It was really only a matter of when, not if. Emerald ash borers, the tree-killing pests from Asia that have swarmed across most of Maryland, have now been spotted in Baltimore County, one of the last places in the metropolitan area where they hadn't been found so far.
Todd Armstrong, a private arborist, emailed in response to a Baltimore Sun story earlier this week about the borers affecting the region that he found the metallic green insects last week in an ash tree in the parking lot of the Glen Meadows retirement community in Glen Arm.
The borers pose a threat to the 5 to 6 million ash trees estimated to be in the Baltimore region, as the insects' larvae bore into the bark and starve trees of water and nutrients in a few years. Emerald ash borers have invaded 12 Maryland counties, including Anne Arundel, Carroll and Howard, as well as Baltimore city. They have yet to be confirmed by state agriculture officials in Baltimore and Harford counties, or on the Eastern Shore.
Armstrong sent along photographs both of a borer and of the ash tree in the retirement community where he found it. The tree's upper branches are mostly bare of leaves, an indication of infestation.
"We have seen borers attack Ash trees for years now, but have not confirmed Emerald Ash borers until this year," wrote Armstrong, who is the North Baltimore district manager for the Davey Tree Expert Co.
Ash trees also suffer depredations from other boring insects. But the emerald ash borer has proven much more destructive since its arrival in the United States from Asia over a decade ago. It's spread to 25 states, including Maryland, and is blamed for killing millions of trees in the Midwest, where the infestation began.
Kimberly Rice, an entomologist with the Maryland Department of Agriculture, said when informed of Armstrong's sighting that it needs to be verified before Baltimore County is declared affected. She emailed that "to do so we would need to collect beetles from the site for confirmation."
With no confirmed emerald ash borer sightings so far in Baltimore County, local officials have no plan at this point to treat or remove ash trees on county property, according to spokeswoman Lauren Watley. Baltimore County is estimated to have 300,000 ash trees, but the vast majority are on private property, she said, so officials consider the infestation primarily an issue for individual landowners to deal with.
But in some communities where ash borers have been confirmed, such as Howard County and Baltimore city, local officials are beginning to treat some of the many ash trees growing along streets and roads. They hope to limit the hazards and costs of removing dead or dying trees in proximity to people, cars and homes. They also are cutting down some ash trees even before they've become infested, especially if the trees appear already stressed or weakened.
For more information on emerald ash borers and what homeowners can do to protect their ash trees, go here and here. Experts also urge people to avoid transporting firewood or tree limbs out of their community, as the wood may harbor borers and help spread them.