GROUNDS:

A New Pest in Town

Emerald Ash Borer

A great deal has already been written in The Ann Arbor News and professional or trade journals about the insect pest we are now commonly calling the Emerald Ash Borer(EAB). This past fall, the Michigan Department of Agriculture (MDA) positively identified this pest as an Asian species of beetle, Agrilus planipennis (Fairmaire). The larvae of this beetle feed on the conductive tissues of ash trees just below the bark, producing cavities that eventually girdle and kill branches and entire trees.

The ash tree (Fraxinus spp.) is a commonly planted street tree; nearly 15% of the street trees in the city of Ann Arbor are ash trees. Our campus has a highly diversified forest of trees with well over 150 species planted on 700 acres. While ash trees account for approximately 900 of the 17, 000 inventoried landscape trees on campus, this is only 5.3% of the campus forest. Based on the mortality rates already observed, MDA extension experts are predicting 75% mortality of all ash trees in our area in the next four years. To compare, it is currently believed that the EAB problem will cause greater mortality and more anxiety than Dutch elm disease did some four decades ago. This exotic pest most likely will be the most dramatic and destructive tree pest problem ever in Michigan. The negative effects of this insect are much greater than what we recently experienced with the European gypsy moth.

Infestations of the Emerald Ash Borer can be difficult to detect until branches begin to die off. Evidence of infestation includes D-shaped exit holes on branches and the trunk. Many trees appear to lose about 30 to 50 percent of the canopy in one year and the tree is often killed after 2-3 years of infestation. EAB has killed trees of various size and condition in Michigan. Stress likely contributes to vulnerability of ash trees; however, the Emerald Ash Borer attacked and killed apparently vigorous trees in woodlots and urban trees that were under regular irrigation and fertilization regimens.

The action plan we have developed to manage this pest includes the following steps:

1. Encourage the campus community to gain information about EAB, via radio, local cable television, the print media, and the Internet
2. Monitor the health of campus ash trees and marking infested trees for removal
3. Remove infested and dying ash trees confirmed to have been infested with EAB from our campus forest immediately
4. Improve our capabilities for wood disposal of dead and dying trees
5. Replace dead campus trees in a timely manner.

The MDA and the U.S. Forest Service conducted a number of trials the past summer to determine whether there are chemical means that could be effective as a management tool for this particular boring insect. We await the results of these trials.

Most likely the emerald ash borer invaded southeast Michigan in pieces of untreated wood from its native home in Asia. In a similar way, it can re-infest ash trees hundreds of miles away from its present location – through movement of infested firewood.

DON’T MOVE ASH FIREWOOD OUT OF THE QUARANTINED AREA! Don’t repeat the process by taking it on vacation with you. In addition to being against the quarantine law, this offense is punishable by fines and/or imprisonment. Imagine how your favorite vacation spot would look with some or all of the trees gone!

~ Marvin Pettway
Grounds & Waste Management