Hemlock Woolly Adelgid
A major threat to our hemlock trees is the Hemlock Woolly Adelgid (Adelges tsugae) Native to Asia, it is a small, aphidlike insect that threatens the health and sustainability of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) in the Eastern United States. HWA are most easily recognized by the white “woolly” masses of wax, about half the size of a cotton swab, produced by females in late winter. These fuzzy white masses are readily visible at the base of hemlock needles attached to twigs and persist throughout the year, even long after the adults are dead. For a valuable introduction see the New York State Hemlock Initiative site.
July 25,2017 DEC Press Release:
A minor infestation of the Hemlock Woolly Adelgid (Adelges tsugae) was
confirmed on Forest Preserve lands in the town of Lake George in
Warren County on July 18, the New York State Department of
Environmental Conservation (DEC) announced today. This is the first
known infestation of Hemlock Woolly Adelgid (HWA) in the Adirondacks.
"To track and prevent the spread of this invasive pest, Hemlock Woolly
Adelgid, DEC has surveyed 250 acres of forest in the Adirondacks,"
said DEC Commissioner Seggos. "Preventing the spread of invasive
species is the most effective way to fight and address the damage
these species can cause to our natural resources. DEC encourages
hikers, campers, boaters, sportsmen, and others recreating on or along
forestlands in northern Schenectady, Saratoga, and southern Warren
counties to check Eastern Hemlock trees and report any HWA
A small cluster of early stage HWA was detected on one branch of an
old-growth Eastern hemlock tree on Prospect Mountain during a field
trip by a Senior Ecologist from the Harvard Research Forest.
DEC immediately dispatched a HWA survey crew to the site and was
joined by staff from Cornell University's New York State Hemlock
Initiative. HWA was located and confirmed on a number of branches on
the tree by a Cornell scientist and later by DEC's DEC Diagnostic Lab.
The mature tree had no visible sign of crown thinning.
The crews spent 72 person hours surveying 250 acres of forest and
found only one other tree, a small Eastern hemlock near the original
infested tree, that contained one branch with a small cluster of early
This is the first recorded infestation of this invasive, exotic pest
in the Adirondacks. Previously, it has been detected in 29 other
counties in New York, primarily in the lower Hudson Valley and, more
recently, in the Finger Lakes region. Seventeen other states along the
Appalachian Mountain range from Maine to Georgia also have HWA
infestations. HWA is a listed prohibited species under DEC's invasive
species regulations (6 CRR-NY 575.3).
DEC is evaluating means to eradicate this infestation and prevent it
from spreading. This will not include cutting down trees, which is not
an effective means for controlling HWA as it is with other invasive
The most effective treatment method for control of HWA is the use of
insecticides. The insecticide is applied to the bark near the base of
the hemlock tree and are absorbed and spread through the tissue of the
tree. When HWA attaches itself to tree to feed, it receives a dose of
the pesticide and is killed.
In the past three years DEC has treated infested hemlock trees with
insecticides at a few select locations where the control is likely to
slow the spread of HWA, or where the hemlocks provide a significant
public value. New York State Office of Parks, Recreation, and Historic
Preservation has treated many hemlocks trees at a number of State
Parks. Both chemical and biological control options are important in
the long-term fight against HWA.
Dispersal and movement of HWA occur primarily during the first life
stage ("crawler") as a result of wind and animals that come in contact
with the sticky egg sacks and crawlers. Isolated infestations and
long-distance movement of HWA, most often occur as the result of
people transporting infested nursery stock.
DEC monitors the distribution and spread of HWA by annual aerial and
ground surveys as well as reports from partners and the general
public. DEC has been involved in biological control efforts against
HWA since the 1990s, and has released several approved natural enemies
of HWA at locations in the Finger Lakes and Catskills regions.
Recently, DEC has provided funding for the development and operation
of a biological control laboratory at Cornell University associated
with the New York State Hemlock Initiative, in order to enhance the
production and release of these biological controls in New York.
HWA, a tiny insect from East Asia first discovered in New York in
1985, attacks forest and ornamental hemlock trees. It feeds on young
twigs, causing needles to dry out and drop prematurely and causing
branch dieback. Hemlock decline and mortality typically occur within
four to 10 years of infestation in the insect's northern range.
Damage from the insect has led to widespread hemlock mortality
throughout the Appalachian Mountains and the southern Catskill
Mountains with considerable ecological damage, as well as economic and
aesthetic losses. HWA infestations can be most noticeably detected by
the small, white, woolly masses produced by the insects that are
attached to the underside of the twig, near the base of the needles.
Eastern hemlock trees, which comprise approximately 10 percent of the
Adirondack forest, are among the oldest trees in New York with some
reaching ages of more than 700 years. They typically occupy steep,
shaded, north-facing slopes and stream banks where few other trees are
successful. The trees help maintain erosion control and water quality,
and the hemlock's shade cool waters providing critical habitat for
many of New York's freshwater fish, including native brook trout.
Survey efforts by DEC and Cornell's New York State Hemlock Initiative
will continue to determine if other infestations are present in the
surrounding area. As the closest known infestation of HWA is 40 miles
away in Schenectady County, DEC is asking hikers, campers, boaters,
sportsmen, and others recreating on or along forestlands in northern
Schenectady, Saratoga, and southern Warren counties to check Eastern
Hemlock trees and report any HWA infestations.
New York is particularly vulnerable to invasive species due to its
rich biodiversity and role as a center for international trade and
travel. Rapid response and control is a critical line of defense in
minimalizing the establishment, and ultimately permanently removing,
an invasive population. To support this effort, under Governor Cuomo's
leadership, the FY 2017 Budget included an additional $5.5 million in
the Environmental Protection Fund targeted specifically for invasive
More information on HWA [ http://www.dec.ny.gov/animals/82617.html ],
including identification, control techniques, and reporting possible
infestations can be found at Cornell's New York State Hemlock
Initiative [ http://www.nyshemlockinitiative.info ] (link leaves DEC's
website) or DEC's website. You can also call DEC's toll-free Forest
Pest Information Line at 1-866-640-0652 to ask questions and report
The following are useful articles dealing with this threat: