Hemlock woolly adelgid spreads to Lake Champlain: Understanding the threat 

Invasive insect threatens North American hemlock forests, creating woolly masses

By Mike Lynch

On Monday, the state Department of Environmental Conservation and its partners announced that hemlock woolly adelgid (HWA) had been found in the Port Douglas area on Lake Champlain, the northernmost discovery of the forest pest in New York state. 

Simultaneously, the state announced it had been found at the north end of the Great Sacandaga Lake at Conklingville Dam in Saratoga County. 

Native to Asia, the hemlock woolly adelgid is an aphid-like insect that attacks North American hemlocks. It’s known for creating cotton-like woolly masses on the leaves of hemlocks.

The insect damages the tree canopy as it feeds on the tree’s starches, disrupting the flow of nutrients to the twigs and branches. It is often fatal to hemlock trees, and can kill them in fewer than 10 years, but can sometimes take decades to be fatal. Some hemlocks have shown resistance. 

Here are some takeaways from this most recent discovery based on past reporting and an interview Tuesday with Adirondack Park Invasive Plant Program Director Brian Greene. APIPP is working with the DEC and the New York State Hemlock Initiative at Cornell University (NYSHI) on this issue.

How did the adelgid get this far north?

Greene said it’s unclear how the forest pest arrived on private property in Port Douglas on Lake Champlain, roughly 50 miles north of the Stark Point area on Lake George, the general area previously considered its most northernmost position. The insect can move on its own and also be spread by animals and birds. Humans transport it by moving firewood or through the sale of nursery stock of hemlocks.

How long has HWA been in New York? 

HWA was first confirmed in New York when it was discovered in the lower Hudson Valley in 1985. It then slowly moved up the Hudson Valley, including the Catskill Park, until it was discovered in the Adirondack Park in 2017. It has since become established in the Lake George watershed on both sides of the lake. 

What are the implications of HWA being found this far north?

Port Douglas is located on the shores of Lake Champlain near Keeseville. While the location is significantly farther north than it’s been found before, the area of discovery is still considered to have much milder temperatures than the Adirondack interior. But the Adirondack interior isn’t getting those consistently frigid winter temperatures of minus-20 degrees Fahrenheit that are known to kill the invasive, so higher elevation hemlocks may be vulnerable. Still, the invasive species has only been found on the eastern side of the park in the Lake George watershed and now on the western side of Lake Champlain.

Will this wipe out all the hemlocks in this area?

While this tiny insect does kill many hemlocks it attacks, not all of them die. Forest pests, such as the emerald ash borer, seem to kill their hosts much more quickly than HWA, as fast as two to four years. Some hemlocks show remarkable resistance and live 20-plus years. Other hemlocks appear to have natural resistance and not be affected. Some organizations, such as The Nature Conservancy, are studying naturally resistant hemlocks, with the hope they could provide the key to the trees surviving HWA.

What is the state doing to manage hemlock infestations?

The state and its partners are monitoring the spread of hemlocks and have tried different management tools, including predator beetles and pesticides. One way it has tried to slow the spread of the Lake George infestation is with silver flies, which Explorer reporter Gwendolyn Craig has documented in the past with stories and videos. 

What can you do to help?

APPIP and its partners encourage people to learn about forest pests and report them on the iMapInvasives website and app. Knowing where the invasives are located is key to slowing the spread of them. So is general knowledge of how they are spread. APPIP hosts forest pest hunters workshops on various tree pests for people looking to learn more about the subject. There is a workshop on beech leaf disease coming up in August, and HWA will be featured in the winter months. More information on reporting HWA can be found here. For additional resources on identification, management options and how to report a sighting, visit nyshemlockinitiative.info or email [email protected].

Photo at top: The wool of hemlock wooly adelgid on a branch. Photo courtesy of DEC