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.
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
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
Although many borers go after stressed trees, emerald ash borer
attacks perfectly healthy trees, too.
Emerald Ash Borer traps are used
to detect the insect's presence
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
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.
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
Appearance of bark
Emerald Ash Borer "D-shaped" exit holes
in the trunk of an Ash tree Photo: Sandy Feather
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
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.
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.
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.
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.