Buying Time As Hemlock Invader Eyes Adirondacks

The Adirondack Park is often considered one of the most pristine, beautiful, wild places in New York, if not within the entire eastern forests of America. It is home to vast forests and rolling farmlands, towns and villages, mountains and valleys, lakes, ponds and free-flowing rivers, private lands and public forest.

Throughout this rich and varied landscape are some of the densest quantities of eastern hemlocks, one of New York’s most abundant and significant tree species … and those trees are under attack by an advancing invasive species that State Parks is trying to help hold back.

This invader is the Hemlock Wooly Adelgid (HWA), an invasive forest insect native to Asia that has decimated millions of hemlocks along the eastern seaboard since being accidentally introduced into Virginia in 1951.

Adelgids are tiny insects that insert piercing-sucking mouthparts into hemlock twigs, causing damage to woody tissue that inhibits water and nutrients from reaching emerging hemlock buds. This limits the growth of new twigs and eventually kills the tree.

At about 6/100ths of an inch long, the flightless adelgids are hard to spot with the naked eye, but in the winter through early summer leave distinctive white “woolly” egg masses on hemlock twigs. (Photo Credit – NYS DEC)

Due to the lack of any sort of natural resistance of eastern hemlocks to HWA and without any natural predators to manage populations, the pest has spread quickly. Once infested, a hemlock tree can die in as little as four years, or as long as 20, depending on environmental factors.

During the years since, the insect spread steadily south and northeast, finally making its way to New York in the 1980’s on Long Island and then into the Hudson Valley. With each year, it has expand its range further north and west.

Use the slider bar to compare known Hemlock Wooly Adelgid locations in New York State (left), with the density of hemlock forests in the state (right). Charts from New York State Department of Environmental Conservation

On the left, hemlock trees killed by HWA. On the right, a healthy, uninfested hemlock.

In 2020, HWA was found in hemlocks at two locations in the Adirondacks, most recently along the eastern shores of Lake George, posing a huge threat to spread into some of the finest hemlock forests in New York.

As climate change contributes to more mild winters, experts anticipate more rapid movement and increasing HWA populations. Last winter in New York was extremely mild and there is a boom in HWA populations statewide as the existing population expands.

The insect is now so abundant across the range of eastern hemlocks, it will never be removed, or eradicated, from the environment. The ultimate answer to fighting this threat to our hemlocks to restore the balance. This comes in the form of biological control, using predatory insects from hemlocks in western U.S. that keep HWA from overwhelming and killing hemlock trees.

Since being introduced into Virginia in the early 1950s, the Hemlock Wooly Adelgid has spread steadily south and northeast. It is now in much of New York and this summer was found along the eastern shoreline of Lake George in the Adirondacks. (Map Credit – U.S. Department of Agriculture/Forest Service)

Here in New York, this effort is being led by the New York State Hemlock Initiative (NYSHI) based at Cornell University, where forest entomologist Mark Whitmore heads the Hemlock Woolly Adelgid Biocontrol Research Lab. Several biocontrol species have been evaluated and releases have occurred in New York State Parks and other forests across the state, but it takes time for predators to establish and begin having a measurable reduction of HWA populations.

As research continues on biological control, HWA continues to impact our forests. In the interim, the only viable means of control is using insecticides to temporarily preserve trees until the natural enemies of HWA can take over.

Read more about these natural control efforts in this previous post in the NYS Parks Blog…

Big Hopes for Little “Army” in Parks’ Fight against Hemlock Invaders

As the third most common tree in New York, hemlocks fill our forests and are found in many New York State Parks. Located along hiking trails, streams, gorges, campsites, and lake shores, the evergreens can live to be hundreds of years old, providing vital ecosystem services and supporting unique habitats. In addition to providing homes … Continue reading Big Hopes for Little “Army” in Parks’ Fight against Hemlock Invaders


While the Department of Environmental Conservation (DEC) and others in the Adirondack Park combat HWA within the Blue Line, New York State Parks also is actively playing a role in protecting the Adirondack Park and its precious resources.

By targeting its chemical treatments at Park sites along the “leading edge” of the expanding range, State Parks is trying to slow the spread of HWA and protect some core hemlock patches, buying more time for continued research and establishment of biological control. Reducing or locally eliminating HWA from State Parks not only preserves the hemlocks, but also reduces the possibility of HWA hitching rides on cars or hikers’ boots, a potential a source of introduction to the Adirondack Park or other currently uninfested hemlock forests.

Current efforts to slow the spread include targeted surveys and treatments in state parks in the Saratoga-Capital Region with abundant hemlock forest such as John Boyd Thacher State Park, where treatments were done rapidly following early detections in 2018-19, as well as Moreau Lake and Grafton Lakes State Parks, where HWA has yet to be detected but surveys are on-going.

Another key strategy New York State Parks is employing, is protecting some of the most valuable hemlocks in areas that have been infested for several years before those specimens are lost. In Finger Lakes Region, State Parks staff as part of the Finger Lakes Hemlock Preservation Program have been trained and certified to conduct these treatments which began in 2018 and continue today.

Many of the gorge parks including Taughannock Falls, Buttermilk Falls, Robert H. Treman, and Watkins Glen all have threatened hemlocks growing on the steep slopes and cliff edges where many other tree species would not thrive. Protecting these trees helps maintain the indispensable ecological processes but also preserves the landscape that makes these parks so unique and such a draw to people from across the state and beyond. In other parts of the state, highly specialized contractors are employed to perform these technical treatments.

Statewide, hundreds of acres of hemlock forest including thousands of individual trees have been protected. Once treated, trees are tagged so that they can be identified later and are monitored annually to determine the effectiveness of the treatment and track the tree’s response.

As the HWA and the stress that they cause are removed, trees typically show flushes of bright green new growth the following spring. The insecticides have proven to be very effective but must be used responsibly and within limits. Each year, State Park staff evaluate potential areas for treatment and make difficult decisions working with limited resources as these treatments are expensive, temporary, and labor intensive.

HWA is a serious threat but there is much reason for optimism. Chemical control has proven to be a safe, effective tool against the pest although has its limits in size and scale. Biological control has been increasingly successful in some states to the south where it has been ongoing for longer than New York and there are promising early returns where releases have occurred here but it is still too early to tell if and when the biological controls could become the primary weapon against HWA.

While the management of hemlocks through chemical and biological control can only be done by the experts, you can help by volunteering to look for and report HWA sightings  and even preserving hemlocks right at your own home. Each and every piece of information about the distribution of HWA in New York through volunteer sightings allows land managers and researches to stay right on the heels of this pest.

Invasive Species Spotlight: Monitoring for Hemlock Woolly Adelgid

Hemlock Woolly Adelgid (HWA) is a tiny, invasive insect which kills hemlock trees in a matter of 6 years. Please see the previous post on HWA for more information. The insect was introduced in Virginia in the early 1900’s, and has steadily spread since then. New York state contains all stages of HWA infestation. There are … Continue reading Invasive Species Spotlight: Monitoring for Hemlock Woolly Adelgid


Cover Shot – Hemlocks at Harriet Hollister Spencer State Recreation Area in the Finger Lakes Region.

Post By Nick Marcet, State Parks Forest Health Coordinator

If You Believe You Have Found Hemlock Wooly Adelgid

  1. Take pictures of the infestation signs (include something for scale such as a coin or ruler).
  2. Note the location (intersecting roads, landmarks or GPS coordinates).
  3. Fill out the hemlock woolly adelgid survey form.
  4. Email report and photos to Department of Environmental Conservation Forest Health foresthealth@dec.ny.gov or call the Forest Health Information Line at 1-866-640-0652.
  5. Contact your local Partnership for Regional Invasive Species Management (PRISM) by visiting http://www.nyis.info/.
  6. Report the infestation at iMapInvasives.
  7. Slow the spread of HWA in our forests by cleaning equipment or gear after it has been near an infestation, and by leaving infested material where it was found.



 

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