Identify the Emerald Ash Borer

If there is any good news it’s the fact that the Emerald Ash Borer attacks only ash trees. However, because ash trees make up such a large number of plantings in Iowa, the cost to individuals and taxpayers will be astonishing when it arrives.

(Click on the pictures for a larger view)

How to Identify the Larva or Grub:

The EAB larvae live and feed on the inner bark of ash trees, damaging the ability of the tree to transport water and nutrients. The larvae grow, and will eventually reach 1.25 inches in length.

Note the bell-shaped segments of the larva. These segment shapes tend to identify EAB larvae.

Distinct S-shaped or serpentine tunnels and galleries, often indicate EAB larva. As more larvae are found infesting a tree, galleries may run together with no discernable size or shape.

How to Identify the Adult Beetle:

The beetle is emerald green, half an inch long and about 1/8 inch wide. The abdomen, under the wings, is a bright purple.

The adult Emerald Ash Borer beetle will exit the tree by chewing a distinctive “D” shaped hole through the bark, approximately 1/8 inch wide.

The shape of the exit hole is the exact size and shape of the emerging beetle's body. The D-shaped holes occur in the upper tree canopy first, making it very difficult for homeowners to spot.

(Click on the pictures for a larger view)

How to Identify Ash Tree Symptoms:

By the time a homeowner spots a D-shaped hole at ground level, the tree will likely have been infested by consecutive generations of EAB, as they work the tree from the top down.

Damage is very evident by this time, and is visible by observing the tree canopy dying back.

Tree symptoms include canopy thinning and dieback when first noticed, epicormic sprouting as insect damage progresses, bark cracks, and woodpecker feeding.

Infested trees exhibit top-down dieback, with 1/3 to 1/2 of branches dying the first year, and the remaining canopy dying the following year.

This is often followed by a large number of shoots arising below the dead portions of the trunk. Trees may also exhibit 2-4 inch vertical splits in the bark in response to larval feeding.

(Click on the pictures for a larger view)

Finally, woodpecker activity is another sign of EAB, or other insect activity in a tree. Woodpecker feeding is more visible during the winter months when damage is easier to see. The feeding damage can often be noticed in the smaller, upper most branches of the tree.

Look-Alike Ash Tree Symptoms:

To further complicate the issue, these symptoms are not unique to Emerald Ash Borer. Environmental factors, diseases, and native insects may be responsible for look-alike symptoms.

Insects confused with EAB include the tiger beetle, bronze birch borer, Japanese beetle, two-lined chestnut borer, caterpillar hunter, lilac/ash borer, and redheaded ash borer to name a few.

Link: Michigan State University - Native borers, EAB look-alikes

Link: Michigan State factsheet on EAB look-alikes

Emerald Ash Borer is often moved into new areas by the transport of ash firewood, logs, cut branches or similar material. Once EAB is found in a new area, the movement of such articles are prohibited by the United States Department of Agriculture, APHIS-PPQ.

To report suspect firewood being transported into Iowa from Emerald Ash Borer quarantined areas, please fill out
the Contact Us page.