SHANKSVILLE, Pa. (AP) — An invasive insect is attacking the hemlock grove where United Flight 93 crashed on Sept. 11, 2001, but officials hope a treatment plan will save the trees.

The Flight 93 National Memorial says in a Wednesday release that the grove is infested with hemlock woolly adelgid, an invasive insect that can kill trees within a few years.

Over the next three years workers will use a combination of treatments on more than 1,300 mature trees and many seedlings and saplings at the memorial in Shanksville, which is about 70 miles southeast of Pittsburgh.

Woolly adelgids, native to Asia, lay their eggs on the underside of branches. The young insects feed on the sap of the trees, causing them to lose needles and die.

(Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)

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