The Homeowners Column

The Homeowners Column

Other Borers Besides EAB Can Attack Ash

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

It's a story of desire, disillusion and death. Ash trees have all the markers for desirable shade trees. Most species are native, they grow fast, they tolerate tough soil conditions, and they have great fall color. As with many things desire is followed by over-indulgence. Ash trees have been planted in many landscapes with wild abandon. We are relearning the crucial lesson of diversity in our community landscapes. Now with the recent finding of Emerald Ash Borer (EAB) on north Market Street in Champaign the demise of ash trees is lurking. For information on EAB and treatment options contact us 217-333-7672, stop by our office 801 North Country Fair Drive in Champaign for fact sheets or go to

The adult EAB leaves characteristic one eighth inch "D" shaped holes in ash trees. However a number of other borers besides emerald ash borer attack ash and leave holes in bark according to Dr. Phil Nixon University of Illinois Extension entomologist. Several cause internal damage similar to that of EAB but are readily separated by the trained eye. Others create emergence holes that are sometimes confused with those of EAB. Some of the most common beetle borers in ash in Illinois include ash/privet borer, flatheaded appletree borer, redheaded ash borer, Eastern ash bark beetle and false powderpost beetle.

Ash and privet borer is probably the borer most commonly confused with EAB. Like EAB, it tunnels under the bark; but the tunnels are wider and deeper. Tunnels made by mature larvae are oval and about 3/16 inch across. Unlike EAB, ash and privet borer tunnels significantly into the sapwood. The white, legless larva is oval in cross-section. The tunnels are packed with frass, a combination of wood chips and fecal material produced by the larva.

The larva pupates in the tunnel, and the resulting adult chews its way out through an oval, 3/16-inch-diameter hole. Although the hole is half again wider than that of EAB and does not have the flat side of the D-shape, many convince themselves that it must be EAB. The adult is a longhorned borer, dark in color, with four tan spots and long antennae.

Ash and privet borer attacks dead and dying trees and parts of trees. It is commonly associated with storm damage, poor pruning wounds, and partial trunk dieback due to girdling roots. It does not attack healthy areas of the tree.

Flatheaded appletree borer causes damage to ash, maple, serviceberry, hawthorn, crabapple, and other trees similar in appearance to that of ash and privet borer. It creates tunnels up to 3/16 inch in diameter under the bark. Tunnels are oval in cross-section. The white, legless larvae grow to about 1-1/4 inches long. They have broad, flat heads that create the oval tunnels. The larva pupates in the tunnel, and the resulting adult chews it way out of the bark, creating a 3/16-inch-diameter, oval hole in the process. The adult beetle is about 3/4 inch long, dark-colored, with small, indistinct light spots on its roughly textured back.

Flatheaded appletree borer is a serious pest of young maple trees, commonly creating helical tunnels under the bark (just above the soil line) that extend completely around the tree, girdling it. It is similar in its attack of ash, being found in trees dying from other causes, as well as dead and dying tissue associated with storm damage and girdling roots.

Redheaded ash borer, Eastern ash bark beetle and false powderpost beetle are also common in dead and dying trees of many species including ash.

You should see a reoccurring theme that these borers can cause damage, but often attack dead and dying trees; therefore, try to keep trees healthy by watering and mulching.

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