Hope for hemlocks?

In the last several years the hemlock woolly adelgid has decimated hemlock forests in the East, and until recently scientists were concerned the lacy conifer would go the way of the American chestnut.

The adelgid is a tiny aphid-like insect from China, generally recognizable only by the woolly white sac in which it coats itself on the underside of hemlock needles. In warmer climates, it can kill a tree in as little as five years. Hemlock woolly adelgid was first discovered on the East Coast in the 1950s and eventually showed up in Shenandoah National Park in Virginia in 1988, where it has since destroyed 95 percent of the park's hemlocks.

Initially, foresters depended on an insecticidal soap known as MPedeR and soil injections consisting of a pesticide called Imidacloprid to help fight the adelgid, but neither represented a long-term, practical, or financially feasible option for saving the trees.

But now, things are changing. For the last five years several universities, including Virginia Tech, the University of North Carolina, Clemson, and the University of Tennessee, have worked diligently to raise and distribute predator beetles, another non-native species that feeds exclusively on hemlock woolly adelgid. Forest biologists released the first predator beetles into the Nantahala National Forest in North Carolina in spring 2004. They were released in Great Smoky Mountains National Park in 2002.

Rusty Rhea, an entomologist with the southern region of the U.S. Forest Service, says that while it's too early to tell if the predator beetles will save the hemlock, early results are promising. The beetles are, in places, reproducing and recovering at an annual rate of about 70 to 75 percent. It will take about 10 years of predator beetle reproduction and feeding before a clear impact is felt.

Hemlocks are important to the forest ecosystem, regulating ground and water temperatures along streams where they often grow. Native brook trout, for example, depend on hemlocks for shade and cool water. Some species of warblers are known to nest only in hemlocks.

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Hemlocks are faring better in the Northeast. Robert Jetton, a research associate with the University of North Carolina who has been working on hemlock conservation for several years, says, "In New England, hemlock woolly adelgid seems to die out over the cold winters."

For homeowners, though, a hands-on method--a soil injection of Imidacloprid--is still the best way to save trees. Predator beetles, expensive and difficult to raise in the lab, are not available to the average landowner.

For more information about the hemlock woolly adelgid and how you can help prevent its further spread, visit www.saveourhemlocks.org. For information on how to help hemlocks in your own backyard, contact your local Extension office.