Georgia hemlock trees under siege

Eastern hemlocks, native to north Georgia, are dying rapidly, and one tiny insect, the hemlock woolly adelgid, is to blame.

“Probably 70 or 80 percent of the trees are dead along the [Chattooga River],” said Jim Hanula, research entomologist with the U.S. Forest Service. “It is a matter of time. Eventually it will kill most of the hemlock trees.”

The Asian insect first appeared in the eastern United States in Roanoke, Va., in the 1950s. It headed north in the late ‘80s. In 2003, it crossed the river from South Carolina and started feeding on Georgia trees.

“Hemlock woolly adelgids are working their way to the western extension of the state,” said Wayne Berisford, a retired University of Georgia entomology professor. “They haven’t occupied all of the possible range yet, but they are approaching.”

The tiny pests suck up cells from the tree’s needles, which prevents them from transferring water and conducting photosynthesis.

The first obvious sign of an infestation is thinning foliage. Needles fall off, and the crown starts thinning. From a distance, trees look gray. The trees may uproot or fall apart.

Bersiford has worked with Hanula and other researchers to find ways to combat the adelgid. Their main emphasis has been releasing ladybird beetles, which eat adelgids.

“One beetle species has been established, and populations are growing, but we don’t have any evidence they are controlling the adelgids yet,” Hanula said.

Many groups are releasing adelgid predators, including Young Harris College and North Georgia College and State University. Berisford was part of the initial UGA group to release the beetles in 2004 and was instrumental in getting a beetle-rearing lab at UGA.

Hemlock species differ in their susceptibility to the insect, which offers hope for plant breeders to find resistant genes and produce trees the insects can’t kill. But until then, Georgia’s hemlocks are on the menu and in danger.