Emerald Ash Borer

Ash Tree Symptoms

Host tree indications of EAB

How to Identify Ash Tree Symptoms

The good news is that emerald ash borer attacks only ash trees in Iowa. However because ash makes up such a large number of plantings, the cost to individuals and taxpayers will be astonishing when the pest arrives in full force.

Green, black, and white ashes are highly vulnerable to EAB. Blue ash appears to be the most resistant North American species, but all ash species in the genus 'Fraxinus' are susceptible to emerald ash borer. EAB can also feed on white fringetree; although not common in Iowa, this tree species is sometimes used for landscaping in southern Iowa locations.

Tree symptoms are usually noticed first in the top canopy. By the time a homeower at ground level spots a D-shaped exit hole from an emerging emerald ash borer beetle, the tree will likely have been infested by consecutive generations of EAB. Damage is usually very evident by this time and is visible by observing the upper tree canopy dying back first, followed by the lower canopy within the next two years.

Tree symptoms include canopy thinning and dieback when first noticed, epicormic sprouting and suckering as insect damage girdles the tree, bark splits and cracks, and woodpecker feeding on insect larva.

Infested trees exhibit top-down dieback with 1/3 to 1/2 of the branches dying when first noticed, and the remaining canopy dying within the following 2 years. This is often followed by a large number of shoots arising below the dead portions of the trunk and large branches. Trees may also exhibit 2 to 4 inch vertical splits in the bark in response to larval feeding.

Woodpecker predation of insect larva is another sign of possible EAB activity in a tree. Wood splinters from woodpecker feeding tend to be a light orange-yellow color when the damage is recent. The damage is first noticed in upper branches with a diameter of 3 - 4 inches, but can be found throughout the tree if EAB infestations are in advanced stages. This damage is especially visible from ground level during the winter when woodpecker activity is the greatest. Wood splinters become more weathered in appearance during late spring and into the summer.

Link - The Birdwatcher's Field Guide to Holes in Trees (.pdf)

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.

The document that is seen here is available by clicking on its picture link. It covers many of the more common look alike ash problems that are associated with EAB. Often common diseases such as verticillium wilt and fungal cankers are mistaken for emerald ash borer symptoms.

Trees that have been stressed through the years from site related conditions such as excessively wet soils, or have had roots damaged by construction activities will also exhibit similar symptoms.

If you suspect that emerald ash borer is causing symptoms in local Iowa ash trees, please let us know by visiting our Contact us page. We would appreciate the chance to take a closer look.