For the past 15 years, Chris Miller has served as the manager for The Davey Tree Expert Company in King of Prussia. As an arborist, he has treated and preserved trees of nearly every variety, and has brought back trees that have been on the brink of death and restored them to full health, from the Main Line to Chester County and beyond.

One recent morning, Miller spoke on a cell phone from the Valley Forge National Park. The tone of his voice was layered with both matter-of-fact realities and the timbre of fair warning, reflecting the serious nature of the topic being discussed.

He spoke about the forecasted local arrival of the emerald ash borer [EAB], a half-inch-long beetle whose outer shell is a rich, metallic green. Since it first came to the United States in 2001-- on a shipment of ash wood from China to Detroit -- the EAB has been responsible for killing more than 40 million ash trees in 21 states and two Canadian provinces.

The adult EAB typically emerges between April and July, depositing eggs in bark crevices. The eggs hatch and the larvae bore into the tree to feed just below the bark surface. The larval feeding results in the tree being girdled, preventing the movement of nutrients and water between the roots and the tree crown. The infestation usually kills ash trees in three to four years after being attacked.

Despite efforts to control the population, the EAB invasion has continued eastward. The invasive insect was first found in Pennsylvania in 2007, and in the last eight years, it has infected ash trees in 56 of 67 counties. Chester and Lancaster counties are two of the remaining seven counties in Pennsylvania where EAB has not yet been detected, but it could just be a matter of time, Miller warned.

"My guess is that it is here and we have not yet realized it is here," he said. "I suspect that it will be discovered this year. Based on the life cycle of the insect and research, we've seen its ability to spread everywhere and not be stopped."

Miller then delivered the blow that many in our area are fearing the most.

"There is no way to avoid it," he said. "If we have the same conversation a year from now, we would see severe damage in all five counties in the Philadelphia metropolitan region. If you have an ash tree on your residential property and it is untreated, the tree will die. There is no doubt in my mind. And it's not just trees in backyards. That means all of the trees in the forest will succumb to the insect."

"If you don’t have it already, it is coming and it will kill 99 percent of your ash trees," said Dr. Donald Eggen, forest health manager for the Pennsylvania Department of Conservation and Natural Resources (DCNR). "If you have a lot of ash trees and do absolutely nothing, that is the most costly because they will all die at once -- especially if you have big trees, as they are expensive to take down.

"You never know when the infestation is going to happen. We don’t have a good survey tool for detecting low populations," he said. "It can be percolating and then it appears and it’s here. They also start up high in the trees and by the time they get down to the bottom it’s too late."

Grant Jones, integrated pest management supervisor at Longwood Gardens, suggests that the sheer, enveloping spread of the EAB reminds him of the Dutch Elm Disease and gypsy moth infestation that swept through the eastern portion of the country years ago.

"But I think this is worse," he said. "Before I came to Longwood, I lived in Milwaukee and Chicago, where ash trees are a very large percentage of the tree population. The EAB had a huge impact there, not only environmentally, but economically. For a municipality to treat, remove and replant its ash tree population would be very expensive."

All hope is not lost, experts say.

Methods to contain the rapid spread of EAB have been under way for several years. Although some systemic insecticides are beginning to show promise for the protection of high-value ash trees, sustainable management methods are also being used. One of the long-term strategies being used is through biological control that involves research in China to find, isolate, and identify the pest's natural enemies, ranging from parasites to predators to pathogens. In the U.S., permits for release of highly host-specific natural enemies or "biocontrol agents" may be granted, but they're environmentally risky, Miller said.

"At this point, with the knowledge I have on control measures, if you're going with biological alone, you'll lose everything you have," he said. "But without chemical control, we'll lose all of our residential ash population. There are ash trees that are still alive because people have taken the measures to protect them."

One such chemical solution Miller discussed is made with the active ingredient known as Imidacloprid, which can be mixed with water and drenched around the base of the ash tree. It has the same active ingredient used in flea and tick protection, and very low toxicity.

Research has shown that the soil drench using Imadacloprid provides excellent protection for smaller ash trees in the first year following treatment, but that larger ash trees may require two years of treatment before they are fully protected.

The product is available at most local hardware and garden stores, and should be applied in May or early June, every year.

While there are several products that can be applied by weekend arborists, the severity of the potential damage that is likely to happen to local ash trees demands the attention of a professional, local experts say.

"There are DIY products to protect ash trees, and yes, the homeowner may get some control with the product, but as a homeowner, that's your only weapon to control EAB," Miller said.

"If your tree is 30 percent infested, a home remedy -- or the application of a store-bought product -- will not save the tree. Professional arborists have been educated in the science and symptoms of the EAB, and what we look for is the percentage of infestation."

Jones recommended that homeowners get their ash trees evaluated by professionals, who can help walk the homeowner through the process of what he or she can do to help save the ash trees on their property.

"The earlier you do it, the more choices you have," Jones said. "The longer you wait, the less options you have. It may cost more to take the tree out, as opposed to treating it quickly."

One local town has begun to see hope through the trees. West Chester, in partnership with the DCNR, West Chester University, and borough officials, recently served as a test site for the "Emerald Ash Borer Management Plan for Pennsylvania Communities" – a program that has now expanded to ten communities statewide.

Eggen, WCU graduate student Kendra McMillin, along with WCU professor Gerard Hertel, DCNR forest entomologist Houping Liu, and West Chester Borough urban forester Denise Dunn-Kesterson, worked to implement the ash tree assessment and prevention program to protect ash trees in borough parks. In 2013, the borough initiated the plan as a pilot program, in which ash trees in its three most heavily wooded parks – Hoopes, Marshall Square and Everhart – were evaluated, monitored and treated based on their prognosis. About 100 high-value ash trees in good health were treated with an injectable systematic insecticide to ward off the borer.　

As a result of its success, the West Chester program was awarded federal grant funding to continue its monitoring and prevention efforts.

McMillin said West Chester was ideally suited to be the program’s first site due to its comprehensive and up-to-date tree inventory.

"West Chester was really way ahead of the game in that sense, because the tree inventory is a huge part of it. We had the knowledge of what trees we have and where they are," she said. "For instance, we have a significant amount of mature ash trees in Hoopes Park. Can you imagine if those trees were infected and started coming down in three years?"

Both Eggen and McMillin also emphasized that studies have shown that monitoring, treatment and prevention programs are far more cost effective than the financial burden of paying for the removal of so many dead trees. Part of the reason is that while ash is a hardwood, a borer infection results in the ash tree and its branches becoming increasingly fragile, making it unsafe for an arborist to climb them during removal.

The goal is to save as many trees as possible and to prevent any potentially hazardous or dangerous situations, they said. Though the systemic insecticide injection is highly effective against the borer, once a tree is more than 30 percent in decline, it is beyond saving.

"For 26 consecutive years, West Chester has received the Tree City USA Award for its commitment to maintaining the health, beauty and diversity of trees throughout our parks, neighborhoods and the downtown," Sen. Andy Dinniman said during a recent Arbor Day celebration at Hoopes Park. "I want to thank all the staff and volunteers for their ongoing efforts in safeguarding our trees and preventing invasive species like the emerald ash borer from jeopardizing our rich natural heritage."

To find a licensed arborist in your area, visit www.treesaregood.org.

To contact Staff Writer Richard L. Gaw, e-mail [email protected].

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