By Stephanie Schupska
University of Georgia
The damage isn’t due to clear cutting or development. One tiny insect, the hemlock woolly adelgid, is to blame. The aphid-like pest is quickly killing hemlocks in the South.
“The hemlock is a pretty unique tree,” Berisford said. “It will grow in dense shade. It grows well in poor soil by mountain streams and cools the streams for trout. They’re just really beautiful trees and a really important component of the mountains.”
A hemlock’s death isn’t spectacular. The first evidence that it’s even infested with adelgids is that it doesn’t get much annual growth. It starts to lose its needles, its crown thins, and it looks gray.
Hemlock woolly adelgids “eat the tree’s starch found in its needles and twigs,” Berisford said. The insect first appeared in the eastern United States in Roanoke, Va., in the 1950s. It stayed around there until the late 1980s, when it started north.
In the northern U.S., mature hemlocks live seven to 10 years after they’ve been infested. But in the South, death comes more quickly.
“The adelgid crossed the river from South Carolina in 2003,” Berisford said, “and we’ve seen a lot of tree mortality already.”
Combating adelgidsHe and other scientists in the UGA College of Agricultural and Environmental Sciences and the U. S. Forest Service are working to stop the mass destruction. They’re conducting two studies now to see if different control approaches are effective.
The first involves releasing predacious ladybird beetles into infested hemlock stands. This type of beetle has one specific food source: the woolly adelgid. The only problem is that they must be mature enough to both eat the adelgids and reproduce to sustain the beetle population.
“As soon as ladybird beetle eggs hatch, the larvae feed on the eggs and young of the adelgids,” Berisford said. “For adult beetles, the eggs are a particularly high nutrient source.”
In the second study, the researchers are injecting insecticide into the soil around the hemlocks. The trees then take up the insecticide through its roots, killing the adelgids. This experiment is being conducted specifically along streams to see if any chemical residue is harming delicate aquatic organisms.
“Treatments took place on Nov. 1, 2005, and as of July 2006, we haven’t detected any major changes in the aquatic invertebrate community,” said Missy Churchel, an aquatic entomologist at UGA. She travels to the forest every two weeks to collect samples.
At the UGA Mountain Research and Education Center in Blairsville, entomologist Kris Braman is researching ways to chemically control adelgids in commercial and home landscapes.
“We want to find the safest, quickest control method,” she said. “Hemlocks are found more in home landscapes in north Georgia, but a lot of Georgians in the metro area are interested in our work because they own property in North Carolina near the Smoky Mountains where there are older, huge hemlocks.”
This fall Berisford plans to begin a project revolving around rearing predacious beetles, especially ones native to the western U.S.
A hemlock’s valueIn the past, hemlock was used for lumber, or the bark was used to tan skins. Its aesthetic value far outweighs any other value now. Berisford said many homeowners deeply treasure the trees.
In fact, one couple approached him at a meeting about the problem and donated $20,000 toward adelgid research.
The interest doesn’t stop with landowners. Support for UGA’s effort comes from Georgia Power Company, two divisions of the U.S. Forest Service, the Animal and Plant Health Inspection Service, Georgia Forestry Commission and the Georgia Department of Natural Resources. Several conservation groups, particularly Georgia Forestwatch and the Georgia Wildlife Federation, are raising funds for the project.
“It’s a big deal because nobody wants to see the hemlocks die,” Berisford said.
(Stephanie Schupska is a news editor with the University of Georgia Public Affairs Office.)