Dec 25, 2014 4 min read

During a season when many brought evergreens into their homes, the Pennsylvania Department of Conservation and Natural Resources wants residents of the Keystone State to know their state tree – a member of the pine family known as the eastern hemlock – is under attack.

Though hemlocks are not the typical tannenbaum, an online newsletter from the extension service in West Virginia University writes, “Occasionally you may find Canadian hemlock, Douglas fir or blue spruce Christmas trees, which are also short needled.” The eastern hemlock is also known as the Canadian hemlock or the hemlock spruce.

“They grow very slowly,” said Dr. Mark Faulkenberry, an entomologist with DCNR’s Bureau of Forestry. “It wouldn’t make much sense to plant a Christmas tree farm with them.”

Regardless of its status as a seasonal decoration, the state tree is under siege by the hemlock woolly adelgid, an aphid-like pest from China that feeds on sap, disrupting the storage and transfer of nutrients. This intruder creates white, cottony deposits around egg sacs on hemlock branches.

Although a map within a report on the DCNR website does not show an infestation in Washington or Greene counties, the pest has taken up residence in trees in southern Allegheny County and in neighboring Westmoreland and Fayette. Since it was first found in the state in 1969, the adelgid has spread to 56 of Pennsylvania’s 67 counties, aided by warmer temperatures. It is believed to have been introduced in Virginia in the early 1950s on imported landscaping materials.

The state has developed a conservation plan for the species that addresses insect and other threats, and the DCNR is asking landowners and land managers to inspect their hemlocks annually between November to May while the white, woolly material produced by the adelgid is more apparent. The insect itself can be seen only with the aid of a hand lens.

It has been noted that hemlock growth is hampered or halted when the adelgid has attacked 45 percent of the branches, so if about half the branches have woolly stuff, treatment of the tree with chemicals should begin. Faulkenberry said, “Insecticides do work,” but he declined to endorse a specific product. “It’s not that hard to treat,” he continued, and said homeowners who notice the white deposits should follow directions printed on the product they purchase.

Long-term treatment includes biological control, host resistance and site regeneration.

The hemlock woolly adelgid has killed thousands of hemlocks across Pennsylvania as infestations advanced from the southeast to Clarion and Jefferson counties where very large signature hemlocks are part of state park forests. For this reason, and in the face of the insect’s steady, northwestward spread, DCNR entomologists, foresters and park officials ramped up early detection efforts at Cook Forest and Clear Creek state parks.

DCNR has embarked on a two-pronged treatment effort that relies on selective application of insecticides and the release of predatory beetles. The department also is partnering with the USDA Forest Service, The Nature Conservancy and other interested agencies and partners to develop an eastern hemlock management plan for Northwestern Pennsylvania.

The 99-page conservation plan can be found at http://www.dcnr.state.pa.us/forestry/index.aspx. Faulkenberry has extended the comment period to mid-January if residents want DCNR to focus on hemlocks in a particular area. Comments and questions also can be directed to ra-nreasternhemlock@pa.gov.

Prevalent in Pennsylvania forests, the hemlock was designated the Pennsylvania state tree in 1931. According to the StateSymbolsUSA website, this type of tree was “pronounced the most picturesque and beautiful of the world’s evergreens by A.J. Downing, the father of landscape gardening in America.”

According to an online article by R.M. Godman and Kenneth Lancaster written for the U.S. Forest Service, the eastern hemlock may take 250 to 300 years to reach maturity and may live for 800 years or more. The tallest one ever recorded reached 175 feet, but despite its imposing size, cones of the eastern hemlock are the smallest in the genus.

Hemlock bark was once the source of tannin for the leather industry. Its wood is important to the pulp and paper industry.

Fans of Socrates, take note: the National Park Service says this tree is not to be confused with the herb known as poison hemlock. A tea can be made from the leafy twig tips and inner bark of the hemlock tree. This was sipped for a variety of ailments or used as an external wash. The bark is astringent and, in the past, was used as a poultice on bleeding wounds. The hemlock’s bark was also used as a reddish-brown dye for wool and cotton.