Wandering the other day, saw damage to some Eastern hemlocks that I had checked every year and, until now, they’d be healthy and happy.
Buy now they were finally infested with hemlock woolly adelgid, which is destroying them everywhere.
So, disheartened, I thought I’d repost the article I wrote on the scourge for the CV last year. What s ahme.
By Bob Quartetoni
The state of the state tree: Under severe attack, prognosis unclear.
That’s due to the one-two punch of two highly destructive insects: Hemlock woolly adelgid (HWA) – an aphid-like insect – and elongated hemlock scale (EHS), an armored insect.
Both are foreign invaders: HWA from Asia and EHS from Japan. Because of this, neither has any natural predators here, so they are free to infect Eastern hemlocks without anything to stop, or even slow, them.
And that’s exactly what they’ve done.
First found in the eastern U.S. in the 1950s, HWA now infests hemlock trees from the Canadian border south to Georgia, in some areas killing 95 percent of eastern (and Carolina) hemlocks.
HWA punctures the bases of hemlock needles and sucks out the vital fluids. EHS pierces the underside of the needle with its mouth parts and removes fluids from the needle. Combined, they sap the tree’s vitality and, without treatment, it inevitably succumbs.
Under this blitzkrieg, If left unchecked, the Eastern hemlock could go the way of the American chestnut and suffer what biologists call “functional extinction”: There will be a few around but the vast stands that keep our forests and pristine trout streams cool may go the way of the dodo.
And that would be a catastrophe. Hemlocks – which can reach 175 feet tall and live up to 900 years – fill an important ecological role by providing shade to cool streams where native brook trout live, as well as providing wildlife cover, forest aesthetics and recreational opportunities.
And hemlocks are a “foundation species,” meaning that everything else that lives near those trees, plant or animal, is able to exist because of the hemlock.
How bad is the problem? Very bad. In Shenandoah National Park in Virginia an estimated 80 percent of the hemlocks are infested and the situation may actually be worse in Great Smoky Mountain National Park.
In Pennsylvania, infestations have been found in 58 of the 67 counties, including Luzerne and Lackawanna.
“Currently, HWA conditions are variable across the state,” said Tim Marasco, field operations supervisor with the State Bureau of Forestry, Division of Forest Health. “The two bitter cold winters of 2014 and 2015 caused significant winter mortality and gave the hemlocks a temporary reprieve. However, it doesn’t take long for infestation to rebound where hemlocks are under other stresses: site quality, drought, overly wet conditions or other diseases.
“Right now, many hemlocks are still enjoying the winter-kill reprieve while other areas — the warmer, more southerly reaches of the state — are experience a resurgence of the adelgid.
“In general, the colder northern reaches of the state fare better than the southerly, warmer zones. If we have another mild winter, I expect that infestation will increase significantly in the more vulnerable parts of the state.”
Marasco said the adelgid is the big problem, but it’s been compounded by the hemlock scale.
“The EHS has not been a problem in PA historically,” he said, “until the HWA arrived. When EHS and HWA are on the same tree, the impacts on the tree’s health are multiplied.”
In Luzerne County, as in real estate, the operative words seems to be location, location, location.
“Along with the weather, destruction depends upon location, the tree’s position in the landscape,” said Vincent Cotrone, urban forester, Penn State Extension. “Ridgetop Hemlocks have suffered and been stressed by heat and drought, so they are the first to succumb. Hemlocks set along water are doing better, even though they have HWA infestations.
“It can take years for HWA to cause major defoliation to those trees. I have some on my wife’s family farm along the Little Wapwallopen Creek. The large old Hemlocks have had HWA for years. The hemlocks on the ridge died years ago.”
But all is not lost. DNCR is vigorously fighting back, using what it calls “integrated pest management (IPM),” meaning that they are using a variety of management techniques, from mapping ecologically significant hemlock stands in the state, to using chemical and biological control on public lands on more than 150 sites in the state, focusing on high value (ecological, historical or aesthetic) trees.
But what may be the biggest weapon in their arsenall are two things the size of a pinhead; small but with a big bite.
DCNR is using Laricobius negrinis (Ln) and Lacrobius Osakensis (Lo), pinhead-sized black lady beetles that feed on adeligid in their native range.
The Bureau of Forestry has embarked on a state predator beetle release. Ln and Lo eat only adelgids and they really like them. Each larva eats hundreds of eggs and immature adelgids, known as nymphs or crawlers.
Adult Ln/Lo feed on eggs and young adelgids during the winter and spring when HWA are active. Beetle releases are focused on the leading edge of infestation.
Both Luzerne and Lackawanna counties have at least two release sites each.
DCNR is optimistic, with signs of overwintering success and successful field reproduction by the beetles. Other beetles are also being tested for effectiveness against the adelgid.
Marasco DCNR’s insecticide treatment program, but notes that “The process is labor intensive. Hemlocks must be treated one at a time, as opposed to spraying many acres at a time with aircraft. We can treat several thousand hemlocks in a single year, but as large as that number sounds, it only scratches the surface of the number of hemlocks actually out there. So we prioritize and treat only the most important areas, focusing on ecosystem preservation, aesthetics and recreational areas.”
It’ll be a long battle, Marasco says, but he’s optimistic:
“HWA leads to the death of many hemlock trees, but plenty of them seem to survive, even though they look poorly. The point is that we don’t expect every hemlock in the state to eventually die. There ARE some areas where all the hemlocks succumb, but in many locations we always find survivors. This gives us hope that eventually, HWA will become more balanced in the ecosystem and just be another annoying pest. It could take a long time for that to happen but we’re hopeful it will.”
Information on the adelgid – including what landowners can do to combat the adelgids –is on the DCNR website, in a PDF file called Forest Health Fact Sheet Hemlock Woolly Adelgid.