Deforestation Caused By Insect Pest Threatens Town's Water Supply

BIG STONE GAP, Va. – An invasive insect that has become a nuisance for much of the Appalachian region is quickly becoming a public utility problem for this Southwest Virginia town.

The woolly adelgid infests hemlock trees, feeding on their sap needle by needle, and – within three or four years for most trees – causing them to die.

The problem for Big Stone Gap? Eastern hemlocks line a creek that carries the town’s water supply from the its reservoir to a water treatment plant, and if the tiny parasite kills the trees, the costs would skyrocket to treat daily the 2.2 million gallons of water used by residents, said Freddie Allison, chairman of the town council’s Public Utilities Committee.

“If we lose the hemlocks, we run into all sorts of problems,” he said.

Worse yet, the town’s options for treating a woolly adelgid infestation are limited.

Biological solutions, which would wipe out the pest by introducing a predator species, are still in development, while chemical solutions either would cause more issues or are expensive, said Anna Hess, environmental director of the Clinch Coalition, a local organization committed to protecting plants and animals in the Jefferson National Forest.

Allison and other town officials discovered the problem earlier this year, and most of the trees, save for the ones in the highest elevations, already are showing signs of infestation.

He foresees four problems the town could face if the hemlocks around the stream are lost. The creek will lose its shade and the increased sunlight will raise the water temperature, which causes treatment to be more difficult; fallen trees will narrow the creek, causing it to flow faster; the decaying trees will increase the water’s turbidity, causing the need for more treatment; and streambed washouts will be more probable.

“I guess if you’re a tree-hugger, losing hemlocks is a problem by itself,” Allison added.

None of the problems would make the water untreatable, but they would certainly increase the treatment costs, said Allison. Town employees are working to calculate the actual numbers, but Allison is confident the amount will not be negligible.

The woolly adelgid was brought accidentally to North America in nursery plants in the 1920s, said Hess. The insect first spread north, then south, and only recently hit Southwest Virginia.

The bug feeds on sap, which it takes from the base of hemlock needles, causing them to fall off. Without its needles, a hemlock tree dies, she said.

Woolly adelgids multiply quickly and can kill small trees within a year or so, Hess said. Large trees may take up to five years to die.

Hemlocks are valuable to many ecosystems. Many plants, such as rhododendron, are dependent on it, she said, and the hemlock has the ability to absorb water during the winter when most trees are dormant, helping reduce spring flooding.

Big Stone Gap has to act soon, Hess warns: “You have to hit it as soon as you find it, or it’s too late.”

Unfortunately, it’s easier said than done.

As a biologist, Hess prefers natural solutions to the use of invasive species. Introducing a species that kills or harms the pest species is a way to “level the playing field,” she said, but invasives are harmful themselves because nothing in the ecosystem threatens them.

The method now showing the most promise is a species of beetle that kills the woolly adelgid, but these Japanese beetles can’t keep up because the adelgid reproduces so fast.

“It isn’t quite up to par yet,” said Hess.

Until better biological solutions are available, Big Stone Gap will have to pursue a chemical solution.

One option is imidacloprid, an insecticide that’s closely related to nicotine and can be administered in a few ways.

In one method, the chemical is sprayed on the soil surrounding the tree. The tree’s roots absorb it and the chemical then moves to the needles. where it is ingested by the woolly adelgid.

Alternatively, imidacloprid could be injected directly into the soil.

But with both methods, the chemical likely would wash into the nearby creek – the town’s water supply – said Allison.

Hess said that when hemlocks are near water, the chemical can be injected in the tree’s roots on the side away from the water, but she doubts the method would be acceptable where municipal drinking water is involved.

The only other remaining option is to inject the chemical directly into the tree’s trunk, a method known as stem injection. Multiple capsules of imidacloprid are placed in the tree, and there’s no worry of the chemical getting into the water.

But the injection stresses the trees and could kill them, Hess said. Additionally, it is by far the most expensive method, estimated to cost between $1 and $1.50 for each inch of a treated tree’s diameter.

Officials also would have to decide which trees in the 70-acre area should be saved – likely thousands. So a cost tally is difficult to determine.

Allison doesn’t know where the town would get the money for such treatment efforts, which will have to be repeated every few years until a biological solution is found.

Hess is hopeful, however, adding that biologists are in the process of testing other beetle species to attack the woolly adelgid problem.

TIMOTHY CAMA is an intern with the Herald Courier and can be reached at tcama@bristolnews.com or (276) 669-2181.