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Heroes for Hemlocks: Saving a Keystone Species From An Invasive Insect

Photos and Story by Brad Bowman

Alexandra Blevins, a forest health specialist within the Kentucky Division of Forestry, marks data on her glove regarding a treated hemlock tree. Blevins and two other crew members treated this conservation easement in southeastern Kentucky over a 2-day period.

An all-women crew within the Kentucky Division of Forestry is the last line of defense for the state’s hemlocks against an invasive insect decimating populations across the U.S. 

On a gray mid-March morning, Forestry Health Specialist Alexandra Blevins and Forest Ranger Technicians Kenna Smith and Angie Powell packed up their gear and hiked down into a wooded southeastern Kentucky valley. Clouds obscured the sun, transforming the forest floor into a patchwork of broken light and shadow.

They are battling the hemlock woolly adelgid, a species native to Asia that has infested nearly half of the native hemlock range in the eastern U.S., spreading at almost eight miles per year. It has almost wiped out all of the iconic hemlocks in Shenandoah National Park in Virginia and has had a significant impact on the slow-growing hemlocks in Kentucky.

The team gathered water from a nearby stream to mix with the insecticide imidacloprid, taking care to keep the equipment used to collect water away from the chemicals to minimize risk of contamination.

Using logger tape to measure each hemlock’s breast diameter height, the crew calculated the correct dosage based on the tree’s size. 

There are legal limits per acre for such treatments and the formula, which calculates chemical application rate per inch of tree diameter, was borne out of research studying the effectiveness of the insecticide on treating the insect without adverse effects on the tree. 

Forest Ranger Technician Kenna Smith pours the imidacloprid treatment into a measured bottle for hemlock applications.

The crew logged the diameters on their protective gloves after each treatment and recorded it into field notebooks to be stored digitally later on. 

The hemlock absorbs the treatment, which moves systematically through its sap on which the hemlock woolly adelgid feeds. The crew can treat a designated area within a couple of days. They can treat several hundred trees in a week.

“If we were to lose this species, it would have trickle-down effects on multiple other important species in their habitat,” said Blevins. “…We must act now to save these vital trees.”

Previous Time to Save the Hemlocks

From September through May each year, the Division of Forestry crew members navigate into remote areas of Kentucky’s hemlock region. 

Since the program began in 2009, crews have treated about 180,000 of the estimated 78.5 million hemlock trees in Kentucky, said Abe Nielsen, environmental control supervisor of the Forest Health and Kentucky Forest Conservation Act Section within the Division of Forestry.

Graphic courtesy of the Kentucky Division of Forestry.

The insect can kill a tree in about a decade. This 10-year window has allowed the state precious time to attempt to save the hemlocks, which supply a vital, shady year-round habitat for ecosystems along the state’s streams and provide soil stability on the rocky Kentucky hillsides. 

“We can’t save every single hemlock tree,” Nielsen said. “But this is such an important tree for these ecosystems that we want to conserve select pockets of hemlock so we don’t lose them and their environmental functions.”

Since 2011, federal grants have fully funded the treatment program, which Nielsen said has made it possible to hire personnel to treat hemlocks in state park areas and public properties during the 9-month treatment season. 

Partnerships with advocacy groups and federal counterparts have allowed the Division of Forestry to expand treatment sites to include established hemlock conservation areas in Daniel Boone National Forest.

The funding has also allowed crew members like Smith and Powell to make an immediate impact preserving one of Kentucky’s valuable natural resources. 

The importance of the work isn’t lost on Smith or Powell, who both said they enjoy being stewards of the state’s natural resources and seeing the outpour of support from the public during volunteer events. 

Worth the ‘Blood, Sweat and Tears’

Although it is difficult to compare Kentucky’s work to that of other states because infestation and the efficacy of treatment varies from state to state, Nielsen said the treatments have been very successful in Kentucky.

Division of Forestry Ranger Technician Angie Powell pours water collected from a stream into the treatment container she will use on multiple hemlocks throughout the conservation easement area.

“Our treatment program has treated more hemlocks than most other states,” he said. “Tennessee and North Carolina have a similar system to ours where they hire crews to do treatment work.”

Nielsen said he’s directing the crew to now re-treat surviving hemlocks. Each treatment can protect a tree for up to seven years.

Nielsen said that some states focus less on imidacloprid treatments and instead release beetles that prey on the hemlock woolly adelgid. The Division of Forestry has experimented with the use of beetles to save the hemlocks, he said, but the beetles don’t seem to thrive in Kentucky’s climate. 

So, Kentucky’s crew has continued its work with chemical treatments, which have kept hemlocks alive but may not be sustainable in the long term, Nielsen said. They will continue to release beetles and attempt to establish them in Kentucky. 

The work remains crucial for Blevins and the crew — not just for the hemlocks, but the ecosystems they support. Blevins said it makes her proud to play a role in saving such an important species.

“Yes, it is hard labor to commit to a full day of hemlock work, but it is worth all the blood, sweat and tears we put into it,” she said. “Seeing an old-growth hemlock stand takes my breath away, and it always will.”


The mission of the Kentucky Division of Forestry (KDF) is to protect, conserve and enhance the forest resources of the Commonwealth through a public informed of the environmental, social and economic importance of these resources. Read more about the division here.

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