Tree-killing hemlock pest spreading in Kentucky - WDRB 41 Louisville News

SUNDAY EDITION | Tree-killing hemlock pest spreading in Kentucky

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CORBIN, Ky. (WDRB) – On a wooded hillside above the Cumberland River, Alice Mandt climbed a trail bordered by rock shelters and rhododendron shrubs until she stood amid a range of soaring hemlock trees.

Each tree's trunk bore a pink blaze – a sign that Mandt and other Kentucky Division of Forestry workers had applied a chemical treatment meant to kill a tiny, but fast-moving, insect that threatens tens of millions of hemlocks.

Once confined to the state's southeastern forests, the hemlock woolly adelgid has marched as far west as Pulaski County and attacked trees in more than 30 counties since arriving in Kentucky in 2006. State officials have found the adelgid in the Lexington area and are now monitoring trees at Mammoth Cave National Park south of Louisville, although the pest hasn't been found there.

The adelgid targets the state's 80 million evergreen hemlocks, whose year-round canopies cast shade onto forest floors and keep streams cool – in essence, regulating some of the most sensitive ecosystems in Kentucky. 

"If you look out over the river you can see the sun," said Mandt, the state's hemlock woolly adelgid coordinator. "These trees do not let a whole lot of sunlight come down here, which is one of the reasons why they are so important." 

Mandt spent part of last week at Cumberland Falls State Resort Park, where she and two assistants applied a chemical treatment to hundreds of trees on the border of Whitley and McCreary counties. The park already is dotted with sick hemlocks whose green needles have begun to turn gray.

In the past three years, Mandt estimates that Division of Forestry workers have treated 50,000 trees on state- or publicly-owned land in Kentucky, including popular recreation areas like the Daniel Boone National Forest, Pine Mountain State Park and Natural Bridge State Park.

The forestry division has taken the lead in combating the adelgid at state forests, as well as some federal lands such as the Daniel Boone National Forest. It also works to educate private landowners on how to protect their hemlocks.

But as the reach of the adelgid expands – on average, it has moved into about five new counties annually, Mandt said – one of the state's main funding sources for treating hemlocks faces steep cuts.

The U.S. Forest Service has provided $345,000 to the state to date for its hemlock protection program, while the state Heritage Land Conservation Fund has added $109,300, according to the Energy and Environment Cabinet. Some monies from the fund would be transferred to the General Fund under Gov. Steve Beshear's current budget proposal.

"We'll have to wait and see what money the fund will have in the … state budget," said Jennifer Turner, a forestry division spokeswoman.

A killer pest

The woolly adelgid – a 1/8-inch-long insect – arrived in Virginia from its native Asia in 1951 and has spread to 18 eastern states ranging from Georgia to Maine, according to the U.S. Forest Service.

Without a natural predator, the pest has had free reign to attack hemlocks by feeding on starches inside the trees. The insect reproduces on its own and can produce as many as 300 offspring a year, Mandt said.

"It kills the tree," Mandt said. "In layman's terms, it sucks the life out of a tree. It takes away the food source."

The pest has devastated some forests in the southeastern United States, killing more than 95 percent of the hemlock trees in the Shenandoah and Great Smoky Mountains national parks, according to the U.S. Forest Service.

Mandt won't estimate how many trees in Kentucky are affected, other than to say she expects a "significant loss" of eastern hemlocks, the species widely found in the state.

Drenching the base of hemlocks with insecticide is one way that Kentucky officials hope to save hemlocks. The trees absorb the chemical, which kills the adelgids and lasts for about five years, according to the National Park Service.

Mandt also is trying to help private property owners understand how best to defend their hemlock trees. Because the pest often hitches rides on birds, for example, she warns against birdfeeders in hemlocks.

It can cost $10 to $20 to use insecticide on a hemlock tree, compared with several hundred dollars to remove a sick or dead tree, according to U.S. Forest Service estimates.

"It's not possible to stop it. All we're trying to do here is to minimize the damage and we're trying to chemically treat as many trees in our natural areas as we can," Mandt said. "We're basically trying to keep them alive long enough to get a better answer."

One better answer -- and a long-term solution -- may be small beetles that feed on the adelgids.

While native to the Pacific Northwest and not Asia, the beetles were found to prey on the hemlock pests. University of Kentucky researchers have released more than 13,000 beetles into the state's hemlock forests since 2008, although they say it's too early to know whether that strategy is effective.

The hope is that the beetle will ultimately keep the adelgid population in check. In the meantime, there is evidence that the region's harsh winter may be helping.

Mandt said a UK researcher recently told her that he looked at a branch of an infested hemlock tree and found 30 dead adelgids and just two insects still alive.

Indeed, the cold temperatures have killed the pest in large numbers, said Lynne K. Rieske-Kinney, a UK professor of forest entomology.

"The extensive winter kill is fine," Rieske-Kinney said. "It's great from the trees' perspective.  From the predators' perspective, it's not good news."

Because the adelgid reproduces asexually, she said, the insect won't be eradicated entirely.

"We want the predators to live," she said. "If the adelgid numbers are so low that the predators have problems feeding themselves, then they starve. We have to have those predators to regulate the adelgid population."

"A beautiful tree"

At Cumberland Falls, pockets of hemlocks tower over the park's signature waterfall and hiking trails.

"They're just a beautiful tree and it's so unique to us and to Kentucky that, to me, losing it would be part of our heritage that would disappear," Mandt said.

Scientists are studying the effects of hemlock loss, but the U.S. Forest Service estimates that without the trees' shade, trout populations can fall by as much as 53 percent in some streams.

Some evidence of how hemlock loss affects forests already exists. In the southern Appalachians, species like yellow poplar and birch trees replaced dead hemlocks – and promptly began using as much as 15 percent more water than did the efficient hemlocks, researcher Steven Brantley found.

Brantley, a researcher at the U.S. Forest Service's Coweeta research station in North Carolina, found that water levels in streams near dead hemlocks declined.

"The understory vegetation starts using water the hemlock was using very rapidly," he said.

A forest service study released last month suggests that the loss of hemlocks may not be as bad as previously thought. In studying large swaths of forests, researchers found that "increasing tree density associated with the past century of reforestation and succession in the eastern U.S. may currently be overwhelming the negative impacts of the adelgid at the regional scale."

But, the report found, "the long-term stability of this situation is not known, and data from long-infested counties suggest the landscape may be at a ‘tipping point.'"

Like Mandt, Hugh Archer has worked to protect hemlocks in Kentucky.

But Archer, executive director of the Kentucky Natural Lands Trust, a non-profit land conservation group, said some of the trees his organization chemically treated at the Blanton Forest State Nature Preserve in Harlan County have begun to die.

Archer, a former commissioner of Kentucky's Department of Natural Resources, said the chemical treatments are "a holding pattern, and a very expensive one."

Still, he remains optimistic.

"I still have great hopes that we will keep a reasonable number of hemlocks free of the adelgid," he said.

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