“This has got to be the most aggressive thing I’ve ever seen,” said arborist David Sprinkle, the owner of Hedgewood Tree Care in Piney Flats.
Experts believe the emerald ash borer, a small beetle that feeds on ash trees, first made inroads in the U.S. about 15 to 20 years ago through wood packing material transported to Michigan from Asia, according to the Tennessee Department of Agriculture. The beetles have migrated over the years and have been in Washington County since at least 2017.
Sprinkle said he’s noticed that symptoms of infestation in local trees have grown more prevalent in recent years. “This year ... people are going to start wondering what’s going on,” he said.
According to the Tennessee Department of Agriculture, 62 of Tennessee’s 95 counties, including Washington, Sullivan, Carter and Unicoi counties, are quarantined to prevent the spread of the insect. The department urges residents to avoid transporting firewood within the state or buying it from out of state.
Afflicted trees have a thinner canopy of leaves than their neighbors, Sprinkle said. Adult beetles lay eggs on the trees’ bark, and the hatched larva chew a serpentine path through the trees’ vascular system, which transports water and nutrients to the leaves. Once the leaves waste away, the tree loses its ability to produce energy through photosynthesis. Trees can die within a few years after infestation.
Travis Watson, the arborist at East Tennessee State University and a graduate student in the school’s biology department, said ash trees are a prominent part of the native woodlands in East Tennessee. He estimates that about 80 percent of ash trees on the stretch of highway between Johnson City and Knoxville are dead as a result of infestations from emerald ash borers.
“It has the potential to eradicate ash in our native woodlands,” Watson said.
ETSU has treated all of its ash trees, about 40, with an injectable insecticide, Watson said. Older trees, he said, have a lower chance of successfully responding to treatment.
“As trees age, just like us, their ability to cope with change is reduced,” he said. “They’re not as young and vigorous.”
Younger trees are typically better candidates for treatment, he said, but the process can be a significant commitment for tree owners. “Once you start, you have to continue,” Watson said.
He said injections are effective about two or three years, but trunk spray typically requires annual application. Especially for injections, Watson recommends that owners seek assistance from an arborist or a tree service.
“You’re talking a pretty substantial investment, and you don’t want to mess it up,” he said.
Once the signs of infestations become noticeable, Watson said trees are typically past the point of saving. Property owners interested in preserving their trees, providing that they haven’t displayed signs of infestation, should not delay treatment, he said.
“If they’re interested in saving them, they need to treat them now preventatively,” Watson said.
Ryan Clark, a certified arborist with Bartlett Tree Experts, a shrub and tree service with a location in Johnson City, said that if an ash tree has lost more than 45% to 50% of its canopy, the chances of it recovering are much lower than if it has, for example, 20% canopy loss.
When an ash tree dies, Sprinkle said the branches become extremely brittle within 6 to 12 months, which can make them dangerous to climb on or have hanging over a house. Clark suggests that homeowners prune out dead branches.
Clark said the cost of pesticide injections at Bartlett depend on the diameter of the tree at chest level. The company charges $15 per inch of diameter.
“Pretty much every ash in this area either has it, or is going to have it if it’s not treated,” he said.