Wednesday, January 28, 2015

Emerald Ash Borer

I had not thought much about the emerald ash borer--an invasive beetle from Asia--until I visited my brother west of Chicago a few years ago and saw all the dead ash removed from formerly tree-lined neighborhood streets. The emerald ash borer (or EAB) is a minor pest in its native place: a vast range that includes northeast China, Korea, Japan, Taiwan, Mongolia, and the Russian Far East. But after it was first discovered in Michigan in 2002, it has chewed its way across 22 states including most recently in New Hampshire, killing millions of ash (white, green, and brown).

Emerald ash borer
(Image from Pennsylvania Department of Conservation
and Natural Resources shared via Creative Commons)

This metallic green slender beetle is 1/2 inch long. The adults, which live only 3 weeks after emergence starting in late spring, chew ash leaves with little impact to the tree. The larvae are the killers. Female borers lay dozens of eggs, sometimes a hundred or more, in the tree bark. After hatching, the creamy white, legless larvae burrow into the inner bark and begin feeding on the tissue between the bark and sapwood, disrupting the flow of nutrients and water in the tree. They leave s-shaped feeding galleries filled with sawdust.

Ash trees infested with emerald ash borer,
indicated by s-shaped larval feeding galleries filled with sawdust.

The emerald ash borer is now considered the most destructive forest pest in North America. Its relentless pursuit of healthy ash trees shows no sign of stopping. Once infested, ash trees die within 3 to 5 years.

EAB was first discovered in Concord, New Hampshire in March 2013 and subsequently in Bow, Canterbury, Loudon, Hopkinton, Salem, and Weare. As a result, three southern NH counties--Hillsborough, Merrimack, and Rockingham--are under quarantine, as is all of Massachusetts and Connecticut. The EAB quarantine prohibits the movement of any hardwood firewood, all ash wood products, and ash nursery stock out of the quarantine area unless certain conditions are met. The recommendation for firewood is to use it within 5 miles of its source. Lots more information on EAB is available at nhbugs.

There are native wood boring beetles, but they usually feed on already dead or dying trees, unlike EAB, which feeds on large, healthy ash. There are also some EAB look-alikes--check out these. Since emerald ash borers feed on healthy trees, it often is many years before their presence is detected. One of the first signs is the result of woodpeckers feeding on EAB resulting in "blonding" of the bark.

Molly Heuss, NH Department of Forests and Lands Forest Health Specialist,
showing blonding on ash and extensive EAB larval galleries beneath bark.

Everyone in New Hampshire can be keeping an eye out for emerald ash borer. The goal of reporting its presence and of the quarantines is to slow the advance of the beetle. Whether this is enough to stop the emerald ash borer from killing all the ash in North America is unknown.

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