Emerald Ash Borer

Signs of EAB Damage


D-Shaped exit hole

Symptoms of an early infestation may be difficult to diagnose. Be on the lookout for multiple declining ash in a given area and D-shaped exit holes that are approximately 1/8 “ in diameter. As an infestation progresses, small vertical splits in the bark can be seen on twigs or the main trunk and woodpecker holes may be present on trees. Trees may die after 2-4 years or less.

Thinning canopies are symptoms of EAB

 Physical Appearance


Adult EAB

  • Typically the top 1/3 of crown shows dieback and thins. Trees appear to lose about 30%-50% of their canopy after 2 years of infestation.
  • As the tree declines, epicormic shoots form at the interface between healthy and dead tissue anywhere in the canopy.
  • Distinct “S” shaped, frass-filled larval galleries that can range from 4- 20“ in length etch the xylem and phloem.
  • Adults are slender and can be 1/4” to 1/2” in length, they are dark metallic emerald green.
  • Larvae range in size from 1 -1 1/4” in length with pincer-like appendages on the last segment

Larval galleries under the bark

How Does Emerald Ash Borer Kill a Tree?

As the larvae develop inside the tree, they consume the vascular tissue of the tree. During this process, they weave back and forth creating “S” shaped galleries in the vascular tissue. These “S” shaped galleries essentially suffocate the tree, cutting off vital fluids to the canopy. This activity occurs behind the bark and can go unseen for years before signs or symptoms appear on the tree


Often times, when symptoms begin to appear on the tree, the tree has already been infested for multiple years. Additionally, it is rare to see an adult borer which makes identifying infested ash trees even more difficult. Prevention with insecticide products is critical when it comes to protecting ash trees from emerald ash borer.



Emerald ash borer is a non-native borer that attacks all North American species of ash to varying degrees. Accidentally introduced into southeastern Michigan, it was first detected in 2002 and since has killed millions of ash trees in forests and urban environments.

Emerald Ash Borer Life Cycle

  • Emerald ash borer pupate in early spring and emerge as adults in mid-May and June.
  • They lay their eggs in the bark crevices on ash trees in mid-July.
  • The eggs hatch and the EAB larvae will then bore into the tree and feed in the tree’s vascular tissue.
  • The larvae will overwinter in the tree and emerge in the spring as adults, starting the cycle all over again.
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