Emerald Ash Borer

Purple traps & Ash tree damage

By: Sandy Feather ©2009
Penn State Extension

Q. I have been seeing reports of the emerald ash borer in our area, and I am concerned because I have a number of very mature ash trees that really make my yard. I would hate to lose them. Can you recommend preventative treatments to protect ash trees?

A. The emerald ash borer (Agrilus planipennis) is an introduced pest that was first discovered in southeastern Michigan and Ontario, Canada in 2002. Since that time, EAB has been found in Ohio, Indiana, Illinois, Maryland, Pennsylvania, West Virginia, Missouri, Wisconsin, Virginia and Kentucky. It was first discovered in Pennsylvania in 2007, in southern Butler County.

Additional infestations in the Commonwealth have been found in Allegheny, Armstrong, Beaver, Lawrence, Mercer, Mifflin, Washington and Westmoreland counties, now totaling 10 Pennsylvania counties as of July 26, 2009 (See updates at bottom of page).

Origin of EAB

Entomologists believe Emerald Ash Borer was introduced to the United States in pieces of wood that had been used to stabilize shipping crates in cargo ships, then discarded once they reached their destinations. Since then, it is believed to have spread through the movement of infested firewood, nursery stock, and other ash wood products. This pest impacts only ash trees in the genus Fraxinus; mountain ash trees in the genus Sorbus are not affected.  Although many borers go after stressed trees, emerald ash borer attacks perfectly healthy trees, too.


Detection with Traps

Purple trap used to detect the presence of Emerald Ash Borers
Emerald Ash Borer traps are used
to detect the insect's presence

Life Cycle

Adult female emerald ash borers lay their eggs on the bark of ash trees. The larvae tunnel into the bark as soon as they hatch and begin feeding in the cambium. The cambium is the actively growing tissue just under the bark that gives rise to the tree’s vascular system. It transports water and nutrients from the roots to the leaves, and takes the products of photosynthesis down to the roots for storage. Once the cambium is destroyed around the circumference of the tree, the tree dies because it can no longer transport water and nutrients as needed. Emerald ash borers pupate under the bark, then adults hatch from late May into July, with peak emergence occurring from late June to mid-July. Adults feed on ash foliage, mate and lay eggs, and the whole cycle starts over again. Adults have a long period of egg laying, perhaps right through August. Research has shown that emerald ash borers can take from one to three years to complete their life cycle.

Emerald Ash Borer Prevention

If you have ash trees that are central to your landscape and you live in a quarantined county (or within 15 miles of a known infestation), it is a good idea to treat them preventatively. However, you should scout your trees very carefully - or have a certified arborist inspect them for you – to make certain they are not already infested. The insecticides that have proven most effective against this pest move in the trees’ vascular system. If emerald ash borers have already damaged the vascular system, it may not be possible to get the insecticide to move throughout the tree enough to provide good protection.


Symptoms of borer damage

Symptoms of emerald ash borer infestation include dieback, especially high in the crown of trees, evidence of woodpecker activity (those larvae make a good meal!), vertical splits in the bark, winding galleries under those splits where the larvae feed, and capital “D”-shaped holes where the adults emerge after pupation. Severely infested trees begin to produce sprouts low on the tree in a last ditch effort to survive, known as epicormic shoots. Unfortunately, infested trees often show no symptoms at all until they are almost dead. I have seen infested trees that showed no sign of dieback and looked just fine until a close inspection of the bark showed vertical cracking and “D”-shaped emergence holes. A little work with a knife revealed the winding galleries typical of larval feeding damage under the vertical cracks.

Appearance of bark

Emerald Ash Borer damage
Emerald Ash Borer "D-shaped" exit holes in the trunk of an Ash tree
Photo: Sandy Feather

Control Options

Options for controlling emerald ash borer include soil injection or drench, bark sprays, trunk injection, and bark and foliage cover sprays. Many of these products should only be applied by licensed pesticide applicators who have the training and equipment to use them safely and effectively. Restricted use products include those that have shown to be the most effective in treating large trees. If you have very large trees – over 15-inches in diameter – you should hire a certified arborist to treat them.
The only homeowner product to win approval from the Cooperative Emerald Ash Borer Program is Bayer Advanced Tree and Shrub Insect Control. Imidacloprid is the active ingredient, and is the active ingredient in many professional use products, too. There are other formulations of imidacloprid available to home gardeners, but they have not been evaluated in university tests. Bayer Advanced Tree and Shrub Insect Control has shown some spotty results in university tests, and home gardeners must follow label directions to the letter. Do not treat trees that are under drought stress; water trees thoroughly prior to application, if necessary. Pull back any mulch under the tree and apply the diluted product within 18 inches of the trunk. Replace the mulch after application. Imidacloprid must be applied every year to protect ash trees from emerald ash borers, and is proving to less effective on trees over 15 inches in diameter at currently permitted label rates of application.

A new product on the market – Tree-age™ (pronounced “triage,” emamectin benzoate) – has performed very well in university trials, providing excellent protection from emerald ash borers under heavy pest pressure and for very large trees. It is a restricted use product and must be applied by a licensed pesticide applicator who has been trained to inject it properly. Tree-AGE offers up to two years of protection from a single treatment.

Stressed Trees

Be aware that ash trees die from other factors, including a number of native borers. These include the ash (lilac) borer, banded ash clearwing and redheaded ash borer; all leave ROUND, rather than “D”-shaped exit holes. A condition known as ash decline frequently afflicts ash trees that have been damaged by construction or planted on an inhospitable site. Such stressed trees may be attacked by other microbes or insects that put them out of their misery.



The Pennsylvania Department of Agriculture expanded the Commonwealth's quarantine on firewood movement August 9, 2010 from 12 counties to 43 counties, so the quarantine now covers the western 2/3 of the state and all hardwoods.

Pennsylvania’s Emerald Ash Borer (EAB) quarantine now includes the counties of: Allegheny, Armstrong, Beaver, Bedford, Blair, Butler, Cambria, Cameron, Centre, Clarion, Clearfield, Clinton, Columbia, Crawford, Cumberland, Elk, Erie, Fayette, Forest, Franklin, Fulton, Greene, Huntingdon, Indiana, Jefferson, Juniata, Lawrence, Lycoming, McKean, Mercer, Mifflin, Montour, Northumberland, Perry, Potter, Snyder, Somerset, Tioga, Union, Venango, Washington, Warren and Westmoreland counties. 

It is hoped the quarantine will slow the spread of the beetle by restricting the movement of all ash: nursery stock, green lumber, logs, stumps, roots, branches and wood chips. The quarantine also includes all other hardwoods, namely hickory, maple and oak.

Emerald Ash Borer brochure (PDF 513MB)

APRIL 2010

April 2010 - Emerald Ash Borer has now been detected in 13 US states and 2 Canadian provinces, tracked in this order: Michigan 2002, Ontario 2002, Ohio 2003, Indiana 2004, Illinois 2006, Maryland 2006, Pennsylvania 2007, West Virginia 2007, Missouri 2008, Quebec 2008, Virginia 2008 (originally 2003), Wisconsin 2008, Minnesota 2009, Kentucky 2009, New York 2009.


Photos of landscape insects

Fertilizer burn on lawns

Having fruit tree planting success


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