The Emerald Ash Borer (EAB) is a shiny green, metallic wood-boring beetle that kills living ash (genus Fraxinus) trees. This insect is an exotic pest introduced from Asia. It was first discovered in Detroit, Michigan and Windsor, Ontario in 2002. EAB can now be found in 25 states, mostly those located along the eastern seaboard and the Midwest. This beetle is spread by the movement of ash products such as firewood, nursery stock, and logs. Ash trees generally die within one to three years after infestation. Emerald Ash Borer is one of the most serious threats to our urban, suburban, and rural forests. It has already killed millions of trees resulting in $20 billion dollars or more of damage.
Red dots indicate locations where EAB have been found, map courtesy of USDA
Emerald Ash Borer Life Cycle
EAB adults are shiny emerald or coppery green colored. They are only about 5/16 inch long. Adults emerge from their host tree in mid-May through July. They then feed along the margins of ash tree leaves. Near the end of the summer, adults mate and females deposit their eggs singly in bark crevices or under bark scales. The larvae emerge from the eggs, burrow between the sapwood and bark, and then feed on the tree’s sapwood. The serpentine-shaped tunnels created by feeding larvae effectively stop food and water movement in the tree, starving it to death. The larvae overwinter in the galleries they have created and then enter into their next stage of development. Pupation may last from April through July.The cycle is completed as adults begin to emerge through D-shaded exit holes in early summer.
Life Cycle diagram courtesy of www.entm.perdue.edu
Larval Galleries and D- Shaped Exit Hole
Signs to Look For
The presence of the Emerald Ash Borer typically goes undetected until trees show symptoms of being infested – usually the upper third of a tree will thin and then die back. This is usually followed by a large number of shoots or branches (epicormic branching) arising below the dead portions of the trunk. Look for D-shaped exit holes and vertical splits in the bark. If some of the bark has fallen off, you will notice the serpentine-shaped tunnels in the sapwood.
Epicormic branching, courtesy of Michigan DNR
What Can be Done?
If you have specimen trees in your yard that you want to protect, you can apply a systemic insecticide through a soil drench or you can hire a tree expert to inject your tree. Chemicals that have proven effective against EAB that are available to homeowners include imidacloprid and dinotefuran. As always, when using a pesticide, read the label in its entirety and follow its instructions. The label is the law. You should make sure that the product that you are using is labeled for use on ash trees to control Emerald Ash Borer.
You can do your part to help slow the spread of EAB by not transporting firewood. Buy your firewood where you are going to burn it. Until a solution is found for this problem, refrain from planting ash trees unless you are willing to lose them.
Currently, USDA APHIS and the Forest Service are researching biological controls for EAB. Three potential biological control agents have been identified; Spathius agrili, Tetrastichus planipennisi, and Oobius agrili. Since 2007, releases of these stingless wasps show promise as a long-term management strategy
Woodpecker damage to Ash tree infested with Emerald Ash Borer larvae