Symptoms and Signs of EAB

General Symptoms

Declining ash due to Emerald Ash Borer


As larvae feed beneath the bark they damage tissues responsible for transporting water and nutrients.  Initial damage appears as thinning in the upper canopy of the tree.

Other conditions (disease, soil compaction, etc.) can cause canopy die-back in ash trees, so canopy thinning alone does not definitively indicate EAB.

(See the page on diseases of ash trees for some additional information)



Shoots (suckers) at base of trunk


In addition to canopy thinning, trees infested with EAB often produce many green shoots (suckering) on the lower trunk.

As with canopy thinning, other sources of stress can cause suckering around the base of ash trees, and this symptoms does not specifically indicate EAB.




In addition to the two symptoms above, trees infested with EAB are often sought out and attacked by woodpeckers.  However, woodpeckers will attack just about any tree full of insect larvae.  Thus, while woodpecker activity can be an indicator of EAB, it does not specifically confirm an EAB infestation.

If you see the symptoms mentioned above, take a closer look at your ash trees to check for the specific signs of the emerald ash borer shown below:

Specific Signs of EAB

D-Shaped exit holes



As they emerge from ash trees in June and July, adult emerald ash borers leave behind distinct D-shaped exit holes.  These holes are approximately 1/8″ wide and can be oriented in any direction (i.e., the flat side may be facing upwards, downwards, etc.).  These D-shaped holes are a strong indicator of EAB.




S-Shaped larval galleries


Trees attacked by EAB also have distinct S-shaped or “serpentine” galleries (tunnels) beneath the bark.  These tunnels tend to be about 1/8″ wide and are packed with frass (a fine mixture of sawdust and insect excrement).

If you notice any loose bark on a suspicious ash tree, peeling it back may reveal the presence of these distinct larval galleries as well as insect larvae.



In addition to the D-shaped exit holes and S-shaped larval galleries, collecting an adult EAB beetle or larvae can help confirm an EAB infestation.

If you observe or suspect an EAB infestation, send an insect specimen or digital image of insects or of signs and symptoms to PJ Liesch at the UW Insect Diagnostic Lab. PJ can be reached via email at or through the mail at 1630 Linden Drive, Madison, WI 53706.  You can also call the toll-free Wisconsin emerald ash borer hotline at 1-800-462-2803.