Tyler Arboretum loses 900 ash trees to emerald ash borer, forced to close miles of public trails

Visitors to the 650-acre Tyler Arboretum in Delaware County will soon witness the leaves turn on dogwoods, ginkgo, and maples. They’ll sniff wafts of fall fragrances from katsura, meadow grasses, and asters.

What they won’t be able to do? Hike along 17 miles of trails because of a path of destruction caused by the emerald ash borer — a beetle so metallic green and shimmery that it resembles a bauble on a Mummer costume.

The trails outside the arboretum’s deer fence are now closed to the public for an undetermined period so a contractor can continue removal of 900 ash trees sickened or killed by the invasive pest, a scourge since it began a widespread sweep of Pennsylvania’s private and public forests starting in Butler County in 2007. The arboretum, however, is open with events and programming, as are trails inside the fence.

The pest arrived in the Philadelphia area in about 2012 and is just about done munching its path of destruction through the state. Delaware County is one of the last counties to face an infestation. Some of the trees that emerald ash borers have killed at Tyler Arboretum were more than 100 years old.

The emerald ash borer begins ravaging trees while still a larvae that feeds underneath bark, disrupting the transportation of water and nutrients. It can kill a tree in three to four years. Signs of an attack include a dying upper crown, splitting or flaking bark, tissue damage, D-shaped exit holes, and S-shaped larval feeding galleries just below the bark.

Adult beetles grow to one-half inch long and one-eighth inch wide. They fly from early May until September. Larvae live beneath the bark until emerging as adults through D-shaped holes.

The best way to stop an infestation is to remove trees. But that’s expensive. Chemicals have been shown to be moderately or highly effective depending on which insecticide is used.

The emerald ash borer, or Agrilus planipennis Fairmaire, has killed millions of trees in the U.S. and Canada since it was first discovered in the United States in Michigan in 2002. Though the beetle can spread on its own, it has been transported across the Northeast in firewood, timber, and nursery plants. Pennsylvania alone had an estimated 308 million ash trees in its forests.

The emerald ash borer is just one of several pests threatening private and public forests across Pennsylvania and New Jersey, where it was first detected in 2014. Other pests of concern include the woolly adelgid that attacks hemlocks, and a nematode suspected of causing leaf die-off in beech trees.

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Arboretum officials decided last spring to see how much damage the pest had inflicted on the property in Middletown Township. Their initial estimate was way under.

“We did an updated GIS survey of the property and sort of mapped out where these trees were and we thought we would have a lot less,” said executive director Mike Skuja. “But it turns out we had close to 900 hazard ash trees. They’re not all trees just in the middle of the forest. These are trees near trails that create a risk of falling when they are either dead or almost dead and are a safety risk to the public.”

Some of the larger trees were more than 120 years old. The smaller ones ranged from 30 to 50 years old.

The arboretum has created an “ecological working group” to come up with a plan. The first phase of the job, Skuja said, calls for contractor Cox & Co. to cut down about 584 trees that would lead to the reopening of 9.5 miles of trails. But the going is slow, he said, because of the location of the trees. Tyler officials say the removal of the ash trees will change the look of the forest and is expensive. The arboretum is seeking donations to help pay for the removal.

“We expect our first phase to cost over $500,000,” Skuja said. “We don’t know for certain how much remaining phases will cost because the work and cost will depend on many factors from the location and condition of trees and weather and how both of these affect the equipment and technique needed for their removal.”

He said the arboretum plans to create new habitat, such as native meadow and forest, in areas impacted by the emerald ash borer.

“We face a huge challenge and additional expense,” Skuja said. “Our goal is to raise another $1 million-$2 million to support restoration across the landscape in its entirety. This is an opportunity to face our ongoing loss of the ash trees and come out stronger on the other side with a long-term plan for regeneration.”

Erin Mooney, executive director of the Schuylkill Center for Environmental Education in Philadelphia, said the emerald ash borer has also been a problem within the center’s 365-acre property, though not to the extent of Tyler’s infestation.

“Tyler is not alone,” Mooney said. “We’re incredibly sympathetic to their plight. We have seen the problem at the Schuylkill Center for the past five years.”

Pennsylvania’s Department of Conservation and Natural Resources (DCNR) first launched a plan in 2014 to tackle the problem. At the time, the beetle had already reduced the number of ashes in the state’s forest by 12%.

Houping Liu an entomologist with the DCNR, said the worst of the 18-year infestation is over, given that there’s really nowhere else for the emerald ash borer to go. In other words, it has killed most of the untreated ash trees, which once made up about 4% of Pennsylvania forests.

The pest began making its way through Delaware County about six years ago, the last of the remaining counties to see an infestation. And that’s why Tyler Arboretum is seeing so many dead ash now, Liu said.

Widespread treatment isn’t really an option, he said, because it’s so time consuming and expensive. Aerial spraying is not an option. A main treatment includes injecting emamectin benzoate into each individual tree trunk while larvae are still present. The state has treated about 1,700 trees.

“Right now, if you see any surviving trees in a state forest or park, they’ve likely been chemically treated,” Liu said.

The only hope, Liu said, lies in a small percentage of trees that managed to survive the onslaught. Those “lingering ash,” as they are known, might prove genetically resistant. If so, they could be bred and planted if. But more research is needed.

As of now, Liu said, “we don’t recommend planting ash trees.”