Insect Threat to Hemlock Trees Discovered in Cook Forest, Clear Creek State Parks

COOKSBURG, Pa. – A non-native, invasive insect that attacks and kills Eastern hemlock trees has advanced westward across Pennsylvania to Clarion and Jefferson counties where infestations have been confirmed in two state parks.

“The hemlock woolly adelgid, a pervasive insect threat that has killed thousands of hemlocks across the state, has been detected in both Cook Forest State Park, Clarion County, and Clear Creek State Park in neighboring Jefferson County,” Department of Conservation and Natural Resources Secretary Richard Allan said. “This discovery is especially unsettling due to the signature hemlocks in both parks’ forests.”

Home to the most significant Eastern hemlock stand north of the Smoky Mountains, Cook Forest State Park is famous for its old-growth trees. Its “Forest Cathedral” of towering hemlock and white pine is a National Natural Landmark.

For this reason, and in the face of the insect’s steady, northwestward spread, DCNR entomologists, foresters and park officials had ramped up early-detection efforts at the two parks. Attempts to delineate wooly adelgid infestation and chart feasible methods to combat its spread are now under way, Allan said.

“Park staff members have been regularly monitoring for the pest, and those surveys paid off with early detection that will allow for greater treatment options and better success,” Allan said. “Weather and snow cover have hampered attempts to gauge the insect’s spread, but we know there is infestation along the Clarion River, which flows through both Cook Forest and Clear Creek state parks.”

DCNR will be embarking on a two-pronged treatment effort that relies on selective application of insecticides and the release of predatory beetles.

“We have seen 74 sites and 11,000 trees treated in 21 counties in recent years through the continued cooperative effort among our bureaus of forestry, state parks and others,” Allan said.

DCNR is partnering with the USDA Forest Service, The Nature Conservancy and other interested organizations to develop an Eastern hemlock management plan for northwestern Pennsylvania. In addition, its Bureau of Forestry is drafting a hemlock conservation plan for Pennsylvania.

The Cook Forest State Park infestation area is home to some of the Eastern United States’ tallest hemlocks, including the celebrated Seneca Hemlock, the area’s third-tallest at 147 feet and 4 feet in diameter. Although not yet known to be infested, other old-growth stands at Cook Forest, including the “Forest Cathedral,” are in danger due to the close proximity to this area.

The woolly adelgid is a fluid-feeding insect, easily detected by telltale egg sacs resembling cotton swabs that cling to undersides of hemlock branches. Introduced into the United States from Asia, it first was discovered in southeastern Pennsylvania in 1969 and steadily has been spreading westward. It now is found in 56 of Pennsylvania’s 67 counties.

Homeowners and other private property owners can learn more about the woolly adelgid, damage it causes, and efforts to combat it at (click on “Forestry,” then “Insects and Disease” at upper left).

The Pennsylvania Parks & Forestry Foundation is accepting contributions to be used to combat the insect at Cook Forest and Clear Creek state parks. Donation checks, payable to Pennsylvania Parks & Forestry Foundation, or PPFF, can be sent to Cook Forest State Park, ATTN: HWA Fund, P.O. Box 120, Cooksburg, Pa., 16217.

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