Emerald ash borer

Ashes were long a tried-and-true workhorse as an urban shade tree until the introduction of the emerald ash borer circa 2000. Ashes have since been largely eliminated from the natural and landscaped environment in the lower peninsula of Michigan

The introduction of EAB was truly an environmental disaster. Ashes are (or were!) part of, or dominant in, many forest types. They are easy to propagate and very tolerant of urban conditions. However, none of the major species native to Michigan have shown significant tolerance to emerald ash borer. The insect has spread into much of the midwest.

Ash Trees in Michigan

The emerald ash borer larvae kill trees by eating the phloem under the bark. This leads to the starvation and decline of the tree roots. Both photos on the right courtesy of local research entomologist David Cappaert.

Green ash dies more quickly than white ash. Some, but not many, white ash specimens in prime condition survived the first wave of borers. The uncommon blue ash has a better survival rate, but is usually disfigured.
Control treatments are more successful with isolated specimens.
Commonly the first sign of insect attack is the activity of downy woodpeckers, who seek out the larvae under the bark. Yum!
Small d-shaped exit holes are diagnostic, but when these are found on the main trunk at eye level, the tree is probably beyond saving.

For what it is worth, here are some things we have learned about the insect and its host:

The emerald ash borer is an aggressive insect, and aggressive control measures are required to keep specimen trees healthy.

Control opions include: 1) spraying ash trees several times in late spring and early summer; 2) injecting an insecticide into the soil near the base of the tree, and 3) injecting one of several products directly into tree trunks. For small trees, any one of these methods will likely work.

Large trees are a challenge. Annually-appied trunk injections with formulations of imidicloprid have worked for GreenStreet on average-sized shade trees such as in the picture on the left. "Tree-age" (emamectin benzoate) is a newer formulation that research shows to be superior and, furthermore, it remains effective within the tree for two years or longer. It takes longer to apply and, at $525/liter, is not inexpensive. Special licensing is required to purchase and apply this product.

Maintaining large forest specimens is impractical.

We look forward to seeing to what extend ash trees return to the landscape as stump-sprouts and the millions of seedlings grow to maturity.

A success story: these ash trees along the sidewalk on Ascot St in Ann Arbor still stand, thanks to aggressive treatments by GreenStreet. The rest of the street was lined with ash trees, but they have all died and been removed.