March 24, 2009

Pest Infestation Threatens Hemlock Trees at Cornell

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Hemlock roots led to Socrates’s famous end, but the trees themselves are facing a deadly threat on Cornell’s campus. A devastating infestation of wooly adelgids is currently invading the University’s hemlock trees.
The aphid-like insects appear as fluffy white sacs at the base of the needle, causing infected trees to die within four to eight years of exposure at nearly a 100-percent mortality rate.
Cornell natural areas staff first spotted signs of pest infestation about a month ago above Cascadilla Gorge, according to the University.
Hemlock wooly adelgids, an invasive species native to Japan, have now been identified in 19 areas of the Finger Lakes region, including Cornell Plantations, Cascadilla Gorge and Beebe Lake, according to a University press release.
Hemlock forests currently cover 800 of the 4,300 acres of natural areas of Cornell’s Plantations.
The hemlock infestation will impact the ecology of Ithaca’s gorges. According to the University, the trees play a part in the moderation of summer stream temperatures, creating an amenable environment for brook trout and other wildlife and plants that subsist in cooler microclimates. Hemlocks also help to maintain water quality by controlling sediment runoff from gorge slopes.
Despite the adelgids’ sensitivity to cold, they have survived one of Ithaca’s coldest winters, according to the University.
Prof. Mark Whitmore, natural resources, told the University that the adelgids infesting Cornell’s hemlocks may be adapting to the cold temperatures, and global climate change may impact their spread over the long term.
Cornell is at the northernmost front of the infestation’s spread along the east coast, Todd Bittner, director of Cornell’s natural areas, said in a University press release.
According to the University, natural areas staff are working to survey the spread and severity of the adelgid infestation in Cascadilla Gorge and Beebe Lake. Treatments of individual trees will depend on environmental factors, the severity of the infestation and Plantations resources.
The long-term strategy for control includes the deliberate introduction of natural predators of the wooly adelgids into the environment, most effectively the Laricobius nigrinus, a predatory beetle from the western United States. According to the University, these biocontrol methods are still in development.