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JULY 16, 2009 ISSUE

Going, Going, Gone? Can We Save the Hemlocks From the Wooly Adelgid?

Series 4, Part 2: Don’t Give Up Yet: We Can Save the Ecosystem, If Not Every Tree

Story by Sam Calhoun

A reader last week approached High Country Press about our continuing coverage on the spread of the hemlock wooly adelgid (HWA)—a tiny insect that is killing trees thousands of times its size—and its deadly infestation of indigenous hemlocks in the High Country and up and down the East Coast. Obviously discouraged, the reader gestured to a mountain near our office, pointed out each of the dead hemlocks—which are plentiful and obvious as they rise like grey foreboding giants above the healthy green summer canopy—and, though he cared for their survival, stated that it seemed like it was too late to stop the spread.

“Just look at that. The hemlocks are gone,” he said, sounding deflated. “We can’t stop that.”

Thankfully, the reader is wrong, according to local entomologist Dr. Richard McDonald, who is sole proprietor of Symbiont Pest Management, former biocontrol administrator of the North Carolina Department of Agriculture and one of the leading researchers on HWA biocontrols in the nation. McDonald took High Country Press to four biocontrol test sites in the High Country this week to check on progress—progress that may be hard to immediately see for the untrained eye.

“We’re winning the battle, but we took a hit,” said McDonald.

Concerning our reader’s comments about the prevalence of dead hemlocks all around us, local independent arborist Lear Powell once said that the only time people notice a tree is when it’s dead. At first, said McDonald, all we as humans see are the dead trees, but if we take a moment to refocus, we’ll begin to see the green regrowth of hemlock needles separate from the deep green canvas. What we can’t see from a distance are the smaller new growth of hemlocks that are thriving on our forest floor thanks to predatory beetles that are now in many corners of our region. What we have presently are old-growth hemlocks showing new growth (although, admittedly, about two-thirds have died) and new growth hemlocks popping up all over our forests.

“What’s more, these trees have also just dealt with a 500-year drought,” said McDonald. “If they survived that [and the HWA], they’ll be fine.”

A Tale of Two Hemlocks
Of the 10 old-growth (300- to 500-year-old) hemlocks at Hemlock Hill that were release sites, seven have survived and are showing signs of balance concerning the HWA. In this picture, two dead old-growth hemlocks can be seen to the left of the middle tree, but a vibrant, taller old-growth hemlock can be seen to the right, which is alive and thriving thanks to the introduction of predatory beetles. Photo by Sam Calhoun

Think Beyond the Individual Tree—Save the Ecosystem
“Biocontrol won’t save a specific tree but it will save the ecosystem,” said McDonald.

Biocontrol, or in this case the use of predatory beetles, is winning the battle to save the hemlocks in the High Country, but its reach is limited due to financial and time constraints. That means that some hemlocks will die and some will live—but most importantly, the ecosystem will be preserved.

Throughout the four years of this series, the hemlock plight has been compared to the chestnut blight of the early 20th century. But there’s one difference between the chestnut blight and the attack of the HWA—as a result of the chestnut blight, the ecosystem was altered; the result of the HWA is that an ecosystem could be lost.

What ecosystem, you ask? Hemlocks are referred to in scientific circles as “nature’s air conditioning” for their important role in the ecosystem. Hemlocks grow primarily along riverbanks and beside lakes. Their branches create dense shade that cools the water, allowing trout and other fish populations to thrive. If there were no hemlocks, area waterways would heat up in the sun and reach temperatures too high to support many varieties of aquatic life, and refuge for wildlife would be ruined. What’s more, our dense coverage of hemlocks in the High Country cools our climate; their shade helps foster 50 degree summer mornings and cool breezes.

“If we don’t save the hemlocks, then you can say goodbye to trout and other cool water fish and invertebrate species; also over 90 species of birds nest in hemlocks, not to mention their value as wildlife cover and forage,” added McDonald.

According to McDonald, the ecosystem can be saved, we just have to—as a community and/or region—decide to do something about it on a much larger scale.

New Growth Everywhere
Although its difficult to tell from a distance, baby and medium hemlocks are thriving on our forest floor thanks to predatory beetles that are now in many corners of our region. All sizes of hemlocks are demonstrating signs of regrowth, or bright green tips of new needles on the branches and regrown leaders on the crowns. Photo by Sam Calhoun

Test Site Progress—Four Out of Four Ain’t Bad
This week, High Country Press visited four predatory beetle release sites around the High Country to monitor biocontrol progress and found four success stories. McDonald and entomologists and scientists from Virginia Tech released predatory beetles—both winter and summer predators—at each site between five and seven years ago, and now have achieved bracketing. The HWA has two generations per year: a winter and summer generation. Specific winter and summer predatory beetles— Laricobius nigrinus in the winter and various species of Scymnus in the summer—feed on these successive generations of the HWA, and this is called bracketing. The beetles thus attack all life stages of the adelgid and hold the HWA in balance.

The oldest test site is Hemlock Hill, located near Lees-McRae College in Banner Elk; the second oldest site is Holloway Gap, located off Church Road in Foscoe; the third oldest site is the Lees-McRae Field Lab, located in Avery County; and the fourth site is StillWinds East, located off Shull’s Hollar Road in Sugar Grove.

The result is this: hemlocks at all four test sites are showing signs of regrowth, or bright green tips of new needles on the branches and regrown leaders on the crowns. Yes, some old-growth trees are now dead, but you don’t have to look too far past the dead ones to find another alive and thriving. What’s more, small- and medium-size hemlocks are growing well, and with recommended selective canopy releases—or thinning out the forest canopy to allow sunlight and moisture to come in and nourish the new and old growth—McDonald thinks we can nurture the next generation of hemlocks to grandeur.

“If [biocontrol] is to work, the trees have to start regrowing, and they are,” he said.

Biocontrol had some help this year, though. The High Country experienced a cold winter and then received excessive rain. According to McDonald, a cold winter will kill the HWA and its’ ovisacs, as well as shorten the window for laying the ovisacs for the summer generation. Excessive amounts of rain will knock the HWA off branches.

“We were given the gift of both this past season, which helped a lot, especially after [the hemlocks] had to experience the drought,” said McDonald.

From a distance, Hemlock Hill looks like a morbid example of the effect of the HWA. Dead old-growth hemlocks jut out above the canopy up and down the hillside, but upon closer inspection, signs of old-growths thriving and regrowing can be seen closer to the edge of the forest—an area preferred by predatory beetles because of their love for sunlight, and an area suited for hemlock recovery because of its access to sun, water and rich soil. As you enter the forest, many small- and medium-size hemlocks come into full view. All the hemlocks show signs of HWA infestation, yet most are growing despite the invasive pest—a sign that predatory beetles are working.

“With sun, soil, water and biocontrols, these old-growths are coming back,” said McDonald.

Of the 10 old-growth hemlocks—which are between 300 and 500 years old—at Hemlock Hill that were release sites, seven have survived and are showing signs of balance concerning the HWA.

According to McDonald, the predation rate of the beetles on the HWA at both Hemlock Hill and the Lees-McRae Field Lab is 100 percent, which proves that beetles are working and that bracketing has been achieved. McDonald now knows that biocontrol works for this situation but also knows that more beetles are needed. At the Lees-McRae Field Lab, McDonald released 100 beetles on one old-growth hemlock more than six years ago. If you look at that tree today—which towers more than 80 feet into the air—you would have no idea that the HWA was in the High Country. More beetles equals more trees saved.

And the beetles are spreading for us. While leaving original generations behind to feed on the HWA, new generations of the predatory beetles are seeking new HWA to feed on by traveling to other infested trees in an annually growing radius from the original test sites. McDonald estimates that predatory beetles travel as far as 0.5 miles in four years and as far as 1 mile in five years, meaning their service of eradicating the HWA widens its scope annually.

But what if the HWA is eradicated? What would we do with all these predatory beetles? If the HWA stops laying eggs—which is the goal of the process—then the beetles stop laying eggs. The beetles used are prey specific, meaning that they won’t begin to feed on other beneficial organisms if the HWA happens to become extinct—this had to be proven before they were used for this purpose.

Don’t Judge a Book By Its Cover
From a distance, Hemlock Hill looks like a morbid example of the effect of the HWA. Dead old-growth hemlocks jut out above the canopy up and down the hillside, but upon closer inspection, signs of old-growths thriving and regrowing can be seen closer to the edge of the forest—an area preferred by predatory beetles because of their love for sunlight, and an area suited for hemlock recovery because of its access to sun, water and rich soil. As you enter the forest, many small- and medium-size hemlocks come into full view. All the hemlocks show signs of HWA infestation, yet most are growing despite the invasive pest—a sign that predatory beetles are working. Photo by Sam Calhoun

Next Steps
“Now we know the beetles work; now we need to figure out numbers,” explained McDonald. “We need to find out how many beetles we need and organize around our watersheds, replanting hemlocks, [conducting] selective canopy releases and releasing beetles.”

Understanding that each tree cannot be saved, McDonald believes the plan of attack should be to have local communities organize around their local watershed, find out if anybody is releasing beetles and, if not, get in line to do so themselves. To assist in the release, McDonald is hoping that local insectaries and/or hemlock nurseries come online to rear the beetles needed for such a large release. Multiple businesses in the High Country have already begun setting up these insectaries and hemlock nurseries, and High Country Press will cover this information in more depth once opening dates are solidified. McDonald said an end goal of the four release sites is for them to become insectaries.

The good news is that we don’t have to rush, thanks to Merit, a pesticide manufactured by Bayer that is recommended for use in killing the HWA. In past years of this series, High Country Press discouraged the use of Merit because of its active ingredient, imidacloprid, which has been traced to Colony Collapse Disorder (CCC), the phenomenon that is killing honeybees all over the nation. Since our reporting, though, new evidence has come to light that shows that Merit, if used according to label directions, will not cause harm to honeybees. That doesn’t mean imidacloprid, once sprayed, will not persist for many years. That said, Merit, if sprayed once, can keep a hemlock HWA-free for many years. McDonald recommends spraying infested trees with Merit—according to label directions—just once every few years instead of annually, which will buy some time to get organized behind biocontrols.

“If you don’t have beetles, the next time that [Merit-treated] tree has stress, such as drought or another infestation, it will die,” said McDonald.

“The use of Merit will buy us some time to get on lists for insectaries,” he continued. “And it’s not dangerous if used properly. The problem is people who have been continually treating trees with Merit, they put the trees on a pesticide treadmill. You can only treat with Merit about two times—hit it once and come back in five years. We now know Merit lasts about eight years in trees—much more persistent than it originally led on.”

“We’re not anti-Merit, we’re pro-reality,” added McDonald.

McDonald hopes the High Country’s elected officials—local, county, state and federal—will get behind and champion the use of biocontrol to stop the spread of the HWA in our region. With their support, he hopes a local nonprofit or business will also get behind the effort and bring a higher level of public awareness to the plight, as well as act as a fundraising driver. This all needs to begin soon, though, as the HWA will kill the hemlocks in the coming years if nothing is done. If the community organizes and begins selective beetle releases along High Country waterways, said McDonald, then we will save the ecosystem.

“We may lose some good, old trees, but we will nurture the smaller trees that will take their place,” explained McDonald. “We are the stewards who will grow the next old-growth trees.”