Hemlock Woolly Adelgid and How to Prevent the Destruction of your Hemlock Forest

Until recently, I was unaware that the eastern hemlock trees were under such an all out attack, and now I am on a mission to inform more people and what they can do to help combat this horrible, devastating problem. These trees are under an ever increasing threat from the hemlock woolly adelgid (Adelges tsugae), an invasive insect. This invasive insect can completely decimate a hemlock within 3-6 years after infestation. As part of my job as a Community Engagement Coordinator for Livelihoods Knowledge Exchange Network (LiKEN),

I attended an event by the Kentucky Division of Forestry for training on how to treat hemlock trees to combat the destructiveness of the hemlock woolly adelgid insect. Since part of my job is contacting landowners and helping them assess their property, I immediately wanted to sign up and receive the training at the Cumberland Falls State Park in Corbin, Kentucky.

This invasive adelgid is right in our backyards, and most of us do not even know it. I was in Breathitt County, Kentucky a few weeks ago, in April, when it came to my attention while I was exploring the woods that some hemlock trees were dying. I went to investigate further, and sure enough, they were infested with the hemlock woolly adelgid. Please check your trees! This was a landowner that we, LiKEN, are assisting with a forestry plan for their woods. I showed the landowner the woolly adelgid killing his hemlock trees, and now we are assisting them with information on how to treat their trees for this deadly invasive insect. 

I remember growing up in the mountains of Eastern Kentucky, in the heart of the Appalachian Mountains, where I would spend much of my time exploring the hills, creeks, and rivers that bordered my family farm. My favorite time of the year was always spring and summer, when the mountains were alive with new growth and it was warm enough for me to get out and do my favorite activity: explore the woods.

Photo of an eastern hemlock tree by Tina Johnson.

There was one creek in particular that ran throughout the property I grew up on where it was always cool and damp. You could almost feel the moisture in the air along that small valley. During the spring, I could smell the wonderful scent of fresh mountain air. I can close my eyes now and still almost smell that fresh scent that settles in the mountains after a soft rain. I loved when the sun would come back out after a rainstorm in the woods just as much as when the sun would shine through and glisten off all the tree leaves and various plant life. Rain in the mountains has always been and always will be a joy to my senses, where the joy of my heart meets the warmth and beauty of the mountains, deep in the holler of eastern Kentucky.

The eastern hemlock evergreen tree has always been one of my very favorite trees. I just love the beautiful green color that you do not see anywhere else. Now, because of the hemlock woolly adelgid, many of the trees are dying and just leaving ugly, unsightly trees with snags sticking out. The eastern hemlock (Tsuga canadensis), also called Canada hemlock or hemlock spruce, is a slow-growing long-lived tree, which, unlike many trees, grows well in shade. It may take 250 to 300 years to reach maturity and may live for 800 years or more. A tree measuring (4.5 ft) in d.b.h., or diameter at breast height, and (175 ft) tall is among the largest recorded. Hemlock bark was once the source of tannin for the leather industry; now the wood is important to the pulp and paper industry. Silvics of North America: Your Guide to Silviculture in North America also notes that many species of wildlife, such as white-tailed deer, benefit from the excellent habitat that a dense stand of hemlock provides. Plus, this tree also ranks high for ornamental planting.

Hemlock Woolly Adelgid Identification in Kentucky

The hemlock woolly adelgid is a tiny, sap‑feeding insect native to Asia that has become a major threat to eastern and Carolina hemlock in Kentucky. The University of Kentucky’s Cooperative Extension Service provides these key details for identification:

• Size: About 1/32 to 1/16 inch long.

• Color: Reddish‑purple body.

• Protective covering: As it matures, it develops a dense, white, woolly wax coating that resembles tiny cotton balls 

• Location: These woolly masses are found at the bases of hemlock needles along infested branches, usually on the underside of the branch tips.

• Life cycle: The adelgid is most active in two periods:

  • Spring: After egg hatch (March–April)

  • Fall: From September–October

So, where did the invasive adelgid come from? Hemlock woolly adelgid first came here from Japan on infested trees. They were imported for gardens in Richmond, Virginia, for ornamental purposes. This was before plant importation controls ever existed. The first actual report of the adelgid infestation was in 1951 in Richmond, Virginia, and continued to spread throughout the eastern United States. This invasive insect is spread during the crawler stage by birds, mammals, the wind, humans, and even vehicles as they brush up against any infested hemlock branch. Just one female can cause an outbreak because she lays eggs that are basically clones of herself.

A map of infected counties across the state of Kentucky overlayed with the counties in the natural range of the eastern hemlock. Image downloaded from: https://eec.ky.gov/Natural-Resources/Forestry/forest-health/Pages/default.aspx

Hemlock woolly adelgid was first detected in Kentucky in 2006 across 15 counties. However, now it is found in at least 30 eastern and southeastern counties in Kentucky as shown in the map below, as well as in other Appalachian states from Alabama through New York state and into New England.

A map of infected counties across the United States overlayed with the counties in the natural range of the eastern hemlock across North America. Image downloaded from: https://eec.ky.gov/Natural-Resources/Forestry/forest-health/Pages/default.aspx

This invasive species is most pervasive in the eastern part of the United States, but you can fight back. You can find these destructive insects on the underside of the hemlock branches as white cottony sacs. If you find these sacs, there are two ways to treat the tree: 1) spray foliage with insecticidal soap or horticultural oil at the proper times during the hemlock woolly adelgid’s life cycle which is after the egg hatches from March through April, or 2) use a systemic insecticide like imidacloprid placed at the base of the tree that moves with the tree sap and is consumed by the adelgids as they feed. For more information, you can check out this helpful resource from the University of Kentucky.  

The life cycle of a hemlock woolly adelgid. Image downloaded from: https://savehemlocksnc.org/hemlocks-hwa/hemlock-woolly-adelgid/

The process by which the Kentucky Division of Forestry treats the hemlock woolly adelgid involves using the chemical imidacloprid, a systemic insecticide. To treat a hemlock tree, you must first measure the diameter of the hemlock at approximately 4.5 feet off the ground and compare the diameter to the ounces of imidacloprid needed to treat the tree. After the tree has been measured and the ounces of solution needed is determined, then the duff (leaves, pine needles, and organic debris) must be pushed away from the roots at the base of the tree. After the duff is removed the solution is poured around the root system at the base of the tree all the way around the tree. Then, the duff must be placed back over the solution to keep the solution from being degraded by sunlight. The imidacloprid is absorbed by the tree, travels up the tree and kills the adelgids that feed on the needles of the tree. This process can protect the tree for up to four years. After the tree is treated a dot or small circle is spray painted at the back of the tree, away from the trails. We used bright pink on this day. Other regions use different colors. For instance, North Carolina uses blue. For a visual representation of what to do, see KY Forest Health's video: Hemlock Woolly Adelgid: How to Treat Your Trees. 

Hemlock Woolly Adelgid Infestation: Photo credit: Tina Johnson

For more about how to treat hemlock woolly adelgid on your property, see this page from UK Cooperative Extension: Meeting the Threat of the Hemlock Woolly Adelgid.

The Kentucky Division of Forestry has treated 250,000 trees since 2011. The KDF treated 7,000 trees in Kentucky in 2025. There is still much work to be done. This process isn’t one and done but must be repeated every few years. The preservation of the hemlock trees depends on us. Do you know that you can help? 

How to Report Hemlock Woolly Adelgid Sightings

 Imidacloprid Solution on the Hemlock root system. Photo Credit: Tina Johnson.

If you suspect hemlock woolly adelgid on hemlock trees in Kentucky, you should contact the Kentucky Division of Forestry. While the provided public site does not list a direct “report a pest” form, KDF typically handles reports through:

• Local county forestry offices (contact your county’s KDF office for on-the-ground assessment)

• U.S. Forest Service if the tree is on a federal land

• KDF’s invasive species hotline or email 

• You also apply for help through your local Natural Resources Conservation Service (NRCS)  office for programs like Environmental Quality Incentives Program (EQIP), to help cover some of the cost.

When reporting, provide:

• Location (county, nearest town, GPS coordinates if possible)

• Description of the tree(s) and any visible adelgid (white, cottony masses on branches)

• Date of observation

The end result of not combating this horrible invasive hemlock woolly adelgid species is this:

Dead Hemlock from the Hemlock Woolly Adelgid: Photo Credit: Tina Johnson

For those who enjoy the beauty of the forests and want to take action, please take a moment to inspect the hemlock trees you come in contact with. Look at the hemlock branches and see if you see any white sacs on the underside of the branches. Record the coordinates of the infested tree and report it. Or, take a picture and report it to the organizations listed above. If you take a picture on your cell phone and enable the location, you can also pull the coordinates of where that photo was taken. If we all work together, soon we will have a coalition of people reporting on this deadly invasive species, and WE can make a difference. I encourage you all in this important and vital work. Your care and action can save a hemlock tree, maybe even an entire section of your local forests. Tell your family and friends. WE CAN MAKE A DIFFERENCE! For more about how you can make a difference as a landowner, see HOPE FOR HEMLOCKS OF KENTUCKY, a project by Kentucky Heartwood.

Whether you would like further help with identifying or reporting this deadly hemlock invasive species, or if you are interested in learning more about LiKEN's programs to help landowners with forest management, reach out to us through the interest form on our project page for Community Wealth from Healthy Rivers and Forests | LiKEN Knowledge. A grant from the US Forest Service makes LiKEN's Community Wealth Program in Kentucky possible.