Hemlock Woolly Adelgid

The Hemlock Woolly Adelgid (HWA) (Adelgis tsugae) was imported accidentally from Japan and was first recognized in Richmond, Virginia in 1950.  In the 1990’s it exploded on the scene throughout the Eastern United States, devastating the forests of New Jersey, Virginia and other areas east of the mountains.  It rapidly made its way over the mountains and is found throughout West Virginia.  Luckily, it was not spotted in the WVBG until 2012 and treatment was initiated right away.

Why do we care about hemlocks?

Their dense canopy shades and cools streams providing a very good aquatic habitat; they protect against erosion; the deep duff layer retains moisture and they provide an excellent wildlife refuge.  They are lovely ornamentals and in some places because they are so long-lived they have great historic significance.


Treatment of the Hemlock Woolly Adelgid at the West Virginia Botanic Garden

Our criteria for treatment includes healthy trees within 1 ½ tree lengths of our hiking trails and trees of ecologic importance such as shading streams and providing dense habitat in our forests.  Small trees as well as large old beauties were included.  In all, almost 700 trees on the east side of the reservoir basin were measured and marked and were treated with insecticide in 2012 and 2013.  Trees near streams were treated with an injection into the tree to avoid contamination of waterways. We have also treated hemlocks in the Rhododendron Garden, the Hidden Garden and the upper parking lot.

Another treatment option is the use of biologic controls.  In Asia, there are several beetles that feed only on the Adelgid.  Many of these have been extensively studied, quarantined and then released to slow down the ravages of this invasive insect.

In the years since we completed treatment very cold spells (Polar Vortex) has inhibited the growth of the HWA.  Even untreated trees are looking good.  However, the much warmer 2016/2017 winter has encouraged a resurgence of the infestation.  So far, the treated trees are looking good but that may not last. We will continue to work to preserve these treasures.

– Dr. Ellen Hrabovsky


How do I recognize treated Hemlocks in Tibbs Run Preserve?

All trees that have been treated for the Hemlock Woolly Adelgid are marked near the base of the trunk with a small metal number tag such as those pictured.

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