This story was first published on July 12, 2024.
Ella Katona is a student at Kent State University and one of 10 Pittsburgh Media Partnership summer interns.
A non-native invasive insect, the hemlock woolly adelgid, is causing significant damage to eastern hemlocks in Pennsylvania and across the United States. In Allegheny County, the Hollow Oak Land Trust is treating its hemlocks to keep the state trees on their properties healthy.
They started seeing the hemlock woolly adelgid in their conservation areas five years ago. Last fall, they treated over 250 hemlocks at Montour Woods Conservation Area.
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This spring, Autumn Anderson, conservation ranger for Hollow Oak, and her team treated eastern hemlocks at the nonprofit’s property along Trout Run near the Pittsburgh International Airport twice a week to keep the hemlock woolly adelgid at bay.
“Right now, we are getting ready to mix our chemical Merit 2F, one part chemical to ten parts water,” Anderson said, as her team worked on a tarp spread out in the trailhead parking lot on a busy road in June. “And we’re going to get ready to hike it into the conservation area to get started treating.”
Hookstown Trailhead. Photo: Kathy Knauer / The Allegheny Front
What is the hemlock woolly adelgid?
The hemlock woolly adelgid is an aphid-like insect, native to East Asia, but was found near Richmond, Virginia in 1951. It appears oval-shaped and a pale yellowish-green. They are often covered in a cotton-like white or gray waxy substance, resembling wool, which can be more noticeable than the aphids themselves.
The woolly adelgid feeds on hemlocks by sucking their sap. This damages the trees, eventually killing them. The insecticide the Hollow Oak team is mixing will protect these trees.
“It’s designed to be taken up by the hemlock trees through their root system,” Anderson said. “And then as the hemlock woolly adelgid feeds on the foliage of the tree, they’ll die.”
The treatment process
It usually takes two hours for the team to treat 30 trees, but this section of property is estimated to have 300 hemlocks. The treatments last for five years and the chemical usually costs $74 per gallon. They will start a new section in the fall when the weather is cooler.
“So we can only treat them when environmental conditions are right,” Anderson said. “So if it’s raining heavily we don’t go out, because it could affect how well the tree can take up the chemical through the root systems. We usually try to do most of our treatments in the spring and fall.”
Soil injectors and jugs of treatment ready to be taken onto the trail. Photo: Kathy Knauer/ The Allegheny Front
The insecticide mixture is then poured into two soil injectors that look like pogo sticks and into two additional jugs. After, they strap it all onto a backpack and head onto the trail.
After following a stream, the trail heads up a steep hillside. That’s where the hemlocks grow.
“So, when we’re up here, we’re kind of looking at the trunks of the trees,” Anderson said. “That’s our first indicator that it’s a hemlock. They have a really unique bark pattern. They’re kind of medium-dark brown, and they have branches that start coming out usually kind of low.”
Dillon Penrod measures a hemlock tree’s diameter. Photo: Kathy Knauer / The Allegheny Front
After they spot the hemlocks, the team sets up their equipment and measures the diameter of the first tree at breast height to determine how much chemical to inject around it.
However, Dillon Penrod, another conservation ranger, says they need to be very careful before they start injecting the treatment into the ground surrounding the hemlocks.
“It affects other aphids and small insects like that,” Penrod said. “We don’t want to administer this anywhere where there’s some understory plants that would flower. It can also affect bee populations.”
Angelo Theofanous, a volunteer at Hollow Oak, inserts the nozzle tip into the soil and steps on the footplate until it’s in the ground. Then, he uses the two handles to pump the chemical mixture. With the measurement of the diameter of this tree, he will need to administer 20 pumps of insecticide.
“You want to get all the way around the tree,” Theofanous said. “So then, if you hit a root or something, you just bring it back out.”
Angelo Theofanous uses a soil injector to pump the treatment into the soil surrounding the hemlock tree. Photo: Kathy Knauer /Allegheny Front
Other efforts
Hollow Oak Land Trust doesn’t just protect this property in Moon Township. The organization protects over 700 acres of land in parts of Allegheny and Beaver counties through conservation areas and easements with landowners.
Sean Brady, executive director of Hollow Oak, started seeing hemlock woolly adelgids five years ago. So far, the trees in their conservation areas are healthy, so Brady expects them to respond well to the treatment they’re providing.
“So, we’ve done a lot of research,” Brady said. “We’ve talked to various government agencies at the federal level and at the state level. So, we’re using the best practices to incorporate that treatment as safely and sustainably as possible.”
Brady’s group is also in the process of creating educational pamphlets to help homeowners if they have hemlock trees of their own.
“We’re hoping to inspire private landowners to treat their own hemlocks,” he said. “I’m sure they love their hemlocks. They love their evergreens. They provide the same kind of ecosystem values on private property as they do on public property and they just need some guidance.”
Brady and his organization at Hollow Oak aren’t the only ones concerned about the hemlock woolly adelgid.
Tagging a hemlock tree to keep track of treatments. Photo: Kathy Knauer / The Allegheny Front
The Pennsylvania Department of Conservation and Natural Resources is treating hemlocks in five sections across the state. They are currently using insecticides through soil and tree trunk injections and releasing the Laricobius nigrinus, a predatory beetle native to the western United States.
Another possible biological control is silver flies, which would be released during the summer season to help combat the woolly adelgid. But, according to DCNR, it can take up to 10 years to obtain necessary test results and permits before the fly can be released.
Back on the trail, as the Hollow Oak team finishes their first round of treatment, Anderson emphasizes the importance of hemlocks.
“They’re so paramount to the health of the ecosystem,” she said. “If we lose these trees, there isn’t really something else that’s going to come behind and replace it. They help protect our stream environment by stabilizing stream banks and keeping the water cool for species of trout and the macroinvertebrates that live there as well.”
July 16, 2024: This story has been corrected to reflect how long Hollow Oak Land Trust has been treating hemlocks at Trout Run.
