Attack of the Wooly Adelgid

    One of the most beautiful and until recently most common of the Native evergreens is the Hemlock. No, it’s not related to the plant that poisoned Socrates, although people are often wary of it because of this misperception.

    Unfortunately, our relationship with this plant, which is the State Tree of Pennsylvania, is at least for now at risk of disappearing. The cause is a sap sucking insect, the wooly adelgid, which is native to Asia and was introduced into the US about 80 years ago. Today, infested trees are prevalent in both remote forests and in urban landscapes. Its presence can be seen in the photo above; small, sticky, cottony bits clinging to the base of the needles. These tiny insects can kill a hemlock in as little as four years, although usually the tree will hang on longer in a weakened state.

    The wooly adelgid actually can be controlled, but only by drenching the entire tree with pesticide at significant expense and with unestablished environmental ramifications. Currently, the best hope for the future of this tree is the effort being made to hybridize it with the Chinese Hemlock, a species that has a much greater resistance to this pest. This is at best a long term solution. For now, keep an eye on your hemlocks—some appear to be more naturally resistant than others. For more information, follow the link to this Pennsylvania State Department of Conservation and Natural Resources website, http://www.dcnr.state.pa.us/forestry/woollyadelgid/index.aspx.

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