The ash borer, on its way

The emerald ash borer (EAB) – a tree-eating machine that kills ash trees regardless of age or health – is probably on its way to a tree near you. You’ve probably seen the purple traps hanging in the area to monitor EAB spread. EAB was first discovered in Virginia (Fairfax County) in 2003. An eradication effort ensued and was presumed successful when it was not found for several years. In 2008 it showed up again in Fairfax, at which point a quarantine restricting the movement of wood from the Northern Virginia area was handed down.

Earlier this year, many of us were celebrating that the massive trapping effort revealed no known spread of EAB outside of the quarantine areas at the end of 2011. For several years, the traps didn’t reveal a spread of the beetle . . . until now.

The emerald ash borer is small but its potential for damage is great. Courtesy U.S. Forest Service.
The emerald ash borer is small but its potential for damage is great. Courtesy U.S. Forest Service.

This exotic flat-headed borer has sprung up in nearly every corner of the state. In the past month EAB has been confirmed in Loudoun, Stafford, Caroline, Hanover, Prince Edward, Pittsylvania, Charlotte, Buchanan, Halifax, Mecklenburg, Giles, Lee and Warren counties. Before that, the Northern Virginia counties, as well as Frederick and Clark, were the only areas of the state known to have EAB.

The emerald ash borer is a small, half-inch long metallic green beetle native to eastern Asia. It hitched a ride to our shores in wooden packing crates and pallets from China and was discovered in Michigan ten years ago. Since then it has spread into 15 states in the northeast, midwest and mid-Atlantic areas of the United States, feasting on ash trees wherever it pleases.

In early spring adults climb to the crown of their chosen host trees and modestly nibble on the leaves. By midsummer, the adults mate and the female crawls down the trunk of the tree, laying 30 to 60 (possibly up to 200) eggs in bark crevasses as she goes.

Within seven to 10 days the eggs hatch into small larvae, which burrow through the bark into the cambium and phloem tissue of the tree. This is where the damage begins. The small larvae tunnel upward into the “inner bark” portion of the tree, creating serpentine shaped tunnels that get bigger as the larvae grows.

For a tree, this is like cutting the jugular vein. The cambium and phloem are the living portions of the tree responsible for cell division and the flow of sugars and nutrients. By late fall, the larvae have begun to transform into the pupae stage; the EAB then transforms into an adult in early spring and cuts a perfect “D” shaped emergence hole in the bark of the tree.

Homeowners can pre-treat ash trees if desired. In most cases, by the time damage is obvious to the casual observer, it’s too late to treat the tree with hopes of full recovery. Most insecticides labeled for EAB purposes are restricted use products requiring a license to apply. Information to assist with decision-making and more is available at emeraldashborer.info.

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