Tuesday, July 17, 2012

Emerald Ash Borer Puts 187 Million Ash Trees In Commonwealth At Risk

The emerald ash borer (EAB), Agrilus planipennis, is a non-native, invasive, wood-boring beetle from Asia that was first detected in Detroit in 2002 and has now spread to 15 states, including Virginia. First found in Fairfax County in 2003, it has been recently confirmed in the counties of Pittsylvania, Halifax, Charlotte, Mecklenburg, Lee, Buchanan, Hanover, Warren, Caroline, Prince Edward, Giles, Loudoun and Stafford. Previous finds include the counties of Arlington, Prince William and Frederick.

VDOF Forest Health Specialist Dr. Chris Asaro said, “EAB is capable of killing all 187 million native ash trees in Virginia, regardless of their initial health and condition. In addition to the ecological problems this will cause, it will have a significant economic impact on the Commonwealth.”

For the last four years, the Department of Forestry has partnered with several other Virginia state agencies, private businesses and the federal government to slow the spread of the EAB through a “Don’t Move Firewood” campaign. Unfortunately – and in spite of state-mandated quarantines in several counties – citizens and visitors to the Commonwealth continue to carry firewood from infested areas to non-infested areas thereby delivering the shiny green and highly destructive beetles to new stands of ash trees, which they can kill in just three years.

Dr. Asaro said, “Despite our collective best efforts to slow down the emerald ash borer, the evidence is quite clear that people are inadvertently moving EAB tens or hundreds of miles in one shot via untreated firewood (which may include ash) and other ash wood products. We know this because, on average, adult borers fly no more than a mile or two, if that, on their own each year.”

While reluctant to make any predictions, the VDOF entomologist said, “My guess for the next decade is that EAB will permeate much of the eastern United States from Maine to Minnesota to Texas and Florida. And based on what little I have seen so far, it’s easy for me to imagine emerald ash borer rendering ash trees in Virginia ecologically and economically extinct within a few decades from now. This would put EAB on par with chestnut blight in terms of the speed and efficiency with which American chestnut was effectively eliminated from the Virginia landscape.”

According to the U.S. Forest Service Forest Inventory and Analysis (FIA) plot data, ash in Virginia represents approximately 1.8 percent of total forested volume statewide – that’s 187 million trees. The vast majority of this volume is made up of two species – white ash (Fraxinus americana) and green ash (Fraxinus pennsylvanica) – with several other minor species in the mix (Carolina ash, F. caroliniana; pumpkin ash, F. profunda; black ash, F. nigra). Northern and western Virginia have a slightly higher abundance of ash on average (2 percent to 2.5 percent) compared to the southern piedmont and coastal plain (1 percent to 1.5 percent). These are regional averages, and local variation in ash abundance can be considerable.

Ash abundance can also vary considerably in urban forests. Recent inventory data for many major and minor municipalities across Virginia indicate ash represents between 1 percent and 5 percent of street trees, with most cities averaging between 2 percent and 3 percent ash among street trees.

Dr. Asaro said, “Depending on several factors, such as location and size, removing a dead ash tree in an urban area could easily cost a city or town more than $1,000 per tree. Multiply that by tens of thousands of ash trees and you can easily see the tremendous financial impact EAB will have on Virginia’s local governments.”

EAB is extremely difficult to detect early due to its cryptic nature – it spends most of its life cycle as a grub, or larva, feeding under the bark. Once discovered, it is often determined to have been present in an area for many years. That’s because it can take several years for these relatively small beetles, which have a one-year life cycle, to build up their numbers and overcome a tree by girdling. Often, trees must be infested and re-infested for several years before they begin to show characteristic symptoms, such as branch dieback, epicormic sprouting and D-shaped emergence holes on the bark.

The release of insect biological control agents against emerald ash borer is underway. Biological control, unfortunately, has shown more failures than successes in attempts to deal with other insect populations.

State Forester Garrison said, “On a small scale, there are several systemic chemical control options on the market that are targeted, environmentally safe, and highly effective at protecting trees. This is practical only on a very limited basis, however. Unless individual ash trees are of great size and of significant value – for example those found at Mount Vernon, in the City of Abingdon or at the University of Virginia, the cost and practicality of performing chemical applications on individual trees, let alone 187 million of them, every two to three years is prohibitive.”