SHENANDOAH NATIONAL PARK — Dale Meyerhoeffer reached up to grab a low-hanging branch of a hemlock here in the park, inspecting the needles on the healthy-looking tree.
A few years back, it was on death’s door, infested with and damaged by the hemlock woolly adelgid.
That’s an invasive insect that has destroyed 95 percent of the hemlocks in Shenandoah since being discovered there in 1988.
Meyerhoeffer, a biological science technician who works to combat invasive insects, said treatments of insecticide soap and horticultural oil in the early years of treatment weren’t very effective.
But in recent years, Meyerhoeffer and others on the front lines of the battle to save the hemlocks have found something that does work, the injection of the systematic insecticide midacloprid into the soil at the base of hemlocks.
It’s taken up by the tree, gets into its sap and is then ingested by the adelgid when it feeds.
The result: Some hemlocks treated in that way years ago are healthy now, growing taller with an increase in crown health.
Beyond that, many are now adelgid free, something Meyerhoeffer said was also affected by an increase in rainfall, colder winter temperatures in recent years and a decrease in overall adelgid population pressure.
“It’s been encouraging to see this have some success,” said the technician, noting the branch full of healthy, green needles.
The fact that things looked dire for Shenandoah hemlocks is giving park officials hope they’ll eventually find similar success for a new insect threat, the emerald ash borer.
Those critters, the larval stage of an exotic beetle, were found in the northern end of Shenandoah in 2013, and are already damaging and killing the stately ash trees in the park.
To help in the fight, visitors to Shenandoah need to do their part by following a new policy on park firewood, the likely way the emerald ash borer came into the park and spread quickly.
The new rules: Visitors to Shenandoah are to use only USDA-certified firewood, which is heat-treated to kill insects, or instead simply use gathered down and dead wood.
The USDA-certified wood may be brought in or purchased at camp stores.
As always, visitors are encouraged to use charcoal for cooking fires.
Rolf Gubler, a park biologist, notes that the emerald ash borer burrows under the bark of ash trees to create feeding tunnels that cut off nutrient and water flow to the tree.
He said that the park has been using the same insecticide used on hemlocks to treat some ash trees, mainly those in selected sensitive plant communities and in developed areas of the park where dead, falling trees would pose dangers.
But the application of the insecticide to those trees, done both by ground injection and injections straight into the tree trunks via “plant IVs,” haven’t been nearly as effective on these new pests.
Gubler said the park is working with Virginia Tech on the possibility of using biological controls (things like parasitic wasps) as they become available.
Right now, the prospect of the loss of large numbers of ash trees, which make up about 5 percent of the trees in Shenandoah, is as daunting as the situation the hemlocks faced years earlier.
Meyerhoeffer, who like me is a glass-half-full guy, said he’s given hope by the renewed health of the hemlocks.
“The situation with the ash borers now is where we were with the wooly adelgid years ago,” he said. “We found a way to fight them and that gives us hope that we can find something just as effective on these new pests.”
Meyerhoeffer has had a team of four seasonal employees working with him to treat selected ash trees over a six-week period, the only time of the year that works for those trees.
“That’s one of limiting factors,” he noted, saying that while hemlocks can be treated for adelgids pretty much all year long, the small window of time for treating ash trees limits how many can be treated.
If biological controls are eventually used, the hope is that they can spread on their own and combat the borers year-round.
“We will do as much as we can with the treatment methods now available and hope that more effective and efficient methods can be developed in the future,” said Meyerhoeffer.