Skip to Main Content


Emerald Ash Borer and the Destruction of Kentucky’s Trees

In Kentucky, the landscape includes more than 220 million ash trees. But there’s an invasive species that is threatening to wipe out that population: the emerald ash borer, which was first discovered in the state in 2009.

“[Emerald ash borer] is native to east Asia,” says Jody Thompson, an Environmental Scientist with the Kentucky Division of Forestry. “Roughly 20 years ago, it made its way into the United States in the Detroit area, through the port there. Since that time, it’s been infesting and killing ash trees throughout much of the Eastern United States.”

Emerald ash borers in the larval stage live inside ash trees. They feed just under the bark, damaging the phloem that transport sugars up and down the tree. In large numbers, the borers destroy the phloem and essentially starve the tree. Thompson says the trees will start to decline and die within a couple of years of infestation.

This expanding infestation of the invasive species could have a devastating impact on Kentucky’s forests. Thompson says ash trees make up at least 10 percent of the tree population in much of central and northern Kentucky.

“So if you look out across the landscape and imagine 10 to 15 percent of the landscape is ash trees, the emerald ash borer were kill all of those trees,” he says.

It’s not just the wilderness areas of the state that are affected by the emerald ash borer. Ash trees are found throughout Kentucky’s urban areas as well. Tim Queary, an Urban Forester with the Lexington-Fayette Urban County Government, says that the autumn purple variety of white ash was introduced into the city’s parks and streetside landscaping about 15 years ago.

“In Fayette County alone, we have an estimated half-million ash in our landscape, so we run the risk of losing that tree canopy,” says Queary. “Environmentally speaking, that’s about two percent of our tree canopy in Fayette County.

“Homeowners should be especially concerned,” Queary adds. “Landscaping on residential properties can add up to five to ten percent of the value of the property. A mature tree can greatly reduce your energy consumption. The benefits of trees go on and on. I could talk about that for a long time, but when we start talking about losing a portion of the population of trees in a community, then it’s going to have an effect on everybody.”

Controlling the negative effects of the emerald ash borer isn’t as easy as simply spraying some pesticides and moving on.

“With this pest, eradication is not possible,” says Thompson. “It’s probably the most dynamic, exotic tree pest that we’ve seen in this part of the country. It’s always ahead of us. It’s very aggressive. It reproduces and infests and destroys trees very quickly.”

Thompson says that the main way emerald ash borers have spread is through transportation of firewood. Bringing your own firewood from home to a campsite in a different region, for example, can have devastating consequences. The insects can live in wood for 18 months after the tree has been cut down.

“It doesn’t mean don’t move firewood half mile down the road to your neighbor’s or your mother’s house. It means don’t move it 50 miles,” Thompson explains. “Don’t move it to an area of the state or another state that’s not known to have [emerald ash borers] yet. There are insecticide treatments for this and those treatments work well, but those treatments have to be continual because it’s not just a single infestation, and then it’s done. That tree, until it’s dead, is continuously infested by the new insects.”

For trees owned and managed by cities, that means choosing where to devote resources.

“You’re probably never going to have enough resources to treat every single ash tree that’s owned by the city, so you have to decide which ones are the most significant,” says Queary. “Here in Lexington, we’re in the bluegrass region of Kentucky where we have the old majestic blue ash and some of these are upwards of 300 years old. Our thinking was that we would prioritize the treatments for the emerald ash borer to try to preserve our significant blue ash. You really can’t place a value on a tree of this age and size. As long as we have the resources available we’re going to try to preserve the tree.”

This segment is part of Kentucky Life episode #2010, which originally aired on February 14, 2015. Watch the full episode.