West Virginia Invasion - Hemlock Woolly Adelgid

What is the Hemlock Woolly Adelgid?

Hemlock Woolly AdelgidThe Hemlock Woolly Adelgid (HWA) is a tiny exotic invasive species that gets its name from its woolly white appearance and because its host is the hemlock tree. Adults, as well as the nymphs, suck sap from young twigs on hemlock trees causing the hemlock needles to dry out and drop. This defoliation can cause the hemlock tree to die in only a few years.

How did it get here?

The Hemlock Woolly Adelgid is native to Asia where it is not a problem to native hemlocks. It was introduced via infected nursery stock to the United States in the early 1950s near Richmond, Virginia.

Where is it now?

Lacking natural enemies in North America, it has spread throughout the eastern United States via wind, birds, mammals, human activities, and the transport of infected nursery stock. HWA is prevalent in about half of the hemlock range in the eastern US and has killed about 90% of the hemlocks in Shenandoah National Park in Virginia.

Why is the hemlock so important?

The Eastern hemlock is a large, majestic tree that can live for 800 years or more. A mature tree reaching over 175 feet tall with a diameter of more than 6 feet is among the largest specimens recorded. The dense, evergreen canopy associated with mature hemlock forests creates a unique environment that is a critical habitat for many animal and plant species.
  • Nearly 90 species of birds can be found in hemlock forests. Several species are significantly associated with hemlock forests, including the black-throated green warbler, Blackburnian warbler, and the Acadian flycatcher.
  • A wide variety of aquatic species is more likely to be found in streams sheltered by hemlock than streams sheltered by hardwoods. For example, both brook trout populations and macroinvertebrate diversity are greater in hemlock streams.

What are we doing about it?

Pseudoscymnus tsugae - Predator Beetle if HWA (Photo Courtsey NPS)To assist in the long-term preservation of the hemlock we are establishing our property, along the Mill Creek watershed and Tree Tops Canopy Tour in West Virginia, as a Hemlock Preservation Site. As such, our Canopy Tour staff will implement a long range HWA treatment plan. Every hemlock over 6” in diameter has been surveyed and labeled for treatment. $1 from every canopy tour participant’s fee will be donated to a hemlock preservation fund to assist in the funding of this costly treatment plan and we will match those funds, dollar for dollar! Sadly, it may come to pass that our long-term preservation efforts secure one of only a handful of hemlock forests in the country.

HWA Treatment Options:

  • Systemic Insecticides – Inoculation of each individual tree via application of a systemic insecticide by soil injection at the base of the tree and for stream bank trees by injecting the insecticide directly into the trunk. Treatments remain effective for three or more years.
  • Predator Beetles - Predatory beetles are being studied for the control of hemlock woolly adelgid. Until this can be proven by scientific methodology, chemical treatment is the only solution to keep hemlock trees around for future generations. It is everyone’s hope that the right combination of predatory beetles will be found for a more natural control of hemlock woolly adelgid. In partnership with the USFS and Virginia Tech Entomology Department plans are underway to serve as a research site for predator beetle release research.
For more information on the Hemlock Woolly Adelgid problem in our US hemlock forests, visit the US Forest Service HWA Resource site.