of a match head, on the undersides of hemlock branches. The insect is very easy to locate — its wooly covering make the tree look like it’s dusted with snow. Its appearance is also very similar to a flocked Christmas tree. In spring, the larvae hatch and the tiny adelgids begin sucking the sap from the base of the needle. This deprives the hemlock tree of water and nutrients. After several years of infestation, the tree dies.

The wind disperses the tiny insects through the air from tree to tree. Birds, other animals and even humans carry the crawling insects through the landscape as well.

Right now, the best hope for combating the hemlock wooly adelgid is releasing into the forest exotic beetle species that naturally prey on the pest. The University of Georgia and other institutions are working on research and production of these beetles in the hope they can help save our forests.

No one, however, is sure if the effort will save the hemlocks. Also, introducing an exotic species is risky business. But given the crucial importance of the hemlock and the distinct possibility that we could lose these trees, scientists need to use every resource available to fight the spread of the hemlock wooly adelgid.

There are steps homeowners can take to save their trees. Spray with insecticidal soap or horticultural oil — spray small trees, whose every branch can be reached. Spray upward along the bottoms of boughs April through mid-May. Thoroughly coat the adelgids to the point of dripping. Repeat in spring or fall if the adelgids are still visible. The problem with spraying is that a mature hemlock can reach 40 to 70 feet with a spread of 25 to 35 feet. It is almost impossible to reach the entire tree without professional equipment. If your tree is small enough, spraying is a viable option.

Hold off fertilizing the trees when there is an active adelgid infestation. The nitrogen in the fertilizer pushes out a lot of soft, succulent new growth. The adelgids thrive on the nutrient rich foliage. Remember that if your hemlock is planted near a lawn, its roots extend way out beneath that lawn and will take up any fertilizer meant for the turf.

If you notice the Hemlock Wooley Adelgid on your hemlocks, please call the University of Georgia Cooperative Extension office in Cherokee County for more information at (770) 479-0418.

Information about Extension Solutions for Homes and Gardens can be found on the University of Georgia Cooperative Extension website at www.caes.uga.edu/extension/cherokee or by contacting the Cherokee County Extension Office at 100 North St., Suite G21 in Canton at (770) 479-0418. The Georgia Extension Master Gardener Program is a volunteer training program offered through county offices of the University of Georgia Cooperative Extension.
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