By Stephanie Schupska
University of
Georgia

When University of Georgia entomology professor Wayne Berisford
travels to the north Georgia mountains for research these days,
he’s got a lot less shade to hide under when he steps beneath a
hemlock tree.

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 adelgids

He 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 value

In 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.