By Lee Shearer
http://onlineathens.com/authors/lee-shearer
Saturday, March 22, 2014
Some good came out of the bitter cold that descended on Georgia in January.
University of Georgia scientists say the intense freeze has apparently
depleted populations of an insect pest that has devastated hemlock trees
throughout their entire range, including north Georgia.
Really cold weather can often deplete insect populations, but this was a
first this far south.
"We had just never seen extensive winter mortality," said University of
Georgia entomologist Mark Dalusky.
But the respite from hemlock wooly adelgids may only be for a couple of
years, Dalusky said.
Dalusky and lab coordinator Amanda Mercer recently went out to look for the
imported invasive pest in north Georgia forests. They found far fewer than
they expected, especially at higher elevations.
"For each of our sites we attempted to obtain at least a six twig sample
size, however, in some of our samples, the adelgid was so scarce that we
could not find six suitable twigs to sample," Dalusky wrote in an email
summarizing what they found. At the highest elevation, Wolf Pen Gap at more
than 3,000 feet, they found none.
At two sites between 2,500 and 3,000 feet, Blackwell Creek and Slaughter
Creek, they found an average mortality of 68 percent and 92 percent,
respectively.
At lower elevations they found lower mortality. At Davidson Creek,
mortality averaged 32 percent, for example, and at Mill Creek Road, they
found an average of 48 percent dead adelgids.
The killer insect from Japan first reached Georgia in about 2002, when it
was found in Rabun County. Since then, it has spread to the southern limits
of the hemlock's range in Stephens and Banks Counties, as well as counties
to the west.
Adelgids feed on the nutrients in hemlocks' storage cells, causing the
trees to lose needles and stop growing.
But Dalusky expects the insects will likely rebound in a couple of years,
starting the hemlock decline all over again.
Seventy-five percent of hemlocks in the state are infested and in some
stage of decline, Dalusky said; the exceptions are hemlocks treated with an
insecticide injected into the soil, he said.The insects showed up at a
particularly bad time in Georgia, when years of droughts had weakened the
hemlock trees.
"The trees' resistance was minimal," Dalusky said.
Temperatures in Georgia were their lowest in decades when an arm of the
Polar Vortex dipped down in North America in January, sending Georgia, like
most of the eastern United States, into a deep freeze for a few days.
It was intensely cold, but Dalusky would welcome a cold snap like that
again to keep the adelgids in check, he said.
However, Dalusky and others aren't just waiting for the weather to get cold.
They've released adelgid-eating predatary beetles at numeorous sites across
north Georgia, and there's evidence some of the beetles are surviving on
their own and slowing down the wooly adelgid's depredations.