How to Recognize an Ash Tree Infested with Emerald Ash Borer
Emerald ash borer has now been found in Connecticut – specifically, in sections of New Haven County. These pages have been assembled to assist arborists and others in the identification of the emerald ash borer, and in being prepared for dealing with this insect.
The emerald ash borer is a highly mobile insect that has a history of establishing rapidly into new areas after being introduced. The most common means of introduction are the movement of infested logs, firewood and nursery stock. For those reasons, it is important to be aware of the potential to move the insect, and to comply with all regulatory efforts to limit that spread. In particular, the quarantine to be placed on movement of material out of New Haven County should be followed.
Also Note: If you do find Emerald Ash Borer, you must report your find to the Connecticut Agricultural Experiment Station. EAB is an insect of federal regulatory concern. You may report your find by sending a digital photo via email or by calling the Station. The email address is CAES.StateEntomologist@ct.gov. The phone number is 203-974-8474. Include any information that would be helpful to finding the site (GPS coordinates, street address, etc.) DO NOT MOVE EITHER THE INSECT OR THE WOOD FROM THE SITE!
The three additional pages associated with this page are:
The Life Stages of the Emerald Ash Borer
Dealing with the Emerald Ash Borer
Regulatory Matters
Please visit these pages as well.
The topics on this page are:
Declining Trees
Bark Splitting
Epicormic Sprouts
D-Shaped Exit Holes
Serpentine Galleries
Woodpecker Activity
Use of a Draw Knife
Trap Trees, Purple Traps and Bio-Surveillance
Additional Images
Declining Tree
The emerald ash borer larvae feed on the phloem tissue and cambial layer of the tree, eventually destroying the trees ability to transport sugars and leading to its decline and death. How rapidly this happens is largely determined by how many larvae are feeding in the tree. It is estimated that, in a typical outbreak, trees will succumb to the emerald ash borer within 3-5 years.
Dead limbs, epicormic branches and general decline are all symptoms of the emerald ash borer at work in an ash tree. Of course, many of the ash trees in Connecticut have been displaying these symptoms over a number of years, completely unrelated to EAB. Hence, decline alone is not an indicator of EAB.
As the infestation within that tree advances, the appearance of decline will increase. In the early stages, the symptoms related to decline may not be very obvious. For both of these reasons (the widespread occurrence of ash decline and the relative lack of symptoms early on in an infestation), it is recommended that all ash trees be examined closely for more direct signs of the emerald ash borer.
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Bark Splitting
As the EAB larvae feeds, it causes the localized death of the bark above where it is feeding. As the tree continues to grow, this can cause distortions and damage to the bark, including sunken areas, sloughing and splitting of the bark. These may be helpful indicators in examining trees that are not otherwise showing symptoms of an advanced infestation.
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Epicormic Sprouts
Epicormic sprouts, particularly when found along the lower trunk of the tree, are a clear indication of stress in the tree. It can also be one of the indications that a tree is infested with the emerald ash borer. An exposed EAB gallery can also be seen in this picture.
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D-Shaped Exit Holes
When the adult beetle emerges from the bark, it chews a characteristic D-shaped exit hole on its way out of the tree. This shape accommodates the flat back and rounded abdomen of the adult insect.
D-shaped exit holes are diagnostic of metallic wood-boring beetles in general. For instance, the presence of such exit holes on ornamental white birch trees is a clear sign of the presence of bronze birch borer, while the presence of similar exit holes on oaks indicates the two-lined chestnut borer.
However, while the presence of such an exit hole on an ash tree would confirm the presence of emerald ash borer, this is a sign that is both hard to spot and easy to mis-read. Many times, apparent D-shaped holes in the bark of ash trees turn out not to be so once the layers of bark are shaved down and the true shape of the hole is revealed. The presence of a suspicious hole in the bark of an ash tree should, however, be considered a reason to investigate further.
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Serpentine Galleries
As the EAB larva feeds in the phloem, it leaves behind a trail created by its consumption of phloem and cambium tissue. This trail will often become engraved into the outer layer of sapwood, and is also often filled with frass (packed bark fiber excreted by the insect). This trail is known as a feeding gallery.
On ash trees, EAB galleries are unique in that they are winding and S-shaped – a description that can be summarized in the one word “serpentine”. The presence of a serpentine feeding gallery just under the bark in an ash tree is a very good sign that EAB is or has been present in that tree.
During inspections of suspect ash trees, the bark can be peeled back to expose any galleries that are present. On dead ash trees, this can be done easily as the bark usually simply peels right off. On living ash trees, tools such as a pocket knife, an axe or a draw-knife might be needed to remove the bark and expose any EAB galleries.
Finding feeding galleries of this sort will confirm the presence of EAB. This sign is the least ambiguous and, once the bark has been removed, easiest to see.
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In many infestations such as the one in the vicinity of Saugerties in New York State, woodpeckers have been shearing the outer bark off of ash trees in order to find the pre-pupae in the bark. This feeding behavior exposes lighter colored bark underneath the outer bark. This lighter bark is very obvious to even ground-based observers and looks a lot like the mark the might be left if an adjacent tree had fallen and removed outer bark on its way down. The observers have noted this to be one of the most helpful clues to finding EAB-infested trees.
Additionally, woodpeckers may feed on earlier instar larvae underneath the bark of the tree by boring the typical round woodpecker holes into the bark. In the photo to the far-right, a woodpecker hole can be seen along with exposed serpentine feeding galleries.
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The draw-knife is a handy tool for exposing layers of bark down to the sapwood. In careful hands, the galleries of EAB larva and associated life stages can be quickly found.
In the image on the right, the draw-knife is being used to find EAB in the canopy of a felled ash tree. Two exposed feeding galleries are visible near the area being debarked. As this inspection was being done in February on a relatively thin-barked tree, the only actual beetles found were pre-pupal beetles that had moved into the outer sapwood. A few of these can be seen in the Additional Images, below.
The draw-knife is not the only tool that be used to expose under the bark – hatchets, pocket knives and other types of blades will also work.
Please note – as in the use of any sharp tool, caution and safety are of vital importance. As using the draw knife involves pulling the blade towards the body, it is especially important that care be taken. Practice and patience are of great importance.
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Trap Trees, Purple Traps and Bio-Surveillance
More formalized efforts to find the emerald ash borer involve the use of girdled trees and of traps baited with attractants. Ash trees that have been girdled early in the season are highly attractive to dispersing adult EABs, who will preferentially lay their eggs on these trees. It is then possible to survey for the presence of the beetles later on in the season by felling these trees and looking for the beetles and its galleries.
The purple traps are that color because research has shown purple to be the most successful color in drawing adult EAB’s to the trap. These traps are baited with Manuka oil – oil that is derived from a tree found in New Zealand and Australia. This oil has also proved successful in drawing the beetles to the traps. The University of Connecticut Cooperative Extension Service is overseeing the placement of some 940 purple traps throughout Connecticut during the spring of 2011, in an effort to discover whether EAB is in the state.
A third monitoring technique is known as “bio-surveillance”. This technique takes advantage of the fact that a wasp (Cerceris fumipennis) preferentially hunts down and collects buprestid beetles in order to provide food for its developing larvae. Among the buprestids it will collect is the emerald ash borer, if any are present in the area. Monitoring Cerceris wasps as they return to their nests is currently being used in Connecticut as a third means of sampling for the presence of EAB. (For details, see www.cerceris.infospan)
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The best advice is to keep firewood local.
