Bugs killing off hemlock trees

March 03, 2003|by RICHARD BELISLE

FAYETTEVILLE - The stately hemlock, Pennsylvania's official tree, is going the way of the American elm and the American chestnut, both of which were nearly killed off in the early years of the 20th century.

The killer of hemlocks is the woolly adelgid (pronounced uh-dell-jed), a microscopic insect that entered the United States in the 1920s, according to state foresters. It attaches itself to the underside of hemlocks near the needles and sucks the sap out of them.

An infestation can wipe out a grove of the forest giants in three to four years, said Beth Brantley, a forestry instructor at the Penn State Mont Alto campus.


So far, hemlocks in 37 Pennsylvania counties - about half of the state in the east - have been affected by the infestation, said Bruce Kile, a service forester in the 85,000-acre Michaux State Forest which ranges through Franklin, Adams, York and Cumberland counties.

The forest's headquarters is in Fayetteville.

Brantley said the elegant American elm, standing 120 feet high and once a mainstay in cities and towns across the nation, was virtually wiped out by the Dutch Elm Disease, a fungus transmitted by beetles. The fungus came from Europe.

A few disease-resistant elm remain, Brantley said.

"There's a beautiful population of elm trees at State College and there's a number around here in people's yards," she said.

All of them will eventually die of the fungus, she said.

Likewise, the American chestnut - a giant of the forest, often with a circumference of more than 20 feet at the trunk and which provided food and lumber to the country - fell victim to blight from another fungus, this one imported from Asia. It just about killed off the species, Brantley said.

"The chestnuts were gone by the late 1930s and early 1940s," she said. "There are still a few in the forest, but the blight will get them, too, eventually."

Efforts to cross American chestnuts with a Chinese variety seem to be meeting with some success, she said.

Now, it seems, it's the hemlock's turn. Drive anywhere around Franklin County - or eastern Pennsylvania for that matter - and see the hemlocks in their death throes. The forest behemoths are dead or dying, usually from the top as the insects work their way down.

The adelgids are spread by birds.

"They stick to their feet," Brantley said.

Single trees can be treated from the ground, but those in the forest have no chance because the adelgids attach themselves to the underside of the needles.

"I think they'll go the way of the chestnut. They can only get the hemlocks back if they learn how to control the insect," Brantley said.

The woolly adelgids were first discovered in the United States in the 1920s in the Pacific Northwest. They are believed to have come from Asia, but no one knows how they got here.

"Most likely on some plants," Kile said.

They were first seen on the East Coast in Virginia in the 1950s, he said.

So far, the only ray of hope in saving the hemlocks rests with a pinhead-size ladybug, a natural predator that eats the adelgids. Introduction of the ladybugs into the forests on a large enough scale to establish a breeding population that would eliminate the adelgids is still a decade or more away, Kile said.

The ladybugs are grown in labs in New Jersey and can cost up to $2 each, he said. Foresters in Michaux cut hemlock branches infected with the adelgids and haul them to the New Jersey lab in weekly truckloads to be used as food for the ladybugs growing in the labs.

Most hemlocks in New Jersey have already been wiped out so there are not enough adelgids left there to feed the ladybugs in labs that are gearing up to produce large populations, Kile said.

In 2001, some 1,000 ladybugs were set free in a hemlock grove on Beartown Road in Washington Township, Pa. They were treated with fluorescent dust so they could be found at night.

"We never could find any of them," Kile said.

The Pennsylvania Department of Conservation and Natural Resources got about 10,000 ladybugs from the U.S. Forest Service out of Morgantown, W.Va., and set them free in Caledonia State Park.

"We've confirmed that they are established there now, but the population of adelgids is so high that the ladybugs can't keep up," Kile said. "It will take years before the population of predators is big enough to have a significant impact.

"It's already too late for many hemlocks," he said. "We're seeing a significant number dying off. We're hoping there will be genetic resistance in some trees."

Mike Kusko, chief forester at Michaux, said a predator program worked well on the gypsy moth infestation in forests. A fungus, it was introduced into the gypsy moth populations in the 1930s with seemingly little results.

"We couldn't find any evidence that it was working," Kusko said. "Then about 10 years ago it was discovered again and we saw that the fungus was wiping out the gypsy moths. This summer for the first time we won't have to spray for gypsy moths."

He said it's impossible to say if the ladybug will have a positive effect on the woolly adelgids that are killing hemlocks.

"It could take two years or 20 years. We can't speculate or predict," he said.

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